Spinal Disorders: Fundamentals of Diagnosis and Treatment Part 107. Spinal disorders are among the most common medical conditions with significant impact on health related quality of life, use of health care resources and socio-economic costs. Spinal surgery is still one of the fastest growing areas in clinical medicine. | 1064 Section Tumors and Inflammation Figure 1. Typical imaging findings a Endstage ankylosis of the sacroiliac joint SIJ . b Dense sclerosis and irregularities of the SIJ at the iliac side. Note the osseous bridges crossing the SIJ. c STIR sequence showing increased signal intensity within the SIJ at the sacral side. Joint irregularities are less visible on MRI compared to CT. d Typical syndesmophyte with calcification of the longitudinal ligament and outer anulus fibrosus. Note the preserved disc height. Ankylosing Spondylitis Chapter 38 1065 Table 2. Radiologic grading of sacroiliac joint alterations Grade I suspicious Grade II evidence of erosion and sclerosis Grade III Grade II and ankylosis Grade IV complete ankylosis New York criteria 97 However inflammatory processes in AS must be well differentiated from a septic sacroiliitis . Staphylococcus aureus Streptococcus species . Septic sacroiliitis SS is a rare disease. Typically a septic sacroiliitis shows non-specific symptoms similar to AS such as low back pain pain in the pelvic region and related pain in varying locations hip joints . Typical radiological changes of the spine indicative of AS are 20 58 bony erosions bony sclerosis syndesmophytes Andersson lesions erosive discovertebral lesions 61 ankylosis bamboo spine vertebral osteoporosis Syndesmophytes as a result of an ossification of outer anulus fibrosus Sharpey s fibers must be differentiated from osteophytes by their shape and site Fig. 1d . Syndesmophytes exhibit a slow growth from the cervical to the lumbar spine 17 leading to a kyphotic deformation of the entire spine and often resulting in a progressive sagittal imbalance. The kyphotic deformity is most pronounced in the thoracic spine. During the advanced stage of the disease vertebral column alterations can include severe kyphotic spinal deformity with sagittal imbalance spinal fractures often occult 42 57 75 atlanto-occipital instability Patients with AS are susceptible to fractures of the
