Effectiveness of Custom-Made Orthopaedic Shoes in the Reduction of Foot Pain and Pressure in Patients with Degenerative Disorders of the Foot

Abstract

Background:

Degenerative disorders of the foot often are painful during standing and walking. It is assumed that, because of bone deformity, callus, and deformity of the plantar pads, the plantar pressure distribution changes. Prescription of orthopaedic shoes for patients with degenerative disorders of the foot is based on the hypothesis that excessive pressure under the foot causes pain. The goal of this study was to evaluate the effectiveness of custom-made orthopaedic shoes, in terms of pressure and pain, in patients with degenerative disorders of the foot. Additionally, the relationship between plantar pressure parameters and foot pain was studied, with special emphasis on second and third metatarsal heads.

Methods:

Seventy-seven consecutive patients with degenerative disorders of the foot were recruited from the outpatient clinics of seven rehabilitation centers and rehabilitation departments of university hospitals in the Netherlands. The study was prospective. The Questionnaire for Usability Evaluation for Orthopaedic Shoes was used to measure perceived foot pain. To measure plantar pressures, the Pedar in-shoe pressure measurement system (Novel GmbH, Munich) was used. The effectiveness of custom-made orthopaedic shoes, in terms of pressure and pain in patients with degenerative disorders of the foot, was analyzed by means of a paired sample t-test. To select the pressure parameter (Pmax, P_TI, and P_av) most closely associated with walking pain, within-subject correlation coefficients were calculated.

Results:

Custom-made orthopaedic shoes significantly decreased perceived foot pain by at least 23%, and significantly reduced plantar pressure under all foot regions by at least 9%. A significant correlation (r = 0.521) was found between walking pain and the average pressure beneath the second and third metatarsal heads.

Conclusions:

Based on these results, it can be concluded that custom-made orthopaedic shoes are effective in reducing foot pain and foot pressure. The moderate (significant) relationship between average pressure and walking pain can be used as a tool for evaluating custom-made orthopaedic shoes prescribed for patients with degenerative disorders of the foot.

Keywords

Degenerative Foot Pain Foot Pressure Orthopaedic Shoes

INTRODUCTION

Degenerative disorders of the foot are common in older individuals. Surveys have reported a 10% to 24% prevalence of self-reported foot abnormalities in adults, with the highest rates being found in women and in individuals 65 years of age or older.^8,11,28 The following disorders of the foot are characteristic of the degenerative foot: arthritis of the ankle and subtalar and midtarsal joints, Achilles tendinitis, plantar fasciitis, posterior tibial tendinitis, hallux valgus, prominent or subluxed metatarsal heads, hallux rigidus, claw toes, and hammer toes. As a consequence of the changed shape of the foot, degenerative disorders often are painful during standing and walking.

It is assumed that, because of bone deformity, callus, and deformity of the plantar pads, the plantar pressure distribution changes.¹³ As a result normally unloaded foot regions may become overloaded or more sensitive to pressure.¹³ In general, clinicians try to redistribute plantar pressure over the plantar surface to reduce the pressure in these overloaded foot regions by means of orthopaedic shoes or shoe adaptations. Prescriptions for custom-made orthopaedic shoes for patients with degenerative disorders of the foot are based on the hypothesis that excessive pressure under the foot causes pain. More specifically, pain in the forefoot (under the metatarsal heads) is the problem that is most frequently mentioned.²¹ The prescription of custom-made orthopaedic shoes is mostly a process in which the orthopaedic shoe or inlay is molded in such a way that pressure in painful areas is reduced. In-shoe pressure measurement systems are being used more frequently to obtain objective and more precise information concerning the pressure distribution between foot sole and shoe. However, the relationships between foot pressure parameters and foot pain during walking in patients with degenerative disorders of the foot are not clear. An understanding of the relationship between pressure parameters measured in degenerative disorders of the foot and foot pain will improve the clinical management of these patients.

The clinical practice of redistributing plantar pressure to alleviate foot pain and the availability of foot pressure measurements prompted this study in which we compared perceived foot pain and the plantar pressure between ordinary shoes and custom-made orthopaedic shoes in patients with degenerative disorders of the foot. Additionally, the relationship between plantar pressure parameters (peak pressure, pressure-time integral, and average pressure) under the second and third metatarsal heads during stance phase and perceived foot pain during walking was studied in patients with degenerative disorders of the foot.

