Preventing Tibial Stress Fracture With Custom Shoe Orthoses

Abstract & Commentary

Synopsis: Custom biomechanical orthoses are beneficial in reducing the risk of stress fracture for walking, especially in army boots; however, these orthoses are not helpful in activities that involve running or when athletes are already wearing standard running shoes.

Source: Ekenman I, et al. The role of biomechanical shoe orthoses in tibial stress fracture prevention. Am J Sports Med. 2002;30(6):866-870.

The tibia is the most common location for stress fractures, thought to occur from repetitive loading of the bone with high strains or, especially, high-strain rates. If orthotics could reduce the rate of stress fractures without the need to alter any other training parameters, this would be a major advantage to athletes. Simple over-the-counter, soft, shock-absorbing inserts have been found not to affect the overall incidence of stress fractures. However, one study has shown clinically a 50% reduction in stress fractures when custom biomechanical shoe orthoses were worn in army boots for marching.1 The hypothesis of the present study was that these custom biomechanical shoe orthoses would reduce strain and strain rates when athletes wore them in either army boots or running shoes.

Nine athletically fit members of the special forces unit of the Swedish Police served as "volunteers." It is somewhat amazing what these subjects endured. They had an open surgical procedure on the morning of testing with just local anesthesia to insert a pair of 16-mm bone staples equipped with strain gauges into their tibias at 2 locations. The wounds were left open and just covered with gauze dressing as they then performed the study, having the staples removed at the conclusion of the day and the wounds closed with sutures.

Each of the subjects was custom fitted with biomechanical orthoses of 2 types. One was a semi-rigid, three-quarter length polypropylene orthosis with a thin fabric cover, and the other was a soft, full-length biomechanical orthosis, which was made of 3 different densities of polyurethane. Subjects were issued Nike Air Max running shoes as well as Israeli Army infantry boots 1 month ahead so that they could break in their shoes and orthoses. Measurements were then made during treadmill walking and during serial 2-km treadmill runs at 13 km/h with running shoes, with and without the orthoses, and during serial 1-km runs with army boots, with and without the orthoses. Measurements during walking after the runs were made to look at the possibility of fatigue-induced changes in strain rates.

Ekenman and colleagues found that the addition of both types of orthoses to army boots significantly lowered peak strains while walking, but only the soft orthoses lowered the strain rates with the boots. During running, however, the semi-rigid orthoses significantly increased the strain rates when worn with the boots. There was no advantage to the soft orthoses with the boots during running.

The peak strains were significantly lower when athletic shoes were worn compared to boots. The addition of the orthoses to the boots brought the strains to roughly equivalent levels with athletic shoes. The addition of the orthoses to the running shoes offered no benefit whatsoever during running activities. In fact, the semi-rigid orthoses caused a slight increase in strain and strain rates. They conclude that biomechanical orthoses, either soft or semi-rigid, offer no benefit to running shoes. They do recommend soft orthoses for activities that involve primarily walking in army boots.

Comment by David R. Diduch, MS, MD

Ekenman et al have shown with a very carefully designed study and noble volunteers that custom orthoses offer no benefit with either running shoes or military boots for activities that involve mainly running. Semi-rigid orthoses were actually found to increase strain rates when used together with military boots with running. They conclude that custom biomechanical shoe orthoses have no place in stress fracture prevention in sports in which running is a primary activity. Indeed, semi-rigid orthoses in runners may be even contra-indicated because of increased strain rates during running. They do, however, find benefit to custom orthoses for walking in military boots, just as other authors have demonstrated with a 50% reduction in stress fracture incidence.1

Differences in the biomechanics between walking and running, in particular involving hind foot mechanics and time of heel contact, likely account for the differences in Ekenman et al’s findings between running and walking activities. As such, there are very different recommendations based on the activity encountered. Military recruits in army boots who primarily perform marching activities can benefit from custom full-length, soft, biomechanical orthoses. Simi-rigid, three-quarter length orthoses should be avoided as they actually increase the risk of stress fracture with any running in army boots. Athletes wearing standard running shoes would have no benefit from custom orthoses for stress fracture prevention and may actually see a slight increase in strain rates with the semi-rigid orthoses. Given that other studies have shown no benefit for noncustom, over-the-counter orthoses used as shock absorbers, it is safe to recommend to our athletes that the simple choice of good shoes is sufficient.

Dr. Diduch is Associate Professor, Department of Orthopaedic Surgery, University of Virginia School of Medicine, Charlottesville, VA.

Reference

1. Finestone A, et al. Prevention of stress fractures using custom biomechanical shoe orthoses. Clin Orthop. 1999;360:182-190.