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Semitendinosus muscle
Semitendinosus muscle
Semitendinosus muscle
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Semitendinosus muscle
Muscles of the gluteal and posterior femoral regions. Semitendinosus labeled at bottom left.
Horizontal section of left thigh, viewed from above. Semitendinosus visible at bottom right.
Details
OriginLower quadrangular part of tuberosity of the ischium
InsertionPes anserinus (tibia)
ArteryInferior gluteal artery, perforating arteries
NerveSciatic (tibial, L5, S1, S2)
ActionsFlexion of knee, extension of the hip joint
AntagonistQuadriceps muscle
Identifiers
Latinmusculus semitendinosus
TA98A04.7.02.035
TA22641
FMA22357
Anatomical terms of muscle

The semitendinosus (/ˌsɛmiˌtɛndɪˈnoʊsəs/) is a long superficial muscle in the back of the thigh. It is so named because it has a very long tendon of insertion. It lies posteromedially in the thigh, superficial to the semimembranosus.

Structure

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The semitendinosus, remarkable for the great length of its tendon of insertion, is situated at the posterior and medial aspect of the thigh.

It arises from the lower and medial impression on the upper part of the tuberosity of the ischium, by a tendon common to it and the long head of the biceps femoris; it also arises from an aponeurosis which connects the adjacent surfaces of the two muscles to the extent of about 7.5 cm. from their origin.

The muscle is fusiform 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; it then curves around the medial condyle of the tibia and passes over the medial collateral ligament of the knee-joint, from which it is separated by a bursa, 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, as the semimembranosus is wider and flatter than the semitendinosus, it is 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

[edit]

A lower motor neuron exits to the sacral plexus exiting through the spinal levels L5-S2. From the sacral plexus, the lower motor neuron travels down the sciatic nerve.[1] 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 biceps femoris.[2]

Function

[edit]

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.[1]

Clinical significance

[edit]

Along with patellar ligament and quadriceps femoris, semitendinosus/gracilis (STG) tendon autografts has been used commonly and successfully for anterior cruciate ligament reconstruction.[3] 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.[4]

There is some controversy as to how well a hamstring tendon regenerates after the harvesting. Most studies suggest that the tendon can be regenerated at least partially, though it will still be weaker than the original tendon.[5][6]

Additional images

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  • Right hip bone. External surface.
    Right hip bone. External surface.
  • The popliteal, posterior tibial, and peroneal arteries.
    The popliteal, posterior tibial, and peroneal arteries.
  • Back of left lower extremity.
    Back of left lower extremity.
  • Semitendinosus muscle
    Semitendinosus muscle
  • Semitendinosus muscle
    Semitendinosus muscle
  • Semitendinosus muscle
    Semitendinosus muscle
  • Muscles of thigh. Lateral view.
    Muscles of thigh. Lateral view.
  • Muscles of thigh. Cross section.
    Muscles of thigh. Cross section.
  • Muscles of thigh. Anterior views.
    Muscles of thigh. Anterior views.

See also

[edit]
This article uses anatomical terminology.

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Semitendinosus muscle

View on Grokipedia
from Grokipedia
The semitendinosus muscle is a long, superficial muscle located in the posterior compartment of the , forming one of the three primary muscles alongside the femoris and semimembranosus. It originates from the lower medial surface of the and inserts on the superior anteromedial surface of the via the pes anserinus , contributing to its shape with a prominent long that gives it the "semi-tendinous" . As the longest muscle in the group, averaging 44.3 cm in length, it plays a critical role in lower limb locomotion and is commonly implicated in athletic injuries due to its involvement in explosive movements. Anatomically, the semitendinosus arises not only from the but also from the medial aspect of the femoris and a proximal , allowing for shared fascial connections that enhance stability during contraction. Its distally joins the pes anserinus, blending with the tendons of the gracilis and sartorius muscles to insert on the , which positions it medially among the hamstrings. This arrangement supports its dual-joint spanning capability, crossing both the and joints. The muscle is innervated by the tibial division of the , with contributions from spinal levels L4 through S2, ensuring coordinated neural control for its actions. Blood supply is primarily derived from perforating branches of the profunda femoris artery, with venous drainage following the same pathway. These vascular and neural elements underscore its embryological origin from the mesodermal somites during lower limb development around the 8th week of . Functionally, the semitendinosus extends the hip joint, flexes the joint, and assists in medial rotation of the when the is flexed, often working in synergy with the for rotational stability. In clinical contexts, it is frequently harvested as an autograft for (ACL) reconstruction due to its robust , with studies showing regeneration in approximately 75% of cases post-harvest. strains involving the semitendinosus are prevalent in sports requiring sprinting or sudden deceleration, though it is less commonly injured than its counterparts.

