Effects of Tarsal Coalition Resection on Dynamic Plantar Pressures and Electromyography of Lower Extremity Muscles

ORIGINAL RESEARCH

Effects of Tarsal Coalition Resection on Dynamic Plantar Pressures and Electromyography of Lower Extremity Muscles Roger Lyon, MD, Xue-Cheng Liu, MD, PhD, and Sung-Joon Cho, BS The goal of this study was to evaluate kinetic abnormalities in feet after tarsal coalition resection using plantar pressure measurements and electromyography of 4 muscle groups in the lower limb. Eleven subjects (14 feet) with tarsal coalition (3 feet with calcaneocuboid, 6 feet with calcaneonavicular, and 5 feet with talocalcaneal) underwent coalition excision. Patients ranged in age from 9 to 17 years, and mean follow-up was 20 months. Two feet underwent subsequent subtalar fusion and 1 had a triple arthrodesis. Plantar pressure and electromyography measurements were compared with data taken from 68 normal (control) subjects between the ages of 6 to 16 years. Feet with tarsal coalition showed significant differences in the midfoot region, with increases in contact area (40.36 cm2 ⫾ 14.7 vs 18.02 cm2 ⫾ 8.0, P ⬍ .001), loading (5.63 N/cm2 sec ⫾ 3.4 vs 1.83 N/cm2 sec ⫾ 0.9, P ⬍ .001) and peak pressure (13.38 N/cm2 ⫾ 5.8, 6.81 N/cm2 ⫾ 2.8, P ⫽ .01). Tarsal coalition feet also displayed reduced peak pressure and loading at the region of the fifth metatarsal head as compared with uninvolved feet (P ⬍ .05). Electromyography measurements were also performed on both the affected and unaffected feet of 9 subjects who had undergone resection of their coalition. These measurements revealed nearly consistent abnormal activity in the peroneal, gastrocnemius, and soleus muscles on both the surgically operated foot and the contralateral side, including either prolonged monophasic activity or biphasic activity. These findings suggest that although resection of coalition may have relieved symptoms of discomfort, it did not restore normal foot alignment or muscular balance. ( The Journal of Foot & Ankle Surgery 44(4):252-258, 2005) Key words: tarsal coalition, calcaneonavicular, talocalcaneal, dynamic plantar pressure, electromyography

A tarsal coalition is a congenital foot abnormality representing an abnormal connection between tarsal bones. It results from a failure of differentiation and segmentation in the primary mesenchyme in the developing fetal foot (1). The overall prevalence of tarsal coalitions reportedly ranges from 0.03% to 1% (2). The most common coalitions are of the calcaneonavicular (43.6%) and talocalcaneal joint (48.1%), which account for virtually all of the symptomatic From the Department of Orthopedic Surgery, Medical College of Wisconsin, Milwaukee, WI. Address correspondence to: Roger Lyon, MD, Department of Orthopedic Surgery, Children’s Hospital of Wisconsin, 8701 Watertown Plank Road, Suite 3018, Milwaukee, WI 53226. E-mail: [email protected] Copyright © 2005 by the American College of Foot and Ankle Surgeons 1067-2516/05/4404-0001$30.00/0 doi:10.1053/j.jfas.2005.04.003

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feet of patients with this condition (2). Talonavicular and other foot coalitions are rare and usually asymptomatic (3, 4). In most talocalcaneal and calcanonavicular coalitions, the calcaneus is held in a valgus position as ossification progresses, leading to a rigid hindfoot. Subtalar motion is moderately limited in calcaneonavicular and talonavicular coalitions and is completely restricted in the talocalcaneal type. Tarsal coalitions are also the most common cause of peroneal spastic flatfoot (3). This condition is characterized by peroneal muscle spasms and a painful, rigid valgus deformity of both the forefoot and hindfoot (5–7). These are often the presenting complaints from patients with this condition, and these symptoms can be accompanied by pain on the lateral aspect of the calf, tearing of an ossified coalition, and synovial inflammation (3, 8). These and adap-

