Patellar tendon bearing brace: Combined effect of heel clearance and ankle status on foot plantar pressure

Transcription

1 6916POI / Prosthetics and Orthotics InternationalAlimerzaloo et al. Original Research Report Patellar tendon bearing brace: Combined effect of heel clearance and ankle status on foot plantar pressure INTERNATIONAL SOCIETY FOR PROSTHETICS AND ORTHOTICS Prosthetics and Orthotics International 2014, Vol 38(1) The International Society for Prosthetics and Orthotics 2013 Reprints and permissions: sagepub.co.uk/journalspermissions.nav DOI: / poi.sagepub.com Farnaz Alimerzaloo 1, Reza V Kashani 2, Hassan Saeedi 3, Marjan Farzi 2 and Nader Fallahian 2 Abstract Background: Heel clearance and ankle status (free or locked) are of major determinants affecting peak plantar pressures and contact area in patellar tendon bearing brace and have been separately studied by many researchers. This study investigated the combined effect of ankle status and heel clearance on contact area and peak plantar pressure in different areas of foot (hindfoot, midfoot, and forefoot). Study design: Before after repeated measurement trial. Methods: Nine healthy male volunteers walked 8 m with normal shoe and four conditions of patellar tendon bearing brace wear. Repeated-measure analysis of variance test was used to compare contact area and plantar pressure changes in three areas of the foot. Results: Application of patellar tendon bearing brace significantly reduced overall plantar pressure and contact area (p < 0.01). Although both contact area and plantar pressure significantly decreased in hindfoot and midfoot, plantar pressure increased in forefoot area (p < 0.05). Conclusions: Application of the patellar tendon bearing brace can reduce the overall peak plantar pressure in the foot but increases focal plantar pressure in forefoot. Excessive lifting of the heel seems to minimize the contact area, thus increase focal pressure in forefoot. Overall, plantar pressure seems to be more effectively off-loaded by combining maximum heel clearance and restriction of the ankle joint. Clinical relevance Although effective parameters of patellar tendon bearing brace have been separately addressed in previous studies, no study was found that investigated the combined effect of ankle status and heel clearance. This study investigates the combined effect of these parameters and provides detailed information on clinical application of the patellar tendon bearing brace. Keywords Patellar tendon bearing brace, plantar pressure, foot off-loading, effect of heel clearance and ankle motion Date received: 11 September 2012; accepted: 25 March Background Based on patellar tendon bearing (PTB) concept from prosthetics, Sarmiento 1 used Patellar ligament-bearing brace in treatment of tibial fractures in the 1960s. The brace was considered to off-load tibia, fibula, and foot bones by transmitting the weight bearing loads via lateral uprights. PTB brace is also used to off-load the foot in plantar ulcers, diabetic foot, Charcot joint, ankle instability, pain from arthritis condition, pes planus, and avascular necrosis of talus. The orthosis can be used as an alternative to PTB cast because of more convenient walking, improved hygiene, and washability. 2 5 There are controversial reports by different researchers because of various methods and conditions used by researchers. The effectiveness of orthosis has not been demonstrated in random clinical trials yet. 6 There are also 1 Rehabilitation Center, Tabriz University of Medical Sciences, Tabriz, Iran 2 Orthotics and Prosthetics Department, University of Social Welfare and Rehabilitation Sciences, Tehran, Iran 3 Orthotics and Prosthetics Department, Tehran University of Medical Sciences, Tehran, Iran Corresponding author: Nader Fallahian, University of Social Welfare and Rehabilitation Sciences, Kodakyar St., Daneshjo Blvd., Velenjak, Tehran , Iran. n.fallahian@gmail.com

