Abstract
Thirty-five patients who had had a primary total hip replacement with a porous-coated acetabular component inserted without cement had a revision procedure to treat pelvic osteolysis. The mean age at the time of the revision operation was forty-nine years (range, twenty-nine to eighty-five years). Forty-six distinct pelvic osteolytic lesions were noted radiographically around the thirty-five cups. These lesions ranged in size from 0.5 by 0.5 centimeter to 6.3 by 2.7 centimeters (mean, 2.6 by 1.7 centimeters). Fourteen of the thirty-five patients had no or only slight occasional pain at the time of diagnosis of the pelvic osteolysis, fifteen patients had pain attributed to a loose femoral component, one had pain related to a spontaneous fracture of the greater trochanter, and one had pain related to recurrent subluxation. The remaining four patients had pain in the groin despite radiographically stable implants.All of the metal-backed porous-coated acetabular components were stable according to the preoperative radiographs, and the stability was confirmed at the time of the revision. The metal shell was left in place and the acetabular liner was exchanged in all thirty-five patients. The osteolytic lesions were debrided, and thirty-four of the forty-six lesions were filled with allograft bone chips.The patients were evaluated a minimum of two years (range, two to five years; mean, 3.3 years) after the revision operation, and all thirty-five sockets were found to be radiographically stable. The bone grafts appeared to have consolidated, and none of the osteolytic defects had progressed. One-third of the lesions were no longer visible on radiographs, regardless of whether or not they had been filled with bone graft. The remaining lesions had decreased in size.It appears that, in the short-term, exchange of the liner and débridement of the granuloma, with or without use of allograft bone chips in the osteolytic defect, is a reasonable alternative to revision of the socket provided that the metal shell is solidly fixed at the time of the revision operation. If the metal shell has been markedly damaged by the femoral head, the locking mechanism for the polyethylene liner is not intact, or a satisfactory replacement liner is not available, then revision of the porous-coated acetabular component is indicated.These results must be considered preliminary. Since osteolysis may take several years to redevelop after a revision, additional follow-up is required.
Osteolysis is now recognized as a common complication associated with total hip replacement performed without cement2-4,6-8. The process of osteolysis has been attributed to the biological reaction to wear debris, especially polyethylene. It has been reported in the femur and pelvis with increasing frequency as the duration of follow-up has increased2-4,6,7. The patterns of osteolysis or periprosthetic bone resorption in the pelvis differ according to whether the acetabular component was inserted with or without cement8. With cemented sockets, periprosthetic bone resorption occurs most commonly in a so-called linear manner, resulting in degradation of bone at the cement-bone interface and eventually loosening of the implant8. In contrast, osteolysis of the pelvis associated with well fixed porous-coated acetabular components inserted without cement is more commonly localized and expansile3,8. It is not often associated with loosening of the implant and can lead to extensive destruction of bone in the periacetabular region.
Since a porous-coated acetabular component can remain well fixed by ingrowth of bone despite severe osteolysis of the pelvis, the patient is often asymptomatic. As a result, there can be extensive loss of bone before the diagnosis is made. Our initial operative approach to this problem was to remove the acetabular component, fill the lesion in the pelvis with bone graft, and insert a new component.
Several important observations were made as a result of this early experience. Despite extensive loss of bone in the pelvis, the porous-coated acetabular component can remain rigidly fixed by so-called pods of bone. Removal of a stable shell often leads to destruction of these pods, further compromising the reconstruction. Similarly, removal of a socket stabilized by bone ingrowth can result in a defect of the medial wall of the acetabulum; extensive damage to the anterior and posterior columns; and, in some cases, pelvic discontinuity.
These problems led us to re-evaluate our approach to the treatment of pelvic osteolysis associated with a stable acetabular component inserted without cement. Thus, instead of revising the acetabular component, we removed the acetabular liner; debrided the osteolytic lesion; and, in some cases, packed allograft bone chips into the lesion. A new polyethylene liner was then inserted with the original metal shell left in place. The purpose of the present study was to evaluate the clinical and radiographic results of this approach.
*One or more of the authors has received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this article. In addition, benefits have been or will be directed to a research fund or foundation, educational institution, or other non-profit organization with which one or more of the authors is associated. No funds were received in support of this study.
†Department of Orthopaedic Surgery, Barnes-Jewish Hospital, One Barnes Hospital Plaza, Suite 11300, St. Louis, Missouri 63105.
‡University Hospital Professional Center I, Suite 8A, 820 St. Sebastian Way, Augusta, Georgia 30901-2668.
§Central Dupage Hospital, 25 North Winfield Road, Winfield, Illinois 60190.
