Finite element analysis of mechanical behavior of human dysplastic hip joints: a systematic review

Bibliometric analysis of the acetabular labrum

The acetabular labrum (AL) plays a crucial role in the normal physiological functioning of the hip joint. This study aims to present an overview of the current status and research hotspots concerning the AL and to explore the field from a bibliometric perspective. A total of 1918 AL-related records published between January 1, 2000 and November 8, 2023 were gathered from the Web of Science Core Collection database. By utilizing tools such as HisCite, CiteSpace, VOSviewer, and the R package "bibliometrix," the regions, institutions, journals, authors, and keywords were analyzed to predict the latest trends in AL research. Global research interest and publication output related to this topic continues to escalate. The United States leads in international collaborations, number of publications, and citation frequency, underscoring its preeminent position in this field. The American Hip Institute emerged as the most prolific institution, making the greatest contribution to publications. Notably, Arthroscopy and the American Journal of Sports Medicine are the 2 most popular journals in this domain, accounting for 13.29% and 10.1% of publications, respectively, and were also found to be the most co-cited journals. Amongst authors, Benjamin G. Domb leads with 160 articles (8.35%), while Marc J. Philippon is the most frequently cited author. The keyword co-occurrence network showed 3 hot clusters, including "AL," "femoral acetabular impingement (FAI)," and "osteoarthritis." In addition, "survivorship," "FAI," and "patient-reported outcomes" were identified as trending topics for future exploration. This study represents the first comprehensive bibliometric analysis, summarizing the present state and future trends in AL research. The findings serve as a valuable resource for scholars, offering practical insights into key information within the field and identifying potential research frontiers and emerging directions in the near future.

The role of torsional stress in the development of subchondral insufficiency fracture of the femoral head: A finite element model analysis

BACKGROUND

Subchondral insufficiency fracture of the femoral head generally occurs without evidence of trauma or with a history of minor trauma. Insufficient bone quality is considered one cause; however, the detailed mechanism of fracture development at the subchondral area (SA) is not understood. The aim of this study was to clarify the directions of force that cause subchondral fracture using finite element model analysis.

METHODS

Two types of finite element models were generated from the CT data of femurs obtained from three individuals without osteoporosis (normal models) and another three with osteoporosis (osteoporosis models). Three directions of force, including compressive, shearing, and torsional, were applied to the femoral head. The distribution of von Mises stress (Mises stress) was evaluated at the SA, principal compressive trabeculae (PC), and principal tensile trabeculae.

RESULTS

Under compressive force, the mean Mises stress value was greatest at the PC in both the normal and osteoporosis models. Under shearing force, the mean Mises stress value tended to be greatest at the SA in the normal model and at the PC in the osteoporosis model. Under torsional force, the mean Mises stress value was greatest at the SA in both types of models.

CONCLUSIONS

The torsional force showed the greatest Mises stress at the SA in both the normal and osteoporosis models, suggesting the importance of torsion as a possible force responsible for subchondral insufficiency fracture development.

Neonatal Hip Loading in Developmental Dysplasia: Finite Element Simulation of Proximal Femur Growth and Treatment

Background

Abnormal prenatal hip joint loading can lead to compromised hip joint function. Early intervention is crucial for favorable outcomes.

Purpose

This study investigates the impact of treatment timing (initiation and duration) on cartilage growth and ossification in the proximal femur of infants with developmental dysplasia of the hip, a condition affecting newborns.

Methods

We used a mechanobiological model to simulate proximal femur growth during treatment durations of 3 months, 6 months, and a late-start treatment.

Results

The findings indicate that the timing of treatment initiation is crucial, while a longer treatment duration does not contribute to improved morphological development of the hip joint.

Conclusions

Mechanobiological models of growth can be used to develop treatments and therapies that correct loading conditions. Growing bone is particularly sensitive to loading conditions, and altered loading during growth can affect bone shape and functionality.

Finite element modeling of the human cervical spinal cord and its applications: A systematic review

Background Context

Finite element modeling (FEM) is an established tool to analyze the biomechanics of complex systems. Advances in computational techniques have led to the increasing use of spinal cord FEMs to study cervical spinal cord pathology. There is considerable variability in the creation of cervical spinal cord FEMs and to date there has been no systematic review of the technique. The aim of this study was to review the uses, techniques, limitations, and applications of FEMs of the human cervical spinal cord.

Methods

A literature search was performed through PubMed and Scopus using the words finite element analysis, spinal cord, and biomechanics. Studies were selected based on the following inclusion criteria: (1) use of human spinal cord modeling at the cervical level; (2) model the cervical spinal cord with or without the osteoligamentous spine; and (3) the study should describe an application of the spinal cord FEM.

Results

Our search resulted in 369 total publications, 49 underwent reviews of the abstract and full text, and 23 were included in the study. Spinal cord FEMs are used to study spinal cord injury and trauma, pathologic processes, and spine surgery. Considerable variation exists in the derivation of spinal cord geometries, mathematical models, and material properties. Less than 50% of the FEMs incorporate the dura mater, cerebrospinal fluid, nerve roots, and denticulate ligaments. Von Mises stress, and strain of the spinal cord are the most common outputs studied. FEM offers the opportunity for dynamic simulation, but this has been used in only four studies.

