Semimembranosus tendonitis / tendinopathy can occur anywhere from origin to insertion of the tendon; there is also a bursa in this region that can become inflamed. Semimembranosus bursitis is a distinct entity from semimembranosus tendonitis, but it will be grouped together here since the approach is similar for a primary care / emergency physician.
The semimembranosus muscle originates at the lateral ischial tuberosity, and the muscle runs down the posterior medial thigh. The muscle belly ends and the tendon begins just above the knee joint. The tendon then has main insertion on the posteromedial tibial plateau; it also spreads out into different insertion points (eg, one anteriorly on the tibia, one on the popliteus muscle fascia, and one on the posterior medial aspect of femoral condyle). The functions of the semimembranosus muscle are knee flexion, internal rotation, and hip extension.
Patients typically fall into 2 categories:
- Relatively young adult, athletic individuals
- Middle-aged / elderly patients
There may be other injuries at the same time, and they may be easier to diagnose. Such injuries may overshadow the semimembranosus tendinopathy; often, they will be part of the pathophysiology:
- Patellar chondromalacia
- Medial meniscal tear (particularly chronic degenerative medial meniscal tear)
- Pes anserine bursitis / pes anserine pain syndrome (also proximal medial tibia, but anterior aspect instead of posterior aspect)
The true incidence of semimembranosus tendinopathy is unknown; it is probably underdiagnosed. Posteromedial knee pain is less common than anterior or lateral knee pain.
M76.899 – Other specified enthesopathies of unspecified lower limb, excluding foot
202873009 – Semimembranosus tendinitis
- Medial collateral ligament (MCL) injury
- Medial meniscus injury
- Chondromalacia patellae
- Pes anserine bursitis
- Popliteal cyst (Baker cyst)
- Snapping knee syndrome
- Strain of medial head of gastrocnemius
- Popliteal strain
- Proximal tibial osteonecrosis
- Lumbar radiculopathy (particularly L3-L4)
- Patellar tendonitis (jumper's knee)
- Osgood-Schlatter disease