Osteoarthritis

Osteoarthritis is a disease of the whole joint organ rather than a wearing away of cartilage. Chondrocytes shift to a catabolic phenotype, upregulating MMP-13 against type II collagen and aggrecanases against proteoglycan, so matrix is degraded faster than it is replaced. Subchondral bone thickens and develops marrow lesions, osteophytes form at the margins, and the synovium carries low-grade inflammation. Cartilage itself is avascular and aneural, so the pain arises from bone, synovium and capsule, not from the cartilage being lost.

Structure and symptoms track each other loosely. Radiographic severity is graded on the Kellgren-Lawrence scale from zero to four using joint space narrowing and osteophytes, and population imaging studies consistently find advanced radiographic change without pain alongside severe pain with mild radiographs. There is still no approved disease-modifying osteoarthritis drug in any major jurisdiction. The clearest illustration is sprifermin, an FGF-18 analogue that produced measurable gains in cartilage thickness on MRI without a corresponding improvement in pain or function.

That gap defines what a trial has to show. A structural readout such as cartilage thickness or joint space width is a surrogate, and it needs years to move; a symptom readout moves quickly but sits against an unusually large placebo response, particularly for intra-articular injections, where the procedure itself is therapeutic in the short term.

The error worth naming is the regeneration claim. Uncontrolled injection series, whether of peptides, platelet preparations or cell products, report pain improvement over three to six months, exactly the window and magnitude an injected placebo produces. Improvement on that design is not evidence that cartilage was rebuilt.