tive shortening of the peroneal tendons can lead to reflex spasms (3, 8). In severe cases, the muscle spasms may also involve the extensor digitorium longus and peroneous tertius muscles. The spasms eventually subside, but degenerative arthritis often results from both the deformity and altered intraarticular mechanics (8). Talocalcaneal coalitions with posterior and anterior muscle spasms that lead to varus deformity have been reported but are extremely rare (9). Symptomatic calcaneonavicular and talocalcaneal coalitions are often treated with surgical management if nonoperative treatment fails to alleviate the patient’s symptoms. Operative methods are primarily limited to either excision of the coalition or arthrodesis. Patient age, type and extent of the coalition, and the presence of degenerative changes in the joints affect the choice of procedures. Excision of the calcanonavicular bar has been reasonably successful in some patients. Patients with persistent pain after coalition excision may need a subsequent triple arthodesis (10, 11). Although the triple arthodesis is occasionally needed for patients with a talocalcaneal bar, simple resection has yielded good results (12–16). There are several instruments that can be used to assess the functional characteristics of feet with tarsal coalitions after radiographic diagnosis has been made. Besides clinical examination, electrodynography, electromyography (EMG), force plates, and plantar pressure platforms can evaluate the foot’s performance. Bowen et al (17) established the dynamic foot-pressure pattern of a normal population, dividing plantar surfaces into 5 segments: lateral forefoot, medial forefoot, lateral midfoot, medial midfoot, and heel. Lyon et al (18) further divided the plantar surface into 8 segments and reported dynamic plantar pressure measurements in a patient with a talocalcaneal coalition. However, few objective studies have documented the effects of coalition resection on plantar pressure distribution (4, 17, 19), and no previous studies have evaluated dynamic muscular activity as a function of the gait cycle after surgical tarsal coalition resection. A comparison of EMG findings in patients following a resected tarsal coalition with that of a normal standard can be used to infer whether the muscle is behaving appropriately or pathologically. When these data are used in conjunction, much more specific information can be obtained (20). The goal of this study was to determine whether coalition resection can restore normal biomechanical function on the basis of these parameters.

Materials and Methods The experiment involved 3 components of physical examination, EMED plantar pressure measurements, and dynamic EMG measurements of the peroneous longus, gastrocnemius, tibialis anterior, and soleus muscles during walking. Patients with tarsal coalition were recruited from

our pediatric orthopedic clinics. The control group was recruited from the family and siblings of patients and children of the staff. These patients were between the ages of 6 and 16 years and were screened for foot pain and activity limitations. Their feet and gait were examined. No radiographs were performed during the screening process. Exclusion criteria included the presence of a lower extremity injury within 1 year, any history of lower extremity fractures, neuromuscular disease, foot deformities, or an inability to ambulate. Physical examination of each subject in the experimental and control group was conducted by our senior pediatric orthopedic surgeon (R.L.). Using a goniometer (21), passive motion was measured for ankle plantarflexion, ankle dorsiflexion with the knee flexed at 90° and 0°. The lateral malleolus served as the fulcrum, and tibia and plantar surface as the tangents, with normal range of dorsiflexion considered to be 10° to 20°, and plantarflexion to be 35° to 50°. Strength of the anterior tibialis, posterior tibialis, gastrocnemius, peroneal longus and brevis, and extensor hallucis longus and brevis muscles was measured on a standard scale from 0 to 5. Gait analysis was performed on all subjects by experienced researchers, including authors and technical staff in the Motion Analysis Lab of Children’s Hospital of Wisconsin and Froedtert Memorial Lutheran Hospital. Plantar pressure measurements were performed using the EMED-NT platform system (Novel Inc, St. Paul, MN), which is specially designed for the small size of children’s feet. The system’s sensor plate dimensions are 582 ⫻ 340 ⫻ 20 mm and consist of a total of 2,736 sensors with a resolution of 4 sensors per cm2 at a frequency of 60 Hz (frame rates per seconds). The accuracy of the EMED pressure system is ⫾5% of mean value (22). Hughes et al (22) found that this system produced excellent reliability for most force, contact area, and pressure variables when the mean of 3 results was used. Those variables had reliability coefficients above 0.9. Each subject stepped on the EMED pressure platform 3 times per foot while walking at a self-selected pace along a 5-meter walkway. EMG analysis was performed with the MA-300 EMG System (Motion Lab System, Inc, Baton Rouge, LA), which consisted of a backpack, desktop unit, and double-differential surface EMG preamplifiers. The system provides detection of full-bandwidth EMG activity from 20 to 2000 Hz. The subject carried the backpack, which is strapped on by a belt during walking. The EMG signals are digitized and processed within the backpack and transmitted to the desktop unit by a coaxial cable. Four EMG surface pre-amplifiers were taped on each leg corresponding to the anterior tibialis, soleus, peroneous, and gastrocnemius muscles. Two reflective markers on each foot, located at the head of the second metatarsal and at the calcaneal tuberosity, were used to determine stance and swing phases during EMG recordings using a 15-camera VOLUME 44, NUMBER 4, JULY/AUGUST 2005

