Foot kinematics and kinetics during adolescent gait
Introduction
Computerized gait analysis is often performed to enhance clinical decision making. Typically, only two markers are used to track the foot and ankle complex. This single rigid link model has only one center of rotation for dorsi/plantar flexion and internal/external rotations. Frontal plane rotations (pronation/supination or inversion/eversion) cannot be determined. There are two problems with such simplified modeling techniques. First, the information can be misleading when motion occurs between the ankle and the toe markers. For example, in a subject with the common combination of equinus and mid-foot break, rotations occurring at the tarsalmetatarsal and midtarsal joints may be interpreted as normal ankle motion. Second, even when abnormalities are present in the ankle joint data, it is not possible to isolate the problem to a particular joint. To address these problems multiple joint models have been developed [1], [2], [3], [4], [5], [6], [7], [8].
Multi-segmented models of the foot that include the forefoot are very recent. One such model utilized 12 markers to determine four segments [5], [6]. Radiographic measurements were taken to index the reflective markers to the underlying bony anatomy. A further adaptation calculated kinetic information using both force and pressure plate data [7]. Data was reported from five pediatric subjects. Another model consisting of five segments was created using sets of rigid marker clusters to track the shank, calcaneus, mid-foot, first metatarsal and the hallux of nine adult subjects. The marker clusters were referenced to anatomical bony landmarks on the foot [8].
These previous publications have focused on methodology. To date, only one study has presented comprehensive kinematic results determined using such a model [8]. There are no comprehensive reports of kinetics. Prior models have focused on examining proximal mechanics without considering medial/lateral differences. The aim of the current study is to present the results of a kinematic and kinetic normal database established using a nine-segment foot model on an adolescent population. The model includes medial/lateral subdivisions of the forefoot and toes. The validation procedures of this model and comprehensive details of marker placements and segment definitions have been reported [9], [10].
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Subjects
Eighteen subjects between the ages of 7 and 16 were evaluated (average age 12.4±2.6 years, 10 female, eight male). Subjects were screened for exclusion criteria including previous lower limb trauma or a current condition affecting gait. Only right feet were evaluated. A breakdown of subjects' age, gender and anthropomorphic data is given in Table 1.
Instrumentation
Nineteen 10 mm diameter reflective markers were used to identify eight segments of the foot plus the shank (Fig. 1, Table 2, Table 3). Six cameras
Results
Using wedges placed under the foot, the mean errors between the model results and the predicted angles at three ankle angle settings (20 and 10° plantarflexion and 10° dorsiflexion) averaged over four subjects were 1.4°. Similarly, for two separate angles of toe extension (15 and 30°) mean errors were 1.6° for the hallux, 3.3° for the medial toes, and 1.8° for the lateral toes. Comparisons with the radiographic parameters of Cavanagh et al. [13] are presented in Table 6. Of the three angles,
Discussion
In recent years, improvements in gait analysis technology have made quantitative studies of individual joints of the foot feasible. The current study adds to a growing body of work by presenting kinematic and kinetic data collected for adolescents from a three dimensional model with medial/lateral segmentation, and a complete reporting of both segmental joint kinematics and kinetics. The goal of this work is to provide a model and associated data capable of being used for clinical decision
Acknowledgments
Supported by the Shriners Hospitals for Children grant #8530. The authors gratefully acknowledge the support of Sonya Rees, PT, Barbara Johnson, PT, Drs Jacques D'Astous, M.D. and Peter Armstrong, M.D.
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