Influence of Foot Type and Orthotics on Static and Dynamic Postural Control

Influence of Foot Type and Orthotics on Static and Dynamic Postural Control Lauren C. Olmsted and Jay Hertel Context: The effects of custom-molded foot orthotics on neuromuscular processes are not clearly understood. Objective: To examine these effects on postural control in subjects with different foot types. Design: Between-groups, repeated-measures design. Setting: Athletic training laboratory. Subjects: 30 healthy subjects assigned to groups by foot type: planus (n = 11), rectus (n = 12), or cavus (n = 7). Interventions: Custom-fit semirigid orthotics. Main Outcome Measures: Static postural control was measured on a force plate. Dynamic postural control was measured using the Star Excursion Balance Test. Both measurements were assessed with and without orthotics at baseline and 2 weeks later. Results: For static postural control, a significant conditionby-group interaction was found. Subjects with cavus feet had a decreased center-ofpressure velocity while wearing orthotics. For dynamic postural control, a significant condition-by-direction-by-group interaction was found. Subjects with cavus feet had increased reach distances in 3 of 8 directions while wearing orthotics. Conclusions: Custom orthotics were associated with some improvements in static and dynamic postural control in subjects with cavus feet. Key Words: orthoses, balance, Star Excursion Balance Test, functional performance Olmsted LC, Hertel J. Influence of foot type and orthotics on static and dynamic postural control. J Sport Rehabil. 2004;13:54-66. 2004 Human Kinetics Publishers, Inc. Foot orthotics have been demonstrated to be effective in improving clinical outcomes in lower extremity pathologies such as patellofemoral pain syndrome, 1 medial tibial stress syndrome, 2 and lateral ankle sprain. 3 Orthotics are hypothesized to work primarily by limiting excessive hyperpronation of the foot and subsequent rotations of the lower limb, thus reducing mechanical stress on tissues that have been injured. 4 An alternative hypothesis is that orthotics have beneficial effects on the sensorimotor system and result in improved neuromuscular function of the lower extremity. 4 For example, foot orthotics have been shown to improve postural control in both healthy 5,6 and ankle-injured subjects. 3,7 It is plausible that orthotics are effective by improving both biomechanical and neuromuscular function. One measure of sensorimotor function of the lower extremity that has received considerable attention in sports medicine is postural control. The authors are with The Pennsylvania State University Dept of Kinesiology, University Park, PA 16802. 54

Orthotics and Postural Control 55 Postural control is frequently assessed by having subjects stand on 1 leg as still as possible on a force plate; this is often referred to as static postural control. The force plate permits calculation of variability in the regulation of stance. Greater variability is typically associated with postural instability. 8 For example, static postural control has been consistently shown to be impaired in individuals with lateral ankle instability. 3,7,9 Static postural control has, however, been criticized as a measure of sensorimotor function because measurement techniques might not be sensitive enough to detect deficits in impaired subjects. 10 Quiet standing in singleleg stance might be a task that is too unconstrained, thus affording subjects the opportunity to use alternative motor strategies to adequately accomplish the task even in the presence of pathology. 11 This has led to the development of more complex and dynamic postural-control tasks. One such task is the Star Excursion Balance Test (SEBT), a series of lower extremity reaching tasks. 12-16 The SEBT has been shown to be sensitive to detecting deficits in subjects with chronic ankle instability 15 and patellofemoral pain syndrome. 17 The effect of foot orthotics on static postural control has been previously studied in both healthy and injured populations, although the role of foot type has not been examined in previous investigations. We chose to study the effects of orthotics in subjects with different foot types because there is some evidence to suggest that some measures of static postural control are affected by foot type. 18 We are unaware of previous research examining the effects of foot orthotics on dynamic postural control. Therefore, our purpose was to examine the effects of foot orthotics on static and dynamic postural-control measures in healthy subjects with different architectural foot types. Design Methods We used a mixed-model design with repeated measures to assess the effects of orthotic intervention on static and dynamic balance in healthy subjects with different foot types. For static postural control, 2 separate 3 2 2 repeated-measures ANOVAs were calculated with center-of-pressure velocity (COPV) and center-of-pressure area (COPA) used as the dependent variables. Independent variables were group at 3 levels (rectus, planus, cavus), day at 2 levels (day 1, day 14), and condition at 2 levels (orthotics, no orthotics). For dynamic postural control, a 3 2 2 8 repeated-measures design was calculated, with normalized reach distance in centimeters used as the dependent variable. Independent variables were group at 3 levels (rectus, planus, cavus), day at 2 levels (day 1, day 14), condition at 2 levels (orthotics, no orthotics) and reach direction at 8 levels (8 reach directions).

