This research was supported by the National Institutes of Health (NIH) under grant numbers S10 RR026565, R21 AR063844, F32 AR067075, R01 R077636, R56 AR074416, R01 GM083925. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.

The authors have no conflicts of interest.

Dual fluoroscopy is a powerful tool for the investigation of in vivo kinematics, especially for the hip, which is difficult to accurately measure using traditional optical motion capture. However, fluoroscopy equipment is specialized, wherein a unique system setup may be required when imaging other joints of the human body. For example, several modifications were made to the mounting of the image intensifiers, positioning of the system, and settings of the beam energy in the application of dual fluoroscopy to the study of ankle kinematics32,33,34,35. In addition to requiring considerable study preparation, dual fluoroscopy requires the acquisition of additional data, including 3D medical imaging and potentially traditional skin marker motion capture to track whole-body kinematics, as well as lengthy post-processing, including CT image segmentation and markerless tracking of the acquired images. Fortunately, fully processed data from dual fluoroscopy can be used in various applications with capabilities reaching far beyond those available with traditional motion capture.
Optical motion capture utilizes the motion of markers on the skin to estimate body segment positions, while radiation-based dual fluoroscopy allows for direct measurement of only the bone positions. While significant effort has been dedicated to quantifying soft tissue dynamics relative to bone motion36, 37, it is inherently difficult to measure the motion patterns of the large mass of soft tissue between the outer layer of skin and the bones. However, for thinner tissues in direct contact with the bones, such as the cartilage and labrum of the hip, the combination of dual fluoroscopy and CT arthrogram imaging provides the ability to dynamically evaluate their spatial relationship. The data collected during supine clinical exams were used to show that the location of clinically observed damage to the acetabular labrum aligned with the position of contact between the femur and labrum during supine impingement exams38. Importantly, this analysis identified that the region of initial and greatest contact between the femur and labrum did not align with the location of the smallest distance between the bones.
Individuals with hip pathoanatomy are at risk of damage to the cartilage and labrum. However, the mechanisms responsible for chondrolabral injuries are not well understood. Conceivably, arthrokinematics data built from CT arthrogram data could be analyzed to study the mechanics of the cartilage and labrum. For example, the observed penetration between surface reconstructions representing soft tissue (e.g., labrum, cartilage) and bone could be analyzed and interpreted to approximate the strain experienced by these tissues. However, even slight errors in the tracking of kinematics or reconstruction of surfaces could result in drastic differences in estimated strains and joint loads. Thus, more advanced modeling methods, such as the FE method, may be required to comprehensively evaluate chondrolabral mechanics in the hip. Data from dual fluoroscopy, traditional skin marker motion capture of whole-body kinematics, and the instrumented treadmill can serve as input for models that estimate muscle forces and joint reaction loads and torques. These kinetic data can then serve as loading conditions to FE models that estimate chondrolabral stresses and strains.
In addition to the specific steps involved in the protocol, the scheduling of different aspects of the study is also relevant to successful data acquisition. First, in studies using arthrogram imaging, which is inherently invasive due to the injection of contrast into the hip capsule, the arthrogram must be performed either several days before or any time after the completion of motion capture experiments to avoid any effect on patient motion patterns. Second, all calibration must be performed prior to, but just before, the arrival of the participant to ensure that the system configuration is not altered between calibration and image acquisition. Third, the participant should be instructed to perform dynamic trials in a random order to eliminate any effect of ordering on the performance of tasks.
Another major consideration for the use of dual fluoroscopy for the measurement of hip kinematics is radiation exposure. It is important to note, however, that 80% of the estimated dose equivalent of radiation in the described protocol is from the CT scan. One solution to reduce exposure is the substitution of magnetic resonance imaging (MRI) for CT imaging. While MRI can be used for surface reconstruction, the tracking of dual fluoroscopy images also relies on the projection of bone densities from the digitally reconstructed radiographs. Although MRI cannot directly measure bone density, specific sequences, such as the dual echo steady state (DESS), provide some differentiation between the denser cortical bone and the less dense cancellous bone. These images can be transformed to have a similar appearance to CT images and could potentially reduce the radiation exposure of participants in dual fluoroscopy studies.
Owing to the large amount of soft tissue surrounding the hip joint, the specific positioning of the dual fluoroscopy system must be optimized to reduce X-ray scatter. The position of the participant relative to the X-ray emitters and the angle between the image intensifiers were found to be important factors. This protocol indicates the positioning of the dual fluoroscopy system used to study hip motion in participants during weight-bearing activities. It is, however, also relevant to note that the participant cohort was limited to individuals with a BMI less than 30 kg/m2. A similar BMI limit is recommended when capturing dual fluoroscopy images of joints surrounded by large masses of soft tissue.
The protocol described herein can be applied to various dual fluoroscopy system configurations and joints, including supine and weight-bearing hip kinematics, both treadmill and overground weight-bearing ankle kinematics, and sitting shoulder kinematics16,&#160;17,&#160;18,&#160;19,&#160;20,&#160;21,&#160;22,&#160;23,&#160;24,&#160;25,&#160;26,&#160;27,&#160;28,&#160;29,&#160;30,&#160;31,&#160;32,&#160;33,&#160;34,&#160;35. Owing to the minimal global motion of the hip joint during treadmill gait, an instrumented treadmill was used for the assessment of weight-bearing kinematics of the hip joint. Without a treadmill or a moving fluoroscope system, it would only be possible to capture the hip joint during activities performed in a confined field of view. However, the use of a treadmill is not appropriate for all joints. As an example, application of this protocol to the investigation of ankle kinematics during treadmill walking captured only a small portion of gait due to the inherent motion of the treadmill32,35, while overground gait was able to capture a larger portion of gait, spanning from prior to heel-strike to after toe-off33,40,41.

