ORIGINAL ARTICLES
Effects of Off-the-Shelf Foot Orthoses on Plantar Foot Pressures in Patients with Early Rheumatoid Arthritis Derek Santos, PhD* Vicki Cameron-Fiddes, PhD* Background: Rheumatoid arthritis (RA) often affects feet with progressive pathologic changes to foot morphology and pressure distribution. Studies in RA suggest that reductions in forefoot peak pressures can reduce pain. We investigated the effects of offthe-shelf foot orthoses on plantar foot pressures in patients with early RA. Methods: Thirty-five patients with early RA were recorded walking. Variables measured were forefoot peak plantar pressure (PPPft), forefoot pressure-time integral (PTIft), and hallux and lesser toe and midfoot contact areas. Patients were analyzed while walking barefoot, with shoes, and with shoes and foot orthoses. Measurements were taken at baseline and at 3 and 6 months. Results: There were significantly increased PPPft values between barefoot and shod and between barefoot and orthoses (P , .01). However, there was a significant reduction in PPPft during the 6 months with orthoses compared with shoes only (P , .01). Foot orthoses significantly reduced PTIft over 6 months (P , .01). Results also demonstrated a significant increase in hallux and lesser toe (P , .01) and midfoot (P , .01) contact areas during the 6 months with foot orthoses. Conclusions: In patients with early RA, off-the-shelf foot orthoses cause a significant reduction of 22% in PPPft and 14% in PTIft as soon as insoles are worn compared with shod. Further reductions for orthoses compared with baseline were found by 3 months (15% in PPPft and 14% in PTIft) and 6 months (33% in PPPft and 33% in PTIft). These findings could contribute to reductions in foot pain. (J Am Podiatr Med Assoc 104(6): 610-616, 2014)
Patients with early rheumatoid arthritis (RA) often note pain over the ball of the foot, likened to ‘‘walking on pebbles.’’ This can lead to reduced activity and a poor quality of life.1 As the disease becomes more established, forefoot plantar pressures are known to further increase, as the lesser toes start to claw, and distal displacement of the plantar fat pad occurs.2 Peak plantar pressures in the forefoot in RA have been shown to be associated with severe pain and tissue breakdown.3 This makes patients with RA at risk for foot ulceration and subsequent infection and amputation.4 Functional foot orthoses are special insoles worn inside the shoe to control any abnormal movement of the foot during walking to limit foot pain and *Queen Margaret University, Edinburgh, School of Health Sciences, Musselburgh, Scotland. Corresponding author: Derek Santos, PhD, Queen Margaret University, Edinburgh, School of Health Sciences, Queen Margaret University Dr, Musselburgh, East Lothian EH21 6UU, United Kingdom. (E-mail: [email protected])
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deformity.5 Podiatric physicians use foot orthoses in the management of RA to reduce pressure over the forefoot by redistributing the forces more equally over the plantar surface of the foot. This is achieved by increasing the contact area of the hallux and lesser toes and of the midfoot.6 Redmond et al7 found that prefabricated orthotic devices increased hallux contact area by 3.6% and midfoot contact area by 32.6%. In addition, foot orthoses may influence foot function and so are capable of altering the timing of the phases of gait.8 Otter et al9 found that peak pressures in the forefoot of patients with RA were similar to those in participants in a control group, but what was different was that patients with RA significantly prolonged the duration that these peak pressures were applied to the forefoot. They attributed these findings to reduced walking speed and increased double support time. In comparison, the control group had a more transient or reduced duration of peak pressures applied to the forefoot.9 Otter et al9 suggested that this prolonged duration
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of peak pressures applied to the forefoot may account for pain and greater deformity in the RA group. Because duration of pressure can be investigated using the pressure-time integral, this is a useful variable to evaluate the effects of prolonged peak plantar pressures.8,9 We investigated whether an off-the-shelf functional foot orthosis reduces the pressure-time integral (ie, the duration that peak pressures are applied to the sole of the foot) and its effect on pain. Custom-molded foot orthoses are specially made for the individual and have been shown to be effective in patients with RA.10-12 However, the process of manufacturing these custom-molded devices can be lengthy and expensive.13,14 Off-theshelf foot orthoses are ready-made devices that can be dispensed at the chairside on the day of diagnosis and have been shown to achieve comparable kinetic results as custom-molded foot orthoses.7 This has important clinical implications for patients with RA, as early intervention is thought to make a difference in long-term outcome, and in the short-term it relieves severe pain and disability.15 This often means the difference between staying at work and becoming unemployed.16 This study examines patients diagnosed as having RA in the past 2 years. All of the previous studies investigating foot pressures in RA have included patients with more established disease (mean disease duration, 8–22 years).6,9,17-19 Research is needed to provide clinicians with evidence of optimal management for patients with early disease if current guidelines advocating early intervention are to be met. The aim of this study was to investigate the effects of off-theshelf foot orthoses on plantar foot pressures in patients with early RA.
