Unique Opportunity to Study Noncontact ACL InjuryResearchers are actively seeking information and knowledge that can reduce the number of anterior cruciate ligament (ACL) injuries in women. Several studies are ongoing collecting information about hip and knee function and strength in jumping athletes.
And it just so happened that one of those athletes (a basketball player) was in a study when she ruptured her ACL. Approximately 45 minutes after recreational basketball play started, she landed from a jump stop and injured her knee. Just hours before the game, she had been seen by a physical therapist.
The therapist was able to review the athlete's records from eight months before the ACL injury up to four hours before the injury. Measures available included quadriceps muscle strength and activation, kinetic data on movement, and reaction force generated by drop jump landings.
Quadriceps activation was measured using an electrical stimulus. The minimum amount of electrical impulse needed to cause a contraction of the muscle was recorded. Then the athlete maximally contracted the muscle and the researcher re-measured the force needed to complete the contraction. From these measurements, the researchers could calculate force production of the muscle.
The data showed that force production was decreased four hours before the injury compared with just one week prior to the injury. The same data was collected again shortly after the injury, before surgery, and after surgery. Unfortunately, because of the nature of the injury (ACL rupture), data on the kinetics during a drop jump landing could not be collected after the injury (before surgery).
Surgery was delayed by three months as the athlete completed a rehab program. The program included range-of-motion, pain relief, quadriceps strengthening, and exercises to improve neuromuscular control. Strength and force generated by the quadriceps muscle was improved as shown by measurements taken the day before surgery.
Five months after surgery, these same measurements were repeated. The maximum voluntary muscle contraction was better than before the injury but not quite as good as just before surgery.
Looking back over all the data collected, it appears that this athlete had some risk factors for ACL injury. Her knees were both in a position of valgus (knock-knee position) during her drop jump landings. The left foot (which she injured) was positioned slightly forward of the uninjured foot. And there was a reduced or incomplete activation of the quadriceps muscle.
The authors suspect that muscle fatigue from playing basketball was a significant factor in this injury. According to some studies, quadriceps force output is less after the muscle has been in use. There are fewer motor neurons to fire when contracting the muscle. Decreased muscle activation along with fatigue may be just the right combination of risk factors to result in an ACL injury.
Obviously, a large study of this type isn't possible. But future studies may be able to compare preseason data as a baseline with number of injuries that occur during season practices and play. A pattern or trend may be identified that could help prescreen athletes for injury risk and begin a prevention program.
Terry L. Grindstaff, DPT, ATC, SCS, CSCS, et al. Decreased Quadriceps Activation Measured Hours Prior to a Noncontact Anterior Cruciate Ligament Tear. In Journal of Orthopaedic & Sports Physical Therapy. August 2008. Vol. 38. No. 8. Pp. 502-507.
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