Dynamic Foot Pressure Measurements for Assessing Foot Deformity in ...

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ORIGINAL ARTICLE

Dynamic Foot Pressure Measurements for Assessing Foot Deformity in Persons With Spastic Cerebral Palsy Eun Sook Park, MD, PhD, Hyun Woo Kim, MD, PhD, Chang Il Park, MD, PhD, Dong-wook Rha, MD, MS, Chan Woo Park, MD ABSTRACT. Park ES, Kim HW, Park CI, Rha D, Park CW. Dynamic foot pressure measurements for assessing foot deformity in persons with spastic cerebral palsy. Arch Phys Med Rehabil 2006;87:703-9. Objectives: To identify characteristics of foot pressure distribution in different foot deformities using a computerized insole sensor system, and to identify changes in these parameters after corrective surgery in children with spastic cerebral palsy (CP). Design: Before-after trial. Setting: University hospital. Participants: Sixty-seven limbs of 44 children with spastic CP were assessed (35 equinus, 17 equinovarus, 15 equinovalgus). Intervention: Orthopedic surgery for foot deformities. Main Outcome Measures: Parameters of foot contact pattern, pressure-time integral (PTI), and center of pressure (COP) trajectories were assessed before and at a minimum of 6 months postsurgery, using the F-scan system. Results: Prior to surgery, the medial midfoot relative impulse, which is PTI normalized by a percentage of the entire foot, differed significantly between foot deformity groups. Relative impulse was high on the lateral column of the foot in the equinovarus group and on the medial column of the foot in the equinovalgus group. Center of pressure index (COPI) and coronal index reflecting the asymmetry of the medial and lateral columns of the foot differed significantly between the equinovalgus and equinovarus groups. After surgery, significant changes occurred in foot contact patterns, including total contact area, contact length, contact width of hindfoot, and the relative impulse of specific areas of the foot. In addition, there were significant changes in the parameters of COP, such as anteroposterior displacement, slope, and velocity. Conclusions: In dynamic foot pressure measurements using a computerized insole sensor system, the parameters reflecting medial or lateral changes in weight bearing, such as COPI and coronal index, appear to be useful for evaluating abnormalities and improvements after intervention in the frontal plane, such as varus and valgus. Additionally, assessment of parameters in foot contact patterns, PTIs, and COP path trajectories appears to be helpful in evaluating outcomes after corrective surgery.

From the Department and Research Institute of Rehabilitation Medicine (ES Park, CI Park, Rha, CW Park), Department of Orthopaedic Surgery (Kim), and BK 21 Project for Medical Sciences (ES Park), Yonsei University College of Medicine, Seoul, South Korea. 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 Dong-wook Rha, MD, MS, Seodaemun-gu Shinchon-dong 134, Rehabilitation Hospital, Yonsei University College of Medicine, Seoul, Korea, 120752, e-mail: [email protected]. 0003-9993/06/8705-10352$32.00/0 doi:10.1016/j.apmr.2005.12.038

Key Words: Cerebral palsy; Foot deformities; Rehabilitation. © 2006 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation QUINUS IS THE MOST COMMON foot deformity in E people with cerebral palsy (CP) and often is associated with varus or valgus deformity of the hindfoot. Foot defor1,2

mity is caused by spasticity and an imbalance of muscles; it may adversely affect standing and walking ability. Operative treatment for foot deformity is recommended for cases in which prolonged nonoperative therapies such as physiotherapy, ankle-foot orthoses, casting, nerve block, and injections of botulinum toxin have failed. An objective evaluation of foot disorders would be useful in planning surgical management and in assessing the outcome of treatment. Although the 3-dimensional gait analysis system has been widely used for planning corrective musculoskeletal surgery in people with CP, the system has limited ability to reveal significant changes of foot deformity after surgery.3 Radiographic measurements of foot deformity have been considered the most useful tools for preoperative assessment when surgery is indicated.1 The dynamic deformity that occurs during walking, which needs to be accurately assessed for a successful surgical outcome, may not, however, be adequately judged with radiographic measurements.1 Measuring foot pressure during walking may be useful for demonstrating dynamic changes in the foot. With the computerized insole sensor system, this pressure measurement can be reliably and quantitatively assessed.4-7 The clinical relevance of the pressure measurement in the evaluation of foot deformity caused by neurogenic and congenital disorders has been reported.1,2,8 There are several parameters in dynamic foot pressure measurements. These parameters can be grouped into 3 categories: measurements of foot contact pattern, measurements of plantar pressure distributions (eg, peak pressure time, pressure-time integrals [PTIs]), and assessment of the center of pressure (COP) trajectories. Foot contact patterns were used in a previous study8 to assess the improvement of a pes planovalgus deformity after lateral column lengthening. The characteristics of the PTI of foot pressure have been reported previously for evaluation of foot deformities.1,2 The changes of peak pressure at the heel after botulinum toxin injection for equinus foot were also reported.9 The COP trajectories during the stance phase have been used to assess a subject’s locomotion and sense of balance.5,10-12 In addition, COP trajectories were used to detect pronation movement of the subtalar joint immediately after heel strike, which was related to poor long-term functional outcome in surgically treated clubfeet.12 COP parameters have not, however, been used to evaluate foot deformity in subjects with CP. To our knowledge, all parameters of foot pressure measurement in different foot deformities have not been simultaneously assessed and compared in subjects with CP. Arch Phys Med Rehabil Vol 87, May 2006