56 Olmsted and Hertel Subjects Thirty subjects (17 men, 13 women) with no lower extremity musculoskeletal injury volunteered to participate. After reading and signing an informed-consent form approved by the university institutional review board, they were placed into groups based on foot type (rectus, planus, cavus). All subjects were categorized by foot type by 3 independent examiners using the methods previously reported by Dahle et al. 19 If results were inconsistent between examiners, the subject was then reassessed in the presence of all 3 and consensus was reached. Each foot was categorized separately, and all 30 subjects had both of their feet classified into the same category. Subjects reported on day 1 for testing and were tested for both static and dynamic postural control with and without orthotics. Eleven subjects were placed in the planus group (age 22.5 ± 2.2 years, height 172.2 ± 7.9 cm, mass 76.7 ± 14.1 kg), 12 were placed in the rectus group (age 22.3 ± 2.5 years, height 166.8 ± 10.3 cm, mass 72.4 ± 17.6 kg), and 7 were placed in the cavus group (age 24.9 ± 4.8 years, height 181.1 ± 8.3 cm, mass 88.8 ± 29.8 kg). Materials Custom, semirigid orthotics (Ortho-Arch II, Foot Management Inc, Pittsville, Md) were manufactured for each subject based on foot measurements taken with a laser foot scanner (Foot Management Inc). Subjects were seated in an adjustable chair with 1 foot placed on the glass of the foot scanner, with the hip, knee, and foot at 90 angles. The foot was held in subtalar-joint neutral by the examiner while the laser passed under it. Subtalar neutral was found and maintained by methods previously reported by Laughton et al. 20 The laser scan was electronically transferred to a computer, saved to a disk, and sent to the manufacturer for orthotic construction. No additional posting or alterations were made. The reliability and validity of the laser-scanning techniques have been previously reported. 20 Instrumentation Static postural control was assessed using an AMTI AccuSway force platform (AMTI Corp, Watertown, Mass) interfaced with a laptop computer using SWAYWIN TM software (AMTI Corp). Three-dimensional groundreaction forces were recorded at 50 Hz, and the software program calculated COP excursions. The origin of the COP path was the initial point of COP during each trial. Dependent measures of postural control included COP-excursion area and velocity. Area represents the magnitude of distribution of COP excursions during a trial, and velocity represents the average speed of COP movement over the course of a trial. Dynamic postural control was measured using the SEBT. The SEBT is a set of functional tests that incorporate a single-leg stance with maximum

Orthotics and Postural Control 57 reach of the opposite leg. They are performed with the subject standing at the center of a grid placed on the floor, with 8 lines, constructed with athletic tape extending at 45 increments from the center of the grid. The 8 lines positioned on the grid are labeled according to the direction of the excursion relative to the stance leg: anterior, anterolateral, lateral, posterolateral, posterior, posteromedial, medial, and anteromedial. Procedures For static postural control, subjects performed three 15-second trials of quiet standing in single-leg stance, with their eyes open, on their right and left legs with and without orthotics. They stood with arms folded across their chest while focusing on a stationary visual target located on a wall 1 m from the force platform. We instructed subjects to remain as motionless as possible. Trials were discarded and repeated if a touchdown (the nonstance leg touching the ground) occurred during the course of a trial. For dynamic postural control, subjects performed 3 reaches in each of the 8 directions with both the right and left legs with and without orthotics. They maintained a single-leg stance on the stance leg while reaching with the opposite leg to touch as far as possible along the appropriate line. Subjects touched the farthest point possible on the line with the most distal part of their reach foot. The reach foot touched the farthest point on the line as lightly as possible so that the reach leg did not provide considerable support in maintaining upright posture. Subjects then returned to a bilateral stance while maintaining their equilibrium. The examiner marked the point touched along the line and then manually measured the distance from the center of the grid to the touch point with a tape measure. Trials were discarded and repeated if the examiner thought that the reach foot was used to provide considerable support when touching the ground, if the subject lifted the stance foot from the center of the grid, or if he or she lost equilibrium at any point in the trial. These methods have been previously reported. 13-16 All reach distances were normalized to subjects leg lengths. 16 Test leg (right, left), condition (orthotic, no orthotic), and posturalcontrol test (static, dynamic) were counterbalanced to control for any learning or order effects. Subjects then wore the orthotics for at least 4 h/day for a 2-week interval between testing sessions. After 2 weeks, they returned to the laboratory for day 2 of testing. The same protocol used for day 1 testing was repeated, with the order of testing (orthotic/no orthotic, static/dynamic) reversed on day 2. Statistical Analysis Paired t tests were run to compare the right and left dependent measures on day 1 for both the orthotic and no orthotic conditions. Because there were no side-to-side differences for any of these measures (P >.05), the

