原 康

OBJECTIVE:  The aim of this study was to identify risk factors for refracture after radial union in small-breed dogs. STUDY DESIGN:  In our retrospective study, medical records of radial-ulnar fracture cases in small dogs treated with plates and screws were reviewed. General information and postoperative course (days until confirmed radial fracture healing, with or without ulnar union, time to final follow-up, with or without plate removal and refracture) were recorded. The fracture line location, screw positions, radial thickness and width, and pixel values throughout the postoperative periods were obtained from the radiographs. The affected limbs were classified into non-plate removal (P) and plate removal (R) groups. RESULTS:  Refracture occurred in 5 of the 141 limbs at the most distal screw in the P group and 5 of the 40 limbs at the same site as the initial fracture in the R group. Multivariate analysis indicated that refracture was linked to the amount of relative change with growth in the position of the most distal screw in the P group, with pixel value and radial thickness ratios at the same site as the initial fracture in the R group. CONCLUSION:  Reducing the screw diameter relative to the radial width to the appropriate extent may be considered in cases where the screw positioned at the most distal end of the radius is expected to be relatively proximal as the distal radius grows; not removing the plate may be considered in cases with a decreased radial thickness or bone mineral density beneath the plate during plate removal.

OBJECTIVE:  The aim of this study was to evaluate the stress changes in the radii beneath the locking plates (LP) of dogs implanted with LP using finite element analysis (FEA). STUDY DESIGN:  The study included radii harvested from eight dogs. After computed tomography (CT) scans of the forelimb, the articular surface of the radius was fixed using resin. Material tests were conducted to identify the yield and fracture points and for verification with FEA. The CT data of the radius were imported into FEA software. The radii were classified into three groups based on the placement of the LP (nonplate placement, intact group; 1 mm above the radial surface, LP + 1 mm group; 3 mm above the radial surface, LP + 3 mm group). Equivalent, maximum, and minimum principal stresses and minimum principal strain were measured after FEA at the radial diaphysis beneath the plate. RESULTS:  In shell elements, the LP + 1 mm and LP + 3 mm groups showed a significantly lower maximum principal stress compared with the intact group. In solid elements, the LP + 1 mm and LP + 3 mm groups showed a significantly higher equivalent stress and a significantly lower maximum principal stress compared with the intact group. CONCLUSION:  When an axial load is applied to the radius, LP placement reduces the tension stress on the cortical bone of the radius beneath the plate, possibly related to implant-induced osteoporosis and bone formation in the cortical bone beneath the plate.

Abstract Background Cranial closing wedge osteotomy (CCWO) is a functional stabilisation technique for cranial cruciate ligament (CrCL) ruptures. This biomechanical study aimed to evaluate the influence of CCWO on the stability of the stifle joint. Eighteen Beagle stifle joints were divided into two groups: control and CCWO. The stifle joints were analyzed using a six-degree-of-freedom robotic joint biomechanical testing system. The joints were subjected to 30 N in the craniocaudal (CrCd) drawer and proximal compression tests and 1 Nm in the internal–external (IE) rotation test. Each test was performed with an extension position, 135°, and 120° of joint angle. Results The stifle joints were tested while the CrCLs were intact and then transected. In the drawer test, the CCWO procedure, CrCL transection, and stifle joint flexion increased CrCd displacement. The CCWO procedure and CrCL transection showed an interaction effect. In the compression test, the CCWO procedure decreased and CrCL transection and stifle joint flexion increased displacement. In the IE rotation test, CCWO, CrCL transection, and stifle joint flexion increased the range of motion. Conclusions CCWO was expected to provide stability against compressive force but does not contribute to stability in the drawer or rotational tests. In the CCWO-treated stifle joint, instability during the drawer test worsened with CrCL transection. In other words, performing the CCWO procedure when the CrCL function is present is desirable for stabilizing the stifle joint.

Abstract OBJECTIVE To verify the validity of finite element analysis (FEA) predictions obtained from a canine lumbar segment model in comparison with experimental biomechanical testing results from the same subjects. ANIMALS 6 healthy beagle dogs were euthanized for other purposes. METHODS The L1–2 and L5–6 segments were harvested from euthanized animals and subjected to rotation tests and compression tests, respectively, using both ex vivo mechanical testing and FEA. For each method, we recorded the maximum torque value and angle of vertebral body rotation at rupture observed in rotation tests, as well as the maximum stress value and displacement of the vertebral body endplate at rupture measured from compression tests. We then calculated Pearson’s correlation coefficient to determine correlations between the angle of gyration and displacement at rupture determined by mechanical testing and FEA. The study started on March 26, 2021, and ended on March 18, 2023. RESULTS For the rotation test, correlation coefficients for the maximum torque and rotation angle of the vertebral body at rupture were r = 0.92 and 0.96, respectively. For the compression test, correlation coefficients for the maximum stress and displacement of the vertebral body endplate at rupture were r = 0.73 and 0.94, respectively. All results showed strong correlations between the FEA predictions and ex vivo mechanical test results. CLINICAL RELEVANCE These findings suggest that FEA predictions are sufficiently reliable for ex vivo mechanical test results for biomechanical studies of canine lumbar segment models.