A 28-year-old male footballer presents with acute right knee pain and swelling following a varus stress injury during a match. On examination, there is increased laxity on varus stress testing at 30° flexion. MRI coronal imaging shows the structure marked **D** to be intact and cord-like in appearance, separated from the lateral meniscus by the popliteus tendon. Which of the following best explains why isolated injuries to the structure marked **D** are less commonly associated with meniscal tears compared to injuries affecting the structure marked **C**?

Explanation

## Why option 1 is right The lateral collateral ligament (structure **D**) is extracapsular and separated from the lateral meniscus by the popliteus tendon, allowing the lateral meniscus greater mobility and freedom from mechanical coupling during rotational stress. This anatomical separation means that varus injuries affecting the LCL do not directly transmit force to the lateral meniscus in the same way that valgus injuries transmit force to the medial meniscus (which is C-shaped, larger, and firmly attached to the MCL and joint capsule). The lateral meniscus's increased mobility and loose attachment to the LCL (compared to the medial meniscus's firm capsular attachments) explains why isolated LCL injuries are less commonly associated with lateral meniscal tears. This is a key anatomical principle from Maheshwari Orthopedics 10e and Sutton Radiology. ## Why each distractor is wrong - **Option 2**: Incorrect. The structure marked D (LCL) is extracapsular, NOT intracapsular. It is separated from the lateral meniscus by the popliteus tendon, so it does not have direct attachments that would cause entrapment. - **Option 3**: Incorrect. The structure marked D (LCL) is NOT firmly adherent to the medial meniscus. The MCL (structure C) is the ligament that is firmly attached to the medial meniscus and joint capsule, making medial meniscal injuries more common in valgus injuries. - **Option 4**: Incorrect. The structure marked D (LCL) is cord-like and relatively narrow, NOT fan-shaped. Its cord-like morphology and extracapsular position are precisely why it does not transmit force directly to the lateral meniscus. **High-Yield:** LCL is extracapsular and separated from lateral meniscus by popliteus tendon → lateral meniscus is mobile and less commonly injured in varus injuries; MCL is intracapsular and firmly attached to medial meniscus → medial meniscus is less mobile and more commonly injured in valgus injuries (classic unhappy triad). [cite: Maheshwari Orthopedics 10e; Sutton Radiology]