FOOT & ANKLE INTERNATIONAL Copyright 2004 by the American Orthopaedic Foot & Ankle Society, Inc.
A Prospective Study of the Effect of Foot Orthoses Composition and Fabrication on Comfort and the Incidence of Overuse Injuries Aharon Finestone, M.D.∗ ; Victor Novack, M.D.∗ ; Alon Farfel, M.D.∗ ; Alon Berg, M.D.∗ ; Hagi Amir, M.D.∗ ; Charles Milgrom, M.D.† Jerusalem, Israel
ABSTRACT
Key Words: Comfort; Foot Orthoses; Overuse Injuries
Background: Foot orthoses are widely prescribed both to treat existing pathological conditions and to prevent overuse injuries, but little is known about the effect of their material composition and fabrication technique on patient comfort and the incidence of overuse injuries. Materials and Methods: The acceptance rates and comfort scores of soft custom, soft prefabricated, semirigid biomechanical, and semirigid prefabricated orthoses and their effect on the incidence of stress fractures, ankle sprains, and foot problems were studied in a prospective, randomized, single-blinded clinical trial among 874 infantry recruits during basic training. Results: A statistically significantly lower number of recruits given soft prefabricated orthoses (53%) finished basic training in their assigned devices than in the soft custom group (72%), in the semirigid biomechanical group (75%), and in the semirigid prefabricated group (82%) (p = .003). For recruits who finished training in their assigned orthoses, the soft custom (3.54) and soft prefabricated (3.43) orthoses had significantly higher comfort scores than the semirigid biomechanical (3.23) and prefabricated (3.17) orthoses, (p = .0001). There was no statistically significant difference in the incidence of stress fractures, ankle sprains, or foot problems between recruits using the different types of orthoses. Conclusions: These findings suggest that if a foot orthosis is being dispensed as prophylaxis for overuse injuries in an active, healthy population, there is little justification for prescribing semirigid biomechanical orthoses. Their cost is high compared to other types of orthoses, without an advantage in comfort or a reduction in stress fractures, ankle sprains, and foot problems.
INTRODUCTION
Foot orthoses are defined as devices worn within shoes that are designed to allow the foot to function better.4 They are usually prescribed to treat specific existing pathological conditions5,6 or are used prophylactically in an attempt to prevent the development of a musculoskeletal problem. They may be custom fabricated for the individual or prefabricated for the average patient or for a specific population. Foot orthoses were divided by Bordelon into three general types1 : Devices designed to reduce impact, cushion the foot, and reduce shear within the shoe; those used to relieve areas of pressure; and biomechanical orthoses. The biomechanical type is custom fabricated from neutral subtalar position casts or impressions and designed with the notion that it brings the foot into proper alignment as it strikes the ground and thereby improves function.8,13 Changes, however, in skeletal movements due to foot orthoses seem to be small and not consistent.11 Foot orthoses may be fabricated from soft or semirigid materials, or a combination of both. The type and material composition of the orthoses prescribed is often based on the user’s activity or specific problem, but tradition and personal experience also play a role. Bordelon states that, as a general rule, soft orthoses are more appropriate for the more rigid foot and semirigid orthoses for the flexible foot which needs stabilization in the push-off phase.1 The comfort of foot orthoses is of primary importance to the user. There is evidence to support the hypothesis that shoe inserts that improve footwear comfort decrease injury frequency, but the issue is not well studied in controlled trials.10 In one of the few prospective, randomized studies published comparing orthosis comfort with injury frequency, infantry recruits who trained in soft biomechanical orthoses were found to be more comfortable
∗ Israeli Defense Forces Medical Corps, Military P.O. Box 02149, Israel †Department of Orthopaedics, Hadassah University Hospital, Jerusalem, Israel
Corresponding Author: Charles Milgrom, M.D. Hadassah University Hospital Department of Orthopaedics Ein Kerem Jerusalem, il-91120 Israel milgrom@md2.huji.ac.il For information on prices and availability of reprints call 410-494-4994 X226.
