The effect of adding tobramycin to Simplex P cement on femoral stem micromotion as measured by radiostereometric analysis: A 2-year randomized controlled trial

BACKGROUND: Previous in vitro research on addition of antibiotics to bone cement has found no statistically significant deterioration in mechanical properties. However, no clinical studies have compared the performance of tobramycin-laden bone cement with that of standard bone cement (Simplex P). PATIENTS AND METHODS: 23 patients (25 hips) were randomized to receive an Exeter (Stryker Orthopaedics) femoral stem cemented with either Simplex P (standard) or Simplex T (tobramycin-laden) cement. There were 2 years of follow-up, with scheduled radiostereometric (RSA) examinations. RESULTS: All stems migrated distally and showed some degree of retroversion. No clinically significant differences in stem subsidence or retroversion were found between the Simplex T and Simplex P cement groups after 2 years. Overall subsidence was less than in previous studies, probably due to a postponed initial post-surgical examination. Rates of subsidence in both cement groups were consistent with those from previous studies of Exeter stems. INTERPRETATION: Subsidence of the femoral stem after 2 years was similar in the Simplex T (tobramycin-laden) and Simplex P (standard) groups.