Background: Rheumatoid arthritis is sometimes associated with
radiographic evidence of instability of the cervical spine, most commonly an
abnormal subluxation between vertebrae. When this instability compromises the
space that is available for the spinal cord, it may be predictive of
paralysis. However, the prevalence of radiographic signs of instability that
are predictive of paralysis among patients with nonspinal orthopaedic
manifestations of rheumatoid arthritis is unknown.
Methods: Radiographs of the cervical spine of patients with
rheumatoid arthritis who had undergone total joint arthroplasty over a
five-year period were retrospectively reviewed. The radiographs were evaluated
for predictors of paralysis (a posterior atlantodental interval of <14 mm
or a subaxial space available for the cord measuring <14 mm) and were
compared with traditional parameters of instability (an anterior atlantodental
interval of >3 mm or subaxial subluxation of >3 mm).
Results: Forty-nine of the sixty-five patients who were identified
had flexion and extension lateral radiographs available for review. Only one
of these patients had a posterior atlantodental interval of <14 mm, and
only three had a space available for the cord that measured <14 mm at one
level or more. In comparison, twenty patients had radiographic evidence of
instability on the basis of traditional parameters.
Conclusions: Although nearly one-half of the patients in the present
study had radiographic evidence of cervical instability on the basis of
traditional measurements, only four patients (8%) had a radiographic finding
that was predictive of paralysis. Thus, while radiographic evidence of
cervical instability was not infrequent in this population of patients who
underwent total joint arthroplasty for rheumatoid arthritis, radiographic
predictors of paralysis were much less common.