TO THE EDITOR:
The article "Charnley Total Hip Arthroplasty in Patients Less Than Fifty Years Old. A Twenty to Twenty-five-Year Follow-up Note" (80-A: 704—714, May 1998), by Callaghan et al., is an interesting documentation of the long-term results of total hip arthroplasty in the most challenging population of patients who are managed with this procedure: those who are less than fifty years old. The 23 percent rate of revision due to aseptic loosening is evidence of an important complication associated with a procedure that is being performed at a reported rate of increase of 5 to 8 percent per year2. One of the criteria that Callaghan et al. used as evidence of loosening was the appearance of a radiolucent line at the bone-cement interface. A more quantitative measure of loosening could perhaps provide earlier recognition of this complication and lead to earlier and more effective treatment.
During the last decade, much work has been done on the use of dual-energy x-ray absorptiometry for the early diagnosis of periprosthetic loosening. Software is now available for the quantitative measurement of bone-mineral density around the femoral implant according to the zones of Gruen et al.1. By measuring decreases in bone-mineral density around prosthetic components, an investigator can now detect loosening earlier than is possible by waiting for the appearance of a radiolucent line at the bone-cement or bone-implant interface. Studies currently are being performed to investigate the use of antiresorptive drugs, such as bisphosphonates, to treat early loosening medically. These drugs may counteract osteolysis in the periprosthetic environment by inhibiting the activation of osteoclasts and the recruitment of osteoclast precursors.
This is an exciting field of study because some of these new developments in the early diagnosis and treatment of periprosthetic loosening may give us new techniques that will enable us to decrease this important complication of total hip arthroplasty.
John D. Kaufman, M.D.: 24355 Lyons Avenue, Suite 240, Santa Clarita, California 91321
Dr. Callaghan, Dr. Forest, Mr. Olejniczak, Dr. Goetz, and Dr. Johnston reply:
As Dr. Kaufman noted, the rate of aseptic loosening in our study was 23 percent (twenty-one of ninety-three hips). However, the rate of loosening on the femoral side was much lower (13 percent; twelve of ninety-three hips). In addition, the failures on the femoral side always occurred at the prosthesis-cement interface, not the bone-cement interface. We do not believe that the bone-cement interface is disrupted until later in hips in which optimum cementing techniques have been used. This is especially true for hips that have been treated with a polished stem, such as the Charnley flat-back stem that we used. We agree that a more quantitative measure of early loosening may be beneficial, especially in consideration of medical treatment with drugs such as bisphosphonates. In fact, investigators at our laboratory are working on edge-detection techniques that may help to identify loosening earlier. We agree that dual-energy x-ray absorptiometry is an excellent tool with which to measure bone loss accurately; however, we believe that loosening at the bone-cement interface is rare after primary total hip arthroplasty (except in cases of infection). It would be interesting to perform prospective studies to determine whether dual-energy x-ray absorptiometry can predict early loosening of cemented total hip prostheses; however, we would be somewhat skeptical that the test would be helpful because we believe that complications at the bone-cement interface on the femoral side are a rare cause of mechanical failure.
John J. Callaghan, M.D.; Erin E. Forest, M.D.; Jason P. Olejniczak, B.A.; Richard C. Johnston, M.D.: Department of Orthopaedic Surgery, University of Iowa College of Medicine, Iowa City, Iowa 52242
Devon D. Goetz, M.D.: Des Moines Orthopaedic Surgeons, 6001 Westown Parkway, West Des Moines, Iowa 50266-7702