The number of total hip arthroplasty (THA) procedures performed on adults aged 45-64 years suffering from hip osteoarthritis (OA) more than doubled between 2000 and 20101. Based on the increases in THA procedures from 2000 to 2014, a recent study predicted that the overall number of yearly procedures may triple over the next twenty years2. These large increases in THA procedures are alarming considering that current treatment costs exceed $18 billion annually in the United States alone3.
Developmental dysplasia of the hip (DDH) and femoroacetabular impingement syndrome (FAIS), which describe an under- or over-constrained hip, respectively, are believed to be the primary etiology of hip OA4. The high prevalence of these structural hip deformities in individuals undergoing THA was initially described more than three decades ago5. Still, the relationship between abnormal hip anatomy and osteoarthritis is not well understood. One challenge to improving the working understanding of the role of deformities in the development of hip OA is that abnormal hip morphology is very common amongst asymptomatic adults. Notably, studies have observed morphology associated with cam-type FAIS in approximately 35% of the general population6, 83% of senior athletes7, and more than 95% of collegiate male athletes8. In another study of female collegiate athletes, 60% of participants had radiographic evidence of cam FAIS, and 30% had evidence of DDH9.
Studies demonstrating a high prevalence of deformities amongst individuals without hip pain point to the possibility that morphology commonly associated with FAIS and DDH may be a natural variant that only becomes symptomatic under certain conditions. However, the interaction between hip anatomy and hip biomechanics is not well understood. Notably, there are known difficulties with measuring hip joint motion using traditional optical motion capture technology. First, the joint is relatively deep within the body, such that the location of the hip joint center is difficult to both identify and track dynamically using optical skin marker motion capture, with errors on the same order of magnitude as the radius of the femoral head10,11. Second, the hip joint is surrounded by large soft tissue bulk, including subcutaneous fat and muscle, that moves relative to the underlying bone, resulting in soft tissue artifact12,13,14. Finally, using optical tracking of skin markers, kinematics are evaluated relative to generalized anatomy and thus do not provide insight into how subtle morphological differences might affect the biomechanics of the joint.
To address the lack of accurate kinematics in combination with subject-specific bone morphology, both single and dual fluoroscopy systems have been developed for analyzing other natural joint systems15,16,17. However, this technology has only recently been applied to the native hip joint, likely due to the difficulty in acquiring high-quality images through the soft tissue surrounding the hip. The methodology to accurately measure in vivo hip joint motion and display this motion relative to subject-specific bone anatomy is described herein. The resulting arthrokinematics provide an unparalleled ability to investigate the subtle interplay between bone morphology and biomechanics.
Herein, the procedures for acquiring and processing dual fluoroscopy images of the hip during activities of daily living have been described. Owing to the desire to capture whole-body kinematics with optical marker tracking simultaneously with dual fluoroscopy images, the data collection protocol requires coordination between several sources of data. Calibration of the dual fluoroscopy system utilizes plexiglass structures implanted with metallic beads that can be directly identified and tracked as markers. In contrast, dynamic bone motion is tracked using markerless tracking, which utilizes only the CT-based radiographic density of the bones to define orientation. Dynamic motion is then tracked simultaneously using dual fluoroscopy and motion capture data that are spatially and temporally synced.
The systems are synced spatially during calibration through concurrent imaging of a cube with both reflective markers and implanted metal beads and the generation of a common coordinate system. The systems are synced temporally for each activity or capture through the use of a split electronic trigger, which sends a signal to end the recording of the dual fluoroscopy cameras and interrupts a constant 5 V input to the motion capture system. This coordinated protocol enables the quantification of the position of body segments that fall outside the combined field of view of the dual fluoroscopy system, expression of kinematic results relative to gait-normalized events, and characterization of the soft tissue deformation around the femur and pelvis.

