A native of Philadelphia, Robert Karpman (Fig 1) was educated at LaSalle College (BA, 1973), and the University of Pennsylvania (MD, 1977). He then moved to the University of Arizona in Tucson where he received his orthopaedic training. Karpman finished his training in 1981. After this, Karpman moved to Phoenix where he entered private practice. In addition to his practice, Karpman has held numerous important positions in the teacing programs of the Maricopa Medical Center including Director of Academic Affairs (1991–1996), Chief of Orthopaedics (1986–1998), and Medical Director of Physical Medicine and Rehabilitation (1988–1996). His academic appointments include Clinical Professor, Department of Orthopedics, University of Arizona; Associate Professor, Mayo Medical School, Scottsdale, Arizona; and Adjunct Professor, Department of Chemical and Bioengineering, Arizona State University. In addition to these activities, Karpman obtained an MBA from the University of Phoenix in 1991. His interest in research and teaching is reflected in a substantial bibliography, which includes the following classic article on the use of focused shock waves in orthopaedic surgery.Fig 1.: Dr. Robert R. Karpman.Interest in focused shock waves began during World War II when observers at the Dormier factory in Germany became interested in patterns of injuries in tank crews when the turrets were struck by shells, and when pitting of metal surfaces was observed associated with supersonic flight. The wife of one of the engineers suggested the possible application of this knowledge to the fragmentation of kidney stones, which lead to the development of lithotripsy. Perfection of this technique led to the thought that a similar application to the loosening of cement in the revision of total hip arthroplasty might be feasible. The following article is one of the first to explore this possibility. ABSTRACT Revision total hip arthroplasty, particularly femoral component replacement, has proved extremely difficult and has met with frequent complications. Despite a variety of devices and techniques that have been developed to facilitate removal of the femoral stem, the procedure remains difficult. Extracorporeal shock wave lithotripsy (ESWL) is a new technique initially created to pulverize renal stones by means of repetitive shock waves delivered to a discrete area. It was felt that perhaps this technique might also be utilized to facilitate the removal of the femoral component and cement from the femoral canal in revision total hip arthroplasty. Using bone cement, cadaveric canine femora were implanted with stainless steel rods placed within the medullary canal. The implanted femora were treated with ESWL, sectioned, and examined, using scanning electron microscopy. Microfracturing of the cement and a disruption of the cement bone interface were seen in the treated specimens. ESWL has the potential to be used prior to revision total hip arthroplasty to facilitate cement and component removal, although there are several questions that need to be answered prior to considering its clinical use. The incidence of revision of failed cemented total hip replacement is rapidly increasing and, consequently, there have been numerous developments of new techniques to improve the efficacy of this complex surgical procedure. It has been recently estimated that more than 100,000 total hip arthroplasties are done every year, and revision rates for clinical failure have been variously reported between 1% and 29%. The incidence of failure will continue to increase, since roentgenographic evidence of aseptic loosening appears to increase as a function of time. This is complicated by the poor long-term results of the revision procedures, eg, second revisions (9%), increased incidence of radiographic loosening (53%) and symptomatic loosening (14%) of the femoral component, and a continuing attrition in the rate of mechanical failure of 29%. Hoogland and co-workers reported that a second revision was required in 22% of their revision total hip replacement series. More recently, Tapadiya and associates reported a second-revision rate of 29% after revision for total hip replacement component loosening based on an average follow-up period of 3.1 years. Recent advances in materials, techniques, and instrumentation have not demonstrated an improvement in more recently treated patients who have had revision arthroplasties. One of the more challenging technical aspects of revision procedures is the removal of adherent cement from the femoral canal within the diaphyseal region. This has been addressed with an armamentarium of techniques, beginning with the “window,” or “gutter,” cut into the cortical bone. This technique was eliminated with the advent of intramedullary hand and powered drilling instrumentation, fiberoptic headlights, and sliding hammer extractors. Unfortunately, numerous intraoperative complications have occurred, such as perforation of the femoral cortex by the drilling, instruments due to difficulties in differentiating between the hard, brittle cement and adjacent cortical bone, particularly in the intramedullary canal at the level of the isthmus, where blind drilling becomes hazardous. Hoogland and associates reported a 12% rate of intraoperative complications, including femoral shaft fracture during cement removal, femoral shaft perforation, and severe hypotensive crisis secondary to heavy blood loss. Inadvertent perforation of the femoral shaft occurred in 14% of the revision cases during the attempt to remove cement from the intramedullary canal. There continues to be a persistent need for research and innovation to identify a more efficient method of facilitating cement removal. One high technology approach involved an attempt to use lasers, but no further information on this application has been reported. Extracorporeal shock wave lithotripsy (ESWL) is a new technique presently being used to pulverize renal stones by means of repetitive shock waves delivered to a discrete area. This technique may be effective in disrupting the bone/cement interface prior to revision surgery to facilitate cement removal. A Shattering Technique ESWL, a noninvasive, contact-free, kidney-stone shattering technique, was developed in Munich in the mid 1970s and has now been brought