However, MRI scans, particularly used with gadolinium dye, provide a much better view of the knee joint. This MRI technology, boosted with a 7 Tesla magnetic coil, has the power to yield an ultra-high-field view of the knee joint, particularly the cartilage. Further, the researchers noted that 7T gadolinium-enhanced MRI has never been used before to monitor the knee joint over a period of time to check for post-traumatic osteoarthritis progression. “The big thing you have to think about is the thickness of the cartilage,” said Filgueira. “The 7T magnetic coil offers a high-resolution way to quantify very small-scale changes in cartilage thickness.” Specifically, among other quantities, the researchers measured the delayed gadolinium-enhanced MRI of cartilage or the dGEMRIC index. Here, lower index values indicate degenerative changes or thinning in the articular cartilage. For their study, the team chose rabbits as their model systems and induced an ACL tear surgically in these animals. The large animal model allowed the researchers to reproduce the ACL tear across experiments and the ability to systematically follow the cartilage over 10 weeks of recovery. In addition, rabbit knees from the same animal, one with the ACL tear and one without, both fit into the coil of the 7T MRI scanner at the same time, facilitating comparisons between the joints.

Upon refining their scanning protocol several times to optimize parameters that improved the signal to noise ratio, the team found that compared to the intact cartilage, there was a 35% and 39% decrease in the dGEMRIC index of the ACL on the medial side of the injured knee joint at seven and 10 weeks, respectively. “This result is really key because we now have a time point when there is real evidence of cartilage degradation,” said Filgueira. “You can now say ‘OK, here's a time when we should be intervening’ and if we wait too long, any type of intervention is going to be too late because we've lost the cartilage.” Thus, with an established model for post-traumatic osteoarthritis, the success of an intervention, such as nanomedicine, can be evaluated reliably. More broadly, their observations, although in rabbits, also make a strong case for early intervention and rehabilitation of the human knee after an ACL injury. “Now, we have printed studies that show that you do need to intervene early, and you need to be put on a regimen that can prevent cartilage loss,” said Filgueira. “I think and hope that our study can help change people's mindsets.” The research was supported by the Department of Orthopedics Pilot Project Initiative and funds from Houston Methodist Research Institute.