Shock absorbing insoles and lower limb injury

Abstract

Achilles, the mythical Greek warrior who fought in the Trojan Wars, was supposedly immortalized by his mother, Thetis, as she dipped him in the river Styx. However, his invincibility had a flaw—his mother failed to dip the heel she held into the sacred waters. Thus, the heel that was not immersed in the river was Achilles' eventual downfall. An arrow was shot into the heel and he ultimately succumbed to the wound. Like Achilles, foot orthoses and shoe insoles have experienced an invincible run in the sports and exercise arena. However, the Achilles heel of orthoses is that they lack rigorous evaluation of their effectiveness in preventing or treating injuries. The manufacture and supply of foot orthoses or insoles is a multi-million dollar industry. Prescriptions of these devices are made under the assumption that they realign the foot and leg or provide increased shock-absorption during activity. By doing so, it is believed that they reduce undesired stress or strain on bodily structures involved in standing and ambulation. The literature is abundant with poorly controlled studies and expert opinion on the benefits of orthoses.1 However, there is little in the way of good quality randomized trials evaluating the effectiveness of such devices. It is pleasing, therefore, to see the inclusion of a high quality trial evaluating shoe insoles in this issue of the journal [see Withnall et al., p. 32]. The randomized trial on page 32 by Withnall, Eastaugh and Freemantle evaluates the effectiveness of different types of shock absorbing insoles in reducing the rate of injuries in military recruits undergoing basic training. Trials such as this are important given that the burden of musculoskeletal disease has been known for some time, but is not well represented in national health priorities.2 Good quality randomized trials are paramount to advancing our understanding of prevention and treatment of musculoskeletal disorders. Without rigorous application of methodology and controls to clinical trials, we are, due to inherent bias, left uncertain of the validity of the results.3,4 Withnall et al. should be commended for undertaking their trial, which is one of the largest of its kind. They have answered a clinically worthwhile question that has the potential to be economically important as well. The findings of the study reveal that there are no differences between shock absorbing and non-shock absorbing insoles in reducing lower limb injuries during basic training for military recruits. Interestingly, a number of other randomized trials have investigated the effectiveness of foot orthoses in reducing injury in military populations. The results of those that have evaluated shock absorbing insoles are equivocal; some found no benefit, while others observed a reduction in stress fractures in particular.5-8 Generally, however, these studies were not as well designed and controlled as the trial by Withnall, Eastaugh and Freemantle which provides a far superior level of evidence; that shock absorbing insoles do not reduce the rate of injury in military recruits. Despite these findings, it remains to be seen whether different orthosis designs (e.g. more biomechanically-orientated devices) are more effective than simple shock absorbing insoles. Although generally of low quality, the randomized trials undertaken thus far9-11 suggest that biomechanically-orientated foot orthoses may reduce the incidence of injuries, specifically stress fractures and medial tibial stress syndrome (shin splints). However, further high quality randomized trials, such as the one published in this issue of the journal, are needed to confirm these findings. Only then will the Achilles heel of orthotic therapy be somewhat addressed.