Transverse osteotomy in medial opening wedge high tibial osteotomy with distal tibial tubercle osteotomy gets closer to the tibial articular surface in patients with steep posterior tibial slope

In medial opening wedge high tibial osteotomy (OWHTO) with distal tibial tubercle osteotomy (DTO), the transverse osteotomy is typically made perpendicular to the tibial axis in the sagittal plane to avoid posterior gap behind the tibial tubercle. However, directing the osteotomy toward the fibular head may place the osteotomy line too close to the tibial articular surface. The purpose of this study was to investigate the relationship between fibular height on intra-operative fluoroscopy, the true fibular–articular distance, and the transverse osteotomy–articular distance. Seventy-five patients (92 knees) who underwent OWHTO with DTO were evaluated retrospectively. Medial and lateral posterior tibial slopes (mPTS and lPTS) were measured on pre-operative computed tomography (CT) scans. On sagittal CT images, the anterior and posterior distances from the fibular head to the articular surface of the lateral tibial plateau (AD and PD) were measured, and their difference (AD-PD) was used as a surrogate for fibular height on fluoroscopy. On post-operative CT scans, the minimum distance from the transverse osteotomy line to the articular surface (TO-A) was measured. Correlations among these parameters were analyzed. The mean AD, PD, AD-PD, and TO-A was 13.1 ± 2.2 mm, 9.5 ± 2.3 mm, 3.6 ± 1.9 mm, and 15.5 ± 3.0 mm, respectively. TO-A correlated positively with PD and negatively with AD-PD. PD and TO-A correlated negatively, and AD-PD correlated positively with both mPTS and lPTS. Linear regression analysis showed that lPTS was a predictor of TO-A. In patients with steep posterior tibial slope, the transverse osteotomy in OWHTO with DTO may be closer to the articular surface than expected, even when the fibular head appears low on fluoroscopy. Surgeons should therefore avoid placing the osteotomy too close to the articular surface in such cases. • Fibular height on fluoroscopy does not reliably reflect the true distance to the tibial articular surface. • The minimum distance from the osteotomy to the articular surface was associated with the posterior tibial slope (PTS). • A steep PTS may increase the risk of placing the osteotomy too close to the articular surface in OWHTO with DTO.