These authors sought determine the characteristics of patients who developed Cutibacterium acnes spinal implant-associated infection (SIAI) and the associated risk factors. They conducted two parallel case–control studies comparing 59 patients with SIAI caused by C. acnes (cases 1) and 93 patients with SIAI caused by other microorganisms (cases 2) diagnosed during 2010–2015 with 302 controls who underwent spinal instrumentation without subsequent infection.
That late-onset infections (median time to diagnosis, 843 days versus 23 days; p < 0.001) were more common in Cutibacterium infections (group 1) than in infections by other organisms (group 2) . However, 20/59 (34%) of cases 1 occurred within the first 3 months after the index surgery.
Cutibacterium infections were less likely to have fever (27%, 16/59 versus 58%, 54/93; p 0.001) or wound inflammation (39%, 23/59 versus 72%, 67/93; p < 0.001).
Moreover, 24/59 (40%) of cases 1 presented with polymicrobial infections, and staphylococcal pathogens accounted for 22/24 (92%) of the co-infections.
By comparing and contrasting the two multivariate risk models (cases 1 versus controls and cases 2 versus controls), the following factors associated with C. acnes SIAI development were identified: age <54 years (adjusted odds ratio (aOR) 2.43, 95% confidence interval (CI) 1.09–5.58, p 0.03), a body mass index <22 kg/m2(aOR 2.47, 95% CI 1.17–5.29, p 0.02), and thoracic instrumentation (aOR 16.1, 95% CI 7.57–37.0, p < 0.001).
Comment: The results of this study can be compared to that of a recent study of the characterisics of patients with Cutibacterium shoulder infections (see below). In both studies, it is the young, thin patient who is at highest risk for Cutibactetrium infections - a demography quite different from that for other bacteria and also from that for hip and knee infections. It is of note that the shoulder and the back are two areas of the body with high density of Cutibacterium-containing sebaceous glands. It is of interest that the spine study did not identify male sex as a risk factor for Cutibacterium infections, whereas this is a well-documented risk factor for shoulder periprosthetic infections.
Cutibacterium are the most common cause of periprosthetic shoulder infections, as defined by 2 deep cultures. Established Cutibacterium periprosthetic infections cannot be resolved without prosthesis removal. However, the decision for implant removal must be made from an assessment of infection risk before the results of intraoperative cultures are finalized. These authors hypothesized that the risk for a Cutibacterium infection is associated with characteristics that are available at the time of revision arthroplasty.
In a retrospective review of 342 patients having prosthetic revisions between 2006 and 2018 for whom definitive deep culture results were available, they used univariate and multivariate analyses to compare the preoperative and intraoperative characteristics of 101 revisions with Cutibacterium periprosthetic infections to the characteristics of 241 concurrent revisions not meeting the definition of infection.
Patients with definite Cutibacterium periprosthetic infections were younger (59 ± 10 vs. 64 ± 12, P <.001), were more likely to be male (91% vs. 44%, P <.001), were more likely to have had their index procedure performed for primary osteoarthritis (54% vs. 39%, P . .007), were more likely to be taking testosterone supplements (8% vs. 2%, P ..02), had lower American Society of Anesthesiologists scores (1.9 ± 0.7 vs. 2.3 ± 0.7, P < .001), and had lower body mass indices (29 ± 5 vs. 31 ± 7, P ..005). Patients with definite Cutibacterium periprosthetic infections also had significantly higher preoperative loads of Cutibacterium on their unprepared skin surface (1.7 0.9 vs. 0.4 0.8, P < .001) and were more likely to have the surgical finding of synovitis (41% vs. 16%, P < .001).
This study indicates that the risk of a revised shoulder arthroplasty having a definite Cutibacterium periprosthetic infection was associated with certain readily available preoperative and intraoperative observations, such as patient age and sex, ASA, BMI, the use of testosterone supplements, the results of preoperative skin surface cultures, and the intraoperative finding of synovitis. Because these observations are available to the surgeon at the time of revision arthroplasty, they may be considered in the intraoperative decisions regarding the advisability of prosthesis exchange.
Comment: This study suggests that, contrary to the experience with hip and knee periprosthetic infections, patients with shoulder periprosthetic infections are more likely to be young, healthy males. There is evidence to suggest that the levels of the male sex hormone, testosterone, may increase the production of sebum in the sebaceous glands of the dermis overlying the shoulder as well as the number of cutbaterium in these glands. Thus young male, healthy patients having shoulder arthroplasty appear more likely to have Cutibacterium introduced into their wounds at the time of shoulder arthroplasty.
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