Tibial tubercle osteotomy decreases femorotibial rotation in patients with patellar instability

Abstract

Background: Patellar instability is a multifactorial pathology that poses significant challenges for orthopaedic surgeons in accurately diagnosing and effectively addressing its 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 patella. However, there is a paucity of evidence regarding interventions that influence this parameter.

Hypothesis/purpose: To assess whether patellar stabilizing procedures influence FT rotation in patients with trochlear dysplasia (TD) in the setting of patellar instability. It was hypothesized that tibial tubercle osteotomy (TTO) reduces FT rotation by changing the vector acting on the proximal tibia.

Study design: Retrospective cohort study, level of evidence 3.

Methods: One-hundred-forty-four knees 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 into 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). Group 4 showed a significant reduction of FT rotation postoperatively, indicating a decrease in external rotation (ΔFT rotation: -2.0 ± 3.5°, p = 0.003). Group 1, 2 and 3 showed no reduction of FT rotation (group 1: 0.6 ± 4.8°; group 2: -1.3 ± 7°, group 3: 0.0 ± 5.3°, n.s.). Comparing knees with and without TTO, those with concomitant TTO (groups 2 and 4; n = 56) showed a significantly reduced postoperative FT rotation by a mean of 1.7 ± 5.3° compared to knees without TTO (0.3 ± 5°, groups 1 and 3; n = 88) (p < 0.021). The reduction in FT rotation significantly correlated with the reduction of the TT torsion but not with the medialization achieved by TTO (r = 0.511, p < 0.001 and r = 0.185, p = 0.173, respectively).

Conclusion: Tibial Tubercle Osteotomy effectively reduces femorotibial rotation in patients with patellar instability and trochlear dysplasia. This reduction is directly associated with the decrease in tibial tubercle torsion. Therefore, TTO should be considered for patients with increased TT-TG distance and elevated femorotibial rotation to improve patellar stability outcomes.

Keywords: Femorotibial rotation; MPFL reconstruction; Patellar instability; Trochleoplasty; Tuberosity osteotomy.

Fig. 1

Measurement of femorotibial (FT) rotation