Comparative Study of Antibiotic Elution Profiles From Alternative Formulations of Polymethylmethacrylate Bone Cement.

BACKGROUND: Polymethylmethacrylate (PMMA) bone cement is commonly used in orthopedic surgery for implant fixation and local antibiotic delivery following surgical debridement. The incidence of nephrotoxicity necessitates the balance of antiinfective properties with the potential for toxicity. Thus, understanding antibiotic elution characteristics of different PMMA formulations is essential. We sought to address this by assessing elution of vancomycin, daptomycin, and tobramycin from Palacos LV (Palacos), Stryker Surgical Simplex P (Simplex), BIOMET Cobalt HV (Cobalt), and Zimmer Biomet Bone Cement R (Zimmer) radiopaque bone cements. METHODS: Antibiotics were mixed with each cement formulation, and molds were used to produce beads of cement. Beads were incubated in phosphate-buffered saline at 37°C, and antibiotic elution was measured daily for 10 days with vancomycin and 5 days with daptomycin and tobramycin. Active antibiotic was quantified by serial dilution and comparison to the minimum inhibitory concentration. RESULTS: The elution profiles of Simplex were significantly lower than all other cements with all antibiotics (P < .00093). Palacos exhibited a significantly higher vancomycin elution profile than all other cements (P < .00001). The difference in daptomycin elution profiles for Cobalt and Palacos was not significant (P > .43), but both were significantly higher than Zimmer (P < .0006). CONCLUSION: Overall, Stryker Surgical Simplex P exhibits a significantly lower elution profile than all other cements tested. In general, Palacos LV exhibits an increased elution profile compared with other cements. This elution information may assist the surgeon in choosing different cement formulations for the local delivery of antibiotics.

How is forearm compliance affected by various circumferential dressings?

BACKGROUND: The forearm is the second most common location for extremity compartment syndrome. Compliance is a physical property that describes a material's ability to expand with an increasing internal volume. The effect of circumferential dressings on extremity pressures has been investigated in various animal models and in some nonphysiologic mechanical models, but the importance of this effect has not been fully investigated in the human upper extremity. In addition, the physical property of compliance has not been reported in the analysis of compartment volume-pressure relationships. QUESTIONS/PURPOSES: We created a physiologic cadaver model for acute compartment syndrome in the human forearm to determine (1) how much volume is required to reach the pressure threshold of 50 mm Hg in forearms, undressed and dressed with various circumferential dressings, (2) differences in forearm compliances that result from dressings, and (3) whether univalving or bivalving of those dressings adequately reduces compartment pressures. METHODS: A sealed inflatable bladder was placed deep in the volar compartment of seven fresh-frozen cadaveric forearms and overlying fascia and skin were closed. Compartment pressures were measured as saline was infused in the bladder, and compliance was calculated from pressure versus volume curves. This was repeated for each specimen using five external wraps, splints, and casts. At a baseline of 50 mm Hg, each dressing then was univalved (and bivalved, when appropriate for the material) and the decrease in compartment pressure was measured. For each of the seven cadaver forearms, one test was performed without dressings and then for each of five dressing conditions. RESULTS: Forearms in fiberglass casts accommodated only a mean of 19 mL (SD, 11 mL; 95% CI, 9-28 mL) before reaching the 50 mm Hg pressure threshold, which was much less than in undressed forearms (mean, 77 mL; SD, 25 mL; 95% CI, 55-98 mL; p < 0.001). Mean compliances were as follows: ACE™ wrap (1.75 mL/mm Hg; SD, 0.41 mL/mm Hg), Webril™ (1.54 mL/mm Hg; SD, 0.56 mL/mm Hg), Kling(®) (1.23 mL/mm Hg; SD, 0.52 mL/mm Hg), sugar tong splint (1.05 mL/mm Hg; SD, 0.52 mL/mm Hg), and fiberglass cast (0.38 mL/mm Hg; SD, 0.27 mL/mm Hg). Univalving of all circumferential wraps dropped the mean compartment pressure from the 50 mm Hg starting point: ACE™ (46%; SD, 14%), Webril™ (52%; SD, 20%), Kling(®) (70%; SD, 18%), sugar tong splint (52%; SD, 19%), and fiberglass cast (58%; SD, 7%), with p less than 0.001 for all dressings. CONCLUSIONS: We observed the compressive effect of various commonly used upper-extremity splints and wraps, finding the least amount of accommodation afforded by fiberglass casts. Univalve release resulted in reduction in forearm compartment pressures, even in fiberglass casts. CLINICAL RELEVANCE: A rigid circumferential dressing can have a dramatic effect on extremity compartment compliance. Contrary to common clinical teaching, univalving of forearm circumferential dressings effectively reduced compartment pressures, as shown in this physiologic model.