MATERIALS AND METHODS

Subjects

A total of 77 consecutive patients with degenerative disorders of the foot were recruited from the outpatient clinics of seven rehabilitation centers and rehabilitation departments of university hospitals in the Netherlands, from September, 2001, to February, 2003.

The inclusion criteria specified that patients had degenerative disorders of the foot accompanied by foot pain, had a prescription for custom-made orthopaedic shoes, were able to read Dutch, and were older than 18 years. Rehabilitation specialists associated with the seven participating centers established the presence of degenerative disorders of the foot.

Patients were excluded if they had rheumatoid arthritis, diabetes mellitus, neurologic disorders, or active infections, or if they were taking analgesics, were wheelchair bound, had experience with orthopaedic shoes, or were to receive off-the-shelf orthopaedic shoes. Table 1 gives the baseline characteristics of the study population. Three months after the delivery of their orthopaedic shoes, 64 patients (83%) wore their orthopaedic shoes more than 3 days per week, and 13 patients (17%) wore their orthopaedic shoes fewer than 3 days per week.

Measurements

The Questionnaire for Usability Evaluation of Orthopaedic Shoes (QUE) was used to measure foot pain in several situations (standing, walking, climbing stairs, activities of daily life, and work).^14,15 The foot pain-related items in the QUE were rated on a visual analogue scale (VAS). The VAS consisted of a straight, horizontal line, 100 mm long bounded by two anchor phrases (‘little pain’ and ‘severe pain'). The line was not divided into any sections. Besides foot pain, the amount of use of custom-made orthopaedic shoes was measured by means of the QUE.¹⁴ The QUE is a reliable (reproducible, internally consistent) questionnaire.^14,15

Table 1:

Summary of baseline characteristics of study population

Variable	N = 77
Age (years: mean (SD))	60.5 (14.8)
Gender
male	30 (39%)
female	47 (61%)
Degenerative disorder (n)^*
arthrosis	30
Achillis tendinitis	2
plantar fasciitis	2
tibialis posterior tendonitis	0
hallux valgus	35
prominent metatarsal heads	58
hallux rigidus	34
claw toes	32
hammer toes	18

More than one degenerative disorder per person can be present.

Apparatus

To measure plantar pressures, an in-shoe pressure measurement system (Pedar-mobile expert version 129wo; novel-win version 08.7, Novel GmbH, Munich, Germany) was used. It has been demonstrated that this Pedar in-shoe pressure measurement system is reliable and valid.¹⁷ Insoles consisted of 256 matrix-configured sensors, each of which was sampled at 50Hz. With the aid of the Trublu calibration device (Novel GMGH, Munich, Germany), all sensors in the insoles were individually calibrated with air pressure. By means of homogeneous air pressure on all sensors through incrementally increased steps in pressure, a calibration curve was retrieved. Calibration occurred every 3 months, as prescribed by the manufacturer (www.emed.de/productinfo/systems.pedar.htm).

Custom-made Orthopaedic Shoes

Custom-made orthopaedic shoes were defined as complete individually manufactured low or high shoes (Figure 1). A more detailed prescription and characterization of these custom-made orthopaedic shoes are published elsewhere.¹⁵ The orthopaedic shoe technician used a blue-print of the foot, a plaster cast of the foot, and a vacuum footprint to manufacture an individual last. The individual last was used to make a plastic proof shoe, which is a transparent shoe by which orthopaedic shoe technicians and medical specialists can examine the foot for pressure points, with which the clinicians and orthopaedic shoe technicians detected pressure points and studied the patient's gait cycle on an empirical base. After this evaluation, the final custom-made orthopaedic shoe was manufactured. All custom-made orthopaedic shoes were provided with custom-made insoles made of Plastazote (Zole Foams Inc., Walton, KY) and PPT (Sammons Preston, Rolyan, IL). Plastazote is a foamed polyethylene with a closed-cell construction, and PPT is an open-cell, porous, firm foam material that relieves local pressure, labelled as a ‘high energy-absorbing substance'.

Procedures

The study was conducted as a cohort study. Each patient was examined by a rehabilitation specialist who explained the project. The protocol was approved by the local Human Ethics Committee, and all subjects signed a disclosure form and informed consent. Subjects were assessed twice: a baseline assessment was made of the patients wearing their present shoes, 1 month before receiving custom-made orthopaedic shoes (T0), and a followup measurement was made 3 months after delivery of the custom-made orthopaedic shoes (T1).

