(Fig 3-A.33) Five Major Semimembranosus Expansions

https://youtu.be/AkCrMM3gSjw

https://youtu.be/GSIg93UH3Oc

 

📌Semimembranosus tendon and its five major expansions:

1️⃣Direct Arm (Principal Attachment):

• Attaches directly to the posteromedial aspect of the tibia, just distal to the joint line, in a groove known as the tuberculum tendinis.
• Forms a C-shaped, 5-mm-thick band with the anterior arm along the posteromedial tibia, difficult to distinguish from each other.
• Exhibits hyperintensity at its insertion site on MRI, which may be due to fat accumulation or magic angle artifact, and is not abnormal.

2️⃣Anterior Arm (Tibial or Reflected Arm, Pars Reflexa):

• Inserts into the medial proximal tibia, superior to the superficial MCL, and under the POL.
• Seen on peripheral medial sagittal images curving anteriorly and on coronal images as a hypointense structure adjacent to the medial tibia.
• Magic angle artifact noted in its thicker posterior portion.

3️⃣Capsular Arm (Posterior Oblique Ligament Arm):

• Connects to the posteromedial joint capsule, blending with the POL and the capsular portions of the OPL.
• Described as the tendon sheath attachment to the PMC, crucial for posteromedial knee stability.

4️⃣Extension to the OPL (Oblique Popliteal Ligament Insertion):

• Forms a tendinous expansion towards the OPL, running along the posterior capsule of the knee about 2 cm above the joint line.

5️⃣Inferior (Popliteal) Arm (Popliteus Aponeurosis Expansion):

• Forms a fascial layer over the popliteus muscle belly.
• Divided into medial and lateral divisions, where the medial division attaches to the medial tibia and the lateral division extends over the popliteal fascia.
• Best visualized in axial and sagittal imaging planes as a band-like structure.

✅ Short Meniscal Arm:

• Described as a separate arm connecting to the meniscotibial ligament or part of the direct/anterior arm.
• Attaches to the coronary ligament of the posterior horn of the medial meniscus, located between the posterior meniscotibial ligament and the meniscotibial POL attachments.

 

Radiographics. 2015 Jul-Aug;35(4):1123-37

Skeletal Radiol. 2014 Jun;43(6):781-91.

J Am Acad Orthop Surg. 2017 Nov;25(11):752-761

Am J Sports Med. 2019 Jul;47(8):1797-1803

 

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