The Effect of Preoperative Planning Method on Recommended Tibial Tuberosity Advancement Cage Size

Abstract

To determine if use of various commonly practiced tibial tuberosity advancement (TTA) preoperative planning methods leads to variable TTA cage size recommendations. Radiographic study. Dogs (n = 14) with naturally occurring cranial cruciate ligament disease. TTA was planned by a single observer on mediolateral stifle radiographs of each dog using 2 sets of tibial plateau landmarks (anatomic [A] vs. femorotibial common tangent [T]) and 2 advancement measurement techniques (transparent overlay [O] vs. simulated TTA using imaging software [S]) for 4 different planning methods (AO, AS, TO, TS). Cage size recommendations for each stifle were tabulated for each of the 4 planning methods. Mean advancement (mm) required to obtain patellar tendon angle (PTA) = 90° for each of the 4 planning methods were statistically compared. In the 14 stifles studied, the 4 planning methods evaluated led to 4 different cage size recommendations in 1 stifle, 3 different recommendations in 8 stifles, 2 different recommendations in 3 stifles, and 1 recommendation in only 2 stifles. There was a significant difference in the mean advancement measurement between the 4 planning methods (P < .0001); the AS technique was the largest whereas TO resulted in the smallest measurement. Overall, larger advancement was associated with use of anatomic landmarks (vs. common tangent) and imaging software to simulate TTA (vs. overlays). Currently practiced methods for TTA pre-planning led to variable cage size recommendations in 86% of the stifles evaluated and may be a source of inconsistent functional outcomes.