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To identify possible abnormal pressure distribution in more specific regions, the experimental model mapped 8 anatomical regions: lateral hindfoot (M01), medial hindfoot (M02), midfoot (M03), fifth metatarsal head (M04), second to fourth metatarsal head (M05), first metatarsal head (M06), fifth to second toes (M07), and hallux (M08). The boundaries were determined as seen in Fig 1. A total of 4 pressure parameters were calculated at each of those mapped regions. Pressure parameters consisted of plantar contact area, maximal ground reaction force, peak pressure, and pressure time (loading). The Wald-Wolfowitz runs test for nonparametric data was performed to compare EMED metric changes between the tarsal coalition group and the control group. Data of pressure measurements were also analyzed using the Wilcoxon matched-pairs test to compare the involved and uninvolved feet. EMG data were analyzed to determine whether there was a difference in the EMG interval between patients after coalition resection and existing normative data (23, 24). In the gait analysis, the mean time of each muscle activity versus gait cycle (%) was plotted and compared with the existing normative data (23, 24). We defined abnormal activity as premature or prolonged activity. Phasic activity was judged to be premature if the time of onset of activity preceded the mean time of onset for normal level walking, and to be prolonged if the duration of phasic activity exceeded the mean duration for normal level walking by more than 10% of the gait cycle (25). Furthermore, a panel of 3 experts in gait analysis further independently validated the abnormal activity of 4 EMG trials and judged it to be abnormal if at least 2 experts agreed. A probability of less than .05 was considered to be statistically significant. The surgical technique for excision of the calcaneonavicular bar was performed via a lateral Ollier incision (11). We also adopted Scranton’s surgical technique for talocalcaneal coalition excision (26), finding that a medioposterior approach met with greater success. FIGURE 1 Divisions of the entire foot into regions. MO1, Lateral hindfoot. Line ab extends through a middle point (a and b) on the anterior and posterior aspect on the heel, dividing into lateral and medial heel. MO2, Medial hindfoot. MO3, Midfoot. Area bcf (points c and f are an intersection of a line cf tangential to mid-arch). MO4, Fourth-fifth metatarsal head. An area divided by a line cf and a line through the fifth toe perpendicular to line cf. MO5, Second-fourth metatarsal heads. An area divided between a line through the fourth-fifth toes and a line through the first-second toes, perpendicular to the line cf. MO6, First metatarsal head (an area around first metatarsal head). MO7, Second-fifth toes. MO8, Hallux (an area around the first toe).

