Obesity has been associated with the incidence of orthopedic disorders such as pes planus, knee malalignment, and osteoarthritis.1–3 Compared with healthy-weight individuals, people with obesity were twice as likely to have chronic pain and severely obese people were four times as likely to have chronic pain.4 Lower-quarter pain may be linked through the interrelated joint alignments of the foot, knee, and lower kinetic chain.5 For instance, pes planus has occurred with lower-limb dysfunction and was correlated with osteoarthritis-related knee pain in people with obesity.6 Obese individuals were 2.7 times more likely to have pes planus and 3.2 times more likely to have knee osteoarthritis than nonobese people.7,8 Once knee malalignment has developed, the progression increased with each 2-unit body mass index (BMI) increase.9
Foot orthoses have altered the alignment and biomechanics of the foot and the ankle,10 the lower leg,5 the knee,11 the hip, and the pelvis.12 Such biomechanical changes may explain observed reductions in back,13 knee arthritis,14 and foot pain15 in nonobese individuals. Because reduced physical activity and functional levels associated with obesity may be associated with orthopedic conditions,16 foot orthoses have been recommended within the conservative care for people with obesity.17 However, limited evidence supports using foot orthoses to increase physical activity level in people with obesity or to reduce orthopedic pain, and no standard methodology exists for foot orthoses prescription in cases of obesity.
The purpose of a pilot study is to provide insights into the feasibility of a larger-scale study by evaluating the subject completion rate for the tested protocol and the potential for adverse events. Outcomes are secondary and used to determine effect sizes for future sample size calculations and to develop theory.18 The specific aims of this pilot study were to assess the completion rate for people with obesity prescribed with foot orthoses for yearlong use; calculate effect sizes for future sample size calculations; and explore associations among foot orthoses use, physical activity, and functional level.
This study was conducted according to the protocols approved by the participating university medical center institutional review boards. All subjects provided informed consent before participating in this research.
This repeated-measures study spanned 12 months. Community-dwelling adult volunteers of any sex and cultural background who were obese, as defined by BMI of 30 kg/m2 or greater, were recruited by announcements to obesity support groups and weight loss programs. Subjects were excluded if they were younger than 18 years, not obese (BMI < 30 kg/m2), or not independently ambulatory. Also excluded were pregnant women; people with leg amputation; and people who could not comprehend the instructions, had impaired sensation, or were medically unstable.
Demographic information included age, sex, culture, and foot orthoses use. Anthropometric information included height, weight, and shoe size. Subjects also reported orthopedic conditions such as arthritis as well as back, pelvis/hip, knee, and foot pain. Subjects self-reported pain with walking using a numeric pain rating scale (NPRS), physical activity using the Physical Activity Level (PAL) scale, and functional ability in 20 daily tasks using the Lower Extremity Functional Scale (LEFS). The NPRS was used to measure the subjects’ overall intensity of pain subjectively on a scale of 0 (no pain) to 10 (intense pain). The PAL scale is a self-reported questionnaire used to measure level of activity in work and leisure activities.19 The LEFS is a self-reported questionnaire that quantifies daily function in individuals with lower-limb dysfunction.20 Each participant was weighed, and BMI was calculated. The rate of foot orthoses use was measured subjectively on a scale between 0 (never) and 10 (always) to determine how often the foot orthoses were worn. Questionnaires and pain measures were tested again at 1 year. The change in the rate of foot orthoses use was measured by the difference between final and initial rates of foot orthoses use.
Arch type classification was determined using arch index values obtained using a mirrored box to record digital plantar foot photographs. The mirrored-box arch index measure has shown excellent reliability and arch type classification had excellent agreement in a sample with obese, overweight, and normal-weight individuals.21
Values were used to prescribe foot orthoses posting on semirigid, semicustom, commercially available orthoses. Arch indices of 0.260 or greater were classified as low arched and arch indices between 0.210 and 0.260 were classified as normal arched, which received 5° and 2° medial noncompressible wedge posts, respectively. Arch indices of 0.210 or less were high arched and received no posting.21,22 The acrylic thermoplastic composite foot orthoses three-fourths in length were 1.5-mm thick and lightweight “J-GLAS PRE FABS” with full-length top covers (J-GLAS PRE FABS, JMS Plastics Supply, Neptune, NJ, USA). All participants received J-GLAS PRE FABS orthoses with posting respective to their classified foot type. The subjects were instructed to wear the orthoses 2 hours daily until they were able to wear the orthoses all day, then to wear the orthoses daily for 1 year. One-year follow-up was chosen to give enough time for the intervention to have an effect on pain and musculoskeletal dysfunction as well as avoid early gains that recede with weight regain common to weight loss efforts.23,24 All adverse events were to be recorded, including orthosis breakage or new-onset pain occurring when first adopting the foot orthoses.
