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Due to various policy and health infrastructure issues, it is not uncommon to present developmental dysplasia of hip(DDH) at walking-age in India. The purpose of this study was retrospective analysis of operated cases of walking-age DDH with “inferior over-reduction”.
Methods
“Inferior over-reduction” was defined as break in the Shenton's arc inferiorly in an operated hip which otherwise appears reduced. After Ethical Committee approval, we searched children operated for walking-age DDH. Children suggestive of syndromic association were excluded. We collected demographic data, follow-up, procedures performed, inferior over-reduction and complications. The IHDI grade, Acetabular Index(AI), Smith's ratio for superior (h/b) & lateral displacement(c/b) of femur, and clinical outcome (Modified McKay criteria) were evaluated. The outcomes of cases with inferior over-reduction(Group A) were compared with those without(Group B).
Results
42 patients with average follow-up of 23 months were enrolled. 21 hips belonged to Group A. By 6 months follow up, all these cases recovered. On comparison of Smith's ratio, group A had significantly higher c/b for the operated hip at 3-month follow-up(p < 0.05). Patients undergoing acetabuloplasty had significantly lower c/b versus all other groups(p < 0.05). Correlation between h/b or c/b with age did not show any significant finding. 15 cases in group A and 14 cases in group B had excellent outcome as per modified McKay's criteria. None of the patients had inferior over-reduction, inferior or obturator dislocation at final follow-up. Three patients with group B had re-dislocation with poor outcome. we recorded 3 hips with AVN (7%).
Conclusions
This study highlights that after OR of walking-age DDH, the inferior over-reduction may be noted in as much as 50% of the cases. However, this is transient, and all cases recover by the 6 months follow up. There is no significant difference between group A & B in functional outcome, AVN rate. Long-term studies are required to see outcome differences between two groups.
Since DDH is a spectrum of disorder, the exact incidence will always be debatable. Due to lack of well-established surveillance program in India as well as poor healthcare system, it is common for DDH to present at walking-age.
During OR of DDH, various anatomical structures obstructing an acceptable reduction of joint are released by surgeon. These anatomical structures may include capsule, Iliopsoas tendon, pulvinar and transverse acetabular ligament.
A new radiographic classification system for developmental hip dysplasia is reliable and predictive of successful closed reduction and late pelvic osteotomy.
The choice of adjunct procedures depends on intra-operative findings as well as surgeon's preference. Apart from surgical complexity of OR, various complications encountered by surgeon include re-dislocation, avascular necrosis of femoral head and residual dysplasia etc.
We noticed that occasionally, after OR, few cases had transient inferior over-reduction post-operatively. In these cases, after OR, Shenton's arc was slightly broken in opposite direction due to inferior over-reduction (Fig. 1&2). To our knowledge, we did not find such description in the treatment of DDH in literature.
Fig. 1Post-operative Radiograph after Open Reduction in a nineteen Months old girl.
The purpose of this study was retrospective analysis of clinical and radiological outcome of these cases with “transient inferior over-reduction”.
2. Material & methods
After approval from Institutional Ethical Committee, we reviewed hospital records retrospectively to identify children operated with OR for DDH between January 2018 to July 2021. Children with DDH beyond walking-age treated with OR with or without adjunct procedures were included in this study. Children with associated congenital anomalies suggestive of syndromic association, neurogenic dislocations, bilateral DDH, revision DDH hips and cases lost to follow up were excluded from the study. To have a normal hip for comparison, we included only unilateral hip DDH in this study.
The radiograph of pelvis with both hips (PBH) were scrutinized to identify hips with “inferior over-reduction”. The “Inferior over-reduction” was defined as break in the Shenton's arc inferiorly (opposite to usual classical break in DDH) in an operated hip which otherwise appears reduced (Fig. 2). The radiographs were evaluated pre-operatively, immediate post-operatively, at 03 months post-operatively and final follow up visit.
Fig. 2Same radiograph with tracing marked for Shenton's arc, showing clear break in right hip (Operated hip).
We collected data on sex, age at the time of procedure, total follow up duration, procedures performed, inferior over-reduction/break in Shenton's arc, details of complications like re-dislocation, avascular necrosis of hip (AVN),
wound infection etc. The IHDI (International Hip Dysplasia Institute) grade, Acetabular Index (AI) were evaluated on radiographs. Smith's ratio (for superior & lateral displacement of femur) was measured on standard antero-posterior radiographs at 3 months post-operatively and final follow up (Fig. 3).
