Cadaveric Simulation of a Pes Cavus Foot

Transcription

1 FOOT &ANKLE INTERNATIONAL Copyright 2009 by the American Orthopaedic Foot & Ankle Society DOI: /FAI Cadaveric Simulation of a Pes Cavus Foot S. Bradley Daines, BA; Eric S. Rohr, MS; Andrew P. Pace, BA; Michael J. Fassbind, MS; Bruce J. Sangeorzan, MD; William R. Ledoux, PhD Seattle, WA ABSTRACT Background: The pes cavus deformity has been well described in the literature; relative bony positions have been determined and specific muscle imbalances have been summarized. However, we are unaware of a cadaveric model that has been used to generate this foot pathology. The purpose of this study was to create such a model for future work on surgical and conservative treatment simulation. Materials and Methods: We used a custom designed, pneumatically actuated loading frame to apply forces to otherwise normal cadaveric feet while measuring bony motion as well as force beneath the foot. The dorsal tarsometatarsal and the dorsal intercuneiform ligaments were attenuated and three muscle imbalances, each similar to imbalances believed to cause the pes cavus deformity, were applied while bony motion and plantar forces were measured. Results: Only one of the muscle imbalances (overpull of the Achilles tendon, tibialis anterior, tibialis posterior, flexor hallucis longus and flexor digitorum longus) was successful at consistently generating the changes seen in pes cavus feet. This imbalance led to statistically significant changes including hindfoot inversion, talar dorsiflexion, medial midfoot plantar flexion and inversion, forefoot plantar flexion and adduction and an increase in force on the lateral mid- and forefoot. Conclusion: We have created a cadaveric model that approximates the general changes of the pes cavus deformity compared to normal feet. These changes mirror the general patterns of deformity produced by several disease mechanisms. Clinical Relevance: Future work will entail increasing the severity of the model and exploring various pes cavus treatment strategies. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. This work was supported in part by the Medical Student Research and Training Program at the University of Washington School of Medicine, and the Department of Veterans Affairs, Rehabilitation R&D Service grant number A2661C. Corresponding Author: William R. Ledoux, PhD VA Puget Sound RR&D Center of Excellence for Limb Loss Prevention and Prosthetic Engineering MS S. Columbian Way Seattle, WA wrledoux@u.washington.edu For information on pricings and availability of reprints, call , x Key Words: Pes Cavus; Foot Deformity: Foot Structure; Cadaver; Muscle Imbalance INTRODUCTION Pes cavus is an umbrella term encompassing several high arch conditions; it can affect primarily the hindfoot or the forefoot, or it can affect the foot more globally. 9,18 Though a universal definition of pes cavus is unavailable, there are common descriptions of the deformity frequently mentioned in the pes cavus literature. 2,4,9,10,16,18 These include inversion of the calcaneus, inversion of the midfoot, adduction of the forefoot and plantarflexion of the first metatarsal resulting in a high medial longitudinal arch, and an increase in force along the lateral border of the foot during weightbearing. Muscular imbalances stemming from neurologic disorders have long been considered underlying primary factors for development of the pes cavus deformity. 1,2,4,10,18 Brewerton et al. cited several proposed neurological etiologies including peroneal muscular atrophy, Friedreich s ataxia, myelodysplasia, poliomyelitis and others. 1 This important study also implicated Charcot-Marie-Tooth disease in many cases of pes cavus previously classified as idiopathic. Wapner described various potential causes of the deformity, including: hereditary motor-sensory neuropathy, poliomyelitis, spinocerebellar degeneration, congenital spinal cord lesion and trauma. 18 Mann described a frequent imbalance found in pes cavus patients with Charcot-Marie-Tooth disease. 10 He noted normal muscle strength in the peroneus longus (PL) and tibialis posterior (TP), causing a functional overpull due to the marked decreases in the muscle strength their respective antagonists, the tibialis anterior (TA) and peroneus brevis (PB). In another study, Dehne described how acquired neurological disorders of the central nervous system can cause overpull of the Achilles tendon, TA, flexor hallucis longus (FHL) and flexor digitorum longus (FDL), an imbalance that leads to an equinovarus foot. 4 Burns et al. recorded significant weakness in all muscle groups of pes cavus patients. 2 This study also notes higher strength ratios of inversion to eversion and plantarflexion to dorsiflexion

