Introduction: Despite the important role of synovial joints in equine orthopedics, our current knowledge of their biomechanical function is still sparse. Synovial joints place few constraints on movement within a physiologic range, produce little friction, and facilitate motion with load transfer. Instantaneous center of rotation (ICR) has been used to describe joint motion. The ICR is a point in a plane of motion around which a bone rotates, and is characterized by having zero velocity within the plane at the instant considered. Theoretically, there are infinite such instances as the joint articulates through it's range of motion. However, the range of motion may be divided into finite steps of motion and the centers of rotation may be determined for each of the steps.1 The objective of this study was to determine the instant centers of rotation for the cubital, antebrachiocarpal, middle carpal, metacarpophalangeal, proximal interphalangeal, and distal interphalangeal joints for the range of motion encountered during racing in the Thoroughbred racehorse. Materials & Methods: A three dimensional model of the two dimensional sagittal plane movement of an isolated limb of a Thoroughbred racehorse was developed using commercial software. An isolated limb was stabilized in the standing position with a cast and spherical lead markers, and scanned using computed tomography (CT). The uncasted limb was placed in a materials testing system and incrementally loaded while serial radiographs were taken orthogonal to each joint in 10-20 increments throughout the range of motion for each joint. Bone and CT landmarks were digitized from the radiographs for calculation of ICRs at each angle of rotation, and incorporation in the model. Results: The range of motion evaluated for the elbow, antebrachiocarpal, middle carpal, metacarpophalangeal, proximal interphalangeal, and distal interphalangeal joints were 99º, 92º 53º, 146º, 23º, and 63º, respectively. The proximal and distal sesamoid bones had a range of motion of 63º and 49º, respectively. Coupled with the ICR at each incremental angle measured, this information describes the sagittal planar motion of each joint. Discussion: The ICR and angles of rotation of the joints proximal to the phalanges are in general agreement with previous studies.2,3 In contrast, we found substantial motion at the proximal interphalangeal joint, and further documented motion of the distal sesamoid (navicular) bone during distal interphalangeal joint motion. Motion of the proximal interphalangeal joint should be considered an important component in the biomechanics of the distal limb. Comprehension of the motion of the navicular bone is important in consideration of the biomechanical etiopathogenesis and treatment of navicular syndromes.
In vitro assessment of the instant centers and angle of rotation of the equine Thoroughbred forelimb joints.
ZARUCCO, Laura;
1997-01-01
Abstract
Introduction: Despite the important role of synovial joints in equine orthopedics, our current knowledge of their biomechanical function is still sparse. Synovial joints place few constraints on movement within a physiologic range, produce little friction, and facilitate motion with load transfer. Instantaneous center of rotation (ICR) has been used to describe joint motion. The ICR is a point in a plane of motion around which a bone rotates, and is characterized by having zero velocity within the plane at the instant considered. Theoretically, there are infinite such instances as the joint articulates through it's range of motion. However, the range of motion may be divided into finite steps of motion and the centers of rotation may be determined for each of the steps.1 The objective of this study was to determine the instant centers of rotation for the cubital, antebrachiocarpal, middle carpal, metacarpophalangeal, proximal interphalangeal, and distal interphalangeal joints for the range of motion encountered during racing in the Thoroughbred racehorse. Materials & Methods: A three dimensional model of the two dimensional sagittal plane movement of an isolated limb of a Thoroughbred racehorse was developed using commercial software. An isolated limb was stabilized in the standing position with a cast and spherical lead markers, and scanned using computed tomography (CT). The uncasted limb was placed in a materials testing system and incrementally loaded while serial radiographs were taken orthogonal to each joint in 10-20 increments throughout the range of motion for each joint. Bone and CT landmarks were digitized from the radiographs for calculation of ICRs at each angle of rotation, and incorporation in the model. Results: The range of motion evaluated for the elbow, antebrachiocarpal, middle carpal, metacarpophalangeal, proximal interphalangeal, and distal interphalangeal joints were 99º, 92º 53º, 146º, 23º, and 63º, respectively. The proximal and distal sesamoid bones had a range of motion of 63º and 49º, respectively. Coupled with the ICR at each incremental angle measured, this information describes the sagittal planar motion of each joint. Discussion: The ICR and angles of rotation of the joints proximal to the phalanges are in general agreement with previous studies.2,3 In contrast, we found substantial motion at the proximal interphalangeal joint, and further documented motion of the distal sesamoid (navicular) bone during distal interphalangeal joint motion. Motion of the proximal interphalangeal joint should be considered an important component in the biomechanics of the distal limb. Comprehension of the motion of the navicular bone is important in consideration of the biomechanical etiopathogenesis and treatment of navicular syndromes.
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