GENDER DIFFERENCES IN KNEE ANGLE WHEN LANDING FROM A JUMP

Participants: B. Vibert, L. J. Huston, J. A. Ashton-Miller, E. M. Wojtys

Keywords: knee, jumping, female

Introduction

Jumping and landing movements are integral features of many sporting activities. Unfortunately, one of the most frequent mechanism of ACL injury in women is landing from a jump in a noncontact setting (Ferretti, 1992). The purpose of this study was to compare knee flexion angles in men and women during and after the impact associated with landing from a drop jump. The null hypothesis was that no significant gender differences would exist in the knee flexion angle upon landing from a drop jump.

Materials and Methods

Twenty subjects (10 males, 10 females, mean (SD) age =28(5) years) agreed to participate in the study. As part of the inclusion criteria, all participants were required to have no previous or current problems in their backs, hips, knees, or ankles. The activity levels ranged from recreational sports to competitive team sports. Subjects were instructed to perform three unconstrained jumps from three different vertical heights (20, 40, 60 cm) onto a concrete floor. In order to reduce variability, these three vertical height distances were normalized according to the subject’s height. Reflective markers were placed on the right side of the body at six sites: the head of the 5th metatarsal, the lateral malleolus, the lateral femoral condyle, the greater trochanter, the posterior superior iliac spine, and the anterior superior iliac spine. Marker trajectories were measured using a laterally placed 2-D motion analysis system (MacReflex; Qualisys, Glastonbury, CT). The vertical distance from the floor to each of these marker sites were also recorded.

Results

There were significant gender differences in knee flexion angles at ground impact when landing from a jump (p<0.05). The largest gender difference in knee angles occurred at the lowest jump height of 20 cm. At this height, men initially landed with 16° of knee flexion, while the women landed with a significantly straighter knee angle (7°, p<0.05). Similarly, a gender difference was seen at the medium jump height (40 cm), where the initial knee flexion angles at impact were nearly twice as large for men as for women (10° vs. 5.4°, p<0.05).

There were no significant gender differences in maximum knee flexion angles or change in knee flexion angle (‘absorption’). At the low jump height, men flexed their knee an average of 58° in order to adequately absorb the impact, while women flexed their knee an average of 54°. At the highest jump height (60 cm), men flexed their knee an average of 75°, while women flexed an average of 77°.

Conclusions

There are currently some provocative gender differences in patterns of knee injuries, particularly involving the ACL. The present data suggests that women may expose their knee joint to higher forces per unit bodyweight when landing from a jump than men do. The significantly smaller knee flexion angles employed by women during the impact phase of landing will systematically tend to increase their vertical ground reaction forces and knee joint loads (Nigg, 1986). These results should be considered in the pathomechanics of the higher rates of knee injuries seen in women.