C hronic back pain is common worldwide and is cared for by a variety of providers, but specific, satisfactory treatment is often lacking. Ankylosing spondylitis, an inflammatory disorder that in its extreme form can lead to the bony fusion of vertebral joints, is an uncommon but well-established cause of chronic back pain. During the past decade, ankylosing spondylitis has come to be considered as a subset of the broader and more prevalent diagnostic entity referred to as axial spondyloarthritis. The estimated prevalence of axial spondyloarthritis in the United States is 0.9 to 1.4% of the adult population, similar to that of rheumatoid arthritis. 1 Axial spondyloarthritis is generally diagnosed and treated by rheumatologists, and there is specific treatment for it. However, prolonged delay in reaching the diagnosis is common and is usually the result of the failure of recognition by nonrheumatologists. 2 This review is intended to enhance awareness and understanding of axial spondyloarthritis and ankylosing spondylitis -and the relationship between the two -in order to facilitate prompt and accurate diagnosis and proper treatment. Recent advances in our understanding and treatment of these conditions are discussed.Concep t ua l His t or y a nd Cl a ssific ation

When possible, direct repair remains the current standard of care for the repair of peripheral nerve lacerations. In large nerve gaps, in which direct repair is not possible, grafting remains the most viable option. Nerve scaffolds include autologous conduits, artificial nonbioabsorbable conduits, and bioabsorbable conduits and are options for repair of digital nerve gaps that are <3 cm in length. Experimental studies suggest that the use of allografts may be an option for repairing larger sensory nerve gaps without associated donor-site morbidity.

MRN has come a long way in the past 2 decades. Excellent depiction of 3D nerve anatomy and pathology is currently possible. Further technical developments in diffusion-based nerve and muscle imaging, whole-body MRN, and nerve-specific MR contrast agents will likely play a major role in advancing this novel field and understanding peripheral neuromuscular diseases in the years to come.

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Normative diffusion values for MR neurography of the median nerve with DTI depend on the anatomic location and age but not on sex. Age-specific FA and ADC threshold values might be used to diagnose carpal tunnel syndrome.