#Department of Orthopaedic Surgery, University of Pittsburgh, Lilliane Kaufmann Building, 3471 5th Avenue, Suite 1010, Pittsburgh, Pennsylvania 15213.
**Anderson Orthopaedic Clinic, 2445 Army Navy Drive, 4th Floor, Arlington, Virginia 22206.
We retrospectively reviewed the records on 162 consecutive revision hip operations performed, between January 1991 and June 1994, to treat problems related to a porous-coated acetabular component that had been inserted without cement during a total hip arthroplasty. Thirty-five of these operations, in thirty-five patients, had been performed because radiographic evidence of pelvic osteolysis had developed. The revision consisted of exchange of the polyethylene liner; débridement of the osteolytic lesion; and, in some patients, bone-grafting. These thirty-five patients make up the study group for this report.
During the time-period of the present study, it was our routine not to remove a well fixed porous-coated acetabular component associated with pelvic osteolysis if the acetabular component had been designed to allow for replacement of the polyethylene liner and a replacement liner of adequate thickness was commercially available, if the locking mechanism for the polyethylene liner remained competent so that the replacement liner remained stable within the metal shell, if the metal shell itself had not been damaged by the femoral head, and if the acetabular component was positioned satisfactorily so that the reconstruction was stable from the standpoint of dislocation.
The twenty-three men and twelve women had a mean age of forty-nine years (range, twenty-nine to eighty-five years) at the time of the revision operation. The mean weight of the patients was seventy-nine kilograms (range, forty-eight to 127 kilograms). The diagnosis at the time of the primary hip replacement had been osteoarthrosis in twenty-three patients; avascular necrosis in five; congenital dysplasia of the hip in three; and Legg-Perthes disease, fusion, fracture, and previous infection in one patient each. The mean duration from the primary hip replacement to the revision operation was 5.5 years (range, one to ten years).
All anteroposterior pelvic radiographs and lateral radiographs of the hip that had been made preoperatively and at the time of the most recent follow-up were reviewed. An acetabular component was considered to be loose if there was a complete radiolucent line at the implant-bone interface or if the component had migrated, as assessed with the method of Massin et al. Vertical migration was determined by measurement of the distance from the interteardrop line to the center of the hip on serial radiographs. Horizontal migration was determined by measurement of the distance between the center of the hip and a vertical line drawn through the teardrop perpendicular to the interteardrop line. A difference of more than two millimeters on serial radiographs was considered evidence of loosening.
The location of the osteolytic lesions was recorded as the ilium, ischium, or pubis, or a combination of these. The approximate size of a lesion was determined by measuring its longest diameter and then measuring a second diameter perpendicular to the first diameter (Fig. 1). Measurements were performed with a pair of calipers and were recorded to the nearest 0.1 millimeter. Intraobserver variability was not assessed.
Regression or resolution of a lesion was determined according to several criteria, including loss of a distinct border between the lytic defect and pelvic bone, return of the bone density in the area of osteolysis to that of the surrounding bone, and development of a trabecular bone pattern in a region previously devoid of bone. The presence or absence of eccentricity of the femoral head within the socket was also noted on the preoperative radiograph. The final review of all of the radiographs was performed by one of us (W. J. M.).
At the time of the revision, a complete capsulectomy was performed and the hip was dislocated. The stability of the femoral component was assessed manually. If it was unstable, it was removed. If it was stable, it was mobilized to allow exposure of the acetabulum. Hypertrophied synovial tissue was debrided, and the acetabular liner was removed. The integrity of the locking mechanism was checked. The stability of the metal acetabular shell was confirmed with use of a clamp and manual pressure. If the metal shell was stable, the granulomatous tissue in the osteolytic lesions was debrided. The lesions in the ilium were accessed around the periphery of the acetabular component and, less commonly, through holes in the acetabular component. The granuloma was debrided as completely as possible; however, the inability to remove all of the tissue from the osteolytic lesion was not considered a contraindication to this procedure. The decision to use bone graft in the defect was made by the surgeon. Three of the four surgeons used bone graft in all of the lesions, and one surgeon did not use bone graft in any of the lesions. Allograft bone chips were packed into thirty-four lesions (twenty-six patients). The remaining twelve lesions (nine patients) were debrided but no graft was used. A new polyethylene liner was inserted, and the femoral head was downsized to allow for a thicker polyethylene liner if indicated. The hip was moved through a range of motion to document stability at the end of the operation.