Structure

Origin and insertion

The semitendinosus muscle originates from the inferomedial impression on the tuberosity of the , sharing a common of origin with the long head of the . This proximal measures approximately 12 to 15 cm in length before transitioning into the muscle belly, which then narrows distally into a long, flat, cord-like that constitutes nearly half of the muscle's total length. Distally, the semitendinosus tendon inserts primarily on the medial surface of the proximal via the pes anserinus, a conjoined structure shared with the sartorius and gracilis muscles, where it forms the superficial division of the anserine . The courses inferomedially, passing posterior to the medial femoral condyle and curving around the medial tibial condyle, separated by a from the . Additionally, the distal expands with accessory fibers that attach to the medial head of the and the investing of the medial leg. Anatomical variations in the insertion of the semitendinosus include accessory slips that may attach to the popliteal fascia or extend to the fascia overlying the , potentially creating a "double" pes anserinus configuration when blending with the gracilis tendon. In some cases, the primary insertion may occur into the crural fascia of the leg rather than directly onto the .

Relations

The semitendinosus muscle occupies a superficial position within the posterior compartment of the , lying medial to the biceps femoris and lateral (or superficial) to the semimembranosus throughout its course. Proximally, the muscle arises deep to the muscle and lies adjacent to the and the posterior femoral cutaneous nerve as it descends from the . In the mid-thigh, the semitendinosus transitions from a muscular belly to a long , while crossing posterior to the . Distally, the of the semitendinosus grooves behind the medial tibial condyle, passing deep to the sartorius tendon and superficial to the tibial attachment of the semimembranosus as it contributes to the pes anserinus. In the , the and popliteal vessels pass deep to the semitendinosus muscle, which forms part of the superomedial boundary of the region.

Innervation

The semitendinosus muscle, located in the posterior compartment of the , receives its primary motor innervation from the tibial division of the , which arises from the ventral rami of spinal segments L4 through S3. This nerve originates in the and descends through the gluteal region into the , where its tibial component specifically targets the muscles, including the semitendinosus. The innervation involves a convergence of fibers from the L4-S3 roots within the sciatic nerve, forming a shared supply often referred to as the hamstring nerve plexus that distributes to the posterior thigh musculature. Typically, two muscular branches emerge from the tibial division in the mid-to-lower posterior thigh, prior to the sciatic nerve's bifurcation in the popliteal fossa; these rami penetrate the deep surface of the semitendinosus muscle belly, with the superior branch entering the upper third and the inferior branch primarily the middle third. In addition to motor supply, the tibial division provides sensory innervation to proprioceptive structures within the muscle, including muscle spindles that detect length changes and Golgi tendon organs that sense tension, enabling feedback on position and during movement. Rare anatomical variations in semitendinosus innervation may include occasional contributions from adjacent segments such as L4 or S3, or altered branching patterns where a single or additional ramus supplies the muscle, potentially affecting surgical approaches in the posterior .