Conclusions

Spinal cord FEM provides unique insight into the stress and strain of the cervical spinal cord in various pathological conditions and allows for the simulation of surgical procedures. Standardization of modeling parameters, anatomical structures and inclusion of patient-specific data are necessary to improve the clinical translation.

LibHip: An open-access hip joint model repository suitable for finite element method simulation

BACKGROUND AND OBJECTIVE

population-based finite element analysis of hip joints allows us to understand the effect of inter-subject variability on simulation results. Developing large subject-specific population models is challenging and requires extensive manual effort. Thus, the anatomical representations are often subjected to simplification. The discretized geometries do not guarantee conformity in shared interfaces, leading to complications in setting up simulations. Additionally, these models are not openly accessible, challenging reproducibility. Our work provides multiple subject-specific hip joint finite element models and a novel semi-automated modeling workflow.

METHODS

we reconstruct 11 healthy subject-specific models, including the sacrum, the paired pelvic bones, the paired proximal femurs, the paired hip joints, the paired sacroiliac joints, and the pubic symphysis. The bones are derived from CT scans, and the cartilages are generated from the bone geometries. We generate the whole complex's volume mesh with conforming interfaces. Our models are evaluated using both mesh quality metrics and simulation experiments.

RESULTS

the geometry of all the models are inspected by our clinical expert and show high-quality discretization with accurate geometries. The simulations produce smooth stress patterns, and the variance among the subjects highlights the effect of inter-subject variability and asymmetry in the predicted results.

CONCLUSIONS

our work is one of the largest model repositories with respect to the number of subjects and regions of interest in the hip joint area. Our detailed research data, including the clinical images, the segmentation label maps, the finite element models, and software tools, are openly accessible on GitHub and the link is provided in Moshfeghifar et al.(2022)[1]. Our aim is to empower clinical researchers to have free access to verified and reproducible models. In future work, we aim to add additional structures to our models.

Biomechanical Characteristics of the Femoral Isthmus during Total Hip Arthroplasty in Patients with Adult Osteoporosis and Developmental Dysplasia of the Hip: A Finite Element Analysis

Objective

This study investigated the underlying mechanisms of high fracture incidence in the femoral isthmus from a biomechanical perspective.

Methods

We retrospectively analyzed a total of 923 primary total hip arthroplasty (THA) patients and 355 osteoporosis (OP) patients admitted from January 2010 to January 2018. Through a series of screening conditions, 47 patients from each group were selected for inclusion in the study. The datasets on the unaffected side and affected side of the patients with unilateral developmental dysplasia of the hip (uDDH) were respectively classified as the normal group (Group I) and he tDDH group (Group II), and that of patients with osteoporosis were classified as the OP group (Group III). In this study, first, we collected computed tomography (CT) images and measured geometric parameters (inner and outer diameters) of the isthmus. Thereafter, to study biomechanical properties, we established six finite element models and calculated values of von Mises stress for each group with the methods of data conversion and grid processing.

Results

Compared with those of patients in the normal group, the values of the inner and outer diameters of femoral isthmus of patients in the DDH group were significantly lower (P < 0.001), while the inner diameters of patients in the OP group were significantly higher (P < 0.001) and the outer diameters of patients in the OP group showed no significant difference (P> 0.05). The cortical rates of patients in the normal group and the DDH group appeared insignificant (P > 0.05), and those of patients in normal group were significantly higher than those of patients in the OP group (P < 0.001). Moreover, patients in the DDH group showed a higher von Mises stress value than patients in the normal group (P < 0.001), but statistically speaking the values between patients in the OP and normal groups were insignificant (P > 0.05).

Conclusions

The relatively shorter inner and outer diameters of the isthmus in DDH resulted in intensive von Mises stress under the torque of the hip location, and induced a high fracture incidence. However, in patients in the OP group, the geometric morphology exhibited no anatomical variation, and the fracture was not due to the intensity of von Mises stress.

The epidemic of thyroid cancer in China: Current trends and future prediction

Background

Thyroid cancer (TC) is one of the most common cancers in China. The aim of this study was to identify the potential age, period, and cohort effect under the long-term trends in TC incidence and mortality, making projections up to 2030.

Methods

Incidence and mortality data on TC were obtained from the Global Burden of Disease Study 2019. The population predictions were obtained from the United Nations World Population Prospects 2019. An age–period–cohort model was used for the analysis.

Results

From 1990 to 2019, the net drift (the overall annual percentage change of TC over time adjusted for age groups) of the TC incidence was 5.01% (95% confidence interval [CI]: 4.72%, 5.29%) for men and 1.48% (95% CI: 1.14%, 1.82%) for women. The net drift of TC mortality was 1.64% (95% CI: 1.38%, 1.91%) for men and –2.51% (95% CI: –2.77%, –2.26%) for women. Regarding the incidence of TC, both the period and the cohort relative risks (RRs) in men and women showed an overall increasing trend. As to the mortality rate of TC, both the period and cohort RRs in women showed a monotonic declining trend. The period RRs for men decreased after 2015, but the cohort RRs revealed a fluctuating upward pattern. From 2019 to 2030, the TC incidence was projected to rise by 32.4% in men and 13.1% in women, the mortality declining by 13.0% in men and 17.3% in women. The elderly was projected to have an increasing proportion of TC occurrence and deaths.

