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Opening wedge high tibial osteotomy for medial compartment knee osteoarthritis: Planning and improving outcomes: Case series and literature review

Published:December 05, 2022DOI:https://doi.org/10.1016/j.jcot.2022.102085

      Abstract

      Background

      Opening wedge high tibial osteotomy (OWHTO) is a safe surgical procedure to treat medial compartmental osteoarthritis caused by a varus deformity. Over-correction of this varus deformity can lead to lateral compartment over-loading. In our study, we planned our correction by using the mechanical axis deviation (MAD).

      Purpose

      The purpose of this study is to evaluate the clinical and radiological results of OWHTO based on planning using the MAD measurements.

      Study Design

      Retrospective Case Series.

      Methods

      14 patients with Kellgren- Lawrence classification (KL) grade 3 or above underwent OWHTO, with plans to have the mechanical axis pass through 5–15 mm lateral to the center of the tibial plateau. Pre-operative and post-operative radiographic measurements were made and compared using the student t-test. SF-36 scores were obtained for clinical performance.

      Results

      Our patients experienced MAD from 25.9 mm medial to the center of the tibial plateau pre-operatively to 12.7 mm lateral to the center of the plateau post-operatively. The mean change in MAD was 38.7 mm (p < 0.0001). The accuracy of our correction compared to the planned MAD was 98.3%. The mechanical axis angle shifted from 7.35° of varus to 3.5° of valgus (p < 0.0001). All patients had post-operative alignments of 1–6° of valgus, with 11 of out the 14 patients with alignments less than 5° of valgus, preventing over-loading of the lateral compartment.

      Conclusion

      Using MAD measurements is an accurate planning method for OWHTO that corrects varus deformity without over-loading the lateral compartment, and leads to improved clinical outcomes.

      Keywords

      Abbreviations:

      OWHTO (opening wedge high tibial osteotomy), MAD (mechanical axis deviation)
      What is known about the subject: Correcting varus deformity by OWHTO requires a balance. Too little of correction will still cause stresses on the medial compartment. Correcting too much will overload the lateral compartment. Previous biomechanical studies suggested 0-4 degrees of valgus alignment as the optimal correction goal.
      What this study adds to existing knowledge: By planning the surgery to have the mechanical axis pass through 5–15 mm lateral to the center of the knee, post-operative alignment of the knee is at a mean 3.5° of valgus, achieving the balance of relieving medial compartment stress, while avoiding lateral compartment over-load.

      1. Introduction

      Osteoarthritis (OA) of the knee is a debilitating disease. A contributing factor to OA degenerative changes is varus deformity which overloads the articular cartilage of the medial compartment, leading to early degenerative OA.
      • Mina C.
      • Garrett W.E.
      • Pietrobon R.
      • Glisson R.
      • Higgins L.
      High tibial osteotomy for unloading osteochondral defects in the medial compartment of the knee.
      Recently, the number of young patients with knee OA has increased due to increasing rates of obesity among the population and increasing middle-aged patients participating in high-impact activity.
      • Freitag J.
      • Norsworthy C.
      • Wickham J.
      • Shah K.
      • Tenen A.
      High tibial osteotomy in combination with arthroscopic abrasion arthroplasty and autologous adipose-derived mesenchymal stem cell therapy in the treatment of advanced knee osteoarthritis.
      ,
      • Spahn G.
      Complications in high tibial (medial opening wedge) osteotomy.
      ,
      • Spahn G.
      • Kirschbaum S.
      • Kahl E.
      Factors that influence high tibial osteotomy results in patients with medial gonarthritis: a score to predict the results.
      ,
      • Witjes S.
      • Gouttebarge V.
      • Kuijer P.P.F.M.
      • van Geenen R.C.I.
      • Poolman R.W.
      • Kerkhoffs G.M.M.J.
      Return to sports and physical activity after total and unicondylar knee arthroplasty: a systematic review and meta-analysis.
      Total knee arthroplasty (TKA) is a widely accepted and standard treatment for knee OA. However, high rates of TKA wear and revision operations in younger patients have urged the consideration of other joint sparing surgical options for young patients with knee OA.
      • Woodacre T.
      • Ricketts M.
      • Evans J.T.
      • et al.
      Complications associated with opening wedge high tibial osteotomy — a review of the literature and of 15years of experience.
      Closing wedge proximal tibial osteotomy (CWPTO) has been used in the treatment of knee OA in the past. However, this procedure is associated with a high rate of complications, namely injuries to the common peroneal nerve and alterations to the shape of the proximal tibia, resulting in tibial deformity. Crucially, the altered morphology of the proximal tibia after CWPTO makes a subsequent TKA procedure more difficult to perform.
      • Bonasia D.E.
      • Dettoni F.
      • Sito G.
      • et al.
      Medial opening wedge high tibial osteotomy for medial compartment overload/arthritis in the varus knee: prognostic factors.
      ,
      • Woodacre T.
      • Ricketts M.
      • Evans J.T.
      • et al.
      Complications associated with opening wedge high tibial osteotomy — a review of the literature and of 15years of experience.
      Opening wedge high tibial osteotomy (OWHTO), on the other hand, optimizes the geometry of the proximal tibia in order to achieve ideal alignment of the limb and to improve clinical outcomes in patients with knee OA and varus deformity. The results and safety of OWHTO have been positive.
      • Miller B.S.
      • Joseph T.A.
      • Barry E.M.
      • Rich V.J.
      • Sterett W.I.
      Patient satisfaction after medial opening high tibial osteotomy and microfracture.
      ,
      • Schuster P.
      • Schulz M.
      • Mayer P.
      • Schlumberger M.
      • Immendoerfer M.
      • Richter J.
      Open-wedge high tibial osteotomy and combined abrasion/microfracture in severe medial osteoarthritis and varus malalignment: 5-year results and arthroscopic findings after 2 years.
      Identifying and stratifying the outcome predictors of OWHTO in patients with uni-compartmental knee OA would provide surgeons with an improved treatment algorithm to determine the ideal treatment to offer patients. Some such parameters have been studied to assess for prognostic factors of outcomes. Extraction and pooling of these results would clarify the effects of prognostic factors on clinical outcome.
      Several clinical studies report different degrees of optimal alignment correction in patients with varus knee OA.
      • Bonasia D.E.
      • Dettoni F.
      • Sito G.
      • et al.
      Medial opening wedge high tibial osteotomy for medial compartment overload/arthritis in the varus knee: prognostic factors.
      ,
      • Matsunaga D.
      • Akizuki S.
      • Takizawa T.
      • Yamazaki I.
      • Kuraishi J.
      Repair of articular cartilage and clinical outcome after osteotomy with microfracture or abrasion arthroplasty for medial gonarthrosis.
      Mina et al. demonstrated that, based on contact pressures, the medial compartment is completely unloaded after correction to 6–10° valgus in a biomechanical study. In the lateral compartment, they showed 1–4° of valgus alignment prevents overloading and OA development and progression.
      • Mina C.
      • Garrett W.E.
      • Pietrobon R.
      • Glisson R.
      • Higgins L.
      High tibial osteotomy for unloading osteochondral defects in the medial compartment of the knee.
      This study aimed to report the clinical and radiological results of OWHTO in our patients with varus deformity and uni-compartmental knee OA with application of our pre-operative planning method based on mechanical axis deviation (MAD) measurements to achieve reliable alignment corrections to unload the medial compartment without overloading the lateral compartment. Additionally, prognostic factors and treatment options were extracted from current literature. Prevention and treatment of probable surgical complications were also reviewed from the current literature.

