HR-pQCT measurements of changes in periarticular bone density and microarchitecture one year after acute knee injury and after reconstructive surgery.

ACL injuries commonly lead to post-traumatic osteoarthritis (PTOA), but the underlying mechanism is not well-understood. One theorized mechanism is pathological bone remodelling following an ACL tear, for which high-resolution peripheral quantitative computed tomography (HR-pQCT) is uniquely positioned to investigate in vivo in humans. In this study, we longitudinally investigate the one-year changes in periarticular bone density and microarchitecture in the human knee following an ACL tear and reconstructive surgery using data sampled from an on-going observational cohort study. We reduce the number of individual microarchitectural parameters using factor analysis and model one-year changes with mixed-effects models, adjusting for the effects of age, sex, meniscus status, and the baseline microarchitectural state. We find significant evidence of persistent bone density losses one year after both injury and surgery. We also observe significant increases in trabecular separation post-injury, indicating significant structural degradation, and significant increases in subchondral bone plate density post-surgery, a sign of early stiffening. Finally, we observe minimal significant contrasts for the effects of age, sex, and meniscus status, while we observe that the state of the microarchitecture at baseline has significant and varied effects on the subsequent changes, suggesting that the influence of PTOA risk factors on post-injury and post-surgery bone changes may be mediated through the state of the periarticular microarchitecture at injury and/or at surgery. In summary, we found that degradation of periarticular bone microarchitecture was observed post-injury, densification of the subchondral bone plate was observed post-surgery, and the state of the bone microarchitecture at baseline may mediate the influence of PTOA risk factors on post-injury microarchitectural adaptations.