Human hip joint cartilage: MRI quantitative thickness and volume measurements discriminating acetabulum and femoral head

Fully automatic system to detect and segment the proximal femur in pelvic radiographic images for Legg-Calvé-Perthes disease

This study aimed to develop a method using computer vision techniques to accurately detect and delineate the proximal femur in radiographs of Legg-Calvé-Perthes disease (LCPD) patients. Currently, evaluating femoral head deformity, a crucial predictor of LCPD outcomes, relies on unreliable categorical and qualitative classifications. To address this limitation, we employed the pretrained object detection model YOLOv5 to detect the proximal femur on over 2000 radiographs, including images of shoulders and chests, to enhance robustness and generalizability. Subsequently, we utilized the U-Net convolutional neural network architecture for image segmentation of the proximal femur in more than 800 manually annotated images of stage IV LCPD. The results demonstrate outstanding performance, with the object detection model achieving high accuracy (mean average precision of 0.99) and the segmentation model attaining an accuracy score of 91%, dice coefficient of 0.75, and binary IoU score of 0.85 on the held-out test set. The proposed fully automatic proximal femur detection and segmentation system offers a promising approach to accurately detect and delineate the proximal femoral bone contour in radiographic images, which is essential for further image analysis in LCPD patients. Clinical significance: This study highlights the potential of computer vision techniques for enhancing the reliability of Legg-Calvé-Perthes disease staging and outcome prediction.

Accuracy of conventional motion capture in measuring hip joint center location and hip rotations during gait, squat, and step-up activities

Accurate measurements of hip joint kinematics are essential for improving our understanding of the effects of injury, disease, and surgical intervention on long-term hip joint health. This study assessed the accuracy of conventional motion capture (MoCap) for measuring hip joint center (HJC) location and hip joint angles during gait, squat, and step-up activities while using dynamic biplane radiography (DBR) as the reference standard. Twenty-four young adults performed six trials of treadmill walking, six body-weight squats, and six step-ups within a biplane radiography system. Synchronized biplane radiographs were collected at 50 images per second and MoCap was collected simultaneously at 100 images per second. Bone motion during each activity was determined by matching digitally reconstructed radiographs, created from subject-specific CT-based bone models, to the biplane radiographs using a validated registration process. Errors in estimating HJC location and hip angles using MoCap were quantified by the root mean squared error (RMSE) across all frames of available data. The MoCap error in estimating HJC location was larger during step-up (up to 89.3 mm) than during gait (up to 16.6 mm) or squat (up to 31.4 mm) in all three anatomic directions (all p < 0.001). RMSE in hip joint flexion (7.2°) and abduction (4.3°) during gait was less than during squat (23.8° and 8.9°) and step-up (20.1° and 10.6°) (all p < 0.01). Clinical analysis and computational models that rely on skin-mounted markers to estimate hip kinematics should be interpreted with caution, especially during activities that involve deeper hip flexion.

The Effects of Residual Femoral Deformity on Computed Contact Mechanics in Patients Treated With In Situ Fixation for Slipped Capital Femoral Epiphysis

OBJECTIVE

In situ fixation for treatment of slipped capital femoral epiphysis (SCFE) can stabilize the epiphysis and prevent further joint deformation but often leaves residual deformity that may adversely affect intra-articular contact mechanics. The purpose of this study was to investigate the relationship between residual deformity and contact mechanics in the post-SCFE hip.

METHODS

Patient-specific hip models were created for 19 patients with SCFE treated with in situ fixation. For each model, discrete element analysis was used to compute cumulative acetabular and femoral contact stress exposure during a walking gait cycle. Slip severity was evaluated for each patient using the two-dimensional Southwick angle and a novel three-dimensional (3D) assessment of multiplanar femoral deformity (3D slip angle).

RESULTS

Of the SCFE cases, 2/7 mild (Southwick angle ≤30 degrees) had peak cumulative femoral exposures equivalent to that of severe (Southwick angle ≥60 degrees) cases. Severe SCFE cases had higher peak ( P = 0.015) and mean ( P = 0.028) femoral contact stress exposure and lower cumulative femoral contact area ( P = 0.003) than mild (Southwick angle ≤30 degrees) SCFE cases. Mean femoral contact stress exposure was also higher in severe SCFE cases than in moderate SCFE cases ( P = 0.027). Acetabular and femoral contact mechanics metrics typically demonstrated stronger correlations with 3D slip angle than two-dimensional Southwick angle.