Methods Participants Thirty-five patients (6 men and 29 women) participated in the study, with data collected for each participant over a 6-month period. This ratio of men to women reflects average prevalence rates. Participants were 26 to 80 years of age (mean 6 SD age, 52.4 6 13.3 years). Disease duration ranged from 1 month to 1 year and 9 months (mean 6 SD disease duration, 0.7 6 0.6 years). No individual had been managed previously with foot orthoses. Patients with concomitant musculoskeletal disease, endocrine disorders (especially diabetes mellitus), and neurologic disease were also excluded from the study. Ethical approval was obtained from the
Queen Margaret University Research Ethics Committee, Edinburgh, East Lothian, UK, and the NHS South East Scotland Research Ethics Committee, Edinburgh, Lothian, UK. Equipment The HR Walkway and F-Scan in-shoe plantar pressure measurement systems (Tekscan, Boston, Massachusetts) were used to investigate the effects of off-the-shelf foot orthoses on plantar pressure. The HR Walkway and F-Scan in-shoe systems record data at the same frequency with the spatial resolution of 4 sensels/cm2, allowing comparisons to be made between the barefoot and in-shoe states. Procedure The study design was a within-subject controlled study. Patients presented for data collection at baseline, 3 months, and 6 months. Patients randomly walked barefoot, with shoes only, and with shoes and foot orthoses. The type of foot orthosis used was the Slimflex Plastic (A. Algeo Ltd, Liverpool, England).20 Patients wore standardized footwear throughout the study. At each visit, the patient was weighed with validated electronic scales. The correct size of shoe was then selected for each patient, and a new F-Scan insole was trimmed to fit inside the shoe. The patient then conditioned the HR Walkway and the sensor insole, as recommended by the manufacturer, before data collection. The two systems were then calibrated using the patient’s weight. Six walking trials were recorded with the HR Walkway when the patient was barefoot. With the in-shoe system, six walking trials were recorded with shoes only and six trials with shoes and foot orthoses. No individual wore socks or hosiery. The same procedure was repeated at 3 and 6 months. The same set of in-shoe sensor insoles were used for each individual patient at all three of the data time points. Data Analysis A repeated-measures design was used. Peak plantar pressure in the forefoot (PPPft), pressure-time integral in the forefoot (PTIft), hallux and lesser toe contact area (HLT), and midfoot contact area (MF) were the variables measured. These variables were tested for normal distribution using ShapiroWilks tests, box plots, and histograms. All PPPft and PTIft values presented with a nonparametric distribution. All HLT and MF values were found to have a
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Table 1. Peak Plantar Pressure at the Forefoot Measured at Baseline, 3 Months, and 6 Months Forefoot Peak Plantar Pressure (kPa) Barefoot State Period
Shod State
Shod Wearing Orthoses State
Median (IQR)
Mean 6 SD
Median (IQR)
Mean 6 SD
Median (IQR)
Mean 6 SD
P Value
Baseline
334 (474)
347 6 100
1,691 (4,432)
2177 6 1,369
1,325 (9,355)
2,032 6 1,755
.001a
3 months
335 (588)
349 6 110
1,726 (3,668)
1,900 6 1,083
1,124 (3,697)
1,401 6 912
.001a
6 months
362 (531)
356 6 121
1,117 (3,420)
1,453 6 887
1,158 6 1,412
.001a
P values
.217
.001a
892 (8,081)
.001a
Note: The data for these variables were nonparametric, hence the median values are more representative of the measure of centrality of the data. Abbreviation: IQR, interquartile range. a Shows statistically significant differences at P , .01.
parametric distribution, with skewness and kurtosis between 1 and 1. Statistical analyses were then undertaken to compare any potential effects of the foot orthoses over time (ie, baseline, 3 months, and 6 months) for each separate state and between states (ie, barefoot, shod, and shod with orthoses). The significance level was set at 5% (P , .05). For parametric data, a repeated-measures analysis of variance test was used where sphericity was achieved. Pairwise comparisons determined where the significant changes were occurring. For nonparametric data, a Friedman test was used. An exact Wilcoxon signed rank test with Bonferroni multiple corrections was performed to determine where the significant changes were occurring. With Bonferroni multiple comparisons, the significance level was adjusted accordingly by dividing the P value by the number of comparisons being tested, so significance was set at P , .02. Data were analyzed with SPSS for Windows, version 16.0 (SPSS Inc, Chicago, Illinois).
Results All of the tables show mean 6 SD and median (interquartile range) values for patients walking (ie, barefoot, with shoes, and with shoes and foot orthoses) at baseline, 3 months, and 6 months. For the nonparametric variables (ie, PPPft and PTIft), the median is more representative of the measure of centrality, hence this is reported in the text. For the parametric variables (ie, HLT and MF), the mean is reported in the text because it is more reflective of the measure of centrality. Table 1 shows that there was no significant change in PPPft in the barefoot state during the 6 months (P . .05). In the shod state there was a significant change in PPPft during the 6 months (P
612
, .01). This change was a significant increase in median pressure between baseline (1,691 kPa) and 3 months (1,726 kPa) (P , .01) but a significant decrease in median PPPft between baseline (1,691 kPa) and 6 months (1,117 kPa) and between 3 months (1,726 kPa) and 6 months (1,117 kPa) (P , .01). There was also a significant change in the orthoses state over the 6 months (P , .01). This was also a significant reduction in median PPPft occurring between baseline (1,325 kPa) and 3 months (1,124 kPa), baseline (1,325 kPa) and 6 months (892 kPa), and 3 months (1,124 kPa) and 6 months (892 kPa) (P , .01). At baseline, 3 months, and 6 months, there were significant variations in PPPft (P, .01) across the barefoot, shod, and orthoses states. There was a significant decrease in PPPft between the shod and orthoses states (P , .01); however, there was a significant increase in PPPft at baseline, 3 months, and 6 months between the barefoot and shod states and between the barefoot and orthoses states (P , .01). Thus, overall, all of the barefoot pressures were significantly lower than those of the shod and orthoses states. Table 2 shows that there was a significant change in PTIft during the 6 months in the barefoot, shod, and orthoses states (P , .01). Overall, the orthoses state showed the lowest median PTIft values at baseline (53 kPa.s), 3 months (46 kPa.s), and 6 months (36 kPa.s), with a trend toward a reduction of PTIft during the 6 months (P , .01). The shod state also showed a trend toward a reduction in median PTIft from baseline (62 kPa.s) to 3 months (61 kPa.s) to 6 months (50 kPa.s) (P , .01), although the values were higher than those for the orthoses state. The barefoot state showed the highest median PTIft values, with an increase from baseline (66 kPa.s) to 3 months (68 kPa.s) and a
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Table 2. Pressure-Time Integral at the Forefoot Measured at Baseline, 3 Months, and 6 Months Forefoot Pressure-Time Integral (kPa.s) Barefoot State Period
Shod State
Shod Wearing Orthoses State
Median (IQR)
Mean 6 SD
Median (IQR)
Mean 6 SD
Median (IQR)
Mean 6 SD
P Value
Baseline
66 (280)
97 6 63
62 (257)
73 6 59
53 (206)
55 6 40
.001a
3 months
68 (218)
88 6 53
61 (204)
66 6 50
46 (173)
51 6 39
.001a
6 months
61 (204)
78 6 45
50 (182)
59 6 48
36 (156)
47 6 38
.001a
.001a
P values
.001a
.001a
Note: The data for these variables were nonparametric, hence the median values are more representative of the measure of centrality of the data. Abbreviation: IQR, interquartile range. a Shows statistically significant differences at P , .01.
