Purpose - In the human knee, the articular cartilage (AC) and subchondral bone (SB) form a biomechanically and biochemically functional osteochondral unit. Macroscopic cartilage assessment by arthroscopy is commonly used to determine AC lesion severity prior to surgery. We previously reported that the health of the SB could influence outcomes following cell-based therapy for AC repair, but macroscopic assessment gives no indication of SB health. Our aim was to assess correlation between the macroscopic and histological grading systems.
Methods and Materials - Osteochondral tissue samples were collected from patients undergoing total knee replacement surgery (TKR). AC was graded macroscopically using the ICRS Cartilage Lesion Classification System (grade 0 (normal) – grade 4 (severely abnormal)). Two osteochondral fragments, one with the lowest grade (most normal) and one with the highest grade (most abnormal) cartilage, were obtained for each TKR patient. Sections were stained with haematoxylin & eosin and safranin O/fast green before histological assessment. AC was graded using the OARSI OA Cartilage Histopathology Assessment System (grade 0 (normal) – grade 6 (deformation)). SB was graded using the SB Histological Grading System (grade 0 (early OA) – grade 3 (late-stage OA)). The relationship between scores was assessed using Kendall’s rank correlation coefficient (Kendall’s tau).
Results - Sixteen TKR patients (6 female, 10 male; 68.2±6.7SD years-old), were included, resulting in the generation of 32 paired osteochondral fragments with the most normal and most abnormal cartilage for each patient. The ICRS score demonstrated moderate-to-strong correlation with both the AC and SB histological scores (Table 1, Figure 1). The AC and SB histological scores were also strongly correlated (Table 1).
Conclusion - Our results suggest that macroscopic cartilage assessment, using the ICRS scoring system, may give an indication of histologically assessed AC and SB health. This study provides further evidence for the close association between the AC and SB in patients with established knee osteoarthritis.