Computed Tomography: Role in Femoroacetabular Impingement

Femoroacetabular impingement (FAI) physiopathology is still unclear; however, there is a consensus that a pathological mechanical contact between the femoral neck-head junction and the acetabulum leads to pain and cartilage damage. Computed tomography (CT) is useful in FAI diagnosis and surgical planning. In the present chapter, we will analyze the role of CT in FAI, with special emphasis on alignment and comparison of measurements related to epidemiological variables. We analyzed 101 CT of patients that consulted in our institution for a non-joint-or-bone-related reason. Prior to the measurement of acetabular variables, CT image must be corrected in three planes. Acetabular version is a gender- and age-related measurement. As age increased, acetabular version increased, and the same impact age has on Wiberg angle. Femoral FAI-related measurement is not related to epidemiological variables. CT has a very important role for a better understanding of hip anatomy, and further research using CT images should be encouraged

Correlations between the alpha angle and femoral head asphericity: Implications and recommendations for the diagnosis of cam femoroacetabular impingement

pre-printObjective: To determine the strength of common radiographic and radial CT views for measuring true femoral head asphericity. Patients and Methods: In 15 patients with cam femoroacetabular impingement (FAI) and 15 controls, alpha angles were measured by two observers using radial CT (0º, 30º, 60º, 90º) and digitally reconstructed radiographs (DRRs) for the: anterior-posterior (AP), standing frog-leg lateral, 45° Dunn with neutral rotation, 45° Dunn with 40°external rotation, and cross-table lateral views. A DRR validation study was performed. Alpha angles were compared between groups. Maximum deviation from a sphere of each subject was obtained from a previous study. Alpha angles from each view were correlated with maximum deviation. Results: There were no significant differences between alpha angles measured on radiographs and the corresponding DRRs (p = 0.72). Alpha angles were significantly greater in patients for all views (p ≤0.002). Alpha angles from the 45° Dunn with 40° external rotation, cross-table lateral, and 60° radial views had the strongest correlations with maximum deviation (r = 0.831; r 20 = 0.823; r=0.808, respectively). The AP view had the weakest correlation (r = 0.358). Conclusion: DRRs were a validated means to simulate hip radiographs. The 45° Dunn with 40° external rotation, cross-table lateral, and 60º radial views best visualized femoral asphericity. Although commonly used, the AP view did not visualize cam deformities well. Overall, the magnitude of the alpha angle may not be indicative of the size of the deformity. Thus, 3D reconstructions and measurements of asphericity could improve the diagnosis of cam FAI. Key Words: Cam Femoroacetabular Impingement Alpha Angle, Femur Asphericity, Digitally Introduction Cam-type femoroacetabular impingement (FAI) has been implicated as a cause of chondrolabral damage, hip osteoarthritis (OA), and musculoskeletal pain in young adults [1-3]. Cam FAI is characterized by an aspherical femoral head and/or insufficient femoral head-neck offset [4,5]. Identifying the degree of femoral head asphericity is important as the underlying goal of surgery to correct cam FAI is to restore a more normal, spherical morphology to the femoral head. The alpha angle is a two-dimensional (2D) radiographic measure of femoral head asphericity that is commonly used to diagnose cam FAI [6-8]. Although, first proposed by Notzli et al. for only an oblique axial view of the femur, use of the alpha angle has been extended to several radiographic projections and radial computed tomography (CT) or magnetic resonance (MR) views [7,9-14]. Unfortunately, alpha angle measurements can vary between views of the same femur [10,15,16]. Consequently, the ideal view to diagnose cam FAI remains unknown [15,17]. One approach to identify the optimal view in which to measure the alpha angle has been to quantify observer repeatability. However, reports of repeatability have not been consistent and repeatability is not necessarily a measure of effectiveness [18,19]. Another approach has been to correlate alpha angles from standard radiographic views to oblique axial or radial MRI/CT views [12,14,15,17]. Still, alpha angle measurements from radial views are not generated automatically, and thus do not provide a true reference standard. In addition, radial views do not consider the geometry of the entire femoral head. Alternatively, subject-specific 3D reconstructions of femur morphology, generated from volumetric CT or MR images, can be used to visualize the anatomy of the entire femoral head. By fitting the 3D reconstruction to a sphere, UU IR Author Manuscript UU IR Author Manuscript University of Utah Institutional Repository Author Manuscript one can quantify the size of a deformity as maximum deviation from the sphere, herein referred to as 'true femoral head asphericity' [20,21]

