Osteoarthritis (OA) isn’t just “wear and tear”—it’s a complex biological process that affects the entire joint, not just the cartilage. Let’s walk through what’s actually happening beneath the surface.
🦴 Step 1: Cartilage Breakdown
Your joints are lined with smooth, rubbery cartilage that allows bones to glide over one another. In OA, this cartilage starts to soften, fray, and eventually wear away. The culprit? A disruption in the balance between the cartilage-building cells (chondrocytes) and the enzymes and inflammatory molecules (like matrix metalloproteinases and cytokines) that break cartilage down. As the breakdown process accelerates, the cartilage can no longer cushion the joint properly.
⚙️ Step 2: Bone Changes
With less cartilage to absorb shock, bones begin to rub against each other. In response, the body tries to protect itself by building more bone—a process called sclerosis. Unfortunately, this leads to bony overgrowths known as osteophytes (bone spurs), which can cause pain, reduce mobility, and irritate surrounding tissues.
💧 Step 3: Synovial Inflammation
OA isn’t a purely mechanical disease. There’s also a low-grade inflammatory component. The synovium (the lining of the joint capsule) becomes inflamed and produces excess synovial fluid. While fluid normally lubricates the joint, in OA, this fluid can be rich in pro-inflammatory mediators that contribute to joint swelling, stiffness, and pain.
🧱 Step 4: Ligament and Muscle Involvement
Over time, the ligaments that stabilize your joints can loosen or thicken, leading to joint instability. Meanwhile, muscles surrounding the joint may weaken due to pain or disuse, which further reduces joint support and increases the risk of injury.
🧠 Why Does It Hurt?
Pain in OA isn’t only about the bones and cartilage. Nerve endings in the subchondral bone (just beneath the cartilage) become more exposed as cartilage thins, leading to increased sensitivity. Inflammation and chemical changes in the joint fluid can also activate pain receptors.
So, while OA often begins as a mechanical issue, it quickly becomes a full-joint condition—impacting bones, cartilage, synovium, ligaments, and muscles. Understanding this helps us design better, holistic treatment plans at the Muscle and Joint Clinic.