The head-shaft angle of the hip in early childhood: a comparison of reference values for children with cerebral palsy and normally developing hips

Hip Surveillance and Management of Hip Displacement in Children with Cerebral Palsy: Clinical and Ethical Dilemmas

Hip displacement is the second most common musculoskeletal deformity in children with cerebral palsy. Hip surveillance programs have been implemented in many countries to detect hip displacement early when it is usually asymptomatic. The aim of hip surveillance is to monitor hip development to offer management options to slow or reverse hip displacement, and to provide the best opportunity for good hip health at skeletal maturity. The long-term goal is to avoid the sequelae of late hip dislocation which may include pain, fixed deformity, loss of function and impaired quality of life. The focus of this review is on areas of disagreement, areas where evidence is lacking, ethical dilemmas and areas for future research. There is already broad agreement on how to conduct hip surveillance, using a combination of standardised physical examination measures and radiographic examination of the hips. The frequency is dictated by the risk of hip displacement according to the child's ambulatory status. Management of both early and late hip displacement is more controversial and the evidence base in key areas is relatively weak. In this review, we summarise the recent literature on hip surveillance and highlight the management dilemmas and controversies. Better understanding of the causes of hip displacement may lead to interventions which target the pathophysiology of hip displacement and the pathological anatomy of the hip in children with cerebral palsy. We have identified the need for more effective and integrated management from early childhood to skeletal maturity. Areas for future research are highlighted and a range of ethical and management dilemmas are discussed.

Proximal Femoral Screw Hemiepiphysiodesis in Children With Cerebral Palsy Improves the Radiographic Measures of Hip Subluxation

BACKGROUND

Proximal femoral screw hemiepiphysiodesis (PFSH) is a promising technique for treatment of hip subluxation in children with cerebral palsy (CP). The aim of this study is to report radiographic outcomes of PFSH and to evaluate its role in changing the natural history of hip displacement in children with CP.

METHODS

This is a single center retrospective chart review of children with CP that underwent PFSH with at least 2 years of radiographic follow-up. Demographic information, surgical details, complications, additional surgical procedures, and need for screw exchange were recorded. Radiographs were assessed for migration percentage (MP), neck shaft angle (NSA), head shaft angle (HSA), and articular trochanter distance preoperatively as well as at 6 months, 1 year, 2 year, and latest follow-up postoperatively. Hips were divided into group 1 (no previous hip surgery) and group 2 (PFSH performed after hip reconstruction). Hips with 2 years of preoperative radiographic data were included in the natural history cohort.

RESULTS

Twenty-three patients (44 hips) met inclusion criteria with an average age of 7.3±1.7 years and a mean follow-up of 33.5 months. Group 1 and group 2 had 32 and 12 hips, respectively. Group 1 had significant improvement in all parameters (ΔMP=5%, ΔNSA=13 degrees, ΔHSA=15 degrees) group 2 showed improvements in NSA and HSA (ΔNSA=4 degrees ΔHSA=8 degrees) with only HSA reaching significance and MP remaining unchanged. All radiographic measurements worsened in the 2 years before surgery (N=25, natural history group) and improved after PFSH. Screw exchange occurred in 12 hips (27.2%) at an average of 33 months (range 27 to 42 mo) with 2 hips also undergoing pelvic osteotomy at that time. Three hips had a MP >50% at follow-up with 2 hips in group 1 undergoing hip reconstruction. No complications were noted.

CONCLUSION

PFSH effectively alters proximal femoral growth and can improve hip subluxation in children with CP. Screws often need to be exchanged and hips should be carefully monitored.

LEVEL OF EVIDENCE

Level III-retrospective comparative study.

