[Age-related force distribution at the proximal end of the femur in normally growing children]

The Etiology of Neuromuscular Hip Dysplasia and Implications for Management: A Narrative Review

This study summarizes the current knowledge of the etiology of hip dysplasia in children with neuromuscular disease and the implications for management. This article is based on a review of development of the hip joint from embryology through childhood growth. This knowledge is then applied to selective case reviews to show how the understanding of these developmental principles can be used to plan specific treatments. The development of the hip joint is controlled by genetic shape determination, but the final adult shape is heavily dependent on the mechanical environment experienced by the hip joint during growth and development. Children with neuromuscular conditions show a high incidence of coxa valga, hip dysplasia, and subluxation. The etiology of hip pathology is influenced by factors including functional status, muscular tone, motor control, child's age, and muscle strength. These factors in combination influence the development of high neck-shaft angle and acetabular dysplasia in many children. The hip joint reaction force (HJRF) direction and magnitude determine the location of the femoral head in the acetabulum, the acetabular development, and the shape of the femoral neck. The full range of motion is required to develop a round femoral head. Persistent abnormal direction and/or magnitude of HJRF related to the muscular tone can lead to a deformed femoral head and a dysplastic acetabulum. Predominating thigh position is the primary cause defining the direction of the HJRF, leading to subluxation in nonambulatory children. The magnitude and direction of the HJRF determine the acetabular shape. The age of the child when these pathomechanics occur acts as a factor increasing the risk of hip subluxation. Understanding the risk factors leading to hip pathology can help to define principles for the management of neurologic hip impairment. The type of neurologic impairment as defined by functional severity assessed by Gross Motor Function Classification System and muscle tone can help to predict the risk of hip joint deformity. A good understanding of the biomechanical mechanisms can be valuable for treatment planning.

Influence of loading direction due to physical activity on proximal femoral growth tendency

Longitudinal bone growth is regulated by mechanical forces arising from physical activity, whose directions and magnitudes depend on activity kinematics and intensity. This study aims to investigate the influence of common physical activities on proximal femoral morphological tendency due to growth at the femoral head growth plate. A subject-specific femur model based on magnetic resonance images of one able-bodied 6-year old child was developed, and the directions of hip contact force were described as load samples at a constant magnitude. Finite element analysis was performed to predict growth rate and growth direction, and expected changes in neck-shaft angle and femoral anteversion were computed corresponding to circa 4 months of growth. For most loading conditions, neck-shaft angle and femoral anteversion decreased during growth, corresponding to the femur's natural course during normal growth. The largest reduction in neck-shaft angle and femoral anteversion was approximately 0.25° and 0.15°. Our results suggest that most common physical activities induce the expected morphological changes in normal growth in able-bodied children. Understanding the influence of contact forces during less common activities on proximal femoral development might provide improved guidelines and treatment planning for children who have or are at risk of developing a femoral deformity.

Influence of muscle groups' activation on proximal femoral growth tendency

Muscle and joint contact force influence stresses at the proximal growth plate of the femur and thus bone growth, affecting the neck shaft angle (NSA) and femoral anteversion (FA). This study aims to illustrate how different muscle groups’ activation during gait affects NSA and FA development in able-bodied children. Subject-specific femur models were developed for three able-bodied children (ages 6, 7, and 11 years) using magnetic resonance images. Contributions of different muscle groups—hip flexors, hip extensors, hip adductors, hip abductors, and knee extensors—to overall hip contact force were computed. Specific growth rate for the growth plate was computed, and the growth was simulated in the principal stress direction at each element in the growth front. The predicted growth indicated decreased NSA and FA (of about \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$0.1 {^{\circ }}$$\end{document}0.1∘ over a four-month period) for able-bodied children. Hip abductors contributed the most, and hip adductors, the least, to growth rate. All muscles groups contributed to a decrease in predicted NSA (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sim $$\end{document}∼0.01\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${^{\circ }}$$\end{document}∘–0.04\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${^{\circ }})$$\end{document}∘) and FA (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sim $$\end{document}∼0.004\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${^{\circ }}$$\end{document}∘–\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$0.2{^{\circ }}$$\end{document}0.2∘), except hip extensors and hip adductors, which showed a tendency to increase the FA (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sim $$\end{document}∼0.004\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${^{\circ }}$$\end{document}∘–\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$0.02{^{\circ }}$$\end{document}0.02∘). Understanding influences of different muscle groups on long bone growth tendency can help in treatment planning for growing children with affected gait.

