Ligamentous and capsular restraints preventing straight medial and lateral laxity in intact human cadaver knees.

In this study, we determined which hgaments and capsular structures resist medial and lateral opening of the joint space in cadaver knees during clinical testing for straight medial and lateral laxity. Restraining function was recorded as the per cent contribution of each structure in resisting the force applied by the examiner. In sixteen cadaver knees tested at 5 and 25 degrees of flexion from full hyperextension, the collateral ligaments provided the primary restraint (greater than one-half of the total) at both flexion angles. At 5 degrees, 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 one-third of the medial and lateral halves of the capsule, traditionally considered important, provided little restraining force. The iliotibial tract and the pophiteus musculotendinous unit provided little passive restraint. However, a force applied to either the ihiotibial 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 three-dimensional joint motion in six knees during testing for straight varus-valgus laxity by the maneuvers used clinically, we found that axial rotation of the tibia occurred that may be misinterpreted as medial or lateral joint opening. When just the medial or the lateral collateral ligament (the primary re* Read in part at the Annual Meetings of the Orthopaedic Research Society. Dallas. Texas. February 21. 1978. and San Francisco, California, February 20. 1979. r This work was supported in part by Grant ROl AM 21 172 from the National Institutes of Health, Grant 239 from the Orthopaedic Research and Education Foundation, and Air Force Contract F33615-C05 1 1. 4: Department of Orthopaedic Surgery. College of Medicine, 231 Bethesda Avenue, Cincinnati. Ohio 45267. straints) was sectioned, only a three to five-millimeter 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. CLINICAL RELEVANCE: 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 varusvalgus laxity, both diagnosis and treatment can be more precise. In the past, most assessments of ligament function have been based on the changes in laxity observed after cutting selected ligaments3”5’32 or else on the injury patterns associated with observed clinical laxities’M13”4’”” 20,24,25,28 As a result, confusion and disagreement persist as to the ligament injuries associated with specific laxities. Often in clinical practice the ligaments that may be involved are just listed. Accurate diagnosis and optimum treatment require that the function of the ligaments in resisting joint opening be understood and ranked in order of importance. Recently we described a new method for determining the restraining force provided by each ligament and capsulan structure5’6’9. This method allows the ligaments to be ranked in order of importance based on the per cent of the total restraining force that each provides. In addition, the method yields results that are independent of the order in which the ligaments are cut, and therefore all ligaments can be studied in each knee. The purpose of this report is to describe how we applied this method to the measurement of the passive restraints to straight medial and lateral opening of human 1258 E. S. GROOD, F. R. NOYES, D. L. BUTLER, AND W. J. SUNTAY THE JOURNAL OF BONE AND JOINT SURGERY cadaver knees at 5 and 25 degrees of flexion, two positions that commonly are tested clinically. Our goals were to document what ligaments resist the forces applied by the clinician when he or she examines the knee for straight medial and lateral laxity; to measure the joint motions that actually occur during the examination; and to determine the biomechanical interactions of the ligaments as they function as stabilizers of the joint. Specimens Materials and Methods we measured the restraining action of the ligaments in sixteen knees (eight right and eight left) obtained from eleven cadavera, eighteen to fifty-five years old (mean age, 36.8 years). Two were female and nine, male. The causes of death included drug overdose, gunshot wound, acute myocardial infarct, stroke, automobile accident, and (in two cadavera that provided three knees) leukemia and septicemia. Only the medial restraints were determined in three knees and only the lateral restraints, in three. In the remaining ten knees, both medial and lateral restraints were measured. Prior to testing, all knees were placed in plastic bags and frozen at -30 degrees Celsius except for one which was tested in a fresh state. The night before testing, the specimens were placed in a refrigerator to thaw at 4 degrees Celsius. Final dissection of the specimens and their preparation before testing were carried out as previously described’.