Anthropometric measurements of the pediatric hip using CT-based simulated anteroposterior radiographs of the pelvis

Normal anatomical variants and pathological deformities of the pediatric hip can only be differentiated after a prior definition of normal ranges for anthropometric parameters with increasing age. Aim of the present study was to provide reliable reference values of the pediatric hip morphometry, using computed tomography (CT)-based rotation-corrected summation images of the pelvis that simulate the widely available plain radiograph-based measurements, but offer the higher precision of the CT technique. This retrospective study included 85 patients (170 hips) under 15 years of age (0-15). The measured anthropometric parameters included femur head extrusion index, lateral center-edge angle, acetabular inclination, Tönnis angle, and femoral neck-shaft angle. Mean values, range, SD, P values, intra-rater, and inter-rater reliability were calculated. All measurements correlated with age. None of the measurements correlated with gender or side. Rapid growth phases were noted in all measurements at the age of 12 (14 in males and 11 in females). The inter-rater and intra-rater reliability was high (range inter/intraclass correlation coefficient 0.926-0.998 Cronbach's alpha 0.986-0.998). The present work provides age- and gender-related normative values of the classically used hip measurements as well as growth phases describing pediatric hip morphology in a broad age range. A discrepancy was noted between the values measured in the current study and the classical X-ray-based reference values in the literature especially for the Tönnis angle and LCEA values. This suggests that the rotation and inclination correction in the CT-based techniques might have the advantage of compensating for a possible overestimation in the conventional X-ray-based methods.

Guided Growth of the Proximal Femur for the Management of the 'Hip at Risk' in Children with Cerebral Palsy-A Systematic Review

BACKGROUND

Guided growth is frequently used to modify lower-limb alignment in children, and recently temporary medial hemiepiphysiodesis of the proximal femur (TMH-PF) has been used for the management of hips at risk of subluxation in cerebral palsy (CP) patients. The aim of our study was to evaluate the efficacy of TMH-PF in the management of neuromuscular hip dysplasia in children with cerebral palsy.

METHODS

A systematic search of the literature was performed by using PubMed, EMBASE, CINAHL, MEDLINE, Scopus and Cochrane databases. Pre- and postoperative radiographic changes of the migration percentage (MP), head-shaft angle (HSA) and acetabular index (AI) were included in a meta-analysis. Secondary outcomes were treatment complication rates, technical considerations and the limitations of this novel technique.

RESULTS

Four studies (93 patients; 178 hips) met the eligibility criteria for inclusion in the meta-analysis. All three radiographic measurements showed significant changes at a minimum of 2 years of follow-up. Mean changes for MP were 8.48% (95% CI 3.81-13.14), HSA 12.28° (95% CI 11.17-13.39) and AI 3.41° (95% CI 0.72-6.10), with I² of 75.74%, 0% and 87.68%, respectively. The serious complication rate was overall low; however, physeal 'growing off' of the screw was reported in up to 43% of hips treated.

CONCLUSION

TMH-PF is an effective and predictable method to treat CP patients with 'hips at risk', and the overall complication rate is low; however, further work is required to identify the best candidates and surgical timing, as well as choice of technique and implant.

The influence of tone on proximal femoral and acetabular geometry in neuromuscular hip displacement: A comparison of cerebral palsy and spinal muscular atrophy

PURPOSE

The aim of this article was to compare longitudinal changes in hip morphology in cerebral palsy (hypertonic) and spinal muscular atrophy (hypotonic) to examine the influence of muscle tone on development of hip displacement.

METHODS

Children with spinal muscular atrophy (Types I and II) and cerebral palsy (Gross Motor Function Classification System IV and V) with hip displacement (migration percentage >30%) were included. Head shaft angle, migration percentage, and acetabular index were measured at T1 (1-2.5 years), T2 (3-5 years), and T3 (6-8 years). Analysis of variance testing and linear regression were utilized.