CONCLUSIONS

Increased slip severity adversely impacts intra-articular femoral contact mechanics. Contact mechanics metrics demonstrate higher correlations with 3D slip angle, indicating that this novel measurement may better describe global deformity and its relationship to intra-articular mechanics; however, the modest strength of these correlations may also imply that global impingement-generating deformity is not the primary factor driving contact mechanics in the post-SCFE hip.

CLINICAL RELEVANCE

Greater slip severity adversely impacts contact mechanics in the post-SCFE hip. However, focal regions of high contact stress were seen even in mild SCFE deformities, suggesting some type of deformity correction should be considered even for mild slips to alleviate secondary impingement, address focal incongruities, and reduce osteoarthritis development/progression.

Chronically elevated contact stress exposure correlates with intra-articular cartilage degeneration in patients with concurrent acetabular dysplasia and femoroacetabular impingement

Hip dysplasia is known to lead to premature osteoarthritis. Computational models of joint mechanics have documented elevated contact stresses in dysplastic hips, but elevated stress has not been directly associated with regional cartilage degeneration. The purpose of this study was to determine if a relationship exists between elevated contact stress and intra-articular cartilage damage in patients with symptomatic dysplasia and femoroacetabular impingement. Discrete element analysis was used to compute hip contact stresses during the stance phase of walking gait for 15 patients diagnosed with acetabular dysplasia and femoral head-neck offset deformity. Contact stresses were summed over the duration of the walking gait cycle and then scaled by patient age to obtain a measure of chronic cartilage contact stress exposure. Linear regression analysis was used to evaluate the relationship between contact stress exposure and cartilage damage in each of six acetabular subregions that had been evaluated arthroscopically for cartilage damage at the time of surgical intervention. A significant correlation (R2  = 0.423, p < 0.001) was identified between chondromalacia grade and chronic stress-time exposure above both a 1 MPa damage threshold and a 2 MPa-years accumulated damage threshold. Furthermore, an over-exposure threshold of 15% regional contact area exceeding the 1 and 2 MPa-years threshold values resulted in correct identification of cartilage damage in 83.3% (55/66) of the acetabular subregions loaded during gait. These results suggest corrective surgery to alleviate impingement and reduce chronic contact stress exposures below these damage-inducing thresholds could mitigate further cartilage damage in patients with hip dysplasia.

Determining and Achieving Target Limb Length and Offset in Total Hip Arthroplasty Using Intraoperative Digital Radiography

BACKGROUND

Achieving appropriate limb length and offset in total hip arthroplasty (THA) is challenging. Target limb length and offset may not always mean equal radiographic measurements bilaterally. The goal of this study is to introduce a method for determining as well as achieving target limb length and offset using digital radiographic measurements.

METHODS

One hundred and two consecutive patients with unilateral hip osteoarthritis undergoing primary THA in the lateral decubitus position were included. Limb length and offset were measured on anterior-posterior pelvic radiographs preoperatively, intraoperatively, and postoperatively. Offset was defined as the length of a line parallel to the inter-teardrop line, extending from the edge of the ischium, at about the lower border of the ipsilateral obturator foramen, to the edge of the femoral cortex, usually at, or just below, the neck resection level. Target limb length was determined for each patient based on patient perception and severity of disease. Target offset equaled the contralateral limb. Using intraoperative digital radiography, adjustments were made until targets were achieved and the hip was stable. Patients were followed for an average of 4.2 years postoperatively.

RESULTS

Limb length was within 5 mm of target measurements in 100% of patients and offset was within 5 mm of targets in 97.1%. Target measurements differed by >5 mm from the contralateral side in 2.0% of limb length and 2.9% of offset measurements. There were no significant differences between intraoperative and postoperative limb length (P = .261) or offset (P = .747) measurements. At final follow-up, there were no dislocations or reoperations and average Hip disability and Osteoarthritis Outcome Score for Joint Replacement was 95.78.

