Histological Characteristics of Knee Menisci in Patients with Osteoarthritis

Abstract

Meniscal injury is a common source of knee pain, and it is argued that meniscal lesions can lead to osteoarthritis (OA) or OA can lead to meniscal lesions. Existing data indicate knee menisci in patients with OA show tearing, maceration, and fragmentation. The aim of this study was to evaluate changes in the histological structure of the menisci from patients with clinically diagnosed OA of the knee and to determine factors related to these changes. Medial and lateral menisci samples, demographic data, and Outerbridge classification scores (OCS, range 0–IV) of cartilage from the medial tibial plateau (MTP), medial femoral condyle (MFC), lateral tibial plateau (LTP), and lateral femoral condyle (LFC) were obtained with informed consent from 10 patients (6 female, 4 male) undergoing total knee arthroplasty for treatment of clinically diagnosed OA. Tissue samples were fixed in 10% buffered formaldehyde solution and 5–10 mm cross‐sections were taken from the middle of the medial and lateral menisci for further analysis. Cross‐sections were decalcified and sliced at 10 μm intervals. Three nonconsecutive tissue slices from each cross‐section were stained with hematoxylin and eosin and scanned at 10× magnification for histological scoring using grid counting. The only abnormal feature found was the presence of calcified cartilage matrix, so the percentage of calcified tissue was calculated for each tissue slice. Exact Mann‐Whitney tests and Spearman correlation coefficients were used to test for relationships of the percent calcification in samples with demographic data and OCS. Mean±SD age and weight of patients were 61.9±9.6 years and 98.0±18.5 kg, respectively. For the MTP, 1 patient had an OCS of II, 4 had an OCS of III, and 5 had an OCS of IV. For the MFC, 2 patients had an OCS of II, 5 had an OCS of III, and 3 had an OCS of IV. The mean±SD percentage of tissue calcification for the medial meniscus (MM) was 12.9±4.2% (female=13.2±3.2%, male=12.5±6.1%; P=.91). For the LTP, 1 patient had an OCS of II, 7 had an OCS of III, and 2 had an OCS of IV. For the LFC, 5 patients had an OCS of II, 4 had an OCS of III, and 1 had an OCS of IV. The mean±SD percentage of tissue calcification for the lateral meniscus (LM) was 11.5±4.2% (female=11.5±4.8%, male=11.5±3.9%; P=.91). Age was strongly positively correlated with percent calcification of MM (ρ=0.70, P=.02) but not with percent calcification of LM (ρ=0.15, P=.69). Significant correlations were also found between percent calcification of MM and LM (ρ=0.66, P=.04), OCS of the MTP and MFC (ρ=0.64, P=.05), and OCS of the LTP and LFC (ρ=0.65, P=.04). Percent calcification of MM and LM were not correlated with weight or the corresponding OCS (P≥.11). The most pronounced histological characteristic of the menisci from patients with clinically diagnosed OA was calcification of the cartilage matrix. Of all the factors analyzed, only age was correlated with the degree of calcification of the MM. This correlation was not found in the LM, and additional research is required to understand the significance of this finding. A strong positive correlation existed between percent calcification of medial and lateral menisci, indicating that changes in the fibrocartilage matrix of the menisci caused by OA progressed similarly in the lateral and medial compartments of the knee.