Conclusions

Over the past 30 years, the incidence rate of TC in China has continually increased, and this trend was projected to continue. Although male mortality has increased in the past, it is expected to decline in the future. The proportion of older people among TC occurrence and death was projected to gradually increase, and the difficulties elderly with TC lrequire more attention.

Postoperative stability following a triple pelvic osteotomy is affected by implant configuration: a finite element analysis

BACKGROUND

The triple pelvic osteotomy is an established surgical method with multiple modifications regarding surgical technique and choice of implant. The stability of the osteotomy is affected by numerous factors, and among these, the three-dimensional implant configuration is a scientifically less explored aspect.

METHODS

We used a finite element model of a hemi-pelvis with a standardized triple osteotomy to calculate relative flexibility for loads in all translational degrees of freedom for five different implant configurations. Two of the configurations used entry points only feasible when implant removal was not necessary.

RESULTS

The stability of the osteotomy improved with an increased distance between the implants in the plane of the osteotomy as well as for a more perpendicular angle relative to the osteotomy plane. The implant configurations with more entry points available made this easier to adhere to.

CONCLUSION

The use of bioabsorbable implants may provide better opportunities for optimal implant constructs which can, to a certain degree, compensate for the lesser mechanical stiffness of bioabsorbable polymers as compared to metal implants.

Evaluation of the short-term curative effect of closed reduction in the treatment of developmental dysplasia of the hip based on three-dimensional magnetic resonance imaging finite element analysis

Background

Based on the Digital Imaging and Communications in Medicine (DICOM) data of three-dimensional magnetic resonance imaging (3D-MRI), finite element models of the hip joints of children with developmental dysplasia of the hip were established. The primary objectives included simulation and analysis of the finite element model pre- and post-closed reduction under different stances and loads, and evaluation of the size and distribution of von Mises stress in the acetabulum and femoral head pre- and post-operation and the short-term effects.

Methods

Acetabular index measurements of both the unaffected and affected sides were conducted, alongside International Hip Dysplasia Institute (IHDI) classification of the affected hip. Establishing the finite element model of both the affected and unaffected hips was based on the 3D-T1WI sequence DICOM data, using Mimics, 3-matic, and Ansys software, before and after closed reduction surgery. The size and distribution data of von Mises stress on the affected side of the acetabulum and femoral head were collected pre- and post-operation.

Results

The study indicated that the increasing acetabular index of the affected hip was directly proportional to the increasing severity based on IHDI classification (P < 0.05). Preoperative IHDI classification significantly correlated with the von Mises stress (r = 0.560–0.569, 0.562–0.564, P < 0.05). Under different stances and load conditions, the von Mises stress on the affected side post-operation was lower than that noted pre-operation (P < 0.01), while that on the acetabulum increased proportionally to the load. Although the magnitude and distribution of von Mises stress on the affected side of the acetabulum were similar to those on the healthy side post-operation, there were statistical differences between the two (P < 0.01). The von Mises stress of the lateral column of the femoral head post-operation was significantly lower than that noted pre-operation (P < 0.01). While the high-stress points of the lateral column disappeared post-operation, the von Mises stress was evenly distributed in the femoral head.

Conclusions

The 3D-MRI finite element could provide the von Mises stress value and distribution characteristics of the acetabulum and femoral head pre- and post-operation. Closed reduction can, therefore, improve the size and distribution of von Mises stress on the affected acetabulum and femoral head.

Is Anterior Rotation of the Acetabulum Necessary to Normalize Joint Contact Pressure in Periacetabular Osteotomy? A Finite-element Analysis Study

BACKGROUND

Inappropriate sagittal plane correction can result in an increased risk of osteoarthritis progression after periacetabular osteotomy (PAO). Individual and postural variations in sagittal pelvic tilt, along with acetabular deformity, affect joint contact mechanics in dysplastic hips and may impact the direction and degree of acetabular correction. Finite-element analyses that account for physiologic pelvic tilt may provide valuable insight into the effect of PAO on the contact mechanics of dysplastic hips, which may lead to improved acetabular correction during PAO.

QUESTIONS/PURPOSES

We performed virtual PAO using finite-element models with reference to the standing pelvic position to clarify (1) whether lateral rotation of the acetabulum normalizes the joint contact pressure, (2) risk factors for abnormal contact pressure after lateral rotation of the acetabulum, and (3) whether additional anterior rotation of the acetabulum further reduces contact pressure.