The underused hip in ipsilaterally orthotics-dependent children

BACKGROUND

The aim of this investigation is the development of primarily healthy hips in children who have required orthoses/protheses over the long term due to ipsilateral distally located deformities of the leg. These children show ipsilateral in-toeing gait and Duchenne's limping followed by a coxa valga antetorta and facultative hip decentration. A practical question is whether these hips are in danger of decompensation. An additional theoretical question is how the external shape and internal architecture changes if a primarily healthy hip is underused.

METHODS

Ten children with healthy hips who are unilaterally long-term orthotics/prosthetics-dependent agreed to undergo an instrumental gait analysis. The results were analyzed and correlated with clinical findings, a common activity score and planimetric radiographic data.

RESULTS

The intra-individual comparison revealed a number of significant changes in the hip of the deformed leg (p < 0.05). Clinically, the internal rotation was increased (15° ± 4.2°), while the external rotation was diminished (13° ± 1.3°). Radiologically, the projected caput-collum-diaphyseal angle, the lesser trochanter to articular surface distance and the head-shaft angle were increased by 11.1° ± 15.4°, 5.8 ± 4.2 mm and 11.9° ± 0.6°, respectively. Both the Sharp and acetabular angles were increased, the former by 3.6° ± 0.6° and the latter by 3.2° ± 0.6°. Kinetic gait analysis showed increased stride length (6.8 ± 3.7 cm), shortened stance phase (6.6 ± 1.6 %) and reduced forces transmitted to the ground (92.2 ± 34.3 N). The kinematic analysis showed increased hip abduction (14.0° ± 8.2°), while the pelvic obliquity was not significantly changed (0.01° ± 0.01°).

CONCLUSIONS

Duchenne's limp and lack of weight-bearing stress are the decisive pathogenic factors of the underused coxa valga and acetabular dysplasia. These changes follow the mechanobiological concept of "function modifies design", which means function influences external shape and internal architecture of bones and joints. As a practical consequence we recommend that one pelvic radiograph be performed as a precaution at the end of puberty of children with these conditions.

LEVEL OF EVIDENCE

Level II retrospective study.

Functional integrative analysis of the human hip joint: the three-dimensional orientation of the acetabulum and its relation with the orientation of the femoral neck

In humans, the hip joint occupies a central place in the locomotor system, as it plays an important role in body support and the transmission of the forces between the trunk and lower limbs. The study of the three-dimensional biomechanics of this joint has important implications for documenting the morphological changes associated with the acquisition of a habitual bipedal gait in humans. Functional integration at any joint has important implications in joint stability and performance. The aim of the study was to evaluate the functional integration at the human hip joint. Both the level of concordance between the three-dimensional axes of the acetabulum and the femoral neck in a bipedal posture, and patterns of covariation between these two axes were analysed. First, inter-individual variations were quantified and significant differences in the three-dimensional orientations of both the acetabulum and the femoral neck were detected. On a sample of 57 individuals, significant patterns of covariation were identified, however, the level of concordance between the axes of both the acetabulum and the femoral neck in a bipedal posture was lower than could be expected for a key joint such as the hip. Patterns of covariation were explored regarding the complex three-dimensional biomechanics of the full pelvic-femoral complex. Finally, we suggest that the lower degree of concordance observed at the human hip joint in a bipedal posture might be partly due to the phylogenetic history of the human species.

Subject-specific finite element simulation of the human femur considering inhomogeneous material properties: a straightforward method and convergence study

In numerical finite element (FE) simulations of human bones subject-specific models are necessary to reproduce the physiological conditions, which include the determination of inhomogeneous material properties from computed tomography (CT) scans and their implementation in the numerical model. In the present approach common software packages are directly used for the entire simulation process from segmentation of CT scans, surface reconstruction, mesh generation, calculation of mean element densities to FE simulation. The influence of the mesh discretisation level on the maximum displacement, the total system energy and the principal surface stress distribution of eight human femurs was analysed. Both the maximum displacement and the total system energy showed typical convergence behaviour towards an asymptotic value with decreasing element size. The principal surface stress distribution followed similar qualitative trends at all mesh discretisation levels studied for the same femur. However, the stress distributions did not converge with decreasing element size and still differed significantly between the two smallest element sizes studied of approximately 2mm and 1mm. The magnitude of convergence differed among the individual femurs. Thus, individual convergence studies in terms of local stress or strain distributions are necessary for accurately predicting local stress and strain values in subject-specific FE bone models.

