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The semimembranosus muscle is one of the hamstring muscles in the posterior compartment of the thigh. It accompanies the semitendinosus muscle in the medial aspect of the posterior thigh. The semimembranosus muscle originates with a flat tendon from the superolateral part of the ischial tuberosity, the biceps femoris, and semitendinosus muscles. Its primary function is flexion of the knee. With the knee semi-flexed, the muscle functions as a medial rotator of the lower leg on the knee.
| Characteristics | Values |
|---|---|
| Name | Semimembranosus muscle |
| Type | Hamstring muscle |
| Location | Posterior compartment of the thigh |
| Origin | Superolateral part of the ischial tuberosity |
| Insertion | Tubercle of the medial tibial condyle, medial margin of the tibia, fascia over the popliteus muscle, and lateral femoral condyle |
| Function | Flexion of the knee, medial rotation of the lower leg on the knee, lateral rotation of the thigh with hip extension |
| Innervation | Sciatic nerve (L5-S2) through the tibial division |
| Referred Pain | Posterior thigh, knee, and upper one-third of the posterior calf |
| Needling Technique | Patient in prone position with a pillow under ankles, needle inserted perpendicular to muscle surface |
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What You'll Learn
Semimembranosus muscle anatomy
The semimembranosus muscle is one of the three hamstring muscles in the thigh, alongside the biceps femoris and semitendinosus muscles. It is the most medial of the three. The semimembranosus muscle originates with a flat tendon from the superolateral part of the ischial tuberosity, the biceps femoris, and semitendinosus muscles. It travels deep to the semitendinosus muscle to divide into five components and insert at the tubercle of the medial tibial condyle, the medial margin of the tibia, the fascia over the popliteus muscle, and the lateral femoral condyle.
The semimembranosus muscle is wider, flatter, and deeper than the semitendinosus muscle, with which it shares very close insertion and attachment points. It overlaps the upper part of the popliteal vessels and arises above and medial to the biceps femoris and semitendinosus muscles. The tendon of origin expands into an aponeurosis, which covers the upper part of the anterior surface of the muscle, and from this aponeurosis, muscular fibres arise and converge to another aponeurosis.
The primary function of the semimembranosus muscle is flexion of the knee. With the knee semi-flexed, the muscle functions as a medial rotator of the lower leg on the knee. With the hip extended, the semi-hamstrings are lateral rotators of the thigh. The distal semimembranosus complex stabilizes the posterior capsule through the oblique popliteal ligament. The semimembranosus tendon prevents valgus in knee extension and prevents external rotation in knee flexion.
The semimembranosus muscle is innervated by the tibial part of the sciatic nerve. The sciatic nerve consists of the anterior divisions of ventral nerve roots from L4 through S3. The tibial part of the sciatic nerve is also responsible for the innervation of the semitendinosus and the long head of the biceps femoris.
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Semimembranosus muscle function
The semimembranosus muscle is one of the four posterior thigh muscles, the others being the semitendinosus, biceps femoris, and gluteus maximus. These four muscles are also referred to as hamstring muscles. The semimembranosus is the most medial of the three hamstring muscles in the thigh. It is wider, flatter, and deeper than the semitendinosus muscle, with which it shares very close insertion and attachment points.
The semimembranosus muscle originates with a flat tendon from the superolateral part of the ischial tuberosity, the biceps femoris, and semitendinosus muscles. It travels deep to the semitendinosus muscle to divide into five components and insert at the tubercle of the medial tibial condyle, the medial margin of the tibia, the fascia over the popliteus muscle, and the lateral femoral condyle. The semimembranosus muscle extends (straightens) the hip joint and flexes (bends) the knee joint. It also helps to medially rotate the knee: the tibia medially rotates on the femur when the knee is flexed. It medially rotates the femur when the hip is extended. The muscle can also aid in counteracting forward bending at the hip joint.
The semimembranosus muscle acts synergistically with the popliteus muscle through the fibrous extension towards this muscle. The distal semimembranosus complex actively pulls the posterior horn of the medial meniscus, protecting it from being crushed between the medial femoral condyle and the posterior medial tibial plateau during knee flexion. Furthermore, it provides an element of posterior traction over the posterior horn of the lateral meniscus, along with the structures forming the stabilizing mechanism of the posterolateral aspect of the knee.
The semimembranosus muscle may be reduced or absent, or double, arising mainly from the sacrotuberous ligament and giving a slip to the femur or adductor magnus. The muscle can be tested by flexing the leg at the knee joint against resistance while lying in the prone position, during which the semitendinosus tendon can be seen and palpated.
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Semimembranosus muscle innervation
The semimembranosus muscle is one of the hamstring muscles. It is the most medial of the three hamstring muscles in the thigh. It is also referred to as a hip extensor and a knee flexor/intrarotator. The muscle originates from a small facet on the rough superolateral surface of the ischial tuberosity. The semimembranosus tendon appears at the mid-thigh level and continues towards the point of insertion at the medial condyle of the tibia. The muscle is deep to the semitendinosus, superficial to the adductor magnus, and medial to the biceps femoris.
