Predictors of aggravation of cervical spine instability in rheumatoid arthritis patients: the large joint index

Abstract

BackgroundImproved rheumatic drugs have provided significant benefits, but activities of daily living are not improved if spinal symptoms are overlooked. Furthermore, the appropriate timing for examining the cervical spine during follow-up is unclear. MethodsTo evaluate the relations of cervical spine instabilities and an index for cervical spine lesion in rheumatoid arthritis (RA) based on extremity radiographs, we examined preoperative radiographs of 100 RA patients who underwent total knee arthroplasty. Radiographic results for eight large joints (bilateral shoulders, elbows, hips, and knees) were graded as follows: Larsen grade ≥2 for each joint was scored as 1 point, which we refer to as the “large joint index” (LJI), based on 0–8 points. The associations of radiographic cervical lesions with LJI, Ranawat class, the disease duration, RA drugs, or blood analysis data were evaluated. ResultsAtlantoaxial subluxation (AAS) (≥5mm) was found in 45 patients, vertical subluxation (VS) (≤13 mm) in 42, a posterior atlantodental interval (PADI) (<14mm) in 21, and subaxial subluxation (SAS) (≥3 mm) in 23. Most patients with a PADI < 14mm (19/21, 90%) were complicated with both AAS and VS. LJI had a significant association with AAS (P < 0.0001), VS (P < 0.01), and PADI (P < 0.01). The PADI was significantly lower (P < 0.0001) and the LJI was significantly higher (P < 0.01) in patients of Ranawat class II compared to patients of Ranawat class I. The disease duration, age at surgery, and age at onset were also significantly associated with cervical instabilities. ConclusionsPADI should be recognized as a predictor of paralysis with anteroposterior instability and vertical and middle-low cervical spine instability. The LJI proposed in this study has the possibility of being a predictor of cervical lesions. Patients with RA onset at a young age and a long disease duration also have a risk of progression of cervical spine instability.