Establishment of normal anatomical radial angles in cats

1) To describe a radiographic method for determination of joint orientation lines and anatomical joint angles in orthogonal planes of feline radii; 2) to establish a range of normal radial joint orientation angles and anatomical axes in a feline population; and 3) to assess the repeatability and reliability of this methodology.

The radial anatomical axis, elbow and carpal joint reference lines, and the intersecting angles of each: anatomical medial proximal (aMPRA) and lateral distal radial angles (aLDRA), anatomical caudal proximal (aCdPRA) and distal radial angles (aCdDRA), and sagittal procurvatum (SP) were determined on the orthogonal radiographs of 14 feline limbs. Intra- and inter-observer agreement was determined based on repeated independent readings by two observers using Bland-Altman plots.

The mean ± standard deviation (SD) and 95% confidence interval (CI) for the feline radii were: aMPRA 70.97 ± 3.38° (70.07 - 71.88°), aLDRA 91.72 ± 3.26° (90.84 - 92.59°), aCdPRA 100.5 ± 3.14° (99.62 - 101.3º), aCdDRA 79.95 ± 3.77° (78.94 - 80.96°) and SP 11.07 ± 1.87° (10.57 - 11.58°). The highest mean bias found for both observers was -1.6 to -1.8° for the angle aCdDRA. Sagittal procurvatum had the lowest mean bias for intra- and inter-observer.

The results obtained showed that the methodology used in our study was repeatable and reliable. The values established for the normal radial anatomical angles are relevant for future use as a reference for surgical treatment of angular deformities, malunions, non-unions, comminuted fractures, and future orthopaedic research.