Fig. 3Schematic diagram of pelvis showing Hilgenreiner's line, Perkin's line, center line, distance from center to Perkin's line (b), distance from center line to medial most portion of femoral neck (c), and distance from superiormost part of femoral neck to Hilgenreiner's line (h). h/b and c/b ratio, Smith's ratio for superior and lateral displacement respectively.
Among 42 cases eligible for study, a total of 21 hips were identified with inferior over-reduction on post-operative radiograph. The clinical and radiological outcomes of these cases with inferior over-reduction (Group A) were compared with those without (Group B). All the eligible cases were consecutively enrolled and the two groups were not matched at baseline.
Group A cases with persistent Over-reduction at 3 months were labelled as Group A1 & Group A cases which recovered over-reduction at 3 months as Group A2.
2.1 Institutional protocol
All the cases in this study were operated by two surgeons, independently or together (AS and SC). For the reducible hips under anaesthesia, we first attempted closed reduction/arthrography. None of the hips in this study cohort were stable with <6 mm dye pool after arthrography, so open reduction was done. OR was done in all cases via Smith-Peterson approach using bikini incision. Adductor Tenotomy & Iliopsoas tenotomy was done in all cases as routine. After capsulotomy, Pulvinar was removed from acetabulum and tight transverse acetabular ligament (TAL) was cut in all cases.
Intra-operative ‘test of stability’ was used to decide on femoral varus/derotation osteotomy and need of acetabuloplasty. After reduction, trans-articular smooth k-wire was placed across hip joint under image guidance and capsulorrhaphy was done (we do not excise elongated capsule). Spica was used for 4 weeks with hips immobilized in 30–40° of abduction, 30–40° of flexion. At 4 weeks, k-wire was removed, spica was changed under anaesthesia and maintained for another 4 weeks. After OR, we do not use post-operative CT or MRI scan routinely.
After spica removal at 8 weeks, child was given hip abduction brace, which was weaned gradually over next 12 weeks. During each visit hip was assessed clinically & radiologically for containment, stability, and function.
2.2 Statistical methods
The variables were compared between Group A and Group B. The variables used for comparison included basic demographic parameters, follow up, IHDI grade, AI, AVN, Smiths's ratios, clinical hip stability and Modified McKay criteria. One way ANOVA test was used where comparison was done between >2 groups (Tables 3 and 4). A p-value of <0.05 was considered significant. Statistical analysis was done using SPSS (v.25 SPSS, version 25; IBM, Chicago, IL).
3. Results
The overall and group-wise demographic and baseline details of the patients are mentioned in Table 1. A total of 42 patients were enrolled fulfilling the inclusion criteria with an average follow up of 23 months. Of these, 21 hips were identified as having inferior over-reduction as per accepted definition for this study (Group A).
Table 1Demographic and baseline details of enrolled cases (n = 42).
At 3-months follow-up, 11 of the 21 patients in Group A had persistent inferior over-reduction (broken Shenton's arc with contained hip). At both 6 months and final follow up, none of the patients in Group A had inferior over-reduction or broken Shenton's arc (Fig. 4).
Among 21 cases in Group B, 2 cases had broken Shenton's arc at 3 months due to subluxation/dislocation. At 6 months and final follow up, we noticed total of 3 cases in Group B had re-dislocation with broken Shenton's arc.
Pre-operatively, all patients had IHDI grade 4. At 3-months and final follow-up, all patients in Group A were IHDI grade 1, while 3 of the 21 cases in Group B had IHDI grade 3 at 3-month and grade 4 at final follow-up (Table 2).
Mean pre-operative AI was significantly higher in the group A, when compared to group B (p < 0.05). The subgroup of patients from group A which recovered the inferior over-reduction at 3 months(Group A2,n = 10) had the lowest mean AI (both pre & post-operatively) versus all other group of cases (P < 0.05).
Comparison of Smith's ratio of operated hips is mentioned in Table 3. The patients in group A had significantly higher value for lateral position (c/b) for the operated hip at 3-month follow-up in comparison to the group B (p < 0.05). Table 4 presents various procedures performed while doing OR of DDH. The patients undergoing Dega's acetabuloplasty with adjunct procedures during OR had significantly lower value for lateral position (c/b) in the operated hip, versus the all other groups(p < 0.05) Table 4. In the operated hips, correlation of Smith's ratios (h/b or c/b) with age did not show any significant finding. 15 cases group A and 14 cases in group B had excellent final outcome as per modified McKay's criteria (Table 1). At last follow up none of the patients had inferior over-reduction. None of the patients had inferior or obturator dislocation.
