ACL injury risk greater on the other side

The risk of sustaining a contralateral anterior cruciate ligament (ACL) injury is greater than the risk of sustaining a first-time ACL injury, according to investigators in the department of orthopedics at Lund University and Lund University Hospital, Lund, Sweden. The most important risk factor for sustaining a contralateral ACL injury is return to a high activity level after a unilateral ACL injury.

Swrd and associates¹ conducted a Medline search to find and systematically review studies that investigated risk factors for a contralateral ACL injury and studies in which a contralateral ACL injury was the outcome. In 13 of 20 studies that described the risk of a contralateral ACL rupture or specific risk factors for a contralateral ACL injury, patients were monitored prospectively after a unilateral ACL injury.

Evidence of the relevance of female sex, family history of ACL injuries, and a narrow intercondylar notch as risk factors for a contralateral ACL injury was inconclusive. Risk factors acquired as a result of an ACL injury that affect both the injured and the contralateral leg, such as altered biomechanics and altered neuromuscular function, were thought to further increase the risk of a contralateral ACL injury.

The investigators noted that together with the risk of osteoarthritis of the knee and the risk of rerupture/graft failure, contralateral ACL injuries may be among the most important aspects to consider after an ACL injury. They suggested that clinicians contemplate the increased risk of a contralateral ACL injury when considering an injured patient’s return to a high level of activity after an ACL injury and that a better understanding of the risk factors will help in the management of patients with unilateral ACL injuries and in the development of interventions to prevent contralateral ACL injuries.

In another study, Kulas and colleagues² at East Carolina University in Greenville, North Carolina, noted that because ACL injuries may occur during deceleration maneuvers, biomechanics research has been focused on the lower extremity kinetic chain. Trunk mass and changes in trunk position affect lower extremity joint torques and work during gait and landing, but how the trunk affects knee joint and muscle forces is not well understood.

Therefore, they conducted a crossover study to evaluate the effects of added trunk load and adaptations to trunk position on knee anterior shear and knee muscle forces in landing. Ten men and 11 women performed 2 sets of 8 double-leg landings under 2 conditions: no load and trunk load; the participants were categorized into 1 of 2 groups on the basis of the kinematic trunk adaptation to the load: trunk flexor or trunk extensor. Peak and average knee anterior shear, quadriceps, hamstrings, and gastrocnemius forces were estimated with a biomechanical model.

Adding a trunk load increased peak and average knee anterior shear forces in the trunk-extensor group but did not increase them in the trunk-flexor group. When trunk load was added, peak and average quadriceps forces increased and average gastrocnemius forces increased, regardless of group. There was a condition-by-group interaction for peak and average hamstrings forces. When trunk load was added, average hamstrings forces decreased in the trunk-extensor group but increased in the trunk-flexor group.

The researchers concluded that added trunk loads increase knee anterior shear and knee muscle forces, depending on trunk adaptation strategy.

1. Swrd P, Kostogiannis I, Roos H. Risk factors for a contralateral anterior cruciate ligament injury. Knee Surg Sports Traumatol Arthrosc. 2010 Jan 9; [Epub ahead of print].
2. Kulas AS, Hortobgyi T, Devita P. The interaction of trunk-load and trunk-position adaptations on knee anterior shear and hamstrings muscle forces during landing. J Athl Train. 2010;45:5-15.

References:

1. Swärd P, Kostogiannis I, Roos H. Risk factors for a contralateral anterior cruciate ligament injury. Knee Surg Sports Traumatol Arthrosc. 2010 Jan 9; [Epub ahead of print].
2. Kulas AS, Hortobágyi T, Devita P. The interaction of trunk-load and trunk-position adaptations on knee anterior shear and hamstrings muscle forces during landing. J Athl Train. 2010;45:5-15.