About one in three children with cerebral palsy will develop hip displacement, where the top of the thigh bone gradually slides out of the hip socket. Sadly it's one of the most common orthopedic problems in CP, but also one of the most preventable.
What makes it dangerous is how quietly it happens. Early displacement usually causes no pain at all. A child can be sliding toward a dislocation for years while nothing about their day looks different, and the first clear symptom often arrives at the point where the repair has become a major operation.
Hip surveillance addresses that problem: a set schedule of x-rays and clinical checks, based on age and motor function, designed to find the drift long before anyone feels it.
“A hip that is sliding out of place doesn't typically hurt at first. By the time a child is in pain, simple options may be gone. That gap is the reason for surveillance.”
— Cerebral Palsy Center Editorial Team
Why hips drift out of place
A hip socket deepens in response to force. In typical development, standing and walking press the head of the femur into the socket, and the socket grows around it. When a child has limited weight-bearing, and when spastic muscles pull unevenly across the joint, that shaping force is missing or misdirected. The socket stays shallow and the femoral head slides outward.
Risk tracks closely with the Gross Motor Function Classification System. Children at GMFCS Levels IV and V, who use a wheelchair for most mobility, carry the highest risk. Children at Level I carry the lowest. This explains why surveillance schedules are set by GMFCS level rather than applied identically to every child.
The number to track: migration percentage
On a hip x-ray, a radiologist or orthopedic surgeon measures the migration percentage, which is simply how much of the femoral head sits outside the bony socket. This is the number that factors into most decisions.
Once migration passes 30%, the finding is significant and needs attention. Beyond roughly 50%, care generally moves to hip reconstruction. The window between those two figures is where the less invasive options exist, including procedures such as proximal femoral guided growth, which works with a child’s remaining growth rather than against it.
That window is the whole argument for surveillance. It is a range you can only catch on film, because a child going through the early stages typically feels fine.
What happens when dislocation is missed
A hip left to dislocate completely doesn't simply stay put in the wrong position. The femoral head loses its round shape against the soft tissue it now rests on, and a misshapen head is likely to become painful and arthritic. At that stage, the options are salvage surgery rather than reconstruction, and the goal shifts from preserving a working joint to managing pain.
Programs that screen systematically reduce the number of hips that go on to full dislocation, and reduce the need for salvage procedures. This is the rare situation where a routine, unglamorous x-ray changes the trajectory of a child's outcome.
What surveillance programs look like
The American Academy for Cerebral Palsy and Developmental Medicine publishes a hip surveillance care pathway that sets out when to screen, clinically and radiographically, based on a child’s age and GMFCS level. Shriners Hospitals for Children publishes guidelines as well, and the HipScreen app exists to help clinicians apply the schedule.
Several countries run population-based programs. Sweden and Australia established systematic screening years ago, and in Canada, Child Health BC built a province-wide program whose authors reported a difference in dislocation rates and in the number of surgical interventions required once the systematic approach was in place.
The United States has no single national program. Schedules vary between centers, and in practice that means a family may need to raise the subject themselves.
What to ask at your child's next appointment
- What is my child’s GMFCS level? The whole schedule is built on it, and many families have never been told the number.
- When was the last hip x-ray, and what was the migration percentage? Ask for the figure, not just “it looked fine.”
- When is the next one due? Get it in writing and put it in your own calendar.
- Is anyone tracking this over time? A single reading matters far less than the trend across several years.
Hip health sits alongside the rest of an orthopedic plan. Our guide to surgery in cerebral palsy covers how reconstruction and other procedures fit into long-term care.