<table><tbody><tr><td>Amira Software</td><td>ThermoFisher Scientific</td><td>Version 6.0</td><td></td></tr><tr><td>Calibration Cube</td><td></td><td>Custom</td><td>36 steel beads (3 mm diameter, spacing 6.35 cm, uncertainty 0.0036 mm)</td></tr><tr><td>Calibration Wand</td><td>Vicon</td><td>Active Wand</td><td></td></tr><tr><td>CT Scanner</td><td>Siemens AG</td><td>SOMATOM Definition 128 CT</td><td></td></tr><tr><td>Distortion Correction Grid</td><td></td><td>Custom</td><td>Acrylic plate with a grid of steel beads spaced 10 mm and 31 beads across the diameter (2 mm diameter)</td></tr><tr><td>Dynamic Calibration Plate</td><td></td><td>Custom</td><td>Acrylic plate with 3 steel beads spaced 30 mm (2 mm diameter, uncertainty 0.0013 mm)</td></tr><tr><td>Emitter (2)</td><td>Varian Interay; remanufactured by Radiological Imaging Services</td><td>Housing B-100/Tube A-142</td><td></td></tr><tr><td>Epinephrine</td><td>Hospira</td><td>Injection, USP 10 mg/mL</td><td></td></tr><tr><td>FEBioStudio Software</td><td>FEBio.org</td><td>Version 1.3</td><td>Mesh processing and kinematic visualization</td></tr><tr><td>Graphical Processing Unit</td><td>Nvidia</td><td>Tesla</td><td></td></tr><tr><td>Hare Traction Splint</td><td>DynaMed</td><td>Trac-III, Model No. 95201</td><td></td></tr><tr><td>High-speed Camera (2)</td><td>Vision Research, Inc.</td><td>Phantom Micro 3</td><td></td></tr><tr><td>Image Intensifier (2)</td><td>Dunlee, Inc.; remanufactured by Radiological Imaging Services</td><td>T12964P/S</td><td></td></tr><tr><td>Iohexol injection</td><td>GE Healthcare</td><td>Omnipaque 240 mgI/mL</td><td>517.7 mg iohexol, 1.21 mg tromethamine, 0.1 mg edetate calcium disodium per mL</td></tr><tr><td>ImageJ</td><td>National Institutes of Health and Laboratory for Optical and Computational Instrumentation</td><td></td><td></td></tr><tr><td>Lidocaine HCl</td><td>Hospira</td><td>Injection, USP 10 mg/mL</td><td></td></tr><tr><td>Laser and Mirror Alignment System</td><td></td><td>Custom</td><td>Three lasers adhered to acrylic plate that attaches to emitter, mirror attaches to face of image intensifier</td></tr><tr><td>Markless Tracking Workbench</td><td>Henry Ford Hospital, Custom Software</td><td>Custom</td><td></td></tr><tr><td>MATLAB Software</td><td>Mathworks, Inc.</td><td>Version R2017b</td><td></td></tr><tr><td>Motion Capture Camera (10)</td><td>Vicon</td><td>Vantage</td><td></td></tr><tr><td>Nexus Software</td><td>Vicon</td><td>Version 2.8</td><td>Motion capture</td></tr><tr><td>Phantom Camera Control (PCC) Software</td><td>Vision Research, Inc.</td><td>Version 1.3</td><td></td></tr><tr><td>Pre-tape Spray Glue</td><td>Mueller Sport Care</td><td>Tuffner</td><td></td></tr><tr><td>Retroreflective Spherical Skin Markers</td><td></td><td></td><td>14 mm</td></tr><tr><td>Split Belt Fully Instrumented Treadmill</td><td>Bertec Corporation</td><td>Custom</td><td></td></tr><tr><td>Visual3D Software</td><td>C-Motion Inc.</td><td>Version 6.01</td><td>Kinematic processing</td></tr></tbody></table>

in vivo quantification of hip arthrokinematics during dynamic weight-bearing activities using dual fluoroscopy

Several hip pathologies have been attributed to abnormal morphology with an underlying assumption of aberrant biomechanics. However, structure-function relationships at the joint level remain challenging to quantify due to difficulties in accurately measuring dynamic joint motion. The soft tissue artifact errors inherent in optical skin marker motion capture are exacerbated by the depth of the hip joint within the body and the large mass of soft tissue surrounding the joint. Thus, the complex relationship between bone shape and hip joint kinematics is more difficult to study accurately than in other joints. Herein, a protocol incorporating computed tomography (CT) arthrography, three-dimensional (3D) reconstruction of volumetric images, dual fluoroscopy, and optical motion capture to accurately measure the dynamic motion of the hip joint is presented. The technical and clinical studies that have applied dual fluoroscopy to study form-function relationships of the hip using this protocol are summarized, and the specific steps and future considerations for data acquisition, processing, and analysis are described.

