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.