barefoot state during the 6 months (P . .01), as shown in Table 4. There were, however, significant changes in the shod and orthoses states during the 6 months (P , .01). In the shod state, these significant changes in mean MF were between baseline (23.9 cm2) and 6 months (31.3 cm2) (P , .01) and between 3 months (26.3 cm2) and 6 months (31.3 cm2) (P , .01). In the orthoses state, there was a significant change in mean MF at all of the time points (baseline, 23.9 cm2; 3 months, 28.8 cm2; 6 months, 35.1 cm2) (P , .01). There was no significant change in mean MF at baseline or at 3 months across the three states (P . .05 for both). There was, however, a significant increase in mean MF at 6 months among the three states (P , .01). This significance was between the barefoot (28.5 cm2) and orthoses (35.1 cm2) states (P , .01) and between the shod (31.3 cm2) and orthoses (35.1 cm2) states (P , .01).
decrease from 3 months (68 kPa.s) to 6 months (61 kPa.s). There was no significant change in HLT in the barefoot state (P . .05) or the shod state (P . .05) during the 6 months (Table 3). There was a significant change, however, in mean HLT in the orthoses state during the 6 months (P , .01). This significant increase in mean HLT was between baseline (14.5 cm2) and 6 months (18.0 cm2) (P , .01) and between 3 months (14.3 cm2) and 6 months (18.0 cm2) (P , .01). Between states, at baseline there was a significant change between barefoot, shod, and orthoses states (P , .01). At 3 months there was a significant decrease in mean HLT between the barefoot (15.3 cm2) and shod (10.7 cm2) states (P , .01) and a significant increase in mean HLT between the shod (10.7 cm2) and orthoses (14.3 cm2) states (P , .01). There was a significant increase in mean HLT across the three states at 6 months (P , .01). Overall, by 6 months the orthoses state showed the greatest mean HLT (18.0 cm2) compared with the shod (12.1 cm2) and barefoot (14.0 cm2) states (P , .01). There was no significant change in MF in the
Discussion At baseline, PPPft was significantly reduced between the shod and orthoses states (P , .001). This
Table 3. Contact Area for the Hallux and Lesser Toes Measured at Baseline, 3 Months, and 6 Months Hallux and Lesser Toes Contact Area (cm2) Barefoot State
Shod State
Shod Wearing Orthoses State
Period
Mean 6 SD
Median (IQR)
Mean 6 SD
Median (IQR)
Mean 6 SD
Median (IQR)
P Value
Baseline
14.5 6 4.2
15.0 (18.7)
12.0 6 6.0
11.8 (27.5)
14.5 6 6.5
14.1 (24.8)
.005a
3 months
15.3 6 4.6
15.2 (18.8)
10.7 6 4.9
10.0 (19.5)
14.3 6 5.8
14.1 (22.3)
.001a
6 months
14.0 6 4.4
13.6 (18.8)
12.1 6 5.0
12.1 (19.5)
18.0 6 6.5
18.0 (22.5)
.001a
P value
.054
.117
.001
a
Note: The data for these variables were parametric, hence the mean values are more representative of the measure of centrality of the data. Abbreviation: IQR, interquartile range. a Shows statistically significant differences at P , .01.
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Table 4. Contact Area at the Midfoot Measured at Baseline, 3 Months, and 6 Months Midfoot Contact Area (cm2) Barefoot State Period
Mean 6 SD
Median (IQR)
Shod State Mean 6 SD
Median (IQR)
Shod Wearing Orthoses State Mean 6 SD
Median (IQR)
P Value
Baseline
26.4 6 10.0
26.5 (48.0)
23.9 6 9.8
24.2 (44.1)
23.9 6 10.1
23.5 (47.9)
.166
3 months
27.6 6 10.4
27.2 (50.8)
26.3 6 9.3
26.3 (46.9)
28.8 6 8.8
29.0 (42.8)
.065
6 months
28.5 6 10.4
26.3 (46.5)
31.3 6 9.6
30.7 (47.2)
35.1 6 9.6
36.6 (46.1)
.001a
P values
.375
.001a
.001a
Note: The data for these variables were parametric, hence the mean values are more representative of the measure of centrality of the data. Abbreviation: IQR, interquartile range. a Shows statistically significant differences at P , .01.
finding is of great clinical consequence because it shows that PPPft will be reduced as soon as the patient starts to wear the orthoses in their shoes, and so patients may experience some immediate relief from forefoot pain with foot orthoses. This outcome strengthens the argument for the use of off-the-shelf foot orthoses in patients with early RA because the patient will receive early intervention and so meet the recommendations set out in the current guidelines. There was an 84% increase in PPPft at baseline between the barefoot and shod states and an 83% increase between the barefoot and orthoses states. Comparable results were found at 3 and 6 months, suggesting that PPPft is greater in patients with early RA when they wear shoes with and without foot orthoses compared with the barefoot state. Minns and Craxford21 state that changes seen in the gait of individuals with RA may be a pain-avoidance strategy. A possible reason for this finding is, therefore, that the patient has altered his or her walking pattern to prevent weightbearing on the painful forefoot during barefoot walking. Semple et al19 investigated center of pressure analysis in RA and found a delay of the anterior progression of the center of pressure that remained in the midfoot approximately 6% of stance duration longer than normal. This was followed by rapid transfer of the center of pressure through the forefoot, spending 5% of stance duration less than in the control group. These findings support the conclusions of Keenan et al,22 who described gait changes in patients with RA. The PPPft was significantly increased with shoes, signifying that the patient’s gait is no longer trying to avoid forefoot pain. The significant reduction in PPPft between the shod and orthoses states of 22% demonstrates that the foot orthoses do reduce PPPft and that this effect is due to the foot orthoses and not to the footwear. When comparing baseline
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to 3 months and 6 months a further reduction of 15% and 33% respectively was achieved for PPPft. The PTIft was significantly reduced (P , .01) at baseline, 3 months, and 6 months with the foot orthoses. When comparing shod verses with orthosis, a reduction of 14% was achieved at baseline with further reductions of 14% at 3 months and 33% at 6 months when compared to baseline. This shows that the foot orthoses do alter the function of the foot during dynamic gait to reduce the amount of time that the forefoot is in contact with the ground. These findings are in agreement with those of Otter et al,9 who investigated the magnitude and duration of peak forefoot plantar pressures in RA. They found that duration of pressure was significantly longer in the RA group compared with healthy adults. Reduced PTIft may result in decreased pain in the forefoot for the patient, and the findings suggest that this may be achieved as soon as the devices are worn inside the shoes. Furthermore, this reduced PTIft will help reduce deformity in the long-term because prolonged peak pressures on inflamed joints will inevitably contribute to the development of structural deformity. There was also a significant reduction in PTIft during the 6 months in the barefoot state (P , .01). This result suggests that after foot orthosis use, the foot is trained in some way to uphold the changes brought about by the device even when the foot orthoses are not being worn. The clinical implications of this are meaningful because it means that patients could expect to benefit from the foot orthoses at times when they may not be able to accommodate the devices in their footwear. Further research is required to determine how long this effect could last, yet it is a practical finding for clinicians providing holistic care. The off-the-shelf foot orthoses increased HLT, and this was seen at 6 months (P , .01). These