Doctor of Philosophy

dissertationFemoroacetabular impingement (FAI) describes subtle structural abnormalities, including femoral asphericity and acetabular overcoverage, which reduce clearance in the hip joint. FAI is a common cause of hip pain for young, athletic adults. The first theme of this dissertation investigated if FAI morphology is more prevalent in athletes and if physical exams could be used to identify individuals with underlying FAI morphology. In a cohort of collegiate football players, 95% were found to have radiographic abnormalities consistent with those seen in FAI patients. This finding not only suggests that athletes, such as football players, may have an increased risk for developing symptomatic FAI, but also highlights that FAI morphology may frequently occur in asymptomatic subjects. In the same cohort, radiographic measures of femoral asphericity and femoral head-neck offset were mildly correlated to maximum internal rotation. As such, athletes with diminished internal rotation in whom hip pain develops should be evaluated for FAI. Altered articulation in FAI hips is believed to cause chondrolabral damage and may lead to osteoarthritis, but FAI kinematics have not been accurately quantified. To this end, the second theme of this dissertation focused on developing, validating, and applying a dual fluoroscopy and model-based tracking protocol to accurately quantify three-dimensional in vivo hip kinematics. In a cadaver experiment, model-based tracking was compared to the reference standard, dynamic radiostereometric analysis. Model-based tracking was found to have a positional error less than 0.48 mm and rotational error was less than 0.58°. The methodology was then applied to evaluate a cohort of asymptomatic control subjects and three patients with differing FAI morphology. The results, which represent the most accurate data collected on hip kinematics to date, demonstrate that hip articulation is a highly complex process, including translation, pelvic motion, no bone contact, and labrum involvement in large ranges of motion. Collected data provide necessary baseline results for future comparison studies and could be used to validate computer simulations of impingement, guide pre-operative planning, and serve as boundary conditions in finite element models investigating chondrolabral mechanics

An integrated platform for hip joint osteoarthritis analysis: design, implementation and results

Purpose: We present a software designed to improve hip joint osteoarthritis (OA) understanding using 3D anatomical models, magnetic resonance imaging (MRI) and motion capture. Methods: In addition to a standard static clinical evaluation (anamnesis, medical images examination), the software provides a dynamic assessment of the hip joint. The operator can compute automatically and in real-time the hip joint kinematics from optical motion capture data. From the estimated motion, the software allows for the calculation of the active range of motion, the congruency and the center of rotation of the hip joint and the detection and localization of the femoroacetabular impingement region. All these measurements cannot be performed clinically. Moreover, to improve the subjective reading of medical images, the software provides a set of 3D measurement tools based on MRI and 3D anatomical models to assist and improve the analysis of hip morphological abnormalities. Finally, the software is driven by a medical ontology to support data storage, processing and analysis. Results: We performed an in vivo assessment of the software in a clinical study conducted with 30 professional ballet dancers, a population who are at high risk of developing OA. We studied the causes of OA in this selected population. Our results show that extreme motion exposes the morphologically "normal” dancer's hip to recurrent superior or posterosuperior FAI and to joint subluxation. Conclusion: Our new hip software includes all the required materials and knowledge (images data, 3D models, motion, morphological measurements, etc.) to improve orthopedists' performances in hip joint OA analysi