      2. Methods

      A retrospective study was performed evaluating the result of OWHTO procedures in patients with OA Kellgren-Lawrance classification (KL) of 3 or greater.
      • Kohn M.D.
      • Sassoon A.A.
      • Fernando N.D.
      Classifications in brief: Kellgren-Lawrence classification of osteoarthritis.
      The study was reviewed and approved by our institutional review board (IRB). The inclusion criteria were symptomatic patients with varus deformities and unilateral knee compartment OA, with pain localized to the medial side of the knee. The exclusion criteria were patients with generalized knee pain, neutral or valgus alignment, and severe patellofemoral OA. A total of 14 patients met these selection criteria. Radiographs were obtained both pre-operatively and six months post-operatively. Radiographs included anteroposterior (AP) and lateral views of the knee in addition to 51-inch standing hip-to-ankle x-rays. Measurements such as MAD (mechanical axis deviation), MAA (mechanical axis alignment), MPTA (medial proximal tibial angle), PPTA (posterior proximal tibial angle) and JLOA (joint line orientation angle),
      • Paley D.
      • Herzenberg J.E.
      • Tetsworth K.
      • McKie J.
      • Bhave A.
      Deformity planning for frontal and sagittal plane corrective osteotomies.
      were obtained pre-operatively and six months post-operatively to evaluate the accuracy of the deformity correction in the sagittal and coronal planes.
      MAD was calculated on calibrated standing x-rays as the distance of the mechanical axis (center-of-hip to center-of-talus) from the center of the tibial plateau either laterally or medially. Lateral x-rays were used to measure the patellar height. The Caton-Deschamps Index (CDI), calculated as the distance from the upper tibial plateau to the most inferior aspect of the patellar articular surface divided by the length of the patella articular surface, was used to evaluate the patella height. To measure PPTA, lines were drawn perpendicular to the tibial diaphysis and tangential to the tibial plateau in the lateral view. SF-36 and Oxford clinical scores were used to assess clinical outcomes after surgery.
      MAD measurements were used for planning. The pre-operative goal was correction of the mechanical axis to pass laterally to the lateral tibial spine. To calculate the magnitude of the final correction in the frontal plane to achieve this goal, calibrated x-rays were used to convert the angular measurement to millimeters of wedge required intra-operatively to correct the deformity to the goal. The accuracy of the correction was evaluated by comparing MAD before and after surgery. These results were then compared to MAA changes that were used in planning.

      2.1 Surgical technique

      Patients were prepared for surgery and draped in a standard fashion and placed in the supine position. A well-padded tourniquet was applied. After inflating the tourniquet, a medial incision was made over the proximal tibia. The incision was carried down through skin and subcutaneous tissue to the periosteum. The muscular insertions onto the pes anserine and medial soft tissue sleeve were peeled and retracted posteriorly. The superficial MCL was released as needed. The metaphyseal flare of the tibia was identified, and a guidewire was placed obliquely from the anteromedial tibia 1.5 cm below the lateral tibial plateau. The osteotomy was then performed using an oscillating saw. This included a transverse cut across the distal aspect of wire and an anterior cut underneath the most proximal portion of the tubercle. The lateral cortex in both cuts was left intact. Using the intact lateral cortex as a hinge, the osteotomy site was gradually opened to achieve the planned correction by using a laminar spreader. A metal wedge with a base height matching the planned measurement was trialed. The mechanical axis of the lower extremity was assessed with a 5 mm alignment rod under fluoroscopy, aiming for slight over-correction. The metal wedge was then replaced with an equal sized tri-cortical allograft wedge. The osteotomy site was fixed by application of a locking plate and 4.5–5.0 mm screws. The plate was then locked with 3–4 distal and 4 proximal screws (Fig. 1, Fig. 2).
      Fig. 1
      Fig. 1HTO with plate and screws. Pre-op and post-op.
      Fig. 2
      Fig. 2HTO with plate and screws. Pre-op and post-op Hip to Ankle X-ray.
      Post-operatively, patients were evaluated at 2 weeks, 1 month, 3 months, and 6 months. Each time, the patient was administered the SF-36 and Oxford knee score as post-operative outcome measures. SF-36 was used to assess clinical outcomes. The SF-36 scores included 8 categories such as physical function (PF), role physical (RP), bodily pain (BP), general health (GH), vitality (VT), social functioning (SF), role emotional (RE), and mental health (MH). Pre-operative SF-36 scores were measured at the patients’ pre-operative office visit, and the post-operative SF-36 scores were measured on the date of last follow up. Statistical analysis of radiographic and clinical data was performed using two-tailed t-test of means, with a significant difference considered to be p < 0.05.

      3. Results

      Only patients with OA KL grade 3 or above were included in this study. A total of 14 tibias that underwent OWHTO from 14 total patients were included, with 8 right and 6 left. The mean age was 50.1 years of age (range 32–67) and the mean BMI was 29.1 kg/m2 (range 22.4–35). 5 out of the 14 patients (35.70%) were female (Table 1). The mean follow-up time was 35.1 (15–64) months.
      Table 1Patient demographics. BMI: body mass index.
      # of PatientsAge (Years)BMI (kg/m2)Sex (% Female)EtiologyLateralityComorbidities
      1450.1 (32–67)29.1 (22.4–35)35.70%3 congenital, 1 post-traumatic, 1 developmental, 9 arthritis8 R, 6 L2 Diabetes
      To generate MAD measurements, the distance was measured from the center of the tibial plateau to the mechanical axis of the lower limb. A positive MAD value was recorded if the mechanical axis was medial to the center of the tibial plateau (varus deformity). A negative MAD value was recorded if the mechanical axis was lateral to the center of the tibial plateau (valgus deformity). For 14 patients, the MAD changed from a mean deviation of 26.6 mm (range 12–36 mm, ±9.36 mm) medially to 12.1 mm (range 3–20 mm, ±4.89 mm) laterally. The mean change in MAD was 38.71 mm (range 22–52 mm, ±10.62, p < 0.0001) (Table 2). This change reflects HTO's effectiveness in correcting the alignment from varus deformity.
      Table 2Pre and post-operative radiographic measurements.
      MeasurementsMAD (mm, medial +, lateral -)MAA (+varus, - valgus)MPTA (degrees)Caton Deschamps IndexPPTA (degrees)JLOA (degrees)
      Pre-Op26.67.3583.711.0480.42.7
      Post-Op−12.1−3.593.10.877.31.3
      Δ38.71 laterally10.86 valgus9.43−0.23−3.14−1.42
      p-value0.0001 ∗∗∗0.0001 ∗∗∗0.0001 ∗∗∗0.0001 ∗∗∗0.01 ∗∗0.078
      Asterisks indicate significant p-values, ∗ = p < 0.05, ∗∗ = P < 0.01, ∗∗∗ = p < 0.001.
      The MAA measurements demonstrated a general trend of patients going from varus deformities to valgus deformities (positive MAA designates varus, negative MAA designates valgus). The mean pre-operative MAA +7.35 (range 3–11, ±2.56), and the mean post-operative MAA was −3.5 (range −6 to −1, ±1.29). The mean change was −10.86 (range −16 to −6, ±3.30, p < 0.0001) (Table 2). Postoperatively, all 14 patients achieved correction to less than 6° of valgus, and 11 out of 14 patients had less than 5° of valgus.
      MPTA measurements demonstrated a general increase post-operatively. The mean pre-operative MPTA was 83.71° (range 73–87°, ±3.38°), and the mean post-operative MPTA was 93.1° (range 85–98°, ±3.70). The mean change in MPTA was 9.43 (range 3–14°, ±3.34°, p < 0.0001) (Table 2). The mean pre-operative CDI was 1.04 (range 0.8–1.2, ±0.14), and the mean post-operative CDI was 0.8 (range 0.4–1.1, ±0.17), having a mean decrease of 0.23 (range −0.5 to −0.1, ±0.14, p < 0.0001) (Table 2). The mean pre-operative PPTA was 80.4° (range 72–88°, ±3.74°), and the mean post-operative PPTA was 77.3° (range 69–83°, ±4.01°). The mean change in PPTA was −3.14° (range -9 – 1, ±2.91, p = 0.01) (Table 2). The mean pre-operative JLOA was 2.7° (range -5 – 5°, ±2.61°), and the mean post-operative JLOA was 1.3° (range -2 – 3°, ±1.49°). The mean change in JLOA was −1.42 (range 0–4°, ±1.10°, p = 0.078) (Table 2).
      We set an acceptable goal of post-operative MAD as 5–15 mm lateral from the center of the tibial plateau. This allowed us to calculate the accuracy of our MAD correction. We calculated the accuracy of the MAD correction by using the following equation, derived from Elattar et al.
      • Elattar O.
      • Swarup I.
      • Lam A.
      • Nguyen J.
      • Fragomen A.
      • Rozbruch S.R.
      Open wedge distal femoral osteotomy: accuracy of correction and patient outcomes.
      :
      Accuracy%=100×(1|PostoperativeMADAcceptableMAD|PreoperativeMAD(10mm))


