Pacific Northwest University Yakima, Washington, United States
Abstract Body :The Quadriceps Angle (Q-angle) is the difference between the line of action (resultant force vector) of the quadriceps femoris muscle and patellar ligament in the frontal plane and is presumed to affect patellofemoral kinematics. Clinicians utilize Q-angle to either support or dismiss diagnoses of the lower limb, most notably at the knee joint. A Q-angle within normal limits should provide a balance of forces around the knee joint whereas a larger or smaller Q-angle may indicate an uneven distribution of force on the patella as excessive lateral or medial force components. Previous work has indicated correlation between lower limb trabecular bone morphology and locomotor pattern, suggesting functional adaptation to differential biomechanical forces. If differences in Q-angle affect the magnitude of medial and lateral force components acting on the knee, it could result in corresponding differences of the medial and lateral patellar microstructure. If imbalances in medial and lateral force components result in knee pathology, bony pathologies such as abnormal trabecular thickness and density would be observed. Our aim is to test for these biomechanical relationships by examining Q-angle and trabecular bone microstructure across a cadaveric sample. The Q-angle was measured bilaterally via goniometer on 36 supine cadavers before and after lower limb dissection. Due to variable range of motion, normalized Q-angle range for the sample was calculated as one standard deviation from the average. Patellae were removed and imaged using high resolution computed microtomography (µCT) (slice resolution = 35µm). Image stacks were reconstructed in three-dimensions and processed using the open-source image computing platform 3D Slicer, and volumes of interest (VOIs) were defined to sample subcortical bone of the lateral and medial facet of each patella. Cropped VOIs were imported to Fiji (ImageJ) where images were filtered, binarized, and analyzed. Trabecular spacing maps and metrics including bone volume fraction (BV/TV), trabecular thickness (TbTh), trabecular separation (TbSp), bone volume (BV), and total volume (TV) were computed via BoneJ. Comparisons were made between medial and lateral facets of each patella. Preliminary results indicate no clear relationship between measured Q-angle and predictable patella pathology as measured by trabecular metrics. These results question the clinical practice of using Q-angle to predict patella pathology. The use µCT in clinical practice is still in an investigatory phase and the data collected suggests further evaluation is needed before it could be used in diagnosis of patellar pathology. The data also suggests there may be additional forces outside of the Q-angle that play a role in trabecular bone remodeling on patellar facets.
