Traumatic and Degenerative Meniscus Tears Have Different Gene Expression Signatures

Background: Meniscus tears are classified as traumatic or degenerative based on the tear pattern. There is little evidence demonstrating biological differences between the 2 tear types. Hypothesis: Gene expression signatures in the injured meniscus are different between traumatic (vertical) and degenerative (complex, horizontal, or flap) tears. Study Design: Controlled laboratory study. Methods: Samples of the torn meniscus from the white-white zone were removed at the time of clinically indicated partial meniscectomy from 48 patients (37 with degenerative tears and 11 with traumatic tears). mRNA expression in the injured menisci was measured by quantitative real-time polymerase chain reaction for selected molecular markers of osteoarthritis, inflammation, and cartilage homeostasis (eg, cytokines/chemokines, aggrecanases/metalloproteinases, transcription factors, cartilage matrix genes, and adipokines). The tear pattern (traumatic or degenerative) and location (medial or lateral) were recorded for each patient. Gene expression differences between degenerative and traumatic tears were computed after adjusting for patients' age, sex, and body mass index and for location of the resected meniscus (medial/lateral). Results: Gene expression in meniscus tears varied by pattern. Chemokines (IL8 [P <.001] and CXCL6 [P <.001]) and matrix metalloproteinases (MMP1 [P =.011] and MMP3 [P =.016]) were expressed at a significantly higher level in traumatic tears compared with degenerative tears. In contrast, COL1A1 was expressed at a lower level in traumatic tears compared with degenerative tears (P =.058). None of the genes tested demonstrated significant differences between medial and lateral meniscus tears. Conclusion: Traumatic meniscus tears overall exhibited a higher inflammatory/catabolic response as evidenced by higher levels of chemokine and matrix metalloproteinase expression than degenerative tears. These findings suggest that there is a (molecular) biological distinction between traumatic and degenerative tears. Clinical Relevance: The catabolic/inflammatory differences between traumatic and degenerative tears may be relevant to treatment decisions regarding the meniscus as well as advance our understanding of how meniscus tears relate to the development of knee osteoarthritis.