Non-ionic CT contrast solutions rapidly alter bovine cartilage and meniscus mechanics

Objective: To evaluate effects of a common CT contrast agent (iohexol) on the mechanical behaviors of cartilage and meniscus. Methods: Indentation responses of juvenile bovine cartilage and meniscus were monitored following exposure to undiluted contrast agent (100% CA), 50% CA/water, 50% CA/Phosphate Buffered Saline (PBS) or PBS alone, and during re-equilibration in PBS. The normalized peak force (F_pk¯), effective osmotic strain (ε_osm), and normalized effective contact modulus (E_c¯) were calculated for every cycle, with time constants determined for both exposure and recovery via mono- or biexponential fits to F_pk¯. Results: All cartilage CA groups exhibited long-term increases in F_pk¯ following exposure, although the hyperosmolal 100% CA and 50% CA/PBS groups showed an initial transient decrease. Meniscus presented opposing trends, with decreasing F_pk¯ for all CA groups. Re-equilibration in PBS for 1hr after exposure to 100% CA produced recovery to baseline F_pk¯ in cartilage but not in meniscus, and extended tests indicated that meniscus required ∼2.5 h to recover halfway. E_c¯ increased with CA exposure time for cartilage but decreased for meniscus, suggesting an increased effective stiffness for cartilage and decreased stiffness for meniscus. Long-term changes to ε_osm in both tissues were consistent with changes in E_c¯. Conclusion: Exposure to iohexol solutions affected joint tissues differentially, with increased cartilage stiffness, likely relating to competing hyperosmotic and hypotonic interactions with tissue fixed charges, and decreased meniscus stiffness, likely dominated by hyperosmolarity. These altered tissue mechanics could allow non-physiological deformation during ambulatory weight-bearing, resulting in an increased risk of tissue or cell damage.