U01.11.008 Actions of hip muscles

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Learning Objectives

  • Categorize the primary hip muscles by their mechanical actions (flexion, extension, etc.).
  • Identify the dual roles of muscles like the Gluteus medius and Iliopsoas.
  • Connect hip abductor weakness to clinical gait abnormalities (Trendelenburg sign).

1. Sagittal Plane: Flexors and Extensors

These muscles drive the forward and backward movement of the thigh.

  • Flexors: Iliopsoas (Iliacus + Psoas), Rectus femoris, Tensor fascia lata (TFL), Pectineus, and Sartorius.
  • Extensors: Gluteus maximus and the hamstrings (Semitendinosus, Semimembranosus, and Long head of Biceps femoris).

2. Frontal Plane: Abductors and Adductors

Abductors are critical for pelvic stability during walking.

  • Abductors: Gluteus medius and Gluteus minimus.
    • Clinical: Weakness in these muscles (Superior Gluteal Nerve injury) leads to the Trendelenburg gait, where the pelvis drops toward the unaffected side.
  • Adductors: Adductor magnus, longus, and brevis.

Activity:

3. Rotational Mechanics

Many hip muscles have secondary roles in rotating the femur within the acetabulum.

Action Primary Muscles
Internal Rotation Gluteus medius, Gluteus minimus, TFL.
External Rotation Iliopsoas, Gluteus maximus, Piriformis, Obturator internus/externus.

Clinical Notes & Corrections:

  • Piriformis Syndrome: The Piriformis (an external rotator) can compress the sciatic nerve, leading to pain that mimics a herniated disc.
  • Iliopsoas: This is the most powerful flexor of the hip. In a “psoas abscess,” patients often hold the hip in a flexed, externally rotated position for comfort.

Activity: Hip Muscle Action Match

Memory Hooks:

Gluteus Maximus: The Great Extender (used for climbing stairs).

Medius/Minimus: The Middle and Small ones Abduct and Rotate In.

Sartorius: The “Tailor’s muscle” (Flexion, Abduction, External Rotation—sitting cross-legged).

Activity: