Magnetic resonance measurements of the deviation of the angle of force generated by contraction of the quadriceps muscle in dogs with congenital patellar luxation

Objective-To measure the quadriceps angle (Q-angle) in dogs with congenital patellar luxation using magnetic resonance (MR) methods. Study Design-Prospective clinical study. Animals-Thirty-eight client-owned dogs. Methods-Thirty-eight dogs were examined and placed into the following group s based on the degree of patellar instability: normal, grade I, grade II, a nd grade III. MR images of 37 pelvic limbs without patellar instability, 33 pelvic limbs with patellar luxation, and 6 limbs with cranial cruciate lig ament (CrCL) rupture were made. The Q-angle was calculated using trigonomet ric methods based on MR images. Limbs with patellar luxation were compared with normal stifles and stifle with other disorders. Results-The average Q-angle of the normal group was 10.5 degrees (24.9 degr ees to -2.0 degrees). The grade I group had an average Q-angle of 12.2 degr ees (28.8 degrees to 2 degrees), the grade II group 24.3 degrees (44.6 degr ees to 7.7 degrees), and the grade III group 36.6 degrees (51.4 degrees to 15.6 degrees). The average Q-angle of limbs with an isolated CrCL rupture w as 19.3 degrees (34.7 degrees to 3.9 degrees). Conclusion-MR images can be used to make exact calculations of the Q-angle. Clinical Relevance-MR images can be used to quantify the degree of patellar luxation. (C) Copyright 2001 by The American College of Veterinary Surgeon s.