Radiographic quantitative assessment of cranial tibial subluxation before and after tibial plateau leveling osteotomy in dogs

Objective—To determine the influence of stifle joint flexion angle, cranial cruciate ligament (CrCL) integrity, tibial plateau leveling osteotomy (TPLO), and cranial tibial subluxation on the distance between the location of the origin and insertion of the CrCL (CrCLd) in dogs. Samples—4 pairs of pelvic limbs from adult dog cadavers weighing 23 to 34 kg. Procedures—Mediolateral projection radiographs of each stifle joint were obtained with the joint flexed at 90°, 105°, 120°, 135°, and 150°. Radiopaque markers were then placed at the sites of origin and insertion of the CrCL. Afterward, radiography was repeated in the same manner, before and after CrCL transection, with and without TPLO. Following CrCL transection, radiographs were obtained before and after inducing overt cranial tibial subluxation. Interobserver variation in measuring the CrCLd without fiduciary markers was assessed. The effect of CrCL integrity, cranial tibial subluxation, flexion angle, and TPLO on CrCLd was also determined. Results—Interobserver agreement was strong, with an intraclass correlation coefficient of 0.859. The CrCLd was significantly shorter (< 1 mm) at 90° of flexion; otherwise, flexion angle had no effect on CrCLd. Cranial tibial subluxation caused a 25% to 40% increase in CrCLd. No effect of TPLO on CrCLd was found, regardless of CrCL integrity, forced stifle joint subluxation, or flexion angle. Conclusions and Clinical Relevance—Overt cranial tibial subluxation in CrCL-deficient stifle joints can be detected on mediolateral projection radiographs by comparing CrCLd on neutral and stressed joint radiographs at joint angles between 105° and 150°, regardless of whether a TPLO has been performed.