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Hip and knee replacement — indications and complications
Joint replacement is for end-stage osteoarthritis that hurts and limits function despite conservative care; success is high, and exam questions focus mainly on complications: venous thrombosis, dislocation, infection, periprosthetic fracture, nerve injury and loosening.
Why it matters in the exam
Questions in this area present a patient days or weeks after surgery and ask you to recognise a complication and choose the next step. The decision to operate rests on pain and loss of function, not on radiographic severity alone, and follows a trial of conservative care: weight loss, adapted exercise, physiotherapy and analgesia. Main contraindications are active infection in the joint or elsewhere in the body, a neuropathic joint and a non-functioning extensor mechanism of the knee. After hip replacement, dislocation is common in the first months, mainly after a posterior approach and in a position of flexion, adduction and internal rotation; the nerve at risk is the sciatic nerve, especially its peroneal division. After knee replacement, correcting a valgus deformity with a flexion contracture puts the common peroneal nerve at risk. Thromboprophylaxis follows NICE guidance: after hip replacement about 28 days, and after knee replacement about 14 days, with one of several options (low molecular weight heparin, aspirin after an initial period, or direct oral anticoagulants). A patient with new pain in an established replacement needs an infection work-up before mechanical loosening is assumed. An alternative in younger patients with disease in only one knee compartment is partial (unicompartmental) replacement.
Key points
- Indication: end-stage osteoarthritis with pain and functional loss despite conservative care.
- Hip dislocation: first months, posterior approach.
- Thromboprophylaxis: about 28 days for hip and about 14 days for knee.
- Nerve at risk: sciatic for the hip, peroneal for the knee.
- New pain in an established replacement — exclude infection.
Summary table
| Complication | When and in whom | Finding | Treatment |
|---|---|---|---|
| Hip dislocation | First months, posterior approach | Shortened, internally rotated leg after deep flexion | Closed reduction under anaesthesia; surgical revision for recurrent dislocation |
| Venous thrombosis and pulmonary embolism | First weeks | Calf swelling, breathlessness | Prevention: about 28 days for hip and about 14 days for knee |
| Periprosthetic infection | Any time | Pain, fever, wound discharge, raised CRP | Aspiration and cultures before antibiotics |
| Nerve injury | Hip: sciatic nerve; knee: peroneal nerve | Foot drop | Knee: flex the knee and release dressings; observe or explore |
| Periprosthetic fracture | Fall in a patient with weak bone | Sudden pain and inability to bear weight | Fixation or revision depending on implant stability |
| Loosening and wear | Years after surgery | Pain on weight-bearing, osteolysis on radiograph | Exclude infection, then revision surgery |
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Sources
- Campbell's Operative Orthopaedics, 14th ed. (2021) — Arthroplasty of the Hip; Arthroplasty of the Knee
- NICE Guideline NG157, 2020 — Joint replacement (primary): hip, knee and shoulder
- NICE Guideline NG89, 2018 (updated 2019) — Venous thromboembolism in over 16s
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.