The effect of continuous passive motion on anterior cruciate ligament reconstruction stability

This study was undertaken to examine the immediate effect of continuous passive motion (CPM) on anterior cruciate ligament (ACL) reconstruction stability. Cadaver knees were tested with a knee arthrometer with the anterior cruciate intact and then with the anterior cruciate sectioned. One of three anterior cruciate reconstructions was then performed and stability was restored to the knee and it was again tested with the knee arthrometer. Stability was defined as being within 2 mm of the intact measurement. The three operations selected were the Marshall-MacIntosh "over-the-top," (OTT) a patellar bone-patellar tendon-tubercle bone (BTB) graft, and a semitendinosis reconstruction. The specimens were placed on a CPM device in a cooler at 38 degrees F and put through a range of motion of 20 to 70 degrees at 10 cycles per minute for 3 days. A success was less than a 2 mm increase in the post-CPM measurement compared to pre-CPM. All three bone-tendon-bone operations failed. The semitendinosis operation was successful in only three out of eight specimens. The OTT operation was successful in eight out of nine specimens. The possible reasons for success and failure are discussed. Because of the potential problems with failure of an ACL with CPM it is suggested that the particular technique being used for an anterior cruciate reconstruction be tested prior to it being used with CPM clinically.