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Total hip arthroplasty (THA) is the treatment for end-stage osteoarthritis of hip. Approximately 280,000 primary and over 50,000 revision THA procedures are performed in the USA each year.
The main indications for femoral revision are aseptic loosening and osteolysis. Other indications for revision include infection, dislocation, periprosthetic fracture, and component malposition
. Femoral revision is often complicated by bone loss. The management for femoral revision is based on the femoral defect, the quality and quantity of remaining femoral bone stock.
2. Classification
The most commonly used classification to describe the amount of femoral bone loss and propose guidelines for treatment of each type of femoral bone deficiency are the AAOS Committee on the Hip
The AAOS classification divides the femoral bone defects into segmental, cavitary, combined segmental and cavitary defect, femoral malalignment, femoral stenosis and femoral discontinuity.
is based on the location of femoral bone loss, defining the morphology of remaining proximal femoral bone stock and the amount of isthmus remaining for diaphyseal fixation. It also provides guidelines for treatment (Fig. 1).
Fig. 1The Paprosky classification of femoral bone loss.
Type I femoral bone loss, minimal loss of metaphyseal cancellous bone and an intact diaphysis.
Type II femoral bone loss, extensive loss of metaphyseal cancellous bone and an intact diaphysis.
Type IIIA femoral bone loss, more extensive loss of metaphyseal cancellous bone, non-supportive and there is > 4 cm of intact diaphyseal bone available for distal fixation.
Type IIIB femoral bone loss, severe damage of metaphyseal cancellous bone, non-supportive and there is < 4 cm of intact diaphyseal bone available for distal fixation.
Type IV femoral bone loss, extensive loss of metaphyseal and diaphyseal bone in conjunction with a widened femoral canal. The isthmus is non-supportive.
3. Treatment options
The goals of revision total hip arthroplasty are restoration of hip center, femoral offset, and leg length. The implant options
Cementless or cemented primary stems (common length and geometry)
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Proximally fixed stem (usually modular)
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Calcar replacement stem
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Long cemented stem
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Cylindrical cementless stem with extensively porous coated
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Tapered cementless stem (Wagner type)
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Modular cementless tapered fluted stem
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Impaction bone grafting + cemented stem
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Allograft prosthetic composite
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Megaprosthesis
Type I femoral bone loss refers to a defect which minimal metaphyseal bone loss has occurred, and the proximal femoral bone stock is maintained.
These defects are typically seen after removal of a cementless implant with a narrow metaphyseal geometry, or removal of an implant with minimal proximally ingrowth (Fig. 2). These defects can be treated with a tapered proximally porous coated stems which may remain an option if the proximal metaphyseal bone is sufficient to support osteointegration.
Type II femoral bone loss refer to a defect which the proximal metaphyseal bone has been damaged to a degree where it is may not be mechanically supportive for a proximally fitting implant, proximal biologic fixation is unreliable.
These defects may be associated with subtle varus remodeling of the proximal femur, although the entirety of the diaphysis remains intact. These defects are commonly seen after removal of a cemented femoral implant, or removal of a proximally fitting stem with a wide femoral geometry (Fig. 3).
Fig. 3Full coated cylindrical stem have many options for bony defect for proximal bone loss and can achieve stable fixation.
Although depending on the degree of metaphyseal bone loss, some proximal ingrowth may be expected.
Long cemented stem can be used in this type with comparative results.
Type IIIA and IIIB femoral bone loss
The femur with a type IIIA defect has extensive metaphyseal bone loss, leaving it unsupportive. The diaphysis is also involved, but more than 4 cm of isthmus is remaining to obtain a scratch fit for bony ingrowth.
(Fig. 4). This is probably the most frequently encountered defect in femoral revision surgery. It can be treated with 8 or 10-inch extensive porous coated stem, impaction grafting, or modular tapered cementless stems. The use of extensively porous-coated femoral stems is based on the principle that bypassing the damaged proximal part of the femur and engaging the diaphysis can reliably provide an ingrown and stable reconstruction.
Fig. 4Severe bone loss may come with infection and thin cortical bone that make be more difficult to manage.