At T0 and at T1, the measurement insoles were positioned according to the manufacturer's protocol (Novel GmbH, Munich, Germany). Each subject was allowed 5 minutes to get used to the measurement insoles. Measurements were taken during seven separate trials along a straight, level walkway. As in previous studies, subjects walked at a self-chosen, comfortable walking speed.^1,6,13,18,22 They were allowed to use their personal walking aids (walking stick or crutch). As it is likely that there is a relationship between the two feet of an individual, it was decided to focus only on the right foot during the stance phase in this study. Six stance phases on the right limb from each subject in each test condition were selected for analysis using the following process.

In the middle of a 10-meter long walkway, six stance phases on the right limb of each measured trial were studied, thereby excluding start and end effects. First, the total stance phase duration, the duration taken to record six stance phases on the right limb, of each trial was determined by summation of these six stance phases. Subsequently, the median total stance phase duration was calculated over seven trials. Compared to the mean stance phase duration, the median stance phase duration is less sensitive for outliers. The trial with the median total stance phase duration and two trials adjacent to it were further analyzed. For each of these three trials, the median stance phase time was calculated. Finally, the step with the median stance phase time and the step most similar to this median stance phase time were selected for further analysis. The EMED Pedar Link program (Novel GMGH, Munich, Germany) was used to select these six stance phases (two stance phases × three trials) for further analysis in the EMED Multimask Evaluation program (Novel GMGH, Munich, Germany).

Pressure parameters were calculated for each of nine foot regions: lateral hindfoot (LH), medial hindfoot (MH), lateral midfoot (LM), medial midfoot (MM), first metatarsal head (MTH1), second and third metatarsal heads (MTH2-3), fourth and fifth metatarsal heads (MTH4-5), hallux (H), and toes 2–5 (T2-5). For each region, an average score from six steps was calculated for peak pressure, average pressure, and pressure-time integral. Peak pressure (Pmax; N/cm²) was defined as the maximal pressure that occurred in each region. The pressure-time integral (P_TI; N.s/cm²) equaled the area under the pressure-time curve. The average pressure (Pav; N/cm²) per region was calculated by dividing the pressure-time integral by the time in that particular region.

The QUE was used to measure foot pain at T0 and T1. Patients completed the QUE at home at most 3 days before the foot pressure measurement. Written instructions were given on how to complete the QUE.

Statistical Analysis of Data

For each subject in each condition, an average score from six steps was calculated for peak pressure, average pressure, and pressure-time integral. The effectiveness of custom-made orthopaedic shoes, in terms of pressure and pain in patients with degenerative disorders of the foot, was evaluated by means of a paired sample t-test. Significance was determined at the p = 0.05 level for all tests. Because the probability of finding at least one significant difference is higher than the nominal significance level adopted, a modification by Simes²⁴ was applied. By means of this method the p values were ordered such that p (1) ≤ p (2) ≤ …. p (p). The null hypothesis was rejected at level α if any p(j) ≤ jα/p.

To select the pressure parameter (Pmax, P _TI, and P _av) most closely associated with walking pain, pressure parameters in the second through third metatarsal heads region were studied by calculating within-subject correlation coefficients.²⁵ The within-subject correlation coefficient measures the correlation of foot-pressure deviances and walking-pain deviances within subjects. This correlation was calculated as the correlation coefficient between the within-subject deviation scores of foot-pressure under the second through third metatarsal heads and walking pain.

RESULTS

The mean stance-phase duration wearing ordinary shoes was 0.756 (0.152) seconds, while wearing orthopaedic shoes the mean stance-phase duration was 0.708 (0.130) seconds. A paired t-test indicated a significant difference in stance-phase duration between walking with ordinary shoes and walking with orthopaedic shoes (p = 0.002). However, in respect to the gait cycle (duration stance phase 60%) this would mean a change in walking velocity of about 0.08 m/s between shoewear conditions. According to Perry et al.²⁰, a difference of 0.2 m/s is a clinically reluctant difference in stroke patients.

Foot Pain

The data were analyzed to investigate whether custom-made orthopaedic shoes with inserts had any effect on subjective perceptions of foot pain during standing, walking, climbing stairs, activities of daily life, and work. The mean and standard deviation VAS scores are listed in Table 2. For all situations (standing, walking, climbing stairs, activities of daily life, and work), pain significantly decreased by at least 23% when patients wore orthopaedic shoes with insoles instead of their ordinary shoes.

