Pathomechanics of Hip Joint (part I) 5hLecture Biome II Dr . ManalRadwanSalim Lecturer of Physical Therapy Tuesday 29-10-2013 Saturday 2-11-2013
hip/ Thigh Osteokinematics: • The hip is the articulation between the large spherical head of the femur and the deep socket provided by the acetalum of pelvis, the femoral head is located jut inferior to the middle third of the inguinal ligament
1- The femur: is the longest bone of the human body. The femoral head projects medially for an articulation with the acetabulum. The femoral shaft courses slightly medial, thereby placing the knees and feet closer to the midline of the body.
Angles of the femur: a) Neck shaft angle: (angle of inclination) • It is an angle which presents in the frontal plane between the longitudinal axis of the femoral neck and the longitudinal axis of the femoral shaft. • - The longitudinal axis of the neck : is the line which runs from the center of the head in midline of the neck to the implantation of the neck between the trochanters. • The longitudinal axis of the shaft :is the line drawn from midway of the trochanteric region to the middle of the knee joint (anatomical axis).
Its magnitude: In normal adult person: it is about 125 degrees In children, it is about 150 degrees, but by the process of weight bearing, compression of the head and neck of the femur occurs and then the neck shaft angle decreases.
Its functions: It displace the proximal shaft of the femur laterally away from the joint. Thereby reducing the likelihood of bony impingement against the pelvis. It allows more degrees of freedom of the hip by moving the longitudinal axis of the femur away from the hip bone.
Pathologically: • If the medial angulation between the neck and the shaft increases more than 125 degrees. It is called coxavalga (bend aoutward). • If it decreases less than 125 degree, it is called coxavara(bend inward).
b) Angle of torsion: It describes the relative rotation(twist) that exists between the shaft and neck of the femur. Normally as viewed from above, the femoral neck longitudinal axis projects anterior to a medio-lateral(transverse) axis of the femoral condyles.
Normally the angle faces medially and anteriorly with average 10 to 15 degrees (anteversion). In infants, it is about 30-35 degree due to foetal position.
Its functions: • Since the hip joint can only tolerate a limited amount of torsion of the head without threatening congruence. • It plays a role in hip stability. • - it is one of the possible causes of excessive internal or external rotation of hip joint.
Pathologically: • Any abnormality in the angle can change the hip joint stability via changing the location of the femoral head in the acetabulum. • n.b. greater degree of femoral antversion or retroversion may be seen distally at the femoral condyles.
Excessive Anteversion: • Any increase in the anterior angulation (excessive anteversion)> 15 degree results in a greater internal rotation. Patients who toe in may have excessive anteversion as a compensatory mechanism the patient by which guide the excessively antiverted head more directly into the acetabulum, improves joint congruinty.
Femoral retroversion: • Conversely a greater degree of external rotation. Patients who toe out may have an excessive retroversion.
2- Acetabulum: forms the socket for the hip, cupped shaped, formed by three parts of pelvic bone (ilium, ichium, and pubis). In the anatomical position, the acetabulum projects laterally from the pelvis with a varying amount of inferior and anterior tilt. A misaligned acetabulum doe not adequately cover the femoral head, often causing chronic dislocation and osteoarthritis. Two angles describe the extent to which the shape of the acetabulum naturally covers the femoral head:
Angles of acetabulum: A-Center Edge angle" CEA“: is an angle between two lines: First line connects the lateral rim of the actabulum and the center of the femoral head. Second line is a vertical line. Its functions: *It determines the amount of inferior tilting of the acetabulum. *It describes the extent to which the acetabulum covers the femoral head within the frontal plane i.e. the normal center edge angle provides a protective shelf over the femoral head.
Magnitude: It is highly variable on average measures about 22 to 42 degrees in the x-ray of adults. A smaller CEA of the acetabulum may result in diminished coverage of the head of the femur and an increased risk of superior dislocation.
Pathologically: *a more vertical alignment (i.e., a smaller angle) offers less containment of the femoral head and is associated with an increased risk of superior dislocation. **if this angle increased, it provides more stability to the hip joint structure.
B- Acetabular antevertion angle: It describes the extent to which the acetabulum surrounds the femoral head within the horizontal plane. A normal acetabular anteversion angle is about 20 degrees The angle formed by the intersection between of an antro-posterior reference line and a line across the rim of the acetabulum.
Pathologically: Normally its existence leads to exposure of the anterior side of the femoral head. *The thick anterior capsular ligament of the hip and iliopsoas tendon cover this side of hip *Persons with excessive anteversion of both femur and acetabulum are susceptible to anterior dislocation, especially at extremes of external rotation.