Summary ATI RN COMPREHENSIVE PREDICTOR 2023 LATEST BIOMECHANICS OF THE LOWER LIMB

ATI RN COMPREHENSIVE PREDICTOR 2023 LATEST Biomechanics of the lower limb-extremity Objectives • Explain how anatomical structure affects movement capabilities of lower-extremity articulations. • Identify factors influencing the relative mobility and stability of lower-extremity articulations. • Explain the ways in which the lower extremity is adapted to its weight-bearing function. • Identify muscles that are active during specific lower-extremity movements. • Describe the biomechanical contributions to common injuries of the lower extremity. Although there are some similarities between the joints of the upper and the lower extremities, the upper extremity is more specialized for activities requiring large ranges of motion. In contrast, the lower extremity is well equipped for its functions of weight-bearing and locomotion. Beyond these basic functions, activities such as kicking a field goal in football, performing a long jump or a high jump, and maintaining balance pointe in ballet reveal some of the more specialized capabilities of the lower extremity. The hip is a ball-and-socket joint. The ball is the head of the femur, which forms approximately two-thirds of a sphere. The socket is the concave acetabulum, which is angled obliquely in an anterior, lateral, and inferior direction. Joint cartilage covers both articulating surfaces. The cartilage on the acetabulum is thicker around its periphery, where it merges with a rim, or labrum, of fibrocartilage that contributes to the stability of the joint. Hydrostatic pressure is greater within the labrum than outside of it, contributing to lubrication of the joint. The acetabulum provides a much deeper socket than the glenoid fossa of the shoulder joint, and the bony structure of the hip is therefore much more stable or less likely to dislocate than that of the shoulder. Several large, strong ligaments also contribute to the stability of the hip. The extremely strong iliofemoral or Y ligament and the pubofemoral ligament strengthen the joint capsule anteriorly, with posterior reinforcement from the iliofemoral ligament. Tension in these major ligaments acts to twist the head of the femur into the acetabulum during hip extension, as when a person moves from a sitting to a standing position. Inside the joint capsule, the ligament teres supply a direct attachment from the rim of the acetabulum to the head of the femur. As with the shoulder joint, several bursae are present in the surrounding tissues to assist with lubrication. The most prominent are the iliopsoas bursa and the deep trochanteric bursa. The iliopsoas bursa is positioned between the iliopsoas and the articular capsule, serving to reduce the friction between these structures. The deep trochanteric bursa ... Lower Extremities Landmarks Bones – Hip Joint Structure of the Hip Movements at the Hip Although movements of the femur are due primarily to rotation occurring at the hip joint, the pelvic girdle has a function similar to that of the shoulder girdle in positioning the hip joint for effective limb movement. Unlike the shoulder girdle, the pelvis is a single non jointed structure, but it can rotate in all three planes of movement. The pelvis facilitates movement of the femur by rotating so that the acetabulum is positioned toward the direction of impending femoral movement. For example, posterior pelvic tilt, with the anterior superior iliac spine tilted backward with respect to the acetabulum, positions the head of the femur in front of the hipbone to enable ease of flexion. Likewise, anterior pelvic tilt promotes femoral extension, and lateral pelvic tilt toward the opposite side facilitates lateral movements of the femur. The movement of the pelvic girdle also coordinates with certain movements of the spine. Flexion The six muscles primarily responsible for flexion at the hip are those crossing the joint anteriorly: the iliacus, psoas major, pectineus, rectus femoris, sartorius, and tensor fascia latae. Of these, the large iliacus and psoas major—often referred to jointly as the iliopsoas because of their common attachment to the femur—are the major hip flexors.