TO THE EDITOR:
In "Abrasive Three-Body Wear of Polyethylene Caused by Broken Multifilament Cables of a Total Hip Prosthesis. A Report of Three Cases" (78-A: 1244—1247, Aug. 1996), Bauer et al. reported on osteolysis associated with trochanteric non-union after fixation with cables during total hip replacement. The authors showed that three-body wear of the polyethylene cup (and the femoral head) causing osteolysis originated from intra-articular penetration by macroscopic fragments of cable. However, although large fragments of cable are especially deleterious, we think that trochanteric non-unions can cause osteolysis and loosening even without migration of macroscopic fragments.
Kelley and Johnston1 reported a significant prevalence of loosening of the cup associated with the migration of fragments of not only trochanteric cables but also trochanteric wires toward the acetabular notch, and they hypothesized that the loosening was due to three-body wear of the polyethylene caused by metal debris.
We3 reported on three cases of loosening of cemented femoral total-hip replacement components associated with trochanteric non-union in which osteolysis was caused by microscopic metal debris from the wires and three-body wear of the polyethylene cup. The metal debris (as well as some cement particles) resulted from the relative motion of the trochanteric fragments caused by motion of the hip as well as from the trochanteric wires scratching one another and the proximal part of the stem. Most of the metal fragments were submicrometer particles, which were endocytosed by the macrophages, causing an osteolytic granuloma, especially at the site of the non-union and on the lateral side of the stem. Some of the fragments were larger, twenty to fifty micrometers in size. All of these were released in the so-called effective joint space, and they were able to reach the articular surface and create three-body wear of the polyethylene cup. The metal debris, whether small or large, was identified with electron probe microanalysis (wave length dispersive) as steel particles. Polyethylene particles were also seen in the tissue obtained from the bone-cement interface at revision.
Only non-unions in which there is substantial rubbing of the trochanteric surfaces during motion of the hip produce a large amount of debris. Therefore, this type of osteolysis is observed only in young and active patients who have a tight non-union. In non-active patients, or when the gap between the fragments is more than ten millimeters, little debris is produced.
We2 analyzed a continuous series of thirty-two Charnley total hip replacements performed for congenital dislocation of the hip in younger patients, with an average follow-up of 9.5 years. Four components loosened: one because the cup was too thin and three, which occurred at six years postoperatively, because of a tight non-union that had not been treated because the patients were asymptomatic. The osteolysis started at the site of the non-union and extended to the lateral side and tip of the stem. With the bilateral replacements, the osteolysis was noted only on the side with trochanteric non-union.
In conclusion, we think that metal-induced osteolysis and three-body wear of polyethylene can be observed not only with migration of cable (as reported by Bauer et al.) or wire1 fragments but also with microscopic debris of wires originating at trochanteric non-unions. To prevent early loosening, reoperation for tight non-unions in active patients who are less than fifty years old is advocated when progressive lateral osteolysis is noticed on radiographs.
Frantz L. Langlais, M.D.; Hervé Thomazeau, M.D.: Department of Orthopaedic Surgery, University Hospital Sud, 35200 Rennes, France
Dr. Bauer, Dr. Ming, Dr. D'Antonio, and Dr. Morawa reply:
Langlais and Thomazeau describe several additional cases in which loosening of an implant was attributed to metal debris originating from trochanteric wires or cables. Langlais et al. followed a series of patients who had had hip arthroplasty with the use of a transtrochanteric approach and cement and identified forty-eight patients in whom trochanteric non-union developed3. The implant loosened in several of these patients, who then had revision arthroplasty. Bone cement, polyethylene, and metal particles were identified, and the metal particles were believed to have originated as a consequence of motion between the trochanteric wires themselves and between the wires and the femoral implant. Langlais et al. also noted that this complication was seen only in active patients who had a so-called tight non-union, not in inactive patients or in those in whom the non-union was more than ten millimeters wide.
We have now identified fragments of broken trochanteric wires or cables embedded in seven polyethylene acetabular inserts studied after revision arthroplasty, and in each case the origin of the debris was fretting between a monofilament wire or a braided cable and a metal grip assembly over the greater trochanter. None of these cases was related to a trochanteric non-union. The mechanism of debris formation in our patients may be different than that described by Langlais et al.3, but we agree that it is desirable to use operative techniques and materials that minimize the generation of three-body debris in general and that surgeons should recognize all potential sources of abrasive debris, including wire and cables.
Thomas W. Bauer, M.D., Ph.D.; Jiang Ming, M.D.: Departments of Anatomic Pathology and Orthopaedic Surgery, The Cleveland Clinic Foundation, Cleveland, Ohio 44195
James A. D'Antonio, M.D.: M. H. & D. Orthopedic Associates, 725 Cherrington Parkway, Suite 200, Moon Township, Pennsylvania 15108
Lawrence G. Morawa, M.D.: Dearborn Orthopedic Surgery, 2547 Monroe Street, Dearborn, Michigan 48124