An anteroposterior (AP) pelvic X-ray is taken with the child lying flat with legs parallel. The Reimer's migration percentage (MP) is measured — the percentage of the femoral head that is uncovered by the acetabulum. Normal: less than 30%. At risk: 30–40%. Subluxated: 40–60%. Dislocated: over 60%. X-rays are repeated at intervals determined by the child's GMFCS level and the migration percentage. Non-walkers (GMFCS IV–V) are X-rayed every six months until age seven, then annually. Walkers (GMFCS I–III) are monitored annually.
Children with cerebral palsy have a high risk of hip displacement — approximately 35% of all children with CP, rising to 75–90% in non-ambulant children (GMFCS IV–V). Undetected hip displacement leads to painful dislocation, windswept deformity, and significant deterioration in quality of life. Surveillance enables early intervention — soft tissue release at 30–40% migration, bony reconstruction at 40–60%.
This IS the non-operative monitoring programme. The alternative — not monitoring — risks late diagnosis of hip displacement at a stage when only major salvage surgery is possible.
No preparation needed for X-rays. The programme is coordinated by the child's orthopaedic and physiotherapy team. In the UK, the CPIPS (Cerebral Palsy Integrated Pathway Scotland) and similar regional programmes standardise surveillance.
Early detection of hip displacement at a treatable stage. Prevention of painful hip dislocation. The Swedish hip surveillance programme reduced the rate of hip dislocation in CP from 10% to less than 0.5% over twenty years.
Radiation exposureExpected
Multiple pelvic X-rays over childhood. The dose from each X-ray is very low and the benefit of surveillance far outweighs the minimal radiation risk.
False positivesUncommon
A single elevated MP may not indicate progressive displacement — serial measurements showing a trend are more reliable.
No anaesthesia needed. The child lies on an X-ray table for a few seconds.
No recovery needed. If hip displacement is detected, treatment is discussed — ranging from physiotherapy and positioning to botulinum toxin injection, adductor release, or reconstructive hip surgery, depending on the degree of displacement.
GMFCS IV–V: pelvic X-ray every six months until age seven, then annually until skeletal maturity. GMFCS III: annually. GMFCS I–II: baseline and as clinically indicated. Continue until skeletal maturity.
Why is hip displacement so common in CP?
Spasticity and muscle imbalance cause the hip adductors and flexors to overpower the abductors and extensors, gradually pulling the femoral head out of the socket. The acetabulum does not develop normally without the stimulus of a well-located femoral head.
Does surveillance prevent dislocation?
Surveillance itself does not prevent dislocation — it detects displacement early so that timely intervention can prevent dislocation. The Swedish experience showed that systematic surveillance and early intervention reduced dislocation rates from 10% to less than 0.5%.
What happens if displacement is detected?
MP 30–40%: soft tissue surgery (adductor release, psoas lengthening) is considered. MP 40–60%: bony reconstruction (femoral varus derotation osteotomy with or without pelvic osteotomy). MP over 60%: reconstructive surgery or, in some cases, salvage procedures. The earlier intervention occurs, the simpler and more effective it is.