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findings suggest that the toe deformity has decreased and that the claw toes have become straighter and more functional. Claw toe deformity is associated with RA, and a reduced toe contact area means that the load-bearing area is decreased and so there is more pressure exerted over the metatarsal heads.23,24 Abnormal claw toe and metatarsal area loading in RA may occur as a result of muscle imbalance in the foot or from synovitis in the metatarsophalangeal joints. Muscle imbalance causing claw toe deformity often results from excessive subtalar joint pronation. When the medial longitudinal arch of the foot flattens with subtalar joint pronation, greater-than-normal tension is applied to the structures of the foot. If the flexor digitorum brevis muscle contracts first, the metatarsophalangeal joint dorsiflexes and the proximal and distal interphalangeal joints plantarflex, resulting in a claw toe.25 Small-joint synovitis that produces the daylight sign because of separation of the toes results in joint capsules and collateral ligaments being stretched and weakened. Consequently, first subluxation and eventual dislocation of the metatarsophalangeal joint occurs. This causes a muscle imbalance between the intrinsic and extrinsic muscles, resulting in progressive claw toe deformity.26 The foot orthoses may increase HLT by limiting abnormal subtalar joint pronation, thus maintaining medial longitudinal arch height. This, in turn, will prevent muscle imbalance and so improve lesser toe function. This is in agreement with the findings of Woodburn and Helliwell,27 who noted an important interrelation between the rearfoot position and forefoot pressure sites. No research has identified whether foot orthoses have a direct effect on inflammation, and so it is unknown whether the foot orthoses limit metatarsophalangeal joint subluxation and dislocation. One reason for the increase in HLT not occurring until 6 months is that the study population consisted of patients with early RA and so forefoot deformity, such as clawing of the lesser toes, could have been less severe than that seen in a population with more established disease. A smaller amount of deformity would produce less significant results. In addition, claw toe deformities are associated with distal migration of the fatty pad. Future long-term studies may explore the effects of orthoses on digital deformity but also potentially theoretical changes to fatty pad positioning that may have partly contributed to the incremental decrease in PPPft by 6 months when using orthotic devices owing to improved forefoot cushioning. There was no significant increase in MF at
baseline (P . .05) or at 3 months (P . .05) with shoes and with shoes and orthoses. However, there was a significant change at 6 months (P , .01). This increase was seen between the barefoot and orthoses states and between the shod and orthoses states that illustrate that the increase in MF is due to the foot orthoses and not to the shoes. These results suggest that it may take up to 6 months for MF to be significantly increased in patients with early RA. The increase in MF may indicate that the foot has readjusted to a new position according to Davis’s law. One of the main advantages of this study is that the HR Walkway and the F-Scan in-shoe systems recorded data at the same frequency and spatial resolution. This means that the same rate of sampling and the same number of sensors per square centimeter were used in each system. The size of the sensor is important because size can alter the pressure reading, as pressure depends on force and area. A force applied to a large sensor will not provide the same pressure reading as the same force applied over a small sensor.28 This makes the comparison between the barefoot, shod, and shoes with orthoses states exact. We are not aware of any other published research that has compared barefoot and in-shoe plantar pressures with a platform and an in-shoe system with the same resolution and sampling rate. The most important limitation of the study is that no control group was used to compare with the offthe-shelf foot orthoses. A randomized controlled trial to compare the effects of off-the-shelf foot orthoses with control orthoses is currently being designed and implemented.
Conclusions The findings from this study suggest that off-theshelf foot orthoses positively affect plantar foot pressures in patients with early RA. Clinicians may expect to see a decrease in PPPft and PTIft as soon as the patient starts to wear the devices in their shoes. Other benefits, such as an increase in HLT and an increase in MF by 6 months, might also be seen. The results also propose that foot orthoses could train the foot in some way so that patients continue to benefit from the devices even when they are not worn in their shoes. Further research to substantiate this finding is required. It is proposed that off-the-shelf foot orthoses used in the management of patients with early RA could lessen pain in the short-term and enhance foot health outcomes in the long-term.
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Financial Disclosure: None reported. Conflict of Interest: None reported.
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15. QUINN MA, CONAGHAN PG, EMERY P: The therapeutic approach of early intervention for rheumatoid arthritis: what is the evidence? Rheumatogy 40: 1211, 2001. 16. WORLD HEALTH ORGANIZATION: Chronic rheumatic conditions. Available at: http://www.who.int/chp/topics /rheumatic/en. Accessed November 14, 2007. 17. JACKSON L, BINNING J, POTTER J: Plantar pressure in rheumatoid arthritis using prefabricated metatarsal padding. JAPMA 94: 239, 2004. 18. TUNA H, BIRTANE M, TASTEKIN N, ET AL: Pedobarography and its relation to radiologic erosion scores in rheumatoid arthritis. Rheumatol Int 26: 42, 2005. 19. SEMPLE R, TURNER DE, HELLIWELL PS, ET AL: Regionalised centre of pressure analysis in patients with rheumatoid arthritis. Clin Biomech 22: 127, 2007. 20. CAMERON V, SANTOS D, OSBORNE A: A preliminary survey of podiatry services for patients with RA. Podiatry Now 12: 27, 2009. 21. MINNS RJ, CRAXFORD AD: Pressure under the forefoot in rheumatoid arthritis: a comparison of static and dynamic methods of assessment. Clin Orthop Relat Res 187: 235, 1984. 22. KEENAN MA, PEABODY TD, GRONLEY JK, ET AL: Valgus deformities of the feet and characteristics of gait in patients who have rheumatoid arthritis. J Bone Joint Surg Am 73: 237, 1991. 23. D’AMICO JC: The pathomechanics of adult rheumatoid arthritis affecting the foot. JAPA 66: 227, 1976. 24. HUGHES J, CLARK P, KLENERMAN L: The importance of the toes in walking. J Bone Joint Surg Br 72: 245, 1993. 25. MYERSON MS, SHEREFF MJ: The pathological anatomy of claw and hammer toe. J Bone Joint Surg Am 71: 45, 1989. 26. MOECKEL BH, SCULCO TP, ALEXIADES MM, ET AL: The doublestemmed silicone rubber implant for rheumatoid arthritis of the first metatarsophalangeal joint: long-term results. J Bone Joint Surg Am 74: 564, 1992. 27. WOODBURN J, HELLIWELL PS: Relation between heel position and the distribution of forefoot plantar pressure and skin callosities in rheumatoid arthritis. Ann Rheum Dis 55: 806, 1996. 28. SANTOS D: The Development of a System to Measure the Effects of Plantar Foot Pressure on the Microcirculation of the Foot [PhD thesis], Queen Margaret University, Edinburgh, 2006.
