A new quantitative radiographic measurement of patella for patellar instability using the lateral plain radiograph:
Ryosuke Kuroda1, Kanto Nagai2, Takehiko Matsushita2
1Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, 7-5-1, Kusunoki-cho, Chuo-ku, Kobe, 650-0017, Japan. kurodar@med.kobe-u.ac.jp.
Purpose:
Patellar width ratio, a new measurement of anterior-posterior patellar width, was developed using lateral radiographs. The hypothesis was that patellar width ratio would increase with increasing patellar tilt angle and that patients with patellar instability would have larger patellar width ratio compared to controls.
Methods:
Fifty knees who underwent surgery for patellar instability were enrolled as Group P. The fifty knees without patellar instability were enrolled as controls (Group C). Patellar width ratio was measured using preoperative lateral radiographs. The width between proximal and distal apexes of patella was defined as A. The width between anterior and posterior margins of patella was defined as B. Patellar width ratio was defined as the ratio B/A. Patellar tilt angle was measured on preoperative computed tomography images. Values were compared between groups and their correlation examined, and a receiver operating characteristic (ROC) curve was generated to identify the threshold value.
Results:
Mean patellar width ratio in Groups C and P was 0.54 ± 0.04 and 0.66 ± 0.11 (P < 0.01). Mean patellar tilt angle in Groups C and P was 12.8° ± 4.9° and 32.0° ± 10.3° (P < 0.01). Patellar width ratio was strongly correlated with patellar tilt angle (R = 0.83, P < 0.01). For patellar width ratio, the area under ROC curve was 0.86, and the cut-off value was 0.59 (sensitivity 76.0 %, specificity 90.0 %).
Conclusion:
Patellar width ratio in Group P was significantly larger than in Group C. Patellar width ratio would allow clinicians to evaluate patellar tilt on lateral radiographs.
Level Of Evidence:
III.