2 Foot & Ankle International/Vol. 30, No. 1/January 2009 CADAVERIC PES CAVUS 45 when compared to normal controls. These studies illustrate that a variety of muscular imbalances can produce a pattern of deformity consistent with pes cavus. Previous cadaveric studies have been successful in creating models of pathogenic foot conditions attributed to muscle imbalances. 11,12 However, we are unaware of a cadaveric model of the pes cavus deformity. We hypothesized that by attenuating ligaments and generating pathogenic-like muscle imbalances, we would be able to model the changes seen in the deformity using a cadaver foot. If successful, such a model would be a useful tool for developing better conservative and surgical treatments for patients with the pes cavus deformity. MATERIALS AND METHODS In this IRB approved study, we tested nine freshly-frozen, unpreserved, human cadaver feet (mean age of 77.1 ± 8.3 years; range, 65 to 90 years) (four male, five female; three left, six right) with a customized loading frame (Figure 1) capable of statically loading the extrinsic muscles and tibia/fibula via eight pneumatic cylinders. 11,12 The cylinders air pressure was controlled by LabVIEW via a custom virtual instrument. The largest cylinder (4000 N) was able to apply compressive force to the tibia/fibula. Six smaller cylinders were capable of applying tensile force (maximum 100 N) to the extrinsic tendons of interest, while the Achilles was attached to a cylinder capable of applying a 3000 N tensile force. The feet were screened for osseous deformity by X-ray and gross examination. Evidence of tendon transfer or the presence of surgical hardware were grounds for exclusion from the study. Each foot was dissected above the level of the medial malleolus to expose the tendons of the TA, PL, PB, TP, FHL and FDL muscles as well as the Achilles tendon. A hole was drilled in the tibia (1.27 cm bit) and fibula (0.48 cm bit) to insert the compressive rods. Using a cantilever beam and a calibrated spring, the setup of the frame allowed for an approximately physiologic distribution (85% to the tibia, 15% to the fibula). 17 Tendons were attached to the loading frame with plastic clamps and nylon cords. Holes were drilled in the tibia, talus, calcaneus, navicular, medial cuneiform, cuboid and first metatarsal enabling for the insertion of a carbon fiber rod (diameter 4.78 mm) which was secured with Gorilla glue (Gorilla Glue Company, Cincinnati, OH). Holes were drilled with a 0.44-cm drill bit, which was just smaller than the rod s diameter, helping insure a tight fit. A hammer was used to tap each individual rod into place. A Polhemus Fastrak electromagnetic sensor was then attached to each rod using acrylic blocks, allowing for tracking of the spatial orientation and movements of the bones of interest in the sagittal, frontal, and transverse planes. After placement, each sensor s position was individually normalized to the Polhemus transmitter for each foot. Force distribution was measured using a Novel Pedar insole placed beneath the foot. The dorsal tarsometatarsal ligament (between the medial cuneiform and first metatarsal) and the dorsal intercuneiform ligament (between the medial and intermediate cuneiforms) were weakened by making five incisions with a No. 15 blade scalpel parallel to the ligament s fiber orientation. 11,19 The foot was mounted in the loading frame at 7 degrees dorsiflexion using a wooden ramp to approximate midstance position. 13 Tendon forces were calculated using physiologic muscle cross-sectional areas (PCSA), maximum specific tensions (MST), cosines of pennation angles (PA) and EMG activities to simulate midstance (30% of the gait cycle) according to the following equation (Table 1). 5,12,13,15 : muscleforce = PCSA MST cos(pa) EMG Fig. 1: Anterolateral view of a pilot cadaver foot in the testing apparatus; the setup is similar though not exactly the same as the testing setup. For example, in the actual testing protocol the fourth and fifth metatarsal were not tracked. A, Polhemous electromagnetic sensors in mounts on carbon fiber rods. B, Polhemus transmitter. C, plastic tendon clamps. D, extrinsic muscle tensile nylon cords. E, compressive rod. F, wood block for 7 degrees dorsiflexion. G, acrylic loading frame. Following ligament weakening, the TA and TP were overpulled at 100 N with a frequency of 1 Hz for one hour (3600 cycles), with the other extrinsic muscles pulled at 1/4 of the physiologic norm (Table 1). Pilot studies showed that this process served to further attenuate the ligaments of the midfoot and accentuate bone movements seen during later muscle imbalance testing conditions. The TA, TP, FHL, FDL, and PL were attached to cylinders only capable of applying a maximum of 100 N of force.

