Cerebral Palsy Hip Surveillance

Hip displacement is a predictable musculoskeletal complication of cerebral palsy, especially in children with limited ambulatory function. The hip may migrate laterally before pain is obvious. Once a hip becomes chronically dislocated, stiff and painful, treatment becomes more complex and often shifts from prevention to salvage.

Hip surveillance exists to prevent that pathway. It identifies children at risk, obtains AP pelvis radiographs at scheduled intervals, measures Reimers migration percentage and escalates care when the hip is migrating or symptoms develop. The program is not simply a radiograph schedule; it is a coordinated assessment of mobility, tone, hip motion, pelvis, spine, seating, hygiene and family goals.

The guiding principles are:

• Higher GMFCS level means higher displacement risk.
• Migration percentage trend is more useful than a single number in isolation.
• Loss of abduction and care difficulty are meaningful clinical changes.
• Hip and spine problems interact through pelvic obliquity and windswept posture.
• Early prevention is preferable to late salvage.

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Hip displacement in cerebral palsy is driven by muscle imbalance, spasticity, weakness, abnormal posture and growth. Adductors and hip flexors tend to pull the femoral head laterally and superiorly. Coxa valga, excessive femoral anteversion and acetabular dysplasia reduce containment. Non-ambulant children have less protective loading and less active muscle balance around the hip.

As the femoral head migrates, acetabular development worsens. The acetabulum no longer sees a centred femoral head, so dysplasia can progress. Pelvic obliquity, scoliosis and windswept posture can then magnify asymmetry. A hip that began as a painless radiographic migration may become a painful stiff dislocation that affects sleep, sitting, hygiene and transfers.

History

Do not ask only "does the hip hurt?" A non-verbal or medically complex child may show hip problems through care difficulty, sleep disturbance, irritability or seating intolerance. Confirm or assign GMFCS level from real-world mobility: independent walking, walking with aids, wheelchair use, self-mobility and transfer function.

Ask about:

• Pain during dressing, nappy changes, toileting, transfers or physiotherapy.
• Sitting tolerance, pelvic obliquity, wheelchair fit and equipment problems.
• Sleep disturbance, rest pain or irritability.
• Hygiene difficulty and perineal care.
• Standing frame tolerance and ability to weight bear.
• Previous botulinum toxin, adductor releases, hip surgery or spine surgery.
• Feeding, nutrition, respiratory status, seizures and bone health.
• Family priorities: comfort, sitting, sleep, hygiene and ease of care.

Examination

Examine both hips and the whole sitting unit: pelvis, spine, hips, knees and feet. Measure hip abduction with hips flexed and extended. Assess adductor tone, psoas tightness, hamstring tightness, flexion contracture, pelvic obliquity, scoliosis and windswept posture. Look for pain with gentle range of motion and document skin pressure risk.

AP pelvis

The core investigation is a standardised AP pelvis radiograph. Positioning should be as consistent as possible, because pelvic rotation and abduction can affect measurement. Measure both hips and record migration percentage. Compare with previous images; trend is central.

Reimers migration percentage

Migration percentage is the proportion of the femoral head lateral to the acetabular reference line. It is calculated as lateral uncovered head width divided by total femoral head width, multiplied by 100. It should be recorded consistently and used with the child's age, GMFCS level, hip abduction and symptoms.

Additional imaging

Spine imaging may be needed when scoliosis and pelvic obliquity affect sitting and hip position. CT or additional imaging is selective and usually reserved for complex reconstructive or salvage planning.

Pain or care difficulty in a child with cerebral palsy is not always the hip. The non-verbal child cannot localise the problem, so the clinician must actively exclude common mimics before attributing distress to hip displacement. Migration percentage anchors the assessment, but a high migration percentage does not prove that the hip is the source of a new symptom.

The practical rule: in a distressed non-verbal child, examine the hip, the spine, the abdomen and the skin before concluding the hip is to blame, and confirm the hip hypothesis with a standardised migration percentage rather than examination alone.

Missed or delayed surveillance

• Silent migration progresses to fixed subluxation or dislocation.
• Acetabular dysplasia becomes harder to reconstruct.
• Pain, sleep disturbance and hygiene difficulty become established.

Surgical and postoperative complications

• Wound problems or infection.
• Respiratory, nutrition or medical complications in medically complex children.
• Cast, brace or positioning difficulty.
• Loss of reduction or recurrent subluxation.
• Avascular necrosis, stiffness or heterotopic ossification.
• Hardware pain or need for removal.

Long-term problems

• Painful chronic dislocation.
• Pelvic obliquity and scoliosis interaction.
• Recurrent displacement.
• Persistent care difficulty despite radiographic improvement.

Hip surveillance in cerebral palsy is a prevention pathway. The aim is to identify progressive migration early enough that soft-tissue balancing, bony containment surgery or salvage decisions can be made before the hip becomes painful, fixed or unreconstructable.

