Salvage of Failed Osteoarticular Tibia Allografts with Knee Arthroplasties

Background: Limb preservation in musculoskeletal tumor surgery has largely replaced amputation. Biologic reconstructions are now performed as preferred choice; if not feasible options are “megaprostheses”, allografts or composites. Endoprosthetic reconstructions usually provide immediate function, but fail at long term. Osteochondral allografts allow for one-to-one restoration and have potential for incorporation; however degeneration of the cartilage requiring revision almost inevitably will occur. In most cases, revision is then done by endoprosthetic replacement. Aim: In our patients, resurfacing of retained allografts failed. Problems encountered are presented and solutions proposed. Case Presentation: Resurfacing over retained allografts in the 2 index cases has resulted in failures related to fractures and instability. Revision with massive constrained endoprostheses was needed. Based on the experience with these failures, primary endoprosthetic replacement anchored in vital bone in a following case resulted in stable function. Conclusion: Knee replacement for advanced degeneration of the osteochondral allograft apparently needs choosing increased femoro-tibial constraint systems and stem extensions anchored to vital host bone.

lated to fracture, infection and degeneration of the osteoarticular region.
Toy et al. [2] and Verbeek et al. [3] addressed problems encountered in femoral osteoarticular allografts and complications in revision to total hip replacement (THA) or total knee replacement (TKA); 61% of THA/TKA respectively in retained allografts had complications, mostly structural failures (periprosthetic fractures/allograft fractures [3]). A study comparing outcome of proximal tibia reconstructions with either osteoarticular allografts or endoprosthetic replacement showed separate advantages, however not significantly different overall failure rates (at 10 years 44% for endoprostheses and 32% for allografts [4]).
Details of endoprosthetic salvage procedures of failed allograft reconstructions have been sparsely described [5]. We wish to report on failures experienced with resurfacing arthroplasty for articular degeneration on retained tibial osteochondral allografts. The observations generally lead us to anchor endoprostheses directly to vital autochthonous bone of the patients.

Patients and Methods
Three patients received arthroplasties for failed osteoarticular reconstructions after resection of osteosarcoma.

Results Summarized
Three patients with osteoarticular allograft replacement of the proximal tibia needed knee arthroplasty for cartilage degeneration 10, 11, and 24 years after the initial treatment for proximal tibia osteosarcomas. Two of them were initially treated with standard resurfacing knee arthroplasties that failed within three years due to fracture of the allograft and instability of the non-hinged joints. They were revised to tumor reconstruction systems (MU-TARS, Implantcast) with fully rotating hinged knee replacements resulting in stable well functioning legs.
In a third patient treated with a hemicondylar osteoarticular allograft needing knee replacement 24 years after initial reconstruction, based on the experience with the patients reported before, a fully constrained resurfacing knee arthroplasty system with stem extensions was implanted giving initial stable contact to the vital host bone.

Discussion
Whether it is preferable to perform reconstruction of large segmental bone defects after tumor resections including joints with allografts or with massive endoprostheses is still unsolved. All-over results are comparable, however there are differences with regard to causes of failure [3]  Tibial allograft reconstructions after resection of malignant bone tumors have become standard of care to preserve limb function in skeletally immature growing children, especially to preserve the opposite growth plate, and in young adults [1].
Proximal tibia reconstruction after bone tumor resection with osteoarticular allografts yielded similar failures compared to endoprosthetic replacement, favouring allograft reconstructions in younger patients to achieve better extensor mechanism function [4].
In patients requiring osteoarticular tibial allografts to preserve the knee joint, the articular surface may over time develop secondary degenerative arthritic changes, inevitably needing knee replacement surgery [2].
Successful salvage of failed osteoarticular allografts was reported after endoprosthetic revisions preserving limb function (80% salvage of primary recon-struction at 160 months followup time [6]).
Treating patients with osteoarticular femoral allografts and subsequent degenerative bone disease showed comparable outcome with total knee arthroplasty in retained femoral allografts, endoprosthesis after allograft removal or primary allograft-prosthesis composites [3].
In their series of 26 distal femoral osteoarticular allografts [2], of seven conversions to allograft-prosthetic composites for progressive joint degeneration, four had subsequent allograft fractures or relevant soft-tissue related problems.
Apart of chemotherapy, gender and tumor grade as risk factors for knee arthroplasties after osteoarticular allograft reconstruction about the knee joint, the arthroplasty system was found to be an important factor for component survival and need for revision knee arthroplasty [7]. All of the patients with non-stemmed components suffered major complications, with significant rate of fractures in unsupported regions of retained allografts, requiring operative reinterventions.
Reporting on total knee replacement in a series of 35 previous recipients of fresh osteochondral allograft transplants, a non-constrained knee arthroplasty system was used, only using stemmed components in three cases [8]. These patients did not have complete tibial plateau allograft replacements and therefore cannot be compared to our cases. According to the low number of stem extensions, 17% of the knees required revision knee arthroplasty within the mean follow-up time of 7.5 years because of aseptic loosening.
The MUTARS modular endoprosthesis system has proven a reliable option for primary knee replacement in tumor resection, with durable fixation of the components over midterm follow-up time (89% retention of the implant over 8.9 years [9]). Various surgical difficulties were encountered for limb preserving salvage using the modular MUTARS system even when completely resecting the original allograft due to altered soft tissue and remnant bone structures, yet with reasonable endoprosthesis survival time [5].
Further data hopefully will improve the concept of maximally bone preserving endoprosthetic replacement following failure of the articular component of massive allografts.

Conclusions
From our experience with massive allografts, we would reserve replacement of the proximal tibia with osteoarticular allografts primarily for very young patients in their growing age. Replacement by allograft versus endoprosthesis as initial procedure for reconstructions has to be carefully weighed against either system.
Patients of younger age with osteochondral allograft reconstruction for tumor resection of the proximal tibia will inevitably develop arthritic degeneration of the knee joint, eventually requiring prosthetic knee replacement. Standard resurfacing knee arthroplasty systems after osteochondral allograft reconstructions appear prone to failure, either for early loosening of the arthroplastic component fixed onto the retained osteoarticular allografts or for sequential instability of the tibiofemoral articulation. Therefore knee replacement for advanced knee arthritis under these conditions demands a knee arthroplasty system with increased tibiofemoral constraint to compensate for the weakened ligament structures and stem extensions anchored to vital host bone.