Careful interpretation of the wound status is needed with use of antibiotic impregnated biodegradable synthetic pure calcium sulfate beads: Series of 39 cases

Abstract. Introduction: The use of antibiotic impregnated biodegradable synthetic high purity calcium sulfate (SHPCS) beads is frequently reported as they offer increased concentration of antibiotics locally, without need for removal. However some wound discharge following their use has been noted. The purpose of this study was to determine any correlation between wound discharge and infection remission.

Methodology: Retrospective study of 39 cases of Osteoarticular infections from April 2013 to November 2016 in whom SHPCS beads were used. All patients underwent the standard staged protocol of aggressive debridement, deep tissue biopsy, implant removal where indicated and early soft tissue cover. SHPCS beads were used locally in the second stage combined with appropriate antibiotics based on tissue culture. All patients received systemic antibiotics for a period of 6 weeks and followed up for a minimum period of six months. The study analysed the patient demographics, etiology, surgical procedures, culture patterns, local antibiotics used, radiological status of beads, incidence and characteristics of wound discharge and outcome.

Results: There were 25 cases of chronic osteomyelitis, eight infected non unions, three peri prosthetic joint infections, two soft tissue infections and one case of acute osteomyelitis. 17 of these infections were following osteosynthesis. The cultures were negative on eight occasions in seven patients. A total of 40 organisms were isolated in the other patients; commonest being Staphylococcus aureus (n=16) and E coli (n=7). SHPCS beads were mixed with vancomycin in 17 cases, colistin in 11, vancomycin with colistin in eight and vancomycin with gentamicin in four. Voriconazole was used in one case with fungal infection.

Eight cases (20.51 %) developed discharge from the wound at an average of 6 days after inserting the beads. The discharge was serous with no foul smell in six and purulent in two inflamed wounds. Four cases underwent re-debridement; two cases with purulent discharge and subsequent positive cultures; two with serous discharge early in the series and no evidence of infection on re-exploration with negative cultures. The remaining four patients with serous wound discharge were observed without any further surgical intervention, with the discharge stopping spontaneously between 15 to 36 days post operatively. There was no correlation between antibiotic used and wound discharge. Radiographic analysis showed dissolution of all the beads at an average of 36 days in the 39 cases. Heterotrophic ossification was not observed.

Clinical and radiological remission of infection was observed in 37 cases (94.9%). Two patients died during the course of hospitalization, secondary to septicaemia and multi organ failure. Three patients had an infection recurrence within six months, managed successfully by re-debridement and appropriate antibiotics. Radiological union was achieved in seven of the eight infected non unions.

Conclusions: With the encouraging rates of infection remission we have observed, we continue to use antibiotic loaded SHPCS as an alternative for local antibiotic delivery in the treatment of osteoarticular infections. However, wound discharge is a known potential observation following implantation of calcium sulfate beads, subsiding typically within four to six weeks.

The appearance of wound discharge can vary, ranging from purulent discharges to non-purulent, serous/ sero sanguineous fluid wound discharges. The presence of a wound discharge alone does not necessarily imply a failure to treat the infection.

It is important to be aware of this side effect and guard against unnecessary re- operations, by careful consideration and monitoring all of the available clinical signs of infection, in addition to blood test results and radiographic evidence. Further research is needed to determine the relationship between the implantation of antibiotic loaded calcium sulfates and the incidence and duration of drainage.