Relative motions of the tibia, talus, and calcaneus during the stance phase of gait: a cadaver study.

The motions of the tibia, talus, and calcaneus during walking were analyzed three-dimensionally using a dynamic cadaver model that recreates the stance phase of walking. Rigid marker clusters were attached to each of the three bones, and the rotations of the talus and calcaneus with respect to the tibia and the calcaneus with respect to the talus were analyzed for eight right cadaver feet. The talus rotated primarily in plantarflexion/dorsiflexion about the talocrural joint, with an average range of 18 degrees +/- 4.7 degrees. The calcaneus began in inversion and internal rotation with respect to the tibia, moved into the neutral position at 28% of the stance phase and rotated primarily in plantarflexion from that point onward. Rotation of the calcaneus with respect to the talus at the subtalar joint occurred about all three axes, with approximately 5 degrees of relative dorsiflexion and 7 degrees of relative internal rotation. After 25% of stance, the talus and calcaneus moved together as one body into plantarflexion, providing a rigid lever as toe-off was approached.

Development of an animal model of acetabular fractures.

A closed intraarticular fracture is a complex injury that consists of a physical disruption of the subchondral bone and articular surface, and an impaction injury to the articular surface that occurs at the time of the fracture. Few experimental models have been able to incorporate the elements of displaced articular fractures and blunt impaction injury to the articular surface. This work details the initial stages of an attempt to develop such model. Using a model of a dorsal wall fracture of the acetabulum in a goat, we have developed a bench-top method for assessing articular contact stress. Additionally, preliminary in vivo survival data are presented.

Dynamic loading of the plantar aponeurosis in walking.

BACKGROUND: The plantar aponeurosis is known to be a major contributor to arch support, but its role in transferring Achilles tendon loads to the forefoot remains poorly understood. The goal of this study was to increase our understanding of the function of the plantar aponeurosis during gait. We specifically examined the plantar aponeurosis force pattern and its relationship to Achilles tendon forces during simulations of the stance phase of gait in a cadaver model. METHODS: Walking simulations were performed with seven cadaver feet. The movements of the foot and the ground reaction forces during the stance phase were reproduced by prescribing the kinematics of the proximal part of the tibia and applying forces to the tendons of extrinsic foot muscles. A fiberoptic cable was passed through the plantar aponeurosis perpendicular to its loading axis, and raw fiberoptic transducer output, tendon forces applied by the experimental setup, and ground reaction forces were simultaneously recorded during each simulation. A post-experiment calibration related fiberoptic output to plantar aponeurosis force, and linear regression analysis was used to characterize the relationship between Achilles tendon force and plantar aponeurosis tension. RESULTS: Plantar aponeurosis forces gradually increased during stance and peaked in late stance. Maximum tension averaged 96% +/- 36% of body weight. There was a good correlation between plantar aponeurosis tension and Achilles tendon force (r = 0.76). CONCLUSIONS: The plantar aponeurosis transmits large forces between the hindfoot and forefoot during the stance phase of gait. The varying pattern of plantar aponeurosis force and its relationship to Achilles tendon force demonstrates the importance of analyzing the function of the plantar aponeurosis throughout the stance phase of the gait cycle rather than in a static standing position. CLINICAL RELEVANCE: The plantar aponeurosis plays an important role in transmitting Achilles tendon forces to the forefoot in the latter part of the stance phase of walking. Surgical procedures that require the release of this structure may disturb this mechanism and thus compromise efficient propulsion.

Fiberoptic measurement of tendon forces is influenced by skin movement artifact.

Fiberoptic cables have previously been used for tendon force measurements in vivo. To measure forces in the Achilles tendon, a cable is passed mediolaterally through the skin and tendon, transverse to the loading axis. As the tendon is loaded, its fibers compress the cable and modulate the intensity of transmitted light, which can be related to tendon force by an in situ calibration. The relative movement between skin and tendon at the cable entry and exit sites may cause error by bending the cable and thus altering transducer output. Cadaver simulations of walking were conducted to compare fiberoptic measurements of Achilles tendon forces to known loads applied to the tendon by actuators attached in series. Force measurement errors, which were high when the skin was intact (RMS errors 24-81% peak forces), decreased considerably after skin removal (RMS errors 10-33% peak forces). The fiberoptic transducer is a useful tool for measurement of tendon forces in situ under natural loading conditions when skin can be removed, but caution should be exercised during in vivo use of this technique or under circumstances where skin is in contact with the fiberoptic cable at the insertion and exit sites.

