Hilke Lemke, Sina Stuecker, Andrea Schwab, Agnieszka Halm-Pozniak, Jannik Jahn, Christoph H Lohmann, Jessica Bertrand
Affiliation(s):
University Orthopaedic Clinic, Otto-von-Guericke University Magdeburg, Medical Faculty, Magdeburg, Germany
Introduction: The meniscus, a fibrocartilage tissue, plays an important role in shock absorption, stability and compensation for incongruities in the articular cartilage surface of the human knee. There is a loss of these functions during the progression of osteoarthritis (OA), suggesting that the meniscus is affected by this common joint disease. Only a few studies have focused on OA related changes of the menisci. As calcification of articular cartilage has been associated with its degeneration, a close correlation between calcification and meniscus degeneration is likely. Two calcium crystal types have been described for articular cartilage; basic calciumphosphate (BCP) and calciumpyrophosphate (CPP).
The aim of this study was to detect the calcified area and calcification type and its possible correlation with the degradation grade and OA severity.
Methods: The human menisci characterized in this study were taken from osteoarthritis patients during total knee endoprosthesis surgery (n=93 patients). X-ray images of the knee were used to determine the radiological OA severity by Kellgren-Lawrence-Score (KL Score, 0-4). Medial and lateral menisci were fixed in formalin, paraffin embedded and sectioned. Von Kossa staining was used to identify the calcified area of the menisci. The calcified area relative to the total area of the menisci was quantified using image analysis (ImageJ). The Pauli score (G1-G4) was used to determine the meniscal degeneration. This score evaluates the collagen organization (Picrosirius-Red staining), proteoglycan matrix stain and surface integrity (Safranin-Orange staining) and cellularity (Hematoxylin-Eosin staining). The type of calciumphosphate crystals was identified on deparaffinized sections using Raman spectroscopy (laser: 785 nm).
Results: Von Kossa staining revealed a meniscal calcification in 100% of the samples. The von Kossa positive stained area in medial and lateral menisci was similar (p=0.739, n=80 patients). The von Kossa positive area in menisci of patients scored with KL Score 4 was not significantly larger than in menisci of patients scored with KL Score 3 (p=0.285, n=63). We then investigated the type of the calciumphosphate crystals. The most frequent crystal type found in medial menisci was BCP (73.91%, n=92). CPP was found in 14.13% and both crystal types in 11.96% of the medial menisci. Medial menisci containing CPP crystals showed a larger calcified area compared to menisci with only BCP crystals (p<0.001). BCP crystals were mainly found on the surface while CPP crystals were mainly located deeper within the menisci. Medial menisci showed moderate to severe degeneration (Pauli score G3=60.53%, G4= 39.47%, n=38). A significant larger calcified area was found in severely degenerated menisci (G4) compared to moderately degenerated menisci (G3) (p=0.007).
Conclusion: BCP-based calcification of menisci of OA patients is a common phenomenon. We showed that a higher grade of meniscal degeneration is accompanied by an increased calcified area, but the total joint OA grade did not associate with the calcification grade.