Knee OA: Does It Start with Stiff Menisci or Soft Cartilage?

This post comes from Fred Nelson, MD, an orthopaedic surgeon in the Department of Orthopedics at Henry Ford Hospital and a clinical associate professor at Wayne State Medical School. Some of Dr. Nelson’s tips go out weekly to more than 3,000 members of the Orthopaedic Research Society (ORS), and all are distributed to more than 30 orthopaedic residency programs. Those not sent to the ORS are periodically reposted in OrthoBuzz with the permission of Dr. Nelson.

As an orthopaedic surgeon, I often noticed the rigidity of the meniscus as I excised it during a total knee replacement. Focused on the job at hand, however, I never closely considered the involvement of menisci in degenerative joint disease. But German researchers recently hypothesized that early biomechanical changes in meniscal tissue occur before articular cartilage changes in knee osteoarthritis.¹

To test their hypothesis, they dissected 12 cadaver knees with Kellgren-Lawrence (KL) scores between 1 and 2 and 12 knees with KL scores between 3 and 4. The menisci were carefully embedded in a cast of polymethylmethacrylate using bony attachments to hold the specimens for E_inst testing at the anterior horn, pars intermedia, and posterior horn. (Instantaneous modulus of elasticity [E_inst] is the measure of the initial response of a viscoelastic material to an initial load before long-term deformity occurs.)  The exposed tibial surface was then cut 10 mm below the joint for E_inst testing at the same zones, and the researchers also measured the articular cartilage-to-cartilage contact area.

Mann-Whitney U-testing revealed higher meniscal E_inst values with increasing degeneration for both lateral and medial menisci, while the underlying tibial articular cartilage showed a decrease in E_inst in the medial compartment. These findings suggest that knee joint degeneration might very well begin with a stiffening of the menisci, followed by articular cartilage softening.

The wide variation in E_inst values uncovered in this study leaves open the possibility there is more than one pathway by which the biochemical response to meniscal cytokine expression would lead to subsequent articular cartilage breakdown. Nevertheless, the authors suggest that their findings might prompt the treatment and diagnostic paradigms of knee osteoarthritis to change, “focusing on the degeneration detection of the menisci instead of the articular cartilage.”

Reference 

1. Seitz AM, Osthaus F, Ignatius A, Dürselen L. Degeneration alters first the biomechanical properties of human menisci before affecting the tibial cartilage. ORS 2020 Annual Meeting Paper No.0687