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Piriformis

Contents

Anatomy

Piriformis - posterior
Piriformis - lateral
Piriformis - anterior
Piriformis - posterolateral

General Information

  • This section is strictly limited to anatomy, you might be looking for clinical relevant information which is found under the clinical chapters -- muscles section, click here to go to that page

Position

  • Deep

Origin

  • Sacrum
    • Anterior part between and lateral to 1-4 sacral foramina of the pelvis
  • Sacrotuberos ligament
    • Anterior surface

Insertion

  • Trochanter major femur
    • Superomedial

Main function

  • Hip
    • Lateral rotation

Secondary function

  • Hip
    • Abduction
    • Medial rotation
  • Pelvis
    • Contralateral rotation

Nerve innervation

  • Segmental
    • L5-S2
  • Peripheral
    • Plexus sacralis

Arterial supply

  • Superior gluteal artery
  • Inferior gluteal artery

Palpation

  • Patient positoin
    • Prone
  • The piriformis is deep and is difficult to palpate
  • You can palpate the deep lateral rotator group of the hip, of which the piriformis is a part of, but it is difficult to isolate the palpation of piriformis
  • Place your hand just lateral to sacrum, halfway between SIPS and apex of the sacrum
  • Ask the patient to flex the knee to 90°
  • Give resistance to the patient in a medial rotation direction, so that the patient is giving force towards lateral rotation, while you feel for the contraction of the lateral rotators
  • Note that the deep lateral rotator group also consists of quadratus femoris, obturator internus, obturator externus, gemellus externus, gemellus superior and gemellus inferior
    • It can be difficult to distinguish between these muscles, so be aware that they all will be active during the movement
  • Also note that gluteus maximus can be activated during the movement
    • If you are giving too much force, this muscle will also be activated

Strength test

  • Patient position
    • Sitting with 90° bend of the knees and the leg hanging freely above the ground
  • Place your one hand laterally on the patient's thigh on the side which is to be tested
  • Use the opposite hand to give resistance to the patient
    • Place the hand along the medial aspect of the calf and pull the leg into an internally rotated position of the hip, so that the patient is giving force towards external rotation
  • Note that the test is also testing quadratus femoris, obturator internus, obturator externus, gemellus superior and gemellus inferior that are all lateral rotators of the hip