CONCLUSION

Target limb length and offset goals can be determined for most patients undergoing THA. Targets are not always equal to the contralateral side. Intraoperative digital radiography can allow surgeons to accurately achieve target limb length and offset to within 5 mm in a homogenous cohort of patients with unilateral hip osteoarthritis with excellent clinical outcomes.

Photoacoustic Imaging in Tissue Engineering and Regenerative Medicine

Several imaging modalities are available for investigation of the morphological, functional, and molecular features of engineered tissues in small animal models. While research in tissue engineering and regenerative medicine (TERM) would benefit from a comprehensive longitudinal analysis of new strategies, researchers have not always applied the most advanced methods. Photoacoustic imaging (PAI) is a rapidly emerging modality that has received significant attention due to its ability to exploit the strong endogenous contrast of optical methods with the high spatial resolution of ultrasound methods. Exogenous contrast agents can also be used in PAI for targeted imaging. Applications of PAI relevant to TERM include stem cell tracking, longitudinal monitoring of scaffolds in vivo, and evaluation of vascularization. In addition, the emerging capabilities of PAI applied to the detection and monitoring of cancer and other inflammatory diseases could be exploited by tissue engineers. This article provides an overview of the operating principles of PAI and its broad potential for application in TERM. Impact statement Photoacoustic imaging, a new hybrid imaging technique, has demonstrated high potential in the clinical diagnostic applications. The optical and acoustic aspect of the photoacoustic imaging system works in harmony to provide better resolution at greater tissue depth. Label-free imaging of vasculature with this imaging can be used to track and monitor disease, as well as the therapeutic progression of treatment. Photoacoustic imaging has been utilized in tissue engineering to some extent; however, the full benefit of this technique is yet to be explored. The increasing availability of commercial photoacoustic systems will make application as an imaging tool for tissue engineering application more feasible. This review first provides a brief description of photoacoustic imaging and summarizes its current and potential application in tissue engineering.

Quantification in Musculoskeletal Imaging Using Computational Analysis and Machine Learning: Segmentation and Radiomics

Although still limited in clinical practice, quantitative analysis is expected to increase the value of musculoskeletal (MSK) imaging. Segmentation aims at isolating the tissues and/or regions of interest in the image and is crucial to the extraction of quantitative features such as size, signal intensity, or image texture. These features may serve to support the diagnosis and monitoring of disease. Radiomics refers to the process of extracting large amounts of features from radiologic images and combining them with clinical, biological, genetic, or any other type of complementary data to build diagnostic, prognostic, or predictive models. The advent of machine learning offers promising prospects for automatic segmentation and integration of large amounts of data. We present commonly used segmentation methods and describe the radiomics pipeline, highlighting the challenges to overcome for adoption in clinical practice. We provide some examples of applications from the MSK literature.

Segmentation of hip cartilage in compositional magnetic resonance imaging: A fast, accurate, reproducible, and clinically viable semi-automated methodology

Manual segmentation is a significant obstacle in the analysis of compositional MRI for clinical decision-making and research. Our aim was to produce a fast, accurate, reproducible, and clinically viable semi-automated method for segmentation of hip MRI. We produced a semi-automated segmentation method for cartilage segmentation of hip MRI sequences consisting of a two step process: (i) fully automated hierarchical partitioning of the data volume generated using a bespoke segmentation approach applied recursively, followed by (ii) user selection of the regions of interest using a region editor. This was applied to dGEMRIC scans at 3T taken from a prospective longitudinal study of individuals considered at high-risk of developing osteoarthritis (SibKids) which were also manually segmented for comparison. Fourteen hips were segmented both manually and using our semi-automated method. Per hip, processing time for semi-automated and manual segmentation was 10-15, and 60-120 min, respectively. Accuracy and Dice similarity coefficient (DSC) for the comparison of semi-automated and manual segmentations was 0.9886 and 0.8803, respectively. Intra-observer and inter-observer reproducibility of the semi-automated segmentation method gave an accuracy of 0.9997 and 0.9991, and DSC of 0.9726 and 0.9354, respectively. We have proposed a fast, accurate, reproducible, and clinically viable semi-automated method for segmentation of hip MRI sequences. This enables accurate anatomical and biochemical measurements to be obtained quickly and reproducibly. This is the first such method that shows clinical applicability, and could have large ramifications for the use of compositional MRI in research and clinically. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

A narrative overview of the current status of MRI of the hip and its relevance for osteoarthritis research - what we know, what has changed and where are we going?

