Resurfaced allograft-prosthetic composite for proximal tibial reconstruction in children

Reconstruction of the proximal part of the tibia in children with use of an unconstrained tibial component cemented in an allograftprosthetic composite after proximal tibial resection spares the distal femoral physis and articular cartilage, maintains the bone stock of the tibia, and allows the allograft to be adapted to the small tibial dimension in very young patients. Patients considered for this technique are children or adolescents with a metaphyseal-epiphyseal sarcoma of the proximal part of the tibia, without tumor extension into the knee ligaments or capsule, and with a satisfactory clinical response to preoperative chemotherapy. Multiplanar and multisequence magnetic resonance imaging (MRI) studies are performed to exclude any joint contamination and to determine the level of the distal osteotomy. The allograft is selected preoperatively on the basis of comparative patient and donor imaging and is matched as closely as possible to the host tibia, erring on the side of oversizing. Surgical exposure providing longitudinal access to the knee and the proximal part of the tibia is performed medially or laterally, depending on the side of the biopsy (usually medial). After capsulotomy, the cruciate ligaments are cut close to the femoral attachment, while the capsule and the patellar tendon are cut close to the tibial attachment. If possible oncologically, the posterior cruciate ligament is cut close to the tibial insertion and is later sutured to the posterior capsule of the allograft. The origin of the gastrocnemius muscle is retracted or detached, and the popliteal artery trifurcation is explored. The tibiofibular joint and the common peroneal nerve are exposed by raising the lateral flap.Anintra-articular or extra-articular resection of this joint, as decidedon the basis of the preoperative imaging, is performed. The osteotomy of the tibia is performed at the level determined on the basis of the preoperative imaging. The specimen is freed, with a cuff of tibialis anterior, popliteus, and posterior compartment muscles maintained as required. The allograft is processed on a separate table, leaving the capsule and the patellar tendon attached to the graft. The polyethylene spacer trials, available in various sizes, are placed on the exposed femoral condyles, and the size that most closely matches the condyles is chosen. The allograft is prepared for the tibial prosthesis according to the instructions provided by the implant manufacturer. The tibial component of an unconstrained total knee prosthesis is cemented into the allograft. As the distal part of the femur in a child is generally smaller than that in an adult, we use prosthetic implants that allow the surgeon to choose the appropriate size of polyethylene spacer and proximal tibial prosthesis that will fit the femoral epiphysis of the patient. In patients treated between 1996 and 2005, we used the LCS COMPLETE Mobile-Bearing Total Knee System (DePuy Synthes), which offers revision tray components available in nine sizes. Since 2006, we have used the TC-PLUS SB (Tricompartmental Knee Prosthesis with Self-aligning Bearing; Smith&Nephew), which has six sizes for the tibial component and ultracongruent polyethylene. A plate (4.5 or 3.5 mm, depending on the size of the bone) is molded to fit the contour of the bone. The plate should be long enough to cover the entire length of the allograft and accommodate three or four holes in the host bone. Sutures are placed on the host and grafted capsules. The prepared composite is then fixed to the host bone. A trial spacer is inserted through the medial opening in the capsule, and the one that fits most snugly is chosen and ultimately implanted. The sutures on the most posterior part of the capsule are tied first, followed by those on the lateral capsule and the patellar tendon. If the posterior cruciate ligament can be cut close to the tibial insertion, it is sutured to the posterior capsule of the allograft. Finally, sutures on the medial part of the capsule are tied to enclose the implanted joint snugly. Mediolateral stability, knee range of motion, and patellar tracking are checked. A medial gastrocnemius flap is prepared and is used to cover the composite, whenever such an application is justified because of a lack of satisfactory soft-tissue coverage. The prosthesis usage in this new surgical technique represents off-label use of an implant as it is not intended for use in modular segmental reconstruction after bone resection in limb salvage; therefore, this so-called salvage technique is not approved by the U.S. Food and Drug Administration.