Table 3Comparison of Mean Smith's Ratio of Operated Hips based on over-reduction status.
Parameter assessed
Group A (n = 21)
Group A1 (n = 11)
Group A2 (n = 10)
Group B (n = 21)∗
P value
h/b
At 3 months
0.15 ± 0.03
0.14 ± 0.03
0.15 ± 0.03
0.16 ± 0.03
0.23
Final follow-up
0.15 ± 0.03
0.14 ± 0.02
0.16 ± 0.03
0.15 ± 0.02
0.38
c/b
At 3 months
0.78 ± 0.08
0.79 ± 0.09
0.78 ± 0.08
0.76 ± 0.05
0.01∗
Final follow-up
0.74 ± 0.06
0.74 ± 0.06
0.73 ± 0.05
0.73 ± 0.06
0.29
3 cases with dislocation excluded at final follow up.
Group A1 = Group A cases with persistent Over-reduction at 3 months.
Group A2 = Group A cases which recovered over-reduction at 3 months.
One way ANOVA test was used to compare the means between the various groups (between >2 groups).
P < 0.05 is considered significant by one-way ANOVA test.
None of the patients with group A while 3 of the patients with group B had re-dislocation at last follow up with poor outcome. Of 42 hips, we recorded 3 hips with AVN (7%), 2 hips were in group A (grade 2 = 1, grade1 = 1) and 1 hip in group B (grade 1). K-wire pins-site infection was noted in 2 cases (one in each group) and three patients developed spica plaster sore (2 in group A & 1 in group B) which healed without further complications.
4. Discussion
Early detection and treatment are the key in the management of DDH in children. However, neglected or walking-age DDH is not uncommon presentation in outpatient department, especially in developing countries. Rather, it forms major portion of patients undergoing treatment for hip dysplasia. To achieve stable reduction in late presenting DDH, most of the cases require OR with various adjunct procedures.
In this retrospective study, we noticed that after successful OR, 21 cases had break in Shenton's arc in opposite direction despite good reduction intra-operatively. We labelled these cases as ‘inferior over-reduction’ as defined in methods section of this article. Shenton's arc is classically used to comment on status of hip joint, dislocation/subluxation, or femoral neck fractures.
We believe that the following surgical procedure related factors may have contributed to this inferior break in Shenton's arc noticed post-operatively in our study.
i.
release of TAL
ii.
liberal capsulotomy before capsulorrhaphy (without excising elongated capsule)
iii.
Dega's acetabuloplasty (pushing the femoral head down)
iv.
addition of varus in femoral osteotomy
v.
abducted position of limb after OR.
However, we could not corroborate these suggested factors statistically in present study. Future multicentric study in large sample size with multivariate analysis might be useful to address this aspect.
During OR, it is recommended to remove all anatomical obstacles to achieve a stable reduction.
Among 42 hips operated, we did adductor tenotomy, Iliopsoas tenotomy, pulvinar removal, TAL release and capsulorrhaphy in all the cases. Many authors have described TAL as contracted and one of the major block to concentric reduction of DDH.
In our study, evidently tight TAL was noticed only in 19 cases in this study (group A = 11 and group B = 8). We acknowledge that this tightness of TAL can be subjective finding and as Institutional protocol, we do release it in most of the cases.
At 3 months follow up, 10 of these cases recovered the inferior over-reduction spontaneously and Shenton's arc was maintained. At 6 months follow up, all these cases recovered, and none was having inferior over-reduction in form of break in Shenton's arc. Thus, this inferior over-reduction was transient, self-resolving, without any case of inferior or obturator dislocation in our cohort of cases. González et al. reported a case of obturator dislocation during treatment of DDH using Pavlik harness.
As stated above, the abducted position of limb immediate post-operatively may be one of the contributing factor for inferior over-reduction. However, half of the cases had persistent break in Shenton's arc at 3 month follow up when radiograph was taken in neutral abduction, which got resolved by 6 months. Since Shenton's arc is unaffected by position of limb in a well reduced hip, we feel that position of limb alone should not produce this effect.
