Allograft-Prosthesis Composites for the Reconstruction of the Distal Femur After the Resection of a Bone Tumor in Childhood.

Background: . Description: An anterior longitudinal incision is made encompassing the biopsy tract, either medial or lateral to the midline, depending on the tumor mass. The roof of the adductor canal is opened to expose the femoral vein and artery for protection. The resection length is based on the length of medullary involvement as measured on magnetic resonance imaging (MRI), plus an additional 2-cm margin. The bone marrow from the proximal femur is sent for frozen-section analysis in order to ensure that an adequate margin has been achieved. Depending on the MRI findings, the capsule, collateral ligaments, and cruciate ligaments are incised, and the meniscus on the tibial plateau is preserved, with consideration given to achieving a negative margin. An appropriately sized osteoarticular allograft with the retained capsule and ligaments is obtained from a standard bone bank. The femoral component of the unconstrained total knee prosthesis is matched for size with the patient's tibial plateau and is fixed to the distal end of the osteoarticular allograft with use of bone cement. The resurfaced allograft is fixed to the host bone with a bridging plate. The ligaments and capsule of the allograft are sutured as closely as possible to their counterparts in the proximal tibia. Knee stability is evaluated at the end of the procedure. Two crossed pins are utilized to fix the knee in 15° flexion to prevent joint subluxation in cases of knee instability and are removed after 2 weeks. Alternatives: . Rationale: APC reconstruction preserves the proximal tibial growth plate and retains more bone stock for future revisions. This technique offers benefits over the use of an osteoarticular allograft, including improved knee function and a reduced risk of osteoarthritic changes, and can even be performed on patients <9 years old. Expected Outcomes: . Important Tips: Choose a medial or lateral approach on the basis of the dominant tumor location.During tumor resection, take care to preserve the neurovascular bundle.After opening the adductor canal, detach the medial gastrocnemius head from the distal femur to facilitate genicular artery ligation and the separation of the vascular bundle from the lesion.Try to use an allograft with remaining ligamentous and capsular structures, as attaching these to their host counterparts can enhance the restoration of joint stability.The compression plate should fully cover the allografts and secure them to the host bone, and compression should be maintained with at least 4 screws.The selected cruciate-retaining femoral component of the THA should be secured to the distal allograft with high-viscosity cement according to the total knee method. Acronyms and Abbreviations: rAPC = resurfaced allograft-prosthesis compositesTKA = total knee arthroplastyMRI = magnetic resonance imagingDVT = deep vein thrombosisPE = pulmonary embolismMSTS = Musculoskeletal Tumor SocietyROM = range of motionDJD = degenerative joint disease.