Principles of Management of Hip Deformity in Cerebral Palsy



Principles of Management of Hip Deformity in Cerebral Palsy





INTRODUCTION

Cerebral palsy (CP) is the most common cause of physical disability affecting children in developed countries.1 CP describes a group of permanent disorders of the development of movement and posture, causing activity limitation, which are attributed to nonprogressive disturbances that occurred in the developing fetal or infant brain.2,3 CP is defined by the presence of a static neurologic injury, with associated progressive musculoskeletal pathology.4,5,6 Hip displacement in children with CP is the second most common deformity after spastic equinus of the ankle and may progress from initial silent lateral subluxation to painful dislocation when left untreated.5,7,8

The most useful development in the classification of CP in recent years has been the creation of the Gross Motor Function Classification System (GMFCS).1 The GMFCS is a five-level ordinal grading system based on the assessment of self-initiated movement with emphasis on function with regard to sitting and walking. The risk of progression from hip displacement to dislocation is related to severity of neurologic involvement,9,10 walking ability,11,12 and is directly related to gross motor function as graded by the GMFCS7 (Figure 19.1).






FIGURE 19.1. The relationship between hip displacement (Reimers index >30%) versus gross motor function classification system (GMFCS) level. Adapted from Soo et al.7

Historically, the incidence of CP has been reported to range from 1.5 to 2.5 per 1000 live births in several well-designed, population-based studies.13 However, with recent improved resuscitation and care of the premature infant, a modest increase (3 per 1000 live births) has been reported in North America.14 A series of authors have reported that the prevalence of hip displacement in CP is related to the degree of body involvement, ranging from very low risk in children with spastic hemiplegia (1%) to very high risk in children with spastic quadriplegia (75%).8,11 Three large population-based studies have calculated that the overall prevalence of hip displacement is approximately 35% across a population of children with CP.7,15,16


PATHOPHYSIOLOGY

The majority of children with CP are born with anatomically “normal” hips without evidence of hip displacement or dislocation.17 However, the natural history of spastic hip disease places children at risk for progressive lateral hip displacement.18 In children with CP, this displacement is commonly referred to as “silent subluxation” as children
are often not symptomatic until the hip is dislocated and painful.

The altered brain function characteristic of CP includes loss of selective motor control, abnormal muscle tone, imbalance between agonists and antagonists, and impaired body balance mechanisms. The neurologic lesion associated with CP manifests as a nonprogressive or static encephalopathy; however, the associated musculoskeletal pathology is progressive, resulting in contractures of muscle tendon units, bony torsional deformity, and ultimately joint instability.5,19 Asymmetric muscle spasticity and power has long been felt to be a major contributor to hip instability in children with CP. Sharrard et al20 demonstrated progressive limitation of abduction, often associated with flexion deformity, was an indicator of early instability of the hip. In their study, they found that no hip with radiologic evidence of subluxation had abduction greater than 45°, suggesting limited abduction plays some role in the development of hip instability.

Two critical components to proximal femoral anatomy are anteversion of the femoral neck in the transverse plane and the femoral neck-shaft angle (NSA) in the coronal plane.21,22 Robin et al23 demonstrated that these two deformities were closely related to a child’s GMFCS level. In their study, they propose that increased femoral anteversion and NSA may be caused by persistent fetal alignment because of delayed walking and limitations in gross motor function. The combination of elevated femoral neck anteversion and NSA contributes to the increased risk of hip displacement. A proper understanding of this cascade helps in formulating a treatment plan (Figure 19.2).

Soo et al7 demonstrated a linear relationship between the rate of hip displacement and a child’s GMFCS level. In their population-based study, GMFCS V children demonstrated an incidence of hip displacement of 90%, whereas there were no cases of hip displacement in 114 children with CP who were GMFCS level I. Hägglund et al24 came to very similar conclusions with respect to his population-based study of children with CP in Sweden. Much can be learned from these population-based studies; knowledge and identification of groups of children with “hips at risk” for displacement are critical for planning surveillance programs and initiating early intervention.7,25,26






FIGURE 19.2. Pathophysiology associated with spastic hip subluxation.

In establishing a hip surveillance protocol, reliance on clinical examination alone is not sufficient; regular radiographic examination is also important.27 Early indicators for hip displacement include a patient’s GMFCS level, age, gait classification, and migration percentage (MP).28 Not surprisingly, isolated techniques to reduce spasticity or address adductor contracture alone have been ultimately disappointing in preventing hip displacement in higher level GMFCS children.29,30,31 Hip surveillance identifies children with progressive hip displacement but does not dictate the timing or type of intervention.32 Treatment must be tailored for the individual child taking into consideration all the factors mentioned in this section.