Doctor of Philosophy

dissertationGeometric abnormalities of the human hip joint, as found in femoroacetabular impingement (FAI) and acetabular dysplasia, alter hip biomechanics and may be the primary causes of osteoarthritis in young adults. However, empirical evidence of direct correlations between abnormal geometry, altered biomechanics, and osteoarthritis is scarce. Also, clinical measures used to diagnose FAI and dysplasia still have substantial limitations, including questions about their reliability, assumptions about hip joint geometry and their ability to definitively distinguish pathologic from normal hips. The goals of this dissertation are twofold. First, a set of tools are presented and applied to quantify three-dimensional (3D) anatomical differences between hips with FAI and control subjects. The 3D tools were developed, validated and applied to patients with a subtype of FAI, called cam FAI, to improve basic understanding of the spectrum of FAI deformities, and to provide meaningful new metrics of morphology that are relatable to current diagnostic methods and translate easily for clinical use. The second goal of this dissertation is to improve our understanding of intra-articular hip contact mechanics as well as hip joint kinematics and muscle forces. To do so, a finite element study of intraarticular cartilage contact mechanics was completed with a cohort of live human subjects, using a validated modeling protocol. Finally, musculoskeletal modeling was used with gait data from healthy subjects and acetabular dysplasia patients to provide preliminary estimates of hip joint kinematics, kinetics, and muscle forces and compare differences between the groups. The translational methods of this dissertation utilized techniques from orthopaedics, computer science, physical therapy, mechanics, and medical imaging. Results from this dissertation offer new insight into the complex pathomechanics and pathomorphology of FAI and acetabular dysplasia. Application and extension of the work of this dissertation has the potential to help establish links between FAI and dysplasia with osteoarthritis and to improve patient care

Pelvic kinematics as confounding factor for cam hip impingement

The purpose of this thesis was to explore a range of biomechanical factors linked to the development of symptoms and potentially early onset hip OA in people with cam hip impingement. This was achieved through shape analysis on 3D bone models (segmented from medical images), and motion analysis performed during walking and squatting. Following ethical approval, kinematic and morphological variables were obtained from 19 pre-operative hip impingement patients and 18 healthy controls, and these were compared between groups. Patients demonstrated reduced neck-shaft-angles (-6.0°, p<.01) and increased anterior pelvic tilt during gait (+3.2°, p=.04) which are thought to predispose to impingement by decreasing the proximity between the cam and acetabular rim and making abutment more likely. The transverse pelvic plane is used to measure pelvic tilt during motion analysis, it is therefore interesting that the angle between the transverse and anterior pelvic plane is increased (+4.6°, p=.03) in patients, emphasising that the interplay between shape and function is a priority for further research. Avoidance of hip extension (-5.9°, p<.01) was also observed, which could be a compensatory mechanism to prevent further damages to the hip. Furthermore, large cams are thought to act as a mechanical constraint and limit rotation movement allowed within the acetabulum, as demonstrated by reduced peak hip internal rotation (during squat, -8.5°, p=.03). Controls were regrouped based on morphology to allow comparison between asymptomatic (CAM-; n=11) and symptomatic (CAM+, n=16) cams. Symptomatic cams have an increased width (+41.4°, p<.01), and start more superiorly (-29.4°, p<.01). Increased sagittal pelvic mobility (e.g. during a squat; -11.2° for CAM+, p<.01) is thought to be protective against hip impingement symptoms, as during high flexion angles the pelvic tilts backwards reducing the risk of abutment. These findings highlight the need to establish thresholds taking confounding factors into account.Open Acces

