GENDER DIFFERENCES IN ACTIVE KNEE ROTATIONAL STIFFNESS

Participants: H. J. Schock, L.J. Huston, E.M. Wojtys, J.A. Ashton-Miller

Key words: knee, muscle, gender

Introduction

One of the most common and problematic types of knee injuries suffered by physically active individuals is tearing of the anterior cruciate ligament (ACL). Injuries to the ACL are often a result of forceful oppositional rotation of the femur relative to the tibia sustained during physical activity. A disproportionately high incidence of non-contact ACL injuries occur in females. This study wished to examine possible gender differences in the ability to prevent rotation of the tibia relative to the femur, or active rotational stiffness.

Materials and Methods

Thirteen male and 13 female healthy, young athletes that competed in sports exhibiting high ACL injury rates (basketball, volleyball and soccer) were tested. Subjects competed at the NCAA Division I or comparable level of athletics. Male / female pairs of subjects were selected, matching body mass indices (BMI) and foot size as closely as possible. Subjects were screened and excluded if they had previous knee or ankle injuries.

Subjects were given a KT 2000 test to determine the anterior-posterior laxity of a subject’s knee joint. Maximum isokinetic strength of the quadriceps and hamstrings muscle groups were quantified using a biodex dynamometer. Subjects were then transported to the Biomechanics Research Laboratory where rotational laxity of the knee joint was quantified by measuring internal tibial rotation. The subjects were placed in a seated position with their right foot resting on a freely rotating platform and their knee at 30° of knee flexion. In the first trial set, subjects were directed to relax their lower extremity musculature while a 5-newton medially directed force on the 5^th metatarsal-phalangeal joint forced internal tibial rotation. In the second trial set, EMG biofeedback electrodes were placed on the subjects’ lateral quadriceps and lateral hamstrings. The subjects co-contracted their hamstrings and quadriceps for 3 seconds before the same 5-newton medially directed force was applied. In the 3^rd and 4^th trial sets, the protocol was repeated with the subjects in 60° of knee flexion. In all trials, a mirror was fastened to subject's tibial tuberosity. A laser beam was reflected from the mirror to the wall to allow digital videotaping of the rotation of the subject's tibia. This motion later will be quantified using the Adobe PhotoShop program and geometry. Finally, the subjects were asked to cross their arms in front of their body while attempting to rotate their foot externally against a fixed force plate to determine the magnitude of a voluntary external rotational force they could produce.

Body measurements were taken to determine if there is a correlation between specific anthropometric measurements and performance on the knee stiffness testing apparatus. Measurements taken included: height, weight, shoe size, internal rotation, external rotation, maximum foot length, distance from lateral head of fibula to 5^th metatarsal, maximum foot width, maximum calf circumference, femur length, thigh circumference (at the distal 2/3 point of the femur), and knee joint line to floor.

Progress

Data collection is complete and the results of the testing are still being analyzed. Initially, it appears that there is more passive rotation at 60° than at 30° in both male and females subjects. It also appears that co-contraction of hamstrings and quadriceps significantly increases knee stiffness. At the time of this writing we have not yet determined if a gender difference in active rotational stiffness has been demonstrated.