Agreement Between Radiographic and Anatomic Patellar Tendon-Tibial Plateau Angles for Tuberosity Advancement Determination and Cage Size Recommendation in Dogs

Introduction:
Pre-operative measurements are one of the most critical components of the TTA. The purpose of this study was to determine whether the use of practiced radiographic methods for PTA measurements leads to variable cage size recommendations compared with anatomic measurements.

Material and Methods:
Radiographs of cadaveric stifles (n=20) placed at 135° in true lateral position were obtained for the measurement of the PTA using both methods by six blinded observers. The stifles were dissected and the anatomical PTA was determined by an independent observer on a digital image of the proximal tibia in true lateral position. The patellar tendon length (PTL) was measured on the mediolateral radiographs by one observer, and the advancement (A) was determined for each PTA measurement method using the following mathematical equation: A = PTL*Cosine(180- PTA). The results were used to select the optimal commercially available cage size.

Results:
The agreements between the radiographic and the anatomic methods were low to very low for both radiographic methods, indicating that their overall validity was poor. Out of the 20 pelvic limbs studied, the conventional and common tangent methods led to the same cage size recommendations as the anatomic method in only one (5%) and two (10%) stifles, respectively.

Discussion:
Advancement and cage size recommendation using radiographic methods showed poor concordance with the anatomic PTA. The actual clinical significance of under- or over-estimating the advancement is unknown. However, selecting the preoperative planning method that overestimates the advancement to obtain a PTA ≤ 90° seems rational in clinical situations.