3 46 DAINES ET AL. Foot & Ankle International/Vol. 30, No. 1/January 2009 Table 1: Loading protocol for midstance (30% gait cycle) at full and 1/8 body weight (BW) Midstance BW (N) 1/8 BW Axial compression Achilles tendon Tibialis anterior 0 0 Peroneus longus 53 7 Peroneus brevis 32 4 Tibialis posterior 58 7 Flexor digitorum longus 19 2 Flexor hallucis longus 46 6 Axial compression was calculated as 82% 8 of 667 N with the opposing force of the extrinsic muscles added to balance the load on the tibia. Therefore, in order to maximize the effect of the overpulls, axial compression and muscle forces were scaled down to 1/8 of the calculated forces for a standard body weight. Scaling down forces was also necessary to decrease the risk of the tibia failing under the additional compressive forces required to balance the overpulls and to prevent the tendon clamp on the Achilles tendon from slipping, problems seen in some of the pilot feet. Data for midstance (Table 1) and the following three non-physiologic conditions (Table 2) were collected: 1. Overpull of Achilles tendon, TA, TP, FHL, FDL 2. Overpull of Achilles tendon, PL, TP. 3. Overpull of PL, TP; underpull of TA, PB These conditions were roughly modeled after imbalances described in the literature. 4,10,14 The imbalances were generated by increasing the 1/8 BW midstance forces of specific muscles based on the literature, but actual magnitudes were not necessarily physiologic. However, the final testing conditions relied heavily on the successful generation of the changes typical of the pes cavus foot in our pilot work. The rationale for this strategy is discussed later. The first condition was intended to approximately model an equinovarus deformity due to hemiplegia described by Dehne and Perry et al. (with the addition of TP overpull) while the other two resemble the imbalance described by Mann as seen in patients with Charcot-Marie-Tooth disease. The magnitudes of the overpulls were based on the constraints of the loading frame and the pilot testing. This work also demonstrated that loading the extrinsic musculature after balancing the Achilles and axial compressive forces produced greater changes. Table 2: Condition 1: Adjusted loading protocol for overpull of the axial compression, Achilles tendon, tibialis anterior, peroneus longus, peroneus brevis, tibialis posterior, flexor digitorum longus and flexor hallucis longus for midstance at 1/8 body weight (BW). This condition was loosely based on the muscle imbalance described by Dehne in stroke patients. 4 Condition 2: Adjusted loading protocol for overpull of Achilles tendon, peroneus longus and tibialis posterior for midstance at 1/8 BW. This condition was loosely based on the muscular imbalance described by Mann in Charcot-Marie-Tooth patients. 10 Condition 3: Adjusted loading protocol for overpull of peroneus longus and tibialis posterior, along with underpull of tibialis anterior and peroneus brevis during midstance at 1/8 BW. This condition was loosely based on the muscular imbalance described by Mann in Charcot-Marie-Tooth patients. 10 Overpulls (1/8 BW N) Condition 1 Condition 2 Condition 3 Axial compression Achilles tendon Tibialis anterior Peroneus longus Peroneus brevis Tibialis posterior Flexor digitorum longus Flexor hallucis longus Axial compression was calculated as 82% 8 of 667 N divided by 8 with the opposing force of the extrinsic muscles (including overpulls) added to balance the load on the tibia.