58 Olmsted and Hertel mean of the right and left values was calculated and used for further analysis. For static postural control, 2 separate repeated-measures ANOVAs were performed with 1 between factor (group) and 2 within factors (day, condition) for the COPV and COPA measures. For dynamic postural control, a repeated-measures ANOVA with 1 between factor (group) and 3 within factors (day, condition, direction) was performed for the normalized reach distances. Tukey post hoc testing was used to identify significant differences, with an alpha level set at.05 a priori. Static Postural Control Results For COPV, a significant condition-by-group interaction was found (F 2,27 = 10.15, P =.001). Subjects with cavus feet had a decreased COPV when wearing orthotics, whereas the planus and rectus groups did not differ substantially between the orthotic and no-orthotic conditions (see Figure 1). A main effect for day was also found; COPV was significantly lower on day 14 for all 3 groups (F 1,27 = 9.588, P =.005; see Table 1). For COPA, no significant interactions or main effects were identified. (see Table 2). Dynamic Postural Control A significant condition-by-direction-by group interaction was found for reach distances (F 14,182 = 1.88, P =.03). While wearing orthotics, subjects with cavus feet had increased reach distances in the anterolateral, lateral, and posterolateral directions compared with the rectus and planus groups Figure 1 A significant group-by-condition interaction was found for center-of-pressure (COP) excursion-velocity measures. The cavus group improved significantly with orthotic intervention, whereas the rectus and planus groups did not. *P <.05.

Orthotics and Postural Control 59 Table 1 Means (SDs) of Center-of-Pressure Excursion-Velocity Measures (cm/s) Day 1 Day 14* No orthotics Orthotics No orthotics Orthotics Planus 3.31 (0.29) 3.38 (0.26) 3.16 (0.27) 3.10 (0.23) Rectus 2.77 (0.28) 2.93 (0.25) 2.65 (0.26) 2.65 (0.22) Cavus 3.97 (0.36) 3.39 (0.33) 3.56 (0.34) 3.17 (0.28) *Day 14 measures were significantly less than day 1 measures (P <.05). Table 2 Means (SDs) of Center-of-Pressure Excursion-Area Measures (cm 2 ) Day 1 Day 14 No orthotics Orthotics No orthotics Orthotics Planus 6.00 (0.65) 5.84 (0.62) 6.36 (0.89) 5.87 (0.82) Rectus 5.05 (0.62) 4.88 (0.60) 4.61 (0.85) 4.97 (0.79) Cavus 6.23 (0.81) 6.00 (0.78) 7.77 (1.12) 6.88 (1.03) (see Table 3). A significant day-by-direction-by-group interaction was also identified (F 14,182 = 1.885, P =.034). From day 1 to day 14, subjects with cavus feet had increased reach distances at a greater magnitude than the rectus or planus groups across all directions (see Table 4). Comments Orthotics and Static Postural Control The effect of foot orthotics on static postural control has been previously studied in both healthy and injured populations, although the role of foot type has not been examined in previous investigations. Our results show that subjects with cavus feet had a decreased COPV when wearing orthotics, whereas the planus and rectus groups did not differ substantially

60 Olmsted and Hertel Table 3 Means (SDs) of Normalized Reach Distances for the Star Excursion Balance Test* Group Condition A AM M PM P PL L AL Planus no orthotic 0.91 0.92 0.94 0.97 0.95 0.89 0.78 0.80 (0.03) (0.02) (0.02) (0.03) (0.03) (0.03) (0.03) (0.03) orthotic 0.91 0.92 0.93 0.97 0.94 0.89 0.79 0.8 (0.02) (0.02) (0.03) (0.03) (0.03) (0.04) (0.04) (0.03) Rectus no orthotic 0.94 0.95 0.99 1.02 1.00 0.94 0.85 0.81 (0.02) (0.02) (0.03) (0.03) (0.03) (0.03) (0.03) (0.03) orthotic 0.91 0.94 0.98 1.01 1.01 0.94 0.84 0.80 (0.02) (0.02) (0.03) (0.03) (0.03) (0.04) (0.03) (0.02) Cavus no orthotic 0.92 0.95 0.99 1.02 1.00 0.93 0.79 0.79 (0.03) (0.03) (0.04) (0.04) (0.05) (0.05) (0.04) (0.04) orthotic 0.93 0.95 0.98 1.02 1.01 0.95 0.81 0.81 (0.03) (0.03) (0.04) (0.04) (0.05) (0.05) (0.05) (0.03) *There was a significant group-by-condition-by-direction interaction (P <.05). A indicates anterior; AM, anteromedial; M, medial; PM, posteromedial; P, posterior; PL, posterolateral; L, lateral; and AL, anterolateral.

