Knee replacement

What it is

The worn surfaces at the end of the femur and top of the tibia are cut away and capped with metal components, with a polyethylene insert between them as the new cartilage; the back of the kneecap is often resurfaced. A partial replacement treats one compartment only when the rest of the joint is healthy.

Why it is done

• Severe osteoarthritis (or rheumatoid arthritis) with pain that limits walking, sleep and daily life despite painkillers, physiotherapy, weight loss and injections
• Post-traumatic arthritis after fractures
• Rarely, tumours or failed previous surgery

Before the procedure

• Standing X-rays; blood tests, ECG, MRSA screen, dental check
• 'Joint school' education, prehabilitation exercises, weight optimisation
• Spinal or general anaesthetic with nerve blocks

Step by step

1. A vertical incision over the front of the knee; the kneecap is moved aside
2. Guided cuts remove a few millimetres from the end of the femur and top of the tibia, and worn cartilage and the cruciate ligaments as required
3. Trial components are fitted and the ligament balance and alignment checked through the full range of movement
4. The final metal components are cemented (or press-fitted) and the plastic insert locked in
5. The joint is washed, local anaesthetic infiltrated, and the layers closed

Afterwards

• Standing and walking with a frame the same day or next
• Physiotherapy from day one: bending, straightening, stairs; home in 1-3 days
• Blood-thinning injections or tablets for 2-6 weeks; ice and elevation
• Wound check at two weeks; six-week and one-year reviews

Recovery

Walking without aids by about six weeks, driving at 6-8 weeks, most of the benefit by three months and continued improvement for a year. A knee replacement usually lasts 15-25 years.