Influence of altered gait patterns on the hip joint contact forces

Children who exhibit gait deviations often present a range of bone deformities, particularly at the proximal femur. Altered gait may affect bone growth and lead to deformities by exerting abnormal stresses on the developing bones. The objective of this study was to calculate variations in the hip joint contact forces with different gait patterns. Muscle and hip joint contact forces of four children with different walking characteristics were calculated using an inverse dynamic analysis and a static optimisation algorithm. Kinematic and kinetic analyses were based on a generic musculoskeletal model scaled down to accommodate the dimensions of each child. Results showed that for all the children with altered gaits both the orientation and magnitude of the hip joint contact force deviated from normal. The child with the most severe gait deviations had hip joint contact forces 30% greater than normal, most likely due to the increase in muscle forces required to sustain his crouched stance. Determining how altered gait affects joint loading may help in planning treatment strategies to preserve correct loading on the bone from a young age.

Soft tissue release of the spastic hip by psoas-rectus transfer and adductor tenotomy for long-term functional improvement and prevention of hip dislocation

The purpose of this study was to assess the long-term development of children with cerebral palsy treated with soft tissue releases of the hip and, if necessary, also of the hamstrings and the Achilles tendon. The follow-up had to consider the functional status and the hip centration. Seventy-one patients (46 with tetrapareses, 24 with dipareses, and one with triparesis) who underwent soft tissue releases of the hip by the so-called psoas-rectus transfer at an average age of 7 years were assessed preoperatively, after 1 year and at an average age of 19 years. Functional status and the radiological lapse were assigned. The functional status of the patients significantly improved (P<0.001) after surgery. The number of patients who were able to walk increased from 49.3 to 80.3%. The migration percentage decreased from 26.6 to 17.3%. For medium-to-severe functional deficits, a clear gain of function and a safe prevention of spastic hip luxation were achieved.

Normal development of the hip: a geometrical analysis based on planimetric radiography

The existing studies on the development of the hip joint predominantly focus on either the acetabulum or the proximal femur. This paper investigates the parallel geometrical development of both, the proximal femur and the acetabulum during growth. Six hundred and seventy-five hips with an age from 9 months to 16 years were studied by means of planimetric radiography; angles and lever arms were determined. Although the apophyseal angles remain virtually unchanged throughout growth, the epiphyseal angles and the neck-shaft angle undergo typical changes until the age of 10 years. Subsequently, there are no major changes in the angular conformation of the proximal femur, whereas acetabular coverage and its centric alignment continue to develop further until the end of skeletal growth. The load and muscle lever arms increase until the end of growth with their ratio remaining constant after the age of 10 years. We present correlated data on the geometrical development of the acetabulum and the proximal femur. The interpretation of our findings is to some extent limited by the two-dimensionality of planimetric radiography. Our results do, however, support the timing of corrective osteotomies of the proximal femur relatively soon after the age of 10 years.

[The natural history of developmental dysplasia of the hip. A meta-analysis of the published literature]

Assessment of the natural history of developmental dysplasia of the hip (DDH) is indispensable for age-dependent treatment of these patients. Based on a systematic meta-analysis of the published literature, this study gives an overview of the spontaneous course of DDH in different age decades. Furthermore, these results are discussed in the context of physiologic development of the hip. The data were compiled by a systematic literature search of medical databases from 1975 through 2007. For this evaluation, only papers that presented as high a level of evidence as possible were included. In early childhood, DDH with subluxation or dislocation necessitates treatment; otherwise, the spontaneous course leads invariably to osteoarthritis of the hip. However, a stable, well-centered dysplastic hip has a high potential of developing as a physiologic joint. In the analyzed data, an association between mild or moderate DDH after the end of growth and the development of osteoarthritis could not be demonstrated. The level of evidence of existing data is not sufficient to determine that persisting mild dysplasia is a relevant ethiopathological factor for osteoarthrosis of the hip. Therefore, prospective epidemiological studies are required.

Reconstruction of the greater trochanter with an allograft after resection of a giant cell tumor

Our report involves the rare case of a giant cell tumor which filled out the greater trochanter. After complete resection of the greater trochanter, reconstructive surgery using a bone allograft was performed. Although the allograft healed without any complications, it was resorbed within 28 months, and there were no signs of infection or tumor recurrence during this period. Even though the greater trochanter was missing, the 32-year-old patient did not have any complaints and showed no weakness of the abductor muscles. This shows that compensation for the missing greater trochanter is possible in adulthood. If the vasto-gluteal muscle sling is maintained, the greater trochanter, which would only function as a hypomochlion, may not be necessary. This is why we do not recommend reconstruction of the greater trochanter with an allograft when it is possible to maintain the tendineous junction between the vastus lateralis muscle and the gluteal muscles.