Femoral Revision: Allograft Prosthetic Composites and Proximal Femoral Replacement

Introduction

Revision total hip arthroplasty (THA) in patients with severe proximal femoral bone loss is challenging. Bone loss extending more than 5 cm distal to the lesser trochanter precludes the use of most conventional THA techniques. Salvage procedures such as excision arthroplasty have shown poor results. Arthrodesis is difficult to achieve. Viable options include the use of allograft prosthetic composites, proximal femoral replacements, and impaction bone grafting techniques. The use of allograft prosthetic composites and proximal femoral replacements will be discussed in this chapter.

Proximal femoral replacement (PFR) is defined as a metal femoral implant that is proximally connected to a femoral head to articulate with the acetabulum and distally fixed to the host femur. It may be cemented or uncemented, modular or nonmodular. Historically, PFR was used after tumor resection. The initial designs were cobalt-chrome monoblock with incremental length segments cemented into the distal femur. Later developments included modularity to better accommodate leg length and porous coating to promote bony ingrowth at the junction with extracortical bone bridging, although this concept has not been shown to occur with predictability even with bone grafting. Indications recently have been expanded to include nonneoplastic conditions such as failed THA with massive proximal femoral bone loss and periprosthetic fractures.

Allograft prosthetic composite (APC) in revision THA is defined as a long femoral stem prosthesis that is proximally incorporated into a proximal femoral bone allograft. This technique has gained popularity over the past decade with several encouraging longer-term reports.

When comparing APC with PFR, the advantages of using PFR include easier availability without the need for access to banked bone, easier implantation without the need for expertise in the use of massive bone allografts, and shorter operative duration with potentially lower blood loss and infection rates. The theoretical risk of disease transmission via the allograft bone is also avoided. Patients with PFR are generally allowed to bear weight earlier in the postoperative period and have less demanding postoperative rehabilitation programs.

Revision THA with PFR, however, is associated with higher dislocation rates. PFR provides poor attachment of host bone and soft tissue, leading to weaker abductors and a higher rate of a Trendelenburg lurch. There is also the disadvantage of violating the host distal femoral canal with reaming for stem cementation or press fitting, which is undesirable with regard to bone preservation, especially in younger higher-demand patients. In terms of survival rates, reports have suggested higher rates of loosening and failure with PFR.

The use of APC has the potential to restore proximal femoral bone stock and minimize host distal canal violation to preserve bone stock to aid future reconstructions. By avoiding cementing or significant reaming for press fitting the implant distally, the distal host canal is relatively preserved. The use of proximal allograft aids host bony and soft tissue attachment—in particular, the host greater trochanter. When the host greater trochanter is destroyed, the use of proximal femur–abductor tendon allograft facilitates host abductor tendon repair. APCs with trochanteric and abductor repairs have lower rates of abductor impairment, limping, instability, and dislocation compared with PFR.

Indications and Contraindications

Preoperative Planning

Because the use of PFR is technically similar to that of most distal fixation stems, with the exception of the need for fixation of the hip abductors to the stem, we will focus on the technical details associated with APC.

Allograft Prosthetic Composites

Allograft Availability

We recommend acquiring fresh-frozen allograft from a tissue bank that is accredited by the American Association of Tissue Banks. In general, these allografts are irradiated for sterility and are stored at −70°C.

Preoperative planning is required so that the correct sizes of allograft and implant can be ordered. Anteroposterior (AP) pelvis and full femur radiographic views with a calibrated radiographic marker are obtained to estimate the length and diameter of the graft and implant required. The allograft length is estimated from the length of the proximal femoral deficiency. This usually correlates with the distance from the center of rotation of the hip joint to the level in the distal femur where adequate bone stock is present to support the allograft. This estimation should take into account apparent and functional leg length discrepancy due to stem subsidence or periprosthetic fracture. A graft that is substantially longer than estimated is ordered to allow for intraoperative adjustments and should account for a minimum step cut of 3 to 5 cm at the allograft host-bone junction. The estimated stem length should be generously longer than the estimated graft length. Ideally, there should be a minimum of 2 cortical diameters of stem length beyond the host-graft junction, with the anticipated stem tip more than 4 to 6 cm away from the knee joint, if possible.

In the revision arthroplasty setting, the graft canal diameter is typically narrower than the host canal, which is often widened by cortical thinning from osteolysis and cavitation around previous loose femoral components, infection, or fracture. Avoid choosing a graft with an outer diameter that is substantially narrower than the host to reduce the risk of unstable intussusceptions and uncontrolled subsidence postoperatively. Ideally, the outer diameters of the graft and host should be matched at the distal graft-host junction for optimal junctional stability. Alternatively, using a slightly narrower graft to telescope into the host distal femoral canal by 1 to 2 cm and ensuring initial junctional fixation stability may enhance union and long-term stability ( Fig. 103.1 ).