Biomechanics of Hip Joint PDF

Biomechanics of Hip Joint Dr. Bassem Khalifa Assistant Professor of Orthopedic Physical Therapy OSTEOLOGY OF THE HIP A) Innominate: Each innominate is the union of three bones: the ilium, pubis, and ischium. The right and left innominates connect with each other anteri...

Biomechanics of Hip Joint Dr. Bassem Khalifa Assistant Professor of Orthopedic Physical Therapy OSTEOLOGY OF THE HIP A) Innominate: Each innominate is the union of three bones: the ilium, pubis, and ischium. The right and left innominates connect with each other anteriorly at the pubic symphysis and posteriorly at the sacrum. These connections form a complete osteoligamentous ring, referred to as the pelvis  1st function : the pelvis serves as a common The pelvis is attachment point for many large muscles of the lower extremity and the trunk. associated 2nd function: The pelvis also transmits the with three weight of the upper body and trunk either to important and the ischial tuberosities during sitting or to the lower extremities during standing and very different walking. functions: 3rd function: With the aid of the muscles and connective tissues of the pelvic floor, the pelvis supports the organs involved with bowel, bladder, and reproductive functions.  It is the longest and strongest bone of the human body. At its proximal end, the femoral head projects medially and slightly anteriorly for an articulation with the acetabulum. The femoral neck connects the femoral head to the Femur: shaft. The neck serves to displace the proximal shaft of the femur laterally away from the joint, thereby reducing the likelihood of bony impingement against the pelvis. Distal to the neck, the shaft of the femur courses slightly medially, effectively placing the knees and feet closer to the midline of the body.  What are the common angles at the hip joint and its abnormalities? A.Neck shaft angle(Angle of Inclination) The angle of inclination of the proximal femur describes the angle within the frontal plane between the femoral neck and the medial side of the femoral shaft. At birth this angle measures about 140 to 150 degrees. Primarily because of the loading across the femoral neck during walking, this angle usually reduces to its normal adulthood value of about 125 degrees.  Abnormalities of Neck shaft angle(Angle of Inclination) A change in the normal angle of inclination is referred to as either coxa vara or coxa valga. These abnormal angles can significantly alter the articulation between the femoral head and the acetabulum, thereby affecting hip biomechanics. Severe malalignment may lead to dislocation or stress- induced degeneration of the joint. Coxa valga deformity Coxa valga (Latin valga, to bend outward) describes an angle of inclination markedly greater than 125 degrees. This deformity directs the femoral head more superiorly in the acetabulum. Many biomechanical alterations appear to result from a coxa valga. The joint reaction force on the femur is more parallel to the femoral neck in coxa valga. This alignment subjects the femoral neck to more compressive forces and less of a bending moment, which may explain why, in coxa valga, cancellous bone in the femoral neck appears to be arranged in columns parallel to the neck rather than in the medial and lateral intersecting bundles seen in well-aligned femora. The perpendicular distance between the hip joint centre and the trochanter is decreased in coxa valga, putting the hip abductor muscles at a disadvantage by reducing their moment arm. With decreased moment arms, the hip abductor muscles must generate larger contractile forces to support the hip joint, resulting in increased joint reaction forces. In addition, the joint reaction force is displaced laterally in the acetabulum and is applied over a smaller joint surface, leading to increased joint stress. In other words, coxa valga deformities are likely to increase the risk of degenerative joint disease within the hip by increasing the joint reaction force as well as the stress sustained by the femoral head. Make head liable to superior dislocation Coxa vara deformity Coxa vara (Latin coxa, hip, vara, to bend inward) describes an angle of inclination markedly less than 125 degrees. It is a decrease in the angle between the shaft and neck of the femur leading to increasing the bending moment applied to the femoral neck. The increased bending moment increases the compressive forces on the medial aspect of the femoral neck and the tensile forces laterally.  