X-ray appears unreliable for spotting hip osteoarthritis

by Bruce Sylvester: Researchers report that in most cases hip x-rays are unreliable for diagnosing hip osteoarthritis (OA). The findings appeared on Dec. 8, 2015 in the British Medical Journal.

In this retrospective study, researchers evaluated data from the Framingham Osteoarthritis and Osteoarthritis Initiative studies, with nearly 4,500 subjects.

“The majority of older subjects with high suspicion for clinical hip osteoarthritis did not have radiographic hip osteoarthritis, suggesting that many older persons with hip osteoarthritis might be missed if diagnosticians relied on hip radiographs to determine if hip pain was due to osteoarthritis,” said author Chan Kim, MD, instructor of medicine at Boston University School of Medicine

The investigators evaluated pelvic radiographs for hip osteoarthritis from two groups, the Framingham Osteoarthritis Study (community of Framingham, Massachusetts) and the Osteoarthritis Initiative (a multicenter longitudinal cohort study of osteoarthritis in the United States). Subjects also said whether they had hip pain on most days and identified the location of the pain: anterior, groin, lateral, buttocks, or low back. In the Framingham study, subjects with hip pain were also examined for hip pain with internal rotation.

The researchers analyzed the data for agreement between radiographic hip osteoarthritis and hip pain. For subjects with hip pain suggestive of hip OA they calculated the sensitivity, specificity, positive predictive value, and negative predictive value of radiographs as a diagnostic test for hip OA .

In the Framingham study (n=946), only 15.6% of hips in subjects with frequent hip pain showed radiographic evidence of hip osteoarthritis, and 20.7% of hips with radiographic hip osteoarthritis were frequently painful.

Sensitivity of radiographic hip osteoarthritis for hip pain in the groin was 36.7%, specificity 90.5%, positive predictive value 6.0%, and negative predictive value 98.9%.

The results were similar for hip pain at other locations or for painful internal rotation.

In the Osteoarthritis Initiative study (n=4366), only 9.1% of hips in subjects with frequent pain showed radiographic hip osteoarthritis, and 23.8% of hips with radiographic hip osteoarthritis were frequently painful.

Sensitivity of definite radiographic hip osteoarthritis for hip pain in the groin was 16.5%, specificity 94.0%, positive predictive value 7.1%, and negative predictive value 97.6%.

The results were similar for hip pain at other locations.

“Hip pain was not present in many hips with radiographic osteoarthritis, and many hips with pain did not show radiographic hip osteoarthritis. Most older participants with a high suspicion for clinical hip osteoarthritis (groin or anterior pain and/or painful internal rotation) did not have radiographic hip osteoarthritis, suggesting that in many cases, hip osteoarthritis might be missed if diagnosticians relied solely on hip radiographs,” the authors concluded.

“Given these findings, patients with suspected hip OA should be treated regardless of x-ray confirmation,” Kim added.