Effect of Drop Jumping and Knee Valgus on Femoral Cartilage Thickness

Abstract

Background: The incidence of anterior cruciate ligament (ACL) ruptures is 30-78 per 100,000 people a year. While the main treatment for an ACL rupture is surgery, only 61- 89% of athletes return to sports after surgery. Females are at a 3-5X higher risk for ACL injuries than males. In a prospective study, knee abduction angle, also known as valgus angle, of women who later suffered an ACL injury was ~8° greater vs women who did not tear their ACLs. When landing with high knee valgus angles, it is theorized that the knee joint compresses the lateral femoral cartilage (FC) more vs. the medial FC. Due to this unequal distribution of compression across the knee joint, the lateral FC is hypothesized to be thinner compared to the medial FC after experiencing jumping and landing loads experienced in sports. Purpose: The purpose is to investigate the effect of frontal plane landing technique on FCT in healthy, recreationally active females performing drop jumping activities. Methods: After completing the informed consent process, all subjects had both knees imaged using ultrasound and then performed two series of 10 drop jumping activities from a 30-cm box. Ultrasound images were be taken before and after each drop jump series. Knee FCT were measured in Horos software. Based on recorded videos, subjects were placed into one of two groups based on whether they naturally landed in knee valgus vs those who did not. Results: All 11 subjects were considered to use a valgus landing technique due to the position of their knee to ankle at ground impact as defined by the landing error scoring system. There was no significant difference in any of the compartments throughout the jumps except for the left knee’s lateral femoral cartilage, which decreased by an estimated .104mm or 5.89% (p=0.032). The observed power for the left lateral FCT was 0.658. Significance: With appropriately powered future studies, should the results show that females landing with more knee valgus experience greater lateral FC changes in thickness after the drop jumping tasks, this would support the need for further research investigating 1) whether or not landing technique is indeed a risk factor for FC injury and 2) whether changing landing technique to reduce knee valgus would result in relatively more equal cartilage deformations comparing medial vs lateral FC. Because of the low observed power of the current study, results should be interpreted with caution.