It was the aim of the study to determine retrospectively cranio-caudal stifle instability following TTA (tibial tuberosity advancement) using fluoroscopic kinematography. Ten stifles (eight dogs, mean body weight 27.3 kg) with complete rupture of the cranial cruciate ligament and a mean follow-up of 12.8 weeks (5.4 - 28.4 weeks) after TTA underwent latero-lateral, uniplanar fluoroscopic kinematography while walking on a treadmill. Immediately before TTA, each stifle was explored arthroscopically and in the case of a longitudinal or bucket-handle tear of the caudal horn of the medial meniscus the unstable axial portion was resected. The high-speed fluoroscopic video sequences obtained were inspected visually for femoro-tibial translation (cranial drawer). The influence of postoperative patellar tendong angle (PTA), cage size and meniscal surgery on stifle stability was analyzed using logistic regression analysis. In three stifles, resection of unstable meniscal tissue was necessary. Fluoroscopically, nine out of ten stifles showed cranio-caudal instability. Three stifles were potentially overcorrected (post PTA < 90°), seven potentially undercorrected (post PTA > 90°). None of the three parameters analyzed had a significant influence on postoperative in vivo stability (p=0.0988). In conclusion, it appears that inadequate cranialization of the tibia tuberosity might be an expected result of the TTA procedure, as well as persistent cranio-caudal instability during walking. However, instability cannot solely be attributed to insufficient cranialization because three out of nine unstable stifles were sufficiently or even overcorrected (PTA ≤ 90°). Further in vivo studies are needed to resolve these conflicting findings.
