Osteomyelitis on MR imaging as a key predictor of recurrent septic arthritis of the shoulder.

Objectives: To investigate the clinical and radiologic predictors of postoperative recurrent septic arthritis of the shoulder (SAS) using multivariable analysis.

Methods: Forty-three patients (mean age, 65 years; 24 women) who underwent surgery for SAS between January 2011 and October 2019 were retrospectively enrolled. An orthopedic surgeon assessed clinical (age, sex, comorbidity, duration from symptom onset to MR imaging and surgery, surgical method, antibiotic usage), laboratory (serum white blood cell [WBC] count, C-reactive protein [CRP] level, synovial cell count), and surgical findings (culture/biopsy results). Two musculoskeletal radiologists evaluated MR imaging findings (bone marrow [reactive bone marrow edema, osteomyelitis, osteochondral erosion] and soft tissue [synovitis, bursitis, muscle edema, abscess] abnormalities). Recurrent SAS was evaluated at ≥ 12 months postoperatively. Univariable and multivariable analyses were performed to determine the best predictor of recurrent SAS.

Results: The overall recurrent SAS rate was 33% (14/43). On univariable analysis, mean age (without recurrence vs. recurrence: 68 vs. 59 years, p = .04), mean duration from symptom onset to surgery (18 vs. 25 days, p = .02), serum WBC count (12,000 vs. 9,000 cells/mL, p = .04), CRP level (13 vs. 6 mg/L, p = .01), and osteomyelitis on MR imaging (p < .01 for both readers) significantly differed between patients with and without recurrence; on multivariable analysis, only osteomyelitis on MR imaging was significantly associated with recurrent SAS for both readers (p = .02 and .01 for each reader respectively). The inter-reader agreement was good (κ = .62-1.0) for all MR imaging findings, except for muscle edema (fair, κ = .37).

Conclusion: Osteomyelitis on MR imaging was the best predictor of recurrent SAS.

Key Points: • Osteomyelitis on preoperative MR imaging was the best predictor associated with recurrent septic arthritis of the shoulder on multivariable analysis including clinical, laboratory, and MR findings. • In multivariable analyses focused on each bone marrow abnormality, with adjustment for clinical and laboratory parameters, the presence of reactive bone marrow edema and osteochondral erosion on MR imaging showed no significant association with recurrent septic arthritis of the shoulder.