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Effects of Off-the-Shelf Foot Orthoses on Plantar Foot Pressures in Patients with Early Rheumatoid Arthritis Derek Santos, PhD* Vicki Cameron-Fiddes, PhD* Background: Rheumatoid arthritis (RA) often affects feet with progressive pathologic changes to foot morphology and pressure distribution. Studies in RA suggest that reductions in forefoot peak pressures can reduce pain. We investigated the effects of offthe-shelf foot orthoses on plantar foot pressures in patients with early RA. Methods: Thirty-five patients with early RA were recorded walking. Variables measured were forefoot peak plantar pressure (PPPft), forefoot pressure-time integral (PTIft), and hallux and lesser toe and midfoot contact areas. Patients were analyzed while walking barefoot, with shoes, and with shoes and foot orthoses. Measurements were taken at baseline and at 3 and 6 months. Results: There were significantly increased PPPft values between barefoot and shod and between barefoot and orthoses (P , .01). However, there was a significant reduction in PPPft during the 6 months with orthoses compared with shoes only (P , .01). Foot orthoses significantly reduced PTIft over 6 months (P , .01). Results also demonstrated a significant increase in hallux and lesser toe (P , .01) and midfoot (P , .01) contact areas during the 6 months with foot orthoses. Conclusions: In patients with early RA, off-the-shelf foot orthoses cause a significant reduction of 22% in PPPft and 14% in PTIft as soon as insoles are worn compared with shod. Further reductions for orthoses compared with baseline were found by 3 months (15% in PPPft and 14% in PTIft) and 6 months (33% in PPPft and 33% in PTIft). These findings could contribute to reductions in foot pain. (J Am Podiatr Med Assoc 104(6): 610-616, 2014)
Patients with early rheumatoid arthritis (RA) often note pain over the ball of the foot, likened to ‘‘walking on pebbles.’’ This can lead to reduced activity and a poor quality of life.1 As the disease becomes more established, forefoot plantar pressures are known to further increase, as the lesser toes start to claw, and distal displacement of the plantar fat pad occurs.2 Peak plantar pressures in the forefoot in RA have been shown to be associated with severe pain and tissue breakdown.3 This makes patients with RA at risk for foot ulceration and subsequent infection and amputation.4 Functional foot orthoses are special insoles worn inside the shoe to control any abnormal movement of the foot during walking to limit foot pain and *Queen Margaret University, Edinburgh, School of Health Sciences, Musselburgh, Scotland. Corresponding author: Derek Santos, PhD, Queen Margaret University, Edinburgh, School of Health Sciences, Queen Margaret University Dr, Musselburgh, East Lothian EH21 6UU, United Kingdom. (E-mail: [email protected])
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deformity.5 Podiatric physicians use foot orthoses in the management of RA to reduce pressure over the forefoot by redistributing the forces more equally over the plantar surface of the foot. This is achieved by increasing the contact area of the hallux and lesser toes and of the midfoot.6 Redmond et al7 found that prefabricated orthotic devices increased hallux contact area by 3.6% and midfoot contact area by 32.6%. In addition, foot orthoses may influence foot function and so are capable of altering the timing of the phases of gait.8 Otter et al9 found that peak pressures in the forefoot of patients with RA were similar to those in participants in a control group, but what was different was that patients with RA significantly prolonged the duration that these peak pressures were applied to the forefoot. They attributed these findings to reduced walking speed and increased double support time. In comparison, the control group had a more transient or reduced duration of peak pressures applied to the forefoot.9 Otter et al9 suggested that this prolonged duration
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of peak pressures applied to the forefoot may account for pain and greater deformity in the RA group. Because duration of pressure can be investigated using the pressure-time integral, this is a useful variable to evaluate the effects of prolonged peak plantar pressures.8,9 We investigated whether an off-the-shelf functional foot orthosis reduces the pressure-time integral (ie, the duration that peak pressures are applied to the sole of the foot) and its effect on pain. Custom-molded foot orthoses are specially made for the individual and have been shown to be effective in patients with RA.10-12 However, the process of manufacturing these custom-molded devices can be lengthy and expensive.13,14 Off-theshelf foot orthoses are ready-made devices that can be dispensed at the chairside on the day of diagnosis and have been shown to achieve comparable kinetic results as custom-molded foot orthoses.7 This has important clinical implications for patients with RA, as early intervention is thought to make a difference in long-term outcome, and in the short-term it relieves severe pain and disability.15 This often means the difference between staying at work and becoming unemployed.16 This study examines patients diagnosed as having RA in the past 2 years. All of the previous studies investigating foot pressures in RA have included patients with more established disease (mean disease duration, 8–22 years).6,9,17-19 Research is needed to provide clinicians with evidence of optimal management for patients with early disease if current guidelines advocating early intervention are to be met. The aim of this study was to investigate the effects of off-theshelf foot orthoses on plantar foot pressures in patients with early RA.