Using dual fluoroscopy as a reference standard, the accuracy of skin-marker-based estimates of the hip joint center and the effect of soft-tissue artifact on kinematic and kinetic measurements were quantified22,23,24. The superior accuracy of dual fluoroscopy was then used to identify subtle differences in pelvic and hip joint kinematics between patients with FAIS and asymptomatic control participants25. Dual-fluoroscopy-based arthrokinematics were analyzed to quantify hip joint coverage, the relationship between morphology and kinematics, and bone-to-bone distances during dynamic motions26,27,28,29.
Before developing a protocol to investigate weight-bearing hip joint kinematics, the system was validated in cadaveric specimens with implanted metal beads during supine clinical exams to an accuracy within 0.5 mm and 0.6°30. Once validated, kinematics during clinical exams were measured using dual fluoroscopy in patients with FAIS and asymptomatic control participants. The results demonstrated that patients had altered motion in both internal rotation and adduction31.
Using weight-bearing dual fluoroscopy as a reference standard, the error in identifying the location of the hip joint center as well as the errors caused by soft-tissue artifact were then directly analyzed. Functional methods of identifying the hip joint center, i.e., the star-arc motion, were identified to be more accurate than predictive, landmark-based methods with errors of 11.0 and 18.1 mm, respectively32. Dynamic errors in the hip joint center were similar to those from standing; however, an additional 2.2 mm of spurious hip joint center movement was attributed to soft tissue artifact, with errors of more than 5 cm during dynamic movement for the greater trochanter marker23.
In addition to the errors in identification of the hip joint center, joint angles were underestimated by greater than 20° in internal-external rotation pivots23. While the underestimation of kinematics is cause for concern in itself, these errors reduced the measured range of motion and calculated kinetic variables during even a low range of motion activities, such as gait24. However, accurate dual fluoroscopy kinematic data can be difficult to incorporate into musculoskeletal models. Specifically, model marker errors were approximately 1 cm when running inverse kinematics with dual fluoroscopy-based landmark locations. While this error is relatively small compared to the 5 cm errors due to soft tissue artifact found for skin marker motion capture data, such error is an order of magnitude larger than that of bone positions measured by dual fluoroscopy.
In addition to the quantification of errors in traditional skin marker motion capture, the accuracy and methodology behind dual fluoroscopy provide the capability to evaluate even subtle differences in kinematics between cohorts, which may otherwise be hidden by the errors of the measurement technique. While differences in hip joint kinematics were not observed between patients with cam FAIS and asymptomatic control participants, differences in pelvic kinematics that would have been difficult to detect in the presence of soft-tissue artifact were identified25. This assessment required direct comparison between cohorts. Moreover, the potential relationship between kinematic variation and bone morphology, such as femoral anteversion, was also investigated27. These findings indicated the need for consideration of both morphology and biomechanics in the diagnosis of hip pathologies and the planning of conservative or surgical treatments.
A major hurdle in the use of biomechanical data in a clinical care setting is the difference in coordinate systems used by biomechanists and clinicians. In a biomechanics lab, the landmarks used to define coordinate systems of the femur and pelvis are driven by the ability to identify and track the landmarks from the skin surface during dynamic motion. In contrast, surgical coordinate systems are defined using bony landmarks identifiable during surgery with a patient supine or prone. The direct tracking of the femur and pelvis in dual fluoroscopy allowed for the evaluation of the influence of various coordinate system definitions on kinematic output29. The differences between coordinate system definitions resulted in kinematic offsets greater than 5°. However, these offsets were relatively consistent during motion and could be accounted for through bony landmark identification.
The combination of subject-specific bone morphology and kinematics — arthrokinematics — provides a joint-level assessment of form and function. For patients with DDH, femoral under-coverage is thought to be the cause of degeneration, and therefore, measurements of coverage are used heavily in diagnosis and surgical planning. Unfortunately, these measurements are often limited to static images, obtained with an individual supine, and only in two dimensions. Dual fluoroscopy-derived arthrokinematics were used to directly measure the variability in femoral coverage during dynamic activities26. Importantly, strong correlations between coverage in standing and coverage during gait when evaluated in entirety were found. Yet, regionalized coverage varied for both anterior and posterior regions of the femoral head even during the stance phase of gait.
Extra-articular impingement is a cause of pain at the hip and surrounding region and describes abnormal contact between the femur and regions of the pelvis outside the acetabulum, including the ischium and anterior inferior iliac spine. The dynamic nature of ischiofemoral impingement was evaluated through the comparison of clinical MRI-based measurements of ischiofemoral space and those during dynamic activities28. Therein, decreased space was observed dynamically in comparison to the standard clinical measures; sex-based differences, which could not be attributed to kinematic differences, were also identified. These methods could also be applied to evaluate joint space dynamically, providing insight into the variability of the position of the femoral head within the acetabulum and the variability across patient cohorts (Figure 8).
<img alt="Particle scattering diagram with angles and distances labeled; photon interaction setup." class="xfigimg" src="/files/ftp_upload/62792/62792fig01.jpg" data-altupdatedat="1747911167000" data-alt="Figure 1"> 
Figure 1: Overhead view of the dual fluoroscopy system positioned over the instrumented treadmill for a left hip. The system is positioned to minimize the effect of scatter and maximize the field of view. The image intensifiers are positioned approximately 100-110 cm from the source of the emitter and angled 50° from one another. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62792/62792fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Human gait analysis on a treadmill using infrared cameras; motion capture study with variable incline." class="xfigimg" src="/files/ftp_upload/62792/62792fig02.jpg" data-altupdatedat="1747911167000" data-alt="Figure 2"> 
Figure 2: View from the contralateral (right) side of a participant during dynamic activities. The participant is positioned between the two image intensifiers (II) such that the field of view of the dual fluoroscopy system is centered over the left hip joint. Level and incline walking, internal and external rotation pivots, and range of motion activities are performed on a treadmill platform. Abbreviation: FHJC = functional hip joint center. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62792/62792fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Biomechanics experiment setup diagram with treadmill, dual fluoroscopy, infrared cameras." class="xfigimg" src="/files/ftp_upload/62792/62792fig03.jpg" data-altupdatedat="1747911167000" data-alt="Figure 3"> 
Figure 3: Overhead view of the motion capture system relative to the dual fluoroscopy system. The optical motion capture system includes 10 infrared cameras and a single video-based camera and is positioned on a frame hanging from the ceiling. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62792/62792fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Marker placement for motion capture; diagram of skeletal setup with calibration and tracking points." class="xfigimg" src="/files/ftp_upload/62792/62792fig04.jpg" data-altupdatedat="1747911167000" data-alt="Figure 4"> 
Figure 4: Anterior and posterior view of the marker set used for skin marker motion capture. There are five plates with four markers each, which are positioned on the back, thighs, and shanks of the participants; all other markers are applied directly to the skin. Calibration markers are removed for dynamic motion capture. Marker labels prefaced with an R or L indicate markers on the right or left side of the body; marker labels suffixed with S, L, R, I, A, or P indicate marker locations on a marker plate, specifically superior, left, right, inferior, anterior, or posterior, respectively. Abbreviations: *SHO = shoulder; CLAV = center of clavicles; STRN = bottom of sternum; BACK_* = markers of plate placed on the lower back; *ILC = iliac crest; *ASI = anterior superior iliac spine; *PSI = posterior superior iliac spine; GRT_TRO = greater trochanter; *THI_* = markers of the respective plates placed on the thigh; *KNE_M = medial femoral condyle (knee); *KNE_L = lateral femoral condyle (knee); *TIB_* = markers of the respective plates placed on the shank (tibia); *ANK_M = medial malleolus (ankle); *ANK_L = lateral malleolus; *5TH = fifth metatarsophalangeal joint; *TOE = first metatarsophalangeal joint; *HEE = calcaneus (heel). <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62792/62792fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Pelvis and femur alignment diagram; anterior-posterial, medial-lateral, superior-inferior axes." class="xfigimg" src="/files/ftp_upload/62792/62792fig05.jpg" data-altupdatedat="1747911167000" data-alt="Figure 5"> 
Figure 5: Landmarks and coordinate systems of the femur and pelvis. Landmarks of bilateral anterior superior iliac spine (ASIS; magenta) and posterior superior iliac spine (PSIS; cyan) and their mid-points are used to define the coordinate system of the pelvis. The center of the femoral head (orange) and bilateral femoral condyles (green), their mid-point, and a cylinder fit of the condyles are used to define the coordinate system of the femur (shown for left femur). The third axis of each bone is determined from the cross-product of the two displayed axes. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62792/62792fig05large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="MRI scans showing hip joint rotation analysis; external and internal pivot comparison diagram." class="xfigimg" src="/files/ftp_upload/62792/62792fig06.jpg" data-altupdatedat="1747911167000" data-alt="Figure 6"> 
Figure 6: Dual fluoroscopy images and associated markerless tracking of a left hip. Images are shown for maximum rotation of the external and internal rotation pivots (center), with the image from the anterior fluoroscope (left) and the posterior fluoroscope (right). Markerless tracking solutions for the pelvis (top) and femur (bottom) for each dual fluoroscopy image. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62792/62792fig06large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Joint angle analysis graph; flexion, abduction, rotation; dual fluoroscopy frames; motion study." class="xfigimg" src="/files/ftp_upload/62792/62792fig07.jpg" data-altupdatedat="1747911167000" data-alt="Figure 7"> 
Figure 7: Dual fluoroscopy measured kinematics. Kinematics for 100 frames surrounding the maximum rotation (vertical dotted line) of external and internal rotation pivots for a representative participant. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62792/62792fig07large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Hip joint rotation analysis; color gradient diagram; surface distance measurement in biomechanics." class="xfigimg" src="/files/ftp_upload/62792/62792fig08.jpg" data-altupdatedat="1747911167000" data-alt="Figure 8"> 
Figure 8: Arthrokinematics-based surface distance between a left hemi-pelvis and femur. Arthrokinematics are shown for maximum rotation of the external and internal rotation pivot (center) with respective bone models measured with dual fluoroscopy (outer). <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62792/62792fig08large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about In Vivo Quantification of Hip Arthrokinematics during Dynamic Weight-bearing Activities using Dual Fluoroscopy at JoVE.com