The examination must be linked to the radiograph. Hip abduction, pain with movement, pelvic obliquity, sitting tolerance, hygiene, sleep and transfers matter because the purpose of treatment is not a number on an X-ray; it is a painless, mobile, careable hip. The migration percentage remains the central surveillance measure, but treatment is chosen by combining migration, acetabular development, femoral head shape, femoral anteversion, neck-shaft angle, muscle balance and child-specific goals.

A useful treatment sequence is: identify risk by GMFCS, measure migration reliably, watch the rate of change, preserve abduction, contain the hip before fixed dislocation, and follow long enough to detect recurrence. A child whose migration percentage continues to rise after soft-tissue surgery needs reassessment for bony reconstruction rather than repeated isolated releases.

Hip surveillance is one of the clearest examples in paediatric orthopaedics where coordinated programmes change outcomes at a population level. The principles are remarkably consistent worldwide: stratify by GMFCS, measure migration percentage on a standardised AP pelvis, and act on trend before pain. The differences lie in thresholds, schedules and access.

Global epidemiology

• Cerebral palsy affects roughly 2 per 1000 live births and is the commonest cause of childhood physical disability worldwide.
• Hip displacement is the second most common musculoskeletal deformity in cerebral palsy after equinus.
• Displacement risk tracks GMFCS almost linearly: close to 0 percent at GMFCS I rising to around 60 to 90 percent at GMFCS V across population cohorts.
• CP subtype matters: near 0 percent risk in pure ataxia versus up to about 79 percent in spastic tetraplegia.
• Without surveillance, late painful dislocation historically affected a meaningful minority of non-ambulant children; structured programmes reduce dislocation to around or below 0.5 percent.

Side-by-side guidance

Registries and programmatic data

• CPUP (Sweden) and CPIP (United Kingdom, Scotland and others) are the model national registries, providing the strongest population evidence that surveillance prevents dislocation.
• Registry data underpin risk tools such as the CPUP Hip Score and allow external validation across countries.
• Common themes: standardised migration percentage measurement, GMFCS-linked schedules and prospective audit of dislocation rates.

High- versus limited-resource practice

• High-resource settings: universal registries, scheduled radiographs from age 1 to 2 years, multidisciplinary clinics and timely preventive surgery.
• Limited-resource settings: surveillance may be opportunistic, presentation is often late with established painful dislocation, and salvage rather than prevention may dominate.
• A pragmatic minimum anywhere is to identify GMFCS IV and V children, obtain a baseline AP pelvis, and arrange repeat imaging on any rising migration percentage even when a formal registry is unavailable.

Hip surveillance is well established, but several practical questions remain genuinely contested and are good viva discriminators.

• Exact referral threshold. Migration percentage of 30 percent (AACPDM) versus 33 percent versus 40 percent (several registry definitions of displacement) are all in use. The trend and rate of change often matter more than crossing a single number.
• Best frequency and stopping point of radiographs. Schedules differ by GMFCS level and country, and the optimal point to discharge an ambulant child or a skeletally mature non-ambulant child is debated.
• Role of soft-tissue release alone. Adductor and psoas surgery can slow migration in younger children, but many hips progress and need later bony reconstruction. Selecting which early hips benefit remains imperfect.
• Timing of bony reconstruction. Whether to operate at a defined migration percentage or to wait for clear progression, and how to balance one-stage bilateral correction against staged surgery, varies between centres.
• Salvage choice. For a painful, unreconstructable dislocated hip there is no single best salvage; proximal femoral resection, valgus osteotomy, interposition and arthrodesis all have advocates, and the evidence is largely low level.
• Value of head-shaft angle and additional measures. Newer predictors (head-shaft angle, acetabular index) improve risk scores, but how much they should change individual decisions over migration percentage alone is still being defined.
• Surveillance after intervention. How long and how often to image after preventive or reconstructive surgery to detect recurrence lacks strong consensus.

Structured clinical approach

Use this sequence:

• Confirm or assign GMFCS from real-world mobility.
• Ask about care, sitting, hygiene, sleep, transfers and pain.
• Examine abduction, tone, contracture, pelvis and spine.
• Obtain AP pelvis and measure migration percentage.
• Decide surveillance interval, referral or treatment based on GMFCS, migration percentage, trend, abduction and symptoms.
• State the goal: comfortable located hips that support sitting, hygiene and care.

Common pitfalls

• Waiting for pain before imaging.
• Asking the family for a GMFCS label rather than assigning it from function.
• Treating adductor tightness without measuring migration percentage.
• Measuring only one hip.
• Forgetting pelvic obliquity and scoliosis.
• Offering reconstruction without discussing seating, hygiene and family goals.
• Thinking salvage care is only about the X-ray rather than comfort.