If you have the warning message "Warning: RMS Error on HJC Definition"
This is a WARNING message meaning the calibration has been recorded but accuracy of the calculations is affected by too much movement of the sacrum/pelvis.
This warning message occurs when the patient lacks balance while doing the “Hip Joint Center” calibration step.
- To re-record the calibration, click on the record button manually instead of using the pointer.
*If, after those adjustment, the RMS error is still between 6 and 10 mm, accept the calibration and continue.
If this warning appears, here’s a few tips to ensure the quality of your results:
Patient Positioning
For this movement, the patient must have a solid core and the KneeKG-3D-Tracker-PelvisTM must be stable.
- Increase the stability of the KneeKG-3D-Tracker-Pelvis, position the patient in a comfortable standing position where they can hold on. Ask the patient to stand tall, engage their abdominal muscles, and keep their pelvis stable while performing the movement with slightly smaller circles.
- Adjust the Sacroiliac Belt to limit the movement. Make sure that the pelvic anatomical landmarks are respected (the belt sits below the PSIS and the ASIS) and that the belt is tight enough.
Remember, you can always help the patient stabilize their pelvis to keep the KneeKG-3D-Tracker-Pelvis in the field of view of the camera.
How to Help a Patient with Hip Range of Motion Limitation
Some patients have hip range of motion limitations, requiring a modification to the procedure. There are other possible alternatives to the HJC calibration circumduction:
- A leg swing: The patient performs a simple leg swing in a straight line forward and backward, then side to side, then forward and backward again, and so on.
- A foot slide: Keeping the foot near the treadmill surface, the patient slides their foot forward and then outward and backward in the shape of the letter D, and repeats.
- Assist the patient manually: The Evaluator can hold the patient’s knee or proximal tibia in their hands, without blocking the view of the femoral tracker, and manually move the femur in a circular motion.