      We used −10mm (10 mm lateral from the tibial plateau) as a benchmark value because it is the median of our acceptable post-operative MAD range (5–15 mm lateral). Based on calculations, the mean accuracy of correction was 98.3% (range 87–100%, standard deviation ± 3.3%).
      There were significant improvements in overall SF-36 scores and PF, RP, and BP sub-scores at follow-up time of 35.1 months (range 15–64 months) (Table 3). The mean post-operative Oxford knee score was 42.875 (range 34–48, ±5.28).
      Table 3Pre and post-operative SF-36 scores. Asterisks indicate significant p-values.
      SF-36PFRPBPGHVTSFREMHAverage
      Pre-Op49.451.436.977.767.469.485.284.465.2
      Post-Op9079.967.78673.684.791.783.982.2
      p-value0.000 ∗∗∗0.048 ∗0.008 ∗∗0.3130.3970.1710.5660.9410.041 ∗
      ∗ = p < 0.05, ∗∗ = p < 0.01, ∗∗∗ = p < 0.001.
      Patients were advised to undergo hardware removal 1 year after bony consolidation as confirmed by x-ray. There were no non-unions, delayed unions, losses of correction or hinge fractures among our patients in the study.

      4. Discussion

      High tibial osteotomy is an accepted treatment option for young and active patients with uni-compartmental OA of the knee. Our results showed significant improvement in overall post-operative SF-36 scores, and PF, RP and PB subscores (Table 3). Our preferred technique was 98.3% accurate to achieve the preplanned correction in MAD. Only preliminary radiographic findings of our technique have been previously reported in another paper as a part of a treatment group.
      • Ghasemi S.A.
      • Zhang D.T.
      • Fragomen A.
      • Rozbruch S.R.
      Proximal tibial osteotomy for genu varum: radiological evaluation of deformity correction with a plate vs external fixator.
      There are several studies describing the efficacy of OWHTO and clinical improvement after surgery.
      • Akizuki S.
      • Yasukawa Y.
      • Takizawa T.
      Does arthroscopic abrasion arthroplasty promote cartilage regeneration in osteoarthritic knees with eburnation? A prospective study of high tibial osteotomy with abrasion arthroplasty versus high tibial osteotomy alone.
      ,
      • Da Cunha R.J.
      • Kraszewski A.P.
      • Hillstrom H.J.
      • Fragomen A.T.
      • Rozbruch S.R.
      Biomechanical and functional improvements gained by proximal tibia osteotomy correction of genu varum in patients with knee pain.
      ,
      • James E.W.
      • Corpus K.T.
      • Fragomen A.T.
      • Rozbruch R.
      Opening Wedge High Tibial Osteotomy, Microfracture, and Bone Marrow Aspirate Concentrate for Treatment of Varus Deformity and Osteoarthritis of the Knee.
      ,
      • Schuster P.
      • Schulz M.
      • Mayer P.
      • Schlumberger M.
      • Immendoerfer M.
      • Richter J.
      Open-wedge high tibial osteotomy and combined abrasion/microfracture in severe medial osteoarthritis and varus malalignment: 5-year results and arthroscopic findings after 2 years.
      ,
      • Spahn G.
      Complications in high tibial (medial opening wedge) osteotomy.
      ,
      • Spahn G.
      • Kirschbaum S.
      • Kahl E.
      Factors that influence high tibial osteotomy results in patients with medial gonarthritis: a score to predict the results.
      Patient selection and precise planning are important factors to achieve success. Papers which discussed the indications for surgery, planning technique, and complications after HTO for medial uni-compartmental OA of the knee were reviewed. Additionally, prognostic factors were extracted from the literature to help assist surgeons in patient selection and discuss the outcome of surgery with patients.
      In a knee with normal alignment, the contact pressure is distributed between the medial and lateral compartments. Up to 60% of the total load transferred through the knee is transferred through the medial compartment.
      • Minzlaff P.
      • Feucht M.J.
      • Saier T.
      • et al.
      Osteochondral autologous transfer combined with valgus high tibial osteotomy: long-term results and survivorship analysis.
      ,
      • Mootanah R.
      • Imhauser C.W.
      • Reisse F.
      • et al.
      Development and validation of a computational model of the knee joint for the evaluation of surgical treatments for osteoarthritis.
      This contact pressure is necessary for maintaining normal cartilage physiology.
      • Mina C.
      • Garrett W.E.
      • Pietrobon R.
      • Glisson R.
      • Higgins L.
      High tibial osteotomy for unloading osteochondral defects in the medial compartment of the knee.
      In the setting of a varus deformity, the percentage of total load transferred through the medial compartment can increase up to 80–90%,
      • Bode G.
      • Schmal H.
      • Pestka J.M.
      • Ogon P.
      • Südkamp N.P.
      • Niemeyer P.
      A non-randomized controlled clinical trial on autologous chondrocyte implantation (ACI) in cartilage defects of the medial femoral condyle with or without high tibial osteotomy in patients with varus deformity of less than 5.
      which can damage the cartilage in the medial compartment of the knee. Reduction in the load over the medial compartment increases synovial flow and feeding to the area of a cartilage defect,
      • Tsukada S.
      • Wakui M.
      Is overcorrection preferable for repair of degenerated articular cartilage after open-wedge high tibial osteotomy?.
      and aids in cartilage repair.
      • Mina C.
      • Garrett W.E.
      • Pietrobon R.
      • Glisson R.
      • Higgins L.
      High tibial osteotomy for unloading osteochondral defects in the medial compartment of the knee.
      Thus, unloading the medial compartment and redistributing some of the excessive load from the medial compartment to the lateral compartment can promote cartilage regeneration in the medial compartment.
      Complete unloading of the medial compartment can be achieved by realigning the knee to 6–8° of valgus alignment in most cases in a biomechanical study.
      • Mina C.
      • Garrett W.E.
      • Pietrobon R.
      • Glisson R.
      • Higgins L.
      High tibial osteotomy for unloading osteochondral defects in the medial compartment of the knee.
      In this investigation, complete unloading of the medial compartment was achieved in all specimens in 10° valgus alignment. They suggested that 6–10° of valgus is the optimal knee alignment to treat medial compartment OA with HTO, and this angle is independent of patient specific factors, and body weight does not affect optimal loading in this valgus alignment. However, this amount of valgus alignment causes overloading of the lateral compartment, which can cause lateral compartment OA progression. The authors demonstrated that medial and lateral compartments would have equal loading pressures with the knee at 0–4° of valgus alignment.
      In our study, all 14 patients achieved between 1 and 6° of valgus alignment post-operatively. 11 out of the 14 patients accomplished valgus alignment less than 5°. We feel that using our MAD planning method, we were able to attain an optimal valgus alignment, where the HTO unloads the stresses on the medial compartment, but does not overload the lateral compartment.
      Cartilage regeneration was lower in patients with grade 2 KL OA compared to patients with grade 3 or 4 KL medial compartment OA.
      • Koshino T.
      • Wada S.
      • Ara Y.
      • Saito T.
      Regeneration of degenerated articular cartilage after high tibial valgus osteotomy for medial compartmental osteoarthritis of the knee.
      Additionally, knees with advanced cartilage degeneration have better regeneration than knees with cartilage defects of <50% of the cartilage depth.
      • Tsukada S.
      • Wakui M.
      Is overcorrection preferable for repair of degenerated articular cartilage after open-wedge high tibial osteotomy?.
      For knees with larger cartilage defects in the medial compartment, there is more room for cartilage regeneration after HTO. Fibrocartilage completely fills the defect area over the medial compartment after 2 years.
      • Kanamiya T.
      • Naito M.
      • Hara M.
      • Yoshimura I.
      The influences of biomechanical factors on cartilage regeneration after high tibial osteotomy for knees with medial compartment osteoarthritis: clinical and arthroscopic observations.
      ,
      • Koshino T.
      • Wada S.
      • Ara Y.
      • Saito T.
      Regeneration of degenerated articular cartilage after high tibial valgus osteotomy for medial compartmental osteoarthritis of the knee.
      One possible explanation is that remaining live chondrocytes inhibit cartilage repair in patients with less extensive cartilage damage and lower grades of OA changes. In the cartilage defect, residual cartilage over the subchondral bone acts as an obstacle for growth of new cartilage tissue. The regenerated cartilage consisted of a hyaline component in the deep layer, while the superficial layer was composed completely of fibrocartilage.
      • Koshino T.
      • Wada S.
      • Ara Y.
      • Saito T.
      Regeneration of degenerated articular cartilage after high tibial valgus osteotomy for medial compartmental osteoarthritis of the knee.
      Additionally, the time needed for complete repair of the cartilage defect and maturation of the regenerate cartilage was increased in elderly patients. Removing and shaving damaged cartilage in less advanced defects may improve cartilage repair.
      • Koshino T.
      • Wada S.
      • Ara Y.
      • Saito T.
      Regeneration of degenerated articular cartilage after high tibial valgus osteotomy for medial compartmental osteoarthritis of the knee.
      Regenerative hyaline cartilage is observed more often in patients who underwent combined microfracture and HTO compared to HTO alone.
      • Matsunaga D.
      • Akizuki S.
      • Takizawa T.
      • Yamazaki I.
      • Kuraishi J.
      Repair of articular cartilage and clinical outcome after osteotomy with microfracture or abrasion arthroplasty for medial gonarthrosis.
      Additionally, increased amounts of type II collagen are present in regenerated cartilage in combined HTO and blood mesenchymal stem cell transfusion procedures.
      • Saw K.Y.
      • Anz A.
      • Jee C.S.Y.
      • Ng R.C.S.
      • Mohtarrudin N.
      • Ragavanaidu K.
      High tibial osteotomy in combination with chondrogenesis after stem cell therapy: a histologic report of 8 cases.
      Akizuki et al. reported that the higher cartilage repair was seen in the femoral lesions compared to tibial lesions in patients who underwent combined HTO and abrasion arthroplasty.
      • Akizuki S.
      • Yasukawa Y.
      • Takizawa T.
      Does arthroscopic abrasion arthroplasty promote cartilage regeneration in osteoarthritic knees with eburnation? A prospective study of high tibial osteotomy with abrasion arthroplasty versus high tibial osteotomy alone.
      There were no differences between the femoral and tibial cartilage lesion repair in patients who underwent HTO alone. Cartilage repair in the femoral condyle after abrasion arthroplasty combined with HTO is greater than that of the tibia because of anatomic differences between the distal femur and proximal tibia, in addition to changes in the contact pressure in the femur during flexion of the knee.
      • Akizuki S.
      • Yasukawa Y.
      • Takizawa T.
      Does arthroscopic abrasion arthroplasty promote cartilage regeneration in osteoarthritic knees with eburnation? A prospective study of high tibial osteotomy with abrasion arthroplasty versus high tibial osteotomy alone.
      Patients demonstrated progression of cartilage repair up to 3 or 4 years after surgery and cartilage repair improved over time.

