The Use of Structural Distal Femoral Allografts for Acetabular Reconstruction: Average Ten-Year Follow-Up

Sporer, Scott M. MD, MS; O'Rourke, Michael MD; Chong, Paul BS; Paprosky, Wayne G. MD

Journal of Bone & Joint Surgery - American Volume:
doi: 10.2106/JBJS.D.02099
Scientific Articles
Abstract

Background: Acetabular fixation during revision total hip arthroplasty in patients who have a nonsupportive superior dome and proximal migration of the acetabular component (a Paprosky Type-IIIa defect) cannot be achieved reliably with use of a hemispherical porous-coated component alone. The purposes of the present study were to determine the long-term results associated with the use of a porous-coated hemispherical acetabular component, supported with a distal femoral structural allograft, for revision at the site of a Type-IIIa defect and to determine if graft resorption leads to late failure.

Methods: Thirty-one patients who had an acetabular reconstruction with use of a distal femoral allograft for the treatment of a Type-IIIa defect between January 1985 and December 1990 were followed annually with clinical and radiographic evaluations. At the time of the latest follow-up, eight patients had died and one patient had been lost to follow-up. One of the patients who died had had a clinical failure at 4.5 years postoperatively and was included in the analysis. Therefore, twenty-three patients, who had had an average age of sixty-one years at the time of the index procedure, were evaluated at an average of 10.3 years postoperatively.

Results: Five acetabular components were re-revised because of aseptic loosening at an average of 5.3 years after the index procedure. Radiographically, all but one of the remaining components were stable and showed evidence of bone ingrowth. The average Merle D'Aubigné and Postel hip score improved from 5 points preoperatively to 10 points at the time of the latest follow-up. Allograft bone resorption, although difficult to quantitate, was observed around six of the seventeen stable components and around two of the five components that failed clinically.

Conclusions: Acetabular revision with use of a porous-coated acetabular component along with a structural distal femoral allograft for the treatment of a Type-IIIa defect demonstrated a high rate of clinical and radiographic success after an average of ten years of follow-up.

Level of Evidence: Therapeutic Level IV. See Instructions to Authors for a complete description of levels of evidence.

Author Information

1 Department of Orthopaedic Surgery, Rush University Medical Center, 25 North Winfield Road, Chicago, IL 60190. E-mail address for S.M. Sporer: ssporer@hotmail.com

2 University of Iowa Hospitals and Clinics, 200 Hawkins Drive, Iowa City, IA 52242

3 Vanderbilt University Medical School, 21st Avenue, Nashville, TN 37232

Article Outline

Despite the success of primary total hip arthroplasty, it tinues to account for 17% of all hip arthroplasty procedures performed in the United States Medicare population Dhas been reported that revision hip arthroplasty continues to account for 17% of all hip arthroplasty procedures performed in the United States Medicare population1. It is expected that the number of hip revisions and re-revisions will continue to increase and that the surgical complexity of these procedures will become greater as the indications for primary total hip arthroplasty broaden.

Severe acetabular bone loss can be encountered both in patients who have had multiple revision arthroplasties and in patients who have severe osteolysis. According to the system of Paprosky et al., the acetabulum is classified into one of three categories on the basis of the integrity of the Kohler line, osteolysis of the teardrop, osteolysis of the ischium, and the amount of acetabular component migration2,3. Type-IIIa defects are characterized by >3 cm of superior migration of the femoral component cephalad to the superior obturator line, moderate teardrop and ischial lysis, and an intact Kohler line. These defects are associated with a nonsupportive superior dome. The anterior and posterior columns remain intact, yet a hemispherical shell will have <50% host-bone contact. A high rate of failure has been noted when an unsupported porous-coated acetabular component has been inserted without an associated