into common use in West Germany, the United States, and Sweden. In principle, the shock waves are generated by an underwater high-voltage condenser spark discharge and then focused at the renal stone, using an elliptical reflector. The position of the stone is located by a two-axis x-ray system, whose axes intersect at the second focus of the elliptical reflector. The patient is moved with a high-precision positioning device in three axes so that the stone can be in the second focus with a precision of 1 cm. The shock waves spread through the immersed body evenly, since the acoustic impedance of most body tissue is close to that of water. At the second focus, where the stone with a substantially different density is encountered the shock waves are highly attenuated, leading to a buildup of pressure gradients and formation of tear-and-shear forces. These forces are sufficient to disintegrate the solid kidney stone into small residual concretions, permitting spontaneous discharge. The entire procedure lasts 30 to 45 minutes. This technique has been extremely effective in the treatment of renal and ureteral stones, often relieving the need for open procedures. It was felt by our group that perhaps this technique might also be utilized to facilitate the removal of the femoral component and cement from the femoral canal in revision total hip arthroplasty. The purpose of this paper is to present preliminary observations of the utilization of ESWL in canine cadaver bone to evaluate its disruptive effects on the bone/cement interface. Materials and Methods Three freshly harvested adult canine femora were implanted with a 7-mm × 50-mm stainless steel cylindrical rod using cement fixation (Fig 1). The implantation was carried out by inserting a 3.2-mm Steinmann pin at the trochanteric fossa and entering the proximal medullary canal. A 9-mm cannulated reamer was placed over the pin and the medullary canal reamed to a depth of 60 mm. All reaming -debris and marrow were removed from the femoral canal using suction and irrigation. After placing a medullary plug at the 60-mm level, the canal was filled with polymethyl methacrylate (Surgical Simplex P, Howmedica, Inc) using a cement gun. The stainless steel rod was pressed into the canal, centered, and then fully seated. After 24 hours, the implanted femora were placed in the Dornier Kidney Lithotriptor (Dornier Medical Systems, Munich, West Germany). The lithotriptor includes a water bath in which the test specimen is submerged. A shock wave generator, consisting of a spark plug and a focusing ellipse, is used to generate shock waves and direct them toward the target point. Utilizing a two-axis C-arm image-intensification system, a target location was selected along the length of the femur in the area of the cement/bone interface, and 100 shock waves were delivered (Fig 1) (figure not shown). Using this imaging system, the target spot can be placed in the required position with a precision of 1 cm. High-resolution radiographs of the implanted femur were taken prior to and following lithotriptor treatment on Kodak X-Omat AR film (Eastman Kodak Co, Rochester, NY) in a Megarad 160 (Omega Laboratories, Inc, Los Angeles, Calif.). The specimen was removed from the lithotriptor and examined grossly for any changes or obvious loosening of the implant. The femur was sectioned transversely at the level of the target site, using a low-speed diamond saw (Isomet 11–1180, Buehler, Lake Bluff, Ill.) with constant saline irrigation. Non-lithotriptor-treated areas a minimum of 5 mm proximal and distal to the test site served as controls. Sections were polished using 5-μm levigated alumina on a metallurgic polisher/sander (Leo Corp., St. Joseph, Minn.). All sections were examined using reflected light and scanning electron microscopy. Results Gross examination of the specimens following shock wave exposure demonstrated a 3-cm circular discoloration of the bone at the target point. There was no overt loosening of the implanted rod on digital manipulation. No radiographic differences were noted between the pretreated and the posttreated specimens. Scanning electron microscopy and reflected light microscopy of the lithotriptor-treated areas showed many microfractures within the bone cement and a definite disturbance of the bone/cement interface, with some microfractures seen in the cortical bone (Fig 2A) (figure not shown). The control area showed very homogenous acrylic bone cement with no evidence of fracture or disruption at either the bone/cement interface or the cement/metal interface (Fig 2B) (figure not shown) Discussion This is the first report of potential orthopaedic application of ESWL. These preliminary results have shown that ESWL may have a potential for facilitating cement removal in revision total joint surgery. The experimental protocol used in this study was intended only to evaluate the effects of ESWI on the bone/cement interface. The microfracturing of the bone cement seen in the treated areas demonstrated the ability of the lithotriptor to mechanically compromise the bone cement and, in so doing, to disrupt the bone/cement interface. In this study, the shock waves were directed precisely at the bone/cement interface. Focusing at this point caused some microfracturing in the adjacent cortical bone, which could possibly be avoided by directing the shock waves to the middle of the cement mantle rather than to the bone/cement interface. It is conceivable that a patient would be treated with the lithotriptor prior to revision surgery, with shock waves directed to disrupt the bone/cement interface over the entire length of the implant. However, there are several questions that must be answered prior to clinical feasibility: Is there a dose-response curve regarding the number of shock waves and cement fragmentation? Do the resulting fragmentation of the cement and disruption of the interface create a mechanical advantage in the removal of the implant. Can the shock wave energy be focused precisely enough to prevent microfracture of the cortical bone? Do the shock waves have any effect on the soft tissue elements within the intramedullary canal, on the femoral cortex, or on the surrounding tissues? Continuing studies are being performed at this institution in an attempt to answer these questions.