Allograft Reconstruction after Bone Tumour Resection

Indication. Structural fresh-frozen allograft is used to reconstruct a segmental bone defect after the wide resection of a bone tumour, when the goal is biologic reconstruction — restoring living-quality bone stock and providing sites for tendon and ligament reattachment — rather than simply bridging the gap with metal. It is chosen in three broad situations: - Absolute indications - A diaphyseal or intercalary segmental defect after wide resection of a bone sarcoma (osteosarcoma, Ewing sarcoma, chondrosarcoma) in a patient younger than 40-50 years who desires biologic reconstruction and restoration of bone stock. - An osteoarticular defect requiring joint surface and ligament reconstruction (proximal tibia, distal femur, proximal humerus) in a young, high-demand patient. - The need for tendon or ligament attachment sites that cannot be achieved with a megaprosthesis (patellar tendon, hip abductors, rotator cuff). - Patient preference for allograft after informed discussion of the risks versus endoprosthetic reconstruction.

• Relative indications - Allograft-prosthesis composite (APC) when the joint surface is not reconstructible with osteoarticular allograft but soft-tissue attachment is still desired. - Revision of a failed megaprosthesis where bone stock restoration is required for future longevity. - Aggressive benign tumours (giant cell tumour, chondroblastoma) with massive bone loss after curettage and resection. Contraindications. Absolute: active infection at the resection site, inability to achieve wide surgical margins, patient non-compliance with prolonged protected weight-bearing (minimum 6 months), and severe immunocompromise or uncontrolled diabetes with high infection risk. Relative: age greater than 60-65 years (megaprosthesis usually preferred for faster rehabilitation), a requirement for post-operative radiation (increases nonunion and fracture risk), and smoking or a poor soft-tissue envelope that cannot be optimised. The decision — allograft versus megaprosthesis. This is the central pre-operative choice, and it drives everything that follows:

Evidence for allograft reconstruction. Fresh-frozen structural allografts achieve union in 60-80 percent of host-graft junctions when rigid fixation and autograft augmentation are used. Osteoarticular allografts carry higher complication rates (fracture, joint degeneration) than intercalary grafts but preserve the option for biologic joint reconstruction in young patients. APCs combine the advantages of both techniques and are particularly useful in the proximal tibia, where patellar tendon reattachment is critical. Against a megaprosthesis, allograft offers superior long-term bone stock and the possibility of tendon attachment but requires 6-18 months of protected weight-bearing and carries a 20-40 percent major complication rate in the first two years. Consent. Discuss nonunion (10-30 percent), fracture (5-15 percent), infection (5-15 percent), disease transmission (less than 1 in 1 million), prolonged protected weight-bearing (6-18 months), and the possibility of graft removal and revision to megaprosthesis or amputation if complications occur. Setup. Supine on a radiolucent table with the entire limb prepared and draped free. A tourniquet is usually not used because of the length of the procedure and the need for proximal exposure; a bump under the ipsilateral buttock facilitates lateral access if needed. A size-matched fresh-frozen allograft is ordered from an accredited tissue bank after CT templating of both the defect and the contralateral limb; the graft is thawed in warm saline on the morning of surgery and cultured, and autograft is harvested from the iliac crest or obtained from reamings if an intramedullary nail is used.

The goal: restore a segmental defect after wide tumour resection with a fresh-frozen structural allograft that is rigidly fixed under compression at both host-graft junctions, biologically augmented with autograft, and overlaid with a healthy soft-tissue envelope. The exposure is the wide resection itself — performed through the approach appropriate to the tumour (for the distal femur example, the anterolateral femoral shaft or medial parapatellar approach) — and it is laid out in full as the first steps below.

