The effect of section of the medial collateral ligament on force generated in the anterior cruciate ligament
Shapiro, M.S.; Markolf, K.L.; Finerman, G.A.; Mitchell, P.W.
Journal of Bone and Joint Surgery. American Volume 73(2): 248-256
1991
ISSN/ISBN: 0021-9355 PMID: 1993720 Document Number: 369849
Ten fresh-frozen knees from cadavera were instrumented with a specially designed transducer that measures the force that the anterior cruciate ligament exerts on its tibial attachment. Specimens were subjected to tibial torque, anterior tibial force, and varus-valgus bending moment at selected angles of flexion of the knee ranging from 0 to 45 degrees. Section of the medial collateral ligament did not change the force generated in the anterior cruciate ligament by applied varus moment. When valgus moment was applied to the knee, force increased dramatically after section of the medial collateral ligament; the increases were greatest at 45 degrees of flexion. Section of the medial collateral ligament had variable effects on the force generated in the anterior cruciate ligament during internal rotation but dramatically increased that generated during external rotation; these increases were greatest at 45 degrees. Section of the medial collateral ligament increased mean total torsional laxity by 13 degrees (at 0 degrees of flexion) to 20 degrees (at 45 degrees of flexion). Application of an anteriorly directed force to the tibia of an intact knee increased the force generated in the anterior cruciate ligament: this increase was maximum near the mid-part of the range of tibail rotation and minimum with external rotation of the tibia. Section of the medial collateral ligament did not change the force generated in the anterior cruciate ligament by straight anterior tibial pull near the mid-part of the range of tibial rotation. With the tibia in an externally rotated position, the force generated in the anterior cruciate ligament increased after section of the medial collateral ligament; the increase was greater when the knee was in flexion. CLINICAL RELEVANCE: The medial collateral ligament normally acts to resist external torque, valgus moment, and anterior tibial force (when the tibia is externally rotated). In doing so, it effectively helps to protect the anterior cruciate ligament from high forces; this effect is greatest for positions of the knee in flexion. In a knee in which the medial collateral ligament is deficient, increased force is borne by the anterior cruciate ligament, especially when the knee is flexed. Our data suggest that an individual who has residual valgus laxity as a result of a previous injury of the medial collateral ligament may be at increased risk for potentially injurious forces generated in the anterior-cruciate ligament by these loading modes.