Stemless total shoulders and Propionibacterium infections

High incidence of periprosthetic joint infection with Propionibacterium acnes after the use of a stemless shoulder prosthesis with metaphyseal screw fixation - a retrospective cohort study of 241 patients propionibacter infections after eclipse TSA.

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These authors investigated infections after the Eclipse stemless total shoulder as well as those after conventional shoulder prostheses.

A consecutive series of two hundred and forty-one patients (54.8% females) were operated with a shoulder arthroplasty and followed for median 2.0 (0.1–5.7) years. One hundred and two (42.3%) had received an Eclipse prosthesis, the remaining patients were operated with other implants. There was an overrepresentation of males in the Eclipse group (63.7% males) when compared with the control group (31.7% males). All arthroplasties were performed by two experienced shoulder surgeons in the same operating rooms and with the same staff. In order to ensure that patients had not been revised elsewhere we cross-validated our database with the Swedish Shoulder Arthroplasty Register where all revision procedures are registered on a national basis. At the time of index surgery all patients received perioperative intravenous  cloxacillin or clindamycin for 24 hours. Skin disinfection was performed with chlorhexidine.

Patients with shoulder pain at rest and without probable other causes were suspected to have a periprosthetic joint infection. Eight of 10 patients with suspected periprosthetic infection in the Eclipse group underwent a diagnostic shoulder arthroscopy before revision surgery was performed with the collection of 4-9 tissue samples for culture. In the remaining 2 of the 10 patients tissue samples were obtained during revision surgery. The patient in the control group with a periprosthetic infection developed a fistula and cultures were obtained from this fistula.

Tissue samples were cultured on chocolate blood agar for aerobic incubation, fastidious anaerobic agar for anaerobic incubation, and two serum broths.

In the Eclipse group 10 (9.8%) patients developed a periprosthetic joint infection, as opposed to 1 (0.7%) in the control group. The most common bacteria was Propionibacterium acnes. Unadjusted infection-free survival after 4 years was 88.8% (CI 82.5–95.7) for Eclipse® patients and 95.7% (CI 87.7–100.0) for controls (p = 0.002). After adjustment for age, gender, diagnosis, and type of shoulder prosthesis (total or hemi), the risk ratio for revision due to infection was 4.3 (CI 0.5–39.1) for patients with the Eclipse® prosthesis.

The authors point out that apart from patient-related factors, the higher-than anticipated rate of infections in patients operated with the Eclipse may be related to the material and structure of this implant. The trunnion and cage screw of this implant are manufactured from a titanium alloy that has high biocompatibility and an increased potential of bacterial colonization and biofilm formation. Furthermore, both bacterial adherence and the capacity for biofilm formation are dependent on surface roughness of the material. The metaphyseal cage screw is made of a roughly textured, porous titanium alloy that is unique to this type of implant. It is possible that  surface roughness and alloy composition exert an important influence on bacterial colonization and biofilm formation.

Comment: This study is rigorous in terms of the consecutive nature of the arthroplasties, the fact that only two surgeons were involved, and the special ability of the authors to followup on their patients using the national registry. 

The Eclipse prosthesis was introduced to the practice in 2008. Beyond that it is not clear how the choice among different prostheses was made.

It is of interest that many of these infections were diagnosed long after the index procedure

The relationship of patient and implant factors to the recovery of Propionibacterium in failed shoulder arthroplasties is of great interest. This paper brings new data to the discussion.

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