Sacroiliac joint wear seen by chance on a scan

What the report words mean

Sacroiliac joints. The two joints between the base of the spine and the pelvis. (MedlinePlus ankylosing spondylitis)
Degenerative changes, degeneration or osteoarthritis. Wear of the joint. On CT it can begin in the 20s and tends to progress with age. (Shibata 2002)
Sclerosis or subchondral sclerosis. Denser, whiter bone next to the joint. Seen in 46% of adults without sacroiliac disease on CT. (Ziegeler 2021)
Osteophytes. Small bone spurs at the edge of the joint. Seen in 47% on the same CT study. (Ziegeler 2021)
Joint space narrowing. The gap between the bones looks thinner. Changes in the joint space were seen in 9%, and were very rare under 35. (Ziegeler 2021)
Vacuum phenomenon or gas in the joint. A small pocket of gas inside the joint. Over age 50 on CT, it was seen in 68% of people without ankylosing spondylitis. (Fakih 2023)
Fat metaplasia (on MRI). Fatty bone marrow next to the joint. In people without rheumatic disease it was seen in 51% under 45 and 94% at 75 and over. (Ziegeler 2018)
Erosions. Small notches worn into the bone surface. These were uncommon in people without rheumatic disease: 0.6% under 45 and 2.6% overall on MRI. (Ziegeler 2018)
Sacroiliitis. Inflammation of the sacroiliac joints, a feature of ankylosing spondylitis and axial spondyloarthritis. (MedlinePlus ankylosing spondylitis)(NHS ankylosing spondylitis)

How common it is by age and sex

In a CT study of 818 adults without sacroiliac disease or known back pain, with equal numbers of men and women at each age, all three signs of wear rose with age. (Ziegeler 2021)

Signs of sacroiliac joint wear on CT by age (Ziegeler 2021)
Age	Sclerosis	Bone spurs	Joint space changes
Under 25	17%	10%	1%
25 to 34	36%	15%	0%
35 to 44	52%	33%	5%
45 to 54	43%	53%	8%
55 to 64	46%	54%	9%
65 to 74	51%	71%	12%
75 and over	65%	77%	27%

In another CT study of 373 adults with no back or pelvic pain, 65% had some wear, 31% had substantial wear, and 91% of people in their 80s had wear. (Eno 2015) An earlier CT study found wear beginning in the 20s and some wear in everyone aged 50 and over. (Shibata 2002)

Women. One study found more wear in women than in men at every age, and more after a first birth. (Shibata 2002) Women more often have a joint shape that differs from the typical form (62% of women vs 14% of men), and their bone spurs were more often at the back of the joint. (Ziegeler 2021)
Men. Bone spurs were more often at the front of the joint. (Ziegeler 2021) In men, sacroiliac wear tended to go with wear in the lower spine; in women the two were largely unrelated. (Muellner 2022)

How wear differs from inflammation

Who gets inflammation. Ankylosing spondylitis usually starts before 45, with early symptoms often between 15 and 30. (MedlinePlus ankylosing spondylitis) The NHS says it usually first develops between 18 and 40, with back pain and stiffness that are worse in the morning and at night, ease with movement and may include pain around the buttocks. (NHS ankylosing spondylitis symptoms)
What CT shows over age 50. Compared with people of the same age and sex without the condition, people with ankylosing spondylitis had more joint space narrowing (91% vs 21%), erosions (31% vs 2%) and sclerosis (27% vs 13%), but less gas in the joint (24% vs 68%). In people without it, sclerosis and erosions sat mostly on the upper front part and the pelvis side of the joint. (Fakih 2023)
Wear is the more common finding. On sacroiliac MRI in people being checked for spondyloarthritis, wear was found in 67% and sacroiliitis in 45%. (Morbee 2023)

