Facet joint

What it means

At each level of the spine, two small joints sit on the back side of the vertebrae, one on the left and one on the right. They link the bone above to the bone below and act as guide rails for movement — letting the spine bend forward, lean back, and rotate while keeping the levels lined up. Each one is a true joint, with cartilage on the surfaces, a lining that makes lubricating fluid, and a capsule around it. Some reports use the older name "zygapophyseal joint."

Why it appears on a CT or MRI report

Radiologists describe these joints when they show signs of wear, swelling, or thickening — often called facet arthropathy, facet hypertrophy, or facet osteoarthritis. Reports usually note the level (commonly L4–L5 and L5–S1 in the low back, or C5–C6 in the neck) and the side, and whether the wear is mild, moderate, or severe. If the joint has thickened enough to crowd a nearby nerve exit, that may also be mentioned alongside the description.

What it usually means

Wear at these joints is one of the most common findings on spine imaging from middle age onward, and the majority of people with mild facet wear feel nothing from it. Studies of pain-free adults routinely show this pattern. The joints can become a real source of pain in some people — typically a dull, one-sided low-back or neck ache that's worse leaning backward and easier leaning forward, and that can refer into the buttock, thigh, or shoulder blade. But severity on a scan correlates only loosely with how much pain a person feels. Many factors shape back and neck pain — muscle conditioning, posture, sleep, stress — and the picture of mild wear at these joints is rarely the whole story by itself. The match between symptoms and imaging is what guides treatment.

When to follow up

Mild wear without nerve involvement is usually managed with the everyday basics — regular movement, core and hip strength, posture habits, and time. Talk to your doctor if you have persistent one-sided back or neck pain that doesn't improve with simple measures, pain that radiates down a limb along a clear nerve path, numbness, tingling, or weakness. Sudden weakness, loss of bladder or bowel control, or numbness in the saddle area is a red-flag emergency.

A plain-language way to picture it

Picture a stack of dinner plates held together by two small hinges at the back of each plate. The hinges keep the plates lined up and let the stack tilt and twist, while the cushioning in front (the disc) absorbs the squeeze. After many years of use, the hinges can develop a little roughness around the edges — they still work, but they may creak now and then under load.