      4.1 Indications

      Patient selection for HTO is critical. The main indication for HTO is isolated medial compartment OA of the knee in patients with varus deformity.
      • Bonasia D.E.
      • Dettoni F.
      • Sito G.
      • et al.
      Medial opening wedge high tibial osteotomy for medial compartment overload/arthritis in the varus knee: prognostic factors.
      The ideal age for patients undergoing HTO to treat OA of the knee is 65 years of age or below. However, reasonable clinical outcomes were reported in patients undergoing HTO to treat OA of the knee 70 years of age or below.
      • Jeon Y.S.
      • Ahn C.H.
      • Kim M.K.
      Comparison of HTO with articular cartilage surgery and UKA in unicompartmental OA.
      There are multiple reported values for the total amount of varus deformity correction in HTO to treat OA of the knee. Patients with normal limb alignment as indicated by a femorotibial angle of 174° and symptomatic OA of the medial compartment can be considered candidates for HTO.
      • Tsukada S.
      • Wakui M.
      Is overcorrection preferable for repair of degenerated articular cartilage after open-wedge high tibial osteotomy?.
      Contraindications for HTO include flexion contractures greater than 15°, markedly decreased knee range of motion (ROM), inflammatory arthritis such as rheumatoid arthritis, obvious joint instability, BMI >35, symptomatic patellofemoral OA or radiologic patellofemoral OA of grade 3 or 4, and OA of the lateral compartment of the knee.
      • Bonasia D.E.
      • Dettoni F.
      • Sito G.
      • et al.
      Medial opening wedge high tibial osteotomy for medial compartment overload/arthritis in the varus knee: prognostic factors.
      ,
      • Huan S.
      Effect analysis of opening wedge high tibial osteotomy (OWHTO) for the treatment of medial compartment osteoarthritis.
      ,
      • Spahn G.
      Complications in high tibial (medial opening wedge) osteotomy.
      ,
      • Spahn G.
      • Kirschbaum S.
      • Kahl E.
      Factors that influence high tibial osteotomy results in patients with medial gonarthritis: a score to predict the results.
      ,
      • Tanaka T.
      • Matsushita T.
      • Miyaji N.
      • et al.
      Deterioration of patellofemoral cartilage status after medial open-wedge high tibial osteotomy.
      ,
      • Tsukada S.
      • Wakui M.
      Is overcorrection preferable for repair of degenerated articular cartilage after open-wedge high tibial osteotomy?.
      Some studies disagreed, and did not consider slight degenerative OA changes in the lateral compartment of the knee to be a contraindication for HTO.
      • Tsukada S.
      • Wakui M.
      Is overcorrection preferable for repair of degenerated articular cartilage after open-wedge high tibial osteotomy?.
      In this study, patients’ mean BMI was 29.1 (22.4–35) and mean age was 50.1 (32–64) years old, indicating that all patients were suitable candidates for undergoing HTO (Table 1).

