Limb Salvage — Endoprostheses

Limb-salvage surgery (LSS) with endoprosthetic reconstruction has become the standard of care for most primary bone sarcomas of the extremities, replacing amputation in approximately 85–90% of patients. The endoprosthesis (tumour prosthesis) replaces resected bone and joint segments after wide excision, restoring immediate limb function. Advances in implant design, modular systems, fixation biology, and perioperative management have dramatically improved durability and functional outcomes over the past three decades.

• Limb salvage vs amputation: multiple RCTs and meta-analyses have shown equivalent oncological outcomes (survival) for limb salvage vs amputation in appropriately selected patients — the decision is therefore driven by functional and quality-of-life considerations
• Absolute contraindications to limb salvage: tumour encasing or directly involving the major neurovascular bundle such that adequate oncological margins cannot be achieved without sacrificing the vessels/nerves; major neurovascular involvement making reconstruction non-functional; pathological fracture with contamination of surgical planes (relative); patient factors (severe comorbidity, inability to comply with rehabilitation)
• Most common tumours requiring endoprosthetic reconstruction: osteosarcoma (distal femur, proximal tibia, proximal humerus), Ewing sarcoma, chondrosarcoma, and occasionally giant cell tumour (after failed intralesional treatment) and metastatic disease
• Pre-operative planning: MRI for local extent; CT chest for pulmonary staging; CT of lesion for bony anatomy; nuclear medicine or PET for multifocal/skip lesions; angiography or MRA if neurovascular proximity suspected

• Modular endoprosthetic systems: modern tumour prostheses consist of modular components (stem, body segments, joint components) allowing intraoperative customisation to match the exact length of bone resected; standard modular systems (METS, Stryker Modular, Stanmore, Global) have largely replaced custom-made prostheses
• Fixation: cemented (most common — provides immediate stability, suitable for all patients including those receiving chemotherapy); cementless press-fit (for selected patients with good bone stock and no perioperative chemotherapy effect on bone ingrowth); extracortical bone bridging (ECBB): biological fixation method where cortical bone graft is placed around the prosthesis-bone junction and stimulates bridging bone formation — reduces aseptic loosening risk in young patients; combined cement-ECBB technique increasingly used
• Rotating hinge joint (knee): standard joint for distal femoral and proximal tibial endoprostheses — allows both flexion/extension and controlled rotation; avoids the stress concentration of fixed hinge; more forgiving of minor malalignment than fixed hinge
• Growing prostheses (expandable endoprostheses): for skeletally immature children — expand non-invasively or with minor surgery to maintain limb length equality as the contralateral limb grows; non-invasive magnetic expanding prostheses (MUTARS Xpand, Repiphysis) allow expansion without anaesthesia; require multiple expansions during growth

Henderson et al. (2011) proposed the ISOLS (International Society of Limb Salvage) classification of endoprosthetic failures — the Henderson classification — which is widely used to categorise complications and plan revision surgery.

• Infection rate in endoprostheses: significantly higher than primary OA arthroplasty — approximately 5–10% for tumour prostheses vs 1–2% for standard arthroplasty; contributing factors include prolonged operating time, poor soft tissue coverage, immunosuppression from chemotherapy, and larger dead space; meticulous surgical technique and perioperative antibiotic prophylaxis are critical
• Overall endoprosthetic 10-year survival: approximately 65–75% for distal femoral endoprostheses — implant survival is the major long-term limitation; revision rate increases with time, particularly aseptic loosening

• Proximal tibial reconstruction and gastrocnemius flap: the most important soft tissue consideration in limb-salvage surgery; the thin skin over the proximal tibia is insufficient to cover a large metallic implant without a flap; medial gastrocnemius rotational flap is the standard — reliably covers the proximal tibial prosthesis, provides vascularised muscle coverage, and allows patellar tendon reattachment; failure to use this flap results in wound breakdown rates exceeding 30%
• Extensor mechanism reconstruction after proximal tibial resection: patellar tendon must be reattached to the prosthesis; Dacron tape, LARS ligament, or tube graft secured through drill holes in the tibial component collar; active knee extension is the primary functional goal
• MSTS functional score: Musculoskeletal Tumour Society score (0–30); assesses pain, function, emotional acceptance; widely used for outcome reporting after limb-salvage surgery; mean MSTS score after distal femoral endoprosthesis approximately 70–75% (21–22/30)
• Toronto Extremity Salvage Score (TESS): patient-reported outcome measure specific to extremity tumour surgery; more sensitive to patient experience than MSTS

• Chemotherapy effect on bone ingrowth and fixation: chemotherapy causes impaired bone formation and remodelling; cemented fixation is preferred in patients receiving perioperative chemotherapy; for cementless press-fit, wait until chemotherapy is complete and bone remodelling has recovered; ECBB (extracortical bone bridging) with allograft cortical struts provides biological fixation augmenting cement and is particularly valuable in young patients where long-term fixation is the priority
• Limb salvage in children — growing prostheses: equalisating leg length as the child grows is essential to prevent gait problems and secondary spinal deformity; non-invasive expandable prostheses (Repiphysis, MUTARS Xpand) use an external magnetic device for expansion without surgery; planned expansions every 3–6 months; complications include fatigue failure of expansion mechanism and infection with repeated expansion procedures
• Failed endoprosthesis — amputation: when repeated revision is no longer oncologically or technically feasible, amputation remains the salvage option; however, function after amputation with modern prosthetics can be excellent, particularly below-knee; rotationplasty (Van Nes procedure) provides exceptional prosthetic function in selected children — the ankle is repositioned 180° to act as a knee joint, providing a biological joint for prosthetic attachment
• Periprosthetic fracture around endoprosthesis: occurs at the stem-bone junction when the residual host bone is short or osteoporotic; management options — revision to longer stem bypassing fracture, plate fixation, or allograft strut augmentation; high risk of infection in this scenario

• Limb salvage = equivalent oncological outcome to amputation in appropriately selected patients — decision is functional/QoL, not survival-based
• Absolute contraindication to limb salvage: NV encasement preventing adequate oncological margin AND functional reconstruction
• Proximal tibia reconstruction: gastrocnemius rotational flap mandatory — thin skin + large metal implant + patellar tendon reattachment; without flap, wound breakdown >30%
• Henderson classification: Type 1 soft tissue; Type 2 aseptic loosening (most common long-term); Type 3 structural failure; Type 4 infection; Type 5 tumour recurrence
• Infection rate: 5–10% for tumour endoprostheses vs 1–2% standard arthroplasty; chemotherapy, poor soft tissue, prolonged surgery all contribute
• ECBB (extracortical bone bridging): biological fixation augmenting cement; cortical struts at prosthesis-bone junction; preferred in young patients for long-term fixation
• Growing prostheses: non-invasive magnetic expansion; planned expansions every 3–6 months; for skeletally immature patients
• Rotationplasty (Van Nes): ankle repositioned 180° → acts as knee joint for prosthesis; superior function vs above-knee prosthesis; for selected children with distal femoral tumours
• MSTS score: 0–30; mean approximately 21–22/30 after distal femoral endoprosthesis
• Cemented fixation preferred with perioperative chemotherapy — bone ingrowth impaired by chemotherapy