OBJECTIVE

To review and discuss the role of magnetic resonance imaging (MRI) in the context of hip osteoarthritis (OA) research.

DESIGN

The content of this narrative review, based on an extensive PubMed database research including English literature only, describes the advances in MRI of the hip joint and its potential usefulness in hip OA research, reviews the relevance of different MRI features in regard to symptomatic and structural progression in hip OA, and gives an outlook regarding future use of MRI in hip OA research endeavors.

RESULTS

Recent technical advances have helped to overcome many of the past difficulties related to MRI assessment of hip OA. MRI-based morphologic scoring systems allow for detailed assessment of several hip joint tissues and, in combination with the recent advances in MRI, may increase reproducibility and sensitivity to change. Compositional MRI techniques may add to our understanding of disease onset and progression. Knowledge about imaging pitfalls and anatomical variants is crucial to avoid misinterpretation. In comparison to research on knee OA, the associations between MRI features and the incidence and progression of disease as well as with clinical symptoms have been little explored. Anatomic alterations of the hip joint as seen in femoro-acetabular impingement (FAI) seem to play a role in the onset and progression of structural damage.

CONCLUSIONS

With the technical advances occurring in recent years, MRI may play a major role in investigating the natural history of hip OA and provide an improved method for assessment of the efficacy of new therapeutic approaches.

Segmentation of joint and musculoskeletal tissue in the study of arthritis

As the most frequent cause of physical disability, musculoskeletal diseases such as arthritis and osteoporosis have a great social and economical impact. Quantitative magnetic resonance imaging (MRI) biomarkers are important tools that allow clinicians to better characterize, monitor, and even predict musculoskeletal disease progression. Post-processing pipelines often include image segmentation. Manually identifying the border of the region of interest (ROI) is a difficult and time-consuming task. Manual segmentation is also affected by inter- and intrauser variability, thus limiting standardization. Fully automatic or semi-automatic methods that minimize the user interaction are highly desirable. Unfortunately, an ultimate, highly reliable and extensively evaluated solution for joint and musculoskeletal tissue segmentation has not yet been proposed, and many clinical studies still adopt fully manual procedures. Moreover, the clinical translation of several promising quantitative MRI techniques is highly affected by the lack of an established, fast, and accurate segmentation method. The goal of this review is to present some of the techniques proposed in recent literature that have been adopted in clinical studies for joint and musculoskeletal tissue analyses in arthritis patients. The most widely used MRI sequences and image processing algorithms employed to accomplish segmentation challenges will be discussed in this paper.

Evaluation of Automated Volumetric Cartilage Quantification for Hip Preservation Surgery

Automating the process of femoroacetabular cartilage identification from magnetic resonance imaging (MRI) images has important implications to guiding clinical care by providing a temporal metric that allows for optimizing the timing for joint preservation surgery. In this paper, we evaluate a new automated cartilage segmentation method using a time trial, segmented volume comparison, overlap metrics, and Euclidean distance mapping. We report interrater overlap metrics using the true fast imaging with steady-state precession MRI sequence of 0.874, 0.546, and 0.704 for the total overlap, union overlap, and mean overlap, respectively. This method was 3.28× faster than manual segmentation. This technique provides clinicians with volumetric cartilage information that is useful for optimizing the timing for joint preservation procedures.

Comparison of T2 Values in the Lateral and Medial Portions of the Weight-Bearing Cartilage of the Hip for Patients With Symptomatic Femoroacetabular Impingement and Asymptomatic Volunteers

PURPOSE

To develop a simplified method to define a clinically relevant subregion in the course of arthroscopic treatment of femoroacetabular impingement (FAI) using T2 mapping in patients and asymptomatic volunteers. Additionally, we sought to compare the lateral and medial subregion values in asymptomatic volunteers and in patients presenting with FAI. Finally, we wanted to investigate possible associations between patients' T2 mapping values and demographic variables-i.e., alpha angle, age, sex, and body mass index (BMI).

