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Poor Biomechanics May Lead To ACL Injuries

17 Mar 2015
Randall Cooper
Dynamic knee valgus, or inward turning of the knee, has been associated with Anterior Cruciate Ligament (ACL) injuries for the past 15 years or so, with the most recent research focusing on gender differences in cutting and landing biomechanics. The international sports medical community is targeting efforts to reduce ACL injuries, and a recent study may give us further insight into which sports people are vulnerable to these injuries.

Females have a much greater incidence of ACL injuries. A 2005 study by Hewett and colleagues showed that female athletes that go onto injure their ACL have 8° more knee abduction, 20% greater ground reaction force, and 2.5 x greater knee abduction moments during a drop jump task. Studies such as this one use computerised 3D motion analysis and force plates to gather data, something that lacks widespread clinical application.

Two-dimensional analysis of frontal plane motion has been suggested for the clinical setting using video and an estimation of joint angles and motion. The most well known and used of these 2D assessments is the Landing Error Scoring System (LESS), however no 2D test including the LESS has been shown to predict ACL injuries. Drop jump assessments involve subjects dropping off a box (usually 30cm), landing on two legs, and then immediately jumping in a vertical direction. This assessment is relevant for sports such as basketball and volleyball, however many ACL injuries occur during single leg landings in sports such as netball and Australian rules football, and cutting and pivoting in sports such as soccer and hockey. 

So for quite some time I have wondered about two things;

Firstly, would it be better if these drop jump assessments were performed as single leg assessments? And secondly, do poor mechanics (and dynamic valgus) during a single leg drop jump correlate with poor mechanics during cutting and pivoting tasks?

A recent study performed Jones and colleagues with results published in the American Journal of Sports Medicine last year has help shed some light on these questions. Researchers investigated 20 female soccer players looking for a biomechanical relationship between single leg landing (SLL), cutting (90° cuts), and pivoting (180° turns). In particular researchers were looking for patterns in dynamic valgus between the tasks, and kinetics and kinematics were calculated using 3D motion analysis in a lab setting.

The results indicated significantly moderate to strong biomechanical relationships in frontal plane knee motion and moments between single leg landing, cutting, and pivoting. So in summary, if an athlete lands a single leg drop poorly they are likely to exhibit the same poor biomechanics with cutting and pivoting too. This is clinically useful research as using single leg landing as a screening test may/should help identify at risk athletes, but again, this study needs to be done as a 2D study out of the lab. 



  1. Boden BP, Dean GS, Feagin JA, Garrett WE. Mechanisms of anterior cruciate ligament injury. Orthopedics. 2000;23:573-578.
  2. Salci Y, Kentel BB, Heycan C, Akin S, Korkusuz F. Comparison of landing maneuvers between male and female college volleyball players. Clin Biomech. 2004;19:622-628.
  3. Hewett TE, Myer GD, Ford KR, et al. Biomechanical measures of neuromuscular control and valgus loading of the knee predict anterior cruciate ligament injury risk in female athletes. Am J Sports Med. 2005;33:492-501.
  4. Padua DA, Marshall SW, Boling MC, Thigpen CA, Garrett WE, Beutler AI. The landing error scoring system (LESS) is a valid and reliable clinical assessment tool of jump-landing biomechanics. Am J Sports Med. 2009;37:1996-2002.
  5. Jones PA, Herrington LC, Munro AG, Graham-Smith P. Is there a relationship between landing, cutting, and pivoting tasks in terms of the characteristics of dynamic valgus? Am J Sports Med. 2014;42:2095-2102.

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