Osteochondral Allograft Reconstruction

Historical Perspective

Lexer is credited with the first report of an allograft transplantation as early as 1908. Renewed interest has been sparked by a series of publications in the late 1960s and 1970s. Ottolenghi and others recognized and documented favorable results with smaller grafts since the 1970s. On the other hand, long-term deterioration of bulk allografts has been well documented, largely from the hip literature, since the 1990s. The key to long-term effectiveness resides in the extent of incorporation and revascularization. To enhance these features, vascularized allograft transplantation has been suggested but is not in common use.

Biocompatibility

Graft incorporation depends on the mechanical environment and the type of graft as well as immune factors that are complicated and poorly understood. The immunogenicity of allografts is reduced by freezing or freeze drying, which renders them more suitable for clinical use. However, even preserved allografts provoke recognizable cellular and humoral antibody responses. Donor-specific anti–human leukocyte antigen (HLA) antibodies and cellular antibodies have been identified in frozen and freeze-dried grafts. The major reactivity appears to be cellular because viable bone marrow cells are highly immunogenic and induce both a cell-mediated and a humoral response. Antigens in the extracellular matrix (collagen and noncollagenous proteins) seem to be of much less significance in the clinically observed allograft response. Animal studies and clinical experience indicate that a major cause of failure in total joint allograft replacement is delayed or incomplete union and failure of revascularization. At this time, it has not been possible to identify an immune reaction as the definitive cause of failure of incorporation. However, it is now known that immunogenic peptides longer than five amino acids are associated with an adverse immunoresponse. Hence efforts to denature these harmful allopeptides while preserving the useful collagen is the goal of current investigations. Anxiety over disease transmission, even with the bulk allografts, has largely been resolved, though not eliminated, with improved screening methodology. Obviously, the opportunity for donor interrogation is not available, and there remains the issue of timing and the potential to convert at a later date.

Indications

Use of osteoarticular allograft replacement has limited indications. These include:

• Younger patient

• Loss of only the humeral or ulnar osteoarticular elements

• Potential for adequate soft tissue coverage

• Loss proximal or distal to the ligaments

  Note

  For bone loss distal to the humeral collateral attachments, we use a hemiprosthetic device ( Fig. 112.1 ) (see Chapter 88 )

  

• Ability to stabilize the construct

• Anticipation of subsequent prosthetic replacement with allograft providing bone stock for the subsequent procedure

Total allograft replacement is indicated and reserved for the rare patient who is allergic to a component of the implant alloy ( Fig. 112.2 ).

Contraindications

• Active sepsis

• Subacute sepsis is a relative contraindication

• Access to correctly sized allograft

• Inability to stabilize the joint