METHODS

Twenty-five asymptomatic volunteers and 23 consecutive symptomatic patients with FAI (cam or mixed type) were prospectively enrolled and evaluated with a sagittal T2 mapping sequence. The weight-bearing region of the acetabular and femoral cartilage was manually segmented and divided into medial and lateral subregions. Median T2 values were determined, and patient characteristics were assessed as potential predictors of T2 values.

RESULTS

T2 values in the lateral portion of the acetabulum were lower than in the medial portion for both asymptomatic volunteers (43 v 53 ms; P < .001) and patients with FAI (42 v 49 ms; P = .016). The medial acetabulum (MA) of asymptomatic volunteers had higher T2 values than those of the FAI group (53 v 49 ms; P = .040). The lateral-minus-medial difference was significantly larger among asymptomatic volunteers than in patients with FAI (P = .047). Patients with FAI had higher alpha angles than those of the asymptomatic volunteers, but no other associations with patient characteristics were observed.

CONCLUSIONS

This study's findings suggest that there are differences in cartilage T2 mapping values between medial and lateral weight-bearing aspects of the hip and may expand the application and usefulness of biochemical magnetic resonance imaging (MRI) techniques, specifically T2 mapping, in the diagnosis of hip cartilage damage with the evaluation of clinically relevant subregions. When comparing asymptomatic volunteers and patients with FAI presenting with cam or mixed type deformity, we observed a significant contrast between the T2 mapping values of the lateral and medial portions of the weight-bearing zone of the acetabular cartilage, whereas such contrast was not observed when zone 3 was analyzed as a whole.

LEVEL OF EVIDENCE

Level III, development of diagnostic criteria on the basis of consecutive patients with a universally applied reference gold standard.

COMPUTATIONAL ANALYSIS OF THE REGENERATED KNEE STRUCTURE AFTER BONE MARROW STIMULATION TECHNIQUES

Bone marrow stimulation techniques, such as abrasion arthroplasty or microfracture, have been widely used for repairing cartilage; however, the mechanical stress analysis of these surgical techniques has not been fully investigated. In this study, finite element analysis was used to investigate stresses produced in complex structures (e.g., cartilage, subchondral bone and trabecular bone) using 2D knee structural models. Abrasion arthroplasty creates global damages only in subchondral bone, but, microfracture technique creates local damages in both trabecular and subchondral regions. Although stresses do not significantly change in trabecular bones as 50% recovery occurs in both abrasion and microfacture samples, significant changes are observed in both subchondral bone and cartilage layer depending on the procedure. The maximum stress levels in the microfractured bone represent approximately a 10.48% increase in cartilage and a 38.25% increase in subchondral bones compared to normal conditions. After 150% recovery, however, all three layers increase their stress levels in microfractured samples. Therefore, the 2D computational analysis results suggest that the microfracture technique should be cautiously used.

OARSI Clinical Trials Recommendations: Hip imaging in clinical trials in osteoarthritis

Imaging of hip in osteoarthritis (OA) has seen considerable progress in the past decade, with the introduction of new techniques that may be more sensitive to structural disease changes. The purpose of this expert opinion, consensus driven recommendation is to provide detail on how to apply hip imaging in disease modifying clinical trials. It includes information on acquisition methods/techniques (including guidance on positioning for radiography, sequence/protocol recommendations/hardware for magnetic resonance imaging (MRI)); commonly encountered problems (including positioning, hardware and coil failures, artifacts associated with various MRI sequences); quality assurance/control procedures; measurement methods; measurement performance (reliability, responsiveness, and validity); recommendations for trials; and research recommendations.

MRI of the hip for the evaluation of femoroacetabular impingement; past, present, and future

The concept of femoroacetabular impingement (FAI) has, in a relatively short time, come to the forefront of orthopedic imaging. In just a few short years MRI findings that were in the past ascribed to degenerative change, normal variation, or other pathologies must now be described and included in radiology reports, as they have been shown, or are suspected to be related to, FAI. Crucial questions have come up in this time, including: what is the relationship of bony morphology to subsequent cartilage and labral damage, and most importantly, how is this morphology related to the development of osteoarthritis? In this review, we attempt to place a historical perspective on the controversy, provide guidelines for interpretation of MRI examinations of patients with suspected FAI, and offer a glimpse into the future of MRI of this complex condition.

