Optimal clinical decision making and surgical management of hip dysplasia in children with cerebral palsy (CPHD) requires an understanding of the underlying pathophysiology (pathomechanics and pathoanatomy), incidence, and natural history. The underlying dynamic muscle imbalance (ie, dominance of the hip flexors and adductors over the hip extensors and abductors), occurring in the setting of the growing hip, results in distinct pathoanatomy of both the proximal femur and acetabulum.1–4 The incidence of CPHD is directly related to the degree of motor impairment in children with cerebral palsy (CP).5 A subluxated or dislocated hip in a child with CP can compromise the quality of life of both the child and their caregivers.6–8
The goal of this article is to highlight the events over the last 25 years that have had the greatest impact on the clinical and surgical management of CPHD. Looking back, it is my opinion that the 2 most significant advances during this time have been the development of a classification system based upon motor impairment (the Gross Motor Function Classification System—GMFCS), and the development of hip surveillance programs for CPHD.
THE SAN DIEGO APPROACH
By the early 1990s, surgically oriented pediatric orthopaedic surgeons in North America generally believed that early soft tissue surgery (ie, hip adductor and flexor muscle lengthening) was unpredictable and frequently ineffective in the management of CPHD, and that a single event, comprehensive surgical hip reconstruction (including hip adductor and flexor muscle lengthening; proximal femoral varus and rotation osteotomy—VRO; acetabular osteotomy as described by Dega; and open reduction with capsulorraphy), when done at the proper age (between 6 and 8 y of age) would be definitive (ie, no recurrence of subluxation or dislocation).9,10 This approach was developed at a center with significant technical expertise in the surgical management of developmental dysplasia of the hip (DDH), and a commitment to caring for children with CP. It was this approach that guided my clinical decision making and surgical management of CPHD in the early part of my career (Fig. 1). The early results were generally successful, and seemed to be consistent with my training and validate the paradigm. However, with time there were a few poor outcomes, which appeared to be related to recurrence of CPHD with growth, particularly in younger children with more severe CP.11,12 Critical analysis of these cases, and advances in the understanding of CPHD from centers around the world taught me the following lessons.
LESSONS LEARNED: PATHOPHYSIOLOGY
It is now clear that the pathophysiology of CPHD is distinct from that associated with DDH. In CPHD there are rarely soft tissue obstacles to reduction (which are seen more commonly in DDH). Even in cases of extreme subluxation (ie, migration percentage—MP, up to 100%), as long as a portion of the femoral head is in contact with the margin of the acetabulum, there will not be soft tissue obstacles to reduction of the femoral head within the acetabulum following combined femoral and acetabular osteotomies. Open reduction to remove soft tissue obstacles is only necessary in cases with complete dislocation where the femoral head has migrated proximally and has no contact with the acetabulum (ie, MP >100%). In such cases the interposed iliopsoas tendon, and less frequently a contracted capsule, are the soft tissue structures that need to be addressed to facilitate reduction of the femoral head within the acetabulum. The ligamentum teres may be detached from the femoral head and atrophied, significant pulvinar is infrequent, and tightness of the transverse acetabular ligament is rare. Stability following open reduction is best achieved by the skeletal hypercontainment that occurs by performing both femoral and pelvic osteotomies, obviating the need for capsulorraphy.
The other significant pathophysiological difference between CPHD and DDH relates to the role of growth following surgical reconstruction of the hip. In DDH, subsequent growth, particularly acetabular modeling, is a necessary element for achieving a good long-term outcome.13,14 Subsequent growth is the surgeon’s friend in the management of DDH. However, in CPHD, the underlying muscle imbalance described above usually persists, even after soft tissue or skeletal surgeries, and subsequent growth, particularly of the proximal femur, has been shown to lead to recurrent deformity, which may contribute to recurrent subluxation.15,16 The potential for acetabular modeling in CPHD is less well understood, and will be discussed below. In general, subsequent growth is not the surgeon’s friend in the management of CPHD. Recent animal and clinical studies suggest that there may be a role for guided growth of the proximal femoral physis to either prevent deformity early in the disease process or recurrence of deformity following VRO.17–19 Further study is required before this procedure can be recommended with confidence.