      4.2 Surgical planning

      A crucial component of HTO is defining the correction goal while planning the surgery. There were multiple reported pre-operative goals in the literature. A biomechanical study proposed the goal for correction to be 8–10° of valgus alignment to completely unload the medial compartment.
      • Mina C.
      • Garrett W.E.
      • Pietrobon R.
      • Glisson R.
      • Higgins L.
      High tibial osteotomy for unloading osteochondral defects in the medial compartment of the knee.
      Conversely, a clinical study proposed a femorotibial angle of 170° as the goal for correction in HTO.
      • Tsukada S.
      • Wakui M.
      Is overcorrection preferable for repair of degenerated articular cartilage after open-wedge high tibial osteotomy?.
      In this alignment the mechanical axis of the lower extremity crosses at the lateral third of the tibial plateau.
      • Hsu A.C.
      • Tirico L.E.P.
      • Lin A.G.
      • Pulido P.A.
      • Bugbee W.D.
      Osteochondral allograft transplantation and opening wedge tibial osteotomy: clinical results of a combined single procedure.
      ,
      • Mina C.
      • Garrett W.E.
      • Pietrobon R.
      • Glisson R.
      • Higgins L.
      High tibial osteotomy for unloading osteochondral defects in the medial compartment of the knee.
      This planning goal was used in multiple papers.
      • Akizuki S.
      • Yasukawa Y.
      • Takizawa T.
      Does arthroscopic abrasion arthroplasty promote cartilage regeneration in osteoarthritic knees with eburnation? A prospective study of high tibial osteotomy with abrasion arthroplasty versus high tibial osteotomy alone.
      ,
      • Koshino T.
      • Wada S.
      • Ara Y.
      • Saito T.
      Regeneration of degenerated articular cartilage after high tibial valgus osteotomy for medial compartmental osteoarthritis of the knee.
      ,
      • Tsukada S.
      • Wakui M.
      Is overcorrection preferable for repair of degenerated articular cartilage after open-wedge high tibial osteotomy?.
      Slight overcorrection of varus deformities in elderly patients led to improved clinical outcomes, but slight over- or under-corrections yielded similar results.
      • Bonasia D.E.
      • Dettoni F.
      • Sito G.
      • et al.
      Medial opening wedge high tibial osteotomy for medial compartment overload/arthritis in the varus knee: prognostic factors.
      In patients ages 60–70, this over-correction was defined as 12–14° of valgus.
      • Matsunaga D.
      • Akizuki S.
      • Takizawa T.
      • Yamazaki I.
      • Kuraishi J.
      Repair of articular cartilage and clinical outcome after osteotomy with microfracture or abrasion arthroplasty for medial gonarthrosis.
      In patients with severe varus deformities as defined by lateral distal femoral angle greater than 90°, HTO planning may necessitate wedge sizes up to 20 mm. In these patients, HTO with double level osteotomies may be preferred.
      • Tanaka T.
      • Matsushita T.
      • Miyaji N.
      • et al.
      Deterioration of patellofemoral cartilage status after medial open-wedge high tibial osteotomy.
      However, shifting the mechanical axis from the medial to lateral plateau increases the load in the lateral compartment and increases the risk of developing lateral compartment OA. For this reason, in patients who have underwent lateral partial meniscectomies, a slight under-correction is recommended.
      • Schuster P.
      • Schulz M.
      • Mayer P.
      • Schlumberger M.
      • Immendoerfer M.
      • Richter J.
      Open-wedge high tibial osteotomy and combined abrasion/microfracture in severe medial osteoarthritis and varus malalignment: 5-year results and arthroscopic findings after 2 years.
      Medial compartment cartilage regeneration after HTO was improved in patients with post-operative mechanical axis angles of 0–6° of valgus compared to patients with post-operative mechanical axis angles outside of this range.
      • Jung W.H.
      • Takeuchi R.
      • Chun C.W.
      • Lee J.S.
      • Jeong J.H.
      Comparison of results of medial opening-wedge high tibial osteotomy with and without subchondral drilling.
      Other biomechanical studies showed the post-operative mechanical axis angles of 0–4° of valgus not only partially unloaded the medial compartment but also caused no significant increase in the lateral compartment contact pressure and loading.
      • Mina C.
      • Garrett W.E.
      • Pietrobon R.
      • Glisson R.
      • Higgins L.
      High tibial osteotomy for unloading osteochondral defects in the medial compartment of the knee.
      ,
      • Van Thiel G.S.
      • Frank R.M.
      • Gupta A.
      • et al.
      Biomechanical evaluation of a high tibial osteotomy with a meniscal transplant.
      MAD was used to plan HTO procedures in our patients. Our goal was transferring the mechanical axis 10 mm lateral to the neutral point of the knee and considering a 5–15 mm range to be acceptable.
      • Gordon J.E.
      • Chen R.C.
      • Dobbs M.B.
      • Luhmann S.J.
      • Rich M.M.
      • Schoenecker P.L.
      Interobserver and intraobserver reliability in the evaluation of mechanical Axis deviation.
      ,
      • Paley D.
      Normal lower limb alignment and joint orientation.
      This goal was selected to unload the medial compartment while avoiding overloading the lateral compartment. In our patients, the change in mechanical axis angle was 7.35° varus to 3.50° valgus after HTO and correlated with considerable clinical improvement. Overall, our patients achieved significant clinical improvement with around 3–4° valgus after correction.
      Among 14 included cases, 11 patients achieved correction within the less than 5° of valgus that prevents lateral compartment overloading based on the biomechanical study findings. Three out of 14 patients were corrected to 5–6° of valgus. In our patients, MAD was a useful indicator for both planning and evaluating the outcome of HTO procedures and is a simple and reliable measurement technique.