METHODS

Between 2016 and 2020, 85 patients (92 hips) underwent PAO to treat hip dysplasia. Eighty-two patients with hip dysplasia (lateral center-edge angle < 20°) were included. Patients with advanced osteoarthritis, femoral head deformity, prior hip or spine surgery, or poor-quality images were excluded. Thirty-eight patients (38 hips) were eligible to participate in this study. All patients were women, with a mean age of 39 ± 10 years. Thirty-three women volunteers without a history of hip disease were reviewed as control participants. Individuals with a lateral center-edge angle < 25° or poor-quality images were excluded. Sixteen individuals (16 hips) with a mean age of 36 ± 7 years were eligible as controls. Using CT images, we developed patient-specific three-dimensional surface hip models with the standing pelvic position as a reference. The loading scenario was based on single-leg stance. Four patterns of virtual PAO were performed in the models. First, the acetabular fragment was rotated laterally in the coronal plane so that the lateral center-edge angle was 30°; then, anterior rotation in the sagittal plane was added by 0°, 5°, 10°, and 15°. We developed finite-element models for each acetabular position and performed a nonlinear contact analysis to calculate the joint contact pressure of the acetabular cartilage. The normal range of the maximum joint contact pressure was calculated to be < 4.1 MPa using a receiver operating characteristic curve. A paired t-test or Wilcoxon signed rank test with Bonferroni correction was used to compare joint contact pressures among acetabular positions. We evaluated the association of joint contact pressure with the patient-specific sagittal pelvic tilt and acetabular version and coverage using Pearson or Spearman correlation coefficients. An exploratory univariate logistic regression analysis was performed to identify which of the preoperative factors (CT measurement parameters and sagittal pelvic tilt) were associated with abnormal contact pressure after lateral rotation of the acetabulum. Variables with p values < 0.05 (anterior center-edge angle and sagittal pelvic tilt) were included in a multivariable model to identify the independent influence of each factor.

RESULTS

Lateral rotation of the acetabulum decreased the median maximum contact pressure compared with that before virtual PAO (3.7 MPa [range 2.2-6.7] versus 7.2 MPa [range 4.1-14 MPa], difference of medians 3.5 MPa; p < 0.001). The resulting maximum contact pressures were within the normal range (< 4.1 MPa) in 63% of the hips (24 of 38 hips). The maximum contact pressure after lateral acetabular rotation was negatively correlated with the standing pelvic tilt (anterior pelvic plane angle) (ρ = -0.52; p < 0.001) and anterior center-edge angle (ρ = -0.47; p = 0.003). After controlling for confounding variables such as the lateral center-edge angle and sagittal pelvic tilt, we found that a decreased preoperative anterior center-edge angle (per 1°; odds ratio 1.14 [95% CI 1.01-1.28]; p = 0.01) was independently associated with elevated contact pressure (≥ 4.1 MPa) after lateral rotation; a preoperative anterior center-edge angle < 32° in the standing pelvic position was associated with elevated contact pressure (sensitivity 57%, specificity 96%, area under the curve 0.77). Additional anterior rotation further decreased the joint contact pressure; the maximum contact pressures were within the normal range in 74% (28 of 38 hips), 76% (29 of 38 hips), and 84% (32 of 38 hips) of the hips when the acetabulum was rotated anteriorly by 5°, 10°, and 15°, respectively.

CONCLUSION

Via virtual PAO, normal joint contact pressure was achieved in 63% of patients by normalizing the lateral acetabular coverage. However, lateral acetabular rotation was insufficient to normalize the joint contact pressure in patients with more posteriorly tilted pelvises and anterior acetabular deficiency. In patients with a preoperative anterior center-edge angle < 32° in the standing pelvic position, additional anterior rotation is expected to be a useful guide to normalize the joint contact pressure.

CLINICAL RELEVANCE

This virtual PAO study suggests that biomechanics-based planning for PAO should incorporate not only the morphology of the hip but also the physiologic pelvic tilt in the weightbearing position in order to customize acetabular reorientation for each patient.

Does Patient-specific Functional Pelvic Tilt Affect Joint Contact Pressure in Hip Dysplasia? A Finite-element Analysis Study

BACKGROUND

Although individual and postural variations in the physiologic pelvic tilt affect the acetabular orientation and coverage in patients with hip dysplasia, their effect on the mechanical environment in the hip has not been fully understood. Individual-specific, finite-element analyses that account for physiologic pelvic tilt may provide valuable insight into the contact mechanics of dysplastic hips, which can lead to further understanding of the pathogenesis and improved treatment of this patient population.

QUESTION/PURPOSE

We used finite-element analysis to ask whether there are differences between patients with hip dysplasia and patients without dysplasia in terms of (1) physiologic pelvic tilt, (2) the pelvic position and joint contact pressure, and (3) the morphologic factors associated with joint contact pressure.

METHODS

Between 2016 and 2019, 82 patients underwent pelvic osteotomy to treat hip dysplasia. Seventy patients with hip dysplasia (lateral center-edge angle ≥ 0° and < 20° on supine AP pelvic radiographs) were included. Patients with advanced osteoarthritis, femoral head deformity, prior hip or supine surgery, or poor-quality imaging were excluded. Thirty-two patients (32 hips) were eligible to this finite-element analysis study. For control groups, we reviewed 33 female volunteers without a history of hip disease. Individuals with frank or borderline hip dysplasia (lateral center-edge angle < 25°) or poor-quality imaging were excluded. Sixteen individuals (16 hips) were eligible as controls. Two board-certified orthopaedic surgeons measured sagittal pelvic tilt (the angle between the anterior pelvic plane and vertical axis: anterior pelvic plane [APP] angle) and acetabular version and coverage using pelvic radiographs and CT images. Intra- and interobserver reliabilities, evaluated using the kappa value and intraclass correlation coefficient, were good or excellent. We developed individual-specific, finite-element models using pelvic CT images, and performed nonlinear contact analysis to calculate the joint contact pressure on the acetabular cartilage during the single-leg stance with respect to three pelvic positions: standardized (anterior pelvic plane), supine, and standing. We compared physiologic pelvic tilt between patients with and without dysplasia using a t-test or the Wilcoxon rank sum test. A paired t-test or the Wilcoxon signed rank test with a Bonferroni correction was used to compare joint contact pressure between the three pelvic positions. We correlated joint contact pressure with morphologic parameters and pelvic tilt using the Pearson or the Spearman correlation coefficients.

