The Increased Tibiofemoral Rotation: A Potential Contributing Factor for Patellar Maltracking in Patients with Recurrent Patellar Dislocation

Abstract

Objective: The purpose of this study was to analyze the relationship between tibiofemoral rotation and patellar maltracking in patients with recurrent patellar dislocation.

Methods: A total of 143 consecutive knees (118 patients) with clinically diagnosed recurrent patellar dislocation from January 2018 to December 2019 were retrospectively analyzed. Patellar tilt angle and bisect offset index were recorded on axial CT to assesses the severity of patellar maltracking. Tibiofemoral rotation angle is measured by comparing the angle between the posterior femoral and tibial condylar lines on three-dimensional CT. The Pearson correlation was calculated to investigate the association between tibiofemoral rotation angle and patellar maltracking. Patients were divided into the rotation group (≥15°) and control group (<15°) based on the value of tibiofemoral rotation and a further comparison was performed. To further clarify the complicated relationship among tibial tubercle-trochlear groove (TT-TG), tibial tubercle-posterior cruciate ligament distance (TT-PCL), tibiofemoral rotation, and patellar maltracking, patients were divided into four subgroups according to the value of TT-TG and TT-PCL.

Results: The mean preoperative tibiofemoral rotation angle was 12° ± 6° (range, 0°-31°). Pearson correlation between patellar maltracking parameters (bisect offset index, patellar tilt angle) and various bony deformities found that the tibiofemoral rotation angle was moderately correlated with bisect offset index (r = 0.451, p < 0.001) and patellar tilt angle (r = 0.462, p < 0.001). Further results demonstrated that bisect offset index (152.1 vs 121.2, p < 0.001) and patellar tilt angle (41.2° vs 33.5°, p < 0.001) were significantly higher in the rotation group than that in control group. For patients with a TT-TG distance of >20 mm, the increased TT-TG distance was mainly caused by tibiofemoral rotation angle in group C (TT-TG > 20 mm, TT-PCL < 24 mm) and predominantly induced by tibial tubercle lateralization in group D (TT-TG > 20 mm, TT-PCL > 24 mm). Bisect offset index and patellar tilt angle were significantly higher in the group C than group D.

Conclusion: The increased tibiofemoral rotation angle is associated with patellar maltracking in patients with recurrent patellar dislocation. Patients with increased tibiofemoral rotation angle usually have more severe patellar maltracking.

Keywords: patellar dislocation; patellar maltracking; tibial tubercle-trochlear groove; tibiofemoral rotation.

Fig. 1

Measurement of patellar maltracking. (A), BOI measurements (a/b × 100%) were performed by measuring the percentage of the width of the patella that was lateral to a line through the deepest point of the trochlear groove. (B), patellar tilt angle measures the angle between the medial–lateral axis of the patella and the posterior condylar axis of the femur.

Fig. 2

Measurement of rotational parameters of the lower extremity. (A), femoral anteversion angle is defined as the angle formed between the axis of the femoral neck and distal femur. (B), tibiofemoral rotation angle is measured by comparing the angle between the posterior femoral and tibial condylar lines. (C), tibial torsion angle is assessed by measuring the rotational angle of the proximal tibia relative to the distal tibia.