Anatomic and Microbiological Analysis of Upper Extremity Nonunions Undergoing Revision Surgery: A Multicenter Retrospective Study

Objective: The primary goal of this study was to determine the rate of occult fracture-related infection associated with nonunion of upper extremity fractures following open reduction internal fixation (ORIF). Methods: We performed a retrospective analysis of patients treated for upper extremity nonunion after ORIF at five urban hospitals, including two level I trauma centers, between the years 2000 and 2020. Patient demographics, operative reports, and laboratory data were collected. An unexpected positive intraoperative culture (UPIC) was defined as a positive intraoperative culture from a nonunion without overt signs of infection. Descriptive statistics were performed. Results: Of 363 patients with an upper extremity nonunion after ORIF, 197 had culture data available. Sixty-seven percent (67%) of nonunions occurred proximal to the elbow. Positive cultures were identified in 84 patients (43%), with the distal humerus showing the highest rate (33%). A total of 51 UPICs were identified. Cutibacterium acnes was present in 48% of all culture-positive nonunions and Coagulase-negative Staphylococci (CoNS) was represented in 43% of all culture-positive nonunions. C. acnes culture positivity rates decreased by proximal-to-distal anatomic location with 100% of culture-positive clavicle nonunions sampled growing C. acnes and 25% of culture-positive ulnar nonunions growing C. acnes. Among culture-positive nonunions, 94% of the UPIC group grew C. acnes or CoNS, compared with 52% of the overt FRI (fracture-related infection) group. The posterior mean rate of UPICs, when normalized to the clavicle, ranged from 5.1% to 23.5%. The clavicle demonstrated the highest rate (0.24; 95% CI, 0.11–0.39). The distal humerus had a comparable rate (0.22; 95% CI, 0.12–0.34; normalized ratio, 0.94). Nonunions with a high pre- or intraoperative concern for infection had a 48% rate of growing virulent bacteria compared to a 6% rate in the UPIC group. Conclusion: In total, 31% of aseptic-appearing nonunions yielded positive cultures and 94% of UPICs grew predominantly low-virulence organisms. While there is a high rate of UPICs with C. acnes and Coagulase-negative Staphylococci in upper extremity nonunion, the clinical significance of UPIC FRI remains unclear. Further research is needed to determine the implications of such UPIC in the absence of overt infection.