Orthotics and Postural Control 61 Table 4 Means (SDs) of Normalized Reach Distances for the Star Excursion Balance Test* Group Condition A AM M PM P PL L AL Planus 1 0.91 0.92 0.91 0.95 0.92 0.86 0.79 0.80 (0.03) (0.02) (0.03) (0.03) (0.03) (0.04) (0.04) (0.03) 2 0.91 0.92 0.96 0.99 0.97 0.91 0.78 0.79 (0.03) (0.03) (0.03) (0.03) (0.04) (0.04) (0.03) (0.02) Rectus 1 0.92 0.94 0.98 1.01 0.99 0.93 0.83 0.79 (0.02) (0.02) (0.03) (0.03) (0.03) (0.03) (0.03) (0.03) 2 0.94 0.95 0.99 1.02 1.01 0.96 0.86 0.81 (0.03) (0.02) (0.03) (0.03) (0.03) (0.04) (0.03) (0.02) Cavus 1 0.91 0.93 0.95 0.98 0.97 0.90 0.76 0.77 (0.03) (0.03) (0.04) (0.04) (0.05) (0.05) (0.05) (0.04) 2 0.94 0.96 1.02 1.06 1.04 0.98 0.84 0.83 (0.04) (0.03) (0.04) (0.04) (0.05) (0.05) (0.05) (0.03) *There was a significant group-by-day-by-direction interaction (P <.05). A indicates anterior; AM, anteromedial; M, medial; PM, posteromedial; P, posterior; PL, posterolateral; L, lateral; and AL, anterolateral.

62 Olmsted and Hertel between the orthotic and no-orthotic conditions. Orthotic intervention might provide increased medial stabilization or enhanced plantar cutaneous receptor activity leading to improved neuromuscular control. These effects might be more profound in subjects with cavus feet. In a previous study, orthotics with medial rear-foot posts resulted in lower frontal-plane COP length and velocity measures among 15 healthy subjects whose foot types were not described. 5 Results from this study demonstrated an improvement in static postural control, but the role of foot type was not examined. The improvement seen with medially posted orthotics was thought to be related to foot architecture and limiting the range of pronation. Stude et al 6 examined the effects of simulated golf and orthotic intervention on static balance in experienced golfers. Nine subjects had static-balance measurements taken on the Cybex FASTEX system before and after 9 holes of simulated golf. The simulated golf was used to induce a fatigue factor that one would experience during golf activity. Subjects stood on the FASTEX in single-leg stance for 30 seconds, and a stabilization index was calculated. Subjects were then fit with custom-molded orthotics and returned for the same testing protocol after wearing the orthotics for 2 weeks. Results showed a trend toward a decrease in stabilization time from baseline balance testing to post-golf-simulation balance testing with orthotic use. 6 Although we did not measure stabilization time, our results revealed that after 2 weeks of orthotic intervention, COPV measures decreased significantly in all foot-type groups. This could be attributed to either a learning effect with repeated balance trials or the effects of wearing of the orthotics between testing sessions. Percy and Menz 21 investigated static postural control in 30 asymptomatic professional soccer players in 4 conditions: barefoot, cleats, cleats with soft insoles, and cleats with a prefabricated rigid orthotic. They found no substantial benefits or detriments related to the different shoe and orthotic conditions. Although these findings are different than our current results, it must be noted that the measurement technique of Percy and Menz 21 was based on variations of movement of the trunk as opposed to force-plate measures. Orthotic intervention and static postural control have also been studied in injured populations. Guskiewicz and Perrin 7 demonstrated that orthotic intervention reduced postural sway in subjects with acute lateral ankle sprains compared with uninjured subjects. Similarly, Orteza et al 3 found that the use of molded orthotics significantly improved time-out-of-balance scores and pain while jogging in subjects after ankle sprain. After lateral ankle-ligament injury, orthotic intervention might provide stabilization to the subtalar joint, thus limiting pronation and supination and improving measures of postural control. Conversely, Hertel et al 9 did not find improvements in postural-control measures with the implementation of various orthotic devices after acute ankle sprain.

