In Vivo Quantification of Hip Arthrokinematics during Dynamic Weight-bearing Activities using Dual Fluoroscopy
July 2nd, 2021
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.
This protocol combines measurement of in vivo hip kinematics with whole body motion capture to lose state the role of biomechanics in hip degeneration. In comparison to traditional methods of tracking hip motion, dual fluoroscopy has improved accuracy which allows for investigation of the subtle relationship between hip shape and motion patterns. For the pivot activities, have the participant rotate or translate their feet such that the pelvis is facing forward on the treadmill.
And the hip of interest is in the middle of the combined field of view on the fluoroscopes at the end of the pivot. Once the position is optimized, have the participant perform the pivot during dual fluoroscopy imaging. And save all frames where the femur and pelvis are visible in both fluoroscopy camera views.
Capturing as much of the pivot as possible. On walking drills inform the participant before starting the treadmill belt. Ramp the treadmill speed up to the appropriate walking speed.
And let the participants gait normalized before collecting images. For the inclined walking activity, have the participants step off the treadmill. Unlock the treadmill, set the incline to five degrees and relaunch the treadmill.
Before having the participant step back onto the treadmill to perform the activity. For the abduction adduction activity, have the participant stand in the field of view of the fluoroscopes. And raise the leg of interest approximately 45 degrees up and out to the side without moving the torso.
For the dynamic hip joint center or star arch activity, have the participant stand in the field of view of the dual fluoroscopy system and raise, and then lower their leg anteriorly at 45 degree increments up to 180 degrees. Before placing their leg back onto the ground, have the participant circumduct their leg and return to a standing position. For marker placement apply spray glue to the skin side of the fabric strap of each of five marker plates.
And wrap them tightly around the participant. Check with a participant that the straps feel tight, but are not uncomfortable. Then place the marker plates on the fabric strips.
After cleaning hands to remove any excess spray glue and putting on gloves to protect the markers apply the five markers used only for calibration to the clavicle medial knees and medial malleolar. Next apply the 16 markers for tracking to the superior iliac spines, posterior superior iliac spines, greater trochanter of the femur being imaged, shoulders, sternum, lateral knees, lateral malleolar and feet. For landmark identification of the coordinate system, open the proximal femur as a model file then opened the post tool bar and data panel to add a standard field of first principle curvature.
Select a smoothness of 10 and click apply. Next over select the faces of the femoral head. From the edit panel, click select range to include only negative curvature.
Determine the center of the femoral head using this sphere fit tool from the measure tool. Export this femoral head surface as a surface mesh in k format. Similarly apply first principle curvature to the distal femur with a spoon this of five.
Click select range again to include only the faces with negative curvature. Export this femoral condyle surface for a cylinder fit to determine the medial lateral axis. Next apply second principle curvature to the distal femur using a smoothness of three.
Highlight the ridges of the epicondyle and click select range. Applying an upper cutoff of negative 0.1. Export these faces to generate a plane and use it to isolate the faces of the posterior condyle for the cylinder fit.
For marker-less tracking, select a frame within the desired range with good visualization of the bone. And manually orient the CT based digitally reconstructed radiograph of the bone of interest using the six degrees of freedom available in the software. Once the digitally reconstructed radiograph of the bone appears well aligned in both views, save the solution by clicking on the manual button from the solutions panel.
Next from the solutions panel, click the DHS button to apply the diagonal hession search optimization step and review the result. If the optimized result is preferred, move on to the next frame, otherwise make any necessary adjustments and resave by clicking the manual button within the solutions panel. To complete the first pass of tracking, use the range of LP plus DHS button within the solutions panel.
In the window, enter the set of frames to be tracked and the two frames to be used for reference. Review and refine each frame of the trial using both manual and DHS based solutions. Use the plot of parameters to ensure that the correlation coefficient is sufficiently high, and that the orientation of the bone does not have sudden jumps in any parameter.
To visualize the motion, open the femur and pelvis surfaces in the software for kinematic visualization. If necessary using the convert to mesh function, convert the surfaces to meshes. Select both surfaces and export as a surface mesh in k format.
Using the output from tracking, generate a text file with the coordinate transformations for each bone and frame. Then using the kinematic tool and surface mesh and text files generated earlier animate the kinematics. Using a semi-transparent surface, verify that the animated kinematics look reasonable.
Alternatively using the surface distance tool, run the animated kinematics and verify that the surfaces have an appropriate distance between them. Kinematics for 100 frames surrounding the maximum rotation of external and internal rotation pivots for a representative participant are shown here. This figure shows the measurement of surface distance between a left hemi pelvis and femur.
At maximum rotation of the external and internal rotation pivot with respect of bone models using dual fluoroscopy. Attention to detail is important for accurate tracking of arthrokinematics. It is crucial that each step of data collection and processing is done with intent.