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and to have a lower incidence of stress fractures than those who trained in senirigid biomechanical orthoses or simple shoe inserts.11 There are no published reports of studies in which the subjects were blinded to the type of orthoses they used. The purpose of this study was to determine how shoe orthoses fabrication affects user comfort and the incidence of overuse injuries in a normal physically active healthy young male population, using the well established model of the Israeli infantry recruit.9 Recruits were blinded in this study to as to whether they trained in custom orthoses or prefabricated orthoses since both were made of identical materials. MATERIALS AND METHODS
In the first part of the study, 451 male infantry recruits (mean age 18.74 ± 0.72), training on the same base at the same time, were recruited into the study to assess the comfort of soft custom and soft prefabricated orthoses. All recruits were informed of the goals and methods of the study and were required to sign informed consent according to the Institutional Review Board (IRB) approved protocol. Recruits who already had their own personal orthoses were instructed not to use them at any time without permission of the medical team supervising the study. Prior to beginning basic training, the recruits underwent an assessment by two orthopaedic surgeons, including measurement of height, weight, and arch height. A survey of preinduction participation in sports activity was taken. Before beginning basic training, recruits were assigned to one of two groups according to a randomization program written on Excel. Group 1 consisted of 227 recruits given soft custom orthoses (Tafnit Orthopaedics, Reshon Le Zion, Israel). Impressions of each foot were made with the recruit sitting and an orthotist pressing each foot into a box containing foam, while holding the feet in an approximate neutral subtalar position. Casts were made from the impressions and full-length orthoses with neutral hindfoot posts were molded on them from three layers of material. The outer and inner layers were made from Orthoflex (closed cell cross-linked polyethylene, density = 1.3 g/cm3 ) and the middle layer Plastizote (closed cell cross-linked polyethylene, Zotefoams, Croydon, England, density = 1.125 g/cm3 ). Group 2 consisted of 224 recruits. Impressions were made of their feet using the same technique as for group 1, but were not used in fabricating the orthoses. Soft prefabricated orthoses of the same material composition and general shape as the soft custom orthoses were dispensed according to shoe size. These were manufactured by the same company as group 1. All orthoses were commercially purchased
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to avoid conflict of interest. All recruits wore standard army infantry boots (1450 g for shoe size 45). The inner layer of the sole is composed of 45 durometer polyurethane and the outer, 90 durometer polyurethane. The inner last of the shoe is flat. During 14 weeks of basic training, the recruits were reviewed every 3 weeks in the field by two orthopaedists. All recruits removed their shoes at each review to monitor compliance with orthoses usage. If recruits discontinued use of their orthoses, the reason was recorded. Recruits were monitored for symptoms related to their feet, stress fracture, and ankle sprains. Recruits who were not available for review on two consecutive visits were considered to be dropouts from the study. Data were recorded directly on a notebook computer. At the end of basic training, recruits were asked to evaluate, on a scale of 1 –4, the comfort of their orthoses (1 = not satisfactory, 2 = satisfactory, 3 = good, 4 = excellent). Recruits who stopped using their orthoses because of an inherent problem or dissatisfaction with the orthoses were automatically given a score of 1. In the second part of the study, 423 infantry recruits (mean age 18.91 ± 1.1), training on a different base, were recruited to assess the comfort of semirigid biomechanical orthoses and semirigid prefabricated orthoses. The protocol of the second part of the study was the same as for the first, except for the type of orthoses issued to the recruits. Group 3 consisted of 215 recruits given semirigid biomechanical orthoses (ComfortFit, Roselle, NJ). Feet were casted in the neutral subtalar position by a trained orthotist.13 The casts were read by a scanner and three-fourths length ortholene modules with acrylic neutral rearfoot posts were fabricated by a cad cam milling machine. The thickness of the module was determined by the recruit’s weight. The module had a full-length cover of ethylene vinyl acetate (EVA) topped by vinyl. Group 4 consisted of 208 recruits given prefabricated semirigid orthoses. Their feet were casted in the neutral subtalar position by the same orthotist as in group 3, but were not used in fabricating the orthoses. The prefabricated orthoses were composed of the same materials as group 3, manufactured by the same company, and dispensed according to shoe size. Data were analyzed with the Statistical Analysis System (SAS, Cary, NC). The differences between the percentage of recruits who completed basic training in their assigned orthoses were analyzed by chi-square. Orthoses ratings were analyzed using the GENMOD procedure using a cumulative logit multinomial mode, for each of the four orthoses groups according to recruits who finished the study training in their assigned orthoses. The analysis was repeated for both recruits who finished the study training in their assigned
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Table 1: The incidence of overuse injuries according to type of orthosis used Type of Foot Orthotic Used Overuse Injury
Custom Soft
Soft Prefabricated
Stress fracture Ankle sprain Foot problems
9.1% 9.9% 17.4%
8.9% 10.7% 19.6%
orthoses as well as recruits who discontinued using their orthoses because of dissatisfaction. This latter group was automatically given an orthoses comfort score of 1. The four treatment groups were arranged according to their means, and consecutive groups were compared for statistical significance. The differences between the percentage of recruits who developed stress fracture, ankle sprains, and foot problems according to orthosis use was assessed by chi-square. RESULTS
Full clinical follow-up was available for 204 out of 227 (89.9%) recruits who trained in soft custom orthoses, for 213 out of 224 (95%) recruits who trained in soft prefabricated orthoses, for 180 out of 215 (83.7%) recruits who trained in semirigid biomechanical orthoses, and for 172 out of 208 (82.7%) recruits who trained in semirigid prefabricated orthoses. There was no statistically significant difference between the incidence of stress fractures, ankle sprains, or foot problems according to the type of orthoses that recruits used (Table 1). Figure 1 shows that the percentage of recruits who completed basic training in their assigned orthoses was statistically lower for the soft prefabricated orthoses group (57%) than for the other three orthoses groups
ORTHOSES Fig. 1: Percentage of recruits who finished basic training in their assigned orthoses. The asterisk indicates a statistically significant value.
