Meniscus tears accelerate joint space loss and lateral meniscal extrusion increases risk of knee arthroplasty in middle-aged adults.

We sought to use publicly available data from the Osteoarthritis Initiative (OAI), a multicenter prospective cohort study, to determine the rate of joint space loss and likelihood of knee arthroplasty due to magnetic resonance imaging (MRI)-diagnosed meniscal tears or meniscal extrusion in middle-aged adults with no to mild knee osteoarthritis. Participants (n = 2199; mean age, 60.2 years) with Kellgren-Lawrence osteoarthritis grades 2 (mild) (48.7%) or 0 to 1 (none) (51.3%) underwent knee MRIs at enrollment and were followed radiographically for 8 years and for total knee arthroplasty (TKA) for 9 years. Rate of joint space loss and risk of arthroplasty due to meniscal tears and/or extrusion were determined by multivariate modeling. Prevalence of baseline medial meniscus tears was 21.3% and lateral tears was 12.8%; 26.9% had medial meniscal extrusion (79.6%, <2 mm; 20.4%, +2 mm) and 5.4% had lateral extrusion (75.9%, <2 mm; 24.1%, +2 mm). Median medial joint space loss was 0.06 mm/y and lateral was 0.05 mm/y. Medial tears regardless of extrusion were associated with accelerated medial joint space loss (additional mean, 0.05 mm/y; P = .001). Lateral tears were associated with accelerated lateral joint space loss (additional 0.09 mm/y; P < .001) as was lateral extrusion (additional 0.10 mm/y; P < .001). The yearly incidence of knee arthroplasty was 0.5% without lateral extrusion, 1.5% with extrusion less than 2.0 mm, and 3.7% with extrusion greater than or equal to 2.0 mm. Both medial and lateral tears accelerate joint space loss in middle-aged adults. Lateral meniscal extrusion further accelerates joint space loss and increases risk of progression to TKA within 9 years.