Blood supply

The semitendinosus muscle receives its primary arterial supply from the perforating branches of the (also known as the ), which enter the muscle along its length to nourish the posterior compartment of the . These branches arise sequentially from the as it descends deep to the adductor muscles, providing consistent perfusion to the muscular portion throughout its extent. Proximally, near its origin from the , the muscle is additionally supplied by branches of the , which emerges from the pelvis via the greater sciatic foramen and contributes to the vascular network in the upper posterior thigh. Distally, in the lower thigh, vascularization is augmented by the superior muscular branches of the , which provide supply to the inferior aspects of the group as the vessels course posteriorly behind the . Venous drainage of the semitendinosus parallels its arterial supply, with perforating veins draining into the profunda femoris vein proximally and tributaries converging into the popliteal vein distally, facilitating return flow to the systemic circulation. The long tendinous portion of the semitendinosus, which forms a significant part of its distal structure, exhibits reduced vascularity compared to the muscle belly, featuring hypovascular watershed areas that increase susceptibility to avascular zones in cases of injury.

Function

Knee joint actions

The semitendinosus muscle serves as a primary knee flexor, contracting to bend the joint by drawing the posteriorly relative to the . This action is most forceful in terminal extension, particularly between 0° and 30° of flexion, where the muscle operates near its optimal length for peak production. In addition to flexion, the semitendinosus contributes to medial (internal) rotation of the on the when the is flexed beyond 90°, facilitating the unlocking of the from its close-packed position in full extension. The muscle's length-tension relationship positions it favorably for force generation during mid-range knee flexion (approximately 30° to 70°), where overlap allows efficient actin-myosin cross-bridging, enabling the semitendinosus to produce substantial despite its relatively smaller compared to other s. It accounts for a notable portion of the total hamstring group's knee flexion in dynamic conditions, owing to its elongated and favorable moment arm length. As an to the femoris, the semitendinosus opposes knee extension; however, it exhibits co-activation with the during weight-bearing activities like to enhance joint stability. Kinematically, the semitendinosus stabilizes the medial aspect of the during dynamic movements, such as or pivoting, by countering excessive lateral (external) of the and limiting varus stresses. This medial stabilizing role integrates with its flexion and functions to maintain tibiofemoral alignment under load.

Hip joint actions

The semitendinosus muscle primarily contributes to extension by pulling the posteriorly relative to the , working in synergy with the and the other muscles (semimembranosus and biceps femoris long head) to produce this movement. This action is essential for propelling the body forward during locomotion and straightening the from a flexed position. The muscle's proximal origin at the positions it to generate force along the posterior , enhancing overall extensor torque. As a secondary action, the semitendinosus assists in adduction, particularly when the is in an extended position, by drawing the toward the midline of the body in coordination with the adductor magnus. Additionally, it facilitates medial (internal) of the when the limb is flexed, aiding in the rotational adjustments needed for efficient propulsion and balance. These rotational and adductory roles stem from the muscle's oblique fiber orientation and its insertion via the pes anserinus on the proximal . In terms of force generation, the semitendinosus provides a notable portion of the total extension torque in upright postures based on biomechanical modeling of contributions, with peak activation during loaded extension tasks. During locomotion, it plays a key role in eccentric control during the swing phase of walking, where it lengthens under tension to decelerate the forward swing of the and control flexion velocity, preventing excessive momentum. This eccentric function is critical for smooth transitions into stance phase and reducing injury risk during dynamic activities.

Clinical significance

Injuries

The semitendinosus muscle is frequently affected by strains, which represent the most common injury to this structure, classified into grades I through III based on severity, with damage ranging from mild overstretching to complete tears. These strains typically occur at the proximal musculotendinosus junction during eccentric contractions, such as those experienced in sprinting or rapid deceleration. Hamstring strains, including those involving the semitendinosus, exhibit higher incidence in high-speed sports like soccer and , accounting for up to 12-24% of all musculoskeletal injuries in these athletes. The semitendinosus is involved in a substantial portion of these strains, with reports indicating involvement in approximately 50-68% of cases depending on the cohort studied, often as part of medial injuries. Proximal avulsions of the semitendinosus from the are rare traumatic injuries, more commonly occurring in adolescents due to the incomplete of the apophysis, and are typically triggered by sudden flexion under load. Symptoms of both strains and avulsions include acute in the posterior , localized swelling, and ecchymosis, while chronic overuse can progress to semitendinosus characterized by persistent discomfort and reduced function. Key risk factors for semitendinosus injuries encompass a history of prior hamstring strain, quadriceps-hamstring strength imbalances exceeding 10-20%, and insufficient warm-up routines prior to explosive activities. Diagnosis is primarily confirmed via magnetic resonance imaging (MRI), which reveals muscle edema in mild cases or partial/complete tears in more severe presentations.

