Related Experiment Video
Updated: Jan 26, 2026

Author Spotlight: Evaluating Traditional Chinese Therapy for Ankylosing Spondylitis in Mice
Published on: October 27, 2023
Progressive sacroiliitis due to accessory sacroiliac joint mimicking ankylosing spondylitis: A case report
Ran Song1, Soyun Lee, Sang-Hoon Lee
1Department of Rheumatology, Kyung Hee University Hospital at Gangdong, School of Medicine, Kyung Hee University, Seoul, Korea.
Rationale:
An accessory sacroiliac (SI) joint usually has little clinical significance. However, severe arthritic changes can cause chronic buttock or low back pain and can be misdiagnosed as another disease presenting with sacroiliitis such as ankylosing spondylitis (AS).
Patient Concerns:
A 33-year-old woman was diagnosed with AS due to chronic buttock pain and progressive sacroiliitis on plain X-ray and magnetic resonance imaging (MRI). Her buttock and low back pain gradually worsened despite proper treatment for AS.
Diagnosis:
Computed tomography revealed an accessory SI joint with arthritic changes.
Interventions:
Nonsteroidal anti-inflammatory drugs (NSAIDs) and restricted movement were prescribed.
Outcomes:
The symptoms were controlled with NSAIDs, rest, and restriction of excessive movement. The medication could be stopped after the pain subsided.
Lessons:
An accessory SI joint can be a cause of chronic back pain and can be misdiagnosed as AS with sacroiliitis when progressive arthritic changes are observed. Therefore, additional imaging studies other than conventional X-ray or MRI may be required for accurate diagnosis.
More Related Videos
Related Concept Videos
Accessory Organs
Structural Joints: Synovial Joints
Structural Joints: Fibrous Joints
Suture
All the bones of the skull, except for the mandible, are joined to each other by a fibrous joint called a suture. The fibrous connective tissue found at a suture strongly unites the adjacent skull bones and thus helps to protect the brain and form the face. In...
Structural Joints: Cartilaginous Joints
There are two types of cartilaginous joints:
Synchondrosis
A synchondrosis ("joined by cartilage") is a cartilaginous joint where bones are connected by hyaline cartilage. Synchondrosis may be temporary...
Joints
Structural joint classifications are based on the material that makes up the joint as well as whether or not the joint contains a space between the bones. Joints are structurally classified as fibrous, cartilaginous, or synovial.
Fibrous Joints Are Immovable
The bones of a...
Cytoskeletal Accessory Proteins