RESULTS

Sixty patients (cerebral palsy, N = 41; spinal muscular atrophy, N = 19) were included. Hip displacement occurred earlier in spinal muscular atrophy (34 months) than cerebral palsy (49 months) (p = 0.003). Head shaft angle was high and did not change between T1, T2, and T3, but significant changes in migration percentage were found (cerebral palsy: 23%, 36%, 45% (p < 0.01) and spinal muscular atrophy: 37%, 57%, 61% (p = 0.02)). Migration percentage increased by age in cerebral palsy (r = 0.41, p < 0.001), but not in spinal muscular atrophy (r = 0.18, p = 0.09). Acetabular index increased with migration percentage (cerebral palsy: r = 0.41, p < 0.001; spinal muscular atrophy: r = 0.48, p < 0.001).

CONCLUSION

Persistent lateral physeal tilt by head shaft angle was found for both spinal muscular atrophy and cerebral palsy. Abnormal physeal alignment may be causally related to weakness of the hip abductor muscles rather than spasticity or muscle imbalance, resulting in coxa valga and secondary acetabular dysplasia.

LEVEL OF EVIDENCE

III (case-control study).

Imaging Parameters of Hip Dysplasia in Cerebral Palsy: A Systematic Review

Background

Cerebral Palsy is the leading cause of childhood physical disability globally. The motor disorders of CP are often associated with musculoskeletal anomalies, of which hip displacement is the second most common abnormality after abnormalities of foot and ankle. Various radiological parameters have been described in the literature which detects and quantifies hip dysplasia, with MP being the current gold standard. This study aims to review these radiological indicators of hip dysplasia in children with cerebral palsy from the published literature.

Methods

A literature search using PubMed, Embase, and Google Scholar was done on 15th June 2021 focusing on surveillance of hip dysplasia in cerebral palsy. The studies to be included were to have used anyone or more radiological parameter for detection of hip dysplasia with the use of any of the radiological methods.

Results

The initial search yielded 1184 results. After the screening of the abstracts and full texts, a final of 30 studies was included for this systematic review. The majority of the studies were graded as Level 3 evidence (16/30), followed by Level 2 studies (14/30). X-ray was the most common modality of detection of dysplasia followed by CT scan, ultrasonography, and arthrogram. The reproducibility of the various parameters shows good to excellent intraclass coefficients.

Conclusions

Parameters other than MP can be used to screen hips in CP. This would be useful in patients in whom either the lateral acetabular edge is not discernible on a plain anteroposterior radiograph or there are issues in the positioning of the patient. Additional views and structures can be visualized which can lead to improved screening and planning. Further investigations are required to appreciate the full potential of these parameters and how they can be better utilized.

Graphical abstract

Evolution of head-shaft angle and neck-shaft angle in childhood

The current retrospective study investigates the natural evolution of head-shaft angle (HSA) and neck-shaft angle (NSA) in childhood. It is not known if a high HSA in early childhood leads to a high HSA in adulthood. This study aims to characterize the evolution of HSA and compares it with the more commonly known NSA in healthy children. We measured radiographs of 84 different healthy hips of children between 3 and 14.5 years old who underwent at least 2 radiographs of the pelvis, corresponding to 286 measurements. We used a linear mixed model to determine the covariance between random intercept and slope while allowing each individual hip to change over time. The covariance for HSA between random intercept and random slope was -4.262 (p < 0.001), corresponding to a high negative correlation of -0.717, for NSA -2.754 (p = 0.031) or a high negative correlation of -0.779. HSA and NSA were strongly correlated, a value of 0.736 (p < 0.001) was measured. The high negative correlation for random intercept and random slope means that the higher the initial value (intercept), the steeper the decline (slope). Therefore HSA decreases faster in hips with high HSA at an early age. Hips with high HSA in early childhood do not necessarily lead to hips with high HSA in adulthood. Our results may aid in future clinical decision making in patients with developmental dysplasia of the hip (DDH) with high HSA in particular.

The Femoral Head-Shaft Angle Is Not a Predictor of Hip Displacement in Children Under 5 Years With Cerebral Palsy: A Population-based Study of Children at GMFCS Levels III-V

BACKGROUND

The aim of this study was to evaluate whether the femoral head-shaft angle (HSA) is a predictor of hip displacement in children with cerebral palsy (CP).