Surgical applications

The semitendinosus serves as a primary autologous graft source in anterior cruciate ligament (ACL) reconstruction, frequently combined with the gracilis tendon to form a quadrupled semitendinosus-gracilis (STG) graft that provides robust stabilization following rupture. This technique leverages the tendon's length and strength to create a four-stranded construct, typically measuring 8-10 cm in effective graft length after folding, which is secured via femoral and tibial tunnels to mimic native ACL . Harvesting of the semitendinosus tendon can be performed endoscopically or via an open approach, beginning at the pes anserinus insertion on the anteromedial and involving proximal stripping of the using a specialized stripper to obtain 25-30 cm of usable length while minimizing muscle disruption. Suturing the distal post-harvest promotes regrowth in up to 92% of cases within 6-24 months, preserving overall function with reported strength deficits of 10-20% at 6-12 months postoperatively. Compared to autografts, the semitendinosus-based STG graft offers advantages including a smaller incision (typically 3-4 cm), reduced donor site morbidity, and avoidance of anterior , while exhibiting tensile strength comparable to or exceeding the native ACL in biomechanical studies. Clinical outcomes demonstrate 85-95% success in restoring stability, with failure rates of 5-10% and return to achievable in 6-9 months for most patients. Beyond ACL reconstruction, the semitendinosus tendon is utilized in (MCL) repair, where it acts as a double-bundle autograft to anatomically restore the superficial MCL and posterior oblique ligament, enhancing valgus stability in chronic injuries. It also supports augmentation in chronic ruptures, providing tensile reinforcement through ipsilateral transfer or allograft integration to bridge defects and improve healing. Additionally, pes anserinus transfer incorporating the semitendinosus addresses anteromedial rotatory instability by advancing the tendon's insertion to tighten medial structures.

Other clinical aspects

Diagnostic imaging plays a crucial role in evaluating semitendinosus muscle . is particularly valuable for dynamic assessment of strains, enabling real-time visualization of muscle fiber disruption and integrity during movement, which aids in early detection and grading of acute injuries. (MRI) offers superior detail for , where tears typically appear as high signal intensity on T2-weighted sequences due to and hemorrhage at the myotendinous junction. Rehabilitation protocols for semitendinosus injuries emphasize progressive eccentric strengthening to restore function and prevent recurrence. The Nordic hamstring exercise, which targets eccentric knee flexion, has been shown in systematic reviews to reduce injury rates by up to 51% when incorporated into prevention programs across various sports. neuropathies involving the are rare but can occur due to of the semitendinosus muscle in athletes, particularly runners, leading to compression in the popliteal region and symptoms such as , , or weakness in the lower leg. Myositis ossificans, characterized by heterotopic ossification within the semitendinosus following trauma, presents as a benign, self-limiting process with formation in the muscle tissue. Treatment typically involves conservative management with nonsteroidal drugs (NSAIDs) to control and , alongside focused on gentle range-of-motion and strengthening exercises to promote resolution without surgical intervention.01258-X/fulltext) Biomechanical testing via isokinetic dynamometry assesses flexion strength deficits attributable to semitendinosus impairment, providing objective metrics to guide return-to-play decisions. In professional athletes, residual deficits exceeding 10% in eccentric strength at the time of return to are common and associated with higher reinjury risk, underscoring the need for symmetrical strength restoration prior to clearance.