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DYNAMIC FOOT PRESSURE IN PERSONS WITH SPASTIC CP, Park Table 1: Characteristics of Subjects Characteristics

Equinus

Equinovarus

Equinovalgus

No. of subjects No. of feet Mean age* (y) Follow-up duration* (mo) Boys/girls Diplegia/hemiplegia

21 35 10.3⫾6.1 (5–26) 15.0⫾5.8 (7–28) 9/12 17/4

15 17 9.2⫾3.8 (4–18) 15.1⫾9.5 (6–39) 10/5 9/6

8 15 8.6⫾3.5 (6–19) 13.6⫾3.6 (9–19) 7/1 7/1

*Values are mean ⫾ standard deviation (SD) and range.

Our objective in this study was to demonstrate the overall patterns of dynamic foot pressure in different foot deformities using a computerized insole sensor system and to assess the changes in these parameters after corrective surgery in children with spastic CP who can ambulate independently. METHODS Children were included in the study if they met the following criteria: (1) could walk independently without assistance, (2) had no previous orthopedic surgery, (3) had no injection of botulinum toxin into lower limbs within 1 year, and (4) had corrective surgeries for problematic foot deformities and had a follow-up checkup at a minimum of 6 months postsurgery as part of their routine medical care. The study population included 44 patients (77 involved feet)—11 patients had hemiplegia and 33 had diplegia. We subsequently excluded 10 limbs (in subjects with diplegic CP) on which derotational osteotomy of the tibia or femur was performed. This exclusion decision was based on the possibility that the change of foot progression angle after derotational osteotomy could affect the pressure distribution.13 We therefore analyzed foot pressure data from 67 feet of the 44 subjects, whose general characteristics are shown in table 1. The preoperative foot deformities were classified into 3 groups: equinus, equinovarus, and equinovalgus. The deformities were determined by visual nonquantitative inspection, physical examination, and radiographic examination based on previous studies.1,2,14 All subjects had a heel cord lengthening operation. Additionally, for patients with equinovarus deformity, split tendon transfer or lengthening of tibialis posterior (14 feet) and split tendon transfer of tibialis anterior (3 feet) were performed. Flexor digitorum lengthening (5 feet) and short plantar muscle release (1 foot) were also performed for those patients. For the patients with equinovalgus deformity, calcaneal lengthening osteotomy (10 feet) and extra-articular subtalar arthrodesis with cannulated screw and autogenous iliac crest bone graft (5 feet), were performed along with heel cord lengthening. Other corrective surgical procedures performed for the patients with proximal musculoskeletal problems are listed in table 2. Dynamic foot pressure was measured preoperatively and postoperatively for each subject. The time between preoperative and postoperative tests was 15.0⫾5.8 months for subjects with equinus, 15.1⫾9.5 months for subjects with equinovarus, and 13.6⫾3.6 months for subjects with equinovalgus. The F-scan systema was used to measure foot pressure. The pressure was recorded at 50Hz with a pressure sensitive insole consisting of a 0.15-mm thick sensor with an embedded gridwork of 960 pressure-sensing cells, evenly distributed at 0.5-cm (0.2-in) intervals. Before use, the disposable insole was trimmed to fit into the shoes. Data from 5 trials at a self-selected walking speed were collected for each subject. Each patient was told to look straight ahead and walk as naturally as possible. Patients were allowed Arch Phys Med Rehabil Vol 87, May 2006