VICON 524 (Oxford Metrics, Oxford, England) motionanalysis system. Each subject walked 6 times across a 5-meter walkway, while EMG recordings were measured. The first and last trials were discarded, and only the 4 remaining trials were used for analysis. 254

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Results Eleven subjects (8 men and 3 women; aged 9 to 17 years), with a total of 14 feet with tarsal coalitions, volunteered to participate in the study. All underwent EMED plantar pressure evaluations and physical examination. Types of tarsal coalition were classified as calcaneocuboid in 3 feet, calcaneonavicular in 6 feet, and talocalcaneal in 5 feet. All feet underwent excision of the coalition; 2 also underwent subsequent subtalar fusion and 1 underwent triple arthodesis. The mean follow-up was 20 months (range, 1– 4 years). Three coalition feet had EMG assessment preoperatively but not postoperatively because of a scheduling error at the follow-up. Among coalition patients, our physical examination

TABLE 1 Significant differences in pressure parameters between subjects and control (P < .05) Parameters

FIGURE 2 There are biphasic activities in the peroneus longus in patients with tarsal coalition as compared with normal activity during stance phase (bar).

showed an average 5° of pes valgus, and only 1 foot with mild forefoot adductus. Except for the gastrocnemius with normal strength of 5/5, the anterior tibialis, posterior tibialis, peroneals, extensor hallucis longus, and extensor hallucis brevis muscles were ranked as 4/5 or between 4 and 5/5. Ankle dorsiflexion averaged 11° with the knee at 90° flexion, and 9° with the knee in full extension. Plantarflexion of the ankle was 5°. As compared with normal muscle activity (23, 24), EMG test results showed abnormal peroneous longus activity in all feet with tarsal coalitions (Fig 2). Abnormal activity (premature or prolonged muscle firing) was also observed in the 11 feet with coalitions, in 10 of 11 gastrocnemius, 7 of 11 soleus, and 5 of 11 tibialis anterior muscles. A comparison of EMG activity in the involved versus the uninvolved foot was performed in 7 patients. Uninvolved feet showed similar EMG patterns to the involved feet. The 7 contralateral feet showed abnormal activity in all muscles except the soleus muscle and tibialis anterior of 1 subject, which showed normal activity. There were significant differences in plantar pressure parameters between patients with tarsal coalition and normal subjects (Table 1). These EMED measurement changes were found in peak pressure, contact area, maximum force, and loading. Measurements showed significantly greater peak pressures in the midfoot (13.38 N/cm2 vs 6.81 N/cm2, P ⫽ .01), first metatarsal head (26.06 N/cm2 vs 16.48 N/cm2, P ⫽ .03), and hallux of the operated group (37.27 N/cm2 vs 27.96 N/cm2, P ⫽ .03) than in the normal feet (Fig 3). There were significantly larger contact areas in the midfoot (40.36 cm2 vs 18.02 cm2, P ⬍ .001), fifth metatarsal head (9.83 cm2 vs 6.38 cm2, P ⫽ .03), and first metatarsal head (12.62 cm2 vs 5.95 cm2, P ⬍ .001). There was also a lower maximum force in feet with tarsal coalitions, ranging from 5.86 N to 43.17 N, with respect to normal feet from 27.94 N to 172.93 N, except in the midfoot and first metatarsal. Greater loading was found in the lateral hindfoot (11.47 N/cm2 sec vs 5.03, P ⬍ .001), midfoot (5.63

Peak pressure (N/cm2) Area 3 Area 6 Area 8 Contact area (cm2) Area 3 Area 4 Area 6 Maximum force (N) Area 1 Area 2 Area 4 Area 5 Area 7 Area 8 Load (N/cm2sec) Area 1 Area 3 Area 4 Area 5 Area 8

Coalition

Control

P Value

13.38 ⫾ 5.8 26.06 ⫾ 7.4 37.27 ⫾ 2.5

6.81 ⫾ 2.8 16.48 ⫾ 8.5 27.96 ⫾ 13.1

.01 .03 .03

40.36 ⫾ 14.7 9.83 ⫾ 1.4 12.62 ⫾ 4.5

18.02 ⫾ 8.0 6.38 ⫾ 2.6 5.95 ⫾ 1.9

⬍.001 .03 ⬍.001

35.94 ⫾ 10.4 111.22 ⫾ 44.2 40.00 ⫾ 10.5 130.06 ⫾ 51.1 12.42 ⫾ 8.8 39.35 ⫾ 26.3 43.17 ⫾ 13.4 172.93 ⫾ 74.4 5.86 ⫾ 3.7 27.94 ⫾ 15.5 12.25 ⫾ 9.7 74.61 ⫾ 32.9