Semirigid Biomechanical
Semirigid Prefabricated
9.7% 9.3% 14%
9.1% 8.0% 20.1%
(p = .003). The principal reasons for recruits discontinuing use of the soft prefabricated orthoses were pain in the metatarsal region and arch pain. Figure 2 shows that the orthoses comfort scores for recruits who finished basic training in their assigned orthoses were statistically lower for the semirigid biomechanical and semirigid prefabricated orthoses than for the custom soft and soft prefabricated orthoses (p = .0001). Figure 3 shows that the orthoses comfort scores for both recruits who finished the study training in their assigned orthoses as well as recruits who
ORTHOSES
Fig. 2: Orthoses comfort scores for recruits, which were statistically lower for the semirigid biomechanical and semirigid prefabricated orthoses than for the custom soft and soft prefabricated orthoses. Asterisks indicate statistically significant values.
ORTHOSES Fig. 3: Comfort scores for recruits who finish basic training with their assigned orthoses and recruits who discontinued their use because of dissatisfaction. The asterisk indicates a statistically significant value.
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discontinued using their orthoses because of dissatisfaction were the lowest for the soft prefabricated orthoses (p = .002). Subject height and weight were not found to have a statistically significant relationship with orthoses comfort scores. Recruits with high arch feet were more likely to discontinue use of soft prefabricated orthoses than those with average or low arches (p = .001). This relationship was not found for the other orthoses types used in the study. DISCUSSION
In this study, subjects were blinded as to whether they received custom or prefabricated orthoses. All subjects were young healthy males doing infantry training. This population was chosen rather than sportsmen because infantry recruits have a uniform, controlled training environment and use standard shoes. The orthoses used in the study encompass the major types prescribed by orthopaedists and podiatrists7 : semirigid biomechanical orthoses, fabricated from neutral position casts; custom soft orthoses, fabricated from impressions of the feet made while partial weightbearing; and soft and semirigid prefabricated orthoses (Fig. 4). The orthoses were worn within high-top leather army shoes with a flat inner last and were given universally to the population, without regard to the presence or absence of foot pathology. The comfort of the orthoses and the incidence of stress fracture, ankle sprains, and foot problems as a function of the orthoses used were the outcomes studied. The cost of the orthoses used in this study varied. The semirigid biomechanical orthoses were the most A
B
Fig. 4: Semirigid (A) and soft (B) orthoses used in the study.
