RADIOGRAPHIC, ULTRASONOGRAPHIC AND ELASTOSONOGRAPHIC MEDIUM/LONG TERM EVALUATIONS OF PATELLAR LIGAMENT AFTER TIBIAL PLATEAU LEVELLING OSTEOTOMY IN DOGS

Objective. The aim of the study was to evaluate medium- and long-term changes in thickness and elasticity of the patellar ligament after TPLO. Materials and methods. The patellar ligament was assessed preoperatively (T0), at one (T1), two (T2) and six months (T3) after surgery using radiographs, ultrasound and elastosonography. Knee radiographs were taken in mediolateral view with the stifle and tarsus joints flexed at 90 degrees and femoral condyles superimposed. Patellar ligament thickness was measured one centimeter distal to the base of the patella, one centimeter proximal to the tibial tuberosity and halfway between the first two points. Patients were positioned in lateral recumbency with the stifle in maximum passive flexion during ultrasonographic examination. Percentage of tissue hardness (%HRD) and softness (%SFT) were calculated using dedicated software. Radiographic and sonographic measurements of the patellar ligament, %HRD and %SFT were compared between each time point and with the time elapsed from the onset of clinical signs (0–15 days, 16–60 days and >60 days). Results. Twenty-two stifle joints in 20 dogs were evaluated. At T0, the mean radiographic thickness (mm) of the patellar ligament was 2.4 ± 0.6 in the proximal portion, 2.2 ± 0.5 in the middle portion and 2.3 ± 0.5 in the distal portion. At T3, mean radiographic thickness was 3.7 ± 1.1 in the proximal portion, 4.5 ± 1.8 in the middle portion and 5.2 ± 2.2 mm in the distal portion. At T0, the mean sonographic thickness (mm) of the patellar ligament was 2.3 ± 0.2 in the proximal portion, 2.2 ± 0.3 in the middle portion and 2.6 ± 0.7 in the distal portion. At T3, the mean sonographic thickness (mm) was 2.7 ± 0.9 in the proximal portion, 3.5 ± 1.1 in the middle portion and 4.9 ± 1.5 in the distal portion. Mean %HRD at T0 was 25.8 ± 25.6, at T1 was 52.2 ± 26.0, at T2 was 58.2 ± 23.8 and at T3 was 47.9 ± 23.5. Mean %SFT at T0 was 74.4 ± 25.8, at T1 was 45.9 ± 26.1, at T2 was 44.1 ± 23.6 and at T3 was 52.1 ± 24.3. Thickness was significantly increased between T0 and T1, T0 and T2, and T0 and T3 for both radiographic and sonographic measurements. %HRD was significantly increased and %SFT was significantly decreased between T0 and T1, T0 and T2, and T0 and T3. The patellar ligament was significantly thicker in the middle and distal portions in dogs with onset of clinical signs >60 days only at T0. No other differences were found related to the time elapsed from the onset of clinical signs. Discussion. Radiographic and ultrasonographic findings highlighted a significant thickening of the patellar ligament, especially in the distal portion, which persisted up to 180 days after TPLO. Elastosonography demonstrated a significant increase in patellar ligament hardness following TPLO. The onset of patellar ligament alterations is likely related to biomechanical changes of the stifle occurring after TPLO.