Changes in Patellar Height and Tibial Posterior Slope after Biplanar High Tibial Osteotomy with Computer-Designed Personalized Surgical Guides: A Retrospective Study

Abstract

Objective: Medial opening-wedge high tibial osteotomy (MOWHTO) is a surgical procedure to treat medial compartment osteoarthritis in the knee with varus deformity. However, factors such as patellar height (PH) and the sagittal plane's posterior tibial slope angle (PTSA) are potentially overlooked. This study investigated the impact of alignment correction angle guided by computer-designed personalized surgical guide plate (PSGP) in MOWHTO on PH and PTSA, offering insights for enhancing surgical techniques.

Methods: This retrospective study included patients who underwent 3D-printed PSGP-assisted MOWHTO at our institution from March to September 2022. The paired t-tests assessed differences in all preoperative and postoperative measurement parameters. Multivariate linear regression analysis examined correlations between PTSA, CDI (Caton-Deschamps Index), and the alignment correction magnitude. Receiver operating characteristic (ROC) curve analysis determined the threshold of the correction angle, calculating sensitivity, specificity, and area under the curve.

Results: A total of 107 patients were included in our study. The CDI changed from a preoperative mean of 0.97 ± 0.13 (range 0.70-1.34) to a postoperative mean of 0.82 ± 0.13 (range 0.55-1.20). PTSA changed from a preoperative mean of 8.54 ± 2.67 (range 2.19-17.55) to a postoperative mean of 10.54 ± 3.05 (range 4.48-18.05). The t-test revealed statistically significant changes in both values (p < 0.05). A significant alteration in patellar height occurred when the correction angle exceeded 9.39°. Moreover, this paper illustrates a negative correlation between CDI change and the correction angle and preoperative PTSA. Holding other factors constant, each 1-degree increase in the correction angle led to a 0.017 decrease in postoperative CDI, and each 1-degree increase in preoperative PTSA resulted in a 0.008 decrease in postoperative CDI. PTSA change was positively correlated only with the correction angle; for each 1-degree increase in the opening angle, postoperative PTS increased by 0.188, with other factors constant.

Conclusion: This study highlights the effectiveness and precision of PSGP-assisted MOWHTO, focusing on the impact of alignment correction on PH and PTSA. These findings support the optimization of PSGP technology, which offers simpler, faster, and safer surgeries with less radiation and bleeding than traditional methods. However, PSGP's one-time use design and the learning curve required for its application are limitations, suggesting areas for further research.

Keywords: Knee osteoarthritis; Medial opening‐wedge high tibial osteotomy; Patellar height; Personalized surgical guide plate; Posterior tibial slope angle.

FIGURE 1

The target alignment, based on the Fujisawa point, involved performing simulated surgeries on a 3D model in Mimics 21.0. The generated intraoperative osteotomy data included osteotomy position, correction angle, weight bearing line percentage, distraction angle, sawing direction, depth, and screw sizes used.

FIGURE 2

Osteotomy guides were created using the Offset function and Boolean operations, with a groove matching the osteotomy plane. Surgeons finalized the position of the Kirschner wire and osteotomy plane. Finally, a patient‐specific plate was designed to fit the 3D correction model. After the osteotomy, the Tomofix locking plate is applied for fixation.

FIGURE 3

(A) A 3D‐printed osteotomy guide was placed snugly against the bone surface, and four guide Kirschner wires were used to fix it to the bone surface. The biplanar‐plane osteotomy was performed along the gap of the guide plate using an oscillating saw. (B) After osteotomy, the guide was removed, and the Tomofix locking plate was placed with the Kirschner wires. (C) The osteotomy area was spread open according to the preoperative design angle, and screws were sequentially drilled and inserted. (D) The position of the plate and the length of the screws were confirmed again under fluoroscopy.

FIGURE 4

The Caton–Deschamps index (CDI) is the ratio of the distance from the inferior pole of the patella to the anterior angle of the tibial plateau and the length of the articular surface of the patella. Typically, it ranges between 0.8 and 1.2. The posterior tibial slope angle (PTSA) is the angle between the tibial plateau line and the vertical line to the tibial horizontal axis in the lateral X‐ray, which usually varies between 0 and 18 degrees.

FIGURE 5

The receiver operating characteristic (ROC) curve of the correction angle. The area under the curve (AUC) was 0.702 with a 95% confidence interval of 0.602–0.803. Compared to the reference line, this difference was statistically significant (p = 0.000). In this case, the threshold of correction angle is 9.39, The sensitivity and specificity were 58.3% and 77%, respectively.