Role of pelvic incidence in hip disorders

The pelvis is a rotating modulator connecting the spine and lower limbs; it helps the body to maintain a vertical position. Pelvic incidence (PI) is fundamental, constant, and unique for each individual measure defined as the angle between the line perpendicular to the sacral plate at its midpoint, and the line connecting this point to the axis of the femoral heads. It regulates spinal curvature and has consequently become an important factor in spinal surgery. It also determines a person’s ability to tilt the pelvis into retroversion, which is needed to help compensate for sagittal spinopelvic malalignment in spinal deformities or ageing. When tilting backward and forward, the pelvis rotates around the femoral heads. Both spinal and hip disorders are common, and they often coexist. Descriptive imaging is essential when specific disorders of the spine and hip are being diagnosed or treated surgically. Previously performed hip replacement is a common condition among patients with a spinal deformity or other spinal disease. Thus a reliable measurement of spino-pelvic alignment is necessary even when a femoral head has been replaced. In addition, disorders of the hip and spine are sometimes related, and, therefore, understanding the complexity and connections of this spinopelvic unit is a widespread clinical challenge. The aims of this thesis were 1) to investigate whether pelvic incidence is associated with the wear of hip implants in the studied sample; 2) to determine if the radiographic measurement of spinopelvic parameters after hip replacement overall (and the implant position of metal-on-metal hip implants in particular) is reliable; and 3) to evaluate the previous evidence on the connection between pelvic incidence and hip disorders in general. The study was based on data collected from 101 patients who underwent large-diameter-head, metal-on-metal hip arthroplasty. A systematic review, along with a quantitative analysis of the literature on the topic, was conducted. In this study, no evidence was found that pelvic incidence is associated with metal wear after metal-on-metal hip replacement. The plain radiograph assessment of the position of the total metal-on-metal acetabular component and the spinopelvic parameters was found to be reliable. Hip replacement did not weaken the interpretation of spinopelvic alignment. In addition, pelvic incidence and hip osteoarthrosis seemed to be unrelated. A possible connection between the low pelvic incidence and femoroacetabular impingement observed in this study should be taken into account when clinical decisions are made in spinal and hip surgery

Evaluating the reliability of four-dimensional computed tomography scans of the wrist

Introduction: Four-dimensional CT (or 4D CT) scans are a novel approach to diagnosing musculoskeletal pathology. Although still in its infancy, there has been a surge of interest in identifying clinical applications for musculoskeletal 4D CT. The scapholunate joint has received the most attention thus far due to the complex articulations and challenges faced with prompt diagnosis of scapholunate injuries. The objective of this thesis is to review current literature on musculoskeletal 4D CT and to evaluate the inter- and intra-rater reliability of the assessment of scapholunate stability in 4D CT wrist scans. Methodology: 4D CT scans of thirteen healthy volunteers and four patients were prepared. Seven orthopaedic and plastic surgeons were recruited to qualitatively assess the stability of the scapholunate joint in the 4D CT scans. Statistical analysis included percent agreement, Fleiss’ kappa, and Gwet’s AC1 coefficient. Results: The percent agreement amongst all raters was 0.80392 (95% CI: 0.675 - 0.932). Fleiss’ Kappa was 0.54895 (95% CI: 0.252 - 0.846) and Gwet’s AC₁ was 0.54895 (95% CI: 0.391 - 0.915). The intraclass correlation coefficient (ICC) for intra-rater reliability was 0.71631 (95% CI: 0.5567 – 0.8423). Conclusion: Our pilot study suggests good inter- and intra-rater reliability for the qualitative assessment of scapholunate instability in 4D CT scans. Although further studies are required, this thesis highlights the vast potential of 4D CT as a non-invasive diagnostic technique of dynamic musculoskeletal injuries