2 Alimerzaloo et al. 35 inconsistencies in reports about effectiveness of PTB braces or casts in off-loading the foot. 4,5,7 Plantar pressure (PP) measurement is commonly used as an outcome measure for the assessment of foot off-loading PTB brace can reduce pressure under heel and metatarsal heads. 11 Tanaka et al. reported that in healthy subjects, PTB cast can decrease PP across the entire foot. The pressure was reduced as the depth of free space under the foot (clearance) was increased. 12 Pressure reduction and off-loading techniques have been intensively used in treatment of the diabetic foot. 6,8,13 18 Assessment of the PP is a repeatable method to evaluate the orthosis function. 19 Foot clearance 6,12 and ankle status 20 are the two major determinants of PTB brace in alteration of PPs 3,20 and have been separately addressed by many researchers. The aim of this study was to investigate the combined effect of ankle status and heel clearance of PTB brace on contact area (CA) and peak PP in different areas (hindfoot, midfoot, and forefoot) of plantar surface of the foot. Methods Study design Nine healthy male volunteers were recruited from the University of Social Welfare and Rehabilitation Sciences (USWR) of Tehran for a before after repeated measurement trial design. All procedures followed the ethical codes of the Institutional Review Board of the University of Social Welfare and Rehabilitation Sciences. The stages of the tests were described to all the subjects before taking the written informed consent. Subjects were included if they were years old 5 with no history of gait abnormalities, disease involving cardiovascular and motor systems, and deformities or trauma to lower extremities. 21,22 PTB brace A metal double-upright brace with thermoplastic PTB socket was used for all the subjects (Figure 1). Adjustable thermoplastic socket was assembled on a high top shoe. The height of the orthosis and additional heel clearance was adjusted by vertical shifting of the socket on lateral uprights, performed by an experienced orthotist. Orthosis was made with ankle joints in neutral position (90 ). The ankle joint was later degaged to provide a free range of 5 of plantar and 15 of dorsal flexion motions in sagittal plane, while restricting frontal and transverse plane motions. In order to balance the height on both sides, a rubber wedge (1 or 2 cm height, based on the foot clearance within the orthosis) was used inside the contralateral shoe. One orthotist ensured leg length equality by observation of the height of anterior superior iliac spine (ASIS) on both sides, to be horizontal. Lower level of ASIS on each side indicated a pelvic tilt resulted from a shorter leg length at the same side. Figure 1. PTB brace with metal double-upright brace and adjustable thermoplastic socket assembled on a high top shoe. PTB: patellar tendon bearing. Table 1. Different conditions of ankle status and heel clearance. PTB brace condition Ankle status and heel clearance First condition Second condition Third condition Fourth condition PTB: patellar tendon bearing. Test conditions In order to study the combined effect of ankle status and heel clearance, four conditions of PTB brace were defined (as shown in Table 1) and compared with the normal shoe of the subjects. Measurements Locked ankle and 1 cm of heel clearance Locked ankle and 2 cm of heel clearance Free ankle and 1 cm of heel clearance Free ankle and 2 cm of heel clearance Novel Pedar-X in-shoe pressure measuring system (Novel GmbH, Munich, Germany) was used to record PP and CA data. This system has been used in similar studies, 14,20,21,23 and the repeatability of the system with foot-shaped sensors has been reported adequately. 19 The sensors were chosen based on the foot size of each subject and sandwiched

3 36 Prosthetics and Orthotics International 38(1) Figure 2. Plantar aspect of the foot was divided to three areas of hindfoot, midfoot, and forefoot. Figure 3. Comparison of peak PPs in normal shoe and four conditions of PTB brace use. PTB: patellar tendon bearing; PPs: plantar pressures. between the foot and the shoe, to show the pressure data right under the plantar aspect of the foot. Subjects walked around the laboratory with self-selected pace for almost 5 min to get used to the settings. 22 After 5-min rest, each subject walked on an 8-m straight pathway 24 with normal shoe and all four conditions of PTB brace. Each trial was repeated for 3 times. 25,26 Data were recorded at a sample rate of 50 Hz 19,27 via a data logger on the subject s waist belt and were later transferred to a personal computer. Masking the surface was performed by Novel Pedar software to divide the plantar aspect of the foot into three areas of hindfoot, midfoot, and forefoot 20 (Figure 2). Pressure and CA data were extracted from three middle steps of each trial 19 and exported to Microsoft Excel. Simple percentages of CA and PP were also obtained. Analysis of variance (ANOVA) with significance level of 0.05 was used to assess the effect of PTB brace conditions in three different areas of foot. Results Nine healthy volunteer subjects with an average age of years (range: years), average weight of kg (range: kg), height of 1.74 m (range: m), and body mass index (BMI) of kg/ m 2 (range: kg/m 2 ) completed a total of five test conditions (normal shoe and four conditions of PTB brace use). All four conditions of PTB brace use significantly reduced the overall peak PP (p < 0.01). Besides, compared to normal shoe, all conditions of brace wear significantly reduced peak PPs in hindfoot and midfoot but increased PP in forefoot area (p < 0.05). Figure 3 shows that forefoot and overall PPs were significantly higher with free ankle and 2 cm of heel clearance (fourth condition of PTB brace wear) among the four conditions of PTB brace wear. But overall and segmental PPs were not significantly different among other three conditions of the brace use (p > 0.05). Compared to normal shoe, CA of hindfoot and midfoot was significantly reduced in all the four conditions with PTB brace (p < 0.01). Among the four brace conditions (Figure 4), the CA of hindfoot was significantly reduced less in first condition (locked ankle with 1 cm of heel clearance). All conditions similarly reduced PP in the midfoot area. CA of the forefoot was not significantly different among all four conditions of brace wear and was not significantly altered compared to normal shoe (p < 0.05). Figures 3 and 4 show that CA and PP are similar for all three areas of the foot with the normal shoe. By applying the PTB brace, overall CA and PP significantly reduced in hindfoot and midfoot (p < 0.01) but increased in forefoot area (p < 0.05). Figure 5 compares the percent of overall reduction in CA and peak PPs. The second condition (locked ankle and 2 cm of heel clearance) provided the most reduction in overall PP (47.6% PP reduction), followed by 46.5% in the first (locked ankle and 1 cm) and 40.3% in the third (free ankle and 1 cm of heel clearance) conditions of the PTB