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expensive, costing four times that of the soft prefabricated orthoses, almost three times that of soft custom orthoses, and twice that of the semirigid prefabricated orthoses. In spite of this price deferential, there was no statistical difference in the incidence of stress fractures, ankle sprains, and foot problems among recruits training in the different orthoses. Finestone et al.3 found that infantry recruits training in either semirigid or soft biomechanical orthoses had a lower incidence of stress fractures than a control group training with simple 3mm-thick polyolefin, cambrel-covered shoe insoles. The soft biomechanical orthoses were found to be more effective than the semirigid orthoses. The prefabricated semirigid and soft orthoses used in the current study were more elaborately constructed than the simple insoles used in the Finestone et al.3 study. Both the current study and that of Finestone et al.3 are in agreement that semirigid biomechanical orthoses have no cost benefit over soft custom orthoses in preventing overuse injuries. Ekenman et al., in a study measuring the effect of orthoses use on in vivo tibial strains, found that semirigid biomechanical orthoses actually increased tibial strain rates during running.2 Since high bone strains and strain rates can increase the risk for stress fracture, they concluded that there is little rationale to prescribe such orthoses for sportspeople whose primary activity involves running. Depending on orthosis type used, between 18% and 43% of the recruits in this study discontinued the use of their orthoses because of dissatisfaction. The major reason was discomfort. This was in spite of the fact that two out of four of the orthosis types used in this study were fabricated from impressions of the user’s feet based on the neutral subtlar postion. Pierrynowski and Smith questioned whether routine neutral position casting as advocated by Root at al.13 in fabricating orthoses is justified since they found that for most patients the rearfoot is always everted in stance.12 Recruits who received soft prefabricated orthoses had the highest discontinuation rate, but there was no statistical difference in the discontinuation rate among semirigid prefabricated orthoses, semirigid biomechanical orthoses, and custom soft orthoses. Evaluating orthosis comfort is complicated by how one statistically treats the population who discontinued the use of their assigned orthoses. When only recruits who finished their training in their assigned orthoses were considered, than soft orthoses, whether custom or prefabricated, were more comfortable than semirigid orthoses. This finding is similar to that of Mundermann et al.,10 who found that hard shoe inserts had lower comfort ratings than soft inserts. In the current study, when both recruits who finished training in their assigned orthoses as well as those who discontinued
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them because of dissatisfaction are considered, then the soft prefabricated orthoses has the lowest comfort. This study has several limitations. First, the orthoses were tested only in army boots. The orthoses interaction with other types of shoes may be different. Second, recruits in this study did intense training. Subjects who do less vigorous activities may tolerate these orthoses differently. Third, the subjects in the study were all young. The interaction of these orthoses with feet which have age-related changes may be different. Balancing these limitations is the fact that this study, unlike many clinical articles in the orthosis literature, is a randomized, single-blinded, clinical trial with a large number of subjects. The findings of this study suggest that if an orthosis is being dispensed as prophylaxis in a physically active population, and not designed to treat a specific biomechanical abnormality, then there is little economic justification for prescribing semirigid biomechanical orthoses. Their cost is high without advantages in comfort, patient acceptance, and reduction in the incidence of stress fractures, ankle sprains, and foot problems. ACKNOWLEDGMENTS
Financial support was received as a grant from the Israeli Defense Forces. REFERENCES 1. Bordelon, RL: Orthotics, shoes, and braces. Orthop. Clin. North Am. 20:751 – 757, 1989.
Foot & Ankle International/Vol. 25, No. 7/July 2004 2. Ekenman, I; Milgrom, C; Finestone, A; Begin, M; Arndt, A: The role of biomechanical shoe orthotics in stress fracture prevention. Am. J. Sports Med. 30:866 – 870, 2002. 3. Finestone, A; Giladi, M; Elad, A; Salmon, A; Mendel, D; Milgrom, C: A randomized clinical trial of the effect of custom biomechanical shoe orthotics on the incidence of stress fractures. Clin. Orthop. 360:182 – 190, 1999. 4. Jahss, MH: Arch supports and miscellaneous devices. In: Jahss, MH, ed., Disorders of the Foot, Philadelphia, WB Saunders, 1982. 5. Kannus, VPA: Evaluation of abnormal biomechanics of the foot and ankle in athletes. Br. J. Sports Med. 26:83 – 89, 1992. 6. Kilmartin, TE; Wallac, WA: The scientific basis for the use of biomechanical foot orthoses in the treatment of lower limb sports injuries — a review of the literature. Br. J. Sports Med. 28:180 – 184, 1994. 7. Landorf, K; Keenan, AM; Rushworth, RL: Foot orthosis prescription habits of Australian and New Zealand podiatric physicians. J. Am. Podiatr. Med. Assoc. 207:174 – 183, 1998. 8. Langer, S; Wernick, J: A Practical Manual for a Basic Approach to Foot Biomechanics, New York, The Langer Foundation for Biomechanics and Sports Research, 1990. 9. Milgrom, C: The Israeli elite infantry recruit: a model for understanding the biomechanics of stress fractures. J. R. Coll. Surg. Edinb. 34:18 – 22, 1989. 10. Mundermann, A; Stefanyshyn, DJ; Nigg, BM: Relationship between footwear comfort of shoe inserts and anthropometic and sensory factors. Med. Sci. Sports Exerc. 33:1939 – 1945, 2001. 11. Nigg, BM; Nurse, MA; Stefanyshyn, DJ: Shoe inserts and orthotics for sport and physical activities. Med. Sci. Sports Exerc. 31S:421 – 428, 1999. 12. Pierrynowski, MR; Smith, SB: Rearfoot inversion/eversion during gait relative to the subtalar joint neutral postion. Foot Ankle Int. 17:406 – 412, 1996. 13. Root, M; Orien, W; Weed, J: Biomechanical Examination of the Foot, vol I, Los Angeles, Clinical Biomechanics Corporation, 1971.