The femur with a type IIIB defect has an unsupportive metaphysis secondary to extensive bone loss. Additionally, the diaphysis is more severely damaged, and less than 4 cm of isthmus is remaining (Fig. 5). These defects seem to be increasing in frequency with improved cementing techniques and the use of longer cementless stems. it can be treated with 10-inch extensively porous coated stems, impaction grafting or modular tapered cementless stems.
Fig. 5Cortical and 3-point fixation should be done to make sure that initial good stability can be done to prevent long term subsidence.
identified the use of extensively porous-coated femoral stems in 170 patients, overall mechanical failure was 4.1%, mean follow up was 14.2 years, type II and IIIA failure rate was 5% whereas patients in type IIIB failure rate was 21%. Another study by Engh et al.,
the survival of femoral stems was significantly less if the preoperative bone loss extended more than 10 cm distal to lesser trochanter, with revision for any reason as end point, 97.7% survival at 5 years, and 95.8% at 10 years.
Type IV femoral bone loss
In a type IV defect, there is an extensive metaphyseal and diaphyseal damage in conjunction with a widened femoral canal. No diaphyseal bone of sufficient quality for cementless fixation. In these uncommon cases, the isthmus is non-supportive, and distal fixation cannot be achieved (Fig. 6).
Fig. 6When proximal femur has been ballooning, many types of femoral stem have to prepare and consider before the surgery. Cylindrical full coated stem is one of the choices.
When the proximal femoral cortex is intact, impaction grafting with long cemented stem can be used for femoral reconstruction and bone stock restoration. This technique also showed good results in low-demand elderly patients.
A modular tapered stem, which allow independent sizing of the distal and proximal portions, provides more reliable distal fixation with lower rates of subsidence and improves offset and limb length restoration.
When the proximal cortex is deficient, a femoral allograft-prosthesis composite can be used to reconstitute bone stock in younger patients, but technically demanding and are associated with higher complication rates than other revision procedures. Union at the graft-host junction often requires months, and unprotected weight bearing should be delayed until there is radiographic evidence of union. Fracture is common with unsupported load-bearing allografts, and these grafts should be supported by an intramedullary stem crossing the allograft-host junction. Because of the length of the procedure and the degree of soft-tissue dissection, infection is more common than in other revision arthroplasties.
When the proximal cortex is deficient in elderly, low-demand patients with severely compromised femoral bone, proximal femoral replacement (megaprosthesis) can be used for improved reattachment of soft tissue and bone that have been developed to improve restoration of limb length and instability. In an analysis of the available literature regarding these implants in the treatment of non-neoplastic conditions, Korim et al.
studied 356 hips followed for an average of 3.8 years. The implant retention rate was 83%, with a 23% re-operation rate, most commonly due to instability (16%).
4. Author preferred
The severity of femoral bone loss is not only caused by loosening and osteolysis. Type of previous prosthesis, technique of stem and cement removal, and necessity of extended femoral osteotomy are also the origin of complex complications. In case of proximally loose cemented stem with well supported cement distally, the cement-in-cement revision technique is useful to limit femoral destruction. The extended femoral osteotomy should be done only in the specific unavoidable indications.
The uncommon type I and type II defects can be treated with proximal metaphyseal fixed stem or cemented fixation. The results depend on several factors, such as bone stock and quality, biologic ingrowth or ongrowth, and surgical technique. Distally diaphyseal fit stem which provides more reliable result is a better option.
Type IIIA defect is a most common situation. Most of cases can be treated with cylindrical cementless stem with extensively porous coated. Type IIIB defect is mostly treated by the modular tapered fluted or Wagner type stem. The impaction grafting is not preferred because its risk of disease transmission. The cylindrical full coated stem can also be used in some IIIB defect by enlarged reaming and increasing the length of stem for more contact area. In this situation, weight bearing must be protected for longer period. This type of stem usually solves most of femoral defects after extended femoral osteotomy.
The rare type IV defect should be treated by allograft-prosthesis composite or a megaprosthesis. We had the experience using the cylindrical full coated stem and the modular tapered fluted stem in some selected cases. With precise templating, surgical technique, and specific rehabilitation protocol, the long-term results are comparative to other implant options (Fig. 7).
Fig. 7Long-term results, 16 years follow up when good initial fixation could be achieved. We can have good result of revision THA when step by step of surgical technique have been followed with reliable of good long tern tracking record prosthesis.
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