The semitendinosus () is a long superficial

muscle Skeletal muscles (commonly referred to as muscles) are Organ (biology), organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other ...

in the back of the

thigh In human anatomy, the thigh is the area between the hip ( pelvis) and the knee. Anatomically, it is part of the lower limb. The single bone in the thigh is called the femur. This bone is very thick and strong (due to the high proportion of ...

. It is so named because it has a very long tendon of insertion. It lies posteromedially in the thigh, superficial to the semimembranosus.

Structure

The semitendinosus, remarkable for the great length of its

tendon A tendon or sinew is a tough, high-tensile-strength band of dense fibrous connective tissue that connects muscle to bone. It is able to transmit the mechanical forces of muscle contraction to the skeletal system without sacrificing its ability ...

of insertion, is situated at the posterior and medial aspect of the

. It arises from the lower and medial impression on the upper part of the

tuberosity of the ischium The ischial tuberosity (or tuberosity of the ischium, tuber ischiadicum), also known colloquially as the sit bones or sitz bones, or as a pair the sitting bones, is a large swelling posterior (anatomy), posteriorly on the superior ramus of the ...

, by a tendon common to it and the long head of the

biceps femoris The biceps femoris () is a muscle of the thigh located to the posterior, or back. As its name implies, it has two parts, one of which (the long head) forms part of the hamstrings muscle group. Structure It has two heads of origin: *the ''long h ...

; it also arises from an

aponeurosis An aponeurosis (; plural: ''aponeuroses'') is a type or a variant of the deep fascia, in the form of a sheet of pearly-white fibrous tissue that attaches sheet-like muscles needing a wide area of attachment. Their primary function is to join muscl ...

which connects the adjacent surfaces of the two muscles to the extent of about 7.5 cm. from their origin. The muscle is

fusiform Fusiform means having a spindle-like shape that is wide in the middle and tapers at both ends. It is similar to the lemon-shape, but often implies a focal broadening of a structure that continues from one or both ends, such as an aneurysm on a ...

and ends a little below the middle of the thigh in a long round tendon which lies along the medial side of the

popliteal fossa The popliteal fossa (also referred to as hough, ">/sup> or kneepit in analogy to the cubital fossa) is a shallow depression located at the back of the knee joint. The bones of the popliteal fossa are the femur and the tibia. Like other flexion ...

; it then curves around the medial condyle of the

tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...

and passes over the

medial collateral ligament The medial collateral ligament (MCL), or tibial collateral ligament (TCL), is one of the four major ligaments of the knee. It is on the medial (inner) side of the knee joint in humans and other primates. Its primary function is to resist outwar ...

of the

knee-joint In humans and other primates, the knee joins the thigh with the leg and consists of two joints: one between the femur and tibia (tibiofemoral joint), and one between the femur and patella (patellofemoral joint). It is the largest joint in the h ...

, from which it is separated by a

bursa ( grc-gre, Προῦσα, Proûsa, Latin: Prusa, ota, بورسه, Arabic:بورصة) is a city in northwestern Turkey and the administrative center of Bursa Province. The fourth-most populous city in Turkey and second-most populous in t ...

, and is inserted into the upper part of the medial surface of the body of the tibia, nearly as far forward as its anterior crest. The semitendinosus is more superficial than the semimembranosus (with which it shares very close insertion and attachment points). However, because the semimembranosus is wider and flatter than the semitendinosus, it is still possible to palpate the semimembranosus directly. At its insertion it gives off from its lower border a prolongation to the deep fascia of the leg and lies behind the tendon of the sartorius, and below that of the gracilis, to which it is united. These three tendons form what is known as the pes anserinus, so named because it looks like the foot of a goose.

Innervation

lower motor neuron Lower motor neurons (LMNs) are motor neurons located in either the anterior grey column, anterior nerve roots (spinal lower motor neurons) or the cranial nerve nuclei of the brainstem and cranial nerves with motor function (cranial nerve lower m ...

exits to the

sacral plexus In human anatomy, the sacral plexus is a nerve plexus which provides motor and sensory nerves for the posterior thigh, most of the lower leg and foot, and part of the pelvis. It is part of the lumbosacral plexus and emerges from the lumbar ver ...

exiting through the spinal levels L5-S2. From the sacral plexus, the lower motor neuron travels down the

sciatic nerve The sciatic nerve, also called the ischiadic nerve, is a large nerve in humans and other vertebrate animals which is the largest branch of the sacral plexus and runs alongside the hip joint and down the lower limb. It is the longest and widest si ...

.Saladin, Kenneth S. Anatomy & Physiology: the unity of form and function. 5th ed. New York: McGraw-Hill, 2010. Print. The sciatic nerve branches into the deep fibular nerve and the tibial nerve. The tibial nerve innervates the semitendinosus as well as the other hamstring muscles, the semimembranosus and

Function

The semitendinosus muscle is one of three hamstring muscles that are located at the back of the thigh. The other two are the semimembranosus muscle and the biceps femoris. The semitendinosus muscle lies between the other two. These three muscles work collectively to flex the knee and extend the hip. The muscle also helps to medially rotate the tibia on the femur when the knee is flexed and medially rotate the femur when the hip is extended. It counteracts forward bending at the hips as well.

Clinical significance

Along with

patellar ligament The patellar tendon is the distal portion of the common tendon of the quadriceps femoris, which is continued from the patella to the tibial tuberosity. It is also sometimes called the patellar ligament as it forms a bone to bone connection when ...

and

quadriceps femoris The quadriceps femoris muscle (, also called the quadriceps extensor, quadriceps or quads) is a large muscle group that includes the four prevailing muscles on the front of the thigh. It is the sole extensor muscle of the knee, forming a large ...

, semitendinosus/ gracilis (STG) tendon autografts has been used commonly and successfully for anterior cruciate ligament reconstruction. Sufficient graft size could typically be obtained using either a semitendinosus/gracilis tendon double-bundle technique, or a quadruple-bundle technique using a single tendon.

Additional images

Image:Gray235.png, Right hip bone. External surface. Image:Gray551.png, The popliteal, posterior tibial, and peroneal arteries. Image:Gray1239.png, Back of left lower extremity. Image:Semitendinosus muscle.jpg, Semitendinosus muscle File:Slide2i.JPG, Semitendinosus muscle File:Slide2j.JPG, Semitendinosus muscle File:Slide2DADE.JPG, Muscles of thigh. Lateral view. File:Slide2EA.JPG, Muscles of thigh. Cross section. File:Slide1BIBI.JPG, Muscles of thigh. Anterior views.

References

External links

* *
knee/surface/surface4
at the

Dartmouth Medical School The Geisel School of Medicine at Dartmouth is the graduate medical school of Dartmouth College in Hanover, New Hampshire. The fourth oldest medical school in the United States, it was founded in 1797 by New England physician Nathan Smith. It is ...

's Department of Anatomy
PTCentral
{{Authority control Hip extensors Knee flexors Knee medial rotators Thigh muscles Posterior compartment of thigh Muscles of the lower limb Hamstring