This retrospective evaluation investigated consecutive patients that were treated for SJI with a two staged implantation of a total shoulder arthroplasty (TSA) after debridement and implantation of an antibiotic loaded PMMA-Spacer between 2007 and 2015 in one specialized high volume hospital. Inclusion criteria were 1) the diagnosis of SJI based on clinical presentation, blood infection markers, histological and microbiological findings as well as WBC following 2018s ICM criteria (17), 2) the two staged TSA implantation as described above and 3) available data on PA and IA. Exclusion criteria was age below 18, this criteria was not met in a patient who fitted the inclusion criteria.We identified 35 patients that were eligible for the study (23 periprosthetic shoulder infections (PSI), 8 native joint infections (primary infection, PI), 7 infections after osteosynthesis and/or rotator cuff surgery (secondary infection, SI). The first joint aspiration was performed preoperatively (PA); the second aspiration was performed as interstage aspiration while a spacer was implanted (IA). Patients did not receive antibiotics before PA, all patients were treated with antibiotics after spacer implantation but an antibiotic suspension of 14 days was held before performing IA.
Data for certain aspects was not available in all of the patients, therefore sample sizes differ for different questions. Culture from PA: 35 patients (7 PI, 21 PSI, 8 SI), WBC: 12 patients (3 PI, 9 PSI), IA: 33 patients (6 PI, 21 PSI, 7 SI). Details on demographic data in blood infection markers are provided in Table 1.
Joint aspirations were performed with a sterile canula from either anterior or dorsal approach after 3 minutes skin disinfection by alcoholic skin disinfectant (Octeniderm®, Schuelke and May, Norderstedt, Germany). A minimum volume of 1 ml was required. Aspirated fluid volume was never diluted by using other fluids. Aspirated synovial fluid was transferred to a sterile test tube forWBC calculation and to blood culture bottles for aerobic (BacT/ALERT® FA Plus) and anaerobic (BacT/ALERT® FN Plus) growth (bioMérieux, Marvie-L`Étoile, France). Blood culture vials were incubated for 14 days or until flagged positive in the BacT/ALERT® 3D System (bioMérieux, Marvie-L`Étoile, France). Species diagnosis was established by Matrix-assisted laser desorption/ionization – time of flight (MALDI-TOF) from solid culture media.
Statistical tests were performed using SPSS Statistics® Version 24.0 (IBM, New York, USA) and Microsoft Excel® Version 1908 (Microsoft, Washington, USA). Descriptive statistics were performed to describe means, medians and range for all variables. Receiver Operating Characteristic (ROC) was plotted for WBC depending on culture results from spacer implantation to depict the correlation between sensitivity and specificity. Area-Under-Curve (AUC) analysis and calculation of the Youden index was performed to quantify the quality of the test. The same calculations were performed for WBC depending on culture results from PA.
Microbiological culture from PA was defined as “correct positive” if a microbiological culture from tissue biopsies taken during initial surgery matched the organism of PA. PA was defined “correct negative” if neither the culture from PA nor intraoperative biopsies yielded growth. PA was defined “false negative” if the culture from PA was negative while an intraoperative biopsy yielded growth. PA was defined “false positive” if culture from PA yielded growth and intraoperative biopsies yielded growth of a different bacterium (1 patient) or no growth.
The intraoperative biopsies were taken right after opening the joint capsule and before starting perioperative intravenous antibiotics. At least 3 biopsies were taken from membranes, resected bone and directly surrounding soft tissue. Sterile sample vessels were opened under laminar flow and fractioned. Cultures were nourished in Brain-Heart-Infusion-Bouillon and Thyoglycolate-Bouillon and plated out on Candida-Chrome-Agar, Columbia-Blood-Agar, Cooking-Blood-Agar, MacConkey-Agar and Schaedler-Agar. Cultures were incubated for 14 days. Species were differentiated throughout mass spectrometry (Vitek MS, bioMérieux, Marvie-L`Étoile, France) followed by testing of sensitivity (Vitek 2, bioMérieux, Marvie-L`Étoile, France).
Sensitivity was defined as the ratio of all correct positive PAs on all intraoperative positive cultures. Specificity was defined as the ratio of all positive PAs on all intraoperative positive cultures. The same procedure was used for IAs but with reference to results from either spacer exchange or final implantation of TSA. Cross-tables were used to calculate positive predictive value (PPV) and negative predictive value (NPV) for both PA and IA.
