Clinical optical coherence tomography of early articular cartilage degeneration in patients with degenerative meniscal tears

Abstract

Objective: Quantitative and nondestructive methods for clinical diagnosis and staging of articular cartilage degeneration are important to the evaluation of potential disease-modifying treatments in osteoarthritis (OA). Optical coherence tomography (OCT) is a novel imaging technology that can generate microscopic-resolution cross-sectional images of articular cartilage in near real-time. This study tested the hypotheses that OCT can be used clinically to identify early cartilage degeneration and that OCT findings correlate with magnetic resonance imaging (MRI) T2 values and arthroscopy results.

Methods: Patients undergoing arthroscopy for degenerative meniscal tears were recruited under Institutional Review Board-approved protocols. Thirty consecutive subjects completing preoperative 3.0T MRI, arthroscopy, and intraoperative OCT comprised the study group. Qualitative and quantitative OCT results and MRI T2 values were compared with modified Outerbridge cartilage degeneration scores (0-4 scale) assigned at arthroscopy.

Results: Arthroscopic grades showed cartilage abnormality in 23 of the 30 patients. OCT grades were abnormal in 28 of the 30 patients. Both qualitative and quantitative OCT strongly correlated with the arthroscopy results (P = 0.004 and P = 0.0002, respectively, by Kruskal-Wallis test). Neither the superficial nor the deep cartilage T2 values correlated with the arthroscopy results. The quantitative OCT results correlated with the T2 values in the superficial cartilage (Pearson's r = 0.39, P = 0.03).

Conclusion: These data show that OCT can be used clinically to provide qualitative and quantitative assessments of early articular cartilage degeneration that strongly correlate with arthroscopy results. The correlation between the quantitative OCT values and T2 values for the superficial cartilage further supports the utility of OCT as a clinical research tool, providing quantifiable microscopic resolution data on the articular cartilage structure. New technologies for nondestructive quantitative assessment of human articular cartilage degeneration may facilitate the development of strategies to delay or prevent the onset of OA.

Figure 1. Example Images

Column 1 (a) Arthroscopically firm (b) OCT with birefringence, (c) T2 map (superficial T2 = 54+/−9 ms; deep T2 = 49 +/−11 ms). Column 2 (d) Arthroscopically firm (e) OCT without birefringence (f) T2 map (superficial T2 = 55+/−9 ms; deep T2 = 45+/−8 ms). Column 3 (g) Arthroscopically “softened”, (h) OCT without birefringence (i) T2 map (superficial T2 = 46+/−11ms; deep T2 = 43+/−13 ms). Column 4 (j) Arthroscopic fissured (k) OCT fissured, (l) MRI T2 map (superficial T2 = 55+/−9 ms; deep T2 = 45+/−8 ms).

Figure 2. Subjective OCT grade distribution by Arthroscopic grade

In this study of persons with degenerative meniscal tears, 5/7 subjects with arthroscopically firm (Scope Grade 0) articular cartilage were abnormal by OCT (OCT Grade > 0). All subjects with cartilage graded slightly abnormal (Scope Grade 1) by arthroscopy were abnormal by OCT. The proportion of higher OCT grades reflecting increasing abnormality increased with increasing arthroscopic grade.

Figure 3. OCT and MRI metrics compared to arthroscopic grade as the standard

(a) Subjective grading of OCT images based on characterization of birefringence pattern and surface smoothness shows that OCT grade varies with arthroscopic grade (Kruskal Wallis p=0.004). (b) Mean quantitative OCT values strongly correlate to arthroscopic disease severity grades (Kruskal Wallis p = 0.0002, R=0.85). (c) Mean T2 values demonstrate a complex relationship to arthroscopic grade. The mean superficial T2 value (open circles) is lowest in softened but intact tissue (scope grade 1) and increases with increasing degeneration (scope grades 2–4). Superficial T2 values of healthy tissue (scope grade 0), however, fall in the middle of the range of observed superficial T2s. The mean deep T2 value (closed circles) is lowest in tissue with partial thickness defects and surface fissures. Neither superficial nor deep T2 values varied significantly with cartilage degeneration as assessed by conventional arthroscopy (Kruskal-Wallis p=0.11, p=0.10, respectively).Error bars are ± SEM.

Figure 4. MRI T2 Mapping

(a) T2 values measured in the superficial half of cartilage were found to be 24% higher on average than those measured in the deep half of tissue T-test p≪0.0001, error bars ± 1 SEM). (b) Superficial T2 values discriminated between cartilage with intact articular surfaces and cartilage with surface defects (Mann-Whitney p = 0.04, error bars ± 1 SEM).

Figure 5. Superficial T2 values (open circles) correlate to quantitative OCT values

(Pearson r = 0.39, p=0.03). No correlation is seen between deep T2 values (closed circles) and quantitative OCT values (Pearson r = 0.13, p=0.50).