Articulation of the acetabulum of the pelvis and the head of the femur
Hip joint
Diarthrodial ball-and-socket joint with three degrees of freedom: flexion/extension in the sagittal plane, abduction/adduction in the frontal plane, medial/lateral rotation in the transverse plane
Supports the weight of the head, arms, and trunk (HAT) both in static erect posture and in dynamic postures
"acetabulum"
Lateral aspect of the pelvic bone (innominate or os coxa): ilium, ischium, pubis
Ischium forms 2/5, ilium forms 2/5, pubis forms 1/5 of the acetabulum
Acetabulum
Periphery (lunate surface) is covered with hyaline cartilage (horseshoe-shaped)
Inferior aspect of the lunate surface (the base of the horseshoe) is interrupted by a deep notch called the acetabular notch
The acetabular notch is spanned by the transverse acetabular ligament that connects the two ends of the horseshoe
Forms a fibro-osseous tunnel through which blood vessels pass into the deepest portion of the acetabulum called the acetabular fossa
Deepened by the fibrocartilaginous acetabular labrum, which surrounds the periphery of the acetabulum
Normal functioning of the hip requires optimal femoral head coverage by the acetabulum; femoral head coverage is largely determined by acetabular depth
Acetabular depth
Can be measured as the center edge/angle of Wiberg formed by a line connecting the lateral rim of the acetabulum and the center of the femoral head and a vertical line from the center of the femoral head
Acetabular dysplasia
Abnormally shallow acetabulum that results in a lack of femoral head coverage
Normal->25°, definite dysplasia- <16°, possible dysplasia -16° to 25, may indicate excessive acetabular overcoverage->40°
Coxa profunda and acetabular protrusio
Conditions in which the acetabulum excessively covers the femoral head, leading to limited range of motion (ROM) and internal impingement between the femoral head-neck junction and acetabulum
Anteversion of the acetabulum
Acetabulum is positioned too far anteriorly in the transverse plane
Anteversion of the acetabulum
Acetabulum that is positioned with less inclination
Can lead to instability
Retroversion of the acetabulum
Acetabulum is positioned too far posteriorly in the transverse plane
Retroversion of the acetabulum
Acetabulum that is positioned with more inclination
Can lead to overcoverage and impingement between the acetabulum femoral-head neck junction
Acetabular Labrum
A ring of wedge-shaped fibrocartilage that rims the entire periphery of the acetabulum
Functions of the acetabular labrum
Deepens the acetabulum
Acts as a seal to maintain negative intra-articular pressure
Decreases force transmitted to the articular cartilage
Provides proprioceptive feedback
Abnormally shallow acetabulum
Increases stress on the surrounding capsule and labrum
Transverse acetabular ligament
Considered to be part of the acetabular labrum
Femoral head
Attached to the femoral neck; the femoral neck is attached to the shaft of the femur between the greater and lesser trochanters
Femoral head
Angulated so that the femoral head faces medially, superiorly, and anteriorly
Articular area of the femoral head forms approximately 2/3 of a sphere and is more circular than the acetabulum
Fovea or fovea capitis
Small, roughened pit inferior to the most medial point on the femoral head
Not covered with articular cartilage and is the point at which the ligament of the head of the femur (ligamentum tares) is attached
Angle of inclination
Occurs in the frontal plane between an axis through the femoral head and neck and the longitudinal axis of the femoral shaft
Angle of torsion
Occurs in the transverse plane between an axis through the femoral head and neck and an axis through the distal femoral condyles
Normal angle of inclination
Greater trochanter lies at the level of the center of the femoral head
Normal range 110° to 144° (approximates 125°)
Angle of inclination of the femur changes across the life span
It approximates 150° at birth and gradually declines to about 125° at skeletal maturity, then continue to decline again in the elderly
Coxa valga
Pathological increase in the angulation between the neck and shaft
Coxa vara
Pathological decrease in the angulation between the neck and shaft
Coxa Valga
Angle of inclination in the femur is greater than 125°
Brings the vertical weight-bearing line closer to the shaft of the femur, diminishing the shear, or bending, force across the femoral neck
Decreases the length of the moment arm of the hip abductor muscles
Abductor muscles will be unable to meet the increased demand and will be functionally weakened
Reduction in force is actually reflected in a reduction in density of the lateral trabecular system
Decreases the amount of femoral articular surface in contact with the dome of the acetabulum
Decreases the stability of the hip and predisposes the hip to dislocation
Coxa Vara
Gives the advantage of improved hip joint stability
Decreased angle between the neck and shaft of the femur will turn the femoral head deeper into the acetabulum
Increase the length of the moment arm of the hip abductor muscles by increasing the distance between the femoral head and the greater trochanter
Seen by the increased density of trabeculae laterally in the femur, caused by the increase in tensile stresses
The increased shear force along the femoral neck will increase the predisposition toward femoral neck fracture
Slipped capital femoral epiphysis/SCFE
Results when weight-bearing forces slide the femoral head inferiorly on the cartilaginous epiphysis of the head of the femur
The epiphyseal obliquity makes the plate more vulnerable to shear forces at a time when the plate is already weakened
Most common adolescent hip disorder occurring when the femoral head displaces posteriorly on the femoral neck at the level of the growth plate (physis)
Angle of Torsion of the Femur
Best be viewed by looking down the length of the femur superiorly
Axis through the femoral head and neck in the transverse plane will lie at an angle to an axis through the femoral condyles, with the head and neck torsioned anteriorly (laterally) with regard to an angle through the femoral condyles
Angle of anterior torsion decreases with age
In the newborn, 30° to 40°
This angle decreases of approximately 1.5° per year until skeletal maturity
In the adult, 10° to 20° (15° for males and 18" for females)
Femoral Anteversion
Angle of anterior torsion is greater than 15° to 20°
Associated with increased medial rotation ROM and concurrent decreased lateral rotation so that the total excursion of hip rotation motion remains the same
Femoral anteversion and coxa valga are commonly found together (but each may occur independently of the other)
Reduces hip joint stability because the femoral articular surface is more exposed anteriorly
Line of the hip abductors may fall more posterior to the joint, reducing the moment arm for abduction resulting need for additional abductor muscle force
Medial femoral torsion
Abnormal position of the knee joint axis
Medial femoral torsion
Same abnormal condition as femoral anteversion
Femoral anteversion
Alters the mechanics at the hip joint
Medial femoral torsion
Alters the mechanics at the knee joint
When femoral head is anteverted
1. Anterior capsuloligamentous structures and musculature may push the femoral head back into the acetabulum
2. Causes the entire femur to rotate medially with toe-in
Toe-in position of the foot
May appear to diminish over time
Underlying hip problem
Generally remains, even though foot placement looks better
Femoral retroversion
Opposite of anteversion, creates problems opposite those of femoral anteversion