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 Einst testing at the anterior horn, pars intermedia, and posterior horn. (Instantaneous modulus of elasticity [Einst] 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 Einst testing at the same zones, and the researchers also measured the articular cartilage-to-cartilage contact area.
Mann-Whitney U-testing revealed higher meniscal Einst values with increasing degeneration for both lateral and medial menisci, while the underlying tibial articular cartilage showed a decrease in Einst 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 Einst 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
- 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
Interesting thought, although I did note to myself earlier in my career that there are far more apparently intact lateral menisci excised during a total knee arthroplasty even in the lateral compartment of Grade III-IV changes, mostly on the distal lateral femoral condyle in bi- or tricompartmental osteoarthritis, as compared to the often torn or trimmed medial menisci.
Of course I did not send these intact lateral menici for histopathological analysis (“Where is the justification for the cost?,” I hear the hospital administrators cry) but it would be important not to assume that the process of degenerative wear and associated cartilage lining and fibrocartilage meniscus in the medial compartment would be similar to that in lateral compartment, the interaction complicated by the tibial articular shape as well as other extra-capsular consideration including the “screw-home” mechanism, adding a fifth dimension to the relationship.
Beware of lapsing back to the theories (of yesteryear) of physiology and pathogenesis based on static studies of anatomical models, which led many clinicians and researchers astray.