      4.3 Factors affecting the outcome of the surgery

      The outcome and survival rate of HTO for medial compartment OA was reported as 89.5% at 5 years, 74.7% at 10 years and 66.9% at 15 years after surgery. About 12% of patients achieved complete relief of pain, while others achieved some pain relief.
      • Tang W.C.
      • Henderson I.J.P.
      High tibial osteotomy: long term survival analysis and patients' perspective.
      The factors affecting outcomes of HTO were evaluated in some studies. Some studies reported age below 56 years of age was a positive indicator of improved outcomes,
      • Bonasia D.E.
      • Dettoni F.
      • Sito G.
      • et al.
      Medial opening wedge high tibial osteotomy for medial compartment overload/arthritis in the varus knee: prognostic factors.
      other studies found no correlation between age and outcome within the age range of 31–67 years.
      • Spahn G.
      • Kirschbaum S.
      • Kahl E.
      Factors that influence high tibial osteotomy results in patients with medial gonarthritis: a score to predict the results.
      Older females had slightly worse outcomes than older males. The failure rate was also elevated in patients above the age of 65.
      • Lee S.S.
      • So S.Y.
      • Jung E.Y.
      • Kim H.J.
      • Lee B.H.
      • Wang J.H.
      Predictive factors for patellofemoral degenerative progression after opening-wedge high tibial osteotomy.
      In this patient group, uni-compartmental knee arthroplasty was proposed as an alternative treatment.
      • Jeon Y.S.
      • Ahn C.H.
      • Kim M.K.
      Comparison of HTO with articular cartilage surgery and UKA in unicompartmental OA.
      Age also has an impact on cartilage repair, which could contribute to the increased failure rate in older patients.
      • Akizuki S.
      • Yasukawa Y.
      • Takizawa T.
      Does arthroscopic abrasion arthroplasty promote cartilage regeneration in osteoarthritic knees with eburnation? A prospective study of high tibial osteotomy with abrasion arthroplasty versus high tibial osteotomy alone.
      Excellent preoperative knee scores were an additional indicator of improved outcomes for patients undergoing HTO.
      • Bonasia D.E.
      • Dettoni F.
      • Sito G.
      • et al.
      Medial opening wedge high tibial osteotomy for medial compartment overload/arthritis in the varus knee: prognostic factors.
      Conversely, having more than 24 months of symptoms before surgery was a poor prognostic factor.
      • Spahn G.
      • Kirschbaum S.
      • Kahl E.
      Factors that influence high tibial osteotomy results in patients with medial gonarthritis: a score to predict the results.
      Additionally, preoperative Knee Injury and Osteoarthritis Outcome Score (KOOS) below 50 and preoperative knee injuries were associated with poor results. This may be due to chronic pain causing muscular atrophy and proprioception impairment, which negatively influences the outcome after surgery.
      • Spahn G.
      • Kirschbaum S.
      • Kahl E.
      Factors that influence high tibial osteotomy results in patients with medial gonarthritis: a score to predict the results.
      Knee ROM was reported as a factor that affects the outcome of HTO.
      • Jeon Y.S.
      • Ahn C.H.
      • Kim M.K.
      Comparison of HTO with articular cartilage surgery and UKA in unicompartmental OA.
      Achievement of knee flexion of greater than 120° post-operatively was associated with improved outcomes after HTO.
      • Bonasia D.E.
      • Dettoni F.
      • Sito G.
      • et al.
      Medial opening wedge high tibial osteotomy for medial compartment overload/arthritis in the varus knee: prognostic factors.
      Reduced postoperative knee ROM may be a consequence of knee OA progression or reduced pre-operative knee ROM, which is also a negative predictive factor. Thus, rehabilitation programs after HTO are important to improve both ROM and the overall surgical outcome.
      • Bonasia D.E.
      • Dettoni F.
      • Sito G.
      • et al.
      Medial opening wedge high tibial osteotomy for medial compartment overload/arthritis in the varus knee: prognostic factors.
      Obesity was reported as a negative prognostic factor for patients undergoing HTO. BMI greater than 30 kg/m2 was found to be a risk factor for early surgical failure and acceleration of knee OA progression.
      • Bonasia D.E.
      • Dettoni F.
      • Sito G.
      • et al.
      Medial opening wedge high tibial osteotomy for medial compartment overload/arthritis in the varus knee: prognostic factors.
      ,
      • Spahn G.
      • Kirschbaum S.
      • Kahl E.
      Factors that influence high tibial osteotomy results in patients with medial gonarthritis: a score to predict the results.
      Smoking was an additional negative prognostic factor and may hamper cartilage repair and render the subchondral bone more susceptible to deformation after loading.
      • Spahn G.
      • Kirschbaum S.
      • Kahl E.
      Factors that influence high tibial osteotomy results in patients with medial gonarthritis: a score to predict the results.
      The severity of OA involvement in the medial compartment has been reported as a negative prognostic factor in patients undergoing HTO.
      • Bonasia D.E.
      • Dettoni F.
      • Sito G.
      • et al.
      Medial opening wedge high tibial osteotomy for medial compartment overload/arthritis in the varus knee: prognostic factors.
      The presence of the medial tibial osteophytes, medial joint space less than 5 mm, and grade IV cartilage damage of the tibia were negative prognostic factors in one study.
      • Spahn G.
      • Kirschbaum S.
      • Kahl E.
      Factors that influence high tibial osteotomy results in patients with medial gonarthritis: a score to predict the results.
      In this study, the presence of osteophytes was a better reflection of the severity of OA than medial joint space narrowing. Prior surgery did not influence the results in their study.
      • Spahn G.
      • Kirschbaum S.
      • Kahl E.
      Factors that influence high tibial osteotomy results in patients with medial gonarthritis: a score to predict the results.
      There was no correlation between both post-operative alignment or residual medial laxity and HTO failures.
      • Bonasia D.E.
      • Dettoni F.
      • Sito G.
      • et al.
      Medial opening wedge high tibial osteotomy for medial compartment overload/arthritis in the varus knee: prognostic factors.
      Lateral tibial thrust and joint instability were additional negative prognostic factors.
      • Spahn G.
      • Kirschbaum S.
      • Kahl E.
      Factors that influence high tibial osteotomy results in patients with medial gonarthritis: a score to predict the results.
      The correlation between cartilage regeneration and clinical outcome was evaluated in multiple reviews.
      • Akizuki S.
      • Yasukawa Y.
      • Takizawa T.
      Does arthroscopic abrasion arthroplasty promote cartilage regeneration in osteoarthritic knees with eburnation? A prospective study of high tibial osteotomy with abrasion arthroplasty versus high tibial osteotomy alone.
      ,
      • Kim K.I.
      • Seo M.C.
      • Song S.J.
      • Bae D.K.
      • Kim D.H.
      • Lee S.H.
      Change of chondral lesions and predictive factors after medial open-wedge high tibial osteotomy with a locked plate system.
      Additionally, there were some reports on the correlation between cartilage repair and pre- and post-operative alignment. Tsukada et al. reported no difference in cartilage regeneration between overcorrected and moderately corrected knees.
      • Tsukada S.
      • Wakui M.
      Is overcorrection preferable for repair of degenerated articular cartilage after open-wedge high tibial osteotomy?.
      Other studies show that larger correction angles in the medial tibial condyle and smaller preoperative varus aligment were correlated with improved cartilage regeneration.
      • Kim K.I.
      • Seo M.C.
      • Song S.J.
      • Bae D.K.
      • Kim D.H.
      • Lee S.H.
      Change of chondral lesions and predictive factors after medial open-wedge high tibial osteotomy with a locked plate system.
      Jeon et al. reported greater correction in MA alignment with better cartilage repair in the medial tibial condyle.
      • Jeon Y.S.
      • Ahn C.H.
      • Kim M.K.
      Comparison of HTO with articular cartilage surgery and UKA in unicompartmental OA.
      Additionally, patients with greater than 5° of valgus after HTO had improved cartilage repair compared to patients with fewer than 5° of valgus.
      • Koshino T.
      • Wada S.
      • Ara Y.
      • Saito T.
      Regeneration of degenerated articular cartilage after high tibial valgus osteotomy for medial compartmental osteoarthritis of the knee.
      Superior cartilage regeneration was reported in cases with increased medial joint space after HTO compared to patients without increased medial joint space.
      • Koshino T.
      • Wada S.
      • Ara Y.
      • Saito T.
      Regeneration of degenerated articular cartilage after high tibial valgus osteotomy for medial compartmental osteoarthritis of the knee.
      Formal scoring systems have been proposed for patients being considered for HTO.
      • Spahn G.
      • Kirschbaum S.
      • Kahl E.
      Factors that influence high tibial osteotomy results in patients with medial gonarthritis: a score to predict the results.
      Negative prognostic factors were assigned point values as follows: female sex = 1 point, history of symptom for more than 24 months = 2 points, preoperative KOOS score less than 50 = 2 points, obesity = 2 points, history of smoking = 2 points, medial tibial osteophytes = 2 points, medial joint space width less than 5 mm = 2 points, stage IV of cartilage defect of the tibia = 2 points, severe sclerosis contraindicating microfracture = 1 point. Patients with negative prognostic factor point totals greater than nine are associated with significantly worse outcomes. Additionally, patients with four or more negative prognostic factors are recommended to undergo uni-compartmental knee arthroplasty as opposed to HTO.

