The six musculoskeletal disorders most commonly referenced in medical education and public health are osteoarthritis, rheumatoid arthritis, osteoporosis, low back pain, gout, and sarcopenia. Together, musculoskeletal conditions affected more than 1.63 billion people worldwide in 2020 and rank as the second-highest cause of non-fatal disability globally. Each disorder targets a different part of the musculoskeletal system, from joint cartilage to bone density to muscle mass, and understanding the differences helps explain why they feel and behave so differently.
Osteoarthritis
Osteoarthritis is the most common joint disease and a leading cause of impaired mobility in older adults. It develops when the protective cartilage cushioning the ends of your bones gradually breaks down. Cartilage is made of a dense network of proteins and water-attracting molecules called proteoglycans. As those molecules degrade, the collagen structure holding the cartilage together follows, and the smooth surface that once allowed bones to glide against each other becomes rough, thin, and eventually worn away entirely.
The joints most often affected are the knees, hips, hands, and spine. You might notice stiffness after sitting for a while, pain that worsens with activity, or a grating sensation during movement. Unlike some other musculoskeletal conditions, osteoarthritis is not driven by the immune system. It is primarily a wear-and-repair imbalance: the cartilage cells themselves begin producing more of the enzymes that break tissue down, creating a cycle that accelerates damage over time. Risk increases with age, excess body weight, previous joint injuries, and repetitive occupational stress.
Rheumatoid Arthritis
Rheumatoid arthritis looks similar to osteoarthritis on the surface, with swollen, painful joints, but the underlying process is fundamentally different. It is an autoimmune disease in which the body’s immune system attacks the synovium, the thin membrane lining the inside of joints. Immune cells flood into the synovial tissue and fluid, causing chronic inflammation that gradually damages cartilage, ligaments, and tendons.
The inflammation typically starts in smaller joints like the fingers and wrists and tends to affect both sides of the body symmetrically. Over time it can spread to larger joints and even damage organs outside the musculoskeletal system. Doctors confirm the diagnosis partly through blood markers: rheumatoid factor and antibodies against modified proteins called citrullinated peptides. The presence of these antibodies, particularly at high levels, is a hallmark of the disease and helps distinguish it from other forms of arthritis. Biologic therapies that target specific immune signaling molecules have significantly improved outcomes over the past two decades, and newer approaches using platelet-rich plasma and even RNA-based treatments are being studied to promote tissue repair and control inflammation more precisely.
Osteoporosis
Osteoporosis is a bone disorder in which the internal structure of bones becomes porous and fragile, making fractures far more likely from minor falls or even routine activities like bending. It develops silently over years, which is why it’s often called a “silent disease.” Most people don’t know they have it until a bone breaks.
Diagnosis relies on a bone density scan, typically of the hip and spine, which produces a number called a T-score. A T-score of negative 1 or higher is considered healthy. Between negative 1 and negative 2.5 indicates osteopenia, a milder form of bone loss that serves as an early warning. A T-score of negative 2.5 or lower points to osteoporosis. The most dangerous fractures occur in the hip and spine, where weakened bone can collapse under normal body weight. Women after menopause face the highest risk due to a sharp drop in estrogen, which normally helps maintain bone density. Low calcium intake, vitamin D deficiency, smoking, physical inactivity, and long-term use of certain medications also contribute.
Low Back and Neck Pain
Low back pain affected 619 million people globally in 2020, and that number is projected to reach 843 million by 2050 as populations age and grow. Most people will experience at least one episode during their lifetime, making it one of the most universally shared musculoskeletal complaints. It is also a major cause of lost workdays and reduced quality of life worldwide.
About 90% of low back pain cases are classified as “non-specific,” meaning no single structural cause like a herniated disc or fracture can be identified. Instead, the pain arises from a combination of factors: muscle tension, ligament strain, poor posture, low physical activity, obesity, smoking, and high physical demands at work. The remaining 10% of cases are tied to identifiable causes such as spinal fractures, disc problems, cancer, or pain referred from other organs like the kidneys. Neck pain follows similar patterns and shares many of the same risk factors. Cervical pain is especially common among women and workers who perform repetitive tasks. For most people, staying physically active, maintaining a healthy weight, and taking regular breaks from prolonged sitting or repetitive postures are the most effective strategies for prevention and management.
Gout
Gout is an inflammatory arthritis caused by the buildup of uric acid crystals inside joints. Your body produces uric acid when it breaks down certain compounds found in foods like red meat, shellfish, and alcohol. When uric acid levels in the blood rise high enough, needle-shaped crystals form and deposit in joint tissue, triggering sudden, intense episodes of pain, swelling, and redness.
The base of the big toe is the classic location, though gout can strike ankles, knees, wrists, and fingers as well. Research using ultrasound imaging has shown that crystal deposits can begin forming at blood uric acid levels as low as 5 mg/dL, well below the traditional threshold doctors used to consider dangerous. Among people with levels between 5 and 6 mg/dL, about 24% already had detectable crystal deposits even without symptoms. At levels of 9 mg/dL or higher, half had deposits. This means damage can be quietly accumulating long before a first painful flare. Keeping uric acid levels low through dietary changes, hydration, and medication when needed is the cornerstone of long-term gout management. Without treatment, flares tend to become more frequent and can eventually cause permanent joint damage.
Sarcopenia
Sarcopenia is the progressive loss of skeletal muscle mass and function that accompanies aging. Unlike the other five disorders on this list, which target joints or bones, sarcopenia strikes the muscles themselves, and its consequences ripple outward: frailty, falls, fractures, loss of independence, and higher rates of hospitalization and death.
Diagnosis involves three measurable components: muscle strength, muscle quantity or quality, and physical performance. International expert groups have established a grading system. Probable sarcopenia is identified when muscle strength alone is low. Confirmed sarcopenia adds low muscle mass or quality to that picture. Severe sarcopenia is diagnosed when all three criteria, low strength, low mass, and poor physical performance, are present together. Grip strength and walking speed are common screening tools. The condition typically becomes noticeable after age 60, though muscle loss actually begins in your 30s and 40s at a rate of roughly 3 to 8% per decade. Resistance exercise and adequate protein intake are the most effective countermeasures, and starting early makes a meaningful difference in how much muscle you retain later in life.
Workplace and Lifestyle Risk Factors
Many musculoskeletal disorders share overlapping risk factors rooted in how you move, or don’t move, during daily life. In occupational settings, the three biggest ergonomic risks are awkward postures, repetitive movements, and continuous use of excessive force. Workers who spend hours in fixed positions or perform the same motions repeatedly are especially vulnerable to conditions like carpal tunnel syndrome, rotator cuff injuries, tendon inflammation, and chronic neck pain.
Carpal tunnel syndrome is a particularly common workplace injury. It occurs when the median nerve running through the wrist gets compressed by inflamed tendons, often due to sustained wrist flexion during tasks like typing or assembly work. Beyond the workplace, physical inactivity is a shared thread across nearly all six disorders. It accelerates cartilage loss in osteoarthritis, weakens bones in osteoporosis, contributes to back pain, and drives muscle wasting in sarcopenia. Regular movement, even moderate walking and bodyweight exercises, provides protection across the entire musculoskeletal system in a way that no single treatment can match.