⬍.001 ⬍.001 ⬍.001 ⬍.001 ⬍.001 ⬍.001

11.47 ⫾ 9.0 5.63 ⫾ 3.4 7.28 ⫾ 4.6 11.76 ⫾ 4.8 10.04 ⫾ 9.6

⬍.001 ⬍.001 ⬍.001 .006 .03

5.03 ⫾ 2.3 1.83 ⫾ 0.9 3.73 ⫾ 2.6 6.67 ⫾ 3.4 6.04 ⫾ 3.7

Area 1, lateral hindfoot; Area 2, medial hindfoot; Area 3, midfoot; Area 4, fifth metatarsal head; Area 5, second to fourth metatarsal heads; Area 6, first metatarsal head; Area 7, second to fifth toes; Area 8, hallux.

FIGURE 3 EMED data of left talocalcaneal coalition. Note that there are significantly greater peak pressures and plantar contact area in the left midfoot and first metatarsal head as compared with normal. On the uninvolved side (right), there is increased peak pressure on the third and fifth metatarsal head with absence of the center of pressure on the heel as compared with the involved left side.

N/cm2sec vs 1.83, P ⬍ .001), fifth metatarsal head (7.28 N/cm2 sec vs 3.73, P ⬍ .001), second to fourth metatarsal heads (11.76 N/cm2 sec vs 6.67, P ⫽ .006) and hallux (10.04 N/cm2 sec vs 6.04, P ⫽ .03) when compared with normal feet. VOLUME 44, NUMBER 4, JULY/AUGUST 2005

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TABLE 2

Comparison between involved versus uninvolved tarsal coalition (Wilcoxon matched-pair test, P < .05)

Parameter

Region

Involved Mean ⫾ SD

Uninvolved Mean ⫾ SD

P Value

Max force (N) Peak pressure (N/cm2)

4 4 5 4 5

8.05 ⫾ 4.24 14.22 ⫾ 11.12 28.69 ⫾ 11.67 4.67 ⫾ 3.93 9.32 ⫾ 4.22

11.62 ⫾ 6.04 22.5 ⫾ 13.84 39.19 ⫾ 17.69 7.69 ⫾ 2.46 13.73 ⫾ 5.02

.001 .004 .002 .006 ⬍.001

Loading (N/cm2sec)

Table 2 shows significant differences between involved and uninvolved feet for the same patients (Fig 3). There were no pronounced changes in the contact areas (P ⬍ .05). Maximum force at the fifth metatarsal head of the involved feet (8.05 N) was less than that of the uninvolved feet (11.62 N) (P ⫽ .01). At the region of the fifth metatarsal head and third metatarsal head, tarsal coalition feet displayed reduced magnitudes in both peak pressure and loading (pressure: 14.22 N/cm2 vs 22.5 N/cm2, P ⫽ .04; 28.69 vs 39.19 N/cm2, P ⫽ .002; loading: 4.67 N/cm2 sec vs 7.69, P ⫽ .006; 9.32 N/cm2 sec vs 13.73, P ⬍ .001). Discussion The gastrocnemius and soleus are normally active mainly in phases of midstance between the heel strike and toe-off. Their peak activity occurs at 40% to 50% walking cycle, at the beginning of the push-off phase (23). The peroneus longus also has its peak at push off (50%) and also has an initial peak at foot flat to control foot inversion (24). The tibialis anterior muscle shows 2 peaks: one at the time of heel strike (5% of walking cycle) and one at the beginning of acceleration in the swing phase (70% walking cycle). Mean peak activity during the heel-strike period is 27% (23). As compared with above normal EMG of 3 muscle groups, EMG readings showed spasticity in the peroneous longus muscle in all 11 feet. These findings are consistent with Slomann (7) and Harris and Beath (6) who linked peroneal spastic flatfoot with calcaneonavicular and talocalcaneal coalitions. Furthermore, the dynamic EMG showed abnormal spasticity extending to the gastrocnemius and soleus. Our physical examination findings of ankle dorsiflexion of 9° to 11° and plantarflexion of 5° support a limited motion of the ankle joint with tarsal coalition. Tension on the Achilles’ tendon can prevent dorsiflexion of the calcaneus, which leads to a reduced arch and resultant increase contact area in the midfoot. As seen in Table 1, the contact area in tarsal coalition patients was twice that of the control patients. Although those muscles demonstrated abnormal muscle firing time, their overall strength was essentially normal (4/5 to 5/5). Interestingly, our data show a greater proportion of feet with abnormal muscle activity on the contralateral side in coalition patients than in control subjects. Those patients demonstrating abnormal mus256

