This 40-year-old female presented with headaches and neck pain. She had been previously diagnosed with psoriatic arthritis.
The neutral lateral radiograph demonstrated an atlantodental interspace (ADI) width of 5 mm (Figure A).
Let’s review some of the etiologies for increased ADI:
First and foremost, make sure that the film was taken at a 72 inch FFD; if taken at 40 inches, the ADI, like everything else on the film, will naturally be magnified, and the accepted 3 mm normal limit cannot apply. That said, a variety of disorders may alter the interspace.
Of course, degenerative joint disease would contribute to a decreased space. The more frequent causes of a widened space include trauma, occipitalization, Down’s syndrome, certain pharyngeal infections, and the various inflammatory arthropathies such as ankylosing spondylitis, rheumatoid arthritis, psoriatic arthritis and Reiter’s syndrome. Flexion/extension views are indicated when a widened space is noted on the neutral lateral film, in order to evaluate any upper cervical complex instability. MRI examination will clearly demonstrate transverse ligament status and integrity.•