Methods Participants Thirty-five patients (6 men and 29 women) participated in the study, with data collected for each participant over a 6-month period. This ratio of men to women reflects average prevalence rates. Participants were 26 to 80 years of age (mean 6 SD age, 52.4 6 13.3 years). Disease duration ranged from 1 month to 1 year and 9 months (mean 6 SD disease duration, 0.7 6 0.6 years). No individual had been managed previously with foot orthoses. Patients with concomitant musculoskeletal disease, endocrine disorders (especially diabetes mellitus), and neurologic disease were also excluded from the study. Ethical approval was obtained from the
Queen Margaret University Research Ethics Committee, Edinburgh, East Lothian, UK, and the NHS South East Scotland Research Ethics Committee, Edinburgh, Lothian, UK. Equipment The HR Walkway and F-Scan in-shoe plantar pressure measurement systems (Tekscan, Boston, Massachusetts) were used to investigate the effects of off-the-shelf foot orthoses on plantar pressure. The HR Walkway and F-Scan in-shoe systems record data at the same frequency with the spatial resolution of 4 sensels/cm2, allowing comparisons to be made between the barefoot and in-shoe states. Procedure The study design was a within-subject controlled study. Patients presented for data collection at baseline, 3 months, and 6 months. Patients randomly walked barefoot, with shoes only, and with shoes and foot orthoses. The type of foot orthosis used was the Slimflex Plastic (A. Algeo Ltd, Liverpool, England).20 Patients wore standardized footwear throughout the study. At each visit, the patient was weighed with validated electronic scales. The correct size of shoe was then selected for each patient, and a new F-Scan insole was trimmed to fit inside the shoe. The patient then conditioned the HR Walkway and the sensor insole, as recommended by the manufacturer, before data collection. The two systems were then calibrated using the patient’s weight. Six walking trials were recorded with the HR Walkway when the patient was barefoot. With the in-shoe system, six walking trials were recorded with shoes only and six trials with shoes and foot orthoses. No individual wore socks or hosiery. The same procedure was repeated at 3 and 6 months. The same set of in-shoe sensor insoles were used for each individual patient at all three of the data time points. Data Analysis A repeated-measures design was used. Peak plantar pressure in the forefoot (PPPft), pressure-time integral in the forefoot (PTIft), hallux and lesser toe contact area (HLT), and midfoot contact area (MF) were the variables measured. These variables were tested for normal distribution using ShapiroWilks tests, box plots, and histograms. All PPPft and PTIft values presented with a nonparametric distribution. All HLT and MF values were found to have a
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Table 1. Peak Plantar Pressure at the Forefoot Measured at Baseline, 3 Months, and 6 Months Forefoot Peak Plantar Pressure (kPa) Barefoot State Period
Shod State
Shod Wearing Orthoses State
Median (IQR)
Mean 6 SD
Median (IQR)
Mean 6 SD
Median (IQR)
Mean 6 SD
P Value
Baseline
334 (474)
347 6 100
1,691 (4,432)
2177 6 1,369
1,325 (9,355)
2,032 6 1,755
.001a
3 months
335 (588)
349 6 110
1,726 (3,668)
1,900 6 1,083
1,124 (3,697)
1,401 6 912
.001a
6 months
362 (531)
356 6 121
1,117 (3,420)
1,453 6 887
1,158 6 1,412
.001a
P values
.217
.001a
892 (8,081)
.001a
Note: The data for these variables were nonparametric, hence the median values are more representative of the measure of centrality of the data. Abbreviation: IQR, interquartile range. a Shows statistically significant differences at P , .01.
parametric distribution, with skewness and kurtosis between 1 and 1. Statistical analyses were then undertaken to compare any potential effects of the foot orthoses over time (ie, baseline, 3 months, and 6 months) for each separate state and between states (ie, barefoot, shod, and shod with orthoses). The significance level was set at 5% (P , .05). For parametric data, a repeated-measures analysis of variance test was used where sphericity was achieved. Pairwise comparisons determined where the significant changes were occurring. For nonparametric data, a Friedman test was used. An exact Wilcoxon signed rank test with Bonferroni multiple corrections was performed to determine where the significant changes were occurring. With Bonferroni multiple comparisons, the significance level was adjusted accordingly by dividing the P value by the number of comparisons being tested, so significance was set at P , .02. Data were analyzed with SPSS for Windows, version 16.0 (SPSS Inc, Chicago, Illinois).
Results All of the tables show mean 6 SD and median (interquartile range) values for patients walking (ie, barefoot, with shoes, and with shoes and foot orthoses) at baseline, 3 months, and 6 months. For the nonparametric variables (ie, PPPft and PTIft), the median is more representative of the measure of centrality, hence this is reported in the text. For the parametric variables (ie, HLT and MF), the mean is reported in the text because it is more reflective of the measure of centrality. Table 1 shows that there was no significant change in PPPft in the barefoot state during the 6 months (P . .05). In the shod state there was a significant change in PPPft during the 6 months (P
612
, .01). This change was a significant increase in median pressure between baseline (1,691 kPa) and 3 months (1,726 kPa) (P , .01) but a significant decrease in median PPPft between baseline (1,691 kPa) and 6 months (1,117 kPa) and between 3 months (1,726 kPa) and 6 months (1,117 kPa) (P , .01). There was also a significant change in the orthoses state over the 6 months (P , .01). This was also a significant reduction in median PPPft occurring between baseline (1,325 kPa) and 3 months (1,124 kPa), baseline (1,325 kPa) and 6 months (892 kPa), and 3 months (1,124 kPa) and 6 months (892 kPa) (P , .01). At baseline, 3 months, and 6 months, there were significant variations in PPPft (P, .01) across the barefoot, shod, and orthoses states. There was a significant decrease in PPPft between the shod and orthoses states (P , .01); however, there was a significant increase in PPPft at baseline, 3 months, and 6 months between the barefoot and shod states and between the barefoot and orthoses states (P , .01). Thus, overall, all of the barefoot pressures were significantly lower than those of the shod and orthoses states. Table 2 shows that there was a significant change in PTIft during the 6 months in the barefoot, shod, and orthoses states (P , .01). Overall, the orthoses state showed the lowest median PTIft values at baseline (53 kPa.s), 3 months (46 kPa.s), and 6 months (36 kPa.s), with a trend toward a reduction of PTIft during the 6 months (P , .01). The shod state also showed a trend toward a reduction in median PTIft from baseline (62 kPa.s) to 3 months (61 kPa.s) to 6 months (50 kPa.s) (P , .01), although the values were higher than those for the orthoses state. The barefoot state showed the highest median PTIft values, with an increase from baseline (66 kPa.s) to 3 months (68 kPa.s) and a
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Table 2. Pressure-Time Integral at the Forefoot Measured at Baseline, 3 Months, and 6 Months Forefoot Pressure-Time Integral (kPa.s) Barefoot State Period
Shod State
Shod Wearing Orthoses State
Median (IQR)
Mean 6 SD
Median (IQR)
Mean 6 SD
Median (IQR)
Mean 6 SD
P Value
Baseline
66 (280)
97 6 63
62 (257)
73 6 59
53 (206)
55 6 40
.001a
3 months
68 (218)
88 6 53
61 (204)
66 6 50
46 (173)
51 6 39
.001a
6 months
61 (204)
78 6 45
50 (182)
59 6 48
36 (156)
47 6 38
.001a
.001a
P values
.001a
.001a
Note: The data for these variables were nonparametric, hence the median values are more representative of the measure of centrality of the data. Abbreviation: IQR, interquartile range. a Shows statistically significant differences at P , .01.
