Hip joint pain in spastic dislocation: aetiological aspects

AIM Children with severe forms of cerebral palsy (CP) are at high risk of hip joint displacement. Various studies have found that the pain from affected joints occurs in 40 to 84% of studied individuals. The purpose of this study was to establish a correlation between the density of nociceptors localized in selected areas of the spastic dislocated hip joint and clinical evidence of hip joint pain in children with CP. METHOD Nineteen samples of articular capsule and 19 samples of teres ligaments, collected during open hip joint reduction from 19 non-ambulatory children with spastic CP (Gross Motor Function Classification System level V; mean age 9y 6mo; 10 males, nine females), were studied. Pain was assessed using the numeric rating scale completed by caregivers. The density of nociceptive fibres was compared between the children with painful and children with painless hip joints, using S-100 and substance P monoclonal antibodies. RESULTS The presence of S-100 protein and substance P were significantly increased (p=0.024 and p=0.02 respectively) in the children with painful hip joints. There were significantly positive correlations between the intensity of pain and the density of nerve fibres with S-100 protein (teres ligament, p=0.001; joint capsule, p=0.032) as well as substance P (teres ligament, p=0.001). INTERPRETATION Direct and indirect inflammatory factors, present in dislocated hip joints with cartilage damage in children with spastic CP, lead to hip joint sensitization. Children with severe forms of cerebral palsy (CP) are at high risk of hip joint displacement. 1–4 In spite of the fact that hip joints in children with CP and those in the healthy population are similar at birth, muscle imbalance, leading to an increase in the angle of the femoral neck shaft, femoral anteversion, and acetabular dysplasia, may result in hip joint dislocation. The possibility of hip joint instability is related to motor type, topographical distribution, and the category of muscle pathology, as well as to the functional status of each child. The highest risk groups for hip joint instability are children with spastic quadriplegia (82%) and those with a dystonic and hypotonic type of CP, with a 40% and 44% risk respectively. 5 Moreover, 44% of children classified at Gross Motor Function Classification System (GMFCS) level IV presented hip joint displacement and 64% at GMFCS level V. 6