Ligamentous and capsular restraints preventing straight medial and lateral laxity in intact human cadaver knees
Grood, E.S.; Noyes, F.R.; Butler, D.L.; Suntay, W.J.
Journal of Bone and Joint Surgery. American Volume 63(8): 1257-1269
1981
ISSN/ISBN: 0021-9355 PMID: 7287796 Document Number: 178079
Ligaments and capsular structures which resist medial and lateral opening of the joint space were determined in cadaver knees during clinical testing for straight medial and lateral laxity. Restraining function was recorded as the percent contribution of each structure in resisting the force applied by the examiner. In 16 cadaver knees tested at 5 and 25.degree. of flexion from full hyperextension, the collateral ligaments provided the primary restraint (> 1/2 of the total) at both flexion angles. At 5.degree., the posterior part of the capsule and the cruciate ligaments were important secondary restraints. As flexion increased, the posterior part of the capsule became slack, causing a marked decrease in its restraining action. The middle 1/3 of the medial and lateral halves of the capsule, traditionally considered important, provided little restraining force. The iliotibial tract and the popliteus musculotendinous unit provided little passive restraint. A force applied to the iliotibial band or the biceps tendon, to simulate muscle tension, produced an additional restraint that in vivo presumably would protect the lateral ligaments and capsule. Using an instrumented kinematic chain to determine the 3-dimensional joint motion in 6 knees during testing for straight varus-valgus laxity by the maneuvers used clinically, it was found that axial rotation of the tibia occurred. This may be misinterpreted as medial or lateral joint opening. When just the medial or the lateral collateral ligament (the primary restraints) was sectioned, only a 3-5 mm increase in joint opening occurred. This increase was small because only low forces were applied during the clinical examination and the secondary restraints blocked further opening even though the primary restraint was disrupted. Near full extension, the secondary restraints almost completely blocked opening of the joint after sectioning of the collateral ligaments. With knowledge of the hierarchy of restraining moments contributed by the medial and lateral ligament and capsular structures and an appreciation of the rotatory movements of the knee that may occur during tests for straight varus-valgus laxity, diagnosis and treatment can be more precise.