RECONSTRUCTION OF THE EXTENSOR APPARATUS AFTER PROXIMAL TIBIA ENDOPROSTHETIC REPLACEMENT USING FIBULA TRANSPOSITION

Abstract

Competence of the extensor mechanism is the major determinant of functional outcome after resection of the proximal tibia and tumor prosthesis implantation. Restoration of a compromised active extension of the knee and an extension lag still remains a difficult challenge. Various techniques have been proposed in the past twenty years including direct attachment of the patellar ligament to the prosthesis, transposition of the medial gastrocnemius muscle possibly associated with other muscle flaps, transposition of the fibula and combination of these techniques. Transposition of the fibula was first reported by Kotz in 1983 but not sufficiently described, so that surgeons who want to plane and manage such a procedure can have some difficulties. We present our technique of fibula transposition and report the functional results about seven patients treated for high-grade sarcomas of the proximal tibia. Fibula transposition is carried out only if the entire fibula and its soft-tissues can be preserved. Resection of the tumor and reconstruction is carried out using the same anteromedial approach. After implantation of the prosthesis, the fibula and its muscles are mobilized anteriorly in a ‘baionnette’ shape obtained by performing a two-level osteotomy. The peroneal nerve and the anterior tibial vessels are previously identified and released to prevent tension on these structures during transposition. Care must be taken to preserve as much as possible the muscular insertions on the fibula so that probability of bone fusion increases. The biceps tendon and the lateral collateral ligament inserted in the fibular head are sutured to the patellar ligament. The knee is immobilized in a knee-ankle orthosis for 6 weeks. We have performed this technique in seven cases. A medial gastrocnemius muscle flap was associated in 3 cases to cover the prosthesis. Fusion was achieved in all cases. Full active extension was obtained in all cases with an extensor strength rated 5/5. All patients were ambulatory without external support at the last follow up.