Summary

Patients with patellar instability and trochlear dysplasia have increased femorotibial (FT) rotation. This study shows that Tibial tubercle osteotomy (TTO) can significantly reduce FT rotation, correlating with reduced tibial tubercle torsion. Thus, TTO may be indicated not only for increased TTTG but also for elevated FT rotation to improve outcomes

Abstract

Background

Patellar instability is multifactorial. Different procedures exist to address the underlying causes. Recently, increased femorotibial (FT) rotation has been shown to contribute to patellar instability by further lateralizing the muscle force vector acting on the patellar. However, it is not yet known how to surgically address this parameter.
Hypothesis/Purpose: To assess whether tibial tubercle osteotomy (TTO) and/or trochleoplasty reduce femorotibial rotation in patients with trochlear dysplasia (TD) experiencing patellar instability.
Study Design: retrospective cohort study, level of evidence 3

Methods

One-hundred-forty-four kness who underwent patellar stabilizing surgery between January 2010 and December 2020 were retrospectively analysed. Caton-Deschamps index (CDI), tibial-tubercle-trochlear-groove distance (TTTG), tibial tubercle (TT) torsion, tibial tubercle-to-posterior cruciate ligament distance (TT-PCL), and pre- and postoperative FT rotation were assessed. Based on the performed patellar stabilizing procedures, knees were stratified in 4 groups: 1: Isolated medial patella-femoral ligament (MPFL) reconstruction (n=51), 2: MPFL reconstruction and TTO (n=24), 3: MPFL reconstruction and trochleoplasty (n=37), 4: MPFL reconstruction, trochleoplasty, and TTO (n=32).

Results

Preoperative FT rotation differed significantly between groups (-0.2 ± 6.1° vs 3.1 ± 6.7° vs. 5.0 ± 5.6° vs 9.6 ± 6.0°, p<0.001). Groups 2 and 4 (with TTO) showed a reduction of FT rotation postoperatively, yet group 2 without statistical significance (delta FT rotation: group 2: -1.3 ± 7°, p=0.370, group 4: -2.0 ± 3.5°, p= 0.003). Group 1 and 3 showed no reduction of FT rotation. Knees with concomitant TTO (group 2 + 4; n=56 patients) had a significantly reduced postoperative FT rotation by a mean of 1.7  5.3° compared to knees without TTO (0.3 ± 5°, group 1 + 3, n=88 patients) (p<0.021). Reduction of FT rotation significantly correlated to the reduction of the TT-Torsion but not medialization achieved by TTO (r=0.511, p<0.001 and r=0.185, p= 0.173, respectively).

Conclusion

Patients presenting with patellar instability and trochlear dysplasia show elevated FT rotation. While trochleoplasty addresses trochlear dysplasia, concomitant TTO seems to decrease FT rotation, which is directly associated with the reduction of the TT-torsion. Thus, TTO may be indicated not only in patients with increased TTTG, but also in those with increased femorotibial rotation, to enhance outcomes in patients with patellar instability.