barefoot state during the 6 months (P . .01), as shown in Table 4. There were, however, significant changes in the shod and orthoses states during the 6 months (P , .01). In the shod state, these significant changes in mean MF were between baseline (23.9 cm2) and 6 months (31.3 cm2) (P , .01) and between 3 months (26.3 cm2) and 6 months (31.3 cm2) (P , .01). In the orthoses state, there was a significant change in mean MF at all of the time points (baseline, 23.9 cm2; 3 months, 28.8 cm2; 6 months, 35.1 cm2) (P , .01). There was no significant change in mean MF at baseline or at 3 months across the three states (P . .05 for both). There was, however, a significant increase in mean MF at 6 months among the three states (P , .01). This significance was between the barefoot (28.5 cm2) and orthoses (35.1 cm2) states (P , .01) and between the shod (31.3 cm2) and orthoses (35.1 cm2) states (P , .01).
decrease from 3 months (68 kPa.s) to 6 months (61 kPa.s). There was no significant change in HLT in the barefoot state (P . .05) or the shod state (P . .05) during the 6 months (Table 3). There was a significant change, however, in mean HLT in the orthoses state during the 6 months (P , .01). This significant increase in mean HLT was between baseline (14.5 cm2) and 6 months (18.0 cm2) (P , .01) and between 3 months (14.3 cm2) and 6 months (18.0 cm2) (P , .01). Between states, at baseline there was a significant change between barefoot, shod, and orthoses states (P , .01). At 3 months there was a significant decrease in mean HLT between the barefoot (15.3 cm2) and shod (10.7 cm2) states (P , .01) and a significant increase in mean HLT between the shod (10.7 cm2) and orthoses (14.3 cm2) states (P , .01). There was a significant increase in mean HLT across the three states at 6 months (P , .01). Overall, by 6 months the orthoses state showed the greatest mean HLT (18.0 cm2) compared with the shod (12.1 cm2) and barefoot (14.0 cm2) states (P , .01). There was no significant change in MF in the
Discussion At baseline, PPPft was significantly reduced between the shod and orthoses states (P , .001). This
Table 3. Contact Area for the Hallux and Lesser Toes Measured at Baseline, 3 Months, and 6 Months Hallux and Lesser Toes Contact Area (cm2) Barefoot State
Shod State
Shod Wearing Orthoses State
Period
Mean 6 SD
Median (IQR)
Mean 6 SD
Median (IQR)
Mean 6 SD
Median (IQR)
P Value
Baseline
14.5 6 4.2
15.0 (18.7)
12.0 6 6.0
11.8 (27.5)
14.5 6 6.5
14.1 (24.8)
.005a
3 months
15.3 6 4.6
15.2 (18.8)
10.7 6 4.9
10.0 (19.5)
14.3 6 5.8
14.1 (22.3)
.001a
6 months
14.0 6 4.4
13.6 (18.8)
12.1 6 5.0
12.1 (19.5)
18.0 6 6.5
18.0 (22.5)
.001a
P value
.054
.117
.001
a
Note: The data for these variables were parametric, hence the mean values are more representative of the measure of centrality of the data. Abbreviation: IQR, interquartile range. a Shows statistically significant differences at P , .01.
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Table 4. Contact Area at the Midfoot Measured at Baseline, 3 Months, and 6 Months Midfoot Contact Area (cm2) Barefoot State Period
Mean 6 SD
Median (IQR)
Shod State Mean 6 SD
Median (IQR)
Shod Wearing Orthoses State Mean 6 SD
Median (IQR)
P Value
Baseline
26.4 6 10.0
26.5 (48.0)
23.9 6 9.8
24.2 (44.1)
23.9 6 10.1
23.5 (47.9)
.166
3 months
27.6 6 10.4
27.2 (50.8)
26.3 6 9.3
26.3 (46.9)
28.8 6 8.8
29.0 (42.8)
.065
6 months
28.5 6 10.4
26.3 (46.5)
31.3 6 9.6
30.7 (47.2)
35.1 6 9.6
36.6 (46.1)
.001a
P values
.375
.001a
.001a
Note: The data for these variables were parametric, hence the mean values are more representative of the measure of centrality of the data. Abbreviation: IQR, interquartile range. a Shows statistically significant differences at P , .01.