View the full transcript and gain access to thousands of scientific videos
Overview
This protocol combines in vivo hip kinematics measurement with whole body motion capture to explore biomechanics in hip degeneration. Dual fluoroscopy enhances accuracy in tracking hip motion, revealing subtle relationships between hip shape and motion patterns.
Key Study Components
Area of Science
- Biomechanics
- Motion Capture
- Orthopedics
Background
- Understanding hip kinematics is crucial for studying hip degeneration.
- Traditional motion tracking methods may lack precision.
- Dual fluoroscopy provides improved accuracy for in vivo studies.
- Investigating the relationship between hip shape and motion patterns is essential.
Purpose of Study
- To quantify hip arthrokinematics during weight-bearing activities.
- To integrate dual fluoroscopy with traditional motion capture techniques.
- To enhance understanding of biomechanics in daily activities.
Methods Used
- Participants perform pivot activities while being monitored.
- Fluoroscopy captures images of the femur and pelvis.
- Data is collected during weight-bearing tasks.
- Analysis focuses on the relationship between hip shape and motion.
Main Results
- Improved accuracy in capturing hip motion compared to traditional methods.
- Identification of subtle motion patterns related to hip shape.
- Successful integration of dual fluoroscopy with motion capture.
- Insights into biomechanics during daily activities.
Conclusions
- Dual fluoroscopy is a valuable tool for studying hip kinematics.
- Enhanced methods can lead to better understanding of hip degeneration.
- Future studies can build on these findings to improve clinical outcomes.
Frequently Asked Questions
Executive Industry Relevance
Accurate quantification of in vivo joint kinematics is essential for de-risking target validation in musculoskeletal drug discovery. Dual fluoroscopy enables precise measurement of hip arthrokinematics during dynamic weight-bearing activities, supporting mechanistic understanding of structure-function relationships. This capability improves predictive confidence in preclinical models by reducing biomechanical ambiguity in target engagement studies.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Scientific Value: Enables interrogation of therapeutic hypotheses linking bone morphology to joint biomechanics in hip degeneration pathways.
- Operational Value: Provides quantitative, reproducible motion data to functionally validate targets involved in hip joint mechanics.
- Predictive Value: Supports portfolio triage by clarifying whether observed phenotypic effects stem from on-target biomechanical modulation.
Screening & Assay Development
- Scientific Value: Generates validated, disease-relevant kinematic readouts for assay standardization in preclinical screening cascades.
- Operational Value: Delivers high-fidelity, quantitative outputs enabling reliable compound evaluation across repeated testing sessions.
- Scalability Value: Facilitates platform reuse for longitudinal studies assessing target modulation effects on joint mechanics over time.
Translational & Preclinical Research
- Scientific Value: Establishes disease-relevant system fidelity by capturing native joint motion under physiological loading conditions.
- Operational Value: Ensures translational continuity from discovery through preclinical validation via consistent, biomechanically grounded phenotyping.
- Risk Mitigation: Supports risk-adjusted advancement decisions by identifying off-target biomechanical effects early in the pipeline.
Pipeline & Workflow Integration
The method bridges discovery biology and preclinical validation by delivering biomechanically precise phenotyping that informs target selection and lead optimization decisions.
- Discovery Biology: Supports hypothesis testing and pathway clarification by quantifying how genetic or pharmacological perturbations alter joint kinematics.
- Screening: Enables assay readiness through standardized, reproducible motion capture under controlled weight-bearing conditions.
- Analytics: Yields coordinate transformation data and surface distance metrics that allow teams to compare motion phenotypes across experimental groups.
- Translational Research: Connects to preclinical continuity by providing biomechanically anchored endpoints predictive of clinical joint function outcomes.
- Enterprise Reuse: Functions as a reusable capability for iterative target validation across multiple musculoskeletal programs.
Operational & Enterprise Impact
- Scientific Value: Increases predictive confidence by reducing mechanistic ambiguity in structure-function relationships within joint tissue.
- Operational Value: Enhances standardization and reproducibility of kinematic measurements across sites and studies.
- Strategic Value: Improves go/no-go decision quality by enabling early detection of biomechanically mediated liabilities.
- Portfolio Impact: Enables risk-adjusted prioritization based on quantitative biomechanical de-risking of target candidates.
Implementation Considerations
- Requires expertise in biomechanics, medical imaging, and 3D kinematic modeling for accurate data interpretation.
- Depends on dual fluoroscopy systems, CT image reconstruction software, and synchronized motion capture infrastructure.
- Necessitates cross-team standardization of marker placement, calibration protocols, and tracking parameters to ensure data comparability.
- Involves adaptation considerations when applying the method to different joint types or species-specific anatomies.
- Limited by soft tissue artifact during extreme motion and the need for precise synchronization between imaging and motion capture systems.
