Posterior Thigh Muscles

EXTREMITY ANATOMY: Posterior Thigh Muscles

Overview of Hamstring Muscles

  • Muscle Group Includes:

    • Semimembranosus

    • Semitendinosus

    • Biceps femoris

    • Note: Short head of biceps femoris is not included in basic description.

  • Common Features of Hamstring Muscles:

    • Proximal Attachment: All originate from the ischial tuberosity.

    • Joint Span: They span two joints—namely the hip and knee joints.

    • Actions:

    • Extend the thigh at the hip joint.

    • Flex the leg at the knee joint.

    • Innervation: All are innervated by the tibial branch of the sciatic nerve.

Functional Limitations of Hamstrings

  • Two Actions Cannot Be Performed Maximally Simultaneously:

    • Full Flexion of the Knee: This action impairs hip extension.

    • Full Hip Extension: This action impairs knee flexion.

  • Definitions:

    • Active Insufficiency: This is the inability of a muscle that spans two or more joints to exert enough tension and shorten sufficiently to allow a full range of movement in all joints simultaneously.

    • Passive Insufficiency: Involves the inability of a muscle that spans two or more joints to be stretched sufficiently to enable a full range of motion in all joints at the same time.

  • Clinical Significance: When the thigh and leg are fixed, the hamstrings extend the trunk at the hip joint.

  • Contraction Characteristics: Hamstrings are most active during walking, particularly during eccentric contraction, resisting hip flexion and knee extension.

Semitendinosus

  • Attachment Points:

    • Origin: Ischial tuberosity.

    • Insertion: Pes anserinus (medial aspect of the tibia).

  • Innervation: Tibial division of the sciatic nerve.

  • Actions:

    • Flexes the leg.

    • Extends the thigh.

    • Extends the trunk when the leg/thigh is fixed.

Anatomy of Pes Anserinus

  • Structural Components:

    • Tendon of the semitendinosus muscle.

    • Gracilis tendon.

    • Sartorius tendon.

    • Quadriceps femoris tendon.

    • Semimembranosus muscle and tendon.

    • Patella and patellar ligament (connecting patella to tibial tuberosity).

Semimembranosus

  • Attachment Points:

    • Origin: Ischial tuberosity.

    • Insertion: Posterior aspect of the medial condyle of the tibia.

  • Innervation: Tibial division of the sciatic nerve.

  • Actions:

    • Flexes the leg.

    • Extends the thigh.

    • Extends the trunk when the leg/thigh is fixed.

  • Distal Attachment Features:

    • Comprises three parts:

    1. Direct attachment to the posterior medial tibial condyle.

    2. Blends with the popliteal fascia.

    3. Reflected part which reinforces the intercondylar part of the knee capsule (known as the oblique popliteal ligament).

Biceps Femoris

  • Attachment Points:

    • Origin:

    • Long head: originates from the ischial tuberosity.

    • Short head: originates from the linea aspera and supracondylar ridge of the femur.

    • Insertion: Head of the fibula.

  • Innervation:

    • Long head innervated by the tibial division of the sciatic nerve.

    • Short head innervated by the common peroneal division of the sciatic nerve.

  • Actions:

    • Flexes the leg.

    • Extends the thigh.

  • Noteworthy: The long head of biceps femoris covers the sciatic nerve as it travels down from the medial gluteal region through the posterior thigh into the popliteal fossa.

Hamstring Injuries

  • Mechanics of Injury:

    • During sprints, hamstring muscles develop maximum tension to decelerate the tibia as the knee extends.

    • They extend the hip back once the foot strikes the ground, allowing for the forward movement of the other leg.

    • Most common injury occurs just before foot strikes ground, particularly affecting the biceps femoris when eccentrically activated and at maximum length.

Risk Factors for Hamstring Injury

  • Age: Older individuals are at greater risk for hamstring pulls.

  • Previous Injury: Prior injuries to hamstrings or adductor muscles significantly increase the risk of future damage.

  • Flexibility: Greater flexibility of hamstrings correlates with a lower propensity for injury.

  • Hamstring Strength: Insufficient strength in the hamstrings is connected to higher susceptibility to hamstring strains.

  • Nerve Impingement: Lumbosacral nerve root impingement at L5-S1 can contribute to hamstring weakness.

  • Fatigue and Fitness: Muscle fatigue leads to poor coordination between muscle groups, notably affecting the biceps femoris due to its dual innervation (common fibular and tibial nerves). Disorganization in nerve firing during fatigue increases risk of injury.

Clinical Observations for Hamstring Injuries

  • Case Example: Axial MRI reveals a ruptured intramuscular tendon with a hematoma adjacent to the muscle bundle in a 28-year-old professional Australian football player.

Injury Grades

  • Grade 1: Minor Tear(s)

    • Symptoms: Tightness in the posterior thigh, minimal swelling, possible discomfort while walking.

    • Physical Assessment: No pain during prone lying and knee flexion against resistance.

  • Grade 2: Partial Tear

    • Symptoms: Gait impacts with a limp, occasional twinges of pain during activity, possible swelling, noticeable pain with pressure or resistance during knee flexion.

    • Physical Limitations: Might be unable to completely straighten the knee.

  • Grade 3: Severe Tear or Complete Rupture

    • Symptoms: Severe pain during activities like knee flexion, pronounced swelling, difficulty walking possibly requiring crutches.

Treatment Approaches for Hamstring Injuries

  • Grades 1-2:

    • RICE Protocol: Rest, Ice, Compression, Elevation.

    • Administration of NSAIDs.

    • Emphasis on stretching and strengthening exercises.

    • Expected recovery: Approximately 2-4 weeks.

  • Grade 3 Injuries:

    • Expected recovery time: Often ~10 weeks.

    • May require surgical intervention, particularly for avulsion at the origin of the muscle.