Abstract
The results of the placement of a massive structural acetabular allograft in conjunction with a revision total hip arthroplasty in thirty-two patients (thirty-three hips) were evaluated at a minimum of five years. The graft supported more than 50 per cent of the cup in all of the patients. The goals of a revision operation in a hip that has massive loss of bone are to provide support for the cup, to approximate the normal anatomy, to restore the length of the lower limb, and to restore bone stock should a future revision be necessary.Clinical and radiographic review at an average of seven years (range, five to eleven years) after the revision revealed that eighteen hips had needed no additional operation, seven hips had needed a repeat revision but the structural allograft was intact and had been used to support the cup at the repeat revision, and eight hips had had failure of both the prosthesis and the allograft. The result was considered a clinical and radiographic success when the hip score had increased at least 20 points, the cup was stable, the allograft had united, and no additional operation was necessary. According to these criteria, the rate of success was 55 per cent (eighteen of thirty-three hips). The only factor that was found to be clinically important with respect to outcome was the method of reconstruction. Seven of the eight hips that had been reconstructed with use of a roof-reinforcement ring and a structural allograft had a successful result at an average of 7.5 years (range, five to eleven years).The findings of the present study support the use of a structural allograft in the presence of massive loss of bone in order to achieve the goals of a revision hip replacement. Because of the high rate of success with acetabular reinforcement rings, we now use this method of reconstruction whenever a massive allograft is employed on the acetabular side.
Revision of the acetabular component of a total hip arthroplasty is a challenging problem, especially when there is severe loss of bone stock. The goals of a revision operation on the acetabular side are to provide support for the cup, to reapproximate the normal anatomy, and to restore the length of the lower limb. A structural allograft can be used to accomplish these goals. In addition, these grafts restore bone stock, a benefit should a future repeat revision be necessary.
The results of revision arthroplasty with a bulk allograft on the acetabular side have been mixed. High rates of failure have been reported5-7. In 1993, Kwong et al. noted failure in 47 per cent (fourteen) of thirty hips at an average of ten years postoperatively, and they advised against the use of structural grafts. The senior author (W. H. H.) of that report has advocated a high hip center for placement of the cup in patients who have severe loss of bone stock on the acetabular side14,15. In contrast, Paprosky et al. reported a low rate of failure of 19 per cent (six of thirty-one hips) at an average of 5.7 years (range, three to nine years) after revision operations performed with use of a major structural allograft10,11. Although there is controversy with regard to the success of structural allografts, most agree that the rate of failure definitely increases if more than 50 per cent of the cup is in contact with the structural graft5,6,11,12.
The purpose of the present study was to review the results in a group of patients who had an acetabular defect of a similar magnitude. All of the patients had a major columnar defect, meaning that they had loss of one column or both with a corresponding defect involving at least 50 per cent of the acetabular wall. Only patients who had been followed for at least five years were included.
*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article No funds were received in support of this study.
†Division of Orthopaedic Surgery, University of Toronto, Mount Sinai Hospital, 600 University Avenue, Suite 476A, Toronto, Ontario M5G 1X5, Canada.
‡Department of Orthopaedic Surgery, University of Menoufyia, Menoufyia, Egypt.
From 1983 through 1993, 302 acetabular revisions with an allograft were performed at our institution. Sixty-three revisions included a massive column allograft that supported at least 50 per cent of the cup for the treatment of a defect of one acetabular column or both. Forty-one hips in this group had been operated on at least five years before the time of the review. The acetabular defects were all non-contained and were type III or IV according to the classification of The American Academy of Orthopaedic Surgeons Committee on the Hip2. Because of the magnitude of the defect, treatment with morselized graft was not an option.
Four hips were lost to follow-up because the patients died less than five years after the revision, and four were lost because the patients could not be located. At the most recent evaluation (range, six months to three years) after the operation, none of the eight hips that were lost to follow-up had had clinical or radiographic failure. The thirty-two patients (thirty-three hips) who were followed clinically and radiographically for at least five years (average, seven years; range, five to eleven years) form the basis of the present study.
There were twelve men and twenty women. The average age at the time of the operation was sixty years (range, thirty-two to eighty-five years). All of the patients had had at least one previous hip replacement (average, 1.9 replacements; range, one to three). In addition, two of the patients had had a previous excision arthroplasty. The original diagnoses were congenital dysplasia of the hip (thirteen hips), osteoarthrosis (five hips), rheumatoid arthritis (five hips), post-traumatic osteoarthrosis (five hips), avascular necrosis (two hips), Legg-Perthes disease (two hips), and fibrosarcoma (one hip).
All of the patients were followed prospectively both clinically and radiographically. A modified Harris hip score was used for clinical assessment. The discrepancy between the lengths of the lower limbs was measured from the anterior superior iliac spine to the medial malleolus before and after the operation. The allografts were assessed radiographically for union, as evidenced by trabecular bridging of the host-graft interface; for fracture or fragmentation; and for the presence of radiolucent lines. Resorption of the allograft was measured, in both the vertical and the horizontal direction, on an anteroposterior radiograph of the pelvis that was made at the time of the most recent follow-up examination. It was then compared with the resorption that was measured on the immediate postoperative radiograph. It was graded as minor when less than one-third of the graft was resorbed, moderate when one-third to one-half of the graft was resorbed, and severe when more than one-half of the graft was resorbed3.
