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Effect of Rocker Soles on Plantar Pressures David Brown, BS, CPed, Jacqueline J. Wertsch, MD, Gerald F. Harris, PhD, John Klein, PhD, Dennis Janisse, CPed ABSTRACT. Brown D, Wertsch JJ, Harris GF, Klein J, Janisse D. Effect of rocker soles on plantar pressures. Arch Phys Med Rehabil 2004;85:81-6. Objective: To examine the effect of different types of rocker soles on plantar pressures. Design: In-shoe plantar pressures were measured in subjects without deformity with baseline shoes and 3 types of rockers: toe-only, negative heel, and double. Setting: Medical college. Participants: Forty healthy patients (20 men, 20 women) without foot deformity. Interventions: Plantar pressures were recorded over a 21⁄2hour test period with over 400 steps analyzed for each type of rocker sole. Peak pressures, pressure-time integral (PTI), and sensor contact duration were computed for each step Main Outcome Measures: Peak plantar pressure PTI, and contact duration were compared for each rocker with a baseline shoe. Results: Significant reduction (P⬍.01) in peak pressure and PTI were recorded across the forefoot for all 3 rockers. The reduction of pressure at the forefoot was balanced by shifting pressure to the midfoot with the negative heel and toe-only rockers. Conclusion: This study lends scientific credence to the prescription of rocker soles for patients who need forefoot pressure reduction, such as in diabetic neuropathy and possible ulceration. Key Words: Diabetic foot; Pressure; Rehabilitation; Shoes. © 2004 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation HE NUMBER OF PEOPLE in the United States living with diabetes has been estimated (in 2000) at 15.7 million, and 798,000 new diabetics are diagnosed every year.1,2 Patients with long-term, poorly controlled blood sugar levels can have complications such as coronary disease, peripheral vascular disease, retinopathy, nephropathy, and peripheral neuropathy.3 The loss of sensation in the foot may often lead to hazardous elevated plantar pressure in the diabetic foot.3-9 Because sensory neuropathy fails to warn the body of pain, the diabetic foot is at risk for ulceration. Disordered joint mobility and muscle atrophy can lead to gait abnormalities that may exacerbate plantar pressure.10-12 As a result, ulcers are most often seen on high-pressure areas of the foot, such as the metatarsal heads and toes.3,4,10,13,14 Foot ulcers, if not noticed and/or treated incorrectly, can cause osteomyelitis. Despite advances in blood sugar delivery, glucose monitoring technol-
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From the Departments of PM&R (Brown, Wertsch), Orthopedics (Harris, Janisse), and Biostatistics (Klein), Medical College of Wisconsin, Milwaukee, WI. Supported by the National Institutes of Health (grant no. RO1 HD31389). No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated. Reprint requests to David Brown, BS, 7283 W Appleton Ave, Milwaukee, WI 53216, e-mail:
[email protected]. 0003-9993/04/8501-7938$30.00/0 doi:10.1016/S0003-9993(03)00374-5
ogy, and patient education, diabetes is still the leading cause of lower-extremity amputations.1 The US National Commission on Diabetes reports that 5% to 15% of diabetic patients eventually require some level of amputation.7 While the estimated cost to diabetic Medicare patients with amputations is $150 million, this figure does not reflect the societal costs.1,10 Because amputation is not a cure, the chance for a subsequent amputation on the same or contralateral limb is as high as 50% within 4 years.8 To help protect the neuropathic foot, therapeutic footwear with rocker soles can help to reduce pressure.1,4,5 Depth shoes with rocker soles are designed to relieve highpressure areas, reduce shock to the foot, reduce shear, accommodate deformities, and limit painful joint motion.4 Because pressure varies with each patient, the design of the rocker sole can be specified. Three of the most commonly prescribed rocker soles are the toe-only, negative heel, and double rocker soles.4 The toe-only rocker loads the weight-bearing area of the foot proximal to the metatarsal heads, provides a stable