Table 2:

Comparison of foot pain during standing, walking, climbing stairs, activities of daily life, and work activities between ordinary shoes and orthopaedic shoes

Activities	Ordinary shoes	Orthopaedic shoes	Pain decrease (%)	P
Pain during standing	6.3 (2.7)	3.5 (3.2)	44	0.000
Pain during walking	7.1 (2.6)	5.5 (2.5)	23	0.001
Pain during climbing stairs	3.4 (3.8)	2.2 (3.2)	35	0.007
Pain during activities of daily life	5.2 (3.2)	3.1 (3.5)	40	0.000
Pain during work activities	3.9 (3.9)	2.1 (3.2)	46	0.000

α = 0.05.

The Effect of Custom-made Orthopaedic Shoes on Peak Pressure, Pressure Time Integral, and Average Pressure in Nine Foot Regions

Analyses of the effect of orthopaedic shoes on plantar pressure focused on peak pressure (Pmax), pressure time integral (PTI), and average pressure (Paverage) within each region. A paired t-test was used to study the effect of custom-made orthopaedic shoes on Pmax, PTI, and Paverage pressures for nine regions under the foot. Table 3 shows the mean (standard deviation) pressure parameter data for 77 patients walking with ordinary shoes and orthopaedic shoes. The paired t-test indicated that the plantar pressure under all nine regions significantly decreased by at least 9 % when wearing custom-made orthopaedic shoes with insoles instead of ordinary shoes.

Associations Between Foot Pain During Walking and Foot Pressure Parameters

The highest correlation was found between average pressure and walking pain (Table 4).

Approximately 27% (R²) of the variability could be attributed to the observed association between average pressure and walking pain.

DISCUSSION

The results of this study show that custom-made orthopaedic shoes with custom insoles significantly decrease foot pain during standing, walking, climbing stairs, activities of daily life, and working activities by at least 23% within 3 months. Such results have been reported in several other studies, which found that orthopaedic shoes (custom-made or off-the-shelf) decreased pain during weightbearing activities such as standing and walking.^{4,5,7,16,19,20,26,27}

Previous studies have reported higher plantar pressures as a result of higher walking speeds^17,29 and, therefore, suggested to standardizing walking speed during pressure measurements.^2,9,23 In the present study, however, it was decided not to standardize walking speed by means of a treadmill but to allow patients to walk at their normal comfortable speed and to use stance phase duration as an outcome parameter. According to Cavanagh and Ulbrecht,⁶ this is more meaningful than attempting to make the patients conform to a set of conditions that may be unnatural for them. In the present study, the mean stance-phase duration wearing ordinary shoes was 0.756 (0.152) seconds, while wearing orthopaedic shoes the mean stance-phase duration was 0.708 (0.130) seconds. In respect to the gait cycle, this would mean a change in walking velocity of about 0.08 m/s between shoewear conditions, which is less than 10%. To avoid any speed effects, several other studies applied a threshold of 5% to 10% in walking velocity between shoewear conditions measured at a self-chosen comfortable walking speed.^1,22

Table 3:

Peak pressure (Pmax;; N/cm²), pressure time integral (PTI; N/cm²), and average pressure (Paverage; N/cm²) data (SD) for all regions per shoe type

Foot region	Ordinary shoes; mean (SD)			Orthopaedic shoes; mean (SD)			Pressure decrease (%)

