Although the risk of pulmonary embolism or other embolic events associated with total joint arthroplasty have been recorded for some time, to date no direct means of monitoring these events in human arthroplasty have been reported. The authors used transesophageal echocardiography to monitor directly the release of embolic particles into the circulatory system during the course of total knee arthroplasty. The transesophageal echocardiography, in conjunction with intramedullary instrumentation, revealed that showers of embolic particles entered the heart in repeated and unpredictable patterns during the course of conventional intramedullary instrumented total knee procedures. In response to the presence of these embolic showers in the heart, an extramedullary pneumatically positioned system of instrumentation permitting automatic and accurate alignment of the knee with the mechanical axis of the femur has been developed. This new instrumentation establishes proper knee kinematics by semiautomatically determining and maintaining accurate positioning of the femoral component along the mechanical axis of the knee. Qualitative and quantitative monitoring of embolic events using transesophageal echocardiography in conjunction with conventional intramedullary and the new instrumentation suggests that the embolic risk is substantially reduced using the new procedure. Furthermore, the new extramedullary instrumentation was able to align the femoral knee component to within 1 degree of the mechanical axis in an initial series of 25 procedures. Excellent component alignment in conjunction with a substantially reduced quantity of embolic particles in the right heart as seen using transesophageal echocardiography was achieved using the newly developed extramedullary positioning and alignment arm.