Orthotics and Postural Control 63 Orthotics and Dynamic Postural Control The effects of orthotics on dynamic postural control have been studied less extensively. In the study by Stude et al 6 previously discussed, the 9 golfers were also tested on a single-leg forward-hop task, which objectively measures stabilization time. Subjects were asked to complete 3 single-leg forward hops to 4 platforms in a straight line after a visual cue was given. Once a preset level of stabilization was reached at the first platform, subjects were cued to advance to the next platform. Results indicate no statistical significance in reduction of time-to-stabilization scores with orthotic use before or after 9 holes of simulated golf. 6 The protocol used in this study is dynamic in nature but might not represent dynamic postural control. Results from our study measuring the effects of orthotics on performance of the SEBT might offer a better alternative to measuring dynamic balance. After 2 weeks of wearing orthotics for at least 4 h/day, subjects with cavus feet had increased reach distances at a greater magnitude than the rectus or planus groups across all directions. While wearing orthotics, subjects with cavus feet had increased reach distances in the anterolateral, lateral, and posterolateral planes compared with the rectus and planus groups. In subjects with cavus feet, orthotic intervention might help improve dynamic balance by providing medial support to the foot. Structurally, these subjects might normally have little contact between the ground and the plantar aspect of their feet. Custom-fitted orthotics might enhance plantar cutaneous receptor activity by providing altered pressure distribution on the bottom of the foot. This increased cutaneous receptor activity could lead to enhanced neuromuscular function and allow more stability during dynamic reaches in the lateral directions. The importance of these 2 very different beneficial effects of orthotics physical medial support and enhanced sensory information might contribute to improved clinical outcomes. Clinically, healthy subjects with cavus feet showed improvements on the SEBT while wearing orthotics. The clinical implications of these findings are unknown in pathological conditions. Foot Type, Orthotics, and Postural Control Differences in postural control during single-leg stance in individuals with different foot types have been previously investigated. In a previous study, 18 subjects with cavus feet used significantly larger COPA than did those with rectus and planus feet. No significant differences were found between foottype groups for COPV. Although these results differ from our current findings, both studies found differences in static postural control between those with cavus feet and those with rectus and planus feet. Foot type has not been previously shown to be related to performance on the SEBT. 16 The question that remains unanswered is why subjects with cavus feet would have improvements in static and dynamic postural control with orthotics compared with subjects with rectus or planus feet. The answer

64 Olmsted and Hertel probably lies in the combination of foot biomechanics and postural-control strategies. Individuals with a cavus foot have less contact area between the plantar surface of the foot and the ground than do subjects with rectus or planus feet. Decreased contact-surface area on the medial aspect of the foot might lead to less stabilization, thus hindering postural control. By placing an orthotic in the shoe and providing a mechanical limit to pronation, subjects with cavus feet might show a reduction in COP excursions by having a decreased range and velocity of pronation. These effects might also be seen during dynamic postural-control tasks. It has been suggested that the role of plantar cutaneous receptors in regulating posture might be enhanced with orthotic implementation. 4 This mechanism might help explain the improved postural control seen in subjects with cavus feet in our study. It is also possible that orthotics cause alterations in force-distribution patterns in the foot, leading to altered postural-control strategies. Orthotics can alter where the COP of the foot is distributed during weight bearing. The relationship of the COP to the borders of the base of support might be of clinical importance, 8 although our study did not investigate this relationship. Because we found differential effects of orthotics on postural control in healthy subjects with different foot types, further research on the effects of foot type and orthotics among injured populations and in more functional activities is warranted. Conclusion Custom-fit foot orthotics were associated with some improvements in static and dynamic postural control in healthy subjects with cavus feet but not in those with rectus or planus feet. Although foot orthotics are most commonly prescribed in individuals with pes planus in an effort to limit hyperpronation, their use with individuals with rectus and cavus foot types is not uncommon. Clinically, the beneficial effects of foot orthotics among individuals with different foot types might not only be related to controlling joint motion but also be caused by altered neuromuscular control related to enhanced activity of the plantar cutaneous receptors. Acknowledgments This study was funded by Foot Management Inc (Pittsville, Md). References 1. Eng JJ, Pierrynowski MR. Evaluation of soft foot orthotics in the treatment of patellofemoral pain syndrome. Phys Ther. 1993;73:62-68.

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