Ex Vivo Biomechanical Evaluation of the Canine Cranial Cruciate Ligament-Deficient Stifle with Varying Angles of Stifle Joint Flexion and Axial loads after Tibial Tuberosity Advancement

Objective To evaluate the effect of tibial tuberosity advancement (TTA) on cranial tibial thrust (CrTT), retropatellar force (RPF), patellar tendon load (PTL), and patellar tendon angle determined by the tibial plateau angle (PTATPA) method or common tangent (PTACT) method in the canine cranial cruciate ligament (CrCL)-deficient stifle joint. Study Design Ex vivo cadaver study. Sample Population Cadaveric canine hind limbs (n=30). Methods Stifle joints were subjected to 3 differing loading conditions using a constrained limb press model (Group1: 30% body weight axial load at stifle and talocrural joint angles of 135 +/- 5 degrees and 145 +/- 5 degrees, respectively; Group 2: 30% body weight axial load at stifle and talocrural angles of 145 +/- 5 degrees and 135 +/- 5 degrees, respectively; and Group 3: 50% body weight axial load at stifle and talocrural joint angles of 135 +/- 5 degrees and 145 +/- 5 degrees, respectively). The CrCL was transected in situ under load; sensors allowed direct measurement of CrTT, RPF, and PTL. Lateral radiographic projections were used to assess PTATPA and PTACT. Descriptive statistics were used to report CrTT (by design this force returned to 0-point values, defined as the neutral point of advancement [NPA]). At the NPA, RPF was compared with baseline using a 2-tailed sign test. PTL within groups were compared using a paired t-test; pair-wise comparisons of PTATPA and PTACT were performed using a paired t-test. Comparisons between loading conditions were made with a 1-way ANOVA and Tukey's post hoc test. Equivalence tests were used to test mean PTATPA and PTACT for equivalence to 90 degrees. Significance was set at a P-value of .05. Results CrTT returned to baseline values, and RPF and PTL at NPA were reduced below baseline values in all specimens in a near linear fashion with TTA. At the NPA, PTATPA > PTACT in 2 of the 3 loading conditions, but insufficient evidence to suggest they differed in the third. Mean PTATPA and PTACT varied between loading conditions. The threshold for each of the groups evaluated, at which the PTA could be significantly different from 90 degrees, was larger for PTATPA than PTACT in all groups, as greater variation was observed with PTATPA versus PTACT. Conclusion This study further supports the claim that reduction of CrTT occurs after TTA in the CrCL-deficient stifle joint through an alteration of PTA. Additionally, RPF and PTL also decrease after TTA. The PTACT may be a more precise method of determining PTA.