finding is of great clinical consequence because it shows that PPPft will be reduced as soon as the patient starts to wear the orthoses in their shoes, and so patients may experience some immediate relief from forefoot pain with foot orthoses. This outcome strengthens the argument for the use of off-the-shelf foot orthoses in patients with early RA because the patient will receive early intervention and so meet the recommendations set out in the current guidelines. There was an 84% increase in PPPft at baseline between the barefoot and shod states and an 83% increase between the barefoot and orthoses states. Comparable results were found at 3 and 6 months, suggesting that PPPft is greater in patients with early RA when they wear shoes with and without foot orthoses compared with the barefoot state. Minns and Craxford21 state that changes seen in the gait of individuals with RA may be a pain-avoidance strategy. A possible reason for this finding is, therefore, that the patient has altered his or her walking pattern to prevent weightbearing on the painful forefoot during barefoot walking. Semple et al19 investigated center of pressure analysis in RA and found a delay of the anterior progression of the center of pressure that remained in the midfoot approximately 6% of stance duration longer than normal. This was followed by rapid transfer of the center of pressure through the forefoot, spending 5% of stance duration less than in the control group. These findings support the conclusions of Keenan et al,22 who described gait changes in patients with RA. The PPPft was significantly increased with shoes, signifying that the patient’s gait is no longer trying to avoid forefoot pain. The significant reduction in PPPft between the shod and orthoses states of 22% demonstrates that the foot orthoses do reduce PPPft and that this effect is due to the foot orthoses and not to the footwear. When comparing baseline
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to 3 months and 6 months a further reduction of 15% and 33% respectively was achieved for PPPft. The PTIft was significantly reduced (P , .01) at baseline, 3 months, and 6 months with the foot orthoses. When comparing shod verses with orthosis, a reduction of 14% was achieved at baseline with further reductions of 14% at 3 months and 33% at 6 months when compared to baseline. This shows that the foot orthoses do alter the function of the foot during dynamic gait to reduce the amount of time that the forefoot is in contact with the ground. These findings are in agreement with those of Otter et al,9 who investigated the magnitude and duration of peak forefoot plantar pressures in RA. They found that duration of pressure was significantly longer in the RA group compared with healthy adults. Reduced PTIft may result in decreased pain in the forefoot for the patient, and the findings suggest that this may be achieved as soon as the devices are worn inside the shoes. Furthermore, this reduced PTIft will help reduce deformity in the long-term because prolonged peak pressures on inflamed joints will inevitably contribute to the development of structural deformity. There was also a significant reduction in PTIft during the 6 months in the barefoot state (P , .01). This result suggests that after foot orthosis use, the foot is trained in some way to uphold the changes brought about by the device even when the foot orthoses are not being worn. The clinical implications of this are meaningful because it means that patients could expect to benefit from the foot orthoses at times when they may not be able to accommodate the devices in their footwear. Further research is required to determine how long this effect could last, yet it is a practical finding for clinicians providing holistic care. The off-the-shelf foot orthoses increased HLT, and this was seen at 6 months (P , .01). These
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findings suggest that the toe deformity has decreased and that the claw toes have become straighter and more functional. Claw toe deformity is associated with RA, and a reduced toe contact area means that the load-bearing area is decreased and so there is more pressure exerted over the metatarsal heads.23,24 Abnormal claw toe and metatarsal area loading in RA may occur as a result of muscle imbalance in the foot or from synovitis in the metatarsophalangeal joints. Muscle imbalance causing claw toe deformity often results from excessive subtalar joint pronation. When the medial longitudinal arch of the foot flattens with subtalar joint pronation, greater-than-normal tension is applied to the structures of the foot. If the flexor digitorum brevis muscle contracts first, the metatarsophalangeal joint dorsiflexes and the proximal and distal interphalangeal joints plantarflex, resulting in a claw toe.25 Small-joint synovitis that produces the daylight sign because of separation of the toes results in joint capsules and collateral ligaments being stretched and weakened. Consequently, first subluxation and eventual dislocation of the metatarsophalangeal joint occurs. This causes a muscle imbalance between the intrinsic and extrinsic muscles, resulting in progressive claw toe deformity.26 The foot orthoses may increase HLT by limiting abnormal subtalar joint pronation, thus maintaining medial longitudinal arch height. This, in turn, will prevent muscle imbalance and so improve lesser toe function. This is in agreement with the findings of Woodburn and Helliwell,27 who noted an important interrelation between the rearfoot position and forefoot pressure sites. No research has identified whether foot orthoses have a direct effect on inflammation, and so it is unknown whether the foot orthoses limit metatarsophalangeal joint subluxation and dislocation. One reason for the increase in HLT not occurring until 6 months is that the study population consisted of patients with early RA and so forefoot deformity, such as clawing of the lesser toes, could have been less severe than that seen in a population with more established disease. A smaller amount of deformity would produce less significant results. In addition, claw toe deformities are associated with distal migration of the fatty pad. Future long-term studies may explore the effects of orthoses on digital deformity but also potentially theoretical changes to fatty pad positioning that may have partly contributed to the incremental decrease in PPPft by 6 months when using orthotic devices owing to improved forefoot cushioning. There was no significant increase in MF at
baseline (P . .05) or at 3 months (P . .05) with shoes and with shoes and orthoses. However, there was a significant change at 6 months (P , .01). This increase was seen between the barefoot and orthoses states and between the shod and orthoses states that illustrate that the increase in MF is due to the foot orthoses and not to the shoes. These results suggest that it may take up to 6 months for MF to be significantly increased in patients with early RA. The increase in MF may indicate that the foot has readjusted to a new position according to Davis’s law. One of the main advantages of this study is that the HR Walkway and the F-Scan in-shoe systems recorded data at the same frequency and spatial resolution. This means that the same rate of sampling and the same number of sensors per square centimeter were used in each system. The size of the sensor is important because size can alter the pressure reading, as pressure depends on force and area. A force applied to a large sensor will not provide the same pressure reading as the same force applied over a small sensor.28 This makes the comparison between the barefoot, shod, and shoes with orthoses states exact. We are not aware of any other published research that has compared barefoot and in-shoe plantar pressures with a platform and an in-shoe system with the same resolution and sampling rate. The most important limitation of the study is that no control group was used to compare with the offthe-shelf foot orthoses. A randomized controlled trial to compare the effects of off-the-shelf foot orthoses with control orthoses is currently being designed and implemented.
Conclusions The findings from this study suggest that off-theshelf foot orthoses positively affect plantar foot pressures in patients with early RA. Clinicians may expect to see a decrease in PPPft and PTIft as soon as the patient starts to wear the devices in their shoes. Other benefits, such as an increase in HLT and an increase in MF by 6 months, might also be seen. The results also propose that foot orthoses could train the foot in some way so that patients continue to benefit from the devices even when they are not worn in their shoes. Further research to substantiate this finding is required. It is proposed that off-the-shelf foot orthoses used in the management of patients with early RA could lessen pain in the short-term and enhance foot health outcomes in the long-term.
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Financial Disclosure: None reported. Conflict of Interest: None reported.
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November/December 2014 Vol 104 No 6 Journal of the American Podiatric Medical Association
