The Journal ofArthroplasty Vol. 10 No. 4 1995 Effect of Varying Surface Patterns on Antibiotic Elution From Antibiotic-loaded Bone Cement Bassam A. Masri, MD, FRCSC, Clive P. Duncan, MD, FRCSC, Christopher R Beauchamp, MD, FRCSC, Nancy J. Paris, BASc, and Jennifer Arntorp, BASc Abstract: In an effort to improve the antibiotic elution characteristics of the pros- thesis of antibiotic-loaded acrylic cement, an in vitro study was conducted. Tobramycin-loaded bone cement blocks of three different surface patterns with dif- ferent surface area-to-volume ratios were used. The elution of tobramycin over a 2- month period was investigated. There was a gradual decline in the tobramycin elution rate over time. The surface pattern with the increased surface area-to-vol- ume ratio showed a significant increase in the tobramycin elution rate over the first week of the study. The surface pattern with ridges but no change in the surface area- to-volume ratio did not result in a statistically significant increase in the tobramycin elution rate. Key words: antibiotic, elution, cement, surface, arthroplasty, infection. The introduction of antibiotic-loaded bone cement by Buchholz and Engelbrecht ~ significantly changed the management and outlook of infected total joint arthroplasty prostheses. Other antibiotic depots have been investigated2-~; however, bone cement continues to be the most commonly used carrier today. The elution characteristics of antibiotics from bone cement have been well described. 7-'° The prosthesis of antibiotic-loaded acrylic cement (PROSTALAC) system ~-14 has been the treatment of choice for infected total hip and knee prostheses at our institution for the past 3 years (Fig. 1). We have already reported an infection recurrence rate of only 6% in 64 such treated infected total hip and knee arthroplasties, x4This system consists of tempo- rary hip and l~nee prostheses that are made primar- ily of antibiotic-loaded bone cement with a low-friction articulating surface. This prosthesis acts From the Department of Orthopaedics, Vancouver Hospital and Health Sciences Centre, and University of British Columbia, Vancouver, British Columbia, Canada. Reprint requests: Bassam A. Masri, MD, Department of Orthopaedics, Vancouver Hospital and Health Sdences Centre, Third Floor, Laurel Pavilion, 910 W. Tenth Avenue, Vancouver, British Columbia, Canada V5Z 4E3. as a functional spacer that permits joint mobility and stability, while the patient awaits reimplanta- tion of a definitive prosthesis. While in situ, this prosthesis ehites high concentrations of antibiotics, with levels well maintained up to 3 months follow- ing implantation. 15 Schurman et al., 16 as well as others, ~7.~8suggested that the in vitro antibiotic elution from acrylic cement is proportional to the surface area of exposed cement in a liquid medium. The purpose of this study was to test this hypothesis by means of an in vitro experiment, in which the effect of increasing the surface area of bone cement by applying a prac- tical, easily manufactured pattern to the surface was investigated, to determine if the elution characteris- tics of the PROSTALAC system could be improved by a simple alteration of the surface pattern. Materials and Methods Machinable polyethylene molds were used to manufacture bone cement blocks. Three different surface patterns were used to produce ridged sur- face patterns on four of the six surfaces of the cement blocks. Simplex P bone cement 453