Osteoarthritis develops when the cartilage cushioning your joints breaks down faster than your body can repair it. This isn’t a single event but a gradual process driven by a combination of mechanical wear, inflammation, genetics, and metabolic factors. Understanding what triggers that imbalance helps explain why some people develop it and others don’t.
What Happens Inside the Joint
Healthy cartilage is constantly rebuilding itself. Your body breaks down small amounts of old cartilage and replaces it with new material in a balanced cycle. The cells responsible for this maintenance, called chondrocytes, are the only living cells inside your cartilage, and they manage both the breakdown and the repair.
In osteoarthritis, that balance tips. The enzymes that break down cartilage become overproduced, overwhelming your body’s natural inhibitors. At the same time, an inflammatory signaling molecule ramps up production of those destructive enzymes while simultaneously suppressing the creation of new cartilage material. This creates a two-pronged problem: more destruction and less repair happening at the same time. The inflammatory molecule also triggers cell death within the cartilage itself, further reducing the tissue’s ability to recover. Once this cycle gains momentum, it tends to accelerate. Some of these destructive enzymes can activate their own inactive precursors, creating a feedback loop that makes the degradation self-reinforcing.
The result is a progressive loss of the two main structural components of cartilage: collagen fibers that give it tensile strength and proteoglycans that give it the ability to absorb compression. As these are stripped away, the cartilage thins, roughens, and eventually exposes the underlying bone.
Mechanical Stress and Joint Overload
Your joints are built to handle a certain range of force. Normal, moderate loading actually helps maintain cartilage health by stimulating those chondrocyte repair processes. But when loading becomes excessive, prolonged, or abnormal, it flips the switch toward destruction.
High-intensity mechanical stress causes chondrocytes to shift from maintenance mode into a breakdown-heavy state. Under sustained overloading, joints flood with inflammatory molecules while anti-inflammatory signals drop. The cartilage cells contain pressure-sensing channels that detect mechanical force and translate it into chemical signals. When the force is too high or too frequent, these channels trigger inflammatory pathways that accelerate cartilage loss.
This is why joint alignment matters so much. A knee that bows inward or outward concentrates force on one side of the joint, wearing that area down disproportionately. Previous fractures that healed with even slight misalignment can redirect mechanical loads in ways that slowly destroy cartilage over years. Prolonged disuse is also harmful. Joints that aren’t loaded at all lose the stimulus they need to maintain healthy cartilage.
Joint Injuries and Post-Traumatic Arthritis
A significant joint injury is one of the strongest predictors of osteoarthritis later in life. Torn ligaments, meniscus tears, and fractures that extend into the joint surface all raise risk substantially, even after surgical repair. Among patients who had ACL reconstruction surgery, 37% showed radiographic signs of osteoarthritis in the repaired knee within 10 years. These were young, active patients, not people who would typically be developing age-related arthritis.
The injury itself does direct damage to cartilage, but the bigger issue is what follows. A major joint injury changes the biomechanics of the joint permanently. Subtle shifts in how the joint tracks, how force distributes across the surface, and how stable the joint feels during movement all contribute to accelerated wear. The initial inflammatory response from the injury can also linger at low levels, keeping those destructive enzymes more active than they should be for months or years afterward.
How Obesity Drives Joint Damage
Excess weight contributes to osteoarthritis in two distinct ways. The obvious one is mechanical: every extra pound of body weight adds roughly four pounds of force across your knees with each step. But if weight were the only issue, obesity would only cause arthritis in weight-bearing joints like hips and knees. It doesn’t. Obesity doubles the lifetime risk of symptomatic osteoarthritis compared to people with a BMI under 25, and it increases the risk in non-weight-bearing joints like the hands.
That’s because fat tissue is metabolically active. It releases signaling molecules called adipokines that regulate inflammation throughout the body. In people carrying excess fat, these molecules shift the immune system toward a state of chronic, low-grade inflammation. Higher levels of inflammatory proteins circulate in the blood, reaching joints throughout the body. There’s also evidence that obesity-related changes in gut bacteria allow bacterial compounds to leak into the bloodstream, further sensitizing the immune system and feeding systemic inflammation that reaches the joint lining.
Genetics and Inherited Risk
Osteoarthritis runs in families, though what you inherit is increased susceptibility rather than a guarantee. The genes involved are typically related to the formation and maintenance of bone and cartilage. Researchers have identified several specific genes linked to osteoarthritis risk, including ones involved in cartilage collagen production, bone development, and joint signaling.
No single gene causes osteoarthritis on its own. Instead, multiple small genetic variations combine to raise your overall risk. This means there’s no simple genetic test that predicts whether you’ll develop the condition. But if your parents or siblings have osteoarthritis, particularly if it appeared at a relatively young age or in multiple joints, your baseline risk is higher than average. That inherited risk interacts with everything else on this list: someone with a strong genetic predisposition who also carries excess weight and works a physically demanding job faces a compounding of risk factors.
Occupational and Activity-Related Risk
What you do for a living matters. A large meta-analysis combining 71 studies found that physically demanding jobs increase knee osteoarthritis risk by about 52% compared to sedentary occupations. The specific movements that drive this risk include heavy lifting, frequent kneeling, climbing, squatting, and prolonged standing.
Agriculture workers, construction workers, floor layers, carpenters, metal workers, cleaners, and service workers all face elevated risk. The common thread is repetitive loading in positions that concentrate force on particular joint surfaces. A farmer who spends decades kneeling and squatting subjects the knee cartilage to repeated high-pressure contact in positions the joint tolerates poorly over time. The damage accumulates gradually, often without noticeable symptoms until the cartilage has thinned significantly.
Recreational activities can play a similar role. Elite athletes in high-impact sports develop osteoarthritis at higher rates than the general population, particularly in joints specific to their sport. But moderate, varied exercise is protective rather than harmful. The dose matters enormously.
Age, Sex, and Other Contributing Factors
Age is the single strongest risk factor. Cartilage naturally loses some of its resilience over decades, and the chondrocytes responsible for repair become less effective with time. This doesn’t mean osteoarthritis is inevitable with aging. It means the margin for error shrinks. A joint that could tolerate moderate overloading at age 30 may not handle the same stress at 60.
Women develop osteoarthritis more frequently than men, particularly after menopause. The hormonal shift appears to influence cartilage metabolism and inflammatory regulation, though the exact mechanisms are still being worked out. Women also tend to have differences in joint alignment, particularly at the knee, that may contribute to different loading patterns.
Certain metabolic conditions raise risk independently. Diabetes and hemochromatosis (a condition causing iron buildup) are both associated with higher osteoarthritis rates. Some people are also born with subtle joint malformations or cartilage defects that predispose specific joints to earlier breakdown. Hip dysplasia, where the hip socket is too shallow, is a classic example: the abnormal shape concentrates force on a smaller area of cartilage, accelerating wear.
How These Factors Work Together
Osteoarthritis rarely has a single cause. In most people, it results from several risk factors converging over time. Someone might inherit cartilage that’s slightly less resilient, gain weight in their 40s that adds both mechanical load and systemic inflammation, and work a job that involves repetitive kneeling. None of those factors alone would necessarily cause osteoarthritis, but together they overwhelm the joint’s ability to maintain itself.
This is why the condition appears so variable. One person develops severe knee arthritis by 50 while another has minimal joint problems at 75. The difference usually comes down to which combination of genetic, mechanical, metabolic, and injury-related factors that person accumulated over their lifetime, and how much repair capacity their cartilage retained along the way.