Distal semimembranosus tendon

The distal semimembranosus tendon, distal semimembranosus complex or distal semimembranosus muscle-tendon unit is a major musculotendinous structure of the posteromedial corner of the knee and an important dynamic stabiliser of the knee.

Gross anatomy

The semimembranosus tendon has a complex anatomy and features multiple attachments to the proximal tibia and other ligamentous posteromedial corner structures including the oblique popliteal ligament (OPL), the posterior oblique ligament (POL), the posterior joint capsule and the coronary and mensicocapsular ligaments of the posterior horn of the medial meniscus ^1-6.

It is located at the posteromedial corner of the knee anteromedial to the medial head of the gastrocnemius muscle, anterior to the distal semitendinosus tendon and posterolateral to the sartorius and gracilis muscles and tendons ⁴.

At the posteromedial aspect of the medial tibial plateau, the main semimembranosus tendon splits up into several major extensions including an anterior arm and a direct arm, a lateral extension to the oblique ligament of the knee, a capsular arm with connections to the posterior horn of the medial meniscus and a broad distal tibial expansion that features medial and lateral divisions blending with the posterior popliteus muscle fascia ^1-6. 

Function

The distal semimembranosus tendon transmits the force generated by the semimembranosus muscle to the tibia reinforces and stabilises the posteromedial corner of the knee by its multiple expansions ^2,4-7. With other posteromedial corner structures, it functions as a restraint to anteromedial rotatory instability (AMRI) ^4,5.

Attachments

The distal semimembranosus tendon features several attachments to various structures of the posteromedial corner of the knee ^1,2:

• capsular arm: to the posterior joint capsule including posterior oblique ligament and the meniscocapsular and meniscotibial ligaments
• lateral tendinous expansion: to the distal origin of the oblique popliteal ligament (OPL)
• anterior arm: medial tibial condyle underneath the attachment of the superficial medial collateral ligament
• direct arm: tuberculum tendinis at the posteromedial surface of the proximal medial tibial condyle
• distal tibial expansion: posterior popliteus muscle fascia and posteromedial tibial diaphysis, the superficial arm of the posterior oblique ligament

Relations

The semimembranosus bursa is located just proximal to the osseous attachment of the direct arm onto the posteromedial aspect of the tibia ¹ medially surrounded by the anterior arm and laterally covered by the attachment to the coronary ligament ¹.

The tibial origin and muscle belly of the popliteus muscle are covered by the distal medial and lateral tibial expansions of the semimembranosus tendon ¹.

Radiographic features

MRI

The semimembranosus tendon can be found at the posteromedial aspect of the knee. It features a homogeneously hypointense appearance. Immediately behind the inferior joint line, it can be seen splitting up into several expansions ⁴.  

Related pathology

Pathologies associated with the distal semimembranosus tendoninclude the following ^4-6:

• posteromedial corner injury
  • semimembranosus tendon avulsion
  • semimembranosus tendon tears
  • semimembranosus tendinosis
• ramp lesion