Chapter 41 What Is the Best Treatment for Hip Displacement in Nonambulatory Patients with Cerebral Palsy?
Hip displacement in cerebral palsy (CP) is a common problem, particularly in nonambulant patients.1 Depending on age and severity of involvement, the incidence rate of hip displacement varies between 10% and 70%.2 Lack of stimulation to the femoral head and acetabulum by weight bearing, muscle spasticity, and asymmetrical posture may explain the greater incidence of displacement in the nonambulant children. The displacement is gradual, and secondary changes occur on both sides of the joint. The femoral head becomes oval-shaped, whereas acetabular dysplasia develops gradually with the formation of a grove-shaped deformity proximally. The direction of the displacement is superoposterior in the majority of patients. Posterior acetabular defects are more often seen in patients who progress to subluxation, whereas global defects are more common in patients with fully dislocated hips.3
It has been recommended that the migration percentage should be used to quantify the severity of the displacement,4 but the acetabular index has also been used.5 However, problems with the reliability of both measurements have been reported.1,6 Three-dimensional imaging, particularly as part of preoperative planning may be appropriate in investigating the direction of instability and acetabular deficiency.3
SCREENING FOR HIP DISPLACEMENT IN CEREBRAL PALSY
A retrospective review of the notes and radiographs of 462 patients with CP showed an overall dislocation rate of 10%. Measurement of the acetabular index by a method that allowed for rotation of the pelvis was the single-most important predictor of dislocation. A normal index at the age of 3 years would predict normal development of the hips, provided that clinical examination remained normal and no scoliosis developed5 (Level of Evidence 2).
A similar finding was presented in a prospective, population-based study of hip displacement in CP.4 Migration percentage was thought, however, to be the best guide to hip surveillance. The recommendation was that all children with bilateral CP should undergo a standardized position radiograph of their hips at the age of 30 months, to predict the risk for dislocation (Level of Evidence 2).
A population-based study in southern Sweden claimed that, with adequate screening and early intervention, the incidence of dislocation declined significantly, when compared with historical controls (Level IV evidence).7 The screening was based on a register of children with CP and, therefore, relied on its efficacy.
Radiologic surveillance of children with hips at risk was recommended by a retrospective (Level III evidence) study, which demonstrated a high incidence of dislocation in Gross Motor Function Classification System (GMFCS) level IV and V patients.1 Similarly, a greater risk for dislocation was identified in quadriplegic children who were not walking by the age of 5 years, when compared with diplegic patients.8
In conclusion, two of the studies4,5 suggest that a radiograph of the hips should be taken around the age of 2 to 3 years to assess the risk for hip dislocation. The presence of an abnormal acetabular index of more than 30 degrees or an abnormal migration percentage of more than 15% would indicate a significant risk for dislocation. A normal radiograph at this age would be reassuring, provided no changes occur on clinical examination of the hips over time. There is consensus in these articles that nonambulant children (GMFCS levels IV and V) are at greater risk and should be screened thoroughly (grade C).
Natural History and Indications for Treatment
Hip displacement in CP is a slow process, which allows secondary structural changes in the femoral head and the acetabulum.9 It has been suggested that these secondary changes occur early and, in some cases, before the evolution of hip instability.10
Pain, poor sitting balance, as well as prevention of windswept posture and the resulting pain have been suggested as indications for treatment of the displaced hip in CP.11 Loss of mobility in ambulant children, as well as decubitus ulceration and secondary deformity of the spine in the nonambulant ones, have also been suggested as indications.12 However, a comparison between quadriplegic children with scoliosis and hip displacement and children with the same diagnosis and spinal deformity but no hip displacement showed no effect of the hip displacement on the progression of the spinal curvature (Level III evidence). This was despite the greater incidence of pelvic obliquity in the group with hip displacement.13
Preventing dislocation, or reducing dislocated hips, requires that the treated hip represent an improvement on the natural history of the untreated hip. In 1990, Pritchett14 reported a cross-sectional study of 100 mature patients with total body involvement CP. Fifty had had hip surgery, and 50 had had no treatment. No differences were found in the level or frequency of pain, the sitting ability, pelvic obliquity, scoliosis, or nursing care between the groups. Nursing care difficulties and the ability to sit did not depend on the status of the hip. The conclusion drawn was that the surgical treatment of already dislocated hips of patients with severe CP is not helpful (Level of Evidence III).
