13. Pelvic.pdf

TOPIC 12: PELVIC BIOMECHANICS Basic function 1) attachment point for many muscles of the lower extremity and the trunk. 2) transmits the weight of the upper body and trunk to either ischial tuberosities. 3) with the help of the muscles and connective tissues of the pelvic floor, the pelvis supports...

TOPIC 12: PELVIC BIOMECHANICS Basic function 1) attachment point for many muscles of the lower extremity and the trunk. 2) transmits the weight of the upper body and trunk to either ischial tuberosities. 3) with the help of the muscles and connective tissues of the pelvic floor, the pelvis supports the organs involved with bowel, bladder. Functional Anatomy of the Pelvis Intrinsic joints of the pelvis Sacrococcygeal joint Pubic symphysis Sacroiliac joint Extrinsic joints of the pelvis Lumbosacral joint Acetabulofemoral joint Sacrococcygeal joint Between the apex of the sacrum and the base of the coccyx It is a symphysis, having the two bones lined by hyaline cartilage and connected by an interposed fibrous disc. The movements within the joint are entirely passive and are limited to one degree of freedom, flexion and extension. Function is to increase the anteroposterior diameter of the pelvis during labor and defecation. Pubic symphysis Hyaline cartilage lines the surface of the articulation. The joint is firmly bound by a fibrocartilaginous interpubic disc and ligaments. Up to 2 mm of translation and very slight rotation occur at this joint. Sacroiliac joint (SIJ) In childhood this joint has all the characteristics of a synovial joint being mobile and surrounded by a capsule. Although through puberty, the joint gradually transforms to a modified synarthrodial joint. Functions: -Transition of forces from pelvic to caudal region -Designed primarily for stability, ensuring effective transfer of potentially large loads. SIJ joint stability: ligaments Primary stabilizers Anterior sacroiliac Iliolumbar Posterior sacroiliac Interosseous Secondary stabilizers Sacrotuberous ligament Sacrospinous ligament Kinematic of the Pelvis: SIJ Mainly small rotational & translational movements of the SI joints. Movements based on the compression of articular cartilage. Anthropometric measurements 1-4 dg of rotation and 1-2 mm for translation. Nutation and Counternutation Nutation Defined as the relative anterior tile of the top of the sacrum, relative to the ilium. Counternutation Is a reverse motion defined as the relative posterior tilt of the top of the sacrum relative to the ilium. Functional consideration of Nutation and Counternutation 1. Joint stress relief When we walk, run, give birth: very high mechanical stress on the pelvis. Pelvis generates these movements so that when we are in support phases (load), the SI joint releases the pelvis from joint stress. 2. Stability during load changes When we make load changes, fast or heavy, we need stability. The more congruency the more stability. Pelvis in retroversion: more congruence: sacrum nutation. All the force that go towards nutation will help stabilize the SIJ. Stability during load changes: Kinetics Muscles that reinforce and stabilize the SIJ Erector spinal Lumbar multifidi Abdominal muscles Hip extensors Lattissimus dorsi Iliacus and piriformis Arthrokinematics of the Pelvis Anteversion Anterior tilt Descent of ASIS. Ascent of PSIS SACRUM: COUNTERNUTATION Lumbar extension movement Retroversion Posterior tilt Ascent of ASIS and Descent of PSIS SACRUM: NUTATION Lumbar flexion movement Osteokinematics Lateral tilt Lateral movement Descent of ASIS from one side. Ascent of contralateral ASIS Associated to movements of abduction and adduction. Rotation ANTERIOR movement of ASIS of one side. POSTERIOR Movement of the contralateral ASIS Associated to movements during gait. When I stride, rotation to the opposite side, to the side I am stepping with. Which muscles will act in pelvic movements? Anteversion Caudal Iliopsoas Rectus femoris Sartorius Cranial Erector spinae Trunk extensors Lumbar extensors Retroversion Caudal Gluteus maximus Hamstrings Piriformis Cranial Rectus abdominis External oblique O O O O O O O