RESULTS

The APP angle in the supine and standing positions varied widely among individuals. It was greater in patients with hip dysplasia than in patients in the control group when in the standing position (3° ± 6° versus -2° ± 8°; mean difference 5° [95% CI 1° to 9°]; p = 0.02) but did not differ between the two groups when supine (8° ± 5° versus 5° ± 7°; mean difference 3° [95% CI 0° to 7°]; p = 0.06). The mean pelvic tilt was 6° ± 5° posteriorly when shifting from the supine to the standing position in patients with hip dysplasia. The median (range) maximum contact pressure was higher in dysplastic hips than in control individuals (in standing position; 7.3 megapascals [MPa] [4.1 to 14] versus 3.5 MPa [2.2 to 4.4]; difference of medians 3.8 MPa; p < 0.001). The median maximum contact pressure in the standing pelvic position was greater than that in the supine position in patients with hip dysplasia (7.3 MPa [4.1to 14] versus 5.8 MPa [3.5 to 12]; difference of medians 1.5 MPa; p < 0.001). Although the median maximum joint contact pressure in the standardized pelvic position did not differ from that in the standing position (7.4 MPa [4.3 to 15] versus 7.3 MPa [4.1 to 14]; difference of medians -0.1 MPa; p > 0.99), the difference in the maximum contact pressure varied from -3.3 MPa to 2.9 MPa, reflecting the wide range of APP angles (mean 3° ± 6° [-11° to 14°]) when standing. The maximum joint contact pressure in the standing position was negatively correlated with the standing APP angle (r = -0.46; p = 0.008) in patients with hip dysplasia.

CONCLUSION

Based on our findings that individual and postural variations in the physiologic pelvic tilt affect joint contact pressure in the hip, future studies on the pathogenesis of hip dysplasia and joint preservation surgery should not only include the supine or standard pelvic position, but also they need to incorporate the effect of the patient-specific pelvic tilt in the standing position on the biomechanical environment of the hip.

CLINICAL RELEVANCE

We recommend assessing postural change in sagittal pelvic tilt when diagnosing hip dysplasia and planning preservation hip surgery because assessment in a supine or standard pelvic position may overlook alterations in the hip's contact mechanics in the weightbearing positions. Further studies are needed to elucidate the effect of patient-specific functional pelvic tilt on the degeneration process of dysplastic hips, the acetabular reorientation maneuver, and the clinical result of joint preservation surgery.

Increased Loading Rates During Gait Correlate With Morphology of Unaffected Hip in Juveniles With Treated Developmental Hip Dysplasia

Long-term follow-up studies on children with surgically treated developmental dysplasia of the hip (DDH) have shown that not only the affected side progresses to premature osteoarthritis, but the unaffected side may also suffer from insidious hip dysplasia or osteonecrosis. The current gait analysis study identified the loading and unloading rates of the ground reaction forces (GRF) and lower limb joint axial forces during gait, and their correlations with the hip morphology in twenty juvenile patients with surgically treated unilateral DDH during toddlerhood. In a gait laboratory, each subject walked at preferred speed on a 10-m walkway while the kinematics and the GRF were measured. Loading and unloading rates of the vertical GRF and the joint axial forces were obtained as the maximum instantaneous slope of these force curves. Radiographic measurements of the hips were taken, and the correlations between the morphological parameters and the loading and unloading rates were obtained. The patients showed greater-than-normal peak loading rates of the joint axial forces, and the loading rates on both the affected and unaffected sides were strongly correlated to the acetabular index on the unaffected side, which was also significantly correlated with the peak unloading rates on the affected side. These results suggest that apart from regular follow-up of the affected hip, routine assessment of the morphological changes and/or increased loading rates on the unaffected hip is also important for early identification of any signs of insidious hip dysplasia and risk of premature degeneration of the cartilage.

Effect of acetabular morphological parameters applied in proximal femoral varus osteotomy on the treatment of developmental dysplasia of the hip in children

BACKGROUND

The study was carried out based on the background that though proximal femoral varus osteotomy is one of the most effective methods in treating developmental dysplasia of the hip (DDH), its surgical efficiency and effect need to be improved.

METHODS

The neck shaft angle and acetabular morphological parameters were measured before and after operation and during clinical follow-up. The Severin criteria and McKay criteria were both adopted to score the measurements. The distance from the center of the femoral head to the medial cutting bone (expressed as C value) and the shortened lengths of the proximal femur (expressed as Δ S) calculated by formula and obtained by actual measurement were compared.