In Vivo Quantification of Hip Arthrokinematics during Dynamic Weight-bearing Activities using Dual Fluoroscopy

Dual fluoroscopy accurately captures in vivo dynamic motion of human joints, which can be visualized relative to reconstructed anatomy (e.g., arthrokinematics). Herein, a detailed protocol to quantify hip arthrokinematics during weight-bearing activities of daily living is presented, including the integration of dual fluoroscopy with traditional skin marker motion capture.

In Vivo Quantification of Hip Arthrokinematics during Dynamic Weight-bearing Activities using Dual Fluoroscopy

Several hip pathologies have been attributed to abnormal morphology with an underlying assumption of aberrant biomechanics. However, structure-function ...

in-vivo-quantification-hip-arthrokinematics-during-dynamic-weight

Nanyang Technological University

Research

Education

JoVE Core

JoVE Journal

Anatomy and Physiology

Medicine

Unit 1

The Appendicular Skeleton

SCIENTISTS IN ACTION

3.0K Views.  University of Utah. Dit protocol combineert meting van in vivo heupkinematica met motion capture van het hele lichaam om de rol van biomechanica bij heupdegeneratie te verliezen. In vergelijking met traditionele methoden om heupbewegingen te volgen, heeft dubbele fluoroscopie een verbeterde nauwkeurigheid die onderzoek mogelijk maakt naar de subtiele relatie tussen heupvorm en bewegingspatronen. Laat de deelnemer voor de spilactiviteiten zijn voeten draaien of vertalen zodat het bekken naar voren is gericht op d...

Video: In Vivo Quantification of Hip Arthrokinematics during Dynamic Weight-bearing Activities using Dual Fluoroscopy

A Novel Application of Musculoskeletal Ultrasound Imaging

Ultrasound is an attractive modality for imaging muscle and tendon motion during dynamic tasks and can provide a complementary methodological approach for biomechanical studies in a clinical or laboratory setting. Towards this goal, methods for quantification of muscle kinematics from ultrasound imagery are being developed based on image processing. The temporal resolution of these methods is typically not sufficient for highly dynamic tasks, such as drop-landing. We propose a new approach that utilizes a Doppler method for quantifying muscle kinematics. We have developed a novel vector tissue Doppler imaging (vTDI) technique that can be used to measure musculoskeletal contraction velocity, strain and strain rate with sub-millisecond temporal resolution during dynamic activities using ultrasound. The goal of this preliminary study was to investigate the repeatability and potential applicability of the vTDI technique in measuring musculoskeletal velocities during a drop-landing task, in healthy subjects. The vTDI measurements can be performed concurrently with other biomechanical techniques, such as 3D motion capture for joint kinematics and kinetics, electromyography for timing of muscle activation and force plates for ground reaction force. Integration of these complementary techniques could lead to a better understanding of dynamic muscle function and dysfunction underlying the pathogenesis and pathophysiology of musculoskeletal disorders.