The semimembranosus muscle has several adjacent muscular and neurovascular structures along its course. The proximal part of the muscle is covered by the gluteus maximus and medial to the adductor minimus. Distally, the semimembranosus crosses over and becomes medially related to the medial head of the gastrocnemius before inserting into the medial tibial condyle. The distal portion of the semimembranosus is also medial to the adductor canal, which accommodates the vessels of the lower limb. The largest nerve in the human body, the sciatic nerve, travels lateral to the semimembranosus until it reaches the apex of the popliteal fossa.
The semimembranosus muscle is innervated by the tibial part of the sciatic nerve. The sciatic nerve is formed by the anterior divisions of the ventral nerve roots from L4 through S3. These nerve roots are part of a larger nerve network called the sacral plexus. The tibial part of the sciatic nerve is responsible for the innervation of the semitendinosus and the long head of the biceps femoris, in addition to the semimembranosus.
The semimembranosus muscle may be absent or reduced in size, or it may be double, arising mainly from the sacrotuberous ligament and giving a slip to the femur or adductor magnus. The muscle can be isolated by laterally rotating the leg and keeping the knee in an extended position. The stretch is achieved by increasing the flexion in the hip joint until the end point of the muscle is reached. This stretch is then released, and the leg is returned to the starting position. This sequence is repeated for one or two sets of ten repetitions.
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Semimembranosus muscle needling technique
The semimembranosus muscle is one of three hamstring muscles, along with the semitendinosus and biceps femoris muscles. It is the largest of the hamstring muscles and lies towards the inside of the thigh. The primary function of the semimembranosus muscle is knee flexion, and it also plays an important role in knee stability.
Injuries or dysfunctions in the semimembranosus muscle can cause pain or discomfort in the back of the thigh, lower buttock, or inner knee regions, and sometimes low back pain. Common injuries include hamstring strains or tears, particularly when performing ballistic activities like sprinting or kicking without a proper warm-up. Trigger points in the muscle can also cause discomfort, radiating pain from the buttocks to the knee and even the lower leg.
Needling techniques can be used to treat pain and discomfort in the semimembranosus muscle. One technique involves the patient lying on their back with one leg in 90-degree flexion at both the hip and knee joints. The therapist sits by the table, facing the feet of the patient, and holds the involved leg firmly to avoid unexpected movements. The needle is inserted perpendicular to the muscle surface directly into the TrP taut band identified by a flat palpation technique. It is important to avoid needling the sciatic nerve and needling in a medial direction.
Another needling technique starts with the patient in the prone position with a pillow or bolster under the ankles. The clinician assesses the muscles for spot tenderness using a flat palpation technique or the eraser part of a pencil to get between the metatarsal bones. The needle is inserted from the dorsal aspect towards the tender spot and the opposing finger using a modified pincer palpation. The needle must probe in both lateral and medial directions to explore both heads of the dorsal interosseous and the corresponding plantar interosseous.
Dry needling and acupuncture are also highly effective treatments for trigger points in the semimembranosus muscle, helping to improve flexibility, reduce pain, and prevent hamstring injuries.
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Semimembranosus muscle isolation
The semimembranosus muscle is one of four posterior thigh muscles that are responsible for extending the hip. It is a relatively long muscle that spans the full length of the thigh, from the hip to the knee. The semimembranosus is deep to semitendinosus, superficial to adductor magnus, and medial to biceps femoris along its entirety. It originates with a flat tendon from the superolateral part of the ischial tuberosity, the biceps femoris, and semitendinosus muscles.
To isolate the distal part of the semimembranosus muscle, the leg is rotated laterally. The rope is wrapped around the foot and lower leg to facilitate this lateral rotation, which is held as the knee is kept in an extended position. The stretch is achieved by increasing the flexion in the hip joint until the end point of the muscle is reached. The stretch is released after 2 seconds, and the leg is moved back to the start position, i.e., 90-degree flexion in the hip and knee joint. This stretch sequence is repeated for one or two sets of ten repetitions.
The semimembranosus muscle has several functions. Its primary function is flexion of the knee. With the knee semi-flexed, the muscle functions as a medial rotator of the lower leg on the knee. With the hip extended, the semimembranosus is a lateral rotator of the thigh. It is innervated by the L5, S1, and S2 nerve roots. These fibres access the muscle through the tibial division of the sciatic nerve, the largest nerve in the human body.
The semimembranosus muscle also plays a role in hip extension and knee flexion. It is a hip extensor and a knee flexor/intrarotator. In knee extension, the semimembranosus tendon prevents valgus, whereas in knee flexion, it prevents external rotation. The distal semimembranosus complex stabilizes the posterior capsule through the oblique popliteal ligament.
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Frequently asked questions
The semimembranosus muscle is one of the hamstring muscles in the posterior compartment of the thigh. It accompanies the semitendinosus muscle in the medial aspect of the posterior thigh.
The semimembranosus muscle originates with a flat tendon from the superolateral part of the ischial tuberosity, the biceps femoris, and semitendinosus muscles.
The primary function of the semimembranosus muscle is flexion of the knee. It also functions as a medial rotator of the lower leg on the knee when the knee is semi-flexed.
To isolate the semimembranosus muscle, the leg is rotated laterally. The knee is kept in an extended position while the hip joint is flexed.
The innervation of the semimembranosus muscle is the sciatic nerve (L5-S2) through the tibial division.
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