LESSON LEARNED: THE GMFCS
Development and utilization of the GMFCS, a classification scheme based upon motor impairment level, has contributed greatly to our understanding of the epidemiology and natural history of CPHD, and to the assessment of outcomes following surgical management (Fig. 2).20,21 In children with CP, hips with MP >30% are at risk for the development of CPHD.22–25 Population-based studies have shown that the incidence of CPHD (defined as MP >30%) in children with CP is directly correlated with the degree of motor function impairment as measured by the GMFCS.5 CPHD is very common in children with CP, occurring in 69% and 89% of children at the GMFCS levels IV and V, respectively. Outcomes following surgical management of CPHD are improved when performed earlier in the course of the disease process, supporting efforts at early diagnosis in those groups at the greatest risk for developing CPHD.23,24,26–28 Interestingly, CPHD also occurs in 15% of children functioning at the high motor levels (GMFCS I and II).5 Recent work has identified a subset of children with hemiplegic type CP, with gait kinematic deviations about the hip who are at risk for CPHD.6,13,29 Appropriately timed assessment for CPHD in this group of children is therefore recommended.
Understanding of the natural history of CPHD has previously been focused upon the presence or absence of pain associated with severe subluxated or dislocated hips in adults with CP.6,13 This literature is inconsistent, due in part to a lack of tools to accurately measure relevant clinical status and outcomes. The most reasonable interpretation of these studies is that the longer a subject survives, the greater the likelihood of pain associated with a subluxated or dislocated hip. However, the impact of CPHD on motor function (which is a significant element of quality of life) in subjects with CP can be seen when Gross Motor Function Measure scores relative to age are evaluated with the subjects segregated by GMFCS level (Fig. 3).30 Motor function improves across all GMFCS levels up to 7 years of age. For those children functioning at the highest motor levels (ie, GMFCS I and II), motor function level remains stable into young adulthood. For those at the GMFCS III, IV, and V levels there is deterioration of motor function level beginning in the teenage years and progressing into young adulthood. The distribution of these changes across GMFCS levels closely mirrors the incidence of CPHD between GMFCS levels, suggesting that CPHD may be a contributing factor to the deterioration of motor function in teenagers and young adults with CP.
The GMFCS has also contributed to improved understanding of technical domain outcomes following the surgical management of CPHD. The effectiveness of early soft tissue surgery (lengthening of the hip adductor and flexor muscles) has been shown to be related to the degree of motor impairment present at the time of surgery, with the successful outcomes (ie, maintenance of MP <30%) seen in 94% of children at GMFCS level II, 49% at GMFCS level III, 27% at GMFCS level IV, and only 14% at GMFCS level V.31 As noted by the investigators, unfortunately those that need it the most (ie, children at GMFCS IV and V) benefit the least from early soft tissue surgery for CPHD. Despite these poor results, I still offer early soft tissue surgery to children at the GMFCS IV and V levels as the improved hip range of motion achieved by the surgery facilitates diapering and perineal hygiene. In addition, this relatively simple surgery provides an opportunity for the family and child to experience anesthesia, surgery, and recovery, which can help in deciding whether to undergo the more rigorous skeletal hip reconstruction surgery in the future.
Outcomes following skeletal hip reconstruction surgery for CPHD are best understood through the filter of the GMFCS. Early reports, that did not classify patients by motor functional level, described 95% success rates (ie, maintenance of reduction, no further surgery required) following skeletal hip reconstruction at 7.5 years follow-up.9,32 A subsequent study, which classified patients by GMFCS level, noted a 75% success rate in GMFCS IV and V patients at 5 years of follow-up.33 Several recent reports evaluating acetabular response following isolated VRO for CPHD have shown that measurable remodeling does occur, more commonly in GMFCS II and III patients, but rarely in GMFCS IV and V patients.34–36 Combining this information with previous studies documenting recurrent femoral deformity with growth following VRO for CPHD supports the surgical paradigm of skeletal hypercontainment with combined femoral and pelvic osteotomies for CPHD in GMFCS IV and V patients, and suggests that a second skeletal reconstruction may be necessary when hip reconstructive surgery is required in younger children (ie, between 4 and 6 y of age) with severe CP.
Assessment of health-related quality of life (HRQOL) in children with severe CP (GMFCS IV and V) has been improved by the development of tools such as the Caregiver Priorities and Child Health Index of Life with Disabilities (CPCHILD).37 A recent study of children severe CP undergoing hip reconstruction surgery found a negative correlation between MP and CPCHILD scores both preoperatively and postoperatively, with improved CPCHILD scores following surgery.7 These finding suggest that CPHD negatively impacts HRQOL in children with CP, and that HRQOL is improved following hip reconstructive surgery.
