In vivo femorotibial subluxation during weight-bearing and clinical outcome following tibial tuberosity advancement for cranial cruciate ligament insufficiency in dogs.

Ex vivo studies have been used extensively to investigate the mechanisms of tibial osteotomies but few have explored femorotibial alignment in vivo. The aim of this study was to assess femorotibial joint alignment under static weight-bearing conditions (and subsequent outcome) in dogs treated for cranial cruciate ligament (CrCL) insufficiency with tibial tuberosity advancement (TTA). Twenty-five dogs (30 stifles) with CrCL insufficiency treated by TTA were included. The distance from the origin to insertion of the CrCL (CrCLd) was measured on non-weight-bearing immediate post-operative radiographs and weight-bearing follow-up radiographs. CrCLd values were compared using a paired t test. The relationship between change in CrCLd (ΔCrCLd) and post-operative patellar tendon angle according to the common tangent method (PTACT) was assessed using Pearson's correlation. Outcome was assessed with an owner-completed questionnaire, and peak vertical force (PVF) and vertical impulse (VI) as percentages of bodyweight (BW). Following TTA, 21/30 stifles were persistently subluxated at a follow-up of 18 ± 14 months (mean ± SD). Follow-up weight-bearing CrCLd was greater (P<0.001) than post-operative non-weight-bearing CrCLd, with a mean ΔCrCLd of 5.8 ± 3.4mm (16 ± 10%). Post-operative PTACT was 89 ± 3° and did not correlate with ΔCrCLd (r=0.002, P=0.994). Mean PVF and VI were 65 ± 10% BW and 9±2% BW, respectively. All owners felt TTA provided improvement in lameness. The results indicated that TTA does not normalize sagittal plane femorotibial stability during standing at a PTACT of 90°, but most dogs return to good limb function regardless of femorotibial alignment.