For the purpose of reporting our results, the patients were divided into three groups. The patients in Group 1 had a clinical success (an increase of at least 20 points in the hip score) as well as a radiographic success (a stable cup with a united, structurally intact allograft), and an additional operation was not necessary. The patients in Group 2 had a clinical failure because of a loose cup, but the graft had united and was intact. Subsequent repeat revision was successful, no additional graft was needed, and the original allograft was used in the new reconstruction. The patients in Group 3 had a clinical failure related to failure of the allograft (moderate or severe resorption, fragmentation, or non-union). Subsequent repeat revision involved use of additional graft or excision arthroplasty.
Operative Technique
We prefer a transtrochanteric approach for complex acetabular reconstructions. A Steinmann pin is inserted into the iliac crest as a reference point for the lengths of the lower limbs. After the hip has been dislocated, the acetabular prosthesis and cement are removed. The acetabulum is then cleared of any residual membrane or other soft tissue. The defect is assessed by visualization and palpation as well as with use of a trial cup. At this time, the decision is made regarding whether or not an allograft is needed and, if it is, whether the allograft should be structural or morselized.
Allograft bone is obtained from our bone bank, where it has been deep frozen at -70 degrees Celsius after irradiation with 2.5 megarad (25,000 gray). All or part of a whole acetabulum from a donor is used as the source of the graft material in all of our patients. The acetabular allograft is shaped to fit the defect and then is fixed to the host bone with two 4.5-millimeter malleolar screws or two 6.5-millimeter cancellous-bone screws with washers. The acetabulum is then reconstructed with use of various components. The femoral component is revised if necessary. Postoperatively, all patients are started on partial weight-bearing at three months and progress to full weight-bearing as tolerated during the next three months.
The components used in this series included fourteen all-polyethylene cups inserted with cement, eight roof-reinforcement rings with a polyethylene cup inserted with cement, seven cups inserted without cement, and four bipolar components. The femoral component was also revised in twenty hips.
At the most recent follow-up examination, seventeen patients (eighteen hips) had a clinical success (Group 1), seven patients (seven hips) had a clinical failure but the graft had united (Group 2), and eight patients (eight hips) had a clinical failure and the graft had failed (Group 3). The average hip score in Group 1 was 30 points (range, 12 to 60 points) preoperatively and 71 points (range, 52 to 88 points) at the most recent evaluation. The hip score had increased by at least 20 points for each of the patients in Group 1. Radiographically, all eighteen allografts had united to host bone. Fifteen allografts showed no resorption, and three allografts demonstrated minor lateral resorption.
In six of the seven hips in Group 2, the cup was loose at the time of the repeat revision but the allograft had united to host bone, was structurally intact, did not demonstrate any resorption, and had restored the host bone stock. The repeat revision was successful with use of this previous allograft. In the seventh hip, a second operation for exploration of the sciatic nerve was performed. The hip had been considered a clinical failure on the basis of a low hip score, which was primarily due to the persistent nerve palsy. The allograft had united to host bone and did not demonstrate resorption. The results for the patients in this group were considered a partial success. The duration between the index and repeat revisions averaged 4.6 years (range, 1.2 to 7.0 years).
The time to failure in the eight hips in Group 3 averaged 4.1 years (range, seven months to six years). Five of these hips needed an additional operation. Two of the five hips had complete resorption of the allograft, and a repeat revision was done. Two had fragmentation and non-union of the allograft had a repeat revision and the other, an excision arthroplasty. The fifth hip had a deep infection, and an excision arthroplasty was performed. Of the remaining three hips in Group 3, two were awaiting an additional revision operation because of major resorption of the graft and loosening of the acetabular component. The eighth hip, which had been reconstructed with a bipolar prosthesis, was doing well clinically but the allograft had completely resorbed.
The only factor that was important in determining the outcome was the method of acetabular reconstruction. Whether or not a femoral revision had been performed did not affect the outcome. Eight hips (seven patients) had had acetabular revision with use of a roof-reinforcement ring (Figs. 1-A, 1-B, and 1-C). One of these revisions failed because of infection, and an excision arthroplasty was performed. The remaining seven hips (six patients) were followed for an average of 7.5 years (range, five to eleven years). The average hip score was 29 points (range, 15 to 60 points) preoperatively and 73 points (range, 64 to 88 points) at the most recent examination. All seven allografts completely united to host bone and demonstrated no resorption. Thus, reconstruction with use of a roof-reinforcement ring and a bulk allograft had an over-all rate of success of seven of eight hips. The rate of failure for the hips in which an all-polyethylene cup had been inserted with cement was two of fourteen. For the hips in which a cup had been inserted without cement, the rate of failure was three of seven. For the hips in which a bipolar prosthesis had been used, the rate of failure was two of four.