When another test or referral is suggested

Wear with no symptoms. Wear is so common in people without pain that the authors of a large CT study advise caution in blaming back or pelvic pain on it. (Eno 2015)
Signs that point to inflammation. NICE says a person whose low back pain started before 45 and has lasted longer than 3 months should be referred to a rheumatologist for a spondyloarthritis check if 4 or more further signs are present, including pain that started before 35, waking in the second half of the night, buttock pain, improvement with movement, a parent, sibling or child with spondyloarthritis, and current or past arthritis, enthesitis or psoriasis. With exactly 3, it advises an HLA-B27 blood test first. (NICE NG65) Your doctor decides.
Seeing a GP. The NHS says to see a GP for lasting symptoms of ankylosing spondylitis. (NHS ankylosing spondylitis) It also says to see a GP for back pain that does not improve after a few weeks, stops your daily activities, comes with weight loss without trying, a lump or change in the shape of your back, or is worse at night or after resting. It says to call 999 or go to A&E for back pain with pain, tingling, weakness or numbness in both legs, loss of feeling around the genitals or anus, or changes in bladder or bowel control. (NHS back pain)
Worry is real. See after an abnormal screening result.

How this differs from screening

A scan done for something else is not a screening test for arthritis or for ankylosing spondylitis. Our screenings by age and gender chart lists the checks with screening advice for each age.

Other things a scan may show

The same scan may mention other findings, each with its own page: disc bulge or wear, Schmorl nodes, a Tarlov cyst, a spine hemangioma, pelvic vein stones and low bone density. Wear in other joints has its own page: hip or knee joint wear.

Who it applies to

Adults told that a pelvic or spine X-ray, CT or MRI, done for something else, shows wear of the sacroiliac joints. People who are pregnant or recently gave birth, people with a known rheumatic condition, psoriasis, inflammatory bowel disease or eye inflammation, people scanned after an injury, and a scan done because of back pain are outside this page.

Routine age-based screening

A finding on a scan does not replace the routine screenings for your age. See screenings by age and gender.

Where they differ:

What counts as sacroiliitis on MRI. In one study, 23% of healthy volunteers with no current or past back pain met the international MRI definition of sacroiliitis, though deep bone marrow swelling was not seen in them. (de Winter 2018) Another MRI study found erosions in under 3% of people without rheumatic disease. (Ziegeler 2018)
Women and men. An older CT study found more wear in women at every age. (Shibata 2002) A newer CT study with equal numbers of men and women found the main difference was where the changes sat and the shape of the joint. (Ziegeler 2021)
How common it is. Studies report different rates because they used different scans, readers and definitions: some wear in about 65% of adults on one CT study, sclerosis in 46% and bone spurs in 47% on another, and sclerosis in 14% and bone spurs in 37% on MRI. (Eno 2015)(Ziegeler 2021)(Ziegeler 2018)

Your doctor decides what your result means for you.

Questions people ask

What does sacroiliac joint wear mean?

It means the scan shows age-related changes in the joints where the base of the spine meets the pelvis, such as denser bone by the joint, small bone spurs or a narrower joint space. On CT these changes were found in about two in three adults with no back or pelvic pain. (Eno 2015) (Ziegeler 2021)

Is sacroiliac joint wear normal with age?

It is very common and rises with age. One CT study found it in 91% of adults in their 80s, and another found some wear in everyone aged 50 and over. (Eno 2015) (Shibata 2002)

Is sacroiliac joint wear the same as sacroiliitis?

No. Sacroiliitis means inflammation of the joint, a feature of ankylosing spondylitis, which usually starts before age 45. Over age 50 on CT, erosions were seen in 31% of people with ankylosing spondylitis but in 2% of people without it, while gas in the joint was more common without it. (MedlinePlus ankylosing spondylitis) (Fakih 2023)

Does wear on the scan explain my back pain?

Not by itself. Because wear is so common in people with no pain, the authors of a large CT study advise caution in blaming back or pelvic pain on it. Your doctor decides what your result means for you. (Eno 2015)

When should I see a doctor?

The NHS says to see a GP for back pain that does not improve after a few weeks, is worse at night or after resting, comes with weight loss without trying, or stops you doing daily activities, and to see a GP for lasting symptoms of ankylosing spondylitis. (NHS back pain) (NHS ankylosing spondylitis)