The Lithotriptor and Its Potential Use in the Revision of Total Hip Arthroplasty

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.