Statistical analysis was performed using SPSS 18.0 for Mac (SPSS-UK Ltd, St. Andrews House, West Street, Woking, Surrey, GU21 6EB, United Kingdom). The small sample and specific BMI inclusion criteria predisposed data to a nonnormal distribution; thus, nonparametric two-tailed Wilcoxon signed rank test and Spearman ρ analyses were used. Statistical significance for change in all continuous variables including rate of foot orthoses use was assessed with the Wilcoxon signed rank tests. Cohen d effect sizes were calculated for future sample size estimations. Spearman ρ correlation coefficient assessed associations among changes in rate of foot orthoses use and a measure related to physical activity, pain, or weight loss, such as the PAL, the LEFS, or BMI. Overall feasibility of prescribing foot orthoses using arch index for obese individuals was determined by evaluating the rate of study completion and adverse events.
All nine subjects (seven women) were recruited from a weight loss program, enrolled, and completed the yearlong study. After 1 year, eight of nine women demonstrated adherence to the prescribed semicustom foot orthoses more than 50% of the time. No adverse events occurred. Before the study, two subjects used orthoses more than 50% of the time and three subjects used orthoses less than 50% of the time. After starting the 1-year study, all five wore the prescribed foot orthoses more than 50% of the time. Reasons for adherence and nonadherence were not reported.
The mean (SD) age of the subjects was 49.4 (13.6) years, weighing 115.3 (28.0) kg, with BMI of 42.4 (7.9) kg/m2. Subject arch type classifications were low for 10 feet, normal for 5 feet, and high for 3 feet. Rate of foot orthoses use (p = 0.017) and PAL (p = 0.026) increased significantly from baseline to 1 year (Table 1, which demonstrates significant changes in outcomes measures). Effect sizes for PAL (d = 0.96) and BMI (d = 0.71) indicated that samples of 10 to 15 subjects would suffice for 70% power (α < 0.05); effect sizes for LEFS (d = 0.31) and walking pain (d = 0.18) indicated that 100 to 300 subjects would be required to demonstrate significant changes. Although change in LEFS was not strongly associated with changes in other variables, the change in the ability to walk a mile (LEFS question 12) was strongly associated with changes in rate of foot orthoses use (r = 0.74) and change in BMI (r = 0.73). Two subjects reported an increase in pain, one subject had a decrease in LEFS, and one subject reported decreased rate of foot orthoses use after 1 year. The two participants who had worn foot orthoses more than 50% of the time at baseline before adopting the study-prescribed orthoses demonstrated increases in LEFS question 12.
This pilot study demonstrated the feasibility of a program for obese individuals requiring yearlong adherence to foot orthoses use prescribed using mirrored-box–obtained arch indices.
Near-full adherence without dropouts or clear adverse events suggested that foot orthoses prescribed in this manner were safe and comfortable. Using the mirrored box provided an alternative for people with obesity, which could pose challenges for prescription methods relying on accurate and reliable bony palpation, subtalar joint assessment, and foam impression. Increased pain at the end of the year reported by two subjects was not attributed to the initial orthosis prescription, although association with orthosis use cannot be ruled out. Also a possibility is that more vigorous exercise when wearing the orthoses led to increased pain when walking.
Although both rate of foot orthoses use and PAL increased, the changes in these measures did not correlate and no causative effect was implied. Although changes in rate of foot orthoses use and changes in the ability to walk a mile were correlated, changes in rate of foot orthoses use did not correlate with walking pain or orthopedic disorders. Rate of foot orthoses use may have facilitated increased PAL and walking ability, but the effects of concurrent enrollment in a weight loss program cannot be separated from the results.
The weight loss program included weekly meetings focused on cognitive behavior therapy and reduced caloric intake in a supportive environment. Monthly group activities included walking and bowling as well as encouragement for self-directed exercise. As with other studies involving obesity, however, BMI and PAL changes did not correlate.25 Future studies of physical activity in people with obesity may intentionally combine foot orthoses and weight loss interventions, isolate foot orthoses use as an independent intervention, or consider orthosis use as a variable that may contribute to weight loss.
Because of the absence of a standardized method of foot orthoses prescription and few studies overall documenting effects of foot orthoses use on people with obesity, this single-group pilot study was conducted to determine the feasibility of foot orthoses prescription and yearlong wear. Without a comparison group, no conclusions can be made regarding potential improvement in activity level due to foot orthoses use versus attendance of weight loss program or other variables. Foot orthoses were prescribed according to foot type classification alone in this study; many other variables affecting foot function were not considered in the prescription including pain, foot hypermobility/hypomobility, and other foot/ankle pathology. Other limitations of this study include lack of detailed information regarding previously used commercial foot orthoses, employment or home environment changes that may have affected PAL, self-directed exercise, caloric intake, or attendance at weight loss program meetings.
In this pilot study that used arch index measures to prescribe foot orthoses for obese individuals, the subject completion rate for the yearlong study without the incidence of adverse events suggests that a larger study is feasible and provides the groundwork for future controlled research into the effects of foot orthoses use on physical activity levels during weight loss.
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