Evaluation of Hindlimb Mechanical Axis by Using Single-Plane Fluoroscopy in Beagle Dogs

[Abstract] The mechanical axis has been used as the basis for alignment evaluations in human practice. Many studies have been conducted on the mechanical axis in humans, but there are not many studies that have investigated this in the field of veterinary medicine. The current study compared the values of the mechanical axis of the hindlimb from a stance phase, which is the normal weight-bearing walking posture, to the dorsal recumbent position, without any weight bearing, in beagle dogs. Fluoroscopic images of stifle joints were obtained by using single-plane fluoroscopy during stance phase in 5 healthy beagle dogs. Computed tomography was used to construct a 3D bone model of the hindlimb, and the mechanical axis of the hindlimb was measured after using the shape-matching technique. The mechanical axis of the hindlimb was also measured with X-ray which were taken in the conventional stretched out leg position in dorsal recumbency. The mechanical lateral proximal femoral angle (mLPFA), mechanical lateral distal femoral angle (mLDFA), mechanical medial proximal tibial angle (mMPTA) and mechanical medial distal tibial angle (mMDTA) were measured in both methods. Comparison between the weight bearing stance phase and the non-weight bearing recumbent position, showed significant differences in mLPFA and mLDFA. Differences between the two methods were demonstrated and suggested that measuring the mechanical axis in a natural standing posture of a dog should be considered correct for a more accurate measurement. This data should be utilized as a reference value for surgery of pelvic limb deformity in beagle dogs.