midstance, and reduces toe shock on toe-off.4 The negative heel rocker shifts weight bearing posteriorly and helps to accommodate fixed dorsiflexion.4 Both the negative heel and toe-only rockers help relieve high forefoot pressure. The double rocker is designed to relieve problem areas in the midfoot, while also providing shock relief at toe-off.4 Although rocker soles have been used to help the diabetic foot, the goal of our study was to validate the pressure-reduction capabilities of the toe-only, negative heel, and double rockers compared with a baseline shoe. METHODS Subject Selection Forty healthy subjects (20 men, 20 women) were selected over 3 years. An advertisement for subjects was placed in the weekly Medical College of Wisconsin (MCW) newsletter. All potential subjects were asked to answer a verbal questionnaire that screened for lower-extremity surgeries or chronic pain and severity of flat feet or high arches. Subjects were also asked about history of neuropathy, diabetes, neuromuscular disease, and alcoholism. Each subject was then screened by a physician for hallux rigidus, hallux valgus, severe pes planus, severe pes cavus, and other deformities. Anyone who did not exhibit these deformities and passed the questionnaire was admitted to the study after signing a volunteer consent form. To target the onset of neuropathy, subjects were selected from an age range of 30 to 60 years old. Preparation After admission to the study, a pedorthist measured each subject for exact shoe size. Two pairs of P.W. Minora Extra Depth shoes were ordered. One pair of shoes would serve as a baseline shoe, while the other pair would be modified weekly. The toe-only, negative heel, and double rocker were randomly assigned to each subject by a random number generator program. A sketch of each rocker sole can be seen in figure 1. Arch Phys Med Rehabil Vol 85, January 2004
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diameters were recorded. Electromyography electrodese were placed bilaterally on the rectus femoris, medial hamstring, adductor longus, anterior tibialis, and gastrocnemius muscles. Each subject was then fitted with his/her shoes and insoles. Reflective markers were placed bilaterally on the anterior superior iliac spine, lateral malleolus, lateral condyles, heel, and above the second metatarsal head. Thigh, shank, and sacral wands were also taped to the subjects. The marker set-up is similar to that described by Kadaba et al.16 The electrodes, wands, and insole cables were then secured with 3M Coban wrap.d The Holter-type data acquisition system was set to record at 60Hz, affixed to the subjects’ back with self-adhesive, and secured with a strap across the chest. The motion laboratory was then calibrated, and the forceplates were balanced. The MCW Motion Laboratory uses a 7-camera Viconf data capture system, AMTIg dual forceplates, and a 10-channel surface electromyography electrode system. Test Protocol Subjects began the study in their baseline shoes. The Holtertype system was switched on, and subjects were instructed to walk at their own freely selected cadence. A trial consisted of 3 forceplate strikes for each foot. The subjects were then fitted with the modified shoes and were given approximately 10 to 15 minutes to become accustomed to them before data capture. After trial completion in the gait laboratory, subjects then walked up and down a 78-m (260-ft) hallway at their own pace. The overall protocol is shown in table 1. Total testing lasted approximately 2 hours and 30 minutes. Pressure data was loaded onto a PC after each individual trial.
Fig 1. A diagram of the double, negative heel, and toe-only rocker soles. The double rocker is designed to have a double midstance, and because the midfoot does not touch the floor during foot contact, the ground reaction forces and plantar pressure would be theoretically reduced. The negative heel rocker shifts weight bearing posteriorly by placing the foot in more dorsiflexion, placing the heel below or at the same level as the metatarsal heads. The toe-only rocker is designed to lengthen midstance at the hindfoot and midfoot during walking, while increasing toe spring in late stance.