4 Foot & Ankle International/Vol. 30, No. 1/January 2009 CADAVERIC PES CAVUS 47 Statistics The testing order of these conditions was randomized during data collection, as was the loading order of the extrinsic musculature. Relative changes seen in overpull conditions compared to a neutral condition (roughly based on physiologic midstance at one-eighth body weight) were measured. Overall differences from midstance were assessed using linear mixed effects models. Statistical significance was defined by a p value of less than RESULTS The midstance cadaveric model loaded to 1/8 BW compared well with the literature (Table 3), 3,7 demonstrating the validity of the cadaveric foot model independent of the pes cavus simulation. When compared to static (i.e., standing) data, the same general trends of similar loading on the medial and lateral forefoot, reduced loading on the medial midfoot and increased loading on the heel were demonstrated. When reorganized and compared to dynamic data (i.e., peak force during gait), the relative magnitudes of all three areas were very similar to the published values. Of the three muscle conditions that were implemented, only the first demonstrated a pronounced cavus foot with several significant changes in the hindfoot, midfoot and forefoot alignment consistent with the pes cavus deformity (Figure 2). These changes included inversion of the hindfoot, talar dorsiflexion, plantarflexion and inversion of the medial midfoot, and plantarflexion and adduction of the forefoot, as Table 3: The weight distribution as a percentage of total weight Cadaveric model Peak static force 3 medial forefoot lateral forefoot medial midfoot lateral midfoot heel Cadaveric model Peak dynamic force 7 medial mid/forefoot lateral mid/forefoot heel The data from the cadaveric model were grouped in two ways for ease of comparison with the literature. Static data 3 from were organized into the same 5 categories used in the current study. However, dynamic data 7 were organized into 3 categories; mid/forefoot refers to the mid and forefoot data grouped together. Fig. 2: Medial view of a pilot cadaver foot simulating the pes cavus deformity. Fig. 3: The angular change of the calcaneus (calc.) relative to the ground, tibia and talus. All data are normalized to the balanced condition. An asterisk signifies a significant difference from the balanced condition. Sagittal positive = plantarflexion, sagittal negative = dorsiflexion; frontal positive = inversion, frontal negative = eversion; transverse positive = external rotation, transverse negative = internal rotation. well as increased loading in the lateral forefoot and midfoot. The second and third imbalances failed to reproducibly generate the changes seen in the pes cavus deformity; therefore, unless otherwise stated all results hereafter are from the first imbalance. All angular results are presented as changes relative to our approximation of midstance, which was defined as 0 degrees. Unless otherwise stated, only results that were statistically significantly different (p < 0.01) from 0 degrees are presented. The motion of the hindfoot was, for the most part, consistent with a high arched foot (Figure 3). The calcaneus inverted [mean (SD)] relative to the ground, tibia and talus by 2.8 degrees (1.1 degrees), 2.8 degrees (1.6 degrees) and 2.9 degrees (2.3 degrees) respectively and externally rotated relative to the ground by 1.9 degrees (2.4 degrees). In the sagittal plane, the calcaneus plantarflexed relative to the talus 2.6 degrees (1.7 degrees), but given the relative lack of motion of the calcaneus relative to the ground and the tibia, this motion is better thought of as talar dorsiflexion.

5 48 DAINES ET AL. Foot & Ankle International/Vol. 30, No. 1/January 2009 In a finding not typical of the pes cavus foot deformity, the calcaneus significantly internally rotated relative to the tibia by 3.6 degrees (2.1 degrees) and relative to the talus by 2.9 degrees (2.9 degrees). Representing the movements of the medial midfoot, the navicular and medial cuneiform inverted relative to the talus by 7.9 degrees (5.4 degrees) and 9.3 degrees (4.7 degrees) and internally rotated relative to the talus by 4.7 degrees (5.6 degrees) and 5.4 degrees (5.7 degrees), respectively (Figure 4). The medial cuneiform plantarflexed relative to the talus by 2.0 degrees (1.7 degrees) and the navicular showed a non-significant trend toward plantarflexion. Also, the medial cuneiform inverted relative to the navicular by 1.4 degrees (1.3 