RESULTS

The neck shaft angle and acetabular morphological parameters after operation and during clinical follow-up were significantly lower than those before operation (P<0.05). The proportion of children with McKay scores of I, II, III, and IV after operation was 50.00%, 41.67%, 8.33%, and 0.00%, respectively; while the proportion of children with Severin scores of I, II, III, and IV was 55.00%, 38.33%, 6.67%, and 0.00%, respectively. There were no significant differences in the C value and Δ S obtained after formula calculation and actual measurement (P>0.05).

CONCLUSIONS

The acetabular morphological parameters applied in proximal femoral varus osteotomy are of great value for the treatment of DDH in children.

Discrete element and finite element methods provide similar estimations for hip joint contact mechanics during walking gait

Finite element analysis (FEA) provides a powerful approach for estimating the in-vivo loading characteristics of the hip joint during various locomotory and functional activities. However, time-consuming procedures, such as the generation of high-quality FE meshes and setup of FE simulation, typically make the method impractical for rapid applications which could be used in clinical routine. Alternatively, discrete element analysis (DEA) has been developed to quantify mechanical conditions of the hip joint in a fraction of time compared to FEA. Although DEA has proven effective in the estimation of contact stresses and areas in various complex applications, it has not yet been well characterised by its ability to evaluate contact mechanics for the hip joint during gait cycle loading using data from several individuals. The objective of this work was to compare DEA modelling against well-established FEA for analysing contact mechanics of the hip joint during walking gait. Subject-specific models were generated from magnetic resonance images of the hip joints in five asymptomatic subjects. The DEA and FEA models were then simulated for 13 loading time-points extracted from a full gait cycle. Computationally, DEA was substantially more efficient compared to FEA (simulation times of seconds vs. hours). The DEA and FEA methods had similar predictions for contact pressure distribution for the hip joint during normal walking. In all 13 simulated loading time-points across five subjects, the maximum difference in average contact pressures between DEA and FEA was within ±0.06 MPa. Furthermore, the difference in contact area ratio computed using DEA and FEA was less than ±6%.

Distribution of Femoral Head Subchondral Fracture Site Relates to Contact Pressures, Age, and Acetabular Structure

OBJECTIVE. Nontraumatic subchondral fracture of the femoral head (FH) is often seen in elderly patients with osteoporosis and acetabular dysplasia. Although this injury can also occur in young people, even those without osteoporosis, it remains unclear who is at risk. We examined the acetabular structure and sites of subchondral fracture of the FH in young patients compared with those in middle-aged and older patients. MATERIALS AND METHODS. Forty-eight hips with nontraumatic subchondral fracture of the FH were divided into two groups according to patient age: young (< 40 years) and middle-aged and older (≥ 40 years). Dysplasia and retroversion were defined as a lateral center-edge angle of < 20° and crossover sign on anterosuperior radiographs, respectively. Locations and extents of fracture were evaluated by measuring the edge location of low-signal-intensity bands on coronal T1-weighted MR images. Stress distribution on subchondral bone in young patients was evaluated in contralateral unaffected hips with the same acetabular structure using finite element modeling based on CT. RESULTS. Twelve hips were in young patients and 36 were in middle-aged and older patients. Hips in young patients showed retroversion in 41.7%, whereas those in middle-aged and older patients had dysplasia in 38.9%. Young patients had larger mediolateral fractures; fractures in middle-aged and older patients were laterally located. Anterosuperior fractures were seen in both groups. Contact stress in patients with retroversion was mainly distributed on the mediolateral and superior sides but was concentrated laterally and superiorly in one patient with dysplasia. CONCLUSION. Mediolateral and anterosuperior fractures and stress distribution by retroversion were commonly observed in young patients, suggesting partial involvement of retroversion in the mechanism of injury of nontraumatic subchondral fractures of the FH in young patients.

Effect of sagittal pelvic tilt on joint stress distribution in hip dysplasia: A finite element analysis

BACKGROUND

Physiologic pelvic tilt can change acetabular orientation and coverage in patients with hip dysplasia. In this study, we aimed to clarify the impact of change in sagittal pelvic tilt on joint stress distribution in dysplastic hips.

METHODS

We developed patient-specific finite element models of 21 dysplastic hips and 21 normal hips. The joint contact area, contact pressure, and equivalent stress of the acetabular cartilage were assessed at three pelvic tilt positions relative to the functional pelvic plane: 10° anterior tilt, no tilt, and 10° posterior tilt.

FINDINGS

The mean contact area was 0.6-0.7 times smaller, the mean maximum contact pressure was 1.8-1.9 times higher, and the mean maximum equivalent stress was 1.3-2.8 times higher in dysplastic hips than in normal hips at all three pelvic positions. As the pelvis tilted from 10° anterior to 10° posterior, the mean contact area decreased, and the mean maximum contact pressure and median maximum equivalent stress increased. The latter two changes were more significant in dysplastic hips than in normal hips (total increment was 1.3 MPa vs. 0.4 MPa, P = 0.001, and 3.6 MPa vs. 0.4 MPa, P < 0.001, respectively). The mean equivalent stress increased in the anterosuperior acetabulum during posterior pelvic tilt in dysplastic and normal hips, while the change was not significant in the superior and posterosuperior acetabulum in both groups.