The type of postoperative treatment depended on the type of operation that had been performed. For the patients who had had exchange of the liner only, with or without bone-grafting, full weight-bearing was permitted as tolerated, beginning on the first postoperative day. For the patients who also had had revision of the femoral component, protected weight-bearing with use of two crutches or a walker was recommended for six to twelve weeks after the operation, depending on the complexity of the femoral reconstruction.
Preoperatively and at the latest follow-up examination, the Harris hip score was determined on the basis of the clinical evaluation performed by the operating surgeon. All patients were followed for a minimum of two years (mean, 3.3 years; maximum, five years).
Radiographic Evaluation
All of the acetabular components appeared stable on evaluation of the preoperative radiographs. All but two of the femoral heads appeared eccentric within the metal shell, which is indicative of polyethylene wear. Forty-six distinct pelvic osteolytic lesions were noted radiographically in the thirty-five patients. Thirty-five lesions were in the ilium, eight were in the pubis, and three were in the ischium. All but two patients had at least one osteolytic lesion in the ilium. The cystic lesions appeared radiolucent and devoid of trabecular bone on the radiographs (Figs. 2-A, 2-B, 2-C, 2-D, 3-A, 3-B and 3-C). The margins of the lesions were well defined but were usually not sclerotic. The lesions extended into the cancellous bone of the ilium, ischium, and pubis and did not tend to track along the implant-bone interface.
The thirty-five lesions in the ilium ranged in size from 0.5 by 0.5 centimeter to 6.3 by 2.7 centimeters (mean, 2.4 by 1.7 centimeters). Twenty-three of these lesions were filled with bone graft and twelve were not. The mean size of the lesions that were filled with bone graft was 3.1 by 2.2 centimeters compared with 1.2 by 0.8 centimeter for those that were not filled. The eight lesions in the pubis ranged in size from 1.5 by 1.5 centimeters to 5.0 by 1.0 centimeters, with a mean size of 2.7 by 1.5 centimeters. In the ischium, the three lesions were 2.9 by 0.7 centimeters, 4.0 by 1.9 centimeters, and 4.8 by 3.4 centimeters, with a mean size of 3.9 by 2.0 centimeters. All of the lesions in the pubis and ischium were filled with bone graft.
At the most recent follow-up examination, all thirty-five acetabular components were still radiographically stable. No new osteolytic defects were identified. Eight of the twelve lesions that had not been filled with bone graft appeared to have regressed. The most recent radiographs showed that the border between the radiolucent cyst and the surrounding bone had become less distinct as the difference in density between the lesion and the surrounding bone disappeared (Fig. 3-C). The remaining four lesions that had not been filled with bone graft had resolved completely as determined on the radiographs.
Twenty-two (65 per cent) of the thirty-four lesions that had been filled with bone graft appeared to have regressed (Fig. 2-D). The remaining twelve (35 per cent) had resolved completely radiographically. In one lesion, the graft, which protruded lateral to the normal contour of the iliac wing, had been partially resorbed.
None of the osteolytic lesions increased in size after the operation, irrespective of whether or not they had been filled with bone graft.
Clinical Evaluation
Preoperatively, fourteen of the thirty-five patients had a score of either 40 or 44 points (of 44 points) for the pain in the hip, denoting a slight occasional ache or no pain. One patient had pain only when the hip subluxated, usually when he was rising from a chair; the pain score for this patient was 20 points. One patient had pain that was attributed to a spontaneous fracture of the greater trochanter through an osteolytic defect. By the time of the revision, the fracture had healed and the symptoms had resolved (a pain score of 44 points). In fifteen patients, who had a mean pain score of 18 points, the pain was attributed to a loose femoral component. The remaining four patients, who had a mean pain score of 23 points, had pain in the groin despite components that were seen to be stable both radiographically and at the revision.
The fourteen patients who had no or only slight pain preoperatively, and had only exchange of the acetabular liner, had no pain at the time of the most recent follow-up evaluation. The mean stay in the hospital for these fourteen patients was 3.5 days. They were allowed to bear full weight immediately and generally were able to walk without assistive devices by three weeks.
All four patients who had had pain in the groin preoperatively had less pain postoperatively; however, they were not pain-free. The pain score improved from 30 to 40 points in two patients, from 20 to 30 points in one, and from 10 to 30 points in one. The etiology of the persistent pain in two of these patients was unclear.
All of the patients who had a femoral revision in addition to exchange of the liner had a decrease in pain postoperatively. The mean pain score was 18 points (range, 0 to 30 points) preoperatively compared with 38 points (range, 30 to 44 points) postoperatively.
