Effect of tibial tuberosity advancement on cranial tibial subluxation in canine cranial cruciate-deficient stifle joints: an in vitro experimental study

OBJECTIVE: To evaluate the effect of tibial tuberosity advancement (TTA) on tibiofemoral shear force as reflected by measurement of cranial tibial subluxation (CTS) and patella tendon angle (PTA) in the canine cranial cruciate ligament (CrCL) deficient stifle joint. STUDY DESIGN: In vitro cadaver study. ANIMALS: Canine cadaveric hind limbs (n=10). METHODS: CTS and PTA were evaluated from lateral radiographic projections in axially loaded intact CrCL stifle joints, after transection of the CrCL, at a maximally advanced tibial tuberosity position, and at a critical point position. A custom-designed hinge plate allowed alteration of the tibia to tibial tuberosity distance (Ti-TT) under axial load. Digitized radiographic images were used to quantify CTS, PTA, and Ti-TT. Comparisons within groups were made using 1-way repeated measures ANOVA. A post hoc Tukey's HSD test was used to determine post-ANOVA pair-wise comparison within these groups. Significance was set at a value of P<.05. RESULTS: CTS occurred after CrCL transection, which was significantly different from the intact position (P<.01). Subsequent stability of the stifle joint was obtained by advancing the tibial tuberosity. In the maximally advanced tibial tuberosity position, caudal tibial thrust was generated resulting in caudal tibial subluxation that was significantly different from the transected CrCL position (P<.01) and from the intact CrCL position (P<.01). Despite a stable joint, there was slight CTS at the critical point position, which was significantly different from the intact CrCL position (P<.05). The PTA at the maximally advanced position was significantly different from the intact, critical point and reference 90 degrees PTAs (P<.01). The PTA at the critical point position was significantly different from the intact and maximally advanced tibial tuberosity PTAs (P<.01), but not different (P>.05) from the reference 90 degrees PTA. CONCLUSION: We demonstrated that advancement of the tibial tuberosity neutralized cranial tibial thrust, and converted cranial tibial thrust into caudal tibial thrust. Neutralization of tibiofemoral shear forces occurred at a PTA of 90.3+/-9.0 degrees. CLINICAL RELEVANCE: TTA can effectively change the magnitude and direction of the tibiofemoral shear force, and thus may be used to prevent craniotibial translation in a CrCL deficient stifle joint.