Effect of Cranial Tibial Closing Wedge Angle on Tibial Subluxation: An Ex Vivo Study

Objective: To evaluate the effect of cranial tibial wedge osteotomy (CTWO) angle on cranial tibial subluxation (CTS) and postoperative tibial plateau angle (TPA). Study Design: Ex vivo biomechanical study. Sample Population: Canine pelvic limbs (n=6). Methods: TPA determined from a lateral radiographic projection. CTS under 30% body weight load was measured from radiographs in the intact limb and after transection of the cranial cruciate ligament. A CTWO equal to TPA+10° was performed at the distal extent of the tibial crest, and was stabilized with a custom designed hinge plate and external skeletal fixator. TPA and CTS in the loaded limb was determined from radiographs at 4 CTWO angles: TPA-5°, TPA, TPA+5°, and TPA+7.5°. Comparison of CTS between the intact limb and the 4 CTWO angle groups was performed using 1-way repeated-measures ANOVA and a Dunnett multiple comparison test (significance at P<05). Results: CTS was significantly greater than that of the intact limb in the TPA-5° and TPA groups. CTS was not significantly different from the intact limb in the TPA+5° or TPA+7.5° groups with corresponding TPAs of 5.9° and 3.8°, respectively. Conclusion: Using this model, CTS was neutralized at a TPA of ∼4-6° with a CTWO angle between TPA+5° and TPA+7.5°. Clinical Relevance: A CTWO angle between TPA+5° and TPA+7.5° is necessary to neutralize CTS and achieve a postoperative TPA of 4-6° if the CTWO is performed at the distal extent of the tibial crest and the caudal cortices are aligned.