Patellar Tendon Rupture: Radiologic and Ultrasonographic Findings

Figure 1. Lateral knee radiograph showing patella alta. A 68-year-old male presented to the emergency department with anterior right knee pain after falling at home and directly hitting his patella on the stepladder edge while he was going upstairs. Physical examination revealed infrapatellar region painful swelling and impaired knee extension. Knee radiographs showed no fracture; however, the lateral view revealed a high riding patella, concerning for a patellar tendon lesion (Figure 1). Ultrasounds confirmed radiographic suspect showing complete patellar tendon rupture (Figure 2) with proximal retraction of the patella. In a normal knee the ratio between the patellar tendon length and the diagonal length of the patella (Insall-Salvati ratio) should be approximatiely one, while this patient had a ratio of 2.2. 1 Differential diagnosis of patella alta includes patellar tendon rupture, subluxation of the patella, Sinding-Larsen-Johansson disease and joint effusion. 2 The patellar tendon composes the knee extensor mechanism together with the quadriceps tendon. Patellar tendon ruptures are less common than quadriceps tendon ruptures and are typically Figure 2. Ultrasound longitudinal scan over the infrapatellar region shows the complete patellar tendon rupture, which is swollen and hypoechoic (arrows). PT = patellar tendon. TT = tibial tuberosity.