The GMFCS can provide clinical decision making guidelines for the management of CPHD based upon the subject’s motor impairment level. CPHD is rare at GMFCS I and II levels, but when identified early should be managed by soft tissue surgery. Cases identified later should be managed by skeletal reconstruction with VRO; acetabular osteoteomy is indicated when significant dysplasia is present. Excellent outcomes should be anticipated. CPHD in children at the GMFCS III and IV levels should be managed by early soft tissue surgery, with the family counseled that subsequent skeletal reconstruction surgery will be likely. In cases where hip reconstruction is required at a relatively young age, a second skeletal reconstruction may be required in the future due to recurrence of femoral deformity with growth. Management of CPHD in children with the most severe level of motor impairment (GMFCS V) requires preliminary moral and ethical discussion of proactive versus reactive treatment strategies with the family, due to significant medical comorbidities that increase the risk of perisurgical complications and shorten anticipated lifespan. When a proactive strategy is selected, management of CPHD is similar to that described above for GMFCS III and IV levels. When a reactive strategy is selective, soft tissue release for range of motion and palliative skeletal salvage surgeries are utilized.38
LESSONS LEARNED: HIP SURVEILLANCE
Systematic hip surveillance programs designed to promote early detection and treatment of CPHD in children with CP have been developed in Australia and Sweden.24,25,27,28 These programs have established that hips with MP >30% are at risk for progressive subluxation, that the incidence of CPHD is related to the degree of motor impairment as described by the GMFCS, that the skeletal pathoanatomy of CPHD is related to the degree of motor impairment as described by the GMFCS, and that botulinum toxin injection into the hip adductor and flexor muscle groups is not effective in preventing progression of CPHD.5,22,39,40 Implementation of comprehensive hip surveillance results in an increase in early soft tissue surgeries and skeletal hip reconstructions, and decreases the incidence of hip dislocations and salvage surgeries after 10 to 20 years of screening.27,28 The implementation of hip surveillance results in a switch from a reactive to proactive treatment paradigm, which is beneficial from a population perspective and presumably cost effective from a system perspective.
Australia and Sweden both have comprehensive, centralized health care delivery systems, which facilitate the implementation and utilization of hip surveillance for CPHD in children with CP. The program may be delivered by trained professionals working at tertiary referral centers where children with CP are concentrated to receive specialized care and services; or mandated centrally and implemented in regional centers designated to provide health care services to children with CP. Implementation in countries with limited resources, or with decentralized, market driven health care delivery systems is challenging. In centralized systems, change is general initiated from above, mandating the implementation below. In decentralized systems, change is frequently initiated from below. In this circumstance, any advocate for the child (eg, primary care provider, physical therapist, or parent) may promote hip surveillance.
Several smartphone apps have been developed to educate and empower such advocates. The CPUP Hip Score, developed in Sweden, predicts the risk of developing progressive CPHD, defined as an MP >40%, within 5 years.41–43 The CPUP Hip Score is calculated using 4 variables: the subject’s GMFCS level, age, and 2 x-ray measures of hip dysplasia (MP; and head shaft angle) (Fig. 4). The hipscreen app, developed in the United States, provides educational materials about hip surveillance, proper techniques for obtaining and measuring x-rays of the hips, definitions of GMFCS levels, and summaries of all published hip surveillance programs for CPHD.44 The app provides a specific, detailed hip surveillance schedule based upon age and GMFCS level, to guide providers and advocates that can be applied to individual subjects. The final and most innovative element of the hipscreen app is the Migration Percentage Ruler, which facilitates calculation of the MP from a pelvis x-ray (Fig. 5). The smartphone camera is used to photograph the x-ray, which is then aligned and manipulated using the pan and zoom functions. The ruler function contains guidelines for continued surveillance or referral to a treatment center based upon the calculated MP.
Management of the hip in children with CP over the last 25 years has been enhanced by improved understand of the pathophysiology and pathoanatomy of CPHD. Development and utilization of the GMFCS, a classification system for children with CP, based upon degree of motor impairment, has improved our understanding of the epidemiology and natural history of CPHD; and improved the assessment of technical domain and HRQOL outcomes following surgery. Development and implementation of hip surveillance programs for CPHD leads to earlier diagnosis and treatment, resulting in better outcomes. Implementation of hip surveillance programs in resource poor and decentralized health care delivery systems is challenging and will require innovating thinking and processes.
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Keywords:Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.
cerebral palsy; hip dysplasia; Gross Motor Function Classification System; hip surveillance