An APEXb foot imprinter was used to gauge high-pressure areas. Three dynamic and 3 static shots were taken for each foot, and the average location for the highest pressure was found for the hallux; heel; base of the fifth metatarsal; and the heads of the first, second, between the third and fourth, and the fifth metatarsals. Interlinkc sensors were used to measure pressure, and 18mm diameter stainless steel disks were taped to the sensor backs to minimize hysteresis. The sensors were then soldered to 16-channel 3Md cable. Space was carved into the insole material so that both the sensors and cables would lie in the contact plane, remaining undetected by the subject. Surgical tape covered the sensor locations and the wire channels. The insoles were then calibrated to minimize hysteresis using a load cell, a Holter-type data acquisition system, and personal computer (PC)– based software to calculate pressure in kilopascals. The data acquisition system is described by Abu-Faraj et al.15 Subject Instrumentation Subjects were instructed to wear loose cotton shorts and a cotton shirt to the motion analysis laboratory at MCW. The subjects’ height, weight, leg lengths, knee diameters, and ankle Arch Phys Med Rehabil Vol 85, January 2004
Data Processing After data collection, the data were adjusted to include each calibrated sensor. To negate acceleration and deceleration effects, the first and last step for each gait laboratory and long walk data capture were deleted. Figure 2 shows a typical long walk with all 14 sensor locations in time series. Each channel was demultiplexed, and a PC-based program was implemented to process each sensor. This program is designed to compute the peak pressure, contact duration, and pressure-time integral (PTI). The beginning and end of each step is located by moving arrows on the screen. The peak detection algorithm places an arrow at the peak pressure location, and a trapezoidal rule algorithm computes the area under the waveform. An example diagram is shown in figure 3. The program computes the 3 parameters, and the user proceeds to the next step. After processing, mean contact duration, peak pressure, and PTI values are calculated.
Table 1: The Test Protocol and Approximate Time for Each Trial Trial
Location
Approximate Time (min)
Baseline 1 Modified 1 Long walk 1 Modified 2 Long walk 2 Modified 3 Long walk 3 Modified 4 Baseline 2
Gait lab Gait lab Long hall Gait lab Long hall Gait lab Long hall Gait lab Gait lab
20 20 5 20 5 20 5 20 20
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Fig 2. The simultaneous display of all 14 sensor locations in time series. Abbreviation: met, metatarsal head.
Statistical Methods A random effects analysis of variance model was used to make comparisons between shoe types. In this model, a random effect was used for each subject. Fixed effects for shoe type and period were included in the model. Analysis was conducted using the SASh system. Because of the large number of comparisons, a P value of less than 1% was required to declare significance. Estimates of the magnitude and percentage of the change from baseline for each rocker were obtained from the fitted model. RESULTS The average age of the participants was 441⁄2 years old. The average height of female subjects was 163.3cm (64.7in), and
Fig 3. A representation of the program used to view each sensor, which generates peak pressure, PTI, and contact duration.
average male height was 176.5cm (69.5in). The average female weighed 71.1kg (158lb), and the average male weighed 83.3kg (185lb). Because the number of steps for each rocker sole was greater than baseline steps, an autoregressive model was developed to calculate the mean values for each parameter. The 95% confidence intervals (CIs) were constructed, and statistical significance with P less than .01 is shown in bold. Average pressure values for each sensor are reported in table 2. Magnitude change in peak pressure from baseline is displayed in table 3. Percentage change in magnitude pressure is shown in table 4. The percentage and net change in PTI are shown in table 5. DISCUSSION Rocker-soled shoes are typically prescribed to reduce pressure on high-risk areas of the foot. For the diabetic individual with peripheral neuropathy, the areas at the highest risk are at the forefoot, especially the toes and