degrees). Describing motion of the lateral midfoot, the cuboid was measured relative to the hindfoot (i.e., calcaneus, Figure 5) and medial midfoot (i.e., navicular, Figure 5). The cuboid inverted relative to the calcaneus [2.8 degrees (2.3 degrees)], but everted relative to the navicular [2.1 degrees (1.5 degrees)]. We also observed plantarflexion relative to the navicular [1.3 degrees (0.7 degrees)] and internal rotation relative to the calcaneus [2.4 degrees (2.8 degrees)]. Representing motion of the forefoot, the first metatarsal inverted relative to the talus by 7.5 degrees (5.4 degrees) and adducted relative to the talus by 5.0 degrees (5.4 degrees) (Figure 6). Though not significant, the first metatarsal showed a trend of plantarflexion relative to the talus of 3.0 degrees (2.2 degrees). As expected with the pes cavus deformity, there was an increase in force in the lateral forefoot and midfoot of 9.9 N (5.2 N) and 8.0 N (7.5 N), respectively (Table 4). The other imbalanced conditions did not produce as many significant or interesting differences from midstance. For the second condition, force in the medial forefoot increased by 20.2 N (8.6 N), consistent with strong contraction of the Fig. 6: The angular change of the first metatarsal relative to talus. All data are normalized to the balanced condition. An asterisk signifies a significant difference from the balanced condition. Sagittal positive = plantarflexion, sagittal negative = dorsiflexion; frontal positive = inversion, frontal negative = eversion; transverse positive = external rotation, transverse negative = internal rotation. Fig. 4: The angular change of the navicular to the talus, cuneiforms to talus and medial cuneiform to navicular. All data are normalized to the balanced condition. An asterisk signifies a significant difference from the balanced condition. Sagittal positive = plantarflexion, sagittal negative = dorsiflexion; frontal positive = inversion, frontal negative = eversion; transverse positive = external rotation, transverse negative = internal rotation. Table 4: The loading beneath the foot relative to midstance during the three imbalanced conditions. An asterisk signifies a significant difference from the balanced condition Location Condition 1 Condition 2 Condition 3 Medial 1.0 ± ± ± 6.3 forefoot Lateral 9.9 ± ± ± 3.1 forefoot Medial 0.1 ± ± ± 0.7 midfoot Lateral 8.0 ± ± ± 4.1 midfoot Heel 4.7 ± ± ± 4.4 Fig. 5: The angular change of the cuboid to calcaneus and cuboid to navicular. All data are normalized to the balanced condition. An asterisk signifies a significant difference from the balanced condition. Sagittal positive = plantarflexion, sagittal negative = dorsiflexion; frontal positive = inversion, frontal negative = eversion; transverse positive = external rotation, transverse negative = internal rotation. Condition 1: Overpull of the Achilles tendon, tibialis anterior, tibialis posterior, flexor digitorum longus and flexor hallucis longus; Condition 2: Overpull of Achilles tendon, peroneus longus and tibialis posterior; Condition 3: Overpull of peroneus longus and tibialis posterior, along with underpull of tibialis anterior and peroneus brevis.

6 Foot & Ankle International/Vol. 30, No. 1/January 2009 CADAVERIC PES CAVUS 49 PL (Table 4). There were no other significant changes from midstance. The third condition returned several significant results, though of mostly small magnitudes. The medial cuneiform plantarflexed relative to the talus by 1.9 degrees (1.3 degrees) and relative to the navicular by 1.9 degrees (1.4 degrees). The medial cuneiform everted relative to the navicular by 1.3 degrees (0.8 degrees). The cuboid everted relative the navicular by 1.1 degrees (0.7 degrees). As with condition 2, force in the medial forefoot increased by 15.8 N (6.3 N), again consistent with strong contraction of the PL (Table 4). DISCUSSION Pes cavus, often seen in patients with neuropathies, is a foot deformity characterized by inversion of the hindfoot and midfoot, plantarflexion of the forefoot creating a high medial longitudinal arch, adduction of the forefoot and increase in force with weight bearing on the lateral border of the foot. 4,9,18 We hypothesized that simulating muscle imbalances in a cadaveric foot could produce a model consistent with the changes from normal seen in the pes cavus deformity. Our cadaveric model was validated by comparing the weight distribution across various locations beneath the foot (Table 3). As we were only loading to one-eighth body weight, it was not possible to compare magnitudes; rather, we examined the weight distribution. Similar trends were seen as compared to a heterogenous sample of 107 feet that were studied during barefoot standing. 