has part has part characteristic of part of has modifier Abnormal joint morphology Abnormal ilium morphology Abnormal sacrum morphology Abnormal sacroiliac joint morphology The sacroiliac joint (SIJ) is a true diarthrodial joint: matching articular surfaces separated by a joint space containing synovial fluid and enveloped by a fibrous capsule. It does, however, have unique characteristics not typically found in other diarthrodial joints. The SIJ has fibrocartilage in addition to hyaline cartilage. There is discontinuity of the posterior capsule. Rather than being smooth, the articular surfaces have many ridges and depressions that minimize movement and enhance stability. Primary stability, however, is attributed to the many adjacent ligaments. quality abnormal sacro-iliac joint