26.2.1 Natural History

Children with CP are at increased risk for developing spinal deformity when compared to the general pediatric population. There is large variation in the estimated prevalence of scoliosis in CP, ranging from 20 to 77%. ^{2 ,​ 3 ,​ 4 ,​ 5 ,​ 6 ,​ 7} This variation may be explained by the heterogeneity of CP and the fact that the risk of deformity increases with the severity of CP. For example, scoliosis is more common in children with tetraplegia, when compared with paraplegia or hemiplegia, and is more common in spastic CP. ⁸ Severity of CP as measured by the Gross Motor Function Classification System (GMFCS) is the most important risk factor of scoliosis, with a strong association between increasing GMFCS level and scoliosis. ⁸ Nonambulatory children (GMFCS levels IV and V) have a 50% probability of acquiring a moderate or severe scoliosis by 18 years, whereas for ambulatory children who do not need walking aids (GMFCS levels I and II) the risk of developing scoliosis is not significantly different from the general population. ³ Scoliosis tends to progress most rapidly before skeletal maturity but routinely continues beyond skeletal maturity, particularly in nonambulatory patients with a curve of greater than 40 degrees by 12 years of age. ^{9 ,​ 10} Skeletal maturity may also be delayed in these patients, which also contributes to a prolonged period of increased risk of curve progression.

26.2.2 Comorbidities

The secondary musculoskeletal consequences of CP, including scoliosis, get progressively worse with increasing age. These consequences include the development of contractures of the upper and lower extremities that can interfere with the child’s care and comfort. Patients are at increased risk for progressive hip displacement, and this risk is also strongly related to the GMFCS levels. ⁶ Therefore, a thorough evaluation of the hips for the presence of contractures or dislocation is necessary in the evaluation of spinal deformity. Hip displacement usually precedes the onset of scoliosis, but this is not always the case. These musculoskeletal effects of CP can result in children relying on wheelchairs for their mobility. This immobility and lack of load bearing can lead to osteoporosis. Children are dependent on their caregivers for much of their care and activities of daily living.

Patients with CP who are at greatest risk for developing a spinal deformity are also those most likely to have significant nonmusculoskeletal comorbidities. These comorbidities may include seizure disorder, hydrocephalus, bowel and bladder incontinence, urinary tract infection, gastroesophageal reflux, malnutrition, constipation, aspiration pneumonia, and cardiopulmonary issues. ^{4 ,​ 5} Their neurological impairment can lead to swallowing difficulties, which cause an increased risk for developing aspiration pneumonias. They also experience distressing gastroesophageal reflux, which can be exacerbated in certain positions. Gastric tube feeding is often necessary both to overcome the malnutrition associated with feeding difficulties and to protect against aspiration. Tracheostomy is also common in patients with severe CP, again to protect against aspiration. Most of these patients are incontinent of bowel and bladder. Children may develop pressure sores as their spinal deformity worsens, especially if they are thin.

26.2.3 Spinal Deformity and Comorbidities: Impact on QoL

These comorbidities collectively have a significant impact on the longevity and HRQoL in these severely involved children with CP and scoliosis. An increasing curvature has been implicated in worsening sitting tolerance and impaired mobility. Sitting upright is an important aspect of these children’s lives, given the lack of ambulation. The presence of a significant spinal deformity (specifically, the presence of pelvic obliquity) has the potential to impact sitting balance, comfort, and endurance. The inability to sit upright might compound the impact of patients’ baseline visual impairments and thus affect their ability to process visual information. Furthermore, progressive scoliosis might directly or indirectly exacerbate some of the medical comorbidities. Worsening scoliosis is implicated in decreased pulmonary function, gastroesophageal reflux, and feeding difficulties. The location and magnitude of the curve might negatively impact pulmonary function. Cardiopulmonary function declines with age as a function of the underlying disease, but this deterioration correlates better with GMFCS level than curve magnitude. It can be difficult to test pulmonary function directly in patients with CP due to their inability to participate, particularly those at GMFCS levels IV and V. However, studies have shown no difference between oxygen saturation and heart rate in patients with mild or no scoliosis as compared to those with curves greater than 45 degrees ^{11 ,​ 12} Other factors such as presence of a tracheostomy, ⁹ pelvic obliquity, and hip dislocation ^{13 ,​ 14 ,​ 15 ,​ 16} have been shown to be associated with worsening scoliosis in CP. The relationship between scoliosis and all these factors remains unclear and worsening cardiopulmonary comorbidities may be related to underlying disease severity rather than a causal relationship with scoliosis. What is clear is that this population has significant comorbidities, and these comorbidities lead to challenges in the treatment of the scoliosis.