Impact of hip anatomical variations on the cartilage stress: a finite element analysis towards the biomechanical exploration of the factors that may explain primary hip arthritis in morphologically normal subjects

BACKGROUND

Hip arthritis is a pathology linked to hip-cartilage degeneration. Although the etiology of this disease is not well defined, it is known that age is a determinant risk factor. However, hip arthritis in young patients could be largely promoted by biomechanical factors. The objective of this paper is to analyze the impact of some normal anatomical variations on the cartilage stress distributions numerically predicted at the hip joint during walking.

METHODS

A three-dimensional finite element model of the femur and the pelvis with the most relevant axial components of muscle forces was used to simulate normal walking activity. The hip anatomical condition was defined by: neck shaft angle, femoral anteversion angle, and acetabular anteversion angle with a range of 110-130°, 0-20°, and 0-20°, respectively. The direct boundary method was used to simulate the hip contact.

FINDINGS

The hydrostatic stress found at the cartilage and labrum showed that a ±10° variation with respect to the reference brings significant differences between the anatomic models. Acetabular anteversion angle of 0° and femoral anteversion angle of 0° were the most affected anatomical conditions with values of hydrostatic stress in the cartilage near 5MPa under compression.

INTERPRETATION

Cartilage stresses and contact areas were equivalent to the results found in literature and the most critical anatomical regions in terms of tissue loads were in a good accordance with clinical evidence. Altogether, results showed that decreasing femoral or acetabular anteversion angles isolatedly causes a dramatic increase in cartilage loads.

Preliminary evaluation of an MRI-based technique for displaying and quantifying bony deformities in cam-type femoroacetabular impingement

PURPOSE

Characterizing aspheric deformities of the femoral head-neck junction in cam-type femoroacetabular impingement (FAI) requires representing the location, size, or extent of the bony lesion. The objectives of this work are to (1) assess the feasibility of creating 3D models of cam deformities from MRI sets, (2) present a standardized 2D visualization of the lesion, and (3) present and evaluate the potential utility of summary metrics in distinguishing between FAI patients and control subjects.

METHODS

Using MRIs from five subjects with diagnosed cam-type FAI and four healthy subjects, we developed a technique based on subtracting an estimated normal surface from each subject's actual bone surface in order to generate a subject-specific 2D "diagnosis graph" that characterized the femoral deformity. The models from three control subjects were combined to create the baseline model.

RESULTS

The RMS fitting error between the surface models of individual control subjects and their corresponding baseline models was 1.05 mm across the head and the head-to-neck transition region. In the anterosuperior region of the 2D diagnosis graphs, the mean height of the detected cam deformities relative to the estimated baseline normal shape was 17.9 % of the head radius for the five FAI subjects (95 % CI 8.5-27.3 %) and 7.0 % (95 % CI 2.9-11.1 %) for the four control subjects. A binary logistic regression analysis indicated that an h/r ratio larger than a threshold of [Formula: see text] = 10.7 % (equivalent to approximately 2.3 mm in height) yielded the best discrimination between cam-type FAI subjects and normal subjects.

CONCLUSIONS

Our 2D diagnosis graph qualitatively enabled the cam-type lesions in four of our five diagnosed patients to be clearly visualized on MRI-derived models. We believe this visualization tool may be helpful in better characterizing cam-type lesions for diagnosis and for developing more precise plans for surgical treatment.

Optimization of the position of the acetabulum in a ganz periacetabular osteotomy by finite element analysis

Periacetabular osteotomy (PAO) is a surgical procedure to correct acetabular orientation in developmental dysplasia of the hip (DDH). It changes the position of the acetabulum to increase femoral head coverage and distribute the contact pressure over the cartilage surface. The success of PAO depends significantly on the surgeon's experience. Using computed tomography data from patients with DDH, we developed a 3D finite element (FE) model to investigate the optimal position of the acetabulum following PAO. A virtual PAO was performed with the acetabulum rotated in increments from the original center edge (CE) angle. Contact area, contact pressure, and Von Mises stress in the femoral and pelvic cartilage were analyzed. Five dysplastic hips from four patients were modeled. Contact area, contact pressure, and Von Mises stress in the cartilage all varied according to the change of CE angle through virtual PAO. An optimal position could be achieved for the acetabulum that maximizes the contact area while minimizing the contact pressure and von Mises stress in the pelvic and femoral cartilage. The optimal position of the acetabulum was patient dependent and did not always correspond to what would be considered a "normal" CE angle. We demonstrated for the first time the interrelation of correction angle, contact area, and contact pressure between the pelvic and femoral cartilage in PAO surgery.