In addition, a coxa vara deformity moves the trochanter farther from the joint centre, effectively lengthening the moment arm of the hip abductors. This puts the hip abductors at a mechanical advantage and may actually reduce the force they are required to exert during stance, thus reducing the joint reaction force. Decrease the liability of superior dislocation. More stability. B.Anteversion angle (Femoral Torsion) Femoral torsion describes the relative rotation (twist) between the bone’s shaft and neck. Normally, as viewed from above, the femoral neck projects about 15 degrees anterior to a medial-lateral axis through the femoral condyles. This degree of torsion is called normal anteversion. In Conjunction with the normal angle of inclination , an approximate 15-degree angle of anteversion affords optimal alignment and joint congruence The angle of torsion (AT) :exists within the transverse plane. This angle is best visualized by placing the femoral condyles in the frontal plane and measuring the angle between the frontal plane and a line drawn through the femoral head and neck. A normal range for the AT in adults is 15 to 25 degrees,11 with the femoral head and neck torsioned anteriorly relative to the frontal plane Typically a healthy infant is born with about 40 degrees of femoral anteversion. With continued bone growth, increased weight bearing, and muscle activity, this angle usually decreases to about 15 degrees by 16 years of age. Excessive anteversion that persists into adulthood can increase the likelihood of hip dislocation, articular incongruence, increased joint contact force, and increased wear on the articular cartilage. These factors may lead to secondary osteoarthritis of the hip. Abnormalities of anteversion angle Excessive femoral anteversion angle It places the head of the femur farther anteriorly in the acetabulum than normal. Medial rotation of the hip compensates for excessive femoral anteversion by putting the femoral head in a more normal location within the acetabulum. In standing, such compensatory medial rotation of the hip results in an in-toed posture if accompanied by no other compensation. Because individuals with excessive femoral anteversion compensate for it with medial rotation of the hip, subjects with excessive femoral anteversion typically display decrease in medial rotation ROM.  Children with excessive anteversion frequently choose the “frog sitting” posture over other sitting posture alternatives. Over time, many individuals with continued excessive femoral anteversion develop a secondary compensation in the tibia, lateral tibial torsion, which turns the foot laterally with respect to the knee. As a result, the in-toed standing posture disappears. However, close examination of the femoral condyles reveals that the standing posture continues to be characterized by medial rotation of the hip.  Retroversion It Is a transverse plane deformity in which the femoral neck is rotated posterior to the frontal plane, although lower than normal anteversion is also sometimes described as retroversion. Retroversion or less than normal anterversion typically results in shortening of lateral rotation ROM of the hip. Excessive out-toeing can be a postural manifestation of retroversion What are the common muscles at the hip joint and its abnormalities?  Gluteus maximus Gluteus maximus has several stability roles: 1.Balancing the pelvis on femoral heads thus maintaining upright posture. 2.Its the attachment through the iliotibial tract supports the lateral knee. Its most powerful action is to cause the body to regain the erect position after stooping, by drawing the pelvis backward, being assisted in this action by the biceps femoris (long head), semitendinosus, semimembranosus, and adductor magnus. Weakness of the gluteus maximus : Results in decreased strength of hip extension and lateral rotation. A classic gait pattern resulting from gluteus maximus weakness, known as the gluteus maximus lurch.  Hip Abductors THE ROLE OF THE HIP ABDUCTORS : 1. Many upright activities such as stair ascend and descend require complex stabilization of the hip, knee, and ankle in all three planes of motion. 2. The ability to stabilize the knee and foot in the three planes appears to be in part the responsibility of the hip abductor muscles. Effects of Weakness of the Abductor Muscles: Weakness of the gluteus medius and minimus results in a significant decrease in abduction strength, since they are the primary abductors of the hip. The functional manifestations of such weakness are most apparent in weight-bearing activities, specifically in single-limb support. Hip Adductors  Functional Role of the adductors of the Hip: The 1st important functional role of the adductors is to stabilize the pelvis during weight shifting from one limb to the other. This role is seen during gait as the adductors contract during the transitions from stance to swing and swing to stance. The 2nd important functional role of the adductors to stabilize the hip during squatting activities. Effects of Weakness of the Adductor Muscles: Adductor weakness is not common but may result from an injury to the obturator nerve. Symptoms include gait instability and an abducted gait in which the affected limb contacts the ground with the hip excessively abducted. In an ambulatory individual, extreme tightness of the adductors of the hip can create significant problems in gait, leading to Scissors gait.  Thank You