to walk approximately 20 to 30m to become acquainted with the system. Foot pressure was recorded for 5 steps in the middle of the test walk and the mean value was calculated. After the pressure reading data were saved, they were processed with custom-made software, FSCAN version 4.19F.a We grouped the parameters in dynamic foot pressure measurements into 3 categories: measurements of foot contact pattern, measurements of PTIs, and assessment of the COP trajectories. For the foot contact pattern, we measured total contact area, contact length, and contact width of the forefoot, midfoot, and hindfoot (fig 1); center of pressure index (COPI⫽area lateral/area medial) was calculated with the method described by Oeffinger et al.8 For the PTIs, the foot was divided into 5 sections: medial forefoot, lateral forefoot, medial midfoot, lateral midfoot, and heel, as previously reported (see fig 1).15 The pressure-time data of each individual section were graphed. The integral of the pressure-time graphs showed total pressure achieved by each section of the foot; this total pressure was identified as “impulse” for this study. The relative impulse was defined as the percentage of impulse exerted on each section from the total impulses of the 5 sections. The relative impulse distributed under the medial column of the foot is the sum of relative impulses of the medial forefoot and midfoot; the relative impulse under the lateral column is the sum of relative impulses of the lateral forefoot and midfoot. We defined the coronal index as the relative impulse in the medial column minus the relative impulse in the lateral column, as proposed by Chang et al.1 For the COP trajectories, we calculated the coordinates of COP by summing the product of the pressures recorded by each transducer with its coordinates and dividing the result by the total pressure recorded by all transducers.10 After the COP coordinates were converted to ASCII data, the anteroposterior (AP) and mediolateral (ML) displacement of COP, slope of COP (in degrees relative to the longitudinal axis of the foot) and velocity of COP (in cm/s) were measured using a previously reported technique (see fig 1).10 Table 2: Accompanying Surgical Procedures No. of Sides Type

Psoas lengthening Adductor longus and gracillis lengthening Tensor fascia lata and anterior fiber of gluteus medius lengthening Rectus femoris transfer to sartorius Medial hamstring lengthening Lateral hamstring lengthening

Equinus (n⫽35)

Equinovarus (n⫽17)

Equinovalgus (n⫽15)

10

2

10

1

1

2

6

1

8

16 30 7

11 13 0

8 15 4

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DYNAMIC FOOT PRESSURE IN PERSONS WITH SPASTIC CP, Park

We analyzed all these parameters for identifying the characteristic foot pressure distributions between the foot deformity groups and the changes after corrective surgery. We used analysis of variance (ANOVA) to compare the preoperative foot pressure parameters between the 3 groups of foot deformities. The changes between preoperative and postoperative plantar pressure parameters in each group were compared using a paired t test. For all tests, P values less than .05 were considered statistically significant. RESULTS

Fig 1. Relative distribution of peak pressure in all 5 segments of the foot: (A) lateral forefoot, (B) medial forefoot, (C) lateral midfoot, (D) medial midfoot, (E) heel, (a) contact length, (b) forefoot contact width, (c) midfoot contact width, (d) hindfoot contact width, (e) mediolateral displacement of COP, (f) anteroposterior displacement of COP, and (g) slope of COP path.

Analysis of Dynamic Foot Pressure Parameters in Different Foot Deformities Foot contact pattern. Table 3 shows the preoperative foot pressure parameters of each foot deformity group. There were significant differences in the COPI between foot deformity groups. Values of the COPI (⬍1) in the equinovalgus group indicated more medial weight bearing, while values of the COPI (⬎1) in the equinovarus group indicated more lateral weight shifting. The value of the COPI in the equinus group indicated no shift in weight bearing medially or laterally. There was a significant difference only in the equinovarus group, compared with both the equinus and equinovalgus groups, but not between the equinus and equinovalgus groups. Total contact area, contact length, and contact width did not differ significantly between the foot deformity groups. Pressure-time integral. The distribution of relative impulse in 5 sections of the foot demonstrated different patterns in each foot deformity group (see table 3). In the equinovarus group, patients showed a high relative impulse under the lateral column and a low relative impulse under the medial column. The pattern of relative impulse distribution was reversed in the equinovalgus group. In addition, the medial midfoot relative impulse differed significantly between the 3 groups. The coro-

Table 3: Characteristics of Foot Pressure Measurements in 3 Groups of Foot Deformities Parameters

Foot contact pattern Total contact area (cm2) Contact length (cm) Contact width (cm) Forefoot Midfoot Hindfoot COPI PTI Medial forefoot (%) Lateral forefoot (%) Medial midfoot (%) Lateral midfoot (%) Heel (%) Coronal index Trajectory of COP AP displacement (cm) ML displacement (cm) Slope (deg) COP velocity (cm/s)

