The Pelvic Girdle

The Pelvic Girdle General Structure & Function Structure & Function of Specific Joints Muscular Considerations Specific Functional Considerations Common Injuries

The Hip and Pelvic Girdle General Structure & Function Structure & Function of Specific Joints Muscular Considerations Specific Functional Considerations Common Injuries

General Structure: Pelvic Girdle L/R Pelvic Bones Fusion of: ilium, pubis, ischium 3 Joints: pubic symphysis, 2 sacroiliac The pelvic girdle consists of a right and left innominate (pelvic bone). Each innominate is formed by the fusion of three bones: the ilium, pubis, and ischium. Each innominate connects via 3 joints (anteriorly at the pubic symphysis and posteriorly at the two sacroliac joints ). Pubic symphysis is amphiarthrodial symphysis joint; sacroiliac joints are half amphiarthrodial and half diarthrodial gliding. Points to make: Importance of stress and bone modeling to form hip socket correctly (story of niece’s hip) Fusion of acetabulum and other bone areas occurs around 8 yrs – what are the implications for activity, conditioning, etc (avoid high impact and contact sports prior to epiphyseal closure Contrast with shoulder girdle: structure and function of connecting joints within girdle (shoulder girdle diarthrodial nonaxial AC joint vs. pubic symphysis and sacroiliac) Number and structure of the joints that connect the girdle to the thorax & extremities - one pelvic vs two shoulder girdles (one girdle connected via 3 joints – 2 hips and lumbosacral – vs. 1-to-1 alignment of shoulder girdles

General Structure: The Hip Joint Hip Joint: union of acetabulum of pelvis and head of femur Stable joint, great mobility Surrounded by several large muscles All three bones of the pelvis form part of the acetabulum. The hip joint is formed by the union of the acetabulum of the pelvis with the head of the femur. It is a very stable joint which also allows great mobility. The hip joint has a loose joint capsule, but is surrounded by several large muscles. The femur is the longest and strongest bone of the body.

Structural Factors that Affect Girdle Function: Angle of Inclination Larger at birth, decreases with age…why? Hip abductors? Length of limb? Compression vs. Shear? Angle of Inclination This is the angle formed in the frontal plane between the femoral neck and the femoral shaft, and averages 125 degrees. It is larger at birth, but decreases as the person matures and becomes weight bearing. The range of this angle is 90 to 135 degrees. It determines effectiveness of the hip abductors, the length of the limb, and the forces imposed on the hip joint. > 125 degrees - coxa valga; the limb is lengthened, the effectiveness of the hip abductors is decreased (smaller moment arm), the load on the femoral head is increased, and the stress on the femoral neck is decreased < 125 degrees - coxa vara; the limb is shortened, the effectiveness of the hip abductors is increased (smaller moment arm), the load on the femoral head is decreased, and the stress on the femoral neck is increased. The hip abductors gain a mechanical advantage to counteract the forces produced by body weight; the load on the hip joint and the average muscular force needed to counteract the force of BW is decreased.

Structural Factors that Affect Girdle Function: Angle of Anteversion Gluteus Maximus…ext. rotation? Angle of anteversion This is the angle in the transverse plane of the femoral head. The average value is 12-14 degrees. Anteversion affects the mechanical advantage of the gluteus maximus, and thus, its effectiveness as an external rotator. > 14 degrees to anterior - the head of the femur becomes uncovered and person must assume an internally rotated posture or gait to keep the head in; Q-angle is increased, leg length increases, increased pronation of foot (at subtalar joint), increased lumbar curvature, and increased patellar problems rotation to posterior - retroversion; creates an externally rotated gait, increases supination of foot, and decreases Q-angle

Functional Anatomy of the Hip Joint: Acetabulum Alignment Center-Edge Angle Acetabular Anteversion Angle Center-Edge Angle (angle of Wiberg)- describes the extent to which the acetabulum covers the femoral head within the frontal plane. Provides a protective shelf over the femoral head. Typically measures about 35-40 degrees. The more vertical the alignment (smaller angle), the more likely a dislocation may occur. Acetabular anteversion angle describes the extent to which the acetabulum surrounds the femoral head in the horizontal plane. A value of 20 degrees is typical. The anterior capsular ligament and iliopsoas tendon cover exposed anterior portion of femoral head. Excessive anteroversion may lead to anterior joint dislocation (especially during excessive external rotation).

