Previous                         Home                         Next

The Pelvic Girdle

Functions of the Pelvis
Joint Structure of the Pelvis
Kinematics of the Pelvis
Muscles at the Pelvis
Pelvis Stability
Mechanism of Injury at the Pelvis

Objectives： After studying this topic, the students will be able to

1. to identify the structure of the pelvis, including joint type, articular shape, and the surrounding tissues
2. to describe joint motions occurring at the pelvis, including osteokinematic and arthrokinematic movements, muscle actions, and factors checking pelvic motions
3. to understand the pelvic stability and the possible mechanisms of injury
4. to explain the relationship of the muscle balance in the pelvis to the erect posture

1. Neumann DA (2002).  Axial Skeleton： Osteology and Arthrology.  In Neumann DA: Kinesiology of the Musculoskeletal System: Foundations for Physical Rehabilitation. Philadelphia: Mosby.  Chapter 9, pp. 303-308.
2. Smith LK, Weiss EL, Don Lehmkuhl L (1996). Brunnstrom's Clinical Kinesiology, 5th ed.  Philadelphia, F.A. Davis.  Chapter 8, pp. 266-300.

Functions of the Pelvis

  back to top

Joint Structure of the Pelvis

Joints at the Pelvis

Sacroiliac Joint (SI Joint)

proximal component： sacrum irregular articular surface distal component： innominate irregular auricular surface of the ilium joint type： uneven articular surface no muscles cross over this joint motions sacral flexion sacral extension sacral forward torsion

Joint Structure of the Pelvis
Kinematics of the Pelvis

Pubic Symphysis (Pubic Joint)

amphiarthrosis (fibrocartilage joint)： articular surfaces covered with hyaline cartilage and held togehter by an interpubic disc and ligaments joint type： plane joint motions superior/ inferior glide separation/ compression functions shock absorption during walking for woman's baby delivery

Joint Structure of the Pelvis

Sacral Angle

the angle of the superior margin of the sacrum from the horizontal plane healthy adults： ~30º lumbar lordosis increased if the pelvis is anteriorly tilted. spondylolithesis

Neutral position of the pelvis

  back to top

Kinematics of the Pelvis

Sacral Flexion/ Extension

synonym： sacral flexion = sacral nutation sacral extension = sacral counter-nutation joint involved： sacroiliac joint plane of motion： sagittal plane axis of rotation： a frontal axis passing through S2 motions： sacral flexion： sacral promontory tilts anteriorly and inferiorly
sacral extension： sacral promontory back to the neutral position from an anterior-tilted position

Sacral Forward/ Backward Torsion

joint involved： sacroiliac joint plane of motion： triplanar motion axis of rotation： left and right diagonal axis osteokinematic movements right forward torsion on right diagonal axis (R on R) left forward torsion on left diagonal axis (L on L)

Pelvic Motions

open kinematic chain motions

anterior tilt： ASIS moves anteriorly and inferiorly

posterior tilt： ASIS moves posteriorly and superiorly

lateral tilt to the left/right： one ASIS is higher than the other

rotation to the left/right： one ASIS anterior to the other

pelvic motions at stance (closed kinematic chain motions)

Pelvic Motions	Spinal Motions	Hip Motions
anterior tilt	hyperextension	slight flexion
posterior tilt	flexion	extension
lateral tilt to the left	lateral flexion to the right	right hip： slight adduction left hip： slight abduction
left rotation without turning the trunk or moving the feet	right rotation	right hip： slight external rotation left hip： slight internal rotation

  back to top

Muscles Around the Pelvis

Muscles for Pelvic Anterior Tilt

hip flexors iliopsoas rectus femoris lumbar extensors erector spinae

Muscles for Pelvic Posterior Tilt

abdominal muscles rectus abdominis hip extensors hamstrings gluteus maximus

Muscles for Pelvic Lateral Tilt

Muscles for Pelvic Rotation

  back to top

Pelvis Stability

Factors Affecting Sagittal Plane Stability of the Pelvis

bony configuration trabecular system of the pelvis follows the weight-bearing line tension of ligaments or other connective tissues iliolumbar ligament sacrospinous ligament sacrotuberous ligament sacroiliac ligament： anterior, posterior, and interosseous dynamic stability of muscles stretch-weakness vs. adaptive shortness (Kendall, 1969)

Factors Affecting Frontal Plane Stability of the Pelvis

dynamic stability of muscles stretch-weakness vs. adaptive shortness (Kendall, 1969)

  back to top

Mechanism of Injury at the Pelvis

Malalignment

leg length discrepancy long leg side hip adduction elevated iliac crest sidebending of lumbar spine to the same side compensatory scoliosis at thoracic and cervical regions short leg side hip abduction pelvis lateral tilt to the same side sidebending of lumbar spine to the opposite side compensatory scoliosis at thoracic and cervical regions

  back to top