Diagnostic validity of space available for the spinal cord at C1 level for cervical myelopathy in patients with rheumatoid arthritis.
METHODS
Retrospective cohort study.


OBJECTIVE
To evaluate diagnostic validity of space available for the spinal cord (SAC) at C1 level for myelopathy in patients with rheumatoid arthritis (RA).


BACKGROUND
The relationship of SAC at C1 level with myelopathy has been evaluated by relatively small number of the patients, and 2 criteria have been proposed.


METHODS
Two cohorts of the patients with RA were established. Group A consisted of 140 patients with myeopathy due to upper cervical involvement selected from the database. Group B consisted of 99 patients with upper cervical subluxation, but not associated with myelopathy selected from the consecutive series of the hospitalized patients. Distributions of SAC at C1 level in both groups were evaluated. Efficacy indexes for screening (sensitivity, specificity, etc.) were calculated for these patients' population by previously demonstrated 2 criteria. In addition, analysis according to receiver operating characteristic (ROC) curve was performed.


RESULTS
The average values of SAC were 11.1 mm in Group A and 16.5 mm in Group B. When cut-off point for myelopathy was defined as 13 mm or less, sensitivity and specificity were 82% and 85%, respectively. When it was defined as 14 mm or less, sensitivity increased (88%) while specificity decreased (74%). Accuracies by these 2 criteria were almost the same (83%, 82%). The left upper corner point of ROC curve was located between these 2 cut-off points.


CONCLUSIONS
Distributions of SAC showed that SAC was a reliable parameter for relating myelopathy in patients with upper cervical subluxation in RA. The plots according to ROC curve showed adequacy of previously demonstrated 2 cut-off points. For the purpose to screen the patients with high risk for myelopathy, 14 mm or less was recommended as a cut-off point of SAC.
Oda
Takenori
T
Department of Orthopedic Surgery, Osaka Rosai Hospital, Sakai, Japan. odat@orh.go.jp
Yonenobu
Kazuo
K
Fujimura
Yoshikazu
Y
Ishii
Yushin
Y
Nakahara
Shinnosuke
S
Matsunaga
Shunji
S
Shimizu
Takachika
T
Matsumoto
Morio
M
D001172:Arthritis, Rheumatoid / Q000150:complications*; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging / Q000473:pathology*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011859:Radiography; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013116:Spinal Cord / Q000000981:diagnostic imaging / Q000473:pathology*; D013118:Spinal Cord Diseases / Q000150:complications / Q000175:diagnosis*