COPENHAGEN, Denmark—Anterior cruciate ligament (ACL) ruptures are 4- to 8-fold more likely in female athletes than in males. A new screening method developed by Danish researchers shows why. 

The neuromuscular screening method reported by Mette K. Zebis, PhD, and colleagues in the October American Journal of Sports Medicine¹ shows that ACL injury is most likely in female athletes who have:

• reduced activity in the semitendinosus (ST) prior to the common sidestep movement known as “side cutting,” along with
• increased activity in the vastus lateralis (VL).

The semitendinosus data are particularly worrisome, since grafts taken from this muscle have commonly been used in ACL reconstruction surgery. The researchers suggest that this method “should be reconsidered.” They also note that female athletes with this type of ACL reconstruction are less likely to return to their pre-injury activity level than those who had reconstruction with patellar tendon graft.

ACL injury linked to high rate of later OA

“An ACL injury for a female athlete doesn’t just affect them at the moment of injury; a high percentage of female athletes who suffer an ACL injury experience long-term consequences such as osteoarthritis and disability. This is unacceptable,” says lead author, Mette K. Zebis, PhD, at the Institute of Sports Medicine Copenhagen and the Danish National Research Centre for the Working Environment.

EMG monitoring of leg muscles during side-cutting movements. Surface electrode placement. BF=biceps femoris, ST=semitendinosus, VM = vastus medialis, VL=vastus lateralis, RF=rectus femoris. Source: Zebis MK, et al.1

“Our research aimed to evaluate the possible use of EMG recording as a tool for ACL injury risk screening. If we can identify those at risk for the injury, we can help prevent it.” Dr. Zebis said that ACL injury results in osteoarthritic changes in 50% to 90% of patients 7 to 20 years after injury, regardless of whether reconstruction surgery is done.

Most non-contact ACL injuries occur in activities like side cutting or deceleration, which “involve substantial eccentric muscle force of the knee extensors,” the authors write. The result is substantial anterior-directed shear of the tibia relative to the femur, and this shear can be counteracted either by the ACL or by coactivation of the knee flexors. The media knee flexors (semitendinosus and semimembranosus) play a major role in counterbalancing this shear force.

EMG identifies “high-risk” zone of leg muscle function

The researchers used EMG monitoring of activity in low knee flexor and high knee extensor muscles during a standardized to screen 55 non-injured female soccer or team handball athletes while they performed a standardized side-cutting maneuver. Such maneuvers are commonly used to “fake” the defensive player to one direction while the athlete moves in the opposite direction.

Five of the 55 athletes had a pattern of lower EMG signals in the medial hamstring muscle on the back of their thigh and higher activity in their quadriceps muscles. Those 5 athletes were the only ones who had ACL ruptures during the next 2 competitive seasons.

Analysis was conducted on all subjects' EMG signals, and a high-risk zone was defined. Ten individuals initially fell into the high-risk zone, including the 5 who had subsequent non-contact ACL ruptures.

Dr. Zebis characterized the high-risk zone as a “promising” tool that needs validation in larger studies and standardization before it can be used routinely. “Our study provides a foundation. Larger studies should be conducted to confirm our suspicions that this screening tool will be a huge asset in preventing future female athletic injuries,” she said.

“The present study is the first to provide a solid neuromuscular screening method and to document the mechanism of future injury by showing a specific muscle activation pattern predisposing for future ACL rupture,” Dr. Zebis said.

Translating research into practice: preventing ACL rupture in female athletes

If validated, this EMG screening method may help identify female athletes who are at high risk for non-contact ACL rupture. Dr. Zebis said that this “shows that preventive exercises should be focused on selective upregulation of the medial hamstring.” This can be done through targeted neuromuscular training.

“[U]pregulation of ST activity should be the essence of preventive neuromuscular training,” Dr. Zebis advised.

Reference

1. Zebis MK, Andersen LL, Bencke J, et al. Identification of athletes at future risk of anterior cruciate ligament ruptures by neuromuscular screening. Amer J Sports Med. 2009; 37:1967-1973.