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]

Clinical Presentation/Characteristics

Two patient types are predisposed to developing SMT. Young avid endurance athletes can develop SMT as a primary disorder owing to overuse. More commonly, though, SMT develops in middle-aged to older patients. Other knee pathology often coexists, which may confuse the clinical picture and perhaps be involved in the cause. Chondromalacia and degenerative medial meniscal tears are the 2 most common associations.
Elderly patients with osteoarthritis (OA) can develop SMT in the anterior reflected tendon insertion secondary to adjacent osteophytes on the joint line. These patients also frequently suffer from concomitant pes anserine tendonitis. Total knee replacement components can also cause secondary SMT.
Some authors have noted a high predilection for females,but others have not.One might hypothesize that this is related to increased valgus stress and the Q angle present in women. Similarly, overpronation of the foot may cause increased valgus stress. Both conditions may increase friction between the medial femoral condyle and the SM tendon,but no studies have evaluated any of these variables as risk factors for SMT.
The presentation of SMT can be variable but usually consists of an insidious, progressive ache in the posteromedial knee. The pain may be severe in its acute form following a relatively sudden increase in endurance activity, such as cycling or running. Patients usually localize the pain at the posteromedial knee at the direct insertion, but pain may radiate proximally up the posteromedial thigh or distally to the medial calf. Symptoms increase with activities that involve significant hamstring activation: running, cycling, walking down stairs, or sudden deep knee flexion. [1]
On examination there is tenderness to palpation of the SM tendon near its tibial insertion site (or sites) or slightly more proximally. Resisted flexion of the knee at 90° can make the SM tendon more prominent for easier palpation.
Passive internal tibial rotation of a knee flexed at 90° may localize the pain. Passive deep flexion of the knee may also exacerbate the pain as the affected tendon and/or insertion becomes impinged by adjacent structures.
The hip, ankle, and foot morphology should be evaluated for biomechanical features that can predispose to SM tendon overuse. [1]