3 Furthermore, when compared to peak forces obtained during gait from 20 subjects, the relative percentage of force for each of the areas was within 3%. 7 The first non-physiologic condition (an overpull of the Achilles, TA, TP, FHL and FDL) produced a cadaveric model consistent with the mentioned clinical measures of pes cavus, showing larger magnitudes of change and more significant variables than the other two tested conditions. This condition was largely based on Dehne s description of the imbalance seen in equinovarus, with the addition of an overpulled TP as indicated by our pilot studies. 4 There were several significant measures consistent with a pes cavus deformity in the first condition. The inversion seen in the hindfoot (calcaneus) and medial midfoot (navicular and medial cuneiform) as well as the dorsiflexion of the talus and medial cuneiform are consistent with an elevated medial longitudinal arch. The medial midfoot inversion was contrasted by eversion of the lateral midfoot (cuboid) relative to the navicular. The observed trends of medial midfoot and first metatarsal plantarflexion are also consistent with arch elevation. There was adduction of the forefoot and increase in lateral force distribution in both the forefoot and midfoot reflecting the weight-bearing changes of the pes cavus deformity. The results support the use of this model as a cadaveric simulation of pes cavus. Potential limitations of the study include our inability to simulate constriction of the plantar aponeurosis or dysfunction of the intrinsic foot musculature. 10,18 We did not measure changes within joints. Potentially, our results could have been affected by the relatively old age of the cadaveric specimens. Although we assessed the cadaver feet via x-ray for evidence of gross abnormality, we otherwise assumed that the feet we tested had normal bone, ligament and tendon shapes and sizes. Additionally, we were only able to test at 1/8 body weight and our deformations were created in a relatively brief amount of time, i.e., not over a period of years as typically happens clinically. We also saw unexpected adduction of the calcaneus relative to the tibia and talus. A possible explanation may be the observed significant external rotation of the tibia relative to the ground by 5.5 degrees (4.3 degrees). Because our measurements of calcaneal adduction were relative to the tibia and talus (which should rotate similarly to the tibia), the majority of the calcaneal adduction may actually be a reflection of the external tibial rotation. This is supported by the small but significant adduction of the calcaneus relative to the ground of 1.9 degrees (2.4 degrees). The fact that the midfoot and forefoot abducted is indicative of the decoupling of the tibia and talus from those bones. Note that fixing the tibial shaft rigidly to the compressive shaft may have alleviated this problem; this was not done for the current study, but will be in the future. As mentioned earlier, we chose to use various testing parameters that maximized the movements of interest to best generate the pes cavus deformity. In this study, we only wished to approximate the patterns of change seen in the cavus foot deformity; we did not intend to comment on etiology. Several different types of muscle imbalances have been reported in pes cavus in patients. 2,4,10 Though we did loosely model our overpull conditions on reported trends seen in patients, creating an overpull pattern precisely imitating any particular pathogenesis of pes cavus was not necessary. Rather, we simply tried to produce changes in a foot (through muscle overpull) consistent with the general characteristics of the pes cavus deformity. Further studies could focus on corrective procedures for pes cavus feet. For example, an osteotomy or tendon transfer could be performed on a cadaver foot after running the pes cavus simulation described in this study. 6,16,20 The foot could then be retested with the same protocol of this experiment (i.e., with muscle imbalances). Corrective efficacy could be quantified by loading the corrected foot to the same parameters as the overpull that produced the changes consistent with the pes cavus deformity in our study. An effective procedure for correcting pes cavus should reduce the observed characteristics. This approach could be used to screen the usefulness of new procedures as well as provide insight into the efficacy of current treatments. We successfully created a cadaveric model of pes cavus. Our model was patterned on conditions of muscular imbalance and overpull. We chose several recognized clinical