Doctor of Philosophy

dissertationAltered mechanics are believed to initiate osteoarthritis in hips with acetabular dysplasia. Periacetabular osteotomy (PAO) is the preferred surgical treatment; however, it is unknown if the procedure normalizes joint anatomy and mechanics. Changes in three-dimensional (3D) morphology and chondrolabral mechanics were quantified after PAO. Finite element (FE) models demonstrated that PAO improved the distribution of coverage, reduced stress, increased congruity, and prevented cartilage thinning. However, changes in mechanics were not consistent. In fact, one patient exhibited increased stress after surgery, which was believed to be a result of over-correction. Therefore, methods to integrate morphologic and biomechanical analysis with clinical care could standardize outcomes of PAO. FE simulations are time-intensive and require significant computing resources. Therefore, the second aim was to implement an efficient method to estimate mechanics. An enhanced discrete element analysis (DEA) model of the hip that accurately incorporated cartilage geometry and efficiently calculated stress was developed and analyzed. Although DEA model estimates predicted elevated magnitudes of contact stress, the distribution corresponded well with FE models. As a computationally efficient platform, DEA could assist in diagnosis and surgical planning. Imaging is a precursor to analyzing morphology and biomechanics. Ideally, an imaging protocol would visualize bone and soft-tissue at high resolution without ionizing radiation. Magnetic resonance imaging (MRI) with 3D dual-echo-steady-state (DESS) is a promising sequence to image the hip noninvasively, but its accuracy has not been quantified. Therefore, the final aim was to implement and validate the use of 3D DESS MRI in the hip. Using direct measurements of cartilage thickness as the standard, 3D DESS MRI imaged cartilage to ~0.5 mm of the physical measurements with 95% confidence, which is comparable to the most accurate hip imaging protocol presented to date. In summary, this dissertation provided unique insights into the morphologic and biomechanical features following PAO. In the future, DEA could be combined with 3D DESS MRI to efficiently analyze contact stress distributions. These methods could be incorporated into preoperative planning software, where the algorithm would predict the optimal relocation of the acetabulum to maximize femoral head coverage while minimizing contact stress, and thereby improve long-term outcomes of PAO

Improving research quality on primary cam morphology

Introduction: Primary cam morphology—a cartilage or bony prominence at the head-neck junction of the hip—develops due to high-load sporting activity during maturation. Although prevalent in many athlete populations, this morphology generally occurs without ill-effects; however, some individuals develop femoroacetabular impingement syndrome or hip osteoarthritis. Existing research on primary cam morphology and its natural history is mired in confusion partly because clinicians, athletes, patients, and researchers have not agreed on key primary cam morphology elements or a prioritised research agenda. Aim and objectives: The overall aim of the programme of research presented in this thesis is to support a transformation of both research and clinical practice related to primary cam morphology and its natural history so that it takes a more pragmatist and patient-centred direction, with specific objectives to: (1) explore the concept of primary cam morphology and its natural history; (2) mobilise and engage a community of athletes, patients, clinicians, and researchers; (3) ensure buy-in and diverse participation to facilitate inclusive co-production partnerships; (4) inform a more rigorous, inclusive, and evidence-based approach to research on primary cam morphology and its natural history by ascertaining the level of agreement among experts on key primary cam morphology elements and a prioritised research agenda; (5) surface and discuss competing perspectives on primary cam morphology and its natural history; (6) explore stakeholders’ perspectives on research quality relevant to primary cam morphology and its natural history; and (7) disseminate findings. Methods: The hybrid mixed methods approach adopted for this programme of research include: (1) a literature review of primary cam morphology using concept analysis method; (2) a consensus exercise (Delphi panel, interacting group process and Essential National Health Research ranking strategy) to ascertain the level of agreement among experts on terminology, taxonomy, definitions, and imaging outcome measures for primary cam morphology and to work collaboratively towards agreement on a set of research priorities on conditions affecting the young person’s hip; and (3) a qualitative interview study to explore stakeholders’ perspectives on research quality relevant to primary cam morphology and its natural history. Results: The concept analysis introduced and clarified primary cam morphology. Reported in the Oxford Consensus Study, stakeholders agreed—and surfaced areas of tension and dissent—on: (1) a new conceptual definition for the morphology; (2) more consistent terminology; (3) a taxonomy distinguishing between primary and secondary cam morphology; (4) challenges of operationalising the hip morphology, and (5) a prioritised research agenda for the field. We constructed five action-inviting themes for higher quality research based on stakeholders’ perspectives on research quality, which are that research communities in this field should: (1) partner with athletes/patients; (2) collaborate with one another; (3) champion equity, diversity, and inclusion; (4) pursue open science; and (5) nurture young scholars. Conclusion: The empirical work presented in this thesis could move both research and clinical practice related to primary cam morphology and its natural history in a more pragmatist and patient-centred direction. It serves as a foundation for concrete actions by research communities in the field to pursue high value research and generate less research waste