metatarsal heads. The negative heel and toe-only rocker soles would be indicated for high forefoot plantar pressure.4 Pressure areas in the midfoot, such as a prominent base of the fifth metatarsal, would require a double rocker sole to shift pressure. The contour of the sole is designed to load more stable areas of the foot. Typically, a rigid steel shank is embedded in the shoe’s sole. The shank replaces motion in the foot by limiting active dorsiflexion of the toes during toe-off and, thus, helping to reduce pressure.4 Most rocker soles also incorporate a small walking heel at the posterior edge of the sole. This helps ease plantarflexion at foot contact and can help alleviate foot slap. Because high-pressure areas depend on the condition of the foot, each rocker sole prescription will depend on the patient’s status. The toe-only rocker is prescribed to decrease pressure on the forefoot by increasing the time spent during midstance on the midfoot and hindfoot. The rocker can also replace painful motion, as in the case of hallux rigidus or other limited sagittal plane motion. The toe-only rocker is built up approximately 1⁄2in from the heel to just proximal to the metatarsal heads. The area of the sole from the toe to the metatarsal heads is sanded down to ease toe-off and decrease active toe dorsiflexion. As a Arch Phys Med Rehabil Vol 85, January 2004
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ROCKER SOLES AND PLANTAR PRESSURE, Brown Table 2: Average Pressure Values (kPa) for Each Sensor Location, Including Baseline Values and Rocker Sole Treatments Left Foot
Right Foot
Sensor Location
Baseline
Toe-Only
Negative Heel
Double
Baseline
Toe-Only
Negative Heel
Double
Heel Base of 5th met Head of 5th met Between 3rd and 4th mets Head of 2nd met Hallux Head of 1st met
138.50 58.17 26.48 223.06 232.63 63.17 197.23
133.43 74.63 20.56 171.58 127.08 53.26 155.54
111.67 96.11 31.28 162.77 105.90 15.71 136.66
125.94 53.91 34.56 194.98 140.51 25.65 157.18
37.44 98.72 29.86 127.17 390.53 68.71 544.84
13.20 115.54 8.26 64.34 290.65 19.78 497.04
17.29 129.83 13.76 49.64 282.87 ⫺2.04 474.75
22.35 97.30 16.33 85.37 309.00 ⫺10.33 494.19
Abbreviation: met, metatarsal head. Table 3: Magnitude Change (kPa) in Peak Pressure Compared With Baseline Shoes Left Foot
Right Foot
Sensor Location
Toe-Only Rocker
Negative Heel Rocker
Double Rocker
Toe-Only Rocker
Negative Heel Rocker
Double Rocker
Heel Base of 5th met Head of 5th met Between 3rd and 4th met Head of 2nd met Hallux Head of 1st met
⫺5.08 16.45 ⫺0.59 ⴚ51.48 ⴚ105.54 ⫺9.91 ⴚ41.69
ⴚ26.83 37.93 4.79 ⴚ60.29 ⴚ126.64 ⴚ47.55 ⴚ60.57
ⴚ12.56 ⫺4.27 8.07 ⴚ38.08 ⴚ92.12 ⴚ37.52 ⴚ40.05
ⴚ24.25 16.82 ⴚ21.56 ⴚ62.83 ⴚ99.88 ⴚ48.93 ⴚ47.80
ⴚ20.15 31.10 ⴚ16.07 ⴚ77.53 ⴚ107.66 ⴚ70.75 ⴚ70.09
ⴚ15.09 ⫺1.43 ⴚ13.50 ⴚ41.80 ⴚ80.53 ⴚ79.04 ⴚ50.65
NOTE. Measurements with significance at P⬍.01 are in bold. Table 4: Percentage Change in Peak Pressure Compared With Baseline Shoes Left Foot Sensor Location Heel Base of 5th met Head of 5th met Between 3rd and 4th met Head of 2nd met Hallux Head of 1st met
Right Foot
Toe-Only Rocker
Negative Heel Rocker
Double Rocker
Toe-Only Rocker
Negative Heel Rocker
Double Rocker
–19.37% (–22.38 to –16.36) 65.19% (56.58 to 73.81) 18.11% (0.15 to 36.07) –25.87% (–27.71 to –24.02) –54.44% (–56.70 to –52.17) –75.27% (–92.95 to –57.59) –6.97% (–7.85 to –6.08)
–3.67% (–6.59 to –.75) 28.27% (20.92 to 35.62) –2.24% (–19.04 to 14.56) –22.09% (–23.72 to –20.46) –45.37% (–47.10 to –43.64) –15.68% (–27.92 to –3.44) –4.79% (–5.66 to –3.93)
–9.07% (–11.96 to –6.18) –7.34% (–13.04 to –1.64) 30.47% (11.52 to 49.42) –16.34% (–18.10 to –14.58) –39.60% (–41.62 to –37.58) –59.40% (–74.89 to –43.91) –4.61% (–5.47 to –3.73)
–53.82% (–68.85 to –38.79) 31.51% (27.50 to 35.52) –53.92% (–70.17 to –37.68) –60.96% (–65.04 to –56.89) –27.57% (–28.71 to –26.42) –102.97% (–123.54 to –82.40) –12.86% (–14.38 to –11.35)
–64.76% (–77.75 to –51.77) 17.03% (13.04 to 21.02) –72.34% (–87.18 to –57.51) –49.41% (–52.45 to –46.36) –25.58% (–26.57 to –24.58) –71.21% (–83.66 to –58.77) –8.77% (–10.25 to –7.30)
–40.30% (–53.85 to –26.76) –1.44% (–4.85 to 1.96) –45.31% (–60.51 to –30.12) –32.87% (–36.21 to –29.52) –20.62% (–21.72 to –19.52) –115.03% (–136.87 to –93.20) –9.30% (–10.77 to –7.82)
NOTE. Values with significance at P⬍.01 are in bold. The 95% CIs are in parentheses.
