Comparison of Drop Jumps and Sport-Specific Sidestep Cutting Implications for Anterior Cruciate Ligament Injury Risk Screening
Kristianslund E and Krosshaug T, Am J Sorts Med. 2013 January; [Epub Ahead of Print].
Non-contact anterior cruciate ligament (ACL) injuries occur across many different sports and have been shown to be linked to long-term degenerative joint changes. If we had a gold standard for clinically screening ACL injury risk then we could identify patients at high risk for an ACL injury and determine if prevention programs are having a desired effect on their biomechanics. Screening tests however focus on 2-legged and controlled jumps rather than sidestep cutting and single-legged landing which many ACL injuries occur during. Therefore, Kristianslund and Krosshaug performed a study to describe knee biomechanics in drop jumps and sidestep-faking maneuvers among elite female handball players. A total of 120 players (mean age of 22.4 years) performed sidestep cutting and drop jumps. When players performed the sidestep cutting task they ran down a 5 meter approach and then were told to perform their regular sidestep cut, trying to fake a static defender into going one way while cutting the other. A total of 3 cuts were analyzed. Drop jumps were performed using a 30 cm high box. Players dropped off the box and immediately performed a maximal jump. Both sidestep cutting and drop jumps were analyzed with 2 force plates and 8 infrared cameras. The authors calculated maximum knee abduction and knee internal rotation moments in the first 100 milliseconds after initial contact; maximum knee flexion moments during contact with the force plate; knee flexion, knee abduction, and knee internal rotation at initial contact; as well as maximum knee flexion, knee abduction, and knee internal rotation. Overall, knee biomechanics were different between drop jumps and sidestep cutting. Sidestep cutting exhibited greater valgus and internal rotational angles. Further, knee joint moments (loading) were higher in all 3 planes of motion, with knee abduction moments 6 times higher, in sidestep cutting than drop jumps.
The data presented in this study clearly demonstrates that 2 legged controlled drop jumps, which are typically used for ACL injury screening, are not consistent with the stresses placed on the knee joint during actual competition. This implies that sport-specific tasks, like sidestep-cutting tasks, may be more effective in identifying patients at risk for ACL injury. However, one should be wary that the study was performed in a laboratory setting against a static defender and did not assess whether the new task is actually more predictive of ACL injuries than drop jumps. Another point of concern is the standardization of a sidecutting protocol. All athletes have preferred techniques of sidecutting, which may further affect the forces placed on the knee. This could be advantageous for identifying patients with high-risk techniques but could also make it more challenging for clinicians to implement as a screening test. Overall, this study provides clinicians with another step towards a gold-standard method of ACL injury screening which will inevitably require a task which mimics real-time competition situations for a specific sport. In the meantime, this study questions whether drop jumps, which are biomechanically distinct from cutting tasks, are an ideal method to screen patients for risk of ACL injury. Tell us what you think after seeing these results. Do you think sport-specific tasks (e.g., cutting tasks) will be better at predicting who is at risk for an ACL injury than drop jumps? Do you think new ACL injury screening tests should be sport-specific (i.e. basketball, baseball, football, etc.)?
Written by: Kyle Harris
Reviewed by: Jeffrey Driban