INTERPRETATION

Sagittal pelvic tilt alters the loading environment and joint stress distribution of the hip joint and may impact the degeneration process in dysplastic hips.

Gait kinematics of the hip, pelvis, and trunk associated with external hip adduction moment in patients with secondary hip osteoarthritis: toward determination of the key point in gait modification

Background

A larger daily cumulative hip loading, which is the product of the external hip adduction moment (HAM) impulse during gait and the number of steps per day has been identified as a factor associated with the progression of secondary hip osteoarthritis (OA). The cause of the increased HAM impulse in patients with hip OA has not been identified. The purpose of this study was to identify the gait parameters associated with HAM impulse during gait in patients with secondary hip OA.

Methods

Fifty-five patients (age 22–65 years) with mild-to-moderate secondary hip OA participated in this cross-sectional study. The HAM impulse during gait was measured using a three-dimensional gait analysis system. To identify the gait parameters associated with HAM impulse, hierarchical multiple regression analysis was performed. The first model (basic model) included body weight and stance phase duration. The second models included gait parameters (gait speed; ground reaction force [GRF] in frontal plane; and hip, pelvic, and trunk angle in frontal plane) and hip pain in addition to the basic model.

Results

Body weight and stance phase duration explained 61% of the variance in HAM impulse. In the second model, which took into account body weight and stance phase duration, hip adduction angle (9.4%), pelvic tilt (6.5%), and trunk lean (3.2%) in addition to GRF explained the variance in the HAM impulse. Whereas larger hip adduction angle and pelvic tilt toward the swing limb were associated with a larger HAM impulse, larger trunk lean toward the stance limb was associated with smaller HAM impulse.

Conclusion

In patients with excessive hip adduction and pelvic tilt toward the swing limb during gait, gait modification may contribute to the reduction of hip joint loading.

Gait- and postural-alignment-related prognostic factors for hip and knee osteoarthritis: Toward the prevention of osteoarthritis progression

Osteoarthritis (OA) is a chronic progressive disease, and thus, prevention of this progression is an important issue. Currently, there is little evidence of the effect of exercise therapy for the prevention of hip and knee OA progression. An understanding of prognostic factors is the basis for the prevention of progression. Previous research indicates that in case of knee OA, abnormalities in knee alignment (varus or valgus) while standing, varus thrust during walking, increased knee flexion in the early stance phase, abnormal displacement of the femur in relation to the tibia, and an increase in knee adduction and flexion moment are risk factors for disease progression. At the same time, the prognostic factors in hip OA are anterior spinal inclination while standing, decreased mobility of the thoracolumbar spine, and increased cumulative hip loading during daily walking. Further research is required to investigate these prognostic factors, particularly the modifiable factors, to analyze the relationships between these factors, and to verify the structural and clinical efficacy of modifying these factors through interventions.

Hip Arthroscopy of a Painful Hip with Borderline Dysplasia

Purpose

Hip arthroscopy has been considered for treating hip dysplasia; however, its efficacy is still a matter of controversy. Here, we report outcomes of patients with borderline dysplasia treated with a contemporary hip arthroscopy technique.

Materials and Methods

Forty-seven hips with borderline hip dysplasia were treated using hip arthroscopy. Patients underwent procedures to correct torn labrums or ligamentum teres with additional procedure on the acetabular capsule. Patient outcomes were assessed using visual analogue scale (VAS), modified Harris Hip Score (mHHS), Nonarthritic Hip Score (NAHS) and patient satisfaction. Risk factors for poor prognosis were also investigated.

Results

The mean follow up period was 25.9 months. At the last follow up, mean VAS score decreased from 6.1±1.6 to 3.5±2.8 (P=0.016). The mHHS and NHAS at the last follow up improved from 61.0±7.6 to 78.6±19.5 (P=0.001) and 62.1±7.5 to 80.0±18.5 (P=0.002), respectively. While significant improvement was observed in all patient reported outcome measures tested, 19 (40.4%) hips indicated that “the operation was unsatisfactory.” The only factor shown to influence outcomes was preoperative VAS (i.e., worse scores potentially an indicator of poor outcomes).

Conclusion

The results of the current study indicate that arthroscopic management may be beneficial for a subset of patients with borderline dysplasia; however, the dissatisfaction rate associated with this treatment approach may be as high as 40%. The poor preoperative pain score appears to be the sole indicator for poor outcomes.

Prediction of mechanical behavior of cartilaginous infant hips in pavlik harness: A subject-specific simulation study on normal and dysplastic hips

In dysplastic infant hips undergoing abduction harness treatment, cartilage contact pressure is believed to have a role in therapeutic cartilage remodeling and also in the complication of femoral head avascular necrosis. To improve our understanding of the role of contact pressure in the remodeling and the complication, we modeled cartilage contact pressure in cartilaginous infant hips undergoing Pavlik harness treatment. In subject-specific finite element modeling, we simulated contact pressure of normal and dysplastic hips in Pavlik harness at 90° flexion and gravity-induced abduction angles of 40°, 60° and 80°. We demonstrated that morphologies of acetabulum and femoral head both affected contact pressure distributions. The simulations showed that in Pavlik harness, contact pressure was mainly distributed along anterior and posterior acetabulum, leaving the acetabular roof only lightly loaded (normal hip) or unloaded (dysplastic hip). From a mechanobiological perspective, these conditions may contribute to therapeutic remodeling of the joint in Pavlik harness. Furthermore, contact pressure increased with the angle of abduction, until at the extreme abduction angle (80°), the lateral femoral head also contacted the posterior acetabular edge. Contact pressure in this area could contribute to femoral head avascular necrosis by reducing flow in femoral head blood vessels. The contact pressure we simulated can plausibly account for both the therapeutic effects and main adverse effect of abduction harness treatment for developmental dysplasia of the hip. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Hip Joint Contact Pressure Distribution During Pavlik Harness Treatment of an Infant Hip: A Patient-Specific Finite Element Model

