Friday, November 21, 2008

Cutting-Edge Research: Can Shoe Orthotics Reduce ACL Injury Risk?

ACL injuries in female athletes remain a growing problem. In the post below as well as in others, the role of knee valgus in raisingthe risk of ACL injury has been discussed. Earlier posts also emphasize the importance of neuromuscular training to reduce the risk of ACL injury. In a new study, researchers at the University of Connecticut raise the possibility that the use of orthotic insoles may provide an immediate protection against injury. Using a medial “wedge” placed inside the shoe, knee valgus (a knock-kneed postion) during a drop jump was reduced. Since excessive knee valgus places the ACL under stress, this finding suggests that orthotics may help reduce the risk of ACL injuries. Despite these promising results, there are a few words of caution.

This photo, adapted from Donald Neumann’s textbook, Kinesiology of the Musculoskeletal System, shows that rearfoot eversion / eversion (standing on the medial side of the foot, can induce both valgus stress and internal knee rotation. This position places the ACL in a position of stress (see figure). Stopping, lading or cutting with the knee in this position can greatly increase the risk of injury. Earlier research studies have shown that women who have excessive rearfoot pronation / eversion are at greater risk of injury.

Adding a medial “post” or “wedge” to the insole of shoe can correct rearfoot pronation / eversion and reduce valgus stress (see figure inset). These types of orthotics are very popular with runners who “over-pronate”. They are often used to avoid overuse injuries to the knee. The authors of the study wanted to see if such a wedge would also alter the biomechanics of landing resulting in decreased knee valgus and reduced injury risk.

Ten college aged female athletes performed a series of drop jumps using their regular training shoes. For the drop jump, athletes jumped off of a 12 inch box, landed with two feet onto two force platforms, then performed a maximal vertical jump. Jumps were performed with and without the orthotic posts in their shoes. The orthotic post included a 5 degree medial wedge that ran the entire length of the foot (AliMed, Inc).

When performing the drop jumps with orthotics, the extent of knee valgus was reduced. This was the case for both the initial contact upon landing and maximal valgus during push-off. Knee valgus and inward rotation during landing, stopping and cutting greatly increase the risk of ACL injury. The finding that the orthotics reduced valgus suggests that they may be effective in lowering the risk and incidence of ACL injuries.

There are a few issues that need to be pointed out before rushing out for a new pair of orthodics. First, the study examined knee valgus during drop jumps only. This is a very controlled activity that doe not involve any lateral movement. The researchers did not look at other activities such as cutting and stopping maneuvers, activities that simulate movements on the field. Second, the measurements were limited to knee valgus and ankle eversion only. No other measures of the hip and knee biomechanics were made (such as internal hip and knee rotation). So, it is somewhat difficult to draw a firm conclusion about the orthotic’s ability to reduce ACL injury risk.

What is study does offer is a bit of hope pertaining to other interventions that will reduce ACL injury risk. While orthotics may provide some risk reduction, it is still important to engage in a neuromuscular training program such as those described in earlier posts (click here).

Reference:

Joseph M, Tiberio D, Baird J, Trojian TH, Anderson JM, Kraemer WJ, Maresh CM (2008) Knee valgus during drop jumps in National Collegiate Athletic Association division I female athletes. The effect of a medial post. American Journal of Sports Medicine, 36:285-289.