Radiographic Predictors of Excessive Lower Limb Torsion in Patients With Recurrent Patellar Dislocation
Kyota Ishibashi1, Eiji Sasaki1, Hikaru Kristi Ishibashi1
1Department of Orthopaedic Surgery, Hirosaki University Graduate School of Medicine, Hirosaki, Japan.
Background:
Recurrent patellar dislocation in children and adolescents is a multifactorial condition associated with anatomic risk factors such as patella alta, trochlear dysplasia, and torsional deformities of the lower limb. Although medial patellofemoral ligament reconstruction (MPFLR) is the standard approach, undetected torsional abnormalities may compromise outcomes. While computed tomography (CT) offers precise femoral torsion (FT) and tibial torsion (TT) evaluation, its widespread use is constrained by cost and radiation exposure.
Purpose:
To evaluate whether conventional radiographic parameters can predict excessive lower limb torsion in patients undergoing MPFLR.
Study Design:
Cohort Study (Diagnosis); Level of evidence, 3.
Method:
The authors retrospectively analyzed 104 knees (70 patients) evaluated using CT for FT, TT, and combined torsion (FT+TT) between December 2016 and December 2023. Radiographic measures included the Caton-Deschamps index, congruence angle, sulcus angle, and patellar tilt angle. FT and TT were categorized as <20°, 20° to 30°, or >30°, and FT+TT as <40°, 40° to 50°, or >50°. Receiver operating characteristic (ROC) analysis and multivariate regression were used to assess the diagnostic performance of radiographic variables.
Results:
The patellar tilt angle was significantly associated with FT (r = 0.24; P = .015) and FT+TT (r = 0.27; P = .009). ROC analysis showed the highest predictive accuracy for patellar tilt angle, with an area under the curve of 0.629 for FT >20°, 0.653 for FT >30°, and 0.665 for FT+TT >50°. A threshold of 20° was identified across categories. Body mass index (β = -0.461; P = .019) and patellar tilt angle (β = 0.222; P = .021) were independent predictors of FT (adjusted R 2 = 0.102).
Conclusion:
This study showed that although patellar tilt angle demonstrated the highest predictive value among evaluated parameters, its diagnostic accuracy was limited and insufficient to replace cross-sectional imaging. Comprehensive preoperative evaluation of lower limb torsion remains critical for minimizing residual instability and improving outcomes after MPFLR.
