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Megaprosthesis of the Hip
CASE STUDY
A 76-year-old man sought consultation for a painful revision left hip arthroplasty, limb length discrepancy, and difficulty with ambulation. He had undergone a hip arthrodesis in his mid-40s to address the disabling posttraumatic arthritis that developed after a motor vehicle collision that occurred when he was a young man. This arthrodesis was converted to a hemiarthroplasty and subsequently to a total hip arthroplasty (THA). Since the THA several years earlier, the patient had undergone multiple operations to address instability and recurrent infection. He was last operated on 6 months before our initial consultation. At that time, he had a jumbo, porous tantalum cup implanted with retroacetabular bone grafting and proximal femoral impaction graft reconstruction.
The patient complained of debilitating and constant groin and deep lateral hip pain, which was exacerbated by weight bearing. His medical history was complicated by poorly controlled diabetes and hepatitis C infection. Examination revealed a body mass index of 26.2. The patient had a marked leg length inequality; the left leg was shorter than the right by 4 to 5 inches. He had multiple anterior and posterior incisions in the left hip. His range of motion was measured at 80 degrees of flexion, −10 degrees of extension, 5 degrees of internal rotation, and 10 degrees of external rotation, with pain experienced at the extremes of these ranges.
Preoperative plain radiographs revealed severe superior and medial migration of a cementless acetabular component almost to the level of the sacroiliac joint, with presumed aseptic loosening ( Fig. 66.1 , A ). A cemented femoral component appeared well fixed in a patulous and osteopenic femur, with a trochanteric claw over nonexistent bone (see Fig. 66.1 , B ). The patient was sent for erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) tests and hip aspirate analysis to rule out infection. The ESR and CRP values were elevated, and analysis of the aspirate revealed 8900 polymorphonuclear cells/μL with a 96% neutrophil predominance. Because of the severe superior and medial position of the acetabular component within the pelvis, the patient was sent for a computed tomography (CT) angiogram to assess the proximity of the vascular anatomy.
Four months after resection arthroplasty to remove old components and confirmation of infection eradication, the patient underwent a reimplantation hip arthroplasty with an uncemented, modular TriFlange acetabular component (DePuy, Warsaw, Ind.) and a cemented proximal femoral replacement (Stryker, Mahwah, NJ).
Introduction
Numerous treatment options exist for massive acetabular and pelvic defects, but there is a lack of consensus about the optimal method. Available options include the use of a standard hemispherical component with a high hip center, bipolar hemiarthroplasty, acetabular impaction bone grafting behind a hemispherical cup, massive structural allograft, metal augmentation (e.g., porous metal wedges, buttress augments), oblong acetabular components, and reconstruction cages or combined cup–cage options. Outcomes have not provided consistent or durable enough results to recommend any one of these reconstructive options over another. To address the challenges associated with severe bone loss and pelvic discontinuity, the custom triflanged megaprosthesis was developed to optimize fixation in the critical and often limited areas of viable host bone.
Several treatment options exist for femoral reconstruction in patients with severely compromised proximal bone stock, including cemented femoral components, cementless components (i.e., extensively porous-coated cylindrical implants, and modular or nonmodular, tapered, fluted, titanium stems), impaction grafting, allograft-prosthetic composites, and proximal femoral replacement. Management strategies for femoral implant revision are based on the location of the femoral defect and the quality and quantity of the remaining femoral bone.
Proximal femoral replacements (e.g., megaprostheses) have been used extensively in orthopedic oncology, but there are few reports of proximal femoral replacements used in nonneoplastic conditions. One of the earliest reports of this device used in the adult reconstruction setting was from Sim and Chao. Twenty-one patients underwent proximal femoral replacement for nonneoplastic proximal femoral bone loss. Clinical and radiographic follow-up between 25 and 29 months revealed one acetabular failure from aseptic loosening and no femoral-sided failures.
With the TriFlange component system, the surgeon can address the most severe bone deficiencies and pelvic discontinuity and preoperatively plan the optimal component position and fixation according to the location and quantity of available host bone, with the potential for osseointegration into the highly porous metal surface. Customization of a single construct avoids the prolonged operative time associated with cementing liners into shells, cementing augments to shells, and cementing cages about acetabular components, as well as the frequently cumbersome techniques associated with assembling multiple parts required in other reconstruction methods.
Indications and Contraindications
For patients with severe bone loss and pelvic discontinuity, the advantages of the proximal femoral replacement megaprostheses include relative ease of insertion, particularly with cementation of the intramedullary stem. Immediate weight bearing is afforded the patient due to cementation.
Achieving optimal acetabular component position with correct anteversion and abduction can be challenging and suboptimal because of the limited available host bone available in severe cases. With the custom TriFlange device, the surgeon can orient the acetabular component relatively independently from the bone stock to implant in the optimal position to achieve maximal hip stability, which is always problematic in these cases. The limitations of these custom devices are the time required to fabricate the device (approximately 6 to 8 weeks), the additional imaging required for customization, and the relatively extensive soft tissue dissection required to achieve iliac and ischial screw fixation.
Equipment
The reconstructive devices employed in the case presentation were selected to accommodate the patient’s complicated clinical history. This salvage situation necessitated megaprostheses that could manage his massive acetabular and femoral bone loss.
The implant is tailored to the patient’s three-dimensional anatomy, which is determined by computed tomography (CT) preoperatively. Fixation and stability are achieved through bypassing bone deficiencies that may exist in the acetabular cavity, anterior or posterior columns, and superior dome. The initial fixation is afforded with screw placement through the iliac and ischial flanges. Long-term biologic fixation is accomplished by osteointegration into the highly porous metal surface of the implant.
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