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Using a Reamer-Irrigator-Aspirator Reduces Femoral Intramedullary Pressure During Simulated Total Knee Arthroplasty

Introduction: Fat embolism is a common occurrence following total knee arthroplasty (TKA) [1, 2]. Previous research has shown a positive correlation between an increase in femoral intramedullary pressure and the number of fat particles observed in the lungs postoperatively when a TKA was performed using traditional instrumentation (e.g., drill, intramedullary alignment guide, etc.) [3, 4]. Efforts to reduce the femoral pressure during TKA include using differently sized and shaped intramedullary instrumentation and over-drilling the canal [5], but these approaches have not eliminated the risk of post-operative embolism. Mueller et al [6] demonstrated in a cadaver study that evacuating the intramedullary contents of the femur prior to reaming decreases the pressure produced during instrument insertion, but this technique may be too time consuming and technically challenging to implement intraoperatively. The purpose of this study is to compare the femoral intramedullary pressure during the initial steps of a simulated TKA performed with conventional instrumentation against the intramedullary pressure of a simulated TKA performed with conventional instrumentation and the Reamer Irrigator Aspirator (RIA, Synthes Philadelphia, PA). The RIA is designed to be used after standard canal entry to increase the canal size and aspirate the intramedullary fat and bone chips generated from reaming the femoral canal. We hypothesize that using the RIA will result in lower femoral intramedullary pressures than using only conventional instrumentation during the initial steps of a total knee arthroplasty. Materials and Methods: We performed a simulated TKA on 14 femurs (7 pairs) from fresh-frozen cadavers. The femurs had all soft tissues removed and were mounted horizontally to custom fixtures. Pressure transducers (Omega Engineering Inc, Stamford, CT) were mounted proximally and distally on the femur and took pressure readings at 100 Hz. An experienced orthopedic surgeon performed the initial steps of TKA on all specimens. On the left femurs, he opened the canal with an 8/12.7 mm step drill (Zimmer, Warsaw, IN) and inserted an 8 mm fluted alignment rod (Zimmer, Warsaw, IN). He opened the canal on the 7 right femurs with the same step drill, but then inserted a 2.5 mm ball tip reaming rod for the RIA, reamed the canal with a 12 mm RIA, and then inserted an 8 mm fluted alignment rod. During all simulated TKAs, intramedullary pressure was recorded with the pressure transducers. We used the student’s t-test to compare the maximum recorded pressure from performing the procedure with the two different methods. All statistical tests were performed using SPSS V 14.0 (SPSS Inc, Chicago, IL) and the level of significance was set at α=0.05. Results: Using the RIA resulted in statistically significant lower femoral intramedullary pressures (86% less proximally and 87% less distally) compared to performing the steps of a TKA with conventional instrumentation alone (p<0.001) (Table 1). The maximum pressure with the initial conventional method of TKA occurred during the insertion of the alignment rod (Figure 1). When using RIA along with the conventional TKA method, the average maximum pressure occurred during insertion of the ball tip reaming rod (Figure 2). Discussion: The data suggest that using the RIA during the initial steps of a TKA would result in lower femoral intramedullary pressure than using only conventional instrumentation and could lead to a reduced risk of fat embolism. To our knowledge, this is the first instance of using the RIA for total knee arthroplasty, since the RIA was developed for femoral fracture surgery. Even though the device was not designed specifically for TKA, our study yielded promising results. Future work should be conducted using RIA to investigate the reduced risk of fat embolism in a clinical setting. References: [1] Caillouette JT and Anzel SH. Clin Orthop Relat Res 1990;251:198-199. [2] Dobrjanski D, et al.. J Arthroplasty 2007;22:417-427. [3] Joist A, et al. J Trauma. 2004;57:146-151. [4] Orsini EC, et al. J Bone Joint Surg Am 1997;69:822-832. [5] Ries MD, et al.. Clin Orthop Relat Res 1998;356:154-160. [6] Mueller CA and Rahn BA. et al. J Trauma. 2003;55:495-503. Acknowledgements: Synthes for experimental support. Table 1: Maximum Pressure Through Initial Steps of TKA