result, there was significant reduction of peak pressure and PTI at the heel, hallux, first, second, and between the third and fourth metatarsal heads. We also significantly loaded the base of the fifth metatarsal heads (fig 4). By increasing the midstance time, the toe-only rocker helps to load the more stable midfoot, thus easing forefoot pressure. Reduction in pressure at the heel may be due to the walking heel on the shoe. The baseline shoe lacked a walking heel, which may have increased foot slap shortly after heel contact. The negative heel rocker is also prescribed to decrease forefoot loading, but its modality differs from the toe-only rocker. Because most shoes have some heel height, the inside of the shoe incorporates some degree of forefoot plantarflexion. By adding soling material approximately 1⁄2-in thick proximal to the metatarsal heads without building up the heel area, the negative heel shifts Arch Phys Med Rehabil Vol 85, January 2004
weight bearing posteriorly. With a forefoot rocker, the toe spring in the negative heel rocker approximates that of the toe-only rocker. Because of the biomechanics of the negative heel, patients with poor ankle dorsiflexion or intolerance to posterior weight shift would benefit little from this modification. Like the toe-only rocker, significant reduction of peak pressure and PTI was seen at the hallux and the first, second, and between the third and fourth metatarsal heads with the negative heel (fig 5). Once again, the base of the fifth metatarsal was significantly loaded. While an increase in pressure at the heel was expected, a posterior walking heel was built into the shoe, easing the foot into the foot-flat stage of gait. Because the negative heel rocker adds less overall height to the shoe, patients felt more stable than in the toe-only modification. Two patients complained of cramping in the gastrocnemius after testing, possibly due to the resulting dorsiflexed foot.
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ROCKER SOLES AND PLANTAR PRESSURE, Brown Table 5: Percentage Change and Magnitude of Change in PTI Compared With Baseline Shoes Left Foot Sensor Location Heel
Base of 5th met
Head of 5th met
Between 3rd and 4th met Head of 2nd met
Hallux
Head of 1st met
Right Foot
Toe-Only Rocker
Negative Heel Rocker
Double Rocker
Toe-Only Rocker
Negative Heel Rocker
Double Rocker
[2.86] –20.54% (–22.65 to –18.43) [9.40] 38.11% (34.80 to 41.42) [0.91] –4.00% (–6.76 to –1.25) [–13.32] –20.56% (–21.87 to –19.26) [–25.17] –48.89% (–51.34 to –46.44) [–4.42] –30.33% (–37.55 to –23.11) [–7.93] –4.78% (–5.83 to –3.73)
[–11.87] –4.96% (2.80 to 7.13) [17.55] 20.40% (17.16 to 23.64) [–2.10] 1.73% (–1.10 to 4.57) [–19.68] –13.92% (–15.13 to –12.71) [–30.03] –40.97% (–42.88 to –39.06) [–7.62] –17.61% (–24.05 to –11.17) [–9.43] –4.02% (–5.06 to –2.98)
[–2.58] –4.46% (–6.48 to –2.44) [–0.45] –0.97% (–3.66 to 1.72) [5.08] 9.67% (6.89 to 12.46) [–9.44] –9.86% (–11.12 to –8.61) [–20.50] –33.38% (–35.56 to –31.19) [–8.62] –34.32% (–41.36 to –27.27) [–6.72] –3.41% (–4.45 to –2.37)
[0.22] –57.32% (–64.77 to –49.87) [8.39] 18.98% (17.28 to 20.67) [–10.32] –27.20% (–30.80 to –23.60) [–16.84] –46.46% (–49.49 to –43.43) [–23.74] –20.42% (–21.32 to –19.53) [–11.96] –40.69% (–48.42 to –32.96) [–11.26] –8.58% (–9.98 to –7.19)
[–11.96] –1.08% (–7.07 to 4.91) [14.40] 11.05% (9.32 to 12.79) [–10.32] –28.05% (–31.19 to –24.91) [–21.29] –36.74% (–39.15 to –34.34) [–25.49] –19.02% (–19.83 to –18.20) [–11.55] –42.15% (–48.45 to –35.85) [–13.41] –7.21% (–8.58 to –5.84)
[–1.84] –8.83% (–14.65 to –3.02) [1.43] 1.88% (0.32 to 3.44) [–5.78] –15.25% (–18.68 to –11.83) [–7.97] –17.40% (–19.99 to –14.81) [–17.11] –13.71% (–14.58 to –12.84) [–17.45] –61.52% (–69.93 to –52.11) [–11.30] –7.23% (–8.59 to –5.87)
NOTE. The magnitude of change is in square parentheses. Measurements with significance at P⬍.01 are in bold. The 95% CIs are included in parentheses for percentage change.