We describe a new ultrasound-based vector tissue Doppler imaging technique to measure muscle contraction velocity, strain and strain rate with sub-millisecond temporal resolution during dynamic activities. This approach provides complementary measurements of dynamic muscle function and could lead to a better understanding of mechanisms underlying musculoskeletal disorders.

Ultrasound is an attractive modality for imaging muscle and tendon  motion during dynamic tasks and can provide a complementary methodological  approach ...

An Inertial Measurement Unit Based Method to Estimate Hip and Knee Joint Kinematics in Team Sport Athletes on the Field

Current athlete monitoring practice in team sports is mainly based on positional data measured by global positioning or local positioning systems. The disadvantage of these measurement systems is that they do not register lower extremity kinematics, which could be a useful measure for identifying injury-risk factors. Rapid development in sensor technology may overcome the limitations of the current measurement systems. With inertial measurement units (IMUs) securely fixed to body segments, sensor fusion algorithms and a biomechanical model, joint kinematics could be estimated. The main purpose of this article is to demonstrate a sensor setup for estimating hip and knee joint kinematics of team sport athletes in the field. Five male subjects (age 22.5 &#177; 2.1 years; body mass 77.0 &#177; 3.8 kg; height 184.3 &#177; 5.2 cm; training experience 15.3 &#177; 4.8 years) performed a maximal 30-meter linear sprint. Hip and knee joint angles and angular velocities were obtained by five IMUs placed on the pelvis, both thighs and both shanks. Hip angles ranged from 195&#176; (&#177; 8&#176;) extension to 100.5&#176; (&#177; 8&#176;) flexion and knee angles ranged from 168.6&#176; (&#177; 12&#176;) minimal flexion and 62.8&#176; (&#177; 12&#176;) maximal flexion. Furthermore, hip angular velocity ranged between 802.6 &#176;&#183;s-1 (&#177; 192 &#176;&#183;s-1) and -674.9 &#176;&#183;s-1 (&#177; 130 &#176;&#183;s-1). Knee angular velocity ranged between 1155.9 &#176;&#183;s-1 (&#177; 200 &#176;&#183;s-1) and -1208.2 &#176;&#183;s-1 (&#177; 264 &#176;&#183;s-1). The sensor setup has been validated and could provide additional information with regard to athlete monitoring in the field.&#160;This may help professionals in a daily sports setting to evaluate their training programs, aiming to reduce injury and optimize performance.

Monitoring athletes is essential for improving performance and reducing injury risk in team sports. Current methods to monitor athletes do not include the lower extremities. Attaching multiple inertial measurement units to the lower extremities could improve monitoring athletes in the field.

Current athlete monitoring practice in team sports is mainly based on positional data measured by global positioning or local positioning systems. The ...

Behavior

Combined In vivo Optical and &#181;CT Imaging to Monitor Infection, Inflammation, and Bone Anatomy in an Orthopaedic Implant Infection in Mice

Multimodality imaging has emerged as a common technological approach used in both preclinical and clinical research. Advanced techniques that combine in vivo optical and &#956;CT imaging allow the visualization of biological phenomena in an anatomical context. These imaging modalities may be especially useful to study conditions that impact bone. In particular, orthopaedic implant infections are an important problem in clinical orthopaedic surgery. These infections are difficult to treat because bacterial biofilms form on the foreign surgically implanted materials, leading to persistent inflammation, osteomyelitis and eventual osteolysis of the bone surrounding the implant, which ultimately results in implant loosening and failure. Here, a mouse model of an infected orthopaedic prosthetic implant was used that involved the surgical placement of a Kirschner-wire implant into an intramedullary canal in the femur in such a way that the end of the implant extended into the knee joint. In this model, LysEGFP mice, a mouse strain that has EGFP-fluorescent neutrophils, were employed in conjunction with a bioluminescent Staphylococcus aureus strain, which naturally emits light. The bacteria were inoculated into the knee joints of the mice prior to closing the surgical site. In vivo bioluminescent and fluorescent imaging was used to quantify the bacterial burden and neutrophil inflammatory response, respectively. In addition, &#956;CT imaging was performed on the same mice so that the 3D location of the bioluminescent and fluorescent optical signals could be co-registered with the anatomical &#956;CT images. To quantify the changes in the bone over time, the outer bone volume of the distal femurs were measured at specific time points using a semi-automated contour based segmentation process. Taken together, the combination of in vivo bioluminescent/fluorescent imaging with &#956;CT imaging may be especially useful for the noninvasive monitoring of the infection, inflammatory response and anatomical changes in bone over time.

Combined In vivo Optical and  &#181;CT Imaging to Monitor Infection, Inflammation, and Bone Anatomy in an Orthopaedic Implant Infection in Mice

Combined optical and &#956;CT imaging in a mouse model of orthopaedic implant infection, utilizing a bioluminescent engineered strain of Staphylococcus aureus, provided the capability to noninvasively and longitudinally monitor the dynamics of the bacterial infection, as well as the corresponding inflammatory response and anatomical changes in the bone.

Multimodality imaging has emerged as a common technological approach used in both preclinical and clinical research. Advanced techniques that combine in ...

