Objective

To evaluate the effects of changes in prosthetic cup inclination on impingement-free hip abduction, adduction, and internal and external rotation after simulated total hip replacement in dogs.

Methods

For 6 dogs, CT scans of the hip region were used to prepare 3-D surface models of cementless total hip replacement. For each dog, 15 models with cup inclination ranging from -35° to 35° in 5° increments were prepared using computer-aided design software. For each implant position, impingement-free hip motion in abduction, adduction, and internal and external rotation was evaluated using a custom-built computer program for hip flexion/extension angles ranging from 50° to 160° in 5° increments.

Results

A total of 7,920 computer simulations were conducted. Increased cup inclination led to decreased impingement-free abduction in hip extension and increased abduction in hip flexion. Decreased cup inclination led to decreased abduction at all hip angles. Maximal inclination led to increased external rotation in full hip extension, and maximal declination led to increased internal rotation and adduction in full hip flexion.

Conclusions

During total hip replacement, changes in cup inclination influence hip abduction and, to a lesser extent, internal rotation and adduction in flexion and external rotation in extension. The assessment of intraoperative impingement should include abduction, extension combined with external rotation, and flexion combined with adduction and internal rotation.

Clinical relevance

The inclination of a truncated cup influences impingement-free abduction. Inclination should be controlled during cup insertion to keep the prosthetic neck in the central portion of the cup truncation during abduction.

BACKGROUND:Skin marker-based three-dimensional kinematic gait analysis were commonly used to assess the functional performance and movement biomechanics of the pelvic limb in dogs. Unfortunately, soft tissue artefact would compromise the accuracy of the reproduced pelvic limb kinematics. Multibody kinematics optimization framework was often employed to compensate the soft tissue artefact for a more accurate description of human joint kinematics, but its performance on the determination of canine pelvic limb skeletal kinematics has never been evaluated. This study aimed to evaluate a multibody kinematics optimization framework used for the determination of canine pelvic limb kinematics during gait by comparing its results to those obtained using computed tomography model-based fluoroscopy analysis. RESULTS:Eight clinically normal dogs were enrolled in the study. Fluoroscopy videos of the stifle joint and skin marker trajectories were acquired when the dogs walked on a treadmill. The pelvic limb kinematics were reconstructed through marker-based multibody kinematics optimization and single-body optimization. The reference kinematics data were derived via a model-based fluoroscopy analysis. The use of multibody kinematics optimization yielded a significantly more accurate estimation of flexion/extension of the hip and stifle joints than the use of single-body optimization. The accuracy of the joint model parameters and the weightings to individual markers both influenced the soft tissue artefact compensation capability. CONCLUSIONS:Multibody kinematics optimization designated for soft tissue artefact compensation was established and evaluated for its performance on canine gait analysis, which provided a further step in more accurately describing sagittal plane kinematics of the hip and stifle joints.