IMAGING AND CLASSIFICATION

Decisions for treatment regarding spastic hip displacement must be made in conjunction with a well-taken anteroposterior (AP) radiograph of the pelvis and hip joint in the supine position.33,34 For hip surveillance to be successful, a standardized radiographic technique must be followed, ensuring the reliability between interval radiographs and between patients.35 Recognition and positional correction of excessive femoral anteversion, hip flexion, and adduction contractures are necessary to generate accurate and reliable radiographs.23,34 Unrecognized hip flexion contracture will create a lordotic pelvis (increased anterior pelvic tilt), which can be corrected by raising the legs on pillows to flatten the lumbar spine.25 Positioning the legs parallel to each other will address the
adduction or abduction contractures, and pointing the patella upward will correct for excessive femoral anteversion.26 A film-focus distance of 115 cm has been suggested to standardize film magnification between patients.10

The most accepted and reproducible measurement for spastic hip displacement is Reimers’ MP,36,37 which is a measure of the femoral head’s containment within the acetabulum in the coronal plane.38 This measurement is obtained identifying both Hilgenreiner and Perkin lines and then measuring, as a percentage, the amount of the ossified femoral head that has migrated laterally beyond Perkin line. In cases of severe displacement, there is often a “gothic arch” deformity of the lateral acetabular margin, and in these cases, the midpoint of the lateral acetabular margin is used instead of Perkin line.37 The continuous measurement of the MP has proven to be valid, reliable, and useful in measuring hip displacement in children with CP.27,36,39,40

The definition of a hip “at risk” of instability is defined as having an MP greater than 30%.36 Miller and Bagg39 found that children (2 to 18 years) whose MP was greater than 60% progressed to dislocation (MP >90%) during childhood. Furthermore, those children (2 to 18 years) with an MP between 30% and 60% had equal rates of hip displacement (25%) and recommended close surveillance and surgical intervention to prevent hip dislocation. Settecerri and Karol41 noted that a preoperative MP greater than 50% was associated with poor results and a higher revision rate. Oh et al42 reported similar results using an MP greater than 50%, regardless of whether children were treated with femoral and pelvic osteotomy or femoral osteotomy in isolation. Terjesen43 examined a population-based cohort of 334 children with CP in Norway and found that the mean yearly progression in MP increased markedly with decreasing functional level, from 0.2% for GMFCS I to 9.5% for GMFCS V.

The trajectory of hip development in children and adolescents with CP can be described using a variety of tools, including serial measurement of the MP of Reimers, head shaft angle, and hip morphology at skeletal maturity. In 2008, a new CP hip classification scheme was introduced that included both quantitative (MP) and qualitative features (femoral head and acetabular deformity, pelvic obliquity, and break in Shenton line) of femoroacetabular deformity.44,45 The Melbourne CP Hip Classification System (MCPHCS) is a six-level ordinal grading scheme applied to children at skeletal maturity (closure of the triradiate cartilage).45 Although designed for children at skeletal maturity, Gose et al46 recently validated the MCPHCS for hip disease in children with CP between the ages of 2 and 7 with open triradiate cartilage. Recent studies have demonstrated the correlation between poor hip morphology at skeletal maturity and higher levels of pain and dysfunction.47 In more advanced dysplasia, CT provides essential information about the extent and location of acetabular deficiency.48


HIP SURVEILLANCE

Hip surveillance refers to systematic periodic clinical and radiographic assessment of the hips of children with CP, to detect hip displacement when it is early and more effective management options are available.33 Because of the increased risk of hip displacement in children with CP who do not walk, the first screening radiograph is usually advised at age 12 months and continued every 6 to 12 months until skeletal maturity.34,49,50 Surveillance may need to be continued after skeletal maturity if the hips remain unstable, especially in the presence of symptomatic displacement, pelvic obliquity, and progressive scoliosis. Hip surveillance programs have demonstrated the ability to identify early indicators of progressive hip displacement and, with appropriate and timely surgical intervention, prevent hip dislocation and the need for salvage surgery.33,34,49,50 Available surveillance guidelines on the Internet include the Australian Hip Surveillance Guidelines for Children with Cerebral Palsy (2014),51 the Swedish CPUP Radiographic Follow-Up to Prevent Hip Dislocation,52 the British Columbia Hip Surveillance Program,53 and the American Academy of Cerebral Palsy and Developmental Medicine Hip Surveillance Care Pathway.54

In establishing a hip surveillance protocol, reliance on clinical examination alone is not sufficient; regular radiographic examination is also important.27 Early indicators for hip displacement include a patient’s GMFCS level, age, gait classification and migration percentage (MP).28 Not surprisingly, isolated techniques to reduce spasticity or address adductor contracture alone have been ultimately disappointing in preventing hip displacement in higher level GMFCS children.29,30,31 Hip surveillance identifies children with progressive hip displacement but does not dictate the timing or type of intervention.32 Treatment must be tailored for the individual child taking into consideration all of the above-mentioned factors. Our Boston Children’s Hip surveillance guidelines were developed in 2013 and is used across our enterprise to standardize the practice of radiographic hip surveillance for children with neuromuscular conditions (Figure 19.3).


TREATMENT OPTIONS

Treatment of the hip needs to be considered in the context of overall management of the child, in the context of their family, and in the presence of multiple medical comorbidities. Tone reduction has a primary place in all treatment strategies. Medical comorbidities that may need to be investigated and managed prior to any form of hip surgery include the movement disorder, respiratory illness, epilepsy, bone health, nutrition, and gastrointestinal function. In particular, optimization of the movement disorder using various combinations of oral medications, neurolytic blocks, and occasionally intrathecal baclofen


may result in less postoperative pain and fewer complications than in children in whom movement disorder management has not been optimized. Broad treatment guidelines are shown in Figure 19.4.






FIGURE 19.3. Boston Children’s Hospital Cerebral Palsy Hip surveillance guidelines. AP, anteroposterior; GMFCS, gross motor function classification system; MP, migration percentage.






FIGURE 19.3. (continued)

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May 10, 2021 | Posted by in ORTHOPEDIC | Comments Off on Principles of Management of Hip Deformity in Cerebral Palsy
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