Force-deformation properties of the human heel pad during barefoot walking.

INTRODUCTION: The plantar heel pad is a specialized fibroadipose tissue that attenuates and, in part, dissipates the impact energy associated with heel strike. Although a near-maximal deformation of the heel pad has been shown during running, an in vivo measurement of the deformation and structural properties of the heel pad during walking remains largely unexplored. This study used a fluoroscope, synchronized with a pressure platform, to obtain force-deformation data for the heel pad during walking. METHODS: Dynamic lateral foot radiographs were acquired from 6 male and 10 female adults (mean ± SD; age = 45 ± 10 yr, height = 1.66 ± 0.10 m, and weight = 80.7 ± 10.8 kg) while walking barefoot at preferred speeds. The inferior aspect of the calcaneus was digitized, and the sagittal thickness and deformation of the heel pad relative to the support surface were calculated. A simultaneous measurement of the peak force beneath the heel was used to estimate the principal structural properties of the heel pad. RESULTS: Transient loading profiles associated with walking induced rapidly changing deformation rates in the heel pad and resulted in irregular load-deformation curves. The initial stiffness (32 ± 11 N·mm) of the heel pad was 10 times lower than its final stiffness (212 ± 125 N·mm), and on average, only 1.0 J of energy was dissipated by the heel pad with each step during walking. Peak deformation (10.3 mm) approached that predicted for the limit of pain tolerance (10.7 mm). CONCLUSION: These findings suggest that the heel pad operates close to its pain threshold even at speeds encountered during barefoot walking and provides insight as to why barefoot runners may adopt "forefoot" strike patterns that minimize heel loading.

First ray instability in hallux valgus deformity: a radiokinematic and pedobarographic analysis.

BACKGROUND: Hallux valgus remains a common forefoot condition where different causes may contribute to the pathology. The extent of first ray mobility and, in particular, instability of the first tarsometatarsal joint represents a key argument in the debate on the selection of an appropriate operative treatment. Until now, assessment of first ray instability has relied on clinical examination or static assessment only. For dynamic evaluation in our study, pedobarographic, clinical, and standard weightbearing radiographic findings were correlated with the radiokinematically determined first ray instability in the sagittal plane in hallux valgus patients. METHODS: Eight patients with hallux valgus deformity and a clinically unstable first tarsometatarsal joint were enrolled. Seven patients were females; 1 was male. Mean age was 44 years (range, 15-65). Clinical symptoms, American Orthopaedic Foot and Ankle Society forefoot scores, and standard parameters of weightbearing radiographs in 2 planes of the forefoot were recorded. A mobile C-arm fluoroscope with a novel distortion-free flat-screen detector and a pedobarographic platform were synchronized during the rollover process. Fluoroscopic image analysis was performed employing a specific CAD model. Pedobarographic parameters were determined within 8 defined areas of the forefoot contact zone. RESULTS: The mean dorsiflexion distance and angle of the first ray was 13.9 ± 9.4 mm (range, 6.3 to 34.5) and 5.9 ± 4.0 degrees (range, 2.4 to 14.5). At the first tarsometatarsal joint, the mean maximum dorsiflexion angle was 2.6 ± 1.3 degrees (range, 0.1 to 4.0). The intermetatarsal angle correlated significantly (P = .013) with the radiokinematically determined maximum dorsiflexion. Furthermore, a significant correlation between maximum force transfer to the central (P = .021) and lateral forefoot (fourth metatarsal; P = .032) and first tarsometatarsal joint instability was detected with an unloading of the first metatarsal. CONCLUSION: Although our analysis was limited to the sagittal plane only, we can support the notion that an enlarged intermetatarsal angle was associated with increased maximum dorsiflexion of the first ray during gait in hallux valgus patients. Gross instability of the first tarsometatarsal joint during weightbearing was not detectable in our patients, while first tarsometatarsal joint instability increased maximum force transfer to the central forefoot with the potential risk of metatarsalgia. CLINICAL RELEVANCE: The results here may shed further light on the role of hypermobility of the first ray on hallux valgus deformity which could have implications for its surgical management.