A Method to Estimate Cadaveric Femur Cortical Strains During Fracture Testing Using Digital Image Correlation

This protocol describes the method using digital image correlation to estimate cortical strain from high speed video images of the cadaveric femoral surface obtained from mechanical testing. This optical method requires a texture of many contrasting fiduciary marks on a solid white background for accurate tracking of surface deformation as loading is applied to the specimen. Immediately prior to testing, the surface of interest in the camera view is painted with a water-based white primer and allowed to dry for several minutes. Then, a black paint is speckled carefully over the white background with special consideration for the even size and shape of the droplets. Illumination is carefully designed and set such that there is optimal contrast of these marks while minimizing reflections through the use of filters. Images were obtained through high speed video capture at up to 12,000 frames/s. The key images prior to and including the fracture event are extracted and deformations are estimated between successive frames in carefully sized interrogation windows over a specified region of interest. These deformations are then used to compute surface strain temporally during the fracture test. The strain data is very useful for identifying fracture initiation within the femur, and for eventual validation of proximal femur fracture strength models derived from Quantitative Computed Tomography-based Finite Element Analysis (QCT/FEA).

In this protocol, the femur surface strains are estimated during fracture testing using the digital image correlation technique. The novelty of the method involves application of a high-contrast stochastic speckle pattern on the femur surface, carefully specified illumination, high speed video capture, and digital image correlation analysis for strain calculations.

This protocol describes the method using digital image correlation to estimate cortical strain from high speed video images of the cadaveric femoral ...

Bioengineering

Biplanar Videoradiography Dataset for Model-based Pose Estimation Development and New User Training

Measuring the motion of the small foot bones is critical for understanding pathological loss of function. Biplanar videoradiography is well-suited to measure in vivo bone motion, but challenges arise when estimating the rotation and translation (pose) of each bone. The bone's pose is typically estimated with marker- or model-based methods. Marker-based methods are highly accurate but uncommon in vivo due to their invasiveness. Model-based methods are more common but are currently less accurate as they rely on user input and lab-specific algorithms. This work presents a rare in vivo dataset of the calcaneus, talus, and tibia poses, as measured with marker-based methods during running and hopping. A method is included to train users to improve their initial guesses into model-based pose estimation software, using marker-based visual feedback. New operators were able to estimate bone poses within 2&#176; of rotation and 1 mm of translation of the marker-based pose, similar to an expert user of the model-based software, and representing a substantial improvement over previously reported inter-operator variability. Further, this dataset can be used to validate other model-based pose estimation software. Ultimately, sharing this dataset will improve the speed and accuracy with which users can measure bone poses from biplanar videoradiography.

This work presents an in vivo dataset with bone poses estimated with marker-based methods. A method is included here to train operators in improving their initial estimates for model-based pose estimation and reducing inter-operator variability.

Measuring the motion of the small foot bones is critical for understanding pathological loss of function. Biplanar videoradiography is well-suited to ...

Engineering

Imaging of the Microstructural Failure Mechanism in the Human Hip

Imaging the bone microstructure under progressively increasing loads allows for observing the microstructural failure behavior of bone. Here, we describe a protocol for obtaining a sequence of three-dimensional microstructural images of the entire proximal femur under progressively increasing deformation, causing clinically relevant fractures of the femoral neck. The protocol is demonstrated using four femora from female donors aged 66-80 years at the lower end of bone mineral density in the population (T-score range = &#8722;2.09 to &#8722;4.75). A radio-transparent compressive stage was designed for loading the specimens replicating a one-leg stance, while recording the applied load during&#160;micro-computed tomography (micro-CT) imaging. The field of view was 146 mm wide and 132 mm high, and the isotropic pixel size was 0.03 mm. The force increment was based on finite-element predictions of the fracture load. The compressive stage was used to apply the displacement to the specimen and enact the prescribed force increments. Sub-capital fractures due to opening and shear of the femoral neck occurred after four to five load increments. The micro-CT&#160;images and the reaction force measurements were processed to study the bone strain and energy absorption capacity. Instability of the cortex appeared at the early loading steps. The subchondral bone in the femoral head displayed large deformations reaching 16% before&#160;fracture, and a progressive increase in the support capacity up to&#160;fracture. The deformation energy linearly increased with the displacement up to&#160;fracture, while the stiffness decreased to near-zero values immediately before&#160;fracture. Three-fourths of the fracture energy was taken by the specimen during the final 25% force increment. In conclusion, the protocol developed revealed a remarkable energy absorption capacity, or damage tolerance, and a synergic interaction between the cortical and trabecular bone at an advanced donor age.

The protocol enables the measurement of the deformation of the bone microstructure in the entire proximal human femur and its toughness by combining large-volume micro-CT scanning, a custom-made compressive stage, and advanced image processing tools.

Imaging the bone microstructure under progressively increasing loads allows for observing the microstructural failure behavior of bone. Here, we describe ...

Four-Dimensional CT Analysis Using Sequential 3D-3D Registration

Four-dimensional computed tomography (4DCT) provides a series of volume data and visualizes joint motions. However, numerical analysis of 4DCT data remains difficult because segmentation in all volumetric frames is time-consuming. We aimed to analyze joint kinematics using a sequential 3D-3D registration technique to provide the kinematics of the moving bone with respect to the fixed bone semiautomatically using 4DCT DICOM data and existing software. Surface data of the source bones are reconstructed from 3DCT. The trimmed surface data are respectively matched with surface data from the first frame in 4DCT. These trimmed surfaces are sequentially matched until the last frame. These processes provide positional information for target bones in all frames of the 4DCT. Once the coordinate systems of the target bones are decided, translation and rotation angles between any two bones can be calculated. This 4DCT analysis offers advantages in kinematic analyses of complex structures such as carpal or tarsal bones. However, fast or large-scale motions cannot be traced because of motion artifacts.