METHODS

The patients were recruited from a population-based hip surveillance program. Inclusion criteria were age under 5 years, bilateral CP, Gross Motor Function Classification System (GMFCS) levels III-V, and migration percentage (MP) of both hips <40% at the primary radiograph. With these criteria, 101 children (61 boys) were included. GMFCS was level III in 26 patients, level IV in 23, and level V in 52. An anteroposterior radiograph of the pelvis was taken at diagnosis and at the last follow-up. Only the worst hip of each patient (the hip with the largest MP) was used for the analyses.

RESULTS

The mean age at the primary radiograph was 2.4 years (range, 0.8 to 4.9 y). The mean primary HSA was 171.0 degrees (range, 152 to 190 degrees). The mean follow-up time was 4.3 years (range, 0.9 to 11.8 y). The mean MP at the primary radiograph was 17.5% (range, 0% to 39%) and at the last follow-up 41.9% (range, 0% to 100%). At that point, MP was <40% in 54 hips and ≥40% in 47 hips. There was no significant difference in primary HSA between patients with final MP<40% and those with final MP≥40% (170.8 and 171.3 degrees, respectively; P=0.761). At the last follow-up, the mean HSA was significantly larger in hips with final MP≥40% than in hips with final MP<40% (171.1 vs. 167.4 degrees; P=0.029).

CONCLUSIONS

There was a markedly increased valgus position of the proximal femur in nonambulatory children with CP. However, the primary HSA in children below 5 years of age was not a predictor of later hip displacement, defined as MP≥40%.

CLINICAL RELEVANCE

Measurement of HSA is not necessary in routine hip surveillance in children below 5 years.

LEVEL OF EVIDENCE

Level I-investigating a diagnostic test.

The effect of femoral orientation on the measurement of the head shaft angle: an ex-vivo study

This laboratory study evaluates head shaft angle (HSA) reliability using ranges of simulated femoral orientation often seen in children with cerebral palsy. A dry femur was mounted in a jig that enabled the bone to be positioned in a range of internal and external rotation (-40° to + 40°) and flexion (0°-60°), alone or in combination. A metal wire was placed as a surrogate physis to give two HSA angles of 140° and 160°. Radiographs were taken of the femur in differing combinations of rotation, flexion and the two HSA angles. The HSA was measured by four independent observers on two separate occasions. Intraclass correlation coefficients (ICCs) were used to assess interobserver and intraobserver reliability. The HSA was accurately measured within ± 5° when the femur was positioned between 20° internal rotation and 40° external rotation. Flexion up to 60° did not affect the accuracy of the measurement. The interobserver reliability for the HSA was excellent with an ICC of 0.9970 [95% confidence interval (CI): 0.9995-0.9983] for the first measurement and 0.9988 for the second (95% CI: 0.9979-0.9993, all P < 0.01). The intraobserver reliability was also excellent with an ICC of not less than 0.990 for all four observers (95% CI: 0.9806-0.9986, all P < 0.01). There was excellent interobserver and intraobserver reliability when measuring the HSA in an experimental model provided femoral rotation lay within 20° internal and 40° external rotation and less than 60° of flexion.

The head shaft angle is associated with hip displacement in children at GMFCS levels III-V - a population based study

Background

An increased Head Shaft Angle (HSA) has been reported as a risk factor for hip displacement in children with cerebral palsy (CP) but opinions differ in the literature. The purpose of this study was to re-evaluate the relationship between HSA and hip displacement in a different population of children with CP.

Methods

The Cerebral Palsy Integrated Pathway Scotland surveillance programme includes 95% of all children with CP in Scotland. The pelvic radiographs from 640 children in GMFCS levels III-V were chosen. The most displaced hip was analysed and the radiographs used were those taken at the child’s first registration in the database to avoid the potential effects of surveillance on subsequent hip centration. A logistic regression model was used with hip displacement (migration percentage [MP] ≥40%) as outcome and HSA, GMFCS, age and sex as covariates.

