Histopathological assessment of primary osteoarthritic knees in large patient cohort reveal the possibility of several potential patterns of osteoarthritis initiation

Abstract

Objective: The two main objectives of the study include (1) Test the hypothesis that the lateral femoral condyle (LFC) in patients with primary OA and varus knees undergoing total knee arthroplasty (TKA) can be used as a model to better characterize varying histological features of human OA, (2) Correlate characteristic OA features using the established histopathological scoring systems (HHGS and OARSI) to understand potential histopathological patterns of OA initiation.

Design: Two osteochondral specimens (4×4×8mm) were collected from fifty patient's LFC at the time of TKA (total 100 specimens), who presented preserved lateral knee compartment with joint space width>2mm. Three independent readers graded the sections on three different occasions using HHGS and OARSI systems. The correlation between individual parameters of the two scoring systems and their inter- and intra-reader variability, reliability and reproducibility were estimated.

Results: All samples in this cohort showed abnormal histopathological features. Total histopathological scores of the LFC ranged from HHGS median=4.6 (range=0 to 11), and OARSI median=5.2 (range=0 to 19.5). The four individual sub-items of HHGS scoring system (structure, cells, safraninO staining, tidemark) were weakly correlated, with the correlation between structure and cellularity being the strongest (r=0.40). Both the scoring systems had similar repeatability and reproducibility coefficients of<21%.

Conclusions: OA changes in the LFC are not confined to any one region, and maybe seen in different regions of cartilage, tidemark, subchondral bone, and/or the marrow space vascularity. These variations may point to the possibility of several potential patterns of initiation in OA.

Keywords: Cartilage; Grading; Histology; Histopathology; Primary osteoarthritis.

Fig. 1

Sample of lateral femoral condyle was obtained (A) and cut into 4 mm thick arches through the region of the femur that is weight bearing in extension(B). The central region of one arch was cut into five specimens (4mmx4mm), the second (Lateral) and fourth (Medial) were processed for histology (C). Each specimen was paraffin embedded, sectioned and stained with H&E (E), and SafO-FG (F) for analysis.

Fig. 2

HHGS histological Grading: A. Normal surface (structure=0) and normal cell distribution (cells=0). B. Surface irregularities (structure =1) and diffuse hypercellularity (cells=1). C. Pannus and surface irregularities (structure =2) and hypercellularity (cells=1). D. Clefts to transitional zone (structure=3) with cloning (cells=2). E. Clefts to radial zone (structure=4) with chondrocyte cloning (cells=2). F. Surface irregularities (structure =1) with region of hypocellularity (cells=3). G. Normal even distribution of Safranin O stain throughout the cartilage section except for in the superficial zone (safraninO staining=0). H. Slight reduction of stain area observed near the superficial zone as well as the deep zone above calcified cartilage region (safraninO staining=1). I. Moderate reduction of the stain area detected in superficial, mid and deep zone (safraninO staining=2). J. Severe reduction in stain area in the superficial and mid zone, with loss of intra-territorial matrix in the deep zone (safraninO staining=3) K. Intact single tidemark (tidemark integrity=0). L. Tidemark breached by two blood vessels (tidemark integrity=1). Note: All structure, cell and tidemark features of HHGS were detected using H&E sections.

Fig. 3

OARSI histological Grading: A. Intact cartilage with intact surface (grade=0, stage=0) B. Surface fibrillation with cell proliferation and minor cationic stain depletion (grade=1, stage=2). C. Severe surface fibrillation with cell proliferation and stain loss (grade=1.5, stage=3). D. Discontinuity in superficial zone along with cell proliferation and greater cationic stain loss (grade=2, stage=2). E. Surface abrasion with matrix loss in the superficial zone with predominant cell proliferation (grade=2.5, stage=2). F. Simple clefts through superficial zone to mid zone with cationic stain loss seen till the mid zone (grade=3, stage=3). G. Wider, branched clefts seen to the mid zone with cationic stain loss seen till mid-zone (grade=3.5, stage=3). H. Superficial cartilage delamination with matrix stain loss (grade=4, stage=3). I. Cartilage excavation in the mid-zone along with matrix stain loss and cell cloning (grade=4.5, stage=3). Note: The OARSI scoring was done using SafO-FG sections.