Original article
Can custom-made biomechanic shoe orthoses prevent problems in the back and lower extremities? A randomized, controlled intervention trial of 146 military conscripts

https://doi.org/10.1067/mmt.2002.124419Get rights and content

Abstract

Background: Shock-absorbing and biomechanic shoe orthoses are frequently used in the prevention and treatment of back and lower extremity problems. One review concludes that the former is clinically effective in relation to prevention, whereas the latter has been tested in only 1 randomized clinical trial, concluding that stress fractures could be prevented. Objectives: To investigate if biomechanic shoe orthoses can prevent problems in the back and lower extremities and if reducing the number of days off-duty because of back or lower extremity problems is possible. Design: Prospective, randomized, controlled intervention trial. Study Subjects: One female and 145 male military conscripts (aged 18 to 24 years), representing 25% of all new conscripts in a Danish regiment. Method: Health data were collected by questionnaires at initiation of the study and 3 months later. Custom-made biomechanic shoe orthoses to be worn in military boots were provided to all in the study group during the 3-month intervention period. No intervention was provided for the control group. Differences between the 2 groups were tested with the chi-square test, and statistical significance was accepted at P < .05. Risk ratio (RR), risk difference (ARR), numbers needed to prevent (NNP), and cost per successfully prevented case were calculated. Outcome Variables: Outcome variables included self-reported back and/or lower extremity problems; specific problems in the back or knees or shin splints, Achilles tendonitis, sprained ankle, or other problems in the lower extremity; number of subjects with at least 1 day off-duty because of back or lower extremity problems and total number of days off-duty within the first 3 months of military service because of back or lower extremity problems. Results: Results were significantly better in an actual-use analysis in the intervention group for total number of subjects with back or lower extremity problems (RR 0.7, ARR 19%, NNP 5, cost US $98); number of subjects with shin splints (RR 0.2, ARR 19%, NNP 5, cost US $101); number of off-duty days because of back or lower extremity problems (RR 0.6, ARR < 1%, NNP 200, cost US $3750). In an intention-to-treat analysis, a significant difference was found for only number of subjects with shin splints (RR 0.3, ARR 18%, NNP 6 cost US $105), whereas a worst-case analysis revealed no significant differences between the study groups. Conclusions: This study shows that it may be possible to prevent certain musculoskeletal problems in the back or lower extremities among military conscripts by using custom-made biomechanic shoe orthoses. However, because care-seeking for lower extremity problems is rare, using this method ofprevention in military conscripts would be too costly. We also noted that the choice of statistical approach determined the outcome. (J Manipulative Physiol Ther 2002;25:326-31)

Introduction

The prevalence of back and lower extremity problems in general is high,1 particularly during the first 3 months of military service.2 The most common musculoskeletal problems in the Danish Army are back problems, knee problems, shin splints, Achilles tendonitis, and sprained ankles.2 Shock-absorbing and biomechanic shoe orthoses (BSO) are frequently used in the prevention and treatment of back and lower extremity problems. One review concludes that shock-absorbing insoles in footwear reduces the incidence of stress fractures in athletes and military personnel.3 In several randomized, controlled studies, researchers conclude that preventing overuse injuries in the back and lower extremities by use of shock absorbing insoles is possible.4, 5, 6, 7, 8 We succeeded in finding only 1 randomized clinical trial in which BSO were used for prevention of back and lower extremity problems.9 According to the results from this study, reducing the incidence of stress fractures with semi-rigid and in particular soft BSO is possible.

The theory behind the use of BSO is that control of the subtalar and midtarsal pronation has a positive effect on the closed kinetic, linked movements in the whole lower extremity and back during walking and running.10 Prevention of excessive subtalar and midtarsal joint pronation is thought to prevent excessive medial rotation of the tibia, femur, and pelvis, which in turn prevents further mechanical stress on the knee, hip, and back.10, 11, 12 A connection between subtalar and midtarsal joint problems and lower extremity and back problems has been described.13, 14, 15, 16, 17, 18

The purpose of this trial is to investigate if BSO can prevent problems in the back and lower extremities and if their use can reduce the number of days off-duty during the first 3 months of military service because of back or lower extremity problems.

Section snippets

Study subjects

The estimated sample size was calculated with MEDSTAT (Version 2.12) to 55 subjects per group, with alpha at 5%, beta at 10%, and least relevant difference at 20%. We expected that 10% of subjects would be unwilling to participate and that we would have a drop-out rate of 10%. Therefore, all 154 male and female conscripts (aged 18 to 24 years) from all over Denmark, who were drafted to start in August 1999 at the Jutland Dragoon Regiment, Holstebro, Denmark, were asked to consider joining the

Results

Of the 154 persons drafted, 1 female and 146 male conscripts were available and willing to participate in the trial. One person was excluded because of current use of BSO. After randomization, the two groups consisted of an intervention group of 77 subjects and a control group of 69 subjects (Fig 1). At baseline evaluation, the 3-month period prevalence rates were similar in both groups on all collected data.

At follow-up evaluation, data were collected from 67 (87%) conscripts in the

Discussion

This study clearly illustrates the different results in relation to the choice of analysis. When the actual use of BSO wastested, results were superior to when the actual intervention was tested (ie, intention-to-treat). All significant results were not present in the worst-case analysis.

In addition, estimates of the NNP put the results in perspective. These ranged from 5 in preventing any problems in the back and lower extremities to 200 in preventing off-duty days. However, when the costs of

Conclusion

Although BSO, in accordance with the study by Finestone et al,9 has a statistically significant preventive effect on certain musculoskeletal problems in those who actually use them, the fact that relatively few conscripts seek care for this type of injury prevention is not economically feasible.

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Submit reprint requests to: Kristian Larsen, PT, The Medical Research Unit in Ringkjøbing County, Amtsradhuset, Torvet 7, DK-6950 Ringkjøbing, Denmark (e-mail: [email protected]).

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