Results

The MP was ≥40% in 118 hips with a mean HSA of 164° (range 121–180°) and < 40% in 522 hips with a mean HSA of 160° (range 111–180°). The logistic regression analysis showed no significant influence of age and sex on MP in this population but a high GMFCS level was strongly associated with hip displacement. An increased HSA was also associated with hip displacement, a 10° difference in HSA for children adjusted for age, sex, and GMFCS gave an odds ratio of 1.26 for hip displacement equal or above 40% (p = 0.009) and hips with HSA above 164.5 degrees had an odds ratio of 1.96 compared with hips with HSA below 164.5 degrees (p = 0.002).

Conclusion

These findings confirm that HSA is associated with hip displacement in children in GMFCS levels III-V.

Inter- and intra-rater reliability of the head-shaft angle in children with cerebral palsy

PURPOSE

Children with cerebral palsy (CP) are at increased risk for hip dislocation. This can be prevented in most cases using surveillance programmes that include radiographic examinations. Known risk factors for hip dislocation include young age, high Gross Motor Function Classification System (GMFCS) level and high migration percentage (MP). The head-shaft angle (HSA) has recently been described as an additional risk factor. The study aim was to determine inter- and intra-rater reliability of the HSA in a surveillance programme for children with CP.

METHODS

We included hip radiographs from the CP surveillance programme CPUP in southern Sweden during the first half of 2016. Fifty radiographs were included from children at GMFCS levels II-V, with a mean age of 6.6 (SD 3.2) years. Three raters measured the HSA of one hip (left or right) at baseline and four weeks later; intraclass correlation coefficient (ICC) was used to estimate inter- and intra-rater reliability.

RESULTS

Inter- and intra-rater reliability were excellent for the HSA, with ICC 0.92 (95% CI 0.87-0.96) and ICC 0.99 (95% CI 0.98-0.99), respectively.

CONCLUSION

The HSA showed excellent inter- and intra-rater reliability for children with CP, providing further evidence for use of the HSA as an additional factor for identifying risk for further hip displacement or dislocation.

Is head-shaft angle a valuable continuous risk factor for hip migration in cerebral palsy?

BACKGROUND

Reimer's migration percentage (MP) is the most established radiographic risk factor for hip migration in cerebral palsy (CP), and it assists surgical decision-making. The head-shaft angle (HSA) measures the valgus of the head and neck in relation to the shaft and may also be a useful predictor of hip migration at a young age. This study first defined normal values and investigated whether the head-shaft angle (HSA) is a continuous risk factor for hip migration in CP.

METHODS

Three hundred and fifty AP pelvic radiographs of 100 consecutive children comprising the hip surveillance programme in our region were analysed for MP and HSA. Inclusion criteria were children with spastic CP and Gross Motor Function Classification System (GMFCS) levels of III-V, along with a minimum follow-up of 5 years. The mean age was 8.8 (range 3-18) years and the mean follow-up time was 7.5 (range 5-10) years. Radiographs of 103 typically developing children (TDC) were selected for the control group. The reliability of the measurements was determined. A random effects analysis was used to assess the relationship between MP and HSA for all data and for MP > 40 %.

RESULTS

The TDC cohort had a mean HSA of 157.7° whilst that for the CP cohort was 161.7°. The value declined with age in both groups but remained consistently higher in the CP group. A random effects analysis considering the longitudinal data showed that there was no significant effect of HSA on MP. Similarly, when excluding CP patients with MP < 40 %, there was no significant effect of HSA on MP.

CONCLUSIONS

This study found no correlation between HSA and hip migration in children with CP in this age group. Using the HSA as a routine radiographic measure in the management pathway across childhood does not offer any added value. Early enrolment onto the hip surveillance programme could offer a better prediction of hip migration using the HSA at a very young age.

LEVEL OF EVIDENCE

II retrospective prognostic study.