Which factors increase the risk of hip displacement in CP?

Which factors increase the risk of hip displacement in CP?

• A. Higher GMFCS levels (III-V), hip adductor–flexor spasticity, pelvic obliquity, reduced acetabular containment.
• B. Lower GMFCS levels (I-II) and no spasticity.
• C. Age under 2 years only.
• D. Increased upper limb spasticity only.

Answer: (A)

The main idea here is that hip displacement risk in cerebral palsy is driven by how severely affected the child is and how that affects hip mechanics over time. When someone has greater motor impairment (higher GMFCS level), they’re more likely to develop abnormal muscle forces around the hip, reduced mobility, and longer exposure to inefficient joint positioning. Hip adductor–flexor spasticity tightens the hip into adduction and flexion, creating contractures and changing the way the femoral head sits in the acetabulum. This abnormal positioning applies off-center, uneven loading on the joint, which over time pushes the femoral head out of the true containment of the socket. Pelvic obliquity compounds this problem by tilting the pelvis and altering acetabular orientation, leading to uneven joint forces and further decreasing containment. If the acetabulum itself is shallow or dysplastic, its ability to keep the femoral head centered is diminished, so displacement becomes more likely as the child grows and moves. In contrast, lower GMFCS levels (indicating less severe involvement) with little or no spasticity generally maintain better hip alignment, and age by itself—especially under two years old—does not determine displacement risk. Increased spasticity confined to the upper limbs doesn’t meaningfully affect hip mechanics, so it doesn’t elevate this risk.

The main idea here is that hip displacement risk in cerebral palsy is driven by how severely affected the child is and how that affects hip mechanics over time. When someone has greater motor impairment (higher GMFCS level), they’re more likely to develop abnormal muscle forces around the hip, reduced mobility, and longer exposure to inefficient joint positioning. Hip adductor–flexor spasticity tightens the hip into adduction and flexion, creating contractures and changing the way the femoral head sits in the acetabulum. This abnormal positioning applies off-center, uneven loading on the joint, which over time pushes the femoral head out of the true containment of the socket.

Pelvic obliquity compounds this problem by tilting the pelvis and altering acetabular orientation, leading to uneven joint forces and further decreasing containment. If the acetabulum itself is shallow or dysplastic, its ability to keep the femoral head centered is diminished, so displacement becomes more likely as the child grows and moves.

In contrast, lower GMFCS levels (indicating less severe involvement) with little or no spasticity generally maintain better hip alignment, and age by itself—especially under two years old—does not determine displacement risk. Increased spasticity confined to the upper limbs doesn’t meaningfully affect hip mechanics, so it doesn’t elevate this risk.