The Effect of Foot Structure and Range of Motion on Musculoskeletal Overuse Injuries
Abstract & commentary
Synopsis: The methods used in this study may be useful in identifying high-endurance athletes at risk for lower extremity overuse injury.
Source: Kaufman KR, et al. The effect of foot structure and range of motion on musculoskeletal overuse injuries. Am J Sports Med 1999;27:585-593.
Four hundred forty-nine volunteer trainees at the Naval Special Warfare Training Center, candidates for Navy SEAL training, were enrolled in this prospective study. The purpose of the study was to determine if there was an association between foot structure and musculoskeletal overuse injuries developing during the extremely intensive training program. The program is in three phases, lasting 25 weeks, probably the most rigorous physical training anyone can experience.
Before the training began, a variety of biomechanical characteristics of the subjects’ feet were defined. The arch characteristics of both feet were studied both statically and dynamically. The dynamic assessment was performed in a motion analysis laboratory, with the subjects walking both barefoot and wearing military footwear. A "dynamic arch index" was calculated to define the ratio of the area of contact to the midfoot to the total contact area of the foot to quantify the degree of cavus or planus. In addition, ankle range of motion was measured, both with the knee fully extended and flexed to 90°. The recruits then underwent training and all injuries were tracked prospectively. Particular overuse injuries that were identified were stress fractures, periostitis, iliotibial band syndrome, patellofemoral syndrome, and Achilles tendinitis. A high incidence of overuse injuries was found, with 149 of the 449 subjects (33.2%) sustaining 348 lower extremity overuse injuries during the training period. The most common problems encountered were stress fractures, iliotibial band syndrome, and patellofemoral syndrome. Less commonly, Achilles tendinitis and periostitis without stress fracture also occurred. The most common sites for stress fractures were the lower leg (49%), the foot (39%), and then the femur (12%).
A distinct relationship was found between foot structure and the development of a stress fracture, with an increased relative risk of developing a stress fracture occurring either with pes planus or pes cavus. Interestingly, the increased risk of injury with pes planus was only identified when the deformity was assessed dynamically. Restricted hindfoot inversion increased the risk of developing a femoral stress fracture, while increased hindfoot inversion led to more frequent tarsal and metatarsal stress fractures. Achilles tendinitis occurred more commonly in those individuals with a tight gastrocnemius or increased hindfoot inversion. Despite the fact that the recruits to the SEAL program are healthy, fit individuals who almost uniformly report to training in extremely good physical condition, one-third of these recruits developed significant overuse injuries. Kaufman and colleagues conclude that the methods they employed in this study can be used to identify those high-endurance athletes at risk for lower extremity overuse injury and recommend further research be done to develop specific footwear modifications to prevent these problems.
Comment by James D. Heckman, MD
This study was done in a thorough and thoughtful manner. Biomechanical data were collected prospectively and then the incidence of overuse conditions was measured precisely in this well-controlled population. This is a highly motivated group of individuals and they may have tended to ignore or under-report some injuries because of the fear of washing out of the program. Otherwise, it can be assumed that a complete registry of injuries has been recorded. Certainly the more serious injuries are documented in this study. While few athletes will ever be stressed to the level of Navy SEAL training, the study demonstrates the importance of foot structure in the development of lower extremity overuse injuries. Kaufman et al do not tell us if any of the participants wore orthotic devices in their shoes or had other shoewear modifications that might have affected the mechanics of running. It is assumed that all recruits wore standard issue military boots without specialized inserts.
Of particularly curious note is the fact that despite most subjects coming into the program quite fit and athletically active, one-third still developed overuse problems. Kaufman et al point out that this is an incidence that is not particularly different from the incidence of overuse problems in civilian runners which has been reported to range from 14% to 48% in various studies. This persistently high overuse injury problem may be attributable to foot shape rather than preconditioning, as the study showed that subjects with either pes planus or pes cavus had nearly twice the incidence of stress fractures compared to subjects with normal arch height.
One of the more interesting findings of the study is the high incidence of stress fractures in subjects with flatfoot because other studies of military recruits have shown a protective effect of low arches. Kaufman et al correctly conclude that the techniques used in this study may be useful in identifying at least high-endurance athletes who may be at risk for lower extremity overuse injuries, particularly stress fractures.
You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
- Award-winning Medical Content
- Latest Advances & Development in Medicine
- Unbiased Content