gms | German Medical Science

Objectives: Post-traumatic osteoarthritis constitutes a major cause of disability. As yet, imaging of articular cartilage damage before surface breakdown is not possible by current clinical imaging modalities. The early detection of those posttraumatic changes, while being potentially still reversible, is essential for adequate therapeutic interventions. Optical Coherence Tomography (OCT) is a promising non-destructive imaging technique that allows surface and sub-surface imaging of cartilage at near-histological resolution. Up to now, post-traumatic changes in response to standardized supra-physiological impaction have not been parameterized and quantified.

Methods: Thirty-six human cartilage-bone samples from regions with macroscopically intact cartilage were obtained from 11 total knee arthroplasties. Samples were assigned to 4 groups consisting of 8 samples each, i.e. non-impacted control group and 3 groups of different impact energy levels (low impact - 0.24 J [LIMP]; moderate impact - 0.48 J [MIMP]; high impact - 0.98 J [HIMP]) using a custom-made cylindrical drop tower. OCT measurements took place prior to impaction, immediately after impaction and 1, 4 and 8 days later. At each time point 2 samples of each group underwent routine histological staining (HE, Saf O) for subsequent correlation with OCT images. OCT images were also subjected to qualitative assessment according to the Degenerative Joint Disease (DJD) classification and to quantitative evaluation of surface irregularity (Optical Irregularity Index, OII, i.e. the standard deviation of the native from an idealized surface), tissue homogeneity (Optical Homogeneity Index, OHI, i.e. the number of detected signal edges) and imaging depth (Optical Attenuation Index, OAI, i.e. signal intensity loss below 15% of the initial signal intensity at the sample surface). Samples were histologically evaluated according to the DJD classification. One-way-ANOVA and Tukey's multiple comparison tests were used for statistical analyses of OCT data.

Results and Conclusion: Overall, 72% of the samples (26/36) were qualitatively assessed to have the same DJD grade by means of OCT and histology. Only the HIMP group demonstrated significantly increased mean DJD grades as determined by histology and by qualitative OCT, while the LIMP and MIMP groups did not reveal such significant changes. In terms of quantitative OCT, OII was found to be significantly increased only in the HIMP group (p < 0.0001). For OAI and OHI no significant time-related changes were noted throughout the 8-day culture period independent of impaction.

OCT image-based parameterization and quantification is diagnostically beneficial in detecting loss of surface integrity upon severe traumatic impaction, whereas low-to-moderate traumatic impaction may not be adequately assessable by quantitative OCT.