The double rocker—typically prescribed to relieve midfoot prominences and problem areas— has 2 areas for midstance: the heel and just proximal to the metatarsal heads. Because of the shape of the sole, the midfoot does not reach the ground during midstance. A smaller amount of toe spring is also built into the sole to decrease shock at toe-off. This modification is usually indicated for either a prominent fifth metatarsal base or a rocker-bottom foot deformity. Once again, we saw reduction in peak pressure and PTI at the heel, between the third and fourth metatarsal heads, at the first and second metatarsal heads, and the hallux (fig 6). We did see some pressure reduction at the base of the fifth metatarsal, although it was not significant at the .01 level. The limitations of this study reflect factors associated with the use of discrete pressure sensors and their placement within the shoe. For example, our results along the lateral border of the shoe (head and base of the fifth metatarsal) were inconsistent. Because we translated the inked impressions of each subject’s foot directly onto our insole material, the highest pressure areas on the lateral border of the foot would often be
directly on the border of the insole. Although each sensor was placed within the border of the insole, lateral shoe effects may have increased pressure readings. We believe that the inside of the shoe may have concentrated in-shoe pressure along the lateral side. Pressure readings at the hallux may have also been affected by insole set-up. The solder joint for each hallux sensor was often located under the metatarsophalangeal joint. Dorsiflexion of the toes before toe-off, accompanied by shoe and insole bending at this joint, slowly wore on the solder between the sensors and the cables. After this connection is severed, the data acquisition system ceases to recognize the sensor, and no pressure can be recorded. Sensors would often become defunct midway during testing, when correcting the problem was most difficult. The end result was less data, increased variance in measurements, and less statistical significance. Rocker soles are typically broken in by each patient by wearing them a couple hours the first day and then increasing their use each day by an hour or 2. Because of time constraints
Fig 4. A diagram showing the bilateral average pressure change in negative heel rocker soles compared with the baseline shoes.
Fig 5. A diagram showing the bilateral average pressure change in toe-only rocker soles compared with baseline shoes.
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Fig 6. A diagram showing the bilateral average pressure change in double rocker soles compared with the baseline shoes.
in the motion laboratory, the break-in period may not be completely adequate to gauge complete pressure reduction. After preliminary testing in the baseline shoe, each subject was fitted with their modified shoe, and given approximately 10 minutes before testing. Despite the short break-in period, we achieved significant reduction at many sensor locations. The use of only 7 sensor locations on each foot also limited pressure recording over a larger area of the foot. Patients often remarked they felt more pressure in their arch with both the negative heel and toe-only rockers. Because the only midfoot sensor was located under the base of the fifth metatarsal, we were unable to record this pressure. Other in-shoe pressure recording systems have been reported, but few can record more than a couple of steps; by contrast, the Holter-type system we used can record multiple steps continuously for up to 6 hours.15 The results also confirmed striking differences between right and left feet. Asymmetry in plantar pressures during gait has been reported in able-bodied subjects.17 In that study, 50% of subjects exhibited significantly different pressure between right and left feet while wearing Oxford shoes. CONCLUSIONS Therapeutic footwear with rocker soles is imperative to reducing pressure in the diabetic insensate foot. Depending on the patient, a specific sole can be prescribed to reduce plantar pressure and shear, as well as to improve gait and to limit and/or replace painful motion. The toe-only, negative heel, and double rocker soles can effectively reduce forefoot pressures, helping to preserve the foot and avoid amputation. References 1. White J. Therapeutic footwear for patients with diabetes. J Am Podiatr Med Assoc 1994;84:470-9. 2. National Diabetes Information Clearinghouse. National diabetes statistics. Available at: http://diabetes.niddk.nih.gov/dm/pubs/ statistics/index.htm #7. Accessed December 2, 2003.
