Patterns of Avulsion and Osteochondral Fractures Associated with Patellar Dislocations: A Descriptive Study Using 3-Dimensional Computed Tomography.

Background: This retrospective study aimed to analyze avulsion and osteochondral fractures associated with patellar dislocation using 3-dimensional (3D) computed tomography (CT).

Methods: A retrospective analysis was conducted on patients admitted between 2015 and 2023 with acute or recurrent patellar dislocations. A musculoskeletal radiologist and 2 orthopedic surgeons evaluated CT scans of 148 patients (160 knees) to identify and categorize all avulsion and osteochondral fractures. The included fracture patterns were as follows: pattern I: medial patellofemoral ligament (MPFL) avulsion from the upper two-thirds of the patella, pattern II: medial patellotibial ligament (MPTL) and medial patellomeniscal ligament (MPML) avulsion from the lower one-third, pattern III: inferomedial patellar facet osteochondral fracture, pattern IV: lateral femoral condyle osteochondral fracture, and pattern V: MPFL avulsion from the femoral footprint. The dimensions of patellar articular surface osteochondral fractures were measured, and patient age, sex, and side were recorded. Descriptive statistics and chi-squared tests were performed.

Results: A total of 148 patients (93 female and 55 male patients) with a mean age of 18.7 ± 6.8 years were included. Of these, 116 patients (72.5%) had 1 or more fractures, with 71 (44.4%) having isolated lesions and 45 (28.1%) having combined lesions. Pattern II was the most prevalent, observed in 66 knees (41.2%), followed by pattern I in 52 knees (32.5%), and pattern III in 45 knees (28.1%). Patterns IV and V were seen in 4 (2.5%) and 1 (0.6%) knee, respectively. The mean articular fragment size in pattern III was 128.4 ± 95.6 mm (range, 12-412.5 mm), all involving the inferomedial facet of the patella. Osteochondral fragments were found in the lateral gutter (35.5%), anterior joint space (51.1%), posterior joint space (8.9%), and suprapatellar space (4.5%). No significant sex differences were observed in isolated versus combined lesions ( = 0.542) or fracture patterns ( = 0.274).

Conclusions: This study, the first to evaluate fractures after patellar dislocation using 3D CT, identified 5 distinct fracture patterns. The results show that MPTL/MPML injuries are more common than previously thought, challenging traditional views on patellar dislocation injuries and emphasizing the need for a comprehensive diagnostic approach.