Evaluation of a Sonomicrometry System for the Measurement of Joint Kinematics PDF Download

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Languages : en
Pages : 63

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Book Description
The measurement of joint kinematics in vivo is an important aspect of the development of new treatment methods for orthopaedic injuries. Existing methods for the measurement of knee joint kinematics are limited by their data collection speeds, expense, and invasiveness. A proposed method uses sonomicrometry crystals mounted on blocks in an arrangement that would establish tibial and femoral coordinate systems. The objectives of this thesis were to: 1) determine the effect of different crystal arrangements and mounting block designs on the measurement of absolute distances using sonomicrometry and 2) determine the effect of mounting block size on the measurement of rotations and translations using sonomicrometry. Sonomicrometry crystals (Sonometrics Corp., London, Ontario) were attached to an electromechanical testing machine and used to measure known distances. The experiment was repeated using different crystal mounting block size, geometry, and composition; as well as with different means of affixing the crystals to the block and different numbers of crystals. These changes will be necessary for the mounting of the crystals in the joint for kinematics measurements. Regression lines were fit to plots of measured versus known distances. In the simplest case, that of two crystals in simple rectangular acrylic blocks, the mean slopes were: 1.01"0.00, 1.01"0.00, and 1.01"0.00 (mean " SEM) and the intercepts were: 0.26"0.02, 0.52"0.02, and -0.35"0.05. Under the various test conditions (mounting block geometry, size and composition; crystal affixation method; and number of active crystals), the maximum change in slope was 0.03 and the maximum change in intercept was 2.08 mm compared to the simplest case. The changes in intercept were attributed to differences between individual crystals and their sensitivity settings. These results indicate that a sonomicrometry system will allow accurate, repeatable measurements of in-vivo joint kinematics if each crystal is calibrated prior to testing. To determine the rotational and translational errors, sonomicrometry crystals were mounted on blocks that established Cartesian coordinate systems. Joint translations were simulated using an electromechanical testing machine, and joint rotations were simulated using a stand with a movable arm. Two different sizes of mounting block were used for this experiment. For translations, mean bias (the mean value of the differences between the mean measurement at a given position and the actual position) was 0.26 mm for the smaller blocks and 0.19 mm for the larger blocks. Mean precision (the mean standard deviation of the measurements) was 0.26 mm for the smaller blocks and 0.29 mm for the larger blocks. For rotations, mean bias was 0.29 with the smaller blocks and 0.285 with the larger blocks. Mean precision was 0.30 with the smaller blocks and 0.23 with the larger blocks. The system using the smaller holder blocks recorded translations and rotations as accurately as the system using larger holder blocks. Smaller blocks are preferred for planned in-vivo studies because of reduced invasiveness. Based on this research, future studies in our laboratory will attempt to capture the 3-D kinematics of the caprine stifle joint during various activities. The animal will then be sacrificed, and a robot will be used to recreate the joint motions ex-vivo. Implantable force and pressure transducers will be used to study the interactions between the structures and the relationships between the forces and kinematics of the joint. The current study indicates that the sonomicrometry system will be adequate for capturing joint kinematics for this proposed research by providing accurate, high speed measurements.