Summary

In this study of 38 pure distalization tibial tubercle osteotomies (TTO-d), we find that TTO-d was not associated with a significant change in sagittal plane alignment (i.e. TTO-d did not lead to posteriorization or anteriorization of the tibial tubercle).

Abstract

Introduction

While pure distalization tibial tubercle osteotomy (TTO-d) may be beneficial for patients with recurrent patellar instability or chondral wear in the setting of patella alta and normal axial plane alignment (i.e., normal tibial tubercle-trochlear groove distance), there are theoretical concerns that this procedure may posteriorize the tibial tubercle and thus increase patellofemoral contact pressures. Importantly, however, whether modern TTO-d techniques actually result in increased posteriorization of the tibial tubercle has never been investigated. Therefore, the purpose of this study was to assess the relative amount of anteriorization or posteriorization that occurs following TTO-d.

Methods

Consecutive patients who underwent pure TTO-d from 2015-2023 by two high-volume sports medicine surgeons at a single institution with pre- and postoperative lateral knee radiographs were identified. Measurement of posteriorization was performed by two physician raters using a previously MRI-validated technique. In brief, the distance from the most anterior aspect of the tibial tubercle to the center of the anatomic axis of the tibia was measured pre- and postoperatively, with the difference in these values representing the amount of anteriorization or posteriorization (Figure 1). Demographic, radiographic, and surgical details were collected. Pre- and postoperative measurements were compared with Student t-tests, and the average and median amount of anteriorization/posteriorization was calculated. Change in Caton-Deschamps Index (CDI) and interrater reliability (using Intraclass Correlation Coefficients [ICC]) were also assessed.

Results

There were 38 patients (33 [86.8%] women) with a mean ± SD age of 29.3 ± 9.7 years. The mean preoperative CDI was 1.32 ± 0.13, which significantly decreased to a mean of 1.02 ± 0.1 postoperatively (p<0.001). Average operative distalization was 8.8 ± 1.1 mm. There was no significant change in sagittal tubercle position (i.e., anteriorization/posteriorization) pre- (21.6 mm) to postoperatively (22.4 mm, p=0.14). Consistent with this, the average amount of relative anteriorization/posteriorization following TTO-d was 0.82 ± 1.4 mm anterior (median: 0.75 mm anterior; range: 1 mm posterior to 4 mm anterior). Thirty-one (81.6%) patients experienced no change or slight anteriorization of the tibial tubercle, while 7 patients (18.4%) experienced ≤1 mm of posteriorization. No patient experienced more than 1 mm of posteriorization. There was excellent agreement between raters (ICC 0.93).

Conclusions

TTO-d did not lead to a significant change in sagittal plane alignment. These results support the positive clinical outcomes seen with TTO-ds, including for chondral lesions, and may reduce concern about inadvertent posteriorization when performing TTO-ds. While over distalization with creation of patella baja has been shown to increase patellofemoral contact pressures beyond native ranges, the current results suggest that restoration of normal patellar height may be less likely to do so. In conclusion, pure distalization TTOs do not result in appreciable posteriorization of the tibial tubercle.