Image Interpretation: Incomplete, Partial thickness, undersurface tear of the medial collateral ligament (MCL) at the femoral attachment, consistent with a grade 2 proximal MCL injury.
Teaching Pearl: MCL injury is suggested when greater than 6 mm thick at the femoral attachment or greater than 3.6 mm thick at the tibial attachment. Because the MCL is a relatively flat structure, be sure to scan the full anterior to posterior extent.
Reference: Lee JI, Song IS, Jung YB, Kim YG, Wang CH, Yu H, Kim YS, Kim KS, Pope TL Jr. Medial collateral ligament injuries of the knee: ultrasonographic findings. J Ultrasound Med. 1996 Sep;15(9):621-5. doi: 10.7863/jum.1996.15.9.621. PMID: 8866443.