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cle activity also exhibited similar abnormalities in both involved and uninvolved feet. Postoperative EMED measurements taken after tarsal coalition resection revealed significant differences in peak pressure, contact area, maximum force, and loading when compared with the EMED measurements in normal feet. The midfoot revealed the greatest differences. Although normal pediatric subjects showed lower loading in the medial midfoot (17), our subjects demonstrated greater than 3 times the loading compared with normal, and 2 times the contact area and peak pressures. Although there were no significant changes of plantar contact area between involved and uninvolved feet, involved feet showed significantly reduced force and pressure at the region of the fifth metatarsal head. These combined results may explain why most of the children with tarsal coalition presented with pes valgus, midfoot breaking, and forefoot pronation. These results imply that the midfoot and forefoot deformity remains even after resection of the coalition. It has been reported that 77% of patients with resection of coalitions involving one third or less of the total joint surface result in good or excellent clinical outcomes (12). Our biomechanical results showed discrepancies between normal feet and those with tarsal coalition, and between involved and uninvolved feet after a simple resection. This may suggest that the choice of surgical techniques should be based not only on clinical outcomes, but also on functional studies. A pre- and postoperative assessment of tarsal coalition feet may be clinically essential. In addition, increased midfoot contact area and peak pressure, and reduced peak pressure, loading, and force on the fifth metatarsal head may reflect that pronation of the midfoot and forefoot still exists after excision of coalition, which suggests that additional procedures (fusion or tendon recession or transfer) may need to be considered. Traditionally, triple arthodesis has been a viable option for treatment of symptomatic talocalcaneal coalitions (12–16). The foot rigidity associated with tarsal coalition may alter normal stance to accelerate heel-off, decrease midstance, and increase propulsion. These alterations may be the cause of increased peak pressure in the first metatarsal/hallux area, as is consistent with Pontius et al (27). Rigidity is also the likely reason for a decrease in maximum force throughout most of