Kinematic behavior of the ankle following malleolar fracture repair in a high-fidelity cadaver model.

BACKGROUND: Previous studies involving axially loaded ankle cadaver specimens undergoing a passive range of motion after fracture have demonstrated rotatory instability patterns consisting of excessive external rotation during plantar flexion. The present study was designed to expand these studies by using a model in which ankle motion is controlled by physiologically accurate motor forces generated through phasic force-couples attached to the muscle-tendon units. METHODS: Eight right unembalmed cadaver feet were tested in a dynamic gait simulator that reproduces the sagittal kinematics of the tibia while applying physiological muscle forces to the tendons of the major extrinsic muscles of the foot. Six-degrees-of-freedom kinematics of the tibia and talus were measured with use of a VICON motion-analysis system. The experimental conditions included all combinations of lateral and medial injury to reproduce the clinical classifications of ankle fracture. Statistical analysis was performed with repeated-measures analyses of variance. RESULTS: The talus of the intact ankles demonstrated coupled external rotation and inversion relative to the tibia as the ankle plantar flexed. Osteotomy of the fibula, simulating a lateral ankle fracture, slightly but significantly increased external rotation and inversion of the talus (p < 0.001), whereas disruption of either the superficial or the deep deltoid ligament increased talar eversion (p < 0.003) and disruption of the deep deltoid ligament increased internal rotation (p < 0.0001). The aberrant motions were corrected by repair of the injured structure. CONCLUSIONS: The predominant coupled rotation of the talus is external rotation associated with plantar flexion. Following progressive ankle destabilization, talar external rotation and inversion increased. CLINICAL RELEVANCE: The clinical decision-making process regarding the treatment of ankle fractures centers on determination of whether the injury is expected to result in abnormal motion, which is thought to predispose to the development of arthritis. The present study demonstrated a remarkable degree of ankle stability during stance phase even when there was severe disruption of medial and lateral structures. This finding suggests that a main determinant of clinical outcome after ankle fracture may be ankle motion during swing phase, when ankle stability is not augmented by the combination of axial loading and active motor control of motion. If swing-phase motion is abnormal, then the ankle may be in a vulnerable position at the point of heel-strike.

A dynamic cadaver model of the stance phase of gait: performance characteristics and kinetic validation.

OBJECTIVE: This study was undertaken to evaluate the performance of a new dynamic laboratory model of the stance phase of gait. DESIGN: Five cadaver feet were repetitively tested in the apparatus. BACKGROUND: Typical biomechanical investigations of cadaver feet simply place a static load on the tibia. The present system was designed to better simulate the changing in-vivo loading environment of the foot and ankle during gait. METHODS: The device mimics the behavior of the tibia, foot, and ankle from heel-strike to toe-off by reproducing the physiologic actions of five extrinsic foot muscles and physiologic motion at the proximal tibia. To verify its utility, cadaver gait simulations were conducted while measuring applied muscle forces, ground reaction forces, and plantar pressures. RESULTS: Dynamic muscle forces were consistently delivered to within 10% of pre-programmed values. Dynamic measurements of ground reaction forces and plantar pressure were similar to those measured in healthy human subjects. Peak vertical (y), foreaft (x) and medio-lateral (z) forces were 110, 18, and 4% of body weight respectively. Compressive force in the tibial shaft reached 410% of body weight. RELEVANCE: Cadaver studies have greatly enhanced our understanding of normal and pathologic foot function, but are often limited by over-simplified loading conditions. The apparatus presented here accurately reproduces the in-vivo loading environment and provides a powerful investigational tool for the study of foot and ankle function. With this device, musculoskeletal structures can be examined in detail under biomechanical conditions similar to those they experience in life.