A discrepancy between the lengths of the lower limbs was a major problem preoperatively, at which time it averaged 2.9 centimeters (range, one to six centimeters). At the time of the most recent examination, the limb-length discrepancy averaged 0.8 centimeter (range, zero to three centimeters). Preoperatively, five patients had a limb-length discrepancy of less than two centimeters and twenty-seven patients had one of more than two centimeters. At the most recent examination, twenty-five patients had a limb-length discrepancy of less than two centimeters and only seven patients had one of more than two centimeters.
The complications in the present series included deep infection (one patient), superficial infection (one patient), sciatic-nerve palsy (one patient), and pulmonary embolism (one patient). All of the complications resolved with non-operative treatment with the exception of the nerve palsy, which persisted.
Revision of the acetabular side of a total hip arthroplasty in the presence of severe loss of bone stock is a very difficult reconstructive problem. Although the use of a structural graft restores bone stock and allows reconstruction of the acetabulum at the correct anatomical level, the procedure continues to be controversial. In 1990, Jasty and Harris supported the use of structural allografts. In 1993, Kwong et al. cautioned against the use of bulk allografts in revision operations, reporting a rate of failure of 47 per cent (fourteen of thirty hips) at a ten-year review. They recommended that bulk allografts be employed only in an extreme salvage procedure when the only other option is resection arthroplasty. Russotti and Harris as well as Schutzer and Harris advocated placement of the acetabular component at a high hip center at the time of revision.
Paprosky et al.10,11 reported a low rate of failure of 19 per cent (six of thirty-one hips) at an average of 5.7 years after the use of major bulk allografts. The only failures in that entire series of allografts were in hips in which the allograft supported more than 50 per cent of the cup. In a study of twenty-seven patients, Hooten et al. noted an increase in the rate of failure when the graft supported more than 50 per cent of the host bone. In both series, the acetabulum was reconstructed with a cup inserted without cement. Although the results of revisions with allograft continue to be controversial, the use of structural allografts has been found to restore bone stock and to facilitate a future revision5-7,10,12. The purpose of our study was to review the mid-term to long-term results of acetabular revisions with use of a massive allograft.
In another study, we found a rate of success of 86 per cent (twenty-five of twenty-nine hips) 7.1 years after the use of a minor structural column allograft (an allograft that supported less than 50 per cent of the cup)9. The present series included thirty-three hips that had a major, non-contained defect of an acetabular column that involved more than 50 per cent of the acetabulum. In hips that have a severe deficiency of the acetabular bone stock, a large bulk allograft that supports more than 50 per cent of the cup is necessary to reconstruct the acetabulum at the correct anatomical level. In a recent report, Lawrence et al. reasoned that a repeat revision does not mean failure of the index operation. We agree, especially with regard to complex revisions that involve use of a structural graft. Pollock and Whiteside stated that this type of reconstruction can be considered successful if bone stock is restored for future operations. On the basis of this reasoning, we divided our results into three groups and found that the over-all rate of success in our series was 76 per cent (twenty-five of thirty-three hips). Eighteen (55 per cent) of the thirty-three hips were in Group 1. These hips had a successful result and had had no additional operations at an average of seven years. Seven (21 per cent) of the thirty-three hips were in Group 2 and had a successful repeat revision at an average of 4.6 years after the index revision. The high rate of success in the present series supports the use of structural allografts in revision operations on the acetabulum.
High placement of the cup to avoid the use of a structural graft would have been possible in some of the patients in our series because there was adequate host bone to seat the cup. However, it would not have been an option in many others because of deficient bone stock. The advantages of the use of a structural allograft, as opposed to a high hip center, are placement of the cup at the correct anatomical level, restoration of bone stock, and restoration of the length of the lower limb. The present report demonstrates that these advantages can be achieved. Placement of the cup at the correct anatomical level appears to decrease the risk of impingement and dislocation. None of our patients sustained a dislocation, in contrast to the findings of Schutzer and Harris, who reported a rate of dislocation or subluxation of 11 per cent (six of fifty-six hips in fifty-one patients). Twenty-seven patients in the present series had a preoperative limb-length discrepancy of more than two centimeters, and only seven patients had a limb-length discrepancy of more than two centimeters postoperatively.
Various methods of reconstruction in conjunction with bulk allografts have been described in the literature4-6,10,11. In the present series, the use of a reconstruction ring with a cup inserted with cement was uniformly successful. The ring allows contact with viable host bone and therefore partially protects the graft from excessive forces. The use of a reconstruction ring in revision operations has been supported by three previous studies1,13,16. Because of the high rate of success with this device in our series (the only failure was due to infection), it is now our reconstruction method of choice when a major acetabular column graft is needed.
Revision of an acetabular component in the presence of severe loss of bone stock is a major problem. The findings of the present report, in which the average duration of follow-up was seven years, support the use of a structural graft to reconstruct the deficient acetabulum. When the graft supports more than 50 per cent of the cup, we advocate the use of a reconstruction ring and a cup inserted with cement. The use of a structural graft allows the correct placement of the cup, restoration of the length of the limb, and restoration of bone stock for future revision operations. The longer-term results (at more than ten years) in our series are not yet known. Therefore, in view of the high rate of failure in a report with a longer duration of follow-up7, our results should be considered encouraging but preliminary.
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