Semimembranosus Tendinopathy

Description

Semimembranosus tendinopathy (SMT) is an uncommon cause of chronic knee pain that is rarely described in the medical literature and may be underdiagnosed or inadequately treated owing to a lack of understanding of the condition. [6]
The tendon of the muscles that form the pes anserinus (m. Sartorius, m. Gracilis, m. Semitendinosis) run on the medial side of the knee and insert on the medial side of the tibial plateau just below the tuberosity of the tibia. There is a bursa under the tendon to smooth the movement of the tendons. It is often the bursa that will be ignited by excessive friction. The semimembranosispees is slightly deeper in the knee cavity and can also get overloaded with excessive hamstring activity. [7]
The incidence of Semimembranosus Tendinopathy is unknown in the athletic population and is probably more common by older patients. The usual presentation for SMT is pain on the posteromedial side of the knee. Physical examination can usually localize the area of tenderness to the distal semimembranosus tendon or its insertion on the medial proximal tibia. [8]

Clinically Relevant Anatomy

The origin of the semimembranosus muscle is located at the lateral aspect of the ischial tuberosity, the muscle runs down the posteromedial aspect of the thigh and inserts at the posteromedial aspect of the knee. The muscle belly ends just above the knee joint and forms a thick rounded tendon distally, which passes medial to the medial head of the gastrocnemius but lateral to the smaller semitendinosus tendon.   [1]

The most important function of the semimembranosus muscle is flexion and internal rotation of the knee joint. It also stabilizes the pelvis and causes extension of the hip joint.
There is a U-shaped bursa that surrounds the distal SM tendon, separating the distal aspects of the tendon from the medial tibial plateau, MCL, and semitendinosus. Friction and repetitive eccentric tendon loading can lead to degenerative changes in the tendon and its insertions and irritation of the bursa. [2][3]

Mechanism of Injury / Pathological Process

The muscle belly ends just above the knee joint and forms a thick rounded tendon distally, which passes medial to the medial head of the gastrocnemius but lateral to the smaller semitendinosus tendon.
SMT usually develops at the main (direct) head, at reflected insertions, or in the distal tendon. During repetitive knee flexion, the SM tendon is subjected to increased friction from the adjacent joint capsule, medial femoral condyle, medial tibial plateau, and semitendinosus tendon. [1]
Friction and repetitive eccentric tendon loading can lead to degenerative changes in the tendon and its insertions and irritation of the bursa.
Tendinitis is a condition that is characterized by inflammation of a tendon or the lining (sheath) that surrounds the tendon.
The inflammation is usually caused by damage to the tendon, such as a tendon tear (strain). The semimembranosus tendon attaches one of the muscles on the backside of the thigh (hamstring muscles) to the hip bone and the shinbone (tibia).
The semimembranosus tendon helps the body straighten the hip and bend the knee. Strains are classified into three categories: [1]
1. Grade 1 strains cause pain, but the tendon is not lengthened.

2. Grade 2 strains include a lengthened ligament due to the ligament being stretched or partially ruptured. With grade 2 strains there is still function, although the function may be diminished.

3. Grade 3 strains are characterized by a complete tear of the tendon or muscle, and function is usually impaired.
Semimembranosus tendinitis is the result of damage to the semimembranosus tendon that results in an inflammatory response.
Common mechanisms of injury include: Stress placed on the tendon due to a sudden increase in intensity, frequency, or duration of training & The body trying to compensate for other injuries of the lower extremity (meniscus tear).
Risk increased by Activities that involve repetitive and/or strenuous use of the knee and hip (distance running, triathlon, race walking, weightlifting, or climbing , running down hills. poor strength and flexibility, failure to warm-up properly before activity, Flat feet, Improper knee alignment (knock knees or bowlegged). [1]