Proximal Tibial Endoprosthetic Replacement for Tumour

Indication. A malignant bone tumour of the proximal tibia in a patient in whom a wide margin can be obtained and a functional limb preserved — most often a high-grade osteosarcoma (the commonest primary malignant bone tumour of adolescence, classic metaphyseal location), and also Ewing sarcoma and chondrosarcoma. Selected aggressive benign lesions (recurrent giant-cell tumour of bone) and solitary metastases are occasional indications. For chemo-sensitive tumours the resection follows neoadjuvant chemotherapy and is performed once marrow and systemic disease are controlled. Pre-operative staging is the gate-keeper. Before any resection: local MRI (marrow extent, skip lesions, extraosseous component, joint involvement), staging CT of the chest (osteosarcoma and Ewing sarcoma metastasise to lung), and a whole-body MRI or bone scan to exclude synchronous skip and metastatic deposits. The biopsy tract is excised in continuity with the specimen, so the biopsy must be planned by (and ideally performed by) the resecting surgeon, through the future incision and in a compartment that will be resected. The resection length is templated from the MRI, aiming for a cuff of normal marrow beyond the tumour. The one decision that matters — is limb salvage appropriate, and with what reconstruction? The choice is driven by the margin attainable, the tumour's response to chemotherapy, the state of the soft-tissue envelope, skeletal maturity, and patient preference.

Relative contraindications to limb salvage are an inability to obtain a clean wide margin, frank neurovascular encasement that cannot be segmentally resected and grafted, an inadequate or contaminated soft-tissue envelope, and (in children) an unavoidable catastrophic growth-plate resection without a reconstructable option. Setup. Supine with a thigh tourniquet; the limb is exsanguinated by elevation alone (not Esmarch) to avoid mechanically shedding tumour cells into the circulation. A cell-saver is not used in tumour surgery. Image intensifier confirms the osteotomy level. The whole limb is prepared so the knee can be flexed freely and a gastrocnemius flap harvested. An MDT plan, adequate blood cross-match, and plastic-surgery standby are routine.

The goal: widely excise the proximal tibial tumour en bloc with its biopsy tract and a cuff of normal tissue while protecting the posterior neurovascular bundle and the common peroneal nerve, then reconstruct the segment with a modular endoprosthesis and restore the extensor mechanism over vascularised soft tissue using a medial gastrocnemius flap.

Rehabilitation | Phase | Timing | Protection | Therapy and goals | |-------|--------|------------|-------------------| | 1 | 0–6 weeks | Cylinder cast or brace locked in full extension; non or touch weight-bearing | Flap monitoring, oedema control, ipsilateral ankle/hip and contralateral limb ROM; goal is healing of the extensor reconstruction and flap | | 2 | 6–12 weeks | Hinged brace; flexion progressively unlocked (aim to 90 degrees); protected weight-bearing | Active flexion, passive/assisted extension; active extension only introduced carefully toward 8 weeks | | 3 | 3–6 months | Wean brace; progress to full weight-bearing | Quadriceps and hamstring strengthening, gait re-education; anticipate a residual extensor lag | | 4 | 6 months onward | None | Return to function; the extensor lag often persists and remains the chief functional limitation | Rehab runs alongside ongoing chemotherapy cycles, so timing is modified by wound healing and cytopenias. Most patients walk independently by 3 months; a 10–20 degree extensor lag is common and is managed with quadriceps rehabilitation and, occasionally, an extension-assist brace. Complications

Epidemiology. Osteosarcoma shows a bimodal age distribution, with a dominant peak in adolescence (roughly 10 to 20 years) and a smaller second peak after the age of 60, often in Paget disease or after prior radiation. Its incidence is about 3 to 4 per million per year in the young. The region around the knee is the commonest site, with the distal femur first and the proximal tibia second, accounting for around 15 to 20 percent of cases. Ewing sarcoma and chondrosarcoma make up most of the remainder of resectable proximal-tibial malignancies. Pathoanatomy. Osteosarcoma arises in the metaphysis and expands eccentrically, breaching the cortex and elevating the periosteum. The surgical anatomy that governs this operation is fixed by three landmarks: the patellar tendon inserts on the tibial tuberosity on the anterior proximal tibia and is sacrificed with the specimen; the anteromedial tibia is subcutaneous, with no interposed muscle — hence the cover problem; and the posterior neurovascular bundle (posterior tibial artery with the tibial nerve) lies directly behind popliteus, which is the surgeon's protective buffer. The anterior tibial artery is the first infrageniculate branch of the popliteal and passes forward through the upper interosseous membrane, where it must be ligated, while the common peroneal nerve runs subcutaneously around the fibular neck on the lateral side.

Classification in context. The Enneking surgical stage determines whether limb salvage is appropriate and frames the prognosis. Most high-grade proximal-tibial osteosarcomas present as Stage IIB (high grade, extracompartmental) — resectable but demanding the wide margin, the constrained endoprosthesis, and the extensor and soft-tissue reconstruction described above, together with multi-agent chemotherapy.