Knee Problems: Partial Knee Replacement

Partial knee replacement or Unicondylar Knee Replacement (UKR) has experienced a resurgence of interest with the introduction of minimally invasive surgery. Numerous studies, including the Swedish Registry, have demonstrated 90% or greater 10-year survival rates with unicompartmental knee replacement systems. Unfortunately, survival rates beyond 10 years have proved disappointing, falling to the 80% range. UKR has the disadvantage that the medium and long-term revision rates are generally higher than for TKR. UKR are therefore considered by many to be "pre-total knee replacements", and are only expected to last for a relatively short period.

However, twenty years of experience has led to a better understanding of the optimal design features for unicompartmental replacement. The newest implant systems for unicondylar arthroplasty provide both implants and instruments that are designed specifically for minimally invasive surgery. Medial unicompartmental knee replacement has many advantages over total knee replacement (TKR). As all the undamaged structures of the joint, in particular the cruciate ligaments, are preserved, knee function can be restored to nearly normal. After UKR the range of movement is better than after TKR, the knee feels more natural and pain relief is as good or better. In terms of morbidity, operative blood loss is minimal and transfusion is usually unnecessary, complications are less frequent and less serious and recovery is more rapid.

DePuy PFC Sigma unicompartmental knee implants		Medial unicompartmental knee replacement. (source: www.depuy.com)

The main indication for unicondylar knee replacement is medial compartment osteoarthritis. The anterior cruciate ligament should be functionally intact. Fixed flexion deformity should be less than 15°. Varus deformity should be correctable and there should be full thickness cartilage in the lateral compartment. Knee X-rays, taken while standing, must show complete loss of joint cartilage in the medial compartment. Lateral unicompartmental replacement is still controversial, although several surgeons claim good mid- to long-term outcomes.

Unicomparmental replacement appears to offer an early alternative to osteotomy or tricompartmental arthroplasty in elderly patients with unicompartmental arthritis. Compared to high tibial osteotomy, there is a higher initial success rate and fewer complications. Compared to tricompartmental arthroplasty, there tends to be a better functional outcome with a faster recovery and improved function. With appropriate patient selection, new generation of implant design, and minimally invasive operative techniques, unicompartmental knee arthroplasty should assume its proper role in the knee surgeon's armamentarium. High tibial osteotomy should still be used as an alternative procedure in the young, heavy, active individual.

Further Information:

For more information on partial knee replacements, see: DePuy Preservation http://www.uknee.co.uk/html/index2.htm

Site last updated on: 20 June 2008