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3. Cavanagh PR, Simoneau GG, Ulbrecht JS. Ulceration, unsteadiness, and uncertainty: the biomechanical consequences of diabetes mellitus. J Biomech 1993;26(Suppl 1):23-40. 4. Janisse DJ. Pedorthic care of the diabetic foot. In: Levin ME, O’Neal LW, Bowker JH, editors. The diabetic foot. St Louis: CV Mosby; 1993. p 549-76. 5. Mueller MJ. Therapeutic footwear helps protect the diabetic foot. J Am Podiatr Med Assoc 1997;87:360-4. 6. Nawoczenski DA, Birke JA, Coleman WC. Effect of rocker sole design on plantar forefoot pressures. J Am Podiatr Am Assoc 1988;78:455-60. 7. Most RS, Sinnock P. Epidemiology of lower extremity amputation in diabetic individuals. Diabetes Care 1983;6:87-91. 8. Lavery LA, Lavery DC, Quebedeax-Farnham TL. Increased foot pressures after great toe amputation in diabetes. Diabetes Care 1995;18:1460-2. 9. Isakov E, Budoragin N, Shenhav S, Mendelevic I, Korzets A, Susak Z. Anatomic sites of foot lesions resulting in amputation among diabetics and non-diabetics. Am J Phys Med Rehabil 1995;74:130-3. 10. Day MR, Harkless LB. Factors associated with pedal ulceration in patients with diabetes mellitus. J Am Podiatr Med Assoc 1997; 87:365-9. 11. Boulton AJ, Betts RP, Franks CI, Newrick PG, Ward JD, Duckworth T. Abnormalities of foot pressure in early diabetic neuropathy. Diabet Med 1987;4:225-8. 12. Andersen H, Morgensen PH. Disordered mobility of large joints in association with neuropathy in patients with long-standing insulindependent diabetes mellitus. Diabet Med 1993;14:221-7. 13. Brand PW. Management of the insensitive limb. Phys Ther 1979; 59:8-12. 14. James H. Foot problems in diabetes. Nurs Times 1995;91:65-72. 15. Abu-Faraj ZO, Harris GF, Abler JH, Wertsch JJ. A Holter-type, microprocessor-based, rehabilitation instrument for acquisition and storage of plantar pressure data. J Rehabil Res Dev 1997;34: 187-94. 16. Kadaba MP, Ramakrishnan HK, Wootten ME. Measurement of lower extremity kinematics during level walking. J Orthop Res 1990;8:383-92. 17. Zhu H, Wertsch JJ, Harris GF. Asymmetry of plantar pressure during normal walking [abstract]. Arch Phys Med Rehabil 1990; 71:808. Suppliers a. P.W. Minor and Son Inc, 3 Treadeasy Ave, Batavia, NY 140210678. b. Apex Foot Health Industries, 170 Wesley St, S Hackensack, NJ 07606. c. Interlink Electronics Inc, 546 Flynn Rd, Camarillo, CA 93012. d. 3M, 3M Ctr, St Paul, MN 55144-1000. e. Motion Lab Systems Inc, 15045 Old Hammond Hwy, Baton Rouge, LA 70816-1244. f. Oxford Motion Systems, 14 Minns Business Park, West Way, Oxford, OX2 0JB, UK. g. Advanced Mechanical Technology Inc, 176 Waltham St, Watertown, MA 02172. h. SAS Institute Inc, 100 SAS Campus Dr, Cary, NC 27513.