      4.4 Complications

      Complication rates after OWHTO have been reported to range from 1.9% to 55%.
      • Sikorski J.M.
      • Sikorska J.Z.
      Relative risk of different operations for medial compartment osteoarthritis of the knee.
      Complications following HTO were classified into 4 categories (Table 4).
      • Woodacre T.
      • Ricketts M.
      • Evans J.T.
      • et al.
      Complications associated with opening wedge high tibial osteotomy — a review of the literature and of 15years of experience.
      Deep venous thromboses and lateral hinge fractures were the most common complications following HTO.
      • Woodacre T.
      • Ricketts M.
      • Evans J.T.
      • et al.
      Complications associated with opening wedge high tibial osteotomy — a review of the literature and of 15years of experience.
      There is minimal risk of systemic complications following HTO.
      • Sikorski J.M.
      • Sikorska J.Z.
      Relative risk of different operations for medial compartment osteoarthritis of the knee.
      Pulmonary emboli were the only reported systemic complication following HTO.
      • Han S.B.
      • In Y.
      • Oh K.J.
      • Song K.Y.
      • Yun S.T.
      • Jang K.M.
      Complications associated with medial opening-wedge high tibial osteotomy using a locking plate: a multicenter study.
      Patients with major complications that required additional surgery were reported to have worse outcomes.
      • Han S.B.
      • In Y.
      • Oh K.J.
      • Song K.Y.
      • Yun S.T.
      • Jang K.M.
      Complications associated with medial opening-wedge high tibial osteotomy using a locking plate: a multicenter study.
      Deep wound infection, symptomatic hardware, nonunion, and loss of correction were major complications associated with worse clinical outcomes.
      • Han S.B.
      • In Y.
      • Oh K.J.
      • Song K.Y.
      • Yun S.T.
      • Jang K.M.
      Complications associated with medial opening-wedge high tibial osteotomy using a locking plate: a multicenter study.
      In a review of 84 cases, Bonasia et al. reported six HTO failures requiring TKA, but found no correlation between postoperative alignment and failure.
      • Bonasia D.E.
      • Dettoni F.
      • Sito G.
      • et al.
      Medial opening wedge high tibial osteotomy for medial compartment overload/arthritis in the varus knee: prognostic factors.
      An additional review reported up to 27.4% of patients experienced loss of correction post-operatively and had worse outcomes than patients without loss of correction, while outcomes were positive in patients who progressed to mild valgus post-operatively.
      • Spahn G.
      Complications in high tibial (medial opening wedge) osteotomy.
      Of note, there have been reports of higher failure rates of allograft compared to autograft in OWHTO, but there were no allograft related complications in our study.
      • Kuremsky M.A.
      • Schaller T.M.
      • Hall C.C.
      • Roehr B.A.
      • Masonis J.L.
      Comparison of autograft vs allograft in opening-wedge high tibial osteotomy.
      Table 4Categorization of complications.
      Complication CategoryDescription
      1Persistence of knee pain causing failure and progression to total knee replacement
      2Generalized complication (infection, DVT, etc)
      3Complication related to surgical implant (e.g. painful hardware)
      4Complications related to opening wedge osteotomy (delayed union, nonunion, lateral hinge fracture, loss of correction)
      Lateral hinge fractures are a possible complication during HTO surgery. Risk factors for lateral hinge fracture during HTO include planned opening wedge osteotomies greater than 11 mm and correction angles greater than 12°.
      • Han S.B.
      • Choi J.H.
      • Mahajan A.
      • Shin Y.S.
      Incidence and predictors of lateral hinge fractures following medial opening-wedge high tibial osteotomy using locking plate system: better performance of computed tomography scans.
      ,
      • Spahn G.
      Complications in high tibial (medial opening wedge) osteotomy.
      Some reviews reported lateral hinge fracture rates of 18.2% in their patients undergoing HTO.
      • Spahn G.
      Complications in high tibial (medial opening wedge) osteotomy.
      Unrecognized lateral hinge fractures may contribute to loss of correction or delayed union or nonunion.
      • Miller B.S.
      • Joseph T.A.
      • Barry E.M.
      • Rich V.J.
      • Sterett W.I.
      Patient satisfaction after medial opening high tibial osteotomy and microfracture.
      Other reviews found that the mean opening wedge size in patients who experienced lateral hinge fracture was 13–14 mm, compared to 12 mm in patients who did not experience such fractures.
      • Han S.B.
      • Choi J.H.
      • Mahajan A.
      • Shin Y.S.
      Incidence and predictors of lateral hinge fractures following medial opening-wedge high tibial osteotomy using locking plate system: better performance of computed tomography scans.
      ,
      • Han S.B.
      • In Y.
      • Oh K.J.
      • Song K.Y.
      • Yun S.T.
      • Jang K.M.
      Complications associated with medial opening-wedge high tibial osteotomy using a locking plate: a multicenter study.
      Lateral hinge fractures were classified into three types based on the extension of the fracture line.
      • Takeuchi R.
      • Ishikawa H.
      • Kumagai K.
      • et al.
      Fractures around the lateral cortical hinge after a medial opening-wedge high tibial osteotomy: a new classification of lateral hinge fracture.
      In Type 1 fractures, the fracture line reaches the proximal tibiofibular joint or extends into the joint. In Type 2 fractures, the fracture line extends to the distal aspect of the tibiofibular joint. In Type 3 fractures, the facture line extends to the tibial plateau. There are no reported complications in patients with Type 1 fractures, while there are some delayed unions and 3–7° of loss in correction in patients with Type 2 fractures. However, the soft tissue around the tibiofibular joint is dense enough to provide stability to the fracture, and patients with lateral hinge fractures are recommended to undergo the same rehabilitation as patients without fractures. Specifically, non-weight bearing (NWB) was recommended for patients with Type 2 fractures until the formation of a callous at the tibial osteotomy site. Alternatively, Type 3 fractures are considered more serious complications that require being addressed precisely, as the fracture line extends to the articular surface of the knee joint.
      Screw fixation from lateral to medial is recommended for fixation of intra-operative intra-articular fractures identified during surgery. Screws inserted lateral to medial and distal to proximal are used for fixation of displaced lateral hinge fractures.
      • Bonasia D.E.
      • Dettoni F.
      • Sito G.
      • et al.
      Medial opening wedge high tibial osteotomy for medial compartment overload/arthritis in the varus knee: prognostic factors.
      To prevent lateral hinge fractures, spreading of the osteotomy site should be performed carefully and gradually. Inserting a Kirschner wire in the plane of the osteotomy and cutting the bone below the K-wire can prevent lateral hinge fractures. Other factors which can prevent lateral hinge fractures include the selection of a starting point for the osteotomy above the upper margin of the pes anserine muscular insertion on the tibia, a trajectory towards the tibiofibular joint, and termination of the osteotomy 5 mm from the lateral cortex of the tibia. This region of the lateral cortex has more plasticity, and the osteotomy can be opened without fracturing the lateral cortex. The use of osteotomes with increasing levels of thickness can open the wedge gradually after creating the osteotomy, while care is taken to avoid a lever action. Additionally, biplanar osteotomies can aide in avoiding intra-operative fractures. This is achieved with one osteotomy 1 cm proximal to the tibial tuberosity, and a second frontal osteotomy performed from this point, and can prevent lateral hinge fractures.
      • Spahn G.
      Complications in high tibial (medial opening wedge) osteotomy.
      ,
      • Takeuchi R.
      • Ishikawa H.
      • Kumagai K.
      • et al.
      Fractures around the lateral cortical hinge after a medial opening-wedge high tibial osteotomy: a new classification of lateral hinge fracture.

      4.5 Residual medial laxity and outcomes after HTO

      Soft tissue laxity is a factor that negatively affects alignment after HTO, and may be responsible for changes in the mechanical axis angle. Laxity is assessed by measuring the change in joint line obliquity angle (JLOA), which reflects the laxity of the medial soft tissue and affects the correction of varus deformities with HTO. Additional changes in JLOA transfer the mechanical axis laterally and stretch the soft tissue on the medial side of the knee. Changes in JLOA may explain correction errors after HTO.
      • Lee D kyung
      • Wang J.H.
      • Won Y.
      • et al.
      Preoperative latent medial laxity and correction angle are crucial factors for overcorrection in medial open-wedge high tibial osteotomy.
      Residual medial laxity and opening more than 2 mm was identified in 52% of patients after HTO during valgus stress on physical exam testing with 30° of knee flexion.
      • Bonasia D.E.
      • Dettoni F.
      • Sito G.
      • et al.
      Medial opening wedge high tibial osteotomy for medial compartment overload/arthritis in the varus knee: prognostic factors.
      Medial laxity caused patients knee pain after HTO, however it did not affect the surgical outcome or knee stability. Medial laxity and associated valgus overcorrection deformities might cause further gradual valgus deviation.
      • Bonasia D.E.
      • Dettoni F.
      • Sito G.
      • et al.
      Medial opening wedge high tibial osteotomy for medial compartment overload/arthritis in the varus knee: prognostic factors.
      Detection of latent medial laxity is important in planning HTO, and can be assessed by measuring changes in the JLOA between a weight bearing x-ray and a valgus stress x-ray.
      • Lee D kyung
      • Wang J.H.
      • Won Y.
      • et al.
      Preoperative latent medial laxity and correction angle are crucial factors for overcorrection in medial open-wedge high tibial osteotomy.
      Changes in correction angle are correlated with changes in JLOA, and changes in JLOA are positively correlated with correction angle and latent medial laxity. Large changes in JLOA were correlated with overcorrection. Release of the superficial medial ligaments during HTO affects the tension of the soft tissue and causes additional change in JLOA.
      • Lee D kyung
      • Wang J.H.
      • Won Y.
      • et al.
      Preoperative latent medial laxity and correction angle are crucial factors for overcorrection in medial open-wedge high tibial osteotomy.
      Overcorrection of the mechanical axis can cause progressive degeneration of the patellofemoral joint and may increase the difficulty of future total knee arthroplasty. Large correction angles in patients with severe varus deformities and latent medial laxity are risk factors for overcorrection.
      • Lee D kyung
      • Wang J.H.
      • Won Y.
      • et al.
      Preoperative latent medial laxity and correction angle are crucial factors for overcorrection in medial open-wedge high tibial osteotomy.
      In these patients, it is recommended to change the goal correction angle while planning HTO, by shifting the target point for mechanical axis from passing 62.5%–57.5% through the total medial to lateral width of the proximal tibial plateau to prevent overcorrection. This revised target point corresponds to the mechanical axis with two degrees of valgus.
      JLOA greater than 5° introduces shear stress on the tibial articular cartilage, and large correction angles with resultant JLOA changes of more than 5° may increase such stresses.
      • Nakayama H.
      • Schröter S.
      • Yamamoto C.
      • et al.
      Large correction in opening wedge high tibial osteotomy with resultant joint-line obliquity induces excessive shear stress on the articular cartilage.
      Large correction angles affect the JLOA and causes worse clinical outcomes,
      • Goshima K.
      Editorial commentary: does patellofemoral degenerative progression after open-wedge high tibial osteotomy adversely affect clinical outcomes?.
      thus patients requiring large correction angles should be treated with double level osteotomy as opposed to HTO.
      • Nakayama H.
      • Schröter S.
      • Yamamoto C.
      • et al.
      Large correction in opening wedge high tibial osteotomy with resultant joint-line obliquity induces excessive shear stress on the articular cartilage.

