Thermal tissue damage caused by ultrasonic cement removal from the humerus

BACKGROUND: Ultrasound devices can selectively remove cement during revision arthroplasty. These instruments initially were designed for the hip and knee but also have been applied to the upper extremity. We describe a patient in whom a radial nerve palsy and a pathologic humeral fracture developed after ultrasonic cement removal was performed because of an infection at the site of a total elbow arthroplasty. Biopsies of the humerus, the triceps muscle, and the radial nerve showed widespread necrosis consistent with thermal injury. METHODS: A study involving six human cadaveric specimens was conducted to measure temperature elevations in bone and adjacent soft tissue during cement removal with use of an ultrasound device with and without irrigation. RESULTS: While temperature increased only minimally during cement polymerization, ultrasonic melting and removal of cement with use of constant energy delivery led to markedly elevated temperatures in the humeral cortex, the triceps muscle, and the radial nerve. These temperatures were above the known thresholds for thermal injury and necrosis. Subsequently, strategies designed to allow for safe ultrasonic cement removal from the humerus were applied, including intermittent delivery of energy and the use of cold irrigation between probe passes. These strategies resulted in markedly lower maximum temperatures in all tissues tested. CONCLUSIONS: Temperatures in the humerus, triceps, and, most importantly, the radial nerve can reach potentially dangerous levels when ultrasound technology is used to remove cement from the humerus. We suggest intermittent cold irrigation of the humeral canal, no tourniquet use, education of surgeons with regard to proper techniques designed to limit heat generation, and consideration of exposure and protection of the radial nerve when ultrasound devices are used.