The effect of tibial plateau angles on patella ligament thickness after tibial plateau levelling osteotomy in dogs

Abstract

Background. Cranial cruciate ligament disease is a common orthopaedic condition in dogs. Tibial plateau levelling osteotomy (TPLO) is a dynamic repair for cranial cruciate ligament (CrCL) deficient stifle. The functional tibial plateau angle (fTPA) is novel, measured with reference to the ground at normal pelvic limb angulation during standing, unlike the conventional tibial plateau angle (TPA) measured with the stifle and tarsus flexed at right angles. Post-TPLO surgery patients can develop patellar desmitis. Objectives. To describe the fTPA and to determine if there are postoperative threshold tibial plateau angles to predict patellar ligament thickening. Methods. Pre-operative, post-operative and 8-week post-operative radiographs of dogs undergoing TPLO were collected to measure fTPA, TPA and patellar ligament thickness. The fTPA and TPA were compared using descriptive statistics. A thickened patellar ligament was defined as a 100% increase in thickness at 8-weeks compared to pre-operative. Patellar ligament thickening (Yes/No) was assessed according to TPA using receiver operating characteristic curve analysis to determine the Youden index. Results. Mean (±SD) pre-operative and post-operative fTPA were -5.5 (±7.4) and -23.6 (±6.2) and TPA were 26 (±2.9) and 5.9 (±3.1), respectively. The Youden index (area under the curve: 0.7813) indicated a TPA <10° is 100% sensitive and 78% specific for patellar ligament thickening. vii Conclusion. A TPA of <10° results in patella ligament thickening. A negative fTPA can be associated with increased strain in the patella ligament and contribute to thickening of the patella ligament. Further studies are necessary to evaluate the relationship between fTPA and patella ligament thickness.