Hip Range of Motion

Hip Range of Motion include motion in three planes:

1. sagittal (flexion and extension around a transverse axis),
2. frontal (abduction and adduction around an anteroposterior axis),
3. transverse (internal and external rotation around a vertical axis).

Hip Range of Motion

Hip range of motion is variable. Hip flexion averages 110–120 degrees, extension 10–15 degrees, abduction 30–50 degrees, and adduction 25–30 degrees. Hip external rotation averages 40–60 degrees and internal rotation averages 30–40 degrees.

End-range hip flexion is associated with a posterior rotation of the ilium bone. The end range of hip extension is associated with an anterior rotation of the ilium. Hip abduction / adduction are associated with an upward / downward tilting of the pelvis.

Measuring hip range of motion has consistently been shown to be highly reliable and when limited in three planes can be fairly useful in identifying hip OA (+LR [likelihood ratio] = 4.5 to 4.7).

Assessing pain during range-of-motion measurements can be helpful in identifying both OA and lateral tendon pathologic conditions. Lateral hip pain during passive abduction is strongly suggestive of lateral tendon pathologic disorders (+LR = 8.3), whereas groin pain during active hip abduction or adduction is moderately suggestive of OA (+LR = 5.7).

Limited hip abduction in infants can also be very helpful in identifying hip dysplasia or instability.

See Also: Thomas Test

Hip Biomechanics

In the human body, the center of gravity is located at the second sacral vertebral level, several segments above and medial to the femoral head.

The relationship between the proximal femur, the greater trochanter, and the overall femoral neck width is affected by muscle pull and the forces transmitted across the hip joint. In addition, normal joint nutrition, circulation, and muscle tone during development play an important role.

In the anatomic position, the orientation of the femoral head causes the contact force between the femur and the acetabulum to be high in the anterosuperior region of the joint. Since the anterior aspect of the femoral head is somewhat exposed in this position, the joint has more flexibility in flexion than extension.

The femoral neck is subjected to shearing and torsional strains because of its oblique orientation to the shaft of the femur. Downward forces act to displace the femoral head inferiorly and to bend the femoral neck downward.

The most stable position of the hip is the normal standing position: hip extension, slight abduction, and slight internal rotation.

The commonly cited resting positions of the hip are between 10 and 30 degrees of flexion, 10–30 degrees of abduction, and 0–5 degrees of external rotation.

Hip Inclination Angle

The angle between the femoral shaft and the neck is called the collum/ inclination angle.

This angle is approximately 125–130 degrees but can vary with body types, in a tall person, the collum angle is larger. The opposite is true with a shorter individual.

The collum angle has an important influence on the hips:

• An increase in the Inclination Angle causes the femoral head to be directed more superiorly in the acetabulum and is known as coxa valga.
• If the Inclination Angle is reduced, resulting in a more horizontal orientation of the femoral neck, it is known as coxa vara.

Coxa valga has the following effects at the hip joint:

• It alters the orientation of the joint reaction force (JRF) from the normal vertical direction to one that is almost parallel to the femoral shaft. This lateral shift of the JRF reduces the available weight bearing surface, resulting in an increase in stress applied across joint surfaces not specialized to sustain such loads.
• The moment arm of the hip abductors is shortened, placing these muscles in a position of mechanical disadvantage. This causes the abductors to contract more vigorously to stabilize the pelvis, producing an increase in the JRF.
• It increases the overall length of the lower extremity.
• coxa valga decreases the normal physiologic angle at the knee, which places an increased mechanical stress on the medial aspect of the knee joint and more tensile stress on the lateral aspect of the joint.

Coxa Vara has the following effects at the hip joint:

• Coxa Vara increases the downward shear forces on the femoral head and the tensile stretching forces through the superior trabecular bone along the lateral portion of the neck.
• In coxa vara, the joint compression forces are significantly reduced as the greater trochanter is displaced lateral and superior, which increases the effective angle of pull and the lever arm of the hip abductors.
• While the reduced compressive forces generated across the joint surfaces serve to decrease the incidence of articular cartilage damage, the increase in shearing and torsional forces at the femoral head/neck junction significantly increases the incidence of damage to the epiphyseal plate.

Hip Torsion Angle

Femoral alignment in the transverse plane also influences the mechanics of the hip joint. The hip torsion angle of the femur describes the relative rotation that exists between the shaft and the neck of the femur.

Normally, as viewed from above, the femoral neck projects on average 5–15 degrees anterior to a mediolateral axis to the femoral condyles. An anterior orientation of the femoral neck to the transverse axis of the femoral condyles, is known as hip anteversion, or a reverse orientation known as hip retroversion.

The normal range for femoral alignment in the transverse plane in adults is 5 degrees of anteversion.

Typically, an infant is born with about 30 degrees of femoral hip anteversion. This angle usually decreases to 15 degrees by 6 years of age because of bone growth and increased muscle activity. Subjects with excessive hip anteversion usually have more hip internal rotation ROM than external rotation, and gravitate to the typical “frog sitting” posture as a position of comfort. There is also associated in-toeing while weight-bearing.

Excessive hip anteversion directs the femoral head toward the anterior aspect of the acetabulum when the femoral condyles are aligned in their normal orientation.

When body weight is evenly distributed across both legs during upright standing, the forces acting on the hip joint are equivalent to half the partial weight made up of the trunk, head, and upper extremities. Were this partial body weight to represent 60% of total body mass, then each hip would be compressed by a force equal to 30% of the total body weight.

References

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