Effect of osteoarthritis on the repeatability of patella tendon angle measurement in dogs

Objective To evaluate the influence of osteoarthritis on the measurement of patella tendon angle (PTA) and determine intraobserver and interobserver variability. Study design Retrospective clinical study. Sample population Eighty‐seven mediolateral radiographs that were obtained prior to tibial tuberosity advancement. Methods Radiographic osteoarthritis was scored by 2 observers using guidelines derived from the International Elbow Working Group Protocol. Patella tendon angle was measured by 3 observers on 3 occasions, with at least 7 days between measurements. The data were statistically analyzed via weighted κ and Kruskal‐Wallis testing. Results A fair strength of agreement was found among observers scoring osteoarthritis, with the same grades in 48% of radiographs. The intraobserver average bias between PTA measurements 1 and 3 ranged from −0.38° to −0.94°. Interobserver bias in angle measurement ranged from −0.92° to −2.00°. Observer 1 had the narrowest range of PTA differences (12.1°), and observer 3 had the highest range of PTA differences (23.5°). Observer 2 had the lowest mean bias (−0.38°). The mean bias was lowest between observers 1 and 2 (−0.92°) and highest between observers 1 and 3 (−2.0°). The mean intraobserver standard deviation of the PTA measurement differences was 2.90°, and interobserver standard deviation of the PTA measurement differences was 2.26°. The degree of osteoarthritis did not influence PTA measurements or their variability. Conclusion The current study did not find evidence of an influence of osteoarthritis on PTA or on the repeatability of measurements. Clinical significance Our findings suggest that osteoarthritis should not affect the radiographic planning for tibial tuberosity advancement surgery. The high variances in PTA measurement in less experienced observers may influence the clinical outcome of surgery.