As historically described, Shenton's arc is an imaginary line, so it is difficult to comment on this inferior break quantitatively. For quantitative expression of adequacy of reduction in DDH, Smith et al. described method to quantify superior and lateral displacement of femoral head in children
(Fig. 3). These measurements (called Smith's ratios) avoided the problem with direct measurement & magnification/minification of image. Also, using metaphyseal landmarks on femur made it useful tool for DDH, as most of these cases have delayed or small capital ossification. Yamamuro et al. also described similar measurement techniques for quantitative assessment of hip position in DDH.
In our study, all the cases had Smith's ratio within the normal range (excluding 3 cases with re-dislocation from this calculation). The patients in group A had significantly higher lateral displacement in operated hips at 3 months compared to group B. This difference was not significant at the final follow up suggesting normalization of hip position in group A. The cases undergoing Dega's acetabuloplasty had significantly lower c/b ratio at 3 months as well as final follow up. We believe that one of the reasons for this might be alteration of lateral point for calculation on acetabulum where Perkin's line is drawn. However, further studies with large sample size are required to clarify this assumption. We did not find any significant difference in Smith's ratios when compared with age at the time of surgery.
In our study, we noticed that cases with inferior over-reduction (group A) had significantly higher AI both pre & post-operatively (p < 0.05). The cases with lower AI recovered early (at 3 months) from this transient inferior over-reduction. Thus, a higher AI pre-operatively may also be a risk factor for transient inferior over-reduction apart from surgical procedure related factors listed above.
The safety and efficacy of a transarticular pin for maintaining reduction in patients with developmental dislocation of the hip undergoing an open reduction.
reported no effect on final results. It cannot be overemphasized that concentric reduction is key for OR in DDH and k-wire is not a replacement of it. At our institute, we routinely use trans-articular k-wire, which is removed at 3 weeks. We feel that after proper OR, it is useful in maintaining reduction during spica application and initial few weeks. More studies are required to validate its role in surgical management of DDH.
A metanalysis study reported 19% AVN rate after OR.
We observed 7% AVN till the last follow up. There was no significant difference between group A & B in terms of functional outcome, AVN rate and other minor complications. Three cases in group B and none of the cases in group A had re-dislocation. Thus, in terms of hip stability at final follow up, cases with inferior over-reduction fared better at short term. Although, there may have been other factors contributing for these cases with re-dislocations.
This study has few limitations. This was retrospective study of 42 hips from single center. We acknowledge that the emphasis of this retrospective study is on inferior over-reduction (on plain radiographs) of DDH after OR, which was transient in nature. We did not perform CT or MRI, which would have given 3-dimensional position of these hips. More detailed studies, perhaps cadaveric, are desired to analyze the factors contributing this transient finding. Also, we acknowledge that the finding of break in Shenton's arc, as historically defined, may be subjective in mildly subluxated hips. In attempt to overcome this, quantitative measurement like Smith's ratio were used in this study. The two groups were not matched at baseline for parameters and the variety of surgical procedure utilized in this study make it heterogenous group. The follow up period is very short for DDH and a longer follow up is required to see the clinico-radiological effects of inferior over-reduction.
5. Conclusion
This study highlights that after OR of DDH in walking-age, the inferior over-reduction may be noted in as much as 50% of the cases post-operatively. However, this finding is transient, and all the cases recover by the 6 months follow up. At short term, there is no significant difference between cases with or without transient inferior over-reduction in functional outcome, AVN rate. Further long-term studies are required to see outcome differences between the two groups. Also, suggested factors for this transient finding in current study may be areas of future research.
Funding
NIL.
Author contributions
Suresh Chand & Ajai Singh conceptualised and designed the study. Data analysis and review was carried out by Suresh Chand & Ajai Singh. The first draft of the manuscript was written by Suresh Chand and edited by Syed Faisal Afaque, Vikas Verma & Ajai Singh. All authors read and approved the final manuscript.
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.
Acknowledgement
We thank Mr. Kritarth Singh for his kind help with statistics and data processing for the article.
References
Chand S.
Aroojis A.
Pandey R.A.
et al.
The incidence, diagnosis, and treatment practices of developmental dysplasia of hip (DDH) in India: a scoping systematic review.
A new radiographic classification system for developmental hip dysplasia is reliable and predictive of successful closed reduction and late pelvic osteotomy.
The safety and efficacy of a transarticular pin for maintaining reduction in patients with developmental dislocation of the hip undergoing an open reduction.
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