7 50 DAINES ET AL. Foot & Ankle International/Vol. 30, No. 1/January 2009 measurements to evaluate the legitimacy of our model and believe that similar cadaveric simulations of pes cavus will prove to be valuable tools for assessing current procedures and in aiding innovation and evaluation of new corrective procedures. Ultimately, we hope this potential tool will help improve treatment options for patients with this deformity. ACKNOWLEDGEMENTS Jane B. Shofer, MS, conducted the statistical analyses, while Joey Emmert assisted with the foot dissections. EDITOR S NOTE The authors are to be congratulated for developing the first in vitro pes cavus model. In contrast to pes planus models (ie, PTTD) which rely primarily on cutting structures and then loading specimens until they flatten, this model relies on weakening a few ligamentous structures and then abnormally loading musculotendinous units to augment the arch. This requirement significantly increased the complexity of the model. One reviewer had a significant concern that loading to only 1/8 body weight would not create a physiologic model. As with all cadaveric models, some compromises are made to create the model which in this case was done to avoid destroying the specimens during the testing protocol. Future investigators can decide if they want to load to a greater proportion of body weight with the added risk of specimen failure during the testing process. REFERENCES 1. Brewerton, DA; Sandifer, PH; Sweetnam, DR: Idiopathic Pes Cavus: An Investigation Into Its Aetiology. Br Med J. 2: , Burns, J; Redmond, A; Ouvrier, R; Crosbie, J: Quantification of muscle strength and imbalance in neurogenic pes cavus, compared to health controls, using hand-held dynamometry. Foot Ankle Int. 26: , Cavanagh, PR; Rodgers, MM; Iiboshi, A: Pressure distribution under symptom-free feet during barefoot standing. Foot & Ankle. 7: , Dehne, R: Congenital and acquired neurological disorders, In: Coughlin MJaRAM, (ed.), Surgery of the Foot and Ankle, NewYork,NY,Mosby, , Fukunaga, T; Roy, RR; Shellock, FG; Hodgson, JA; Edgerton, VR: Specific tension of human plantar flexors and dorsiflexors. J Appl Physiol. 80: , Giannini, S; Ceccarelli, F; Benedetti, MG; Faldini, C; Grandi, G: Surgical treatment of adult idiopathic cavus foot with plantar fasciotomy, naviculocuneiform arthrodesis, and cuboid osteotomy. A review of thirty-nine cases. J Bone Joint Surg Am. 84-A Suppl 2:62 69, Ledoux, WR; Hillstrom, HJ: The distributed plantar vertical force of neutrally aligned and pes planus feet. Gait Posture. 15:1 9, Mann, RA: Biomechanics of the foot and ankle, In: Coughlin MJaRAM, (ed.), Surgery of the Foot and Ankle, NewYork,NY,Mosby, 2 35, Mann, RA: Pes Cavus, In: Coughlin MJaRAM, (ed.), Surgery of the Foot and Ankle, New York, NY, Mosby, , Mann, RA; Missirian, J: Pathophysiology of Charcot-Marie-Tooth disease. Clin Orthop Relat Res. 234: , Niki, H; Ching, RP; Kiser, P; Sangeorzan, BJ: The effect of posterior tibial tendon dysfunction on hindfoot kinematics. Foot Ankle Int. 22: , Olson, SL; Ledoux, WR; Ching, RP; Sangeorzan, BJ: Muscular imbalances resulting in a clawed hallux. Foot Ankle Int. 24: , Perry, J: Gait analysis: Normal and pathological function, Thorofare, NJ, SLACK Incorporated, Perry, J; Waters, RL; Perrin, T: Electromyographic analysis of equinovarus following stroke. Clin Orthop , Pierrynowski, MR: A physiological model for the solution of individual muscle force during normal human walking [Ph.D.]. Simon Fraser University, Sammarco, GJ; Taylor, R: Cavovarus foot treated with combined calcaneus and metatarsal osteotomies. Foot Ankle Int. 22:19 30, Wang, Q; Whittle, M; Cunningham, J; Kenwright, J: Fibula and its ligaments in load transmission and ankle joint stability. Clin Orthop Relat Res , Wapner, KL: Pes Cavus, In: Myerson MS, (ed.), Foot and Ankle Disorders, Philadelphia, W. B. Saunders, , Woodburn, J; Cornwall, MW; Soames, RW; Helliwell, PS: Selectively attenuating soft tissues close to sites of inflammation in the peritalar region of patients with rheumatoid arthritis leads to development of pes planovalgus. J Rheumatol. 32: , Wulker, N; Hurschler, C: Cavus foot correction in adults by dorsal closing wedge osteotomy. Foot Ankle Int. 23: , 2002.