	Pmax	PTI	Paverage	Pmax	PTI	Paverage	Pmax	PTI	Paverage
LH	19.8 (4.9)	6.7 (2.2)	10.9 (2.5)	17.5 (5.1)	5.8 (2.3)	9.9 (3.4)	11.7^**	13.4^**	9^*
MH	19.8 (5.2)	6.7 (2.1)	11.1 (3.0)	16.9 (3.8)	5.6 (1.6)	9.2 (2.1)	14.6^**	16.4^**	17^**
LM	15.9 (5.0)	6.7 (2.2)	9.7 (2.6)	14.2 (3.4)	6.1 (2.7)	8.7 (1.7)	10.7^**	9.0^*	10^**
MM	15.9 (5.2)	6.5 (2.2)	9.7 (3.12)	14.1 (3.7)	5.9 (2.5)	8.6 (2.0)	11.3^**	9.2^*	11^**
MTH1	26.0 (13.4)	7.9 (4.0)	12.1 (5.6)	20.6 (8.5)	6.0 (2.6)	9.6 (3.4)	20.8^**	20.7^**	12^**
MTH2-3	25.9 (10.7)	8.3 (3.1)	11.9 (3.9)	20.5 (8.0)	6.5 (3.2)	9.6 (2.9)	20.8^**	19.3^**	19^**
MTH4-5	18.9 (9.5)	6.7 (2.8)	9.5 (3.7)	16.1 (7.4)	5.8 (2.5)	8.4 (2.8)	14.8^**	11.6^**	12^**
Hallux	28.2 (12.9)	8.2 (4.2)	12.1 (5.5)	23.5 (9.1)	6.3 (4.0)	9.6 (3.0)	16.7^**	20.7^**	21^**
T2-5	23.6 (9.7)	7.3 (3.1)	10.5 (4.0)	19.6 (7.6)	5.9 (3.1)	8.9 (2.6)	16.9^**	15.2^**	15^**

p < 0.05;

p < 0.001; lateral hindfoot (LH), medial hindfoot (MH), lateral midfoot (LM), medial midfoot (MM), first metatarsal head (MTH1), second and third metatarsal heads (MTH2-3), fourth and fifth metatarsal heads (MTH4-5), hallux (H), and second through fifth toes (T2-5).

Treatment of degenerative disorders of the foot generally aims at redistributing the plantar pressure by means of different types of materials incorporated in the insoles. When considering the effectiveness of orthopaedic shoes in terms of plantar pressure, the results of this study show a remarkable decrease in average pressure of at least 9% under all nine foot regions, indicating not only a redistribution of plantar pressure but also a decrease of overall pressure. This decrease in overall pressure also was observed in several other studies.^13,21 A plausible explanation for this overall decrease is that the custom-made orthopaedic shoes (including insoles) increased the surface area through which force was transferred, thus reducing pressure in all measured regions.

Table 4:

Correlation between pressure variables in second to third metatarsal heads region and walking pain

Variable	Correlation coefficient (95%-CI)
Peak pressure (N/cm²)	0.444 (0.307–0.563)
Pressure-time integral (Ns/cm²)	0.360 (0.213–0.490)
Average pressure (N/cm²)	0.521 (0.396–0.628)

One of the aims of this project was to study the relationship between plantar pressure (peak pressure, average pressure, pressure-time integral) and foot pain in patients with degenerative disorders of the foot.

Although the average pressure correlated best with walking pain, the correlation accounted for only 27% (R²) of the variability. Other factors, physical, psychological, and sociological, could also play a role in pain sensation. A number of previous studies have investigated the relationship between pressure variables and pain. Postema et al.²¹ studied the effect of orthoses in relieving metatarsalgia. They concluded that custom-molded insoles and a rockerbar resulted in a substantial redistribution of pressure, as expressed by the peak pressure and force impulse. However, they found no statistically significant correlation between peak pressure, force-time integral and pain. Burns et al.³ found a significant correlation between pressure-time integral and foot pain in patients with painful pes cavus (r = 0.49, p < 0.001). Hodge et al.¹³ reported the relationship between pain and different foot pressure parameters in the rheumatoid foot. The authors found a moderate (significant) correlation between average pressure and walking pain (r = 0.562, p < 0.05). Nonsignificant correlations were found for peak pressure (r = 0.166) end pressure-time integral (r = 0.423). They stated that “although peak pressure might be the variable of interest in management of the insensate foot, because of its relationship to mechanical damage and ulceration, average pressure appeared to be the more important variable in the management of pain”. Hodge et al.¹³ provided a plausible explanation for this observation. Based on studies carried out by Garell et al.¹⁰ and Greenspan¹² they stated that, “unlike mechanoreceptors, nociceptors respond slowly to increases in pressure. It is plausible that brief duration peak pressures are insufficient to cause the high frequency discharges from nociceptors that are necessary for the perception of pain”.

Based on the results of this study, it can be concluded that custom-made orthopaedic shoes are effective in reducing foot pain and foot pressure. The moderate (significant) relationship between average pressure and walking pain presented in this study can be used as a tool for evaluating custom-made orthopaedic shoes prescribed for patients with degenerative disorders of the foot.

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