A system for individualized prosthetic modeling of the femoral head

The matching quality between the femoral head prosthesis and the acetabulum plays an important role in the operative treatment of femoral head prosthetics and femoral head replacement. To obtain the optimal model of the femoral head prosthesis for the target sufferer, an individualized modeling system is shown in this paper. It can recover the necrotic femoral heads into the satisfactory models. These models can well match with the acetabulum. This new system affords a theoretical model for the accurate operation position fixing in the orthopedic clinic. And this system also provides an innovative practical means for the individualized modeling of the artificial femoral head prosthesis.

Accuracy limits for the thickness measurement of the hip joint cartilage in 3-D MR images: simulation and validation

This paper describes a theoretical simulation method for ascertaining the inherent limits on the accuracy of thickness measurement of hip joint cartilage in 3-D MR images. This method can specify where and how thickness can be measured with sufficient accuracy under the certain MR imaging conditions. In the numerical simulation, we present a mathematical model for two adjacent sheet structures separated by a small distance, which simulated the femoral and acetabular cartilage and the joint space width in the hip joint; moreover, we perform the numerical simulation of MR imaging and postprocessing for thickness measurement. We especially focused on the effects of voxel anisotropy in MR imaging with variable orientation of cartilage surface and different joint space width. Also, thickness measurement is performed in MR imaging with isotropic voxel. The results from MR data with isotropic voxels show that accurate measurement of cartilage thickness at location of measured values of the hip joint space width and the cartilage thickness being two times as large as the voxel size or above should be possible. The simulation method is validated by comparison with the actual results obtained from the experiments using three phantoms, five normal cadaver hip specimens, and nine patients with osteoarthritis.

Future therapeutics for osteoarthritis

Osteoarthritis (OA) is a disease of the joints that affects several million individuals worldwide. This disease, which involves mainly the diarthrodial joints, is chronic and develops slowly over decades, making it very difficult to precisely identify the different etiological and risk factors that influence its onset. At present, most therapies for OA are symptomatic. This review will focus on new OA therapeutics in development that are directed toward pain relief as well as others with the potential to reduce or stop the progression of the disease (DMOADs). This article is part of a Special Issue entitled "Osteoarthritis".

MR imaging of early hip joint degeneration

MR imaging is one of the most commonly used imaging techniques to evaluate patients with hip pain. Intra-articular abnormalities of the hip joint are better assessed with recent advances in MR imaging technology, such as high-field strength scanners, improved coils, and more signal-to-noise ratio-efficient sequences. This article discusses the causes of early hip joint degeneration and the current use of morphologic and physiologic MR imaging techniques for evaluating the articular cartilage of the hip joint. The article also discusses the role of MR arthrography in clinical cartilage imaging.

Three-dimensional magnetic resonance imaging analysis of hip morphology in the assessment of femoral acetabular impingement

AIM

To determine a possible association between femoral-acetabular impingement (FAI) volume and the development of labral tear using a three-dimensional (3D) model reconstruction of the acetabulum and the femoral head.

MATERIALS AND METHODS

Magnetic resonance arthrography images of the hip in 42 patients with pain and suspected labral tear were acquired using a 1.5T MRI machine. Using 3D analysis software, outlines of the acetabular cup and femoral head were drawn and 3D reconstruction obtained. To control for differences in patient size, ratios of acetabulum : femoral head volume (AFV) and acetabulum : femoral head surface area (AFA) were used for analysis. The association between volume of acetabulum : femoral head and FAI was investigated using ANOVA analysis.

RESULTS

There were 19 men and 23 women with a mean age of 39 years (range 18-78 years). The average AFV was 0.64 (range 0.37-1.05, SD 0.16) and AFA was 0.73 (range 0.36-1.26, SD 0.23). Herniation pit was significantly associated with a small AFV.

CONCLUSION

Femoral neck herniation pits are associated with a low AFV. Gross volume and surface area ratios do not appear to correlate with labral tears or cartilage loss. This technique will enable more advanced analysis of morphological variations associated with FAI.

Role of proinflammatory cytokines in the pathophysiology of osteoarthritis

Osteoarthritis (OA) is associated with cartilage destruction, subchondral bone remodeling and inflammation of the synovial membrane, although the etiology and pathogenesis underlying this debilitating disease are poorly understood. Secreted inflammatory molecules, such as proinflammatory cytokines, are among the critical mediators of the disturbed processes implicated in OA pathophysiology. Interleukin (IL)-1β and tumor necrosis factor (TNF), in particular, control the degeneration of articular cartilage matrix, which makes them prime targets for therapeutic strategies. Animal studies provide support for this approach, although only a few clinical studies have investigated the efficacy of blocking these proinflammatory cytokines in the treatment of OA. Apart from IL-1β and TNF, several other cytokines including IL-6, IL-15, IL-17, IL-18, IL-21, leukemia inhibitory factor and IL-8 (a chemokine) have also been shown to be implicated in OA and could possibly be targeted therapeutically. This Review discusses the current knowledge regarding the role of proinflammatory cytokines in the pathophysiology of OA and addresses the potential of anticytokine therapy in the treatment of this disease.

Fully automated system for the quantification of human osteoarthritic knee joint effusion volume using magnetic resonance imaging

INTRODUCTION

Joint effusion is frequently associated with osteoarthritis (OA) flare-up and is an important marker of therapeutic response. This study aimed at developing and validating a fully automated system based on magnetic resonance imaging (MRI) for the quantification of joint effusion volume in knee OA patients.

METHODS

MRI examinations consisted of two axial sequences: a T2-weighted true fast imaging with steady-state precession and a T1-weighted gradient echo. An automated joint effusion volume quantification system using MRI was developed and validated (a) with calibrated phantoms (cylinder and sphere) and effusion from knee OA patients; (b) with assessment by manual quantification; and (c) by direct aspiration. Twenty-five knee OA patients with joint effusion were included in the study.

RESULTS

The automated joint effusion volume quantification was developed as a four stage sequencing process: bone segmentation, filtering of unrelated structures, segmentation of joint effusion, and subvoxel volume calculation. Validation experiments revealed excellent coefficients of variation with the calibrated cylinder (1.4%) and sphere (0.8%) phantoms. Comparison of the OA knee joint effusion volume assessed by the developed automated system and by manual quantification was also excellent (r = 0.98; P < 0.0001), as was the comparison with direct aspiration (r = 0.88; P = 0.0008).

CONCLUSIONS

The newly developed fully automated MRI-based system provided precise quantification of OA knee joint effusion volume with excellent correlation with data from phantoms, a manual system, and joint aspiration. Such an automated system will be instrumental in improving the reproducibility/reliability of the evaluation of this marker in clinical application.

Extreme leg motion analysis of professional ballet dancers via MRI segmentation of multiple leg postures

PURPOSE

Professional ballet dancers are subject to constant extreme motion which is known to be at the origin of many articular disorders. To analyze their extreme motion, we exploit a unique magnetic resonance imaging (MRI) protocol, denoted as 'dual-posture' MRI, which scans the subject in both the normal (supine) and extreme (split) postures. However, due to inhomogeneous tissue intensities and image artifacts in these scans, coupled with unique acquisition protocol (split posture), segmentation of these scans is difficult. We present a novel algorithm that exploits the correlation between scans (bone shape invariance, appearance similarity) in automatically segmenting the dancer MRI images.

METHODS

While validated segmentation algorithms are available for standard supine MRI, these algorithms cannot be applied to the split scan which exhibits a unique posture and strong inter-subject variations. In this study, the supine MRI is segmented with a deformable models method. The appearance and shape of the segmented supine models are then re-used to segment the split MRI of the same subject. Models are first registered to the split image using a novel constrained global optimization, before being refined with the deformable models technique.

RESULTS

Experiments with 10 dual-posture MRI datasets in the segmentation of left and right femur bones reported accurate and robust results (mean distance error: 1.39 ± 0.31 mm).

CONCLUSIONS

The use of segmented models from the supine posture to assist the split posture segmentation was found to be equally accurate and consistent to supine results. Our results suggest that dual-posture MRI can be efficiently and robustly segmented.