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Osteoarticular and APC variants. For an osteoarticular allograft, joint surface matching is confirmed on the back table before implantation, and the joint capsule and ligaments are reconstructed under appropriate tension with the joint reduced; for a proximal tibial osteoarticular graft the patellar tendon is reattached to the allograft tibial tubercle with transosseous sutures or anchors. For an allograft-prosthesis composite (APC), when the joint surface cannot be reliably reconstructed with osteoarticular allograft, a cemented prosthesis is implanted into the allograft on the back table and the composite is fixed to the host with the same junction principles; the patellar tendon or other soft tissues attach to the allograft portion of the composite.

Rehabilitation | Phase | Timing | Weight-bearing & protection | Priorities | |-------|--------|-----------------------------|------------| | Early | Day 0 to 6 weeks | Touch-down or partial (10-20 kg) with crutches or walker | Drains out at 48 h; 24-48 h IV antibiotics; DVT prophylaxis; gentle active-assisted ROM | | Union monitoring | 6 weeks to union | Continued protected weight-bearing | Serial radiographs at 6 weeks, 3, 6, 9 and 12 months, then 6-monthly; CT if equivocal at 9-12 months | | Return to function | After union (6-18 months) | Progress to full weight-bearing | Progressive resistance; low-impact activity permitted; high-impact generally discouraged | Union is defined as bridging callus on two orthogonal views without a radiolucent line at either junction, and protected weight-bearing continues until union is confirmed. Strengthening begins once full weight-bearing is allowed; return to high-impact sport is generally discouraged, while low-impact activities (swimming, cycling) may be permitted after union. Oncologic surveillance with local and systemic imaging continues per protocol throughout. Managing nonunion. Nonunion is declared only after 12 months — or 18 months in patients who received chemotherapy or radiation — with no radiographic progress. Low-grade infection must be excluded by aspiration or biopsy before any revision. Revision options are compression plating with autograft (iliac crest or vascularised fibula), exchange nailing with compression and autograft if an IM nail was used initially, a bone stimulator or anabolic agents (teriparatide) in recalcitrant cases, and — if multiple revisions fail or infection is present — conversion to megaprosthesis or amputation.

Complications

Host-graft junction biology. The success of structural allograft reconstruction depends on understanding that the graft is avascular. Union occurs by creeping substitution — host vessels and osteoblasts invade the graft from the junction, resorbing and replacing necrotic bone over months to years. The central portion of a long intercalary graft may remain avascular indefinitely, which is why fixation must protect the junctions until union and why the graft never fully remodels to living bone. Fixation principles. The fixation construct must span both host-graft junctions with sufficient working length on the host bone (minimum two cortical diameters) to resist bending and torsional forces during the prolonged healing period. Compression at the junction is achieved with lag screws or compression plating; any gap greater than 1 mm dramatically increases nonunion risk. When an intramedullary nail is used it must be locked proximally and distally, and the junctions should still receive supplemental plate or cerclage compression where possible. Soft-tissue considerations. The soft-tissue envelope after tumour resection is often compromised by the resection itself and by adjuvant therapy. Muscle flaps (gastrocnemius, soleus, latissimus) are frequently required to cover the allograft and provide a vascularised bed. Tendon reattachment (patellar tendon, hip abductors, rotator cuff) is performed with heavy non-absorbable suture through drill holes or through the preserved soft-tissue sleeve on the allograft. For osteoarticular grafts, joint surface matching is critical — the donor is size-matched on pre-operative CT, the articular cartilage is preserved during implantation, and the capsule and ligaments are sutured to the corresponding structures on the allograft under appropriate tension. Graft selection and storage. Use only grafts from accredited tissue banks with negative cultures, serology and irradiation where indicated; size matching is critical, as a graft more than 2 mm smaller in diameter than the host canal leads to poor fit and fixation failure. Fresh-frozen storage at minus 80 degrees Celsius is standard; freeze-dried grafts must never be used for structural applications because of reduced mechanical strength. Viral transmission (HIV, hepatitis) is now less than 1 in 1 million with modern screening, but bacterial contamination during procurement or processing remains a concern.