Abnormal structure or impaired function of the hip—such as a leg-length discrepancy, decreased flexibility, or muscle imbalances—can contribute to stress in the spine or other joints of the lower extremities.
Decreased Flexibility

Decreased flexibility in the structures around the hip joint cause weight-bearing forces and movement to be transmitted to the spine rather than absorbed in the pelvis. Tight hip extensors cause increased lumbar flexion when the thigh flexes. Tight hip flexors cause increased lumbar extension as the thigh extends. Hip flexion contractures with incomplete hip extension during weight bearing also place added stresses on the knee because the knee cannot lock while the hip is in flexion unless the trunk is bent forward. During weight bearing tight adductors cause lateral pelvic tilt opposite the side of tightness and side bending of the trunk toward the side of tightness. The opposite occurs with tight abductors.

Asymmetrical Leg Length
Functional as well as structural asymmetries of the lower extremities affect the posture of the pelvis.

Unilateral short leg. A unilateral short leg causes lateral pelvic tilting (drop on the short side) and side-bending of the trunk away from the short side (convexity of lateral lumbar curve toward side of short leg). This may lead to a functional or eventually a structural scoliosis. Causes of a short leg could be unilateral lower extremity asymmetries such as flat foot, genu valgum, coxa vara, tight hip muscles, anteriorly rotated innominate bone, poor standing posture, or asymmetry in bone growth.

Coxa valga and coxa vara. A pathologically large angle of inclination between the femoral neck and shaft of the femur is called coxa valga, and a pathologically smaller angle is called coxa vara. Unilateral coxa valga results in a relatively longer leg on that side and associated genu varum. Unilateral coxa vara leads to a relatively shorter leg with associated genu valgum.

Anteversion and retroversion. An increase in the torsion of the femoral neck is called anteversion and causes the shaft of the femur to be rotated medially; a decrease in the torsion is called retroversion and causes the shaft of the femur to be rotated laterally. Anteversion often results in genu valgum and pes planus. Unilateral anteversion results in a relatively shorter leg on that side; retroversion causes the opposite effects.

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