Arthritis in the lower back is most commonly caused by the gradual breakdown of cartilage in the facet joints, the small paired joints that connect each vertebra and allow your spine to bend and twist. About 20% of adults show signs of lumbar arthritis by their mid-40s, and it becomes increasingly common after age 65. While wear and tear is the leading driver, the full picture involves genetics, body weight, occupation, and in some cases, an overactive immune system attacking the spine.
How Facet Joints Break Down
Your lumbar spine has five vertebrae, and between each pair sit two facet joints lined with smooth cartilage and enclosed in a small capsule filled with about 1 cc of lubricating fluid. These joints absorb shock and guide movement every time you bend, lift, or rotate your torso. Over decades, repeated loading wears the cartilage thinner, and the exposed bone surfaces begin to grind against each other.
The joint capsule is densely packed with sensory nerve endings. When cartilage loss triggers inflammation, those nerve endings fire, producing the deep, aching pain characteristic of lumbar arthritis. The inflammatory process involves the same chemical signals found in other forms of arthritis, which is why the pain can feel disproportionate to the amount of visible damage on an imaging scan.
Disc degeneration often accelerates the process. As the rubbery discs between your vertebrae lose height and dry out with age, more of your body weight transfers directly to the facet joints. That extra load increases friction and speeds cartilage loss, creating a cycle where disc thinning and joint arthritis worsen together.
Bone Spurs and Nerve Compression
As cartilage erodes, the body tries to stabilize the joint by growing extra bone along its edges. These bony overgrowths, called osteophytes or bone spurs, gradually enlarge the facet joints, a condition known as facet joint hypertrophy. Small bone spurs may cause no symptoms at all, but larger ones can narrow the openings where spinal nerves exit the vertebral column.
When a bone spur compresses a nerve root, it can cause radiculopathy: shooting pain, tingling, numbness, or weakness that travels down into the buttock, thigh, or leg. In rare cases, significant inward growth of bone spurs compresses the spinal cord itself, potentially causing muscle weakness in the lower body or loss of bladder and bowel control. Inflamed facet joints can also produce fluid-filled synovial cysts that press on nearby nerve roots and contribute to spinal canal narrowing.
Body Weight and Spinal Load
Carrying extra weight is one of the strongest modifiable risk factors for lower back arthritis. A large genetic analysis found that each standard increase in BMI raised the risk of low back pain by 28% and disc degeneration by 23%. These aren’t small numbers, and because the study used genetic methods to isolate the effect of weight from other lifestyle factors, the link is likely causal rather than coincidental.
The mechanics explain why. Research measuring spinal compression found that as body weight increased from roughly 110 to 260 pounds, the compressive force on the lowest lumbar segment (L5-S1) jumped by 80% to 147% when standing with no load in hand. During forward-bent lifting, that increase was still 46% to 52%. Every extra pound you carry multiplies the force your facet joints and discs absorb thousands of times a day, accelerating cartilage loss.
Occupation and Physical Demands
Certain jobs put the lumbar spine under repeated stress that outpaces its ability to repair. The primary workplace risk factors are heavy lifting, repeated manual handling of materials, prolonged awkward postures (especially bending or twisting), and whole-body vibration from driving. Long-haul truck drivers, construction workers, and warehouse employees face compounded exposure to several of these at once.
Vibration deserves special attention. Vehicle vibration tends to hit around 5 Hz, which happens to be the natural resonant frequency of the spinal disc. At that frequency, vibration energy is amplified rather than dampened, accelerating disc and joint damage over years of daily driving. This is why professional drivers show higher rates of lumbar degeneration even after accounting for other factors like lifting and posture.
Genetics and Family History
Your genes play a surprisingly large role in how quickly your lumbar spine degenerates. Studies of twins and families estimate that 34% to 61% of the variation in disc degeneration is heritable, depending on which part of the spine is measured. That means genetics can matter as much as, or more than, a lifetime of physical activity.
Researchers have identified several gene variants that influence the process. Some affect the structure of collagen and aggrecan, proteins that give cartilage its strength and springiness. Others influence how aggressively the body breaks down cartilage tissue or how intensely it produces inflammatory signals. If a parent or sibling developed significant spinal arthritis at a relatively young age, your own risk is meaningfully higher.
Inflammatory Arthritis of the Spine
Not all lower back arthritis comes from mechanical wear. In a smaller but significant number of people, the immune system attacks the spine directly. The two most common forms are ankylosing spondylitis and axial psoriatic arthritis, and they behave quite differently from the wear-and-tear type.
Ankylosing spondylitis typically begins before age 45 and carries a hallmark symptom pattern: pain and stiffness that worsen with rest and improve with movement. People often notice the worst pain in the middle of the night or after prolonged sitting, which is the opposite of mechanical arthritis, where activity tends to aggravate symptoms. A genetic marker called HLA-B27 significantly increases the risk. Over time, chronic inflammation can cause vertebrae to fuse together, producing a rigid, inflexible spine. The condition also shows up outside the back, sometimes causing eye inflammation (uveitis), skin plaques (psoriasis), or inflammatory bowel disease.
Psoriatic arthritis can also target the lower back, causing a form of spondylitis with pain and stiffness in the spine and pelvis. It tends to occur alongside skin psoriasis, though the joint symptoms sometimes appear first.
Previous Injury
A fracture, dislocation, or severe sprain in the lumbar spine can set the stage for arthritis years or even just weeks later. When an injury shifts the alignment of a vertebra or damages the cartilage surface of a facet joint, the joint no longer distributes force evenly. High-contact areas wear down faster, and the resulting inflammation can accelerate into full post-traumatic arthritis within months rather than the decades typical of age-related degeneration.
Surgical procedures on the lumbar spine can have a similar effect. Fusing two vertebrae together eliminates motion at that segment but increases the mechanical demand on the joints above and below. This “adjacent segment” stress is a recognized cause of new arthritis developing at levels that were previously healthy.
Age and How These Factors Combine
Age is the single most consistent predictor. Bone spurs in the lumbar spine appear in roughly 20% of people between 45 and 54, rising to about 30% between 55 and 64, with even higher rates after 65. But age alone doesn’t determine severity. Someone with a genetic predisposition, a physically demanding job, and excess body weight can develop significant arthritis in their 40s, while a genetically fortunate person with a healthy weight may show only mild changes in their 70s.
The causes rarely act in isolation. Disc degeneration shifts load to facet joints. Extra body weight amplifies that load. Genetic variants weaken cartilage’s ability to withstand it. Occupational strain accelerates the timeline. Understanding which factors are at play in your own back helps clarify which ones you can actually modify, particularly weight, activity patterns, and workplace ergonomics, to slow the progression.