Rapid polyethylene wear and periarticular osteolysis were not frequently reported in association with all-polyethylene sockets inserted with cement in total hip arthroplasty. In contrast, the use of so-called first-generation porous-coated acetabular components without cement has resulted in an increased rate of polyethylene wear and an increased prevalence of osteolysis. Schmalzried et al. found so-called balloon-like pelvic osteolysis in 17 per cent (nineteen) of 113 hips with a porous-coated titanium acetabular component. The mean thickness of the polyethylene in that series was approximately five millimeters in the dome and 3.5 millimeters in the periphery of the socket. Schmalzried et al. also noted that loss of bone was not generally associated with pain. There was no difference between the clinical scores of the patients who had pelvic osteolysis and those of the patients who did not. One of us (W. J. M.) and colleagues3 reported on fourteen patients (fifteen hips) who had pelvic osteolysis in association with a variety of porous-coated acetabular components inserted without cement. The mean time to presentation was sixty-five months. Despite the destructive nature of the lesions, fourteen of the fifteen sockets were stable and eleven of the fourteen patients had a Harris hip score of more than 90 points.
Analysis of the presenting symptoms in the current series is instructive. As has been reported previously3, severe osteolysis can occur in the absence of clinical symptoms. Fourteen (40 per cent) of our thirty-five patients had no or only slight occasional pain in the hip at the time that the osteolysis and the polyethylene wear were noted. This finding emphasizes the need for postoperative surveillance of patients who have had a total hip replacement. Of the twenty-one patients who had pain before the revision, fifteen had an unstable femoral component, one had a spontaneous fracture of the greater trochanter, and one had pain related to subluxation. The remaining four patients had pain in the groin despite radiographically stable components. At the time of the revision, these four patients had marked synovitis of the hip, which may have caused the pain. When a patient has pain, it is important that other sources be sought, as polyethylene wear and osteolysis alone do not appear to cause pain.
The etiology of the osteolysis in the present study was a biological reaction to the high polyethylene particle load associated with rapid polyethylene wear. Proponents of acetabular revision for the treatment of this problem believe that complete débridement of the granuloma is essential in order to arrest this process. Our premise is that a sustained particle load is a more important variable driving the osteolytic process. As a result, we believed that replacement of the liner and elimination of the source of the high particle load was more important than removal of all of the granulation tissue from the osteolytic lesion. Leaving the metal shell in place prevented complete débridement of the granuloma because it was difficult to access the entire lesion. Despite this, none of the osteolytic defects continued to enlarge after the revision, thus supporting our hypothesis. Furthermore, one-third of the lesions resolved completely whether or not they had been filled with bone graft.
Since this is a relatively new problem, information regarding optimum operative treatment is lacking. The timing of the revision operation, the operative procedure of choice, and the expected outcome are still not known. As previously noted, our initial approach to this problem was to revise the acetabular component and to fill the defects with bone graft. This approach was re-evaluated when it became clear that removal of a well fixed acetabular component commonly resulted in additional loss of bone and, in some cases, pelvic fracture. In the present study, which included at least two years of follow-up, we showed that exchange of the liner and débridement of the osteolytic lesion, with or without bone-grafting, was a reliable alternative to revision of the socket. None of the acetabular components in our study loosened after the revision, and the osteolytic process appeared to be at least temporarily arrested by this procedure. Obviously, additional follow-up studies are needed to determine the long-term results of this procedure.
Several criteria must be met in order for this procedure to be successful. The metal shell must be stable at the revision operation. If it is unstable, the component should be revised. The acetabular component has to be modular or the manufacturer of the implant has to be willing to make a custom liner. This requires careful preoperative planning to determine the manufacturer and the exact style of the implant in place. Consultation with the manufacturer will help the surgeon to determine options for exchange of the liner. It is also important that the locking mechanism be intact and functioning so that the new liner is stable within the acetabular shell. If the locking mechanism is unstable, the component should be revised or, in some select cases, the liner can be cemented into the shell.
The acetabular shell should be of sufficient diameter to permit insertion of a polyethylene liner of adequate thickness. With modular femoral components, it may be possible to downsize the femoral head to allow for a thicker polyethylene liner. Again, consultation with the manufacturer of the implant will help to determine the options for downsizing of the femoral head. If the femoral component is non-modular and has a thirty-two-millimeter head and the acetabular component is relatively small, the liner may be only two to four millimeters thick. In this situation, the manufacturer may be unwilling to supply a replacement liner. If so, the acetabular component may need to be revised. If a replacement liner that is less than six millimeters thick is available, the surgeon needs to weigh factors, such as the age, activity level, medical condition, and life expectancy of the patient, to decide whether it is better to use a thin liner or to revise the component.
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