External stabilization of the anterior cruciate ligament deficient knee during rehabilitation

Using cadaveric specimens, we studied the effect of ACL deficiency upon anterior tibial translation during extension of the knee joint. Five knees were loaded via the quadriceps mechanism until flexion angles of 10 degrees, 25 degrees, 40 degrees, and 60 degrees were attained. At each angle, the anterior-posterior position of the tibia was documented with biplane radiography, both before and after division of the ACL. In every specimen, anterior tibial translation increased with loss of the ACL and was greatest at 25 degrees of flexion, where an average displacement of 3.3 mm was observed. Subluxation was not significant at flexion angles exceeding 60 degrees, regardless of ACL deficiency. We also examined the effect of an external restraining force on tibial subluxation in the ACL deficient knee. Posteriorly directed forces of 0 N, 45 N (10 pounds), 90 N (20 pounds), 135 N (30 pounds), and 225 N (50 pounds) were applied to the tibia at the level of the tibial tubercle. Anterior subluxation was eliminated through application of forces ranging from a maximum of 106 N (23.6 pounds) at 10 degrees to only 13 N (2.9 pounds) at 60 degrees.