OBJECTIVE To describe methods to measure the 3-D orientation of the proximal, diaphyseal, and distal segments of the canine radius by use of computer-aided design software (CADS) and to compare the repeatability and reliability of measurements derived by those methods. SAMPLE 31 canine radii with biapical deformities and 24 clinically normal (control) canine radii. PROCEDURES Select CT scans of radii were imported into a CADS program. Cartesian coordinate systems for the humerus and proximal, diaphyseal, and distal radial segments were developed. The orientation of each radial segment in the frontal, sagittal, and transverse planes was measured in triplicate by 3 methods. The repeatability and reliability of those measurements were calculated and compared among the 3 measurement methods. RESULTS The mean ± SD within-subject repeatability of radial angular measurements for all 3 methods was 1.40 ± 0.67° in the frontal plane, 3.17 ± 2.21° in the sagittal plane, and 3.01 ± 1.11° in the transverse plane for control radii and 2.56 ± 1.95° in the frontal plane, 3.59 ± 2.39° in the sagittal plane, and 3.47 ± 1.19° in the transverse plane for abnormal radii. Mean ± SD bias between radial measurement methods was 1.88 ± 2.07° in the frontal plane, 6.44 ± 6.80° in the sagittal plane, and 2.27 ± 2.81° in the transverse plane. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that use of CADS to assess the 3-D orientation of the proximal, diaphyseal, and distal segments of normal and abnormal canine radii yielded highly repeatable and reliable measurements.

Objective—To compare in vitro axial compression, abaxial compression, and torsional stiffnesses of intact and plated radii from small- and large-breed dogs. Sample—Radii from 18 small-breed and 9 large-breed skeletally mature dogs. Procedures—3 groups were tested: large-breed dog radii plated with 3.5-mm limited-contact dynamic compression plates (LCDCPs), small-breed dog radii plated with 2.0-mm dynamic compression plates (DCPs), and small-breed dog radii plated with 2.0/2.7-mm cut-to-length plates (CTLPs). The axial compression, abaxial compression, and torsional stiffnesses of each intact radius were determined under loading with a material testing machine. An osteotomy was performed, radii were plated, and testing was repeated. The stiffness values of the plated radii were expressed as absolute and normalized values; the latter was calculated as a percentage of the stiffness of the intact bone. Absolute and normalized stiffness values were compared among groups. Results—The absolute stiffnesses of plated radii in axial and abaxial compression were 52% to 83% of the intact stiffnesses in all fixation groups. No difference was found in torsion. There was no difference in normalized stiffnesses between small-breed radii stabilized with CTLPs and large-breed radii stabilized with LCDCPs; however, small-breed radii stabilized with DCPs were less stiff than were any other group. Conclusions and Clinical Relevance—Plated radii of small-breed dogs had normalized stiffnesses equal to or less than plated radii of large-breed dogs. The complications typically associated with plating of radial fractures in small-breed dogs cannot be ascribed to an overly stiff bone-plate construct.

OBJECTIVE To evaluate accuracy of articular surfaces determined by use of 2 perpendicular CT orientations, micro-CT, and laser scanning. SAMPLE 23 cat cadavers. PROCEDURES Images of antebrachia were obtained by use of CT (voxel size, 0.6 mm) in longitudinal orientation (CTLO images) and transverse orientation (CTTO images) and by use of micro-CT (voxel size, 0.024 mm) in a longitudinal orientation. Images were reconstructed. Craniocaudal and mediolateral length, radius of curvature, and deviation of the articular surface of the distal portion of the radius of 3-D renderings for CTLO, CTTO, and micro-CT images were compared with results of 3-D renderings acquired with a laser scanner (resolution, 0.025 mm). RESULTS Measurement of CTLO and CTTO images overestimated craniocaudal and mediolateral length of the articular surface by 4% to 10%. Measurement of micro-CT images underestimated craniocaudal and mediolateral length by 1%. Measurement of CTLO and CTTO images underestimated mediolateral radius of curvature by 15% and overestimated craniocaudal radius of curvature by > 100%; use of micro-CT images underestimated them by 3% and 5%, respectively. Mean ± SD surface deviation was 0.26 ± 0.09 mm for CTLO images, 0.30 ± 0.28 mm for CTTO images, and 0.04 ± 0.02 mm for micro-CT images. CONCLUSIONS AND CLINICAL RELEVANCE Articular surface models derived from CT images had dimensional errors that approximately matched the voxel size. Thus, CT cannot be used to plan conforming arthroplasties in small joints and could lack precision when used to plan the correction of a limb deformity or repair of a fracture.