We analyzed joint kinematics from four-dimensional computed tomography data. The sequential 3D-3D registration method semiautomatically provides the kinematics of the moving bone with respect to the subject bone from four-dimensional computed tomography data.

Four-dimensional computed tomography (4DCT) provides a series of volume data and visualizes joint motions. However, numerical analysis of 4DCT data ...

Biplanar Videoradiography to Study the Wrist and Distal Radioulnar Joints

Accurate measurement of skeletal kinematics in vivo is essential for understanding normal joint function, the influence of pathology, disease progression, and the effects of treatments. Measurement systems that use skin surface markers to infer skeletal motion have provided important insight into normal and pathological kinematics, however, accurate arthrokinematics cannot be attained using these systems, especially during dynamic activities. In the past two decades, biplanar videoradiography (BVR) systems have enabled many researchers to directly study the skeletal kinematics of the joints during activities of daily living. To implement BVR systems for the distal upper extremity, videoradiographs of the distal radius and the hand are acquired from two calibrated X-ray sources while a subject performs a designated task. Three-dimensional (3D) rigid-body positions are computed from the videoradiographs via a best-fit registrations of 3D model projections onto&#160;to each BVR view. The 3D models are density-based image volumes of the specific bone derived from independently acquired computed-tomography data. Utilizing graphics processor units and high-performance computing systems, this model-based tracking approach is shown to be fast and accurate in evaluating the wrist and distal radioulnar joint biomechanics. In this study, we first summarized the previous studies that have established the submillimeter and subdegree agreement of BVR with an in vitro&#160;optical motion capture system in evaluating the wrist and distal radioulnar joint kinematics. Furthermore, we used BVR to compute the center of rotation behavior of the wrist joint, to evaluate the articulation pattern of the components of the implant upon one another, and to assess the dynamic change of ulnar variance during pronosupination of the forearm. In the future, carpal bones may be captured in greater detail with the addition of flat panel X-ray detectors, more X-ray sources (i.e., multiplanar videoradiography), or advanced computer vision algorithms.

Biplanar videoradiography (BVR) is an advanced imaging technique for understanding the three-dimensional movement of skeletal bones and implants. Combining density-based image volumes and videoradiographs of the distal upper extremity, BVR is used to study the in vivo motion of the wrist and distal radioulnar joint, as well as joint arthroplasties.

Accurate measurement of skeletal kinematics in vivo is essential for understanding normal joint function, the influence of pathology, disease progression, ...

Measuring 3D In-vivo Shoulder Kinematics using Biplanar Videoradiography

The shoulder is one of the human body's most complex joint systems, with motion occurring through the coordinated actions of four individual joints, multiple ligaments, and approximately 20 muscles. Unfortunately, shoulder pathologies (e.g., rotator cuff tears, joint dislocations, arthritis) are common, resulting in substantial pain, disability, and decreased quality of life. The specific etiology for many of these pathologic conditions is not fully understood, but it is generally accepted that shoulder pathology is often associated with altered joint motion. Unfortunately, measuring shoulder motion with the necessary level of accuracy to investigate motion-based hypotheses is not trivial. However, radiographic-based motion measurement techniques have provided the advancement necessary to investigate motion-based hypotheses and provide a mechanistic understanding of shoulder function. Thus, the purpose of this article is to describe the approaches for measuring shoulder motion using a custom biplanar videoradiography system. The specific objectives of this article are to describe the protocols to acquire biplanar videoradiographic images of the shoulder complex, acquire CT scans, develop 3D bone models, locate anatomical landmarks, track the position and orientation of the humerus, scapula, and torso from the biplanar radiographic images, and calculate the kinematic outcome measures. In addition, the article will describe special considerations unique to the shoulder when measuring joint kinematics using this approach.

Biplane videoradiography can quantify shoulder kinematics with a high degree of accuracy. The protocol described herein was specifically designed to track the scapula, humerus, and the ribs during planar humeral elevation, and outlines the procedures for data collection, processing, and analysis. Unique considerations for data collection are also described.

The shoulder is one of the human body's most complex joint systems, with motion occurring through the coordinated actions of four individual joints, ...

A Probing Device for Quantitatively Measuring the Mechanical Properties of Soft Tissues during Arthroscopy

Probing in arthroscopic surgery is performed by pulling or pushing the soft tissue, which provides feedback for understanding the condition of the soft tissue. However, the output is only qualitative based on the &#8220;surgeon&#8217;s feeling&#8221;. Herein is described a probing device developed to address this issue by measuring the resistance of soft tissues quantitatively with a tri-axial force sensor. Under both conditions (i.e., pull- and push-probing certain tissues mimicking the acetabular labrum and cartilage), this probing device is found to be useful for measuring some mechanical properties in joints during arthroscopy.

Probing during arthroscopy surgery is normally done to assess the condition of the soft tissue, but this approach has always been subjective and qualitative. This report describes a probing device that can measure the resistance of the soft tissue quantitatively with a tri-axial force sensor during arthroscopy.

Probing in arthroscopic surgery is performed by pulling or pushing the soft tissue, which provides feedback for understanding the condition of the soft ...

In Vivo Quantification of Hip Arthrokinematics during Dynamic Weight-bearing Activities using Dual Fluoroscopy

Samenvatting

Meer video's verkennen