Table 1
Demographic data and preoperative blood infection markers. CRP = C-reactive protein (norm value < 0,8mg/dl), ESR = erythrocyte sedimentation rate (norm value < 28mm/h). * IA was delayed due to intermediate cardic surgery/treatment for pulmonary problems. This two patients were excluded for the calculation of means (marked with **).
DEMOGRAPHIC DATA AND BLOOD INFECTION MARKERS |
patient | sex category | site | initial surgery | age at PA | surgery to PA | spacer to IA | CRP | ESR | blood WBC |
| | | | [years] | [months] | [days] | [mg/dl] | [mm/h] | [10³/mm³] |
1 | female | right | osteosynthesis | 44 | 18 | 55 | 1.6 | 34 | 7.6 |
2 | female | right | no surgery | 74 | | 48 | 4.7 | 67 | 6.1 |
3 | female | left | no surgery | 71 | | 32 | 2.5 | | 10.5 |
4 | malefte | right | TSA | 55 | 35 | 34 | 8.5 | 23 | 9.5 |
5 | female | right | TSA | 71 | 14 | 15 | 4 | | 9.5 |
6 | female | right | TSA | 80 | 32 | 40 | 6.8 | 82 | 8.8 |
7 | female | left | osteosynthesis | 68 | 4 | 52 | 2.9 | 64 | 10.7 |
8 | female | right | TSA | 57 | 11 | 58 | 2.4 | 31 | 12.2 |
9 | male | left | osteosynthesis | 52 | 8 | 52 | 1.5 | | 7.1 |
10 | female | right | TSA | 84 | 4 | 57 | | 21 | |
11 | male | right | TSA | 59 | 155 | 38 | 1.2 | | 7.8 |
12 | male | right | rotator cuff | 68 | 32 | 44 | 1.3 | 18 | 8.6 |
13 | female | right | TSA | 77 | 56 | 318* | 0.4 | | 6.6 |
14 | female | right | osteosynthesis | 66 | 2 | 50 | 1.1 | | 5.4 |
15 | female | left | TSA | 74 | 16 | 46 | 0.4 | | 9.4 |
16 | male | left | TSA | 74 | 13 | 58 | 1.7 | 18 | 11.4 |
17 | male | right | TSA | 55 | 10 | 41 | 2.6 | 64 | 8.1 |
18 | male | right | TSA | 73 | 24 | 44 | 11.3 | 32 | 8.3 |
19 | male | right | TSA | 84 | 8 | 86 | 1.5 | 40 | 4.4 |
20 | female | right | TSA | 65 | 14 | 50 | 4.8 | | 8.8 |
21 | male | right | TSA | 72 | 1 | 74 | 30.4 | 68 | 8.6 |
22 | male | right | TSA | 76 | 2 | 48 | 10 | 44 | 11.1 |
23 | female | right | TSA | 60 | 9 | 44 | 1.4 | | 6.6 |
24 | female | left | TSA | 78 | 37 | 56 | 12.1 | 40 | 13.8 |
25 | female | right | no surgery | 76 | | 332* | 1.6 | | 7.2 |
26 | female | right | TSA | 77 | 28 | 56 | 0.1 | 38 | 5.6 |
27 | female | right | no surgery | 82 | | 41 | 1.9 | 29 | 7.6 |
28 | female | right | no surgery | 84 | | 20 | 7.1 | 8 | 10.3 |
29 | female | right | TSA | 69 | 101 | 58 | 0.1 | 24 | 7.5 |
30 | female | left | no surgery | 83 | | 59 | 0.3 | | 8.3 |
31 | female | right | no surgery | 79 | | | 6.6 | 64 | 6 |
32 | female | left | osteosynthesis | 65 | 2 | 59 | 1 | 31 | 10.5 |
33 | female | left | TSA | 84 | 69 | 56 | 1.8 | 6 | 11.7 |
34 | male | left | rotator cuff | 50 | 127 | | 0 | 29 | 5.4 |
35 | female | right | TSA | 80 | 10 | 58 | 9.7 | 1 | 21.8 |
mean (only patients with TSA) | 72 | 31 | 47** | 5.5 | 35 | 9.5 |
mean (patients with non TSA) | 69 | 28 | 51** | 2.4 | 38 | 7.9 |
mean (total) | 70 | 30 | 49** | 4.3 | 37 | 8.9 |