A similar cross-sectional study of 77 patients older than 21 years with total body involvement CP attempted to correlate the radiographic status of the hip (dislocated, subluxed, arthritic) with clinical symptoms of hip pain, seating difficulty, and contractures.15 Clinical symptoms were obtained by caregiver interview and physical examination. Hip status was determined by radiographs with evaluators blinded to clinical status. The Ashworth scale of knee muscle spasticity was strongly correlated with hip pain, and with radiographic dislocation and osteoarthritis. The overall incidence rate of hip pain was low with only 18% definitely painful. The radiographic status of the hip (dislocated, subluxed, or osteoarthritic) was a poor predictor of which hips were painful. The authors conclude that surgical treatment of the hip be based on the presence of pain or contractures, and not on the radiographic status of the hip. This study can be considered Level II evidence regarding prognosis because it did not directly address the results of therapy.
PREVENTION OF HIP DISPLACEMENT AND THE ROLE OF SOFT-TISSUE SURGERY
It has been suggested that soft-tissue surgery around the hips can result in long-term radiographic stability in previously displaced hips.16–19 Preventative surgery in a cohort of 22 children followed up prospectively for a minimum of 5 years showed that 39 hips remained enlocated, whereas 5 were subluxed. None of the hips that was radiographically normal before surgery deteriorated in the follow-up period20 (Level of Evidence 4). The effectiveness of adductor tenotomy alone compared with more extensive releases and obturator neurectomy remains a controversial issue.21,22 However, agreement exists that a preoperative migration percentage of less than 40% would predict successful outcome22–24 (Level of Evidence 2). It has also been suggested that early surgery, before the age of 6 years, and postoperative bracing contribute to good results24,25 (Level of Evidence 4). Finally, nonsurgical postural control has also been claimed to limit hip displacement.26 These studies are limited by the small numbers of patients assessed, the lack of control subjects, and their retrospective design (Level IV evidence).
In a retrospective study of 65 children treated within a well-defined surgical protocol and followed up for a minimum of 8 years, it was found that prevention of dislocation was achieved in 67% of patients. Migration percentage at 1 year after surgery was a good predictor of outcome. Diplegic pattern and the ability to walk were also positive prognostic factors.27 A similar study of 78 patients followed-up for a mean of 10 years showed a favorable outcome in two thirds of the patients. Preoperative migration percentage of less than 50% was associated with a good result.28 However, a failure rate of 58% with continuing or recurrent subluxation was found in another retrospective study with 8 years of mean follow-up29 (Level of Evidence 4).
Iliopsoas transfer has also been suggested for the treatment of hip instability. A study of 39 patients over a mean of 8 years demonstrated that 45 of the 47 displaced hips remained enlocated. However, sitting ability had deteriorated in 50% of the patients.30 Disappointing results of the same operation have also been reported31 (Level of Evidence 4).
In a population-based study from Sweden, it was shown that the introduction of preventative measures to treat spasticity or dystonia reduced the incidence of hip dislocation, compared with historical control subjects. Preventative measures included selective dorsal rhizotomy, continuous intrathecal Baclofen infusion, botulinum toxin injections, and nonsurgical treatment of contractures.7,32 A prospective, open-label case series has also demonstrated that controlling spasticity with continuous intrathecal Baclofen infusion led to improvement or no deterioration of more than 90% of displaced hips within the first 12 months from implantation of the baclofen pump. The observed changes were not associated with age or severity of involvement33 (Level of Evidence 4). A retrospective study of patients with spastic diplegia before and after selective dorsal rhizotomy showed that 93% of all hips were stable after surgery. However, the follow-up time was short, and no control subjects were used.34
An American Academy of Cerebral Palsy and Developmental Medicine evidence report concludes that the published evidence on the effects of adductor surgery in CP should be “regarded as preliminary at best.”35 The lack of long-term studies and comparison with control subjects was highlighted. The need to study the reliability and validity of the radiographic methods was also discussed (grade I).
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