What is semimembranosus?

Semimembranosus Muscle

Introduction

The semimembranosus is one of the three hamstring muscles located in the posterior compartment of the thigh. It plays an essential role in movements of the hip and knee, contributing to walking, running, and maintaining posture. Its name comes from its partly membranous tendon of origin. Clinically, this muscle is important for physiotherapists, orthopedists, and sports medicine specialists because of its role in lower limb injuries and rehabilitation.

Anatomy

Origin

The semimembranosus muscle originates from the superolateral impression of the ischial tuberosity of the pelvis.

Insertion

It inserts mainly into the posterior aspect of the medial condyle of the tibia. Some fibers also contribute to the oblique popliteal ligament of the knee.

Nerve Supply

It is innervated by the tibial division of the sciatic nerve (L5, S1, S2).

Blood Supply

Blood supply is provided by branches of the profunda femoris artery and the popliteal artery.

Function

  • Hip joint: Extension of the thigh

  • Knee joint: Flexion and medial rotation of the leg

  • Posture: Helps stabilize the pelvis during standing and walking

This combination of actions makes it an important muscle for activities requiring strong hip and knee coordination.

Clinical Assessment

Palpation

The semimembranosus can be palpated at the medial side of the posterior thigh, especially when the knee is flexed against resistance.

Power Test

Ask the patient to flex the knee against resistance while palpating the medial hamstring area. Weakness may indicate hamstring injury or sciatic nerve involvement.

Length Test

A straight leg raise (SLR) test can indirectly assess the hamstring length, including semimembranosus tightness.

Exercises

Strengthening

  • Hamstring curls: Patient lies prone and flexes the knee against resistance.

  • Bridge exercise: Patient lies supine, bends knees, and lifts hips upward.

Stretching

  • Seated hamstring stretch: Patient sits with one leg extended and leans forward to stretch the posterior thigh.

Trigger Points

Trigger points in the semimembranosus may cause referred pain to the posterior knee and medial calf. Release techniques and stretching can help alleviate symptoms.

Related Injuries

Frequently Asked Questions (FAQ)

Q1. Where is the semimembranosus muscle located?
The semimembranosus muscle is located in the back of the thigh, on the medial (inner) side, and is part of the hamstring group.

Q2. What is the main function of the semimembranosus muscle?
Its main functions are hip extension, knee flexion, and medial rotation of the leg. It also helps stabilize the pelvis during walking.

Q3. How is the semimembranosus muscle different from the semitendinosus?
Both are hamstring muscles, but the semimembranosus has a broader, flatter tendon and inserts into the medial tibial condyle, while the semitendinosus has a long, cord-like tendon that inserts into the pes anserinus.

Q4. What injuries commonly affect the semimembranosus?
The most common issues are hamstring strains, tendinopathies, and sometimes avulsion fractures near the ischial tuberosity, especially in athletes.

Q5. How can I stretch the semimembranosus muscle?
You can stretch it by sitting with one leg extended forward and gently leaning toward your toes, or by doing standing hamstring stretches.

Q6. What nerve supplies the semimembranosus muscle?
The tibial division of the sciatic nerve (L5, S1, S2) supplies this muscle.

Q7. Can semimembranosus trigger points cause knee pain?
Yes, trigger points in this muscle can refer pain to the posterior and medial side of the knee, sometimes mimicking joint problems.

References

  1. Standring S. Gray’s Anatomy: The Anatomical Basis of Clinical Practice. 42nd Edition. Elsevier; 2020.

  2. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. 8th Edition. Wolters Kluwer; 2018.

  3. Neumann DA. Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation. 3rd Edition. Elsevier; 2017.

  4. Kendall FP, McCreary EK, Provance PG. Muscles: Testing and Function with Posture and Pain. 5th Edition. Lippincott Williams & Wilkins; 2005.

  5. Physiopedia. "Semimembranosus Muscle." Available at: https://www.physio-pedia.com (Accessed 2025).


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