Hip Joint, Lecture 1 PDF

BiomechanicsI Hip joint 1st lecture D R. A H M E D A B O U L FOTO U H  Introduction Biomechanics is a discipline that uses principles of physics to quantitatively study how forces interact within a living body. Kinematics is a branch of mechanics that describes...

BiomechanicsI Hip joint 1st lecture D R. A H M E D A B O U L FOTO U H  Introduction Biomechanics is a discipline that uses principles of physics to quantitatively study how forces interact within a living body. Kinematics is a branch of mechanics that describes the motion of a body, without regard to the forces or torques that may produce the motion. Kinetics is a branch of the study of mechanics that describes the effect of forces on the body.  Regional biomechanics 1- Hip joint ( 2 lectures) 2- Knee joint ( 2 lectures) 3- Ankle joint ( 2 lectures) 4- Shoulder joint ( 2 lectures) 5- Elbow joint ( 2 lectures) 6- Wrist joint ( 2 lectures)  Each region, Anatomy Mechanics Osteology + arthrology Kinematics Kinetics (Movement ) (Forces) Muscle and Osteokinematics Arthrokinematics joint interaction  Hip joint - The hip is the articulation between the large spherical head of the femur and the deep socket provided by the acetabulum of the pelvis. - Function of hip joint: the hips serve as ―base‖ joints for the lower extremities, and also they serve as basilar joints for the entire superimposed pelvis and trunk. - The hips play a dominant kinesiologic role in movements across a large part of the body. - Pathology or trauma affecting the hips typically causes a wide range of functional limitations, including difficulty in walking, dressing, driving a car, lifting and carrying loads, and climbing stairs. OSTEOLOGY  Innominate bone ILIUM + PUBIS + ISCHIUM + ACETABULUM Femur  - Abnormal growth and development resulting in a misshaped proximal Shape of the Abnormal growth femur is referred to generically as femoral dysplasia. proximal and development resulting in a misshaped proximal femur is referred to generically as femoral dysplasia femur - Two specific angulations of the proximal femur help define its shape: the angle of inclination and the torsional angle.  1- Angle of Inclination The angle of inclination of the proximal femur describes an angle in the frontal plane between the femoral neck and shaft. - At birth this angle measures, on average, about 165 –170 degrees. - Primarily because of muscle activity and loading across the femoral neck during walking, this angulation usually decreases by about 2 degrees per year between 2 and 8 years of age. - The angle of inclination continues to decrease by varying rates until reaching its normal adulthood value of about 125 degrees. Coxa vara & coxa valga 2- Femoral Torsion Excessive anteversion Retroversion Compensation of excessive anteversion by in-toeing  The acetabulum forms the socket of the hip. All three bones of the pelvis contribute to the formation ACETABULUM of the acetabulum: the ilium and ischium contribute about 75%, and the pubis contributes the remaining approximately 25%. ACETABULUM Acetabular alignment - In the anatomic position the acetabulum typically projects laterally from the pelvis with a slight amount of inferior and anterior inclination. - Congenital or developmental conditions may cause an abnormally shaped acetabulum. A malformed, dysplastic acetabulum that does not adequately cover the femoral head may cause chronic dislocation and increased stress, often leading to pain, degeneration, or osteoarthritis. - Two measurements help to define the Acetabular alignment: the center-edge angle and the acetabular anteversion angle. 1- Center-Edge Angle The center-edge angle measures the fixed orientation of the acetabulum within the frontal plane, relative to the pelvis. This measurement defines the extent to which the acetabulum covers the top of the femoral head. - an average CE angle of about 25–35 degrees in the general adult population (with a standard deviation of 4–6 degrees) What about the effect of increasing or decreasing the center edge angle? 