Hip Arthrodesis (Fusion)

Indication. Hip arthrodesis converts a painful, degenerate hip into a painless, stable, durable fused joint. It is offered to the young, high-demand manual labourer with isolated unilateral end-stage arthritis — classically post-traumatic (acetabular or femoral-head fracture sequelae) or post-infective (sequelae of quiescent septic arthritis) — in whom the longevity of a total hip replacement under decades of heavy repetitive loading is a genuine concern, and who accepts a permanently stiff hip in exchange for a painless, dependable hip that will outlast any implant. Assess the whole patient, not just the hip. A successful fusion depends entirely on the neighbouring joints absorbing the lost hip motion for the rest of the patient's life. Before committing, confirm: - Normal ipsilateral KNEE — takes increased sagittal and rotational load.

• Normal contralateral HIP — compensates for lost motion and shares weight-bearing.
• Normal lumbar SPINE — compensates with increased lumbar motion (a frequent later pain source). If any of these is already degenerate, the compensatory burden will be poorly tolerated and arthrodesis is contraindicated or strongly discouraged. The one decision that matters. Reserving fusion for the correct patient versus offering arthroplasty:

Contraindications. - Absolute — Bilateral hip disease (both hips cannot be fused; the patient could not sit, manage stairs or perform perineal hygiene); active sepsis that cannot be eradicated before union (though quiescent prior infection is actually a classic indication); inflammatory arthropathy (rheumatoid arthritis, ankylosing spondylitis) — polyarticular disease with affected adjacent joints and problematic spinal involvement.

• Relative — degenerative change in the ipsilateral knee, contralateral hip or lumbar spine; an older or lower-demand patient in whom arthroplasty durability is adequate; a patient unwilling to accept a stiff hip or its long-term sequelae. Consent explicitly for a permanently stiff hip, the likelihood of ipsilateral knee pain, low-back pain and contralateral hip pain developing over the following decades from compensatory loading, limb-length issues, nonunion, and the realistic prospect of a future conversion to arthroplasty. Set expectations honestly: the trade is hip motion for durability. Setup. Lateral or supine depending on the chosen approach, with the limb free so the final position can be checked against the contralateral side. Plan implant selection (cobra-head plate, or anterolateral/lateral plate with a lag screw across the joint) and template the desired final position and limb length before scrubbing.

The goals are simple and unforgiving: achieve bony union between the femoral head or neck and the acetabulum, in the optimal position, while preserving the structures a future total hip arthroplasty will need — the abductor mechanism, the superior gluteal nerve and the gluteal vessels. The exposure is the step that decides whether that future conversion is even possible, which is why a muscle-sparing approach is the heart of the operation.

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Rehabilitation. Protected weight-bearing is typical until radiographic union is progressing; some surgeons supplement rigid fixation with a spica or brace. Serial radiographs monitor for union, with nonunion the principal early failure to watch for. Rehabilitation focuses on gait re-education with the fused hip and on core and adjacent-joint conditioning. Reinforce the early counselling: expect adjacent-joint symptoms over years and the option of later conversion. Early and technical complications. - Nonunion — the commonest technical failure; minimised by thorough cartilage removal to bleeding bone, congruent surfaces and rigid compressive fixation. Established symptomatic nonunion may require revision fixation and grafting, or conversion to arthroplasty.

• Malposition — especially abduction (functional lengthening, lurching gait, perceived limb-length discrepancy); also excess flexion (back pain) or rotation (gait disturbance). Correction may require osteotomy.
• Limb-length discrepancy — from bone loss at preparation or malposition; managed with a shoe raise or addressed at future conversion.
• Infection — particularly relevant in post-infective cases; deep infection threatens union and may demand debridement.
• Abductor neurovascular injury — to the superior gluteal nerve and vessels, compromising any future conversion. Long-term adjacent-joint sequelae — the key counselling point. The lost hip motion is compensated by the neighbouring joints, which become overloaded and hypermobile over decades. This adjacent-joint degeneration is the principal long-term problem and the commonest reason patients later request conversion: - Ipsilateral KNEE pain — increased sagittal and rotational demand.
• LOW-BACK pain — compensatory lumbar hypermobility; very common with long-term follow-up.
• Contralateral HIP pain — increased load and compensatory motion on the opposite hip.

Conversion to total hip arthroplasty. Most long-surviving fusions eventually present for conversion. The usual drivers are the adjacent-joint sequelae — intractable low-back pain, ipsilateral knee pain and contralateral hip pain — rather than a problem with the fusion itself. Restoring hip motion characteristically relieves the back and knee pain, but conversion is a more demanding operation with less predictable outcomes than a primary THA: - Abductor function is the key variable — years of disuse plus any surgical damage mean abductor strength and gait recovery are unpredictable; a Trendelenburg gait and limp are common afterward.

• A trochanteric osteotomy may be required to mobilise and reattach the abductors and access the joint, adding the risk of osteotomy nonunion and hardware irritation.
• Distorted anatomy, retained hardware, heterotopic bone and a contracted soft-tissue envelope all add complexity. This is precisely why the index fusion is performed with abductor and superior-gluteal neurovascular preservation from the outset.

Rationale and modern role. Hip arthrodesis was historically a mainstay of treatment for end-stage hip disease in young adults, before reliable arthroplasty existed. With modern total hip arthroplasty offering excellent pain relief and durability, hip arthrodesis is now a rare, salvage option — but it retains a defined niche. The enduring logic: in a young, high-demand manual labourer, a well-positioned fusion will outlast any arthroplasty under heavy repetitive loading, with no bearing wear, no dislocation risk and no concern about implant longevity over a multi-decade working life. Why it remains high-yield as an examined principle. Although operative volume is now low, examiners test the reasoning, not your caseload: the position of fusion, the prerequisites (normal adjacent joints), the long-term adjacent-joint sequelae, and the logic of conversion to arthroplasty. A candidate who can articulate these principles fluently demonstrates mature decision-making in the young arthritic hip.