Overview
Definition:
Cerebral palsy (CP) is a group of permanent disorders of the development of movement, posture and activity, attributed to non-progressive disturbances that occurred in the developing fetal or infant brain
Hip involvement is common in CP, leading to subluxation and dislocation
Hip surveillance is a systematic, multidisciplinary approach to monitor and manage hip joint integrity in children with CP to prevent or mitigate hip displacement.
Epidemiology:
Approximately 15-25% of children with CP develop hip subluxation or dislocation
The risk is higher in individuals with more severe motor impairment, particularly those with spastic quadriplegia and ataxic CP
The incidence of progressive hip displacement increases with age and is most rapid during periods of growth spurts.
Clinical Significance:
Untreated hip displacement in CP can lead to significant pain, functional decline, difficulty with sitting and mobility, pressure sores, and challenges with hygiene and caregiving
Early detection and intervention through diligent hip surveillance are crucial to preserve hip joint function, alleviate pain, and improve the overall quality of life for affected children and their families.
Risk Factors For Hip Displacement
Gross Motor Function Classification:
Higher Gross Motor Function Classification System (GMFCS) levels (IV and V) are associated with a significantly increased risk of hip displacement.
Type Of Cp:
Spastic quadriplegia, diplegia, and dyskinetic CP have a higher prevalence of hip involvement compared to hemiplegia or ataxic CP.
Adductor Spasticity:
Severe adductor spasticity contributes to increased medial forces on the femoral head, predisposing to subluxation.
Age And Growth:
The risk of displacement is highest during periods of rapid growth, particularly between ages 4-6 years and during puberty.
Premorbid Hip Abnormalities:
Pre-existing hip dysplasia or instability at birth increases the risk.
Hip Surveillance Protocol
Age Of Initiation:
Surveillance typically begins around 18-24 months of age or when the child is able to sit independently, and continues until skeletal maturity, with frequency adjusted based on risk.
Frequency:
Children at high risk (e.g., GMFCS IV-V, severe spasticity) require more frequent monitoring, often every 6 months initially, then annually
Lower-risk children may be monitored annually.
Imaging Modality:
Standard anteroposterior (AP) pelvis X-rays are the primary imaging modality
Ultrasound may be used in very young infants with risk factors, but X-rays are essential for quantitative assessment of migration percentage.
Radiographic Assessment:
Key measurements include the acetabular index, the center-edge angle of Wiberg, and the migration percentage
Dynamic imaging like fluoroscopy may be used in select cases to assess dynamic subluxation.
Migration Percentage Calculation And Interpretation
Definition:
The migration percentage (MP) is a radiographic measure of hip subluxation
It quantifies the degree to which the femoral head is displaced laterally within the acetabulum.
Measurement Technique:
On an AP pelvic radiograph, the width of the femoral head is measured (FH)
A line is drawn across the superior aspect of the triradiate cartilage (acetabular roof)
A vertical line is drawn from the lateral margin of the acetabulum down to this horizontal line
The distance between the medial edge of the femoral head and this vertical line represents the lateral displacement
MP = (Lateral Displacement / FH) x 100%.
Normal Values:
A migration percentage of 0-30% is generally considered within normal limits or mild subluxation
Values between 30-50% indicate moderate subluxation, and >50% suggests significant subluxation or dislocation.
Interpretation And Thresholds:
A migration percentage >30-40% is often considered a threshold for intervention, though this can vary based on clinical presentation, GMFCS level, and institutional protocols
Progressive increase in MP over serial radiographs is a critical indicator for intervention.
Radiographic Signs Of Instability:
Other signs include a steep acetabular angle, poorly formed acetabulum, and progressive lateralization of the femoral epiphysis.
Management Strategies
Conservative Management:
For mild subluxation (MP 30-40%) or early signs of progression in low-risk children, non-surgical options like bracing (e.g., Pavlik harness, hip abduction orthoses) may be considered
Regular physiotherapy to maintain range of motion and reduce spasticity is crucial.
Surgical Management Indications:
Surgical intervention is generally indicated for MP >40-50%, rapidly progressive subluxation, or painful dislocation
The goal is to achieve a stable, contained femoral head within the acetabulum.
Surgical Procedures:
Surgical options include soft-tissue procedures (e.g., tenotomies of adductors/iliopsoas), bony procedures (e.g., acetabuloplasty like Pemberton or Shelf procedure, femoral osteotomy), or a combination thereof
Hip reduction surgery is performed for irreducible dislocations.
Postoperative Care:
Postoperative management often involves casting (e.g., spica cast) for 6-8 weeks followed by progressive weight-bearing and intensive physiotherapy
Long-term surveillance is essential.
Key Points
Exam Focus:
Understand the definition and calculation of migration percentage
Know the critical MP thresholds for intervention
Be familiar with risk factors for hip displacement in CP (GMFCS, type of CP, spasticity)
Recognize common imaging findings and management options.
Clinical Pearls:
Start hip surveillance early in at-risk children
Adjust surveillance frequency based on risk stratification
Early detection of progressive MP is key to successful management
Multidisciplinary approach involving pediatrics, orthopedics, physiotherapy, and radiology is vital.
Common Mistakes:
Delaying surveillance initiation or follow-up
Underestimating the risk in less severe CP
Misinterpreting radiographic measurements
Not considering the progressive nature of hip displacement in CP
Inadequate multidisciplinary collaboration.