2- Acetabular Anteversion Angle The acetabular anteversion angle measures the fixed orientation of the acetabulum within the horizontal plane, relative to the pelvis. This measurement indicates the extent to which the acetabulum covers the front of the femoral head. More than 20 degree = excessive acetabular anteversion = the hip may become vulnerable to anterior subluxation or dislocation. Less than 20 degree = retroversion  ARTHROLOGY - The hip is the classic ball-and-socket joint of the body, secured within the acetabulum by an extensive set of connective tissues and muscles. Thick layers of articular cartilage and cancellous bone in the proximal femur, along with eccentric muscle action, help dampen the large forces that routinely cross the hip. - Failure of any of these protective mechanisms because of disease, congenital or developmental malalignment or malformation, or trauma may lead to deterioration of the joint structure. Anatomic Features of the Hip Joint FEMORAL HEAD Fovea Ligamentum teres articular cartilage. ACETABULUM Acetabular notch Lunate surface Acetabular fossa Labrum Transverse acetabular ligament  Joint compressive force - During walking, hip forces fluctuate from 13% of body weight during the midswing phase to more than 300% of body weight during the midstance phase. - During the stance phase—when forces are the greatest— the lunate surface deforms and the acetabular notch widens slightly, increasing contact area that reduces peak pressure.  Acetabular Labrum -The acetabular labrum is a strong yet flexible ring of fibrocartilage that encircles most of the outer circumference (rim) of the acetabulum. -The mechanical seal formed around the hip by an intact labrum helps maintain a negative intra-articular pressure. The resulting so-called ―suction seal‖ has been shown to be more effective than the capsule at resisting the first 1–2 mm of joint distraction (separation). - In addition, an intact labrum forms a fluid seal around the joint that helps prevent leakage of synovial fluid to more peripheral regions of the hip. - The acetabular labrum is poorly vascularized, especially in the regions furthest away from the more vascularized articular capsule, For this reason, a torn labrum has only a limited ability to heal on its own accord. - The labrum is well supplied by afferent nerves capable of providing proprioceptive feedback and sensation of pain. CAPSULE AND LIGAMENTS OF THE HIP CAPSULE AND LIGAMENTS OF THE HIP  Close-Packed Position of the Hip The position that produces the greatest simultaneous stretch to most of the capsule combines full extension of the hip (i.e., about 20 degrees beyond the neutral position) with slight internal rotation and slight abduction. - The hip joint surfaces fit most congruently in about 90 degrees of flexion with moderate abduction and external rotation. In this position, most of the capsule and associated ligaments have unraveled to a more relatively slackened state and is considered the open packed position.  Intracapsular Pressure within the Hip - The intracapsular pressure within the healthy hip is normally less than atmospheric pressure. - This relatively low pressure creates a partial suction that provides some stability to the hip. - Except for the extremes of motion, pressures remained relatively low throughout most of flexion and extension and always remained lowest in the middle of the range of motion So, why someone with capsulitis and swelling within the hip tends to feel most comfortable holding the hip in partial flexion?  Osteokinematics Two terms are used to describe the kinematics at the hip: 1- Femoral-on-pelvic hip osteokinematics describes the rotation of the femur about a relatively fixed pelvis. 2- Pelvic-on-femoral hip osteokinematics, in contrast, describes the rotation of the pelvis, and often the superimposed trunk, over relatively fixed femurs. Axis of rotation? Axis of rotation? Axis of rotation? Femoral-on-pelvic osteokinematics  Pelvic-on-femoral osteokinematics Lumbopelvic Rhythm Rotation of the pelvis over the femoral heads changes the configuration of the lumbar spine. 1- Ipsidirectional lumbopelvic rhythm 2- contradirectional lumbopelvic rhythm  Arthrokinematics - During hip motion, the nearly spherical femoral head normally remains snugly seated within the confines of the acetabulum. - The steep walls and relative depth of the acetabulum, in conjunction with the tightly fitting acetabular labrum, restrict the average physiologic translation between articular surfaces to about 2 mm or less. - Hip arthrokinematics are based on the traditional convex-on-concave and concave- on convex principles.