      4.6 Patellofemoral change after HTO and outcomes

      Some studies evaluated the effect of HTO on the patellofemoral joint and outcomes.
      • Goshima K.
      • Sawaguchi T.
      • Shigemoto K.
      • Iwai S.
      • Nakanishi A.
      • Ueoka K.
      Patellofemoral osteoarthritis progression and alignment changes after open-wedge high tibial osteotomy do not affect clinical outcomes at mid-term follow-up.
      ,
      • Lee S.S.
      • So S.Y.
      • Jung E.Y.
      • Kim H.J.
      • Lee B.H.
      • Wang J.H.
      Predictive factors for patellofemoral degenerative progression after opening-wedge high tibial osteotomy.
      ,
      • Lee Y.S.
      • Lee S.B.
      • Oh W.S.
      • Kwon Y.E.
      • Lee B.K.
      Changes in patellofemoral alignment do not cause clinical impact after open-wedge high tibial osteotomy.
      The Q-angle changes distally and laterally after HTO and tibial tuberosity transfer. Patella baja is an additional change after HTO that affects the mechanics of the patellofemoral joint. In our patients, the CDI index decreased from 1.1 to 0.8 although patients did not express any patella pain. Additionally, the tibial slope changed from 80.4 to 77.3 after HTO, and PPTA measurements did not deviate from normal ranges. A biomechanical study demonstrated the increase in posterior tibial slope up to 3° did not significantly affect the contact pressure in the knee.
      • Van Thiel G.S.
      • Frank R.M.
      • Gupta A.
      • et al.
      Biomechanical evaluation of a high tibial osteotomy with a meniscal transplant.
      The incidence of patella baja was reported to be up to 89%.
      • Tanaka T.
      • Matsushita T.
      • Miyaji N.
      • et al.
      Deterioration of patellofemoral cartilage status after medial open-wedge high tibial osteotomy.
      Increasing contact pressure on the articular surface of the patella causes progressive degeneration.
      • Lee S.S.
      • So S.Y.
      • Jung E.Y.
      • Kim H.J.
      • Lee B.H.
      • Wang J.H.
      Predictive factors for patellofemoral degenerative progression after opening-wedge high tibial osteotomy.
      Concerns have been expressed over patellofemoral joint degeneration causing anterior knee pain and crepitus, which may impact the outcome of HTO. However, there was no correlation between patellofemoral changes and clinical outcome.
      • Bonasia D.E.
      • Dettoni F.
      • Sito G.
      • et al.
      Medial opening wedge high tibial osteotomy for medial compartment overload/arthritis in the varus knee: prognostic factors.
      ,
      • Goshima K.
      • Sawaguchi T.
      • Shigemoto K.
      • Iwai S.
      • Nakanishi A.
      • Ueoka K.
      Patellofemoral osteoarthritis progression and alignment changes after open-wedge high tibial osteotomy do not affect clinical outcomes at mid-term follow-up.
      Arthroscopic changes in the patellofemoral joint identified during arthroscopy did not correlate with the clinical outcome.
      • Tanaka T.
      • Matsushita T.
      • Miyaji N.
      • et al.
      Deterioration of patellofemoral cartilage status after medial open-wedge high tibial osteotomy.
      On the other hand, other studies claimed progressive patellofemoral degeneration affected clinical outcome.
      • Lee Y.S.
      • Lee S.B.
      • Oh W.S.
      • Kwon Y.E.
      • Lee B.K.
      Changes in patellofemoral alignment do not cause clinical impact after open-wedge high tibial osteotomy.
      The incidence of progressive cartilage degeneration is higher in the overcorrected patients, and clinical outcomes were significantly worse in these patients compared to acceptable correction and under-corrected patients.
      • Yoon T.H.
      • Choi C.H.
      • Kim S.J.
      • Kim S.H.
      • Kim N.H.
      • Jung M.
      Effect of medial open-wedge high tibial osteotomy on the patellofemoral joint according to postoperative realignment.
      Post-operative mechanical axis angle was the most powerful predictor of degenerative patellofemoral changes after HTO.
      • Lee S.S.
      • So S.Y.
      • Jung E.Y.
      • Kim H.J.
      • Lee B.H.
      • Wang J.H.
      Predictive factors for patellofemoral degenerative progression after opening-wedge high tibial osteotomy.
      Over-correction caused progressive degeneration of patellofemoral cartilage. Degeneration tended to progress after HTO in patients who required correction of greater than 9° of the medial proximal tibial angle and opening wedges greater than 13 mm.
      • Tanaka T.
      • Matsushita T.
      • Miyaji N.
      • et al.
      Deterioration of patellofemoral cartilage status after medial open-wedge high tibial osteotomy.
      There was no correlation between the CDI and progression of degeneration of patellofemoral cartilage, and MPTA changes were more sensitive to mechanical axis changes and predicted progression of cartilage degeneration. Patellofemoral cartilage changes were increased in patients with opening gaps greater than 10 mm.
      • Goshima K.
      • Sawaguchi T.
      • Shigemoto K.
      • Iwai S.
      • Nakanishi A.
      • Ueoka K.
      Patellofemoral osteoarthritis progression and alignment changes after open-wedge high tibial osteotomy do not affect clinical outcomes at mid-term follow-up.
      Alternative techniques for HTO are preferred in patients with planned medial opening wedges greater than 13 mm or greater than 9° of MPTA correction. Hybrid HTO can create additional patellofemoral joint space and improve outcomes in patients with severe patellofemoral OA.
      • Ishimatsu T.
      • Takeuchi R.
      • Ishikawa H.
      • et al.
      Hybrid closed wedge high tibial osteotomy improves patellofemoral joint congruity compared with open wedge high tibial osteotomy.

      4.7 Limitations

      Limitations of the present study include: a small cohort of patients, lack of comparison group, no report of duration of symptoms preoperatively, and long term follow up limited to a few years post-op. Future studies that include a larger number of patients receiving OWHTO with planned varus correction by using MAD would strengthen the findings of this study. Additionally, we did not include a comparison group to assess how outcomes of patients receiving OWHTO for medial compartment OA might compare to patients being treated with conservative measures only or more invasive procedures such as uni-compartmental arthroplasty. Further, certain factors that may affect patient outcomes were not accounted for in this study, most notably duration of symptoms pre-operatively. Although we included pre-operative SF-36 scores for all patients, the duration of symptoms for each patient was not reported here and could have an effect on clinical outcome as reported in previous studies.
      • Spahn G.
      • Kirschbaum S.
      • Kahl E.
      Factors that influence high tibial osteotomy results in patients with medial gonarthritis: a score to predict the results.
      Lastly, this report includes clinical outcomes in patients for a mean follow-up time of 35.1 months, but long-term prognosis after OWHTO is not assessed. Future studies will be necessary to investigate the duration for which OWHTO planned via MAD provides symptomatic relief to patients, and at what point arthroplasty may be subsequently required.

      5. Conclusion

      This study was performed to evaluate the clinical and radiological results of OWHTO in patients with varus deformity and uni-compartmental knee OA. MAD measurements showed significant changes, with significant improvement in patients’ mechanical axis alignments and clinical outcomes. Concerns regarding risk factors, such as smoking, obesity, BMI, and underlying diseases may necessitate future research, including assessment of risk factors and improvement of outcome measurements. The surgical technique described in this study results in very few complications, and provides an accurate correction of varus knee deformities, while preventing lateral compartment overloading.

      Author contributions

      Ghasemi SA: Conceptualization, methodology, investigation, writing.
      Murray BC: Investigation, writing.
      Buksbaum JR: Investigation.
      Shin J: Investigation.
      Fragomen A: Conceptualization, methodology, writing.
      Rozbruch SR: Conceptualization, methodology, writing.

      Declaration of competing interest

      The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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