the foot, which prevents maximal loading except in the midfoot area. Abnormal postoperative EMG and pressure distribution at the midfoot and forefoot suggest that resection of the bar is not sufficient to restore normal foot function. A preoperative dynamic EMG and EMED evaluation may be a useful assessment for patients with tarsal coalition. Limitations of this study include its small number of patients. An increased number of patients with a variety of tarsal coalition types would provide greater information. A prospective study design would also be an improvement instead of a retrospective one. Finally, a comparative analysis of EMED and EMG data between patients receiving conservative treatment, resection, or arthodesis would yield important information regarding the functional outcomes of treatment. Conclusion EMED pressure and EMG results for postcoalition resection feet show significant differences when compared with the results for normal feet and contralateral feet. The midfoot showed that increases in contact area, peak pressure and loading, and fifth metatarsal head had reduced pressure and loading. This indicates that pre- and postassessment of the foot function is critical for patients with tarsal coalition and to determine efficacy of different surgical procedures. Given the fact that the peroneous, gastrocnemius, and soleus muscles showed the most consistent abnormal EMG activity, a preoperative dynamic EMG may become a valuable assessment for patients with tarsal coalition. Acknowledgement The authors would like to thank Ms K. Myer, MS, and G. Harris, PhD, for their help with dynamic EMG. References 1. O’Rahilly R, Gardner E, Gray DJ. The skeletal development of the foot. Clin Orthop 16:7–14, 1960. 2. Kulik SA, Clanton TO. Foot fellow’s review: tarsal coalition. Foot Ankle Int 175:286 –296, 1996. 3. Mosier KM, Asher MA. Tarsal coalition and peroneal spastic flatfoot. J Bone Joint Surg Am 66:976 –983, 1984. 4. Percy EC, Mann DL. Tarsal coalitions: a review of the literature and presentation of 13 cases. Foot Ankle 9:40 – 44, 1988. 5. Cowell HR. Diagnosis and management of peroneal spastic flatfoot. Instr Course Lect 24:94 –103, 1975. 6. Harris RI, Beath T. Etiology of peroneal spastic flat foot. J Bone Joint Surg Am 37A:169 –183, 1955. 7. Slomann HC. On coalition calcaneo-navicularis. J Orthop Surg 3:586 – 602, 1921. 8. Knapp HP, Tavakoli M, Levitz S, Sobel E. Tarsal coalition in an adult with cavovarus feet. J Am Podiatr Med Assoc 88:295–300, 1998. 9. Simmons EH. Tibialis spastic varus foot with tarsal coalition. J Bone Joint Surg Am 47:533–536, 1965.

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Additional References 1. Boulton AJM. The importance of abnormal foot pressures and gait in the causation of foot ulcer, in Connor HBA, Ward JD (eds): The diabetic foot. Chichester, UK, John Wiley and Sons, 1988, pp 11-22. 2. Brand RA, Crowninshield RD. Comment on criteria for patient evaluation. J Biomech 14:655, 1981. 3. Cavanagh PR, Hewitt FG, Perry JE. In-shoe plantar pressure measurement: a review. The Foot 2:2185-2194, 1992. 4. Claeys R. The analysis of ground reaction forces in pathological gait secondary to disorders of foot. Int Orthop 7:113-119, 1983. 5. Cowell HR. Talocalcaneal coalition and new causes of peroneal spastic flatfoot. Clin Orthop 85:16-22, 1972. 6. Deutsch AL, Resnick D, Campbell G. Computed tomography and bone scintigraphy in the evaluation of tarsal coalitions. Radiology 144:137-140, 1982. 7. Goldman AB, Pavlov H, Schneider R. Radionuclide bone scanning in subtalar conditions: differential considerations. Am J Radiol 138:427-432, 1982.

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8. Herzenberg JE, Goldner JL, Martinez S, Silverman PM. Computerized tomography of talocalcaneal tarsal coalition: a clinical and anatomic study. Foot Ankle 6:273-288, 1986. 9. Kumai T, Takakura Y, Akiyami K, Higashiyama I, Tamai S. Histopathological study of nonosseous tarsal coalition. Foot Ankle Int 19:525-531, 1998. 10. Leonard MA. The inheritance of tarsal coalition and its relationship to spastic flatfoot. J Bone Joint Surg Am 56:520-526, 1974.

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11. Mann RA. Rupture of the posterior tibial tendon causing flat foot: surgical treatment. J Bone Joint Surg Am 67:556-561, 1985. 12. Marchisello PJ. The use of computerized axial tomography for the evaluation of talocalcaneal coalition. J Bone Joint Surg Am 69:609-611, 1987. 13. Pineda C, Resnick D, Greenway G. Diagnosis of tarsal coalition with computed tomography. Clin Orthop 208:282-288, 1986. 14.Thomas CK, Lyle J. Resection for symptomatic talocalcaneal coalition. J Pediatric Orthop 18:283-288, 1998.