Predictors of paralysis in the rheumatoid cervical spine in patients undergoing total joint arthroplasty.
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.