The collateral ligament flexion-extension test (CLEFT) in total knee replacement.

We present a simple preoperative clinical test, the collateral ligament extension-flexion test (CLEFT). In patients undergoing total knee arthroplasty, with a preoperative valgus or varus deformity, this test establishes which knees have balanced collateral ligaments. It predicts which knees will not require soft tissue adjustment during the course of their surgery despite, in some cases, large deformities. The mechanism of the test is based on the observation that, in certain patients, a deformity present in extension is seen to correct in flexion. The sensitivity of this observation was checked in 44 consecutive patients undergoing total knee arthroplasty, and who had either a valgus or varus deformity in extension greater than 10 degrees. In 34 patients the test was positive, and none of these required ipsilateral collateral ligament release. All of the 10 patients with a negative test required soft tissue adjustment. In patients undergoing unconstrained total knee arthroplasty this test is reliably predictive of those knees with preoperative deformity which can be corrected simply by correctly aligned bone cuts. It supports the principle of bony resection prior to soft tissue adjustment in this form of surgery.