A 35-year-old woman presents with a 3-month history of chronic medial knee pain and a sensation of the knee 'giving way' during walking. On examination, she has a positive McMurray's test and a positive Thessaly test. Imaging reveals a vertical tear of the medial meniscus in the posterior horn. Which anatomical attachment of the medial meniscus is most likely disrupted, leading to the sensation of instability and the positive McMurray's test?

Explanation

## Medial Meniscus Anatomy and Meniscal Tears ### Attachments of the Medial Meniscus **Key Point:** The medial meniscus is a C-shaped fibrocartilage structure with firm peripheral attachments to the medial collateral ligament (MCL) and the joint capsule. This tight peripheral attachment is the defining anatomical feature that distinguishes the medial meniscus from the lateral meniscus and explains its greater susceptibility to injury. ### Anatomical Attachments Summary | Attachment Site | Structure | Function | | --- | --- | --- | | Anterior horn | Intercondylar area of tibia | Anchors anterior horn | | Posterior horn | Intercondylar area of tibia | Anchors posterior horn | | Peripheral border | Joint capsule AND MCL (deep fibers) | Primary peripheral stabilization; restricts mobility | | Coronary ligament | Connects peripheral border to tibial plateau | Allows limited meniscal mobility | ### Why Option A is Correct **High-Yield:** The medial meniscus is firmly attached along its entire peripheral border to the deep fibers of the medial collateral ligament and the joint capsule. This firm attachment: 1. **Restricts meniscal mobility** — unlike the lateral meniscus, which is separated from the LCL and can glide freely, the medial meniscus is tethered. 2. **Makes it vulnerable to vertical (longitudinal) tears** — when valgus and rotational forces are applied, the tethered meniscus cannot escape, and shear forces produce vertical tears, especially in the posterior horn. 3. **Causes instability when disrupted** — a vertical tear in the posterior horn disrupts the continuity of the meniscal body, allowing the inner fragment to displace ("bucket-handle" pattern), catching between condyles and producing the sensation of "giving way" and a positive McMurray's test. **Clinical Pearl:** The McMurray's test is positive when a torn meniscal fragment catches between the femoral and tibial condyles during knee flexion-extension with rotation, producing a palpable or audible click. This occurs because the disrupted MCL-capsule-meniscus complex allows the inner fragment to subluxate into the joint. ### Thessaly Test Correlation The Thessaly test (performed at 5° and 20° of knee flexion with axial rotation) is positive in meniscal tears because rotational movement causes the unstable meniscal fragment to shift, reproducing medial joint-line pain and the sensation of instability. ### Why the Other Options Are Incorrect - **Option B (Intercondylar tibial attachments via anterior and posterior horns):** These are the horn attachments that anchor the meniscus anteriorly and posteriorly to the tibia. A vertical tear of the posterior horn does not primarily disrupt these bony attachments; the horns remain anchored. The instability arises from disruption of the peripheral MCL-capsule attachment. - **Option C (Medial femoral condyle via coronary ligament):** The coronary ligament connects the peripheral meniscal border to the tibial plateau (not the femoral condyle), and it allows some meniscal mobility rather than providing primary restraint. This is a plausible distractor but anatomically incorrect. - **Option D (Popliteus muscle and posterior capsule):** The popliteus has a functional relationship with the lateral meniscus (via popliteomeniscal fascicles), not the medial meniscus. It does not directly attach to the medial meniscus. [cite: Moore's Clinically Oriented Anatomy, 8th ed., Ch 6; Gray's Anatomy, 41st ed., Knee Joint chapter]