Is an intact anterior cruciate ligament needed in order to have a well-functioning unicondylar knee replacement?

Controversy exists about whether a functional anterior cruciate ligament is necessary to achieve success with unicompartmental knee arthroplasty. When the anterior cruciate ligament was deficient, higher failure rates were reported with mobile-bearing implants and with the Lotus implant, a relatively flat, fixed-bearing component. Most failures were secondary to wear. In contrast, the absence of an anterior cruciate ligament did not lead to failure with the St. Georg and Marmor implants. Theoretically, an absent anterior cruciate ligament would increase the sliding motion that caused accelerated polyethylene wear in laboratory studies. Hypothetically, such motion could lead to accelerated wear of unicompartmental arthroplasty in an ACL deficient knee. Currently, unicompartmental knee arthroplasties should not be done in patients with symptoms of anterior cruciate ligament instability and should judiciously be done in older patients without a functional anterior cruciate ligament but with no symptoms of instability.