Increased external tibial torsion is an infratuberositary de
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A Study was conducted to perform a segmental analysis of tibial torsion in patients, with normal and increased external tibial torsion, suffering from chronic patellofemoral instability (PFI) and to investigate a possible correlation between tibial torsion and the position of the tibial tuberosity.

Patients with chronic PFI who underwent torsional analysis of the lower limb using a standardized hip-knee-ankle MRI were included. For segmental analysis of tibial torsion, three axial levels were defined which divided the tibia into two segments: a distal, infratuberositary segment and a proximal, supratuberositary segment.

Torsion was measured for the entire tibia (total tibial torsion, TTT), the proximal segment (proximal tibial torsion, PTT), and the distal segment (distal tibial torsion, DTT). Based on TTT, patients were assigned to one of two groups: Normal TTT (less than 35°) or increased external TTT (more than 35°). Position of the tibial tuberosity was assessed on conventional MRI scans by measuring the tibial tuberosity-trochlea groove (TT-TG) and the tibial tuberosity-posterior cruciate ligament (TT-PCL) distances.

--91 patients were included. Mean external TTT was 29.6°±9.1° and 24 patients had increased external TTT.

--Compared to patients with normal TTT, patients with increased external TTT demonstrated significantly higher values for DTT (38°±8° vs. 52°±9°), whereas no difference was found for PTT (-13°±6° vs. - 12°±6°.).

--Furthermore, a significant correlation was found between TTT and DTT, whereas no correlation was found between TTT and PTT (n.s).

--With regard to TT-TG and TT-PCL distances, no significant differences were observed between the two groups (TT-TG: 15±6 vs. 14±4 mm; TT-PCL: 22±4 vs. 21±5 mm) and no correlation was found with TTT, DTT, or PTT.

In conclusion, increased external TTT of greater than 35° is an infratuberositary deformity in patients with chronic PFI does not correlate with a lateralized location of the tibial tuberosity.