Causes of knee replacement failure
- Loosening — repetitive stress eventually loosens the bond between the implant and the bone.
- Wear — the polyethylene liner wears down over time. The microscopic plastic debris triggers an immune reaction that can cause bone loss around the implant.
- Infection — superficial or deep infection of the joint, presenting acutely or as a chronic low-grade picture.
- Instability — the soft-tissue restraints around the knee stretch over time.
- Fracture — periprosthetic fracture, usually after a fall.
- Patellofemoral pain — particularly where the kneecap was not resurfaced at the original operation.
Investigation
- X-rays — compared with previous films wherever possible
- CT for detailed assessment of implant position
- MRI for soft tissue evaluation
- Bone scan and SPECT-CT to identify loosening or hot spots
- Ultrasound
- Blood tests including inflammatory markers
- Joint aspiration where infection is suspected
Treatment
Some patients with mild symptoms and stable implants are best managed conservatively with monitoring and physiotherapy. When revision is required, the operation ranges from exchanging the polyethylene liner alone, through to a complete revision knee replacement.