General Function To provide stability for weight bearing To allow for mobility of the leg Load transmission

Movements of the Hip Joint Flexion and Extension Abduction and Adduction External Rotation and Internal Rotation. Range of Motion ROM: Flexion - 0 to 140 degrees Extension - 0 to 15 degrees Abduction - 0 to 30 degrees Adduction - 0 to 25 degrees External Rot. - 0 to 90 degrees Internal Rot. - 0 to 70 degrees (when flexed) less when extended The ROM values reported are very dependent on the position in which the hip, knee, and pelvic girdle is during measurement. Knee joint position is important during flexion because of the large number of muscles that cross the hip and the knee joint. Flexion of the hip is limited primarily by the passive insufficiency of the hamstrings, although active insufficiency is present in the rectus femoris. The influence of pelvic girdle position will be discussed later. Hyperextension is limited primarily by the iliofemoral ligament, the anterior joint capsule, and the strong hip flexors.

The Hip and Pelvic Girdle General Structure & Function Structure & Function of Specific Joints Muscular Considerations Specific Functional Considerations Common Injuries

Kinematics of the Hip Joint Femoral-on-Pelvic Osteokinematics Pelvic-on-Femoral Osteokinematics 1. Femoral-on-Pelvic Osteokinematics: rotation of the femur about a fixed pelvis 2. Pelvic-on-Femoral Osteokinematics: rotation of the pelvis over fixed femurs Names of Movements: Flexion and Extension in Sagittal Plane Abduction and Adduction in Frontal Plane Internal and External Rotation in the Horizontal Plane

Kinematics of the Hip Joint Femoral-on-Pelvic Osteokinematics: Flexion and Extension in Sagittal Plane Flexion - 0 to 140 degrees Extension - 0 to 15 degrees

Kinematics of the Hip Joint Femoral-on-Pelvic Osteokinematics: Abduction and Adduction in the Frontal Plane Abduction - 0 to 30 degrees Adduction - 0 to 25 degrees

Kinematics of the Hip Joint Femoral-on-Pelvic Osteokinematics: Internal and External Rotation in the Horizontal Plane External Rot. - 0 to 90 degrees Internal Rot. - 0 to 70 degrees (when flexed) less when extended

Kinematics of the Hip Joint Pelvic-on-Femoral Osteokinematics: Flexion and Extension in Sagittal Plane

Kinematics of the Hip Joint Pelvic-on-Femoral Osteokinematics: Lumbopelvic Rhythm Two contrasting types of lumbopelvic rhythms. Describe direction of rotation at lumbar spine and pelvis.

Kinematics of the Hip Joint Pelvic-on-Femoral Osteokinematics: Abduction and Adduction in the Frontal Plane Right lateral tilt and left lateral tilt

Kinematics of the Hip Joint Pelvic-on-Femoral Osteokinematics: Internal and External Rotation in the Horizontal Plane Right rotation and left rotation

The Hip and Pelvic Girdle General Structure & Function Structure & Function of Specific Joints Muscular Considerations Specific Functional Considerations Common Injuries Make the point that there are no pelvic girdle muscles.

Muscular Considerations: Sagittal Plane Pelvic Motion Pelvic-on-Femoral Flexion: Anterior Pelvic Tilt Force couple Hip flexors Lower trunk extensors Anterior pelvic tilt is performed by a force-couple bet/ hip flexors and low-back extensor muscles. When the femurs are fixed, contraction of the hip flexors rotates pelvis about the med-lat axis. Femoral-on-Pelvic Hip flexion involves synergy bet/ hip flexors and abdominal muscles

Muscular Considerations: Sagittal Plane Pelvic Motion Pelvic-on-Femoral Flexion: Posterior Pelvic Tilt Force couple Hip extensors Lower trunk flexors Anterior pelvic tilt is performed by a force-couple bet/ hip flexors and low-back extensor muscles. When the femurs are fixed, contraction of the hip flexors rotates pelvis about the med-lat axis. Femoral-on-Pelvic Hip flexion involves synergy bet/ hip flexors and abdominal muscles

Muscular Considerations: Overall Function of the Hip Flexors 2. Femoral-on-Pelvic Hip Flexion synergy between hip flexors and abdominal muscles Femoral-on-Pelvic Hip flexion involves synergy bet/ hip flexors and abdominal muscles. (e.g. consider stabilizing role of abd during leg raise). Requires abdominal muscles to create posterior pelvic tilt to neutralize anterior pelvic tilt created by hip flexors.

Muscular Considerations: Extensors Pelvic-on-Femoral Hip Extension Overall function of hip extensors -Pelvic-on-femoral extension: Posterior pelvic tilt using force coupling with abdominal muscles = hip extension and reduces lumbar lordosis (similar to hip flexor force coupling).

Muscular Considerations: Hip Adductors Hip Adduction Pelvic Action? Muscles being utilized? Frontal plane adductor torque may control both femoral-on-pelvic and pelvic-on-femoral motion within same movement.

The Hip and Pelvic Girdle General Structure & Function Structure & Function of Specific Joints Muscular Considerations Specific Functional Considerations Common Injuries

Specific Functional Considerations Bilateral hip motion in sagittal plane Unilateral hip motion if sagittal plane Single-leg stance Walking Running Untrained