4 Alimerzaloo et al. 37 The percent of reduction in CA was more in free-ankle conditions for both 1 and 2 cm of heel clearances. In both free and locked ankle status, overall CA was reduced by increasing heel clearance. Figure 4. Comparison of CA in normal shoe and four conditions of PTB brace use. CA: contact area; PTB: patellar tendon bearing. Figure 5. Comparison of the percent of overall reduction in PP and CA. PP: peak pressures; CA: contact area. brace use. Pressure reduction was minimal (20.1%) in the fourth condition in which the ankle was free with 2 cm of heel clearance. Discussion The combined effect of ankle status and heel clearance on PP and CA was studied in four conditions of PTB brace use on nine healthy male volunteers. The results demonstrated that PTB brace can significantly reduce CA in hindfoot and midfoot areas by taking off the heel from the shoe. In contrast, the CA is minimally increased in forefoot area, which may be produced by increased pressure in forefoot area. Application of the PTB brace could also reduce the overall peak PP in the foot. In fact, as seen in Figure 5, overall reduction in peak pressure was significantly decreased when the ankle joint was degaged. Usually, freeankle condition seems to let the plantar part of the orthosis move into dorsal flexion and results in PP augmentation over the forefoot and to some extent in midfoot area. In contrast to some studies that reported PP was transmitted to midfoot with decrease in forefoot PP, 11 some studies reported that PTB brace decreased hindfoot and overall PP but increased PP in forefoot area. 4,11 Similarly, the results demonstrate that PTB brace can reduce overall PP by reducing PP in hindfoot and midfoot areas. Indeed, PP seems to be transmitted to forefoot area, which might be a function of reduction in overall CA and focal force concentration. Consequently, it seems that dramatic increase in PP in forefoot area resulted in attenuation of brace efficacy for off-loading the foot. Although this study was performed on a limited number of subjects, it could be recommended that PTB brace with free ankle can be considered in case of fracture or traumatic heel conditions. In such cases, there is a minimal risk of skin breakdown while free ankle of the orthosis serves to keep the range of motion for the ankle. However, excessive lifting of the heel was observed to minimize the CA and to increase the focal pressure in forefoot. That is why excessive heel lift in free-ankle brace (fourth condition) should be avoided in treatment of the vulnerable foot, where pressure concentration may increase the risk of ulceration in forefoot area. The second condition (locked ankle and 2 cm of heel clearance) could be recommended as the best condition for maximal reduction of overall PP in these cases. There are limitations to this study; the limited sample size of subjects reduces the generalizability of the findings. Therefore, studies with greater sample sizes and longer study periods on different patient populations are recommended. However, the exact mechanism that increased PP could not be driven from pure kinetic data. Kinematic data are also required to determine the precise mechanism of PP alterations during gait. Furthermore, the increase in forefoot PP may be a function of calf muscle contraction for

5 38 Prosthetics and Orthotics International 38(1) propulsion demand in the late stance. Electromyographic (EMG) studies are recommended, to define muscle activation patterns while walking within PTB orthosis. Additionally, it is recommended to compare plantar and socket pressures during gait. Because of behavioral and anatomical differences between male and female, 28 it is also recommended to assess gender differences in brace wear. Conclusion Results from healthy subjects of this study suggest that although all different conditions of using PTB brace can significantly decrease the overall CA and peak PP over the foot, alteration of PP was different in locked versus freeankle status. In all four conditions of wearing PTB brace, hindfoot is totally de-weighted. Moreover, midfoot and especially forefoot areas were more de-weighted if the ankle was locked in neutral position. In fact, free-ankle PTB brace should not be recommended for high-risk cases of skin breakdown. In other words, it could be better to fabricate solid ankle orthosis for a diabetic and/or dysvascular patient. Similarly, in case of Charcot joint conditions, degaging the ankle joint and lifting the heel will allow for a wider range of motion in the ankle joint, which may result in deterioration of the condition and hence should be avoided. PP seems to be most effectively off-loaded by increasing heel clearance in a fixed-ankle PTB brace. This is a condition of brace use where an optimal combination of maximum heel clearance and maximum peak PP reduction can be achieved. Conflict of interest The authors declared that there is no conflict of interest. Funding This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors. References 1. Sarmiento A. A functional below-the-knee cast for tibial fractures. J Bone Joint Surg Am 1967; 49: Barocas C. The PTB cast vs the brace. Ort Tech Review 2005; 7(4). 3. Rubin G and Dixon M. 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