Internal Hemipelvectomy (Periacetabular / Enneking Type II Resection)

Indication. A primary malignant bone tumour of the innominate bone — most often chondrosarcoma in adults, osteosarcoma or Ewing sarcoma in younger patients — or a selected locally aggressive lesion, where wide surgical margins are achievable with limb preservation. The resection must leave a sensate, functional limb with adequate soft-tissue cover. Historically the only curative local option was external hemipelvectomy (hindquarter amputation); modern imaging, chemotherapy and reconstruction have made limb salvage the default in specialist centres. Pre-operative assessment is what makes the operation safe and the margins clean. Establish, in this order: - Local staging — MRI of the whole pelvis (marrow extent, soft-tissue mass, neurovascular and sacroiliac joint involvement, sacral foramina) plus CT pelvis for cortical detail and planning the osteotomy levels. The two are complementary, not interchangeable.

• Systemic staging — whole-body bone scan or PET-CT, and CT chest, to exclude metastatic disease that would change the plan.
• Biopsy — performed by the treating surgeon, along the line of the future incision, so the tract is excised en bloc with the specimen. A poorly placed biopsy tract seeds the flank or perineum and converts a salvageable limb into an amputation.
• Medical optimisation — neoadjuvant chemotherapy for osteosarcoma and Ewing sarcoma; pre-operative embolisation for hypervascular tumours; ureteric stents placed before incision; bowel preparation; cross-match of blood and cell-saver set up. The decision. Three management strategies exist for an operable pelvic sarcoma, and the choice is dictated by margins, neurovascular involvement and patient fitness:

Setup. The patient is placed in a semilateral (lazy lateral) position on a bean-bag, freeing both the anterior ilioinguinal window and any posterior extension; all pressure points are padded. Establish large-bore intravenous access with arterial and central lines, a urinary catheter, and pre-incision ureteric stents so the ureters are palpable and identifiable throughout. Cell salvage is running and cross-matched blood is in theatre. Antibiotic prophylaxis is given. The femoral vessels, femoral nerve and ureter must remain identifiable at every stage of the dissection.

The goal: expose the hemipelvis through an ilioinguinal/utilitarian approach, gain control of the iliac vessels and femoral nerve, osteotomise the pubis, ischium and ilium around the tumour, detach and deliver the periacetabular block en bloc with wide margins, then reconstruct the hip–pelvis junction and close with durable soft-tissue cover. The exposure is laid out in full below (and in depth on the ilioinguinal approach to the acetabulum page).

Rehabilitation is reconstruction-dependent and slow, dictated by the implant, the soft-tissue flap and the nerve status. | Phase | Timing | Mobilisation | Focus | |-------|--------|--------------|-------| | 1 | 0–2 weeks | Bed-to-chair; protected, non- or touch-weight-bear | Flap and wound healing; DVT prophylaxis; analgesia | | 2 | 2–6 weeks | Progressive weight-bearing per reconstruction (prosthesis slower; transposition as tolerated) | Hip stability; protect any nerve deficit | | 3 | 6–12 weeks | Full weight-bearing as the construct allows | Gait re-education, abductor strengthening, brace wean | | 4 | 3–12 months | Return to function within the limb's limits | Endurance; limb-length and gait adaptation; ongoing surveillance imaging | Functional outcome tracks the resection zone: Type I (iliac) and Type III (pubic) patients do well when the acetabulum and abductors are spared; Type II patients walk with a limp, often need a walking aid, and never recover a normal gait. MSTS (Musculoskeletal Tumour Society) scores after a Type II resection typically sit around half of normal — functional, but clearly limited. Complications

Epidemiology. Primary malignant bone tumours of the pelvis are uncommon but disproportionately lethal — the pelvis accounts for a minority of all primary bone sarcomas yet a large share of sarcoma mortality, because lesions grow large before they are felt and lie close to viscera and major vessels. Chondrosarcoma is the commonest primary malignant pelvic tumour in adults; osteosarcoma and Ewing sarcoma predominate in adolescents and young adults. Many patients present late with a large, palpable mass. Pathoanatomy. The innominate bone is formed by the fusion of the ilium, ischium and pubis at the triradiate cartilage of the acetabulum. The acetabulum is the keystone of the pelvic ring: remove it (a Type II resection) and the lower limb is disconnected from the axial skeleton, which is why reconstruction is unavoidable and always imperfect. Cradled around the pelvis are the common, external and internal iliac vessels, the femoral nerve on iliacus, the obturator nerve and vessels through the obturator foramen, the lumbosacral plexus and sciatic nerve posteriorly, and the ureter, bladder and rectum medially — every one of them a constraint on what can be excised and reconstructed.

Adjuvant therapy. Neoadjuvant and adjuvant chemotherapy is standard for osteosarcoma (a platinum/doxorubicin/high-dose methotrexate regimen) and Ewing sarcoma (a vincristine/doxorubicin/cyclophosphamide alternating with ifosfamide/etoposide regimen); chondrosarcoma is chemo-resistant, so surgery stands alone. Radiotherapy has a role in Ewing sarcoma and for close or positive margins, and proton-beam therapy is increasingly used for pelvic sarcomas to spare adjacent bowel and bladder. Key evidence. Enneking and Dunham's 1978 description of resection with local reconstruction for primary malignant innominate tumours established the zonal classification and showed that limb salvage could match the local control of amputation in selected patients — the foundation of the modern operation. Reconstruction has since evolved from Harrington-style devices and the saddle prosthesis, through custom and modular implants, to patient-specific 3D-printed endoprostheses championed by high-volume centres, which restore anatomy more faithfully but have not eliminated the persistent infection and mechanical-failure burden. Across series, the two threats that define outcomes remain local recurrence (margin-dependent) and deep infection (the leading cause of secondary ablation).