Purpose: To evaluate the effect of the hinge axis position on the posterior tibial slope (PTS) in medial opening-wedge high tibial osteotomy.
Methods: This study included adults with medial-compartment osteoarthritis who had computed tomography (CT) scans available that were amenable to Bodycad Osteotomy software analysis. Virtual osteotomies modeling a 10-mm medial opening-wedge gap were performed. The hinge axis was rotated internally and externally and was proximalized-extended and distalized-flexed with respect to the anterior tibial cortex for 5°, 10°, 15°, and 20°. Each resultant PTS was recorded and compared with the results obtained from the true lateral hinge position and with the preoperative PTS.
Results: Computed tomography scans from 10 patients were used. Strong linear correlations were found with each hinge axis position change and the resultant PTS. The trend-line differences were statistically significant by single-factor analysis of variance (P < .001). The PTS decreased for an anterolateral hinge, whereas it increased for a posterolateral hinge. Linear regression analysis showed that rotating the hinge axis by 9.0° externally or angulating the hinge axis by 21.8° of distalization-flexion would result in increasing the tibial slope by 1° whereas rotating the hinge axis by 8.7° internally or angulating the hinge axis by 21.6° of proximalization-extension would decrease the tibial slope by 1°.
Conclusions: Distalization-flexion and external rotation of the hinge axis position led to stepwise increases in the PTS, whereas proximalization-extension and internal rotation led to decreases in the PTS.
Clinical relevance: Our findings suggest that when performing medial opening-wedge high tibial osteotomy and aiming to decrease the PTS, the surgeon should aim to achieve maximal internal rotation (producing an anterolateral hinge), as well as proximalization-extension, of the hinge axis. This study quantifies and provides a model for the effect of the hinge axis position for a predetermined angular correction on the PTS.
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