Allograft Prosthetic Composite

David G. Lewallen

Key Concepts

Large segment allograft prosthetic composites (APCs) are used for reconstruction of the femur when other methods of managing femoral bone loss are not possible due to the severity of the defects present.
Standard APC reconstructions involve “end-to-end” contact of the proximal femoral allograft and the more distal host bone which has been resected transversely perpendicular to the long axis of the femur or alternatively the junction can be fashioned into a matching stepcut on both sides for better control of rotation (Figure 33.1)
As femoral revision techniques have evolved and implant options have increased, massive defects of the proximal half of the femur that may have previously been considered for an APC are currently routinely managed with modular tapered implants using distal fixation into the remaining intact diaphysis and with wrapping of the deficient proximal femoral remnants around the proximal part of the modular stem (Figure 33.2).
Widespread adoption of modular tapered stems for most cases with severe proximal femoral bone loss has markedly decreased the use of APCs, especially those entailing direct end-to-end or stepcut abutment of allograft to the intact host femur as ability to achieve good distal cortical contact implies sufficient diaphysis for support of a modular stem instead.
There remain cases of very extensive distal bone loss or vary large capacious damaged femoral canals where adequate support for available tapered fluted implants cannot be achieved and where a special application of allograft prosthetic composites remains useful.
“Intussusception” APCs reconstructions involve the intramedullary placement of the distal portion of the allograft which is driven a substantial distance down inside the intact distal host femur allowing broad contact, reliable union, and excellent proximal support for a very long stem cemented femoral component placed inside the allograft (Figure 33.3).
With both types of APC reconstructions the trochanteric and proximal femoral host bone remnants are wrapped around the allograft and fixed with cerclage in an effort to achieve bony healing between fragmented host bone fragments and the allograft to aid hip stability and muscle control.
A competing technique in these extensive bone loss cases is use of a total femoral replacement implant, but this is best reserved for instances where a relatively normal and well-functioning ipsilateral knee joint is no longer present. APC reconstructions have the advantage of allowing preservation of an intact ipsilateral knee joint.

Sterile Instruments and Implants

Standard hip arthroplasty and revision total hip arthroplasty (THA) instruments and multiple retractors are required.

A whole femoral allograft of appropriate length and outside diameter is required to allow matching to the host femur dimensions as determined from preoperative templating of x-rays of the entire
hip femur and knee of the involved side and of the opposite side for comparison of target anatomic relationships, especially length.

Figure 33.1 ▪ A, Preoperative radiograph of failed loose proximal femoral replacement femoral component and cup. B, Postoperative radiograph showing proximal femoral allograft prosthetic composite with excellent size matching and end-to-end contact.

Calibrated x-rays of any potential femoral allografts are used to find the best match for size and length for the individual patient’s hip.

Figure 33.2 ▪ A, Aseptic loosening of a cemented total hip arthroplasty (THA) with massive proximal femoral osteolysis and a Vancouver type B3 periprosthetic femoral fracture. B, Postoperative radiograph of proximal femoral allograft prosthetic composite (APC) using a step cut at the junction between host and allograft. Cerclage fixation of the proximal femoral remnants and associated muscle attachments have been wrapped about the allograft to improve hip stability and function.

Figure 33.3 ▪ A, Preoperative images showing profound femoral bone loss down to the level of the metaphyseal flare distally due to component loosening and osteolysis. B, Intussusception of a proximal femoral allograft prosthetic composite with the long cemented femoral stem running the length of the allograft which extends well into the distal host femur and shown here to be solidly united and well fixed at 5 years post surgery.

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