Investigation of first ray mobility during gait by kinematic fluoroscopic imaging--a novel method.

BACKGROUND: It is often suggested that sagittal instability at the first tarso-metatarsal joint level is a primary factor for hallux valgus and that sagittal instability increases with the progression of the deformity. The assessment of the degree of vertical instability is usually made by clinical evaluation while any measurements mostly refer to a static assessment of medial ray mobility (i.e. the plantar/dorsal flexion in the sagittal plane). Testing methods currently available cannot attribute the degree of mobility to the corresponding anatomical joints making up the medial column of the foot. The aim of this study was to develop a technique which allows for a quantification of the in-vivo sagittal mobility of the joints of the medial foot column during the roll-over process under full weight bearing. METHODS: Mobility of first ray bones was investigated by dynamic distortion-free fluoroscopy (25 frames/s) of 14 healthy volunteers and 8 patients with manifested clinical instability of the first ray. A CAD-based evaluation method allowed the determination of mobility and relative displacements and rotations of the first ray bones within the sagittal plane during the stance phase of gait. RESULTS: Total flexion of the first ray was found to be 13.63 (SD 6.14) mm with the healthy volunteers and 13.06 (SD 8.01) mm with the patients (resolution: 0.245 mm/pixel). The dorsiflexion angle was 5.27 (SD 2.34) degrees in the healthy volunteers and increased to 5.56 (SD 3.37) degrees in the patients. Maximum rotations were found at the naviculo-cuneiform joints and least at the first tarso-metatarsal joint level in both groups. CONCLUSIONS: Dynamic fluoroscopic assessment has been shown to be a valuable tool for characterisation of the kinematics of the joints of the medial foot column during gait.A significant difference in first ray flexion and angular rotation between the patients and healthy volunteers however could not be found.

Angular and sliding stable antegrade nailing (Targon PH) for the treatment of proximal humeral fractures.

INTRODUCTION: The optimal surgical treatment for displaced proximal humeral fractures continues to be controversial. Different treatment modalities are available. Mechanical implant-related problems, however, and the preservation of the biological integrity of the humeral head remain unsolved. New implants providing angular stability are expected to maintain the intraoperative result of reduction until definitive healing. The purpose of this study was to evaluate the functional outcome and the complication rate of an angular and sliding stable antegrade interlocking nail for the treatment of displaced proximal humeral fractures. MATERIALS AND METHODS: In a prospective study, 112 consecutive patients with displaced proximal humeral fractures were treated. Complete 12 months postoperative follow-up was available for 74 patients. Fracture types were classified according to the Neer-classification. Clinical, functional and radiographic follow-up evaluations were performed 3, 6 and 12 months after surgery. The Constant Score (CS) was used to assess shoulder function. RESULTS: All fractures were united. The CS (MV +/- SD) of the injured side 3, 6 and 12 months after surgery were 42.1 +/- 15.1, 56.1 +/- 20.1 and 70.9 +/- 19.3, respectively. Patients sustaining Neer III and VI/3 fractures revealed better shoulder function (68.8 +/- 14.7, 74.9 +/- 17.6) 12 months postoperatively than those with Neer IV/4 fractures (60.7 +/- 23.2), where most complications occurred. Complications requiring surgical therapy were seen in a total of 24 patients (30%) and included backing out of screws in nails without peak inlay (20%; 2000-2003), protrusion of screws into the gleno-humeral joint (5%), loss of reduction with malunion (9%) and major tubercle displacement (7%). CONCLUSION: The treatment of displaced proximal humeral fractures with an angular and sliding stable antegrade nail (Targon-PH) led to good functional results, especially in 2- and 3-part fractures. There exists a substantial risk for postoperative complications and bad motor function in Neer IV/4 fractures. Lateral backing out of screws was abolished by implant modifications (PEEK-inlay) from 2003 onwards. Additional tension wire banding of the major tubercle may further reduce the risk of secondary displacement.