Developmental dysplasia of the hip (DDH) in infants under 6 months of age is typically treated by the Pavlik harness (PH). During successful PH treatment, a subluxed/dislocated hip is spontaneously reduced into the acetabulum, and DDH undergoes self-correction. PH treatment may fail due to avascular necrosis (AVN) of the femoral head. An improved understanding of mechanical factors accounting for the success/failure of PH treatment may arise from investigating articular cartilage contact pressure (CCP) within a hip during treatment. In this study, CCP in a cartilaginous infant hip was investigated through patient-specific finite element (FE) modeling. We simulated CCP of the hip equilibrated at 90 deg flexion at abduction angles of 40 deg, 60 deg, and 80 deg. We found that CCP was predominantly distributed on the anterior and posterior acetabulum, leaving the superior acetabulum (mainly superolateral) unloaded. From a mechanobiological perspective, hypothesizing that excessive pressure inhibits growth, our results qualitatively predicted increased obliquity and deepening of the acetabulum under such CCP distribution. This is the desired and observed therapeutic effect in successful PH treatment. The results also demonstrated increase in CCP as abduction increased. In particular, the simulation predicted large magnitude and concentrated CCP on the posterior wall of the acetabulum and the adjacent lateral femoral head at extreme abduction (80 deg). This CCP on lateral femoral head may reduce blood flow in femoral head vessels and contribute to AVN. Hence, this study provides insight into biomechanical factors potentially responsible for PH treatment success and complications.

Sagittal alignment and mobility of the thoracolumbar spine are associated with radiographic progression of secondary hip osteoarthritis

OBJECTIVE

To identify predictors of radiographic progression of hip osteoarthritis (OA) over 12 months among functional hip impairments and spinal alignment and mobility.

DESIGN

Fifty female patients with secondary hip OA, excluding those with end-stage hip OA, participated in this prospective cohort study. Joint space width (JSW) of the hip was measured at baseline and 12 months later. With radiographic progression of hip OA over 12 months (>0.5 mm in JSW) as dependent variable, logistic regression analyses were performed to identify predictors for hip OA progression among functional impairments of the hip and spine with and without adjustment for age, body mass index (BMI), and minimum JSW at baseline. The independent variables were hip pain, Harris hip score (HHS), hip morphological parameters, hip passive range of motion (ROM) and muscle strength, and alignment and mobility of the thoracolumbar spine at baseline.

RESULTS

Twenty-one (42.0%) patients demonstrated radiographic progression of hip OA. Multivariable logistic regression analysis showed that larger anterior inclination of the spine in standing position (adjusted OR [95% CI], 1.37 [1.04-1.80]; P = 0.028) and less thoracolumbar spine mobility (adjusted OR [95% CI], 0.96 [0.92-0.99]; P = 0.037) at baseline were statistically significantly associated with radiographic progression of hip OA, even after adjustment for age, BMI, and minimum JSW.

CONCLUSIONS

The findings suggest that spinal alignment and mobility should be considered when assessing risk and designing preventive intervention for radiographic progression of secondary hip OA.

Theoretical Implications of Periacetabular Osteotomy in Various Dysplastic Acetabular Cartilage Defects as Determined by Finite Element Analysis

Background

Different extents and locations of acetabular cartilage defect have been supposed to be a major cause of undesirable outcomes of periacetabular osteotomy (PAO) in patients with developmental dysplasia of the hip (DDH). This study aimed to verify whether different locations of cartilage deficiency affect the biomechanical environment in a three-dimensional model utilizing finite element analysis (FEA).

Material/Methods

We developed 3 DDH models – DDH-1 (normal shape), DDH-2 (superior defect), and DDH-3 (anterosuperior defect) – by deforming from a normal hip model. We also developed 3 PAO models – PAO-1, PAO-2, and PAO-3 – through rotating osteotomized fragments.

Results

The maximum von Mises stress in the normal hip was 13.06 MPa. In the DDH-1 model, the maximum value on the load-bearing area decreased from 15.49 MPa pre-PAO to 14.28 MPa post-PAO, while stresses in the DDH-2 and DDH-3 models were higher than in the DDH-1 model, both pre-PAO and post-PAO (30.46 MPa to 26.04 MPa for DDH-2; 33.89 MPa to 27.48 MPa for DDH-3).

Conclusions

This study shows that, both pre- and post-PAO, different types of cartilage deficiency affect the biomechanical environment. Furthermore, in dysplastic hips, obtaining accurate three-dimensional information about the acetabular cartilage can contribute substantially to PAO decision making.