The patellar tendon wavy sign as a new secondary sign of ACL tear on MRI

OBJECTIVE: The purpose of this study was to evaluate the diagnostic value of the patellar tendon wavy (PTW) sign for an anterior cruciate ligament (ACL) tear on MRI. METHODS: One hundred MRI scans were prospectively analyzed, with 50 patients with an ACL tear underwent an ACL reconstruction (group 1) and 50 patients with knee complaints other than ACL tear (group 2). The PTW sign was confirmed on the sagittal MRI. In addition, the patellar tendon length, tibial-femoral angle and tibial anterior translation (TAT) were compared between the groups. RESULTS: The PTW sign was present in 41/50 (82%) MRI scans in group 1 and 10/50 (20%) in group 2, with significant difference between two groups (p = 0.000). Significant differences were also found, in medial TAT (6.29 ± 3.25 mm versus 3.12 ± 2.85 mm) and in lateral TAT (7.62 ± 3.85 mm versus 1.58 ± 3.93 mm) between two groups (both p = 0.000). Comparison of MRI with and without PTW sign, ACL injury was found to be of significant difference with 41/51 (80.4%) versus 9/49 (18.4%) (p = 0.000), and both medial and lateral TAT were with significant differences, 5.39 ± 3.90 mm versus 3.99 ± 2.71 mm (p = 0.039) and 7.67 ± 3.77 mm versus 1.40 ± 3.81 mm (p = 0.000), respectively. The sensitivity and specificity of PTW sign were 82% and 80%. The positive and negative predictive value were 80.4% and 81.6%. The diagnosis accuracy was 81%. CONCLUSION: The PTW sign is a useful secondary MRI sign to establish the diagnosis of an ACL tear. It may be associated with the TAT secondary to an ACL tear. LEVEL OF EVIDENCE: Level III, diagnostic study.