In the presence of multiple comorbidities, the additional negative impact of scoliosis on HRQoL of these children has been difficult to quantify. It is a challenge to measure patient-reported HRQoL in patients who are unable to communicate their quality of life due to cognitive and/or communication impairments. Consequently, there is some controversy about the benefit and indications for the surgical treatment of scoliosis in this population. These are major interventions with significant complication rates and high costs associated with surgery and rehabilitation. ^{7 ,​ 9} Surgical outcomes have been typically reported based on radiographic measures, fusion rates, early and late complications, and mortality from uncontrolled case series. More important HRQoL outcomes are infrequently reported, mostly using unvalidated measures. There is an imperative for prospective, comparative studies using validated HRQoL measures to address the uncertainty about the true benefits of surgery.

26.2.4 Interventions

The problems associated with increasing spinal deformity in patients with CP might be effectively managed using nonoperative means or by definitive surgical correction. Any intervention should progress from a clear understanding of the natural history of the disease. It should modify the disease in such a way that the patient’s general state of health is improved in some way and the intervention is tolerable. Traditionally, in patients with CP and spinal deformity, radiographic measures or morbidity and mortality data were primarily used to follow the observed natural history and the response to treatments. Validated HRQoL outcomes comparing bracing, observation, or surgery are not currently available in the literature.

26.2.5 Satisfaction and HRQoL Studies

CP is a chronic disease, with no cure. As such, outcome studies should reflect subtle changes in functional status and general well-being, distinguishing the results of an intervention with the natural history. Over the past 20 years, there has been growing interest and understanding of the importance of parent and patient satisfaction following spinal surgery for CP. Given the high rates of complications in this challenging population, the effect of correction and complications on functional outcomes has been examined. Sponseller et al ¹⁷ suggested that deep infection rates were comparatively higher in CP spinal deformity correction population and that such infections may be associated with worse pain outcomes. Posterior-only pedicle screw constructs produce satisfactory radiographic coronal and sagittal correction, without higher complication rates. They are associated with functional improvements (using a modified Rancho Los Amigos Hospital system criteria score). ¹⁸ Another study has suggested that there was no correlation between the occurrence of complications and changes in HRQoL. Furthermore, extension of spinal fusion to the pelvis to manage pelvic obliquity had no impact on the occurrence of complications in these patients. ¹⁹

Several studies report high retrospective parental/caregiver satisfaction with their decision to undergo surgical correction of spinal deformity ^{17 ,​ 20 ,​ 21 ,​ 22 ,​ 23 ,​ 24 ,​ 25 ,​ 26} though these studies did not use validated outcome instruments for children with severe CP. Comstock et al ²⁷ in a series of 79 patients with a median follow-up of 4 years reported a late progression of scoliosis greater than 10 degrees, worsening pelvic obliquity, and decompensation greater than 4cm in more than 30% of patients following surgery, noting that the majority of patients who progressed underwent surgery while skeletally immature. Despite this, the study reported an 85% satisfaction rate from parents or caregivers following surgery and noted a beneficial impact on physical appearance, comfort, ease of care, and sitting ability. A longitudinal study of parental perceptions following spinal surgery using the POSNA (Pediatric Orthopaedic Society of North America) outcomes questionnaire reported no difference between preoperative and postoperative physical functions, comorbidities, and parental health. Patient pain and happiness as well as parental satisfaction were significantly improved by 1 year. ^{28 ,​ 29} The lack of perceived functional improvements in this study may have underestimated the potential functional benefit of surgery secondary to a ceiling effect of this instrument in children with severe CP. In a retrospective study of 84 patients with spastic CP, Watanabe et al ³⁰ reported 85% satisfaction with surgery. Most improvement was felt to be related to posture and sitting balance as well as cosmetic appearance. Interestingly, the least improved scores postoperatively concerned walking ability, use of arms and hands, ability to eat, sleeping patterns, perineal care, number of pressure sores, ability to dress, and pain. ²⁰ Given the lack of validated questionnaires with unknown responsiveness, it is difficult to ascertain the true effects of surgery in children with scoliosis and severe CP. There is a need for a validated measure of quality of life in this population to elucidate which radiographic or clinical outcomes may lead to improved quality of life.