References

  1. https://www.ncbi.nlm.nih.gov/books/NBK539862/
  2. https://www.ncbi.nlm.nih.gov/books/NBK546688/
  3. https://www.aspetar.com/journal/viewarticle.aspx?id=42
  4. https://www.kenhub.com/en/library/anatomy/semitendinosus-muscle
  5. https://www.physio-pedia.com/Semitendinosus
  6. https://pubmed.ncbi.nlm.nih.gov/17611850/
  7. https://www.researchgate.net/figure/Fig3A-GracilisG-semitendinosus-ST-tendons-are-attached-to-the-deep-fascia-DF_fig2_325288134
  8. https://journals.viamedica.pl/folia_morphologica/article/download/FM.a2019.0105/51833
  9. https://www.ncbi.nlm.nih.gov/books/NBK554598/
  10. https://teachmeanatomy.info/lower-limb/muscles/thigh/hamstrings/
  11. https://www.ncbi.nlm.nih.gov/books/NBK482431/
  12. https://teachmeanatomy.info/lower-limb/nerves/sciatic-nerve/
  13. https://emedicine.medscape.com/article/1899189-overview
  14. https://doi.org/10.1007/s00276-024-03371-4
  15. https://pmc.ncbi.nlm.nih.gov/articles/PMC7769215/
  16. https://www.ncbi.nlm.nih.gov/books/NBK544319/
  17. https://rad.uw.edu/muscle-atlas/semitendinosus
  18. https://pmc.ncbi.nlm.nih.gov/articles/PMC8949578/
  19. https://pmc.ncbi.nlm.nih.gov/articles/PMC9446565/
  20. https://pmc.ncbi.nlm.nih.gov/articles/PMC3396299/
  21. https://pubmed.ncbi.nlm.nih.gov/30421166/
  22. https://brookbushinstitute.com/articles/semitendinosus-and-semimembranosus
  23. https://pmc.ncbi.nlm.nih.gov/articles/PMC3057086/
  24. https://www.jospt.org/doi/10.2519/jospt.2022.0301
  25. https://www.orthobullets.com/knee-and-sports/3102/hamstring-injuries
  26. https://bjsm.bmj.com/content/57/5/292
  27. https://pmc.ncbi.nlm.nih.gov/articles/PMC8236328/
  28. https://meridian.allenpress.com/jat/article/59/3/270/495535
  29. https://pmc.ncbi.nlm.nih.gov/articles/PMC6148575/
  30. https://radsource.us/hamstring-tears/
  31. https://www.dynamed.com/condition/hamstring-strain
  32. https://ajronline.org/doi/10.2214/ajr.174.2.1740393
  33. https://pmc.ncbi.nlm.nih.gov/articles/PMC5490845/
  34. https://orthopedicreviews.openmedicalpublishing.org/article/38408-hamstring-graft-preparation-for-acl-reconstruction
  35. https://www.omgtb.com/acl-graft/
  36. https://pmc.ncbi.nlm.nih.gov/articles/PMC4482305/
  37. https://journals.healio.com/doi/10.3928/0147-7447-19970501-06
  38. https://www.sciencedirect.com/science/article/abs/pii/S0968016007000592
  39. https://www.researchgate.net/publication/395810529_Similar_results_with_quadrupled_semitendinosus_and_semitendinosus-gracilis_graft_in_anterior_cruciate_ligament_reconstruction_A_randomised_controlled_trial_with_2-year_follow-up
  40. https://pmc.ncbi.nlm.nih.gov/articles/PMC10838056/
  41. https://pmc.ncbi.nlm.nih.gov/articles/PMC2464596/
  42. https://pubmed.ncbi.nlm.nih.gov/7430186/
  43. https://ajronline.org/doi/10.2214/AJR.12.8784
  44. https://ajronline.org/doi/10.2214/AJR.13.12183
  45. https://journals.lww.com/acsm-csmr/fulltext/2018/09000/myositis_ossificans_in_sport__a_review.7.aspx
  46. https://bjsm.bmj.com/content/48/18/1364
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