Equinus (n⫽35)

62.5⫾30.6 (17.6–115.1) 15.2⫾5.5 (4.8–23.5) 5.9⫾1.0 (4.0–7.6) 3.4⫾2.4 (0.0–7.3) 2.9⫾2.2 (0.0–6.3) 1.0⫾0.2 (0.5–1.6) 43.6⫾13.1 (22.4–77.4) 28.3⫾11.4 (7.9–73.3) 9.3⫾6.2† (0.0–24.1) 10.5⫾7.3 (0.0–24.2) 8.3⫾6.6 (0.0–24.0) 14.1⫾19.5 (⫺46.6 to 56.2) 5.9⫾3.9 (0.3–15.6) 1.0⫾0.5 (0.3–2.3) 17.7⫾15.9 (3.0–59.0) 8.6⫾5.8 (0.3–23.3)


46.4⫾27.2 (17.8–103.4) 13.5⫾5.0 (6.4–21.2) 5.9⫾1.2 (3.4–7.4) 2.5⫾1.6 (0.0–5.0) 2.0⫾2.3 (0.0–5.4) 1.7⫾0.9* (0.9–4.8)


52.5⫾20.0 (22.9–87.7) 14.2⫾4.1 (6.2–20.3) 5.8⫾0.8 (4.5–7.4) 3.7⫾1.8 (0.0–6.3) 1.4⫾1.9 (0.0–5.8) 0.7⫾0.1 (0.5–0.8)

28.9⫾18.3* (3.2–61.3) 43.9⫾24.0* (13.7–84.3) 3.0⫾4.4† (0.0–13.6) 15.6⫾13.1‡ (0.0–39.7) 8.6⫾10.6 (0.0–34.7) ⫺27.5⫾37.7* (⫺93.6 to 22.6) 5.4⫾4.6 (0.6–14.4) 1.1⫾0.5 (0.3–1.9) 21.9⫾19.3 (3.0–61.0) 8.4⫾7.8 (1.0–24.8)

45.9⫾10.9 (26.6–57.8) 23.9⫾9.2 (13.8–43.1) 15.9⫾7.6† (0.8–25.3) 7.3⫾4.6 (1.3–15.9) 7.0⫾7.7 (0.0–26.1) 30.7⫾18.9 (7.0–61.8) 6.5⫾4.2 (1.6–14.0) 1.1⫾0.6 (0.4–2.3) 12.0⫾7.7 (3.0–27.0) 9.3⫾8.6 (1.7–26.9)

NOTE. Values are mean ⫾ SD (range). Comparisons were made by 1-way ANOVA with Tukey post hoc test. Center of pressure index ⫽ (area in lateral column)/(area in medial column). Coronal index ⫽ (relative impulses in medial forefoot and medial midfoot) – (relative impulses in lateral forefoot and lateral midfoot). *P⬍.05, equinovarus group vs equinus and equinovalgus groups. † P⬍.05, equinus group vs equinovarus group vs equinovalgus group. ‡ P⬍.05, equinovarus group vs equinovalgus group.

Arch Phys Med Rehabil Vol 87, May 2006

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DYNAMIC FOOT PRESSURE IN PERSONS WITH SPASTIC CP, Park Table 4: Changes of Parameters of Foot Contact Pattern After Corrective Surgery Equinus (n⫽35) Parameters

Total contact area (cm2) Contact length (cm) Contact width (cm) Forefoot Midfoot Hindfoot COPI



Before

After

Before

After

Before

After

62.5⫾30.6 (17.6–115.1) 15.2⫾5.5 (4.8–23.5)

76.1⫾28.7* (30.4–136.7) 18.3⫾3.0* (13.2–23.3)

46.4⫾27.2 (17.8–93.4) 13.5⫾5.0 (6.4–21.2)

67.2⫾19.1* (18.6–101.6) 18.1⫾2.4* (13.2–23.7)

52.5⫾20.0 (22.9–87.7) 14.2⫾4.1 (6.2–20.3)

77.1⫾17.8* (46.7–110.1) 18.1⫾2.0* (15.5–22.1)

5.9⫾1.0 (4.0–7.6) 3.4⫾2.4 (0.0–7.3) 2.9⫾2.2 (0.0–6.3) 1.0⫾0.2 (0.5–1.6)

6.0⫾0.9 (4.7–7.6) 4.1⫾1.8 (0.0–6.9) 4.9⫾0.9* (3.4–6.7) 1.0⫾0.3 (0.3–2.2)

5.9⫾1.2 (3.4–7.4) 2.5⫾1.6 (0.0–5.0) 2.0⫾2.3 (0.0–5.4) 1.7⫾0.9 (0.9–4.8)

5.9⫾1.8 (4.5–7.6) 3.3⫾1.5 (0.0–5.0) 4.8⫾0.6* (3.9–5.9) 1.1⫾0.3* (0.6–1.7)

5.8⫾0.8 (4.5–7.4) 3.7⫾1.8 (0.0–6.3) 1.4⫾1.9 (0.0–5.8) 0.7⫾0.1 (0.5–0.8)

5.6⫾0.8 (3.8–6.9) 4.4⫾1.5 (1.3–6.3) 5.4⫾0.7* (4.4–6.4) 1.2⫾0.3* (0.9–1.9)

NOTE. Values are mean ⫾ SD (range). Comparisons were made by paired t test. *P⬍.05, preoperative vs postoperative values.

nal index showed a negative value for the equinovarus deformity and positive values for both the equinovalgus and equinus groups. COP trajectory. The COP trajectory did not differ significantly between the foot deformity groups. Changes in Dynamic Foot Pressure Parameters After Corrective Surgery Foot contact pattern. After surgery, total foot contact area, contact length, and contact width of the hindfoot had significantly increased in all 3 groups, but the contact widths of forefoot and midfoot did not change significantly. In addition, the COPI was decreased after corrective surgery in the equinovarus group but was increased in the equinovalgus group. The COPI was not changed in the equinus group postsurgery (table 4). Pressure-time integral. The hindfoot postsurgery relative impulse was increased significantly in all 3 groups. The relative impulse in both the medial and lateral forefoot was decreased for both the equinus and equinovalgus deformities, yet only the lateral forefoot relative impulse was decreased for the equinovarus deformities. Significant changes of relative impulse in the midfoot after surgery were only observed in the equinovalgus deformity group. In this deformity, relative impulse in the medial midfoot was significantly decreased, while relative impulse in the lateral midfoot was significantly increased. In the equinovarus group, coronal index showed a significant shift from lateral to medial weight bearing of the foot. The equinovalgus group showed the inverse pattern of changes in coronal index. In contrast, the coronal index did not change significantly in the equinus group (table 5). COP trajectory. The length of AP displacement of COP and the velocity of COP increased significantly, while the slope of the COP path decreased significantly postsurgery in all 3 groups (table 6). DISCUSSION Foot deformities result in an abnormal distribution of load on the plantar surface of the foot. Therefore, foot pressure measurements have been used to evaluate the high-pressure areas that are at risk for ulceration in diabetic and neuropathic feet,16-18 in order to demonstrate the differences in foot deformities1,2 and to demonstrate changes after surgery.8,19 Digital data obtained from the new foot-pressure measurement system are valuable sources of information for clinical decision making and are a valuable research tool.1 The F-scan insole system we used is known as a reliable and reproducible method for recording pressure distribution on the foot during walking.4,6,7 Among the parameters of foot contact pattern, the COPI was the only parameter to demonstrate significant differences beArch Phys Med Rehabil Vol 87, May 2006

tween foot deformities in our study. A COPI greater than 1 indicates more lateral weight bearing and a COPI less than 1 indicates more medial weight bearing.8 In our study, the values of the COPI in the equinovalgus and equinovarus groups agreed with the results of a previous study.8 These findings suggested that the COPI could be used as a parameter for assessing foot deformities in the frontal plane in subjects with CP. In equinus deformity, however, the range of the COPI was wide, from less than 1 to greater than 1. It indicates weight shifting to the medial side in some cases and to the lateral side in other cases. It is not known with certainty whether the COPI is predictive of eventual development to equinovarus or valgus deformity. A long-term follow-up study would be useful in determining the long-term consequence of weight shifting in these cases. The changes in foot contact area after corrective surgery8,20,21 and botulinum toxin injection for foot deformity9 have been studied previously. The strong relation demonstrated between the changes in foot contact patterns and radiographic measurements after corrective orthopedic surgery for symptomatic flat feet21 and planovalgus deformity8 suggests that changes in foot contact patterns can be helpful in evaluating postsurgery outcomes. In this study, we discovered significant changes in foot contact pattern postsurgery. There were increases in total contact area, contact length, and contact width of the hindfoot in all 3 groups postsurgery. The improvements in these parameters appear to have resulted from the improvement of weight bearing on the heel after heel cord lengthening surgery. Therefore, these parameters are useful in assessing the improvement of the foot abnormalities in the sagittal plane, such as the equinus, but not the changes in the frontal plane, such as the varus or valgus. In a previous report,8 the increase in the COPI from below 1 to above 1 after a lateral column lengthening operation for equinovalgus deformity indicated a change of weight bearing from the medial to the lateral side of the foot. In addition, the improvement in the COPI in that study correlated highly with the improvement in radiographic findings. In our study, significant changes in the COPI were observed postsurgery in the equinovarus and equinovalgus groups, but not in the equinus group. This indicates that the COPI can be accepted as a useful parameter for assessing changes in the frontal plane. Because the COPI does not have an anterior versus posterior component by its definition, it is not useful for assessing changes in the sagittal plane. Bowen et al15 described a method of measuring dynamic foot pressure using integrated pressure-time data, which combines pressure and contact time. The PTI in 5 sections of the foot has been commonly used in plantar pressure measurements to evaluate foot deformities and the changes after cor-

24.0⫾9.0* (15.8–48.1) 18.4⫾4.5* (11.8–24.2) 10.8⫾6.3* (1.4–22.0) 17.0⫾5.8* (7.5–24.7) 29.8⫾10.7* (13.0–49.3) ⫺0.6⫾12.1* (⫺22.9 to 24.6) 45.9⫾10.9 (26.6–57.8) 23.9⫾9.2 (13.8–43.1) 15.9⫾7.6 (0.8–25.3) 7.3⫾4.6 (1.3–15.9) 7.0⫾7.7 (0.0–26.1) 30.7⫾18.9 (7.0–61.8)


28.8⫾7.5 (9.3–39.9) 19.1⫾5.6* (7.6–27.9) 4.3⫾3.4 (0.0–11.0) 13.1⫾10.3 (0.0–45.8) 34.8⫾11.7* (16.8–56.3) 0.9⫾20.4* (⫺58.5 to 30.5) 28.9⫾18.3 (3.2–61.3) 43.9⫾24.0 (13.7–84.3) 3.0⫾4.4 (0.0–13.6) 15.6⫾13.1 (0.0–39.7) 8.6⫾10.6 (0.0–34.7) ⫺27.5⫾37.7 (⫺93.6 to 22.6) 43.6⫾13.1 (22.4–77.4) 28.3⫾11.4 (7.9–73.3) 9.3⫾6.2 (0.0–24.1) 10.5⫾7.3 (0.0–24.2) 8.3⫾6.6 (0.0–24.0) 14.1⫾19.5 (⫺46.6 to 56.2) Medial forefoot (%) Lateral forefoot (%) Medial midfoot (%) Lateral midfoot (%) Heel (%) Coronal index

33.9⫾11.0* (18.2–59.2) 20.1⫾7.5* (7.0–42.2) 8.6⫾4.6 (0.0–18.0) 11.0⫾4.9 (1.7–20.6) 26.4⫾10.1* (9.6–47.3) 11.5⫾13.4 (⫺17.4 to 48.2)

After Equinovarus (n⫽17) Before After Before Parameters

Equinus (n⫽35)

Table 5: Changes in PTIs in Each Specific Area and Coronal Index After Corrective Surgery

Before


After


707

rective surgery.1,2,13,15 The medial midfoot relative impulse differed significantly between the 3 deformities in our study. The equinovalgus deformity is characterized by plantarflexion of the talus and calcaneus, calcaneal valgus, navicular abduction, and subtalar eversion, resulting in midfoot sag, lowering of the longitudinal arch, and excessive stress on the medial side of the foot.22 The medial midfoot in the equinovalgus group had the highest relative impulse value, which reflected the above anatomic changes. Additionally, the relative impulse of the medial forefoot, lateral forefoot, and midfoot was useful for differentiating equinovarus from equinovalgus or equinus deformities. The coronal index measures the discrepancy of the PTI between the medial column and the lateral column. A negative value indicates a foot with varus deformity and a positive value indicates a foot with valgus deformity,1 while a coronal index in a normal foot has a value close to zero. In our study, patients with equinovalgus or equinovarus deformities showed patterns similar to those reported in previous studies.1,2 In the cases with equinus deformity, the mean of the coronal index was above zero before the operation, which suggested more weight bearing of the medial column of the foot. As children grow older, the equinus deformity is known to collapse into planovalgus in most cases, and into varus in some cases.23 The wide range of coronal index made the interpretation difficult, however. Therefore, a long-term follow-up study to investigate the relation between the nature of equinus deformity and the positive mean value of coronal index would be useful. Falso et al9 evaluated children with CP using pedobarometric evaluations while the subjects were standing. They found a significant increase in the peak pressure value at the hindfoot after botulinum toxin injection for equinus foot deformity. They did not, however, investigate the pressure distributions at the medial and lateral sides of the midfoot and forefoot in the equinus deformity, were not investigated in that study or in other previous studies. To our knowledge, this is the first report showing forefoot and midfoot relative impulses in equinus deformities. In the equinus deformity, all the weight is placed on the toes or the forefoot.2 The significant increase in relative impulse of the heel and decrease in relative impulse of the forefoot shown in equinus deformity after surgical intervention indicated that changes in relative impulse in specific areas of the foot can be considered a useful parameter for assessing postsurgical improvements of equinus deformity. In the cases with equinovarus and equinovalgus deformity, the significant postoperative changes of relative impulse appeared to result from both the improvement of weight bearing on the heel and the restoration of balance of weight bearing between the medial column and lateral column. Especially, the significant postoperative changes in coronal index shown in equinovarus and equinovalgus deformities appear to be useful parameters with which to assess the improvement of weight bearing of the foot in the frontal plane. Our findings are in accord with the results of previous studies.1,2 COP is defined as the point at which there is no movement from all of the applied forces.24 During gait, COP will change over time. For example, in the first part of the step, when only the heel is in contact with the ground, the COP is in the heel. Later in the gait cycle, after heel-off, the COP is measured over time, then plotted over a picture of the foot and a path of the COP is eventually produced.24 The measurement of COP has been widely used in evaluating foot function and in understanding the control of balance.10,11,25-27 The COP parameters we measured did not reveal any significant differences between foot deformity groups. After corrective surgery, the AP displacements of COP were increased Arch Phys Med Rehabil Vol 87, May 2006

708

DYNAMIC FOOT PRESSURE IN PERSONS WITH SPASTIC CP, Park Table 6: Changes of Parameters of COP After Corrective Surgery Equinus (n⫽35)



Parameters

Before

After

Before

After

Before

After

AP displacement (cm) ML displacement (cm) Slope (deg) COP velocity (cm/s)

5.9⫾3.9 (0.3–15.6) 1.0⫾0.5 (0.3–2.3) 17.7⫾15.9 (3.0–59.0) 8.6⫾5.8 (0.3–23.3)

11.9⫾2.8* (3.5–17.3) 0.9⫾0.4 (0.3–1.8) 4.3⫾2.4* (1.0–12.0) 17.6⫾4.9* (5.6–26.4)

5.4⫾4.6 (0.6–14.4) 1.1⫾0.5 (0.3–1.9) 21.9⫾19.3 (3.0–61.0) 8.4⫾7.8 (1.0–24.8)

11.7⫾2.7* (6.3–15.9) 1.1⫾0.5 (0.3–1.6) 5.4⫾2.3* (2.0–12.0) 18.2⫾4.9* (7.8–25.5)

6.5⫾4.2 (1.6–14.0) 1.1⫾0.6 (0.4–2.3) 12.0⫾7.7 (3.0–27.0) 9.3⫾8.6 (1.7–26.9)

11.8⫾2.9* (6.9–17.3) 1.2⫾0.5 (0.3–1.9) 5.9⫾2.7* (1.0–11.0) 14.3⫾6.9* (2.7–22.0)


in all groups, apparently the result of the increased heel contact. In addition, the slopes of the COP path in the 3 deformities were significantly decreased postsurgery, almost approaching the value of 6°, as reported previously for unimpaired adults.10 The improvement of slope of the COP postsurgery indicates that it could be useful in evaluating measurements after corrective surgery for foot deformities. The velocity of the COP during the stance phase of normal walking is considered a relatively reliable measure.28 According to Grundy et al,26 the velocity increased for subjects with hallux valgus and metatarsalgia, as compared with normal feet. On the contrary, the velocity of COP decreased significantly in the patients who had undergone amputation of their big toes.29 Although the velocity of COP significantly increased postsurgery in our subjects, the postoperative values were much slower than those of COP in healthy adults, as reported in previous studies.10,28 The validity and clinical relevance of these parameters as a measure of surgical outcome for foot deformities should be further investigated. Dynamic pressure parameters are functional measures of patients’ ability to support and efficiently transfer the body mass during ambulation.21 Therefore, it is a major concern whether the improvement of foot pressure distribution during walking can lead to the improvement of ambulatory function in subjects with CP. There are, however, many factors that may affect ambulatory function, including the time after surgical intervention, the type of surgical procedure performed, the frequency, intensity, and type of physical therapy provided, and a patient’s cognitive status. We did not investigate the ambulatory function in this study because we did not control for these variables. Therefore, we suggest that a future study investigate the effect of the improvement of foot pressure distribution after surgical intervention on gait function. CONCLUSIONS Using a computerized insole sensor system, we assessed the parameters of foot contact pattern, PTIs, and COP trajectories in different foot deformities in subjects with CP. The COPI of foot contact pattern and the PTIs in 5 sections of the foot showed distinctive patterns in different foot deformities. There were significant changes in several parameters of foot contact pattern, relative impulse, and COP trajectories after corrective surgery. Our results suggest that dynamic foot pressure measurements can be a useful tool for documenting foot deformities and for evaluating postsurgical changes in subjects with CP. The parameters reflecting medial or lateral changes in weight bearing, such as the COPI and coronal index, appear to be especially useful for evaluating abnormalities and improvements after intervention in the frontal plane, such as varus and valgus. Total contact area, contact length, contact width of the hindfoot, relative impulse of heel, and AP displacement of COP appear to be useful measurements with which to assess improvements in the sagittal plane after corrective surgery. Acknowledgments: We are grateful to the members of the Department and Research Institute of Rehabilitation Medicine, Yonsei Arch Phys Med Rehabil Vol 87, May 2006

University College of Medicine, for their help with patient recruitment. We thank Don Sin Lee for his technical assistance with data collection. References 1. Chang CH, Miller F, Schuyler J. Dynamic pedobarograph in evaluation of varus and valgus foot deformities. J Pediatr Orthop 2002;22:813-8. 2. Chang CH, Albarracin JP, Lipton GE, Miller F. Long-term follow-up of surgery for equinovarus foot deformity in children with cerebral palsy. J Pediatr Orthop 2002;22:792-9. 3. Abu-Faraj ZO, Harris GF, Smith PA. Surgical rehabilitation of the planovalgus foot in cerebral palsy. IEEE Trans Neural Syst Rehabil Eng 2001;9:202-14. 4. Ahroni JH, Boyko EJ, Forsberg R. Reliability of F-scan in-shoe measurements of plantar pressure. Foot Ankle Int 1998;19: 668-73. 5. Rose NE, Feiwell LA, Cracchiolo A 3rd. A method for measuring foot pressures using a high resolution, computerized insole sensor: the effect of heel wedges on plantar pressure distribution and center of force. Foot Ankle 1992;13:263-70. 6. Young CR. The F-SCAN system of foot pressure analysis. Clin Podiatr Med Surg 1993;10:455-61. 7. Randolph AL, Nelson M, Akkapeddi S, Levin A, Alexandrescu R. Reliability of measurements of pressures applied on the foot during walking by a computerized insole sensor system. Arch Phys Med Rehabil 2000;81:573-8. 8. Oeffinger DJ, Pectol RW Jr, Tylkowski CM. Foot pressure and radiographic outcome measures of lateral column lengthening for pes planovalgus deformity. Gait Posture 2000;12:189-95. 9. Falso M, Fiaschi A, Manganotti P. Pedobarometric evaluation of equinus foot disorder after injection of botulinum toxin A in children with cerebral palsy: a pilot study. Dev Med Child Neurol 2005;47:396-402. 10. Han TR, Paik NJ, Im MS. Quantification of the path of center of pressure (COP) using an F-scan in-shoe transducer. Gait Posture 1999;10:248-54. 11. Scherer PR, Sobiesk GA. The center of pressure index in the evaluation of foot orthoses in shoes. Clin Podiatr Med Surg 1994;11:355-63. 12. Huber H, Dutoit M. Dynamic foot-pressure measurement in the assessment of operatively treated clubfeet. J Bone Joint Surg Am 2004;86:1203-10. 13. Chang WN, Tsirikos AI, Miller F, Schuyler J, Glutting J. Impact of changing foot progression angle on foot pressure measurement in children with neuromuscular diseases. Gait Posture 2004;20: 14-9. 14. Razeghi M, Batt ME. Foot type classification: a critical review of current methods. Gait Posture 2002;15:282-91. 15. Bowen TR, Miller F, Castagno P, Richards J, Lipton G. A method of dynamic foot-pressure measurement for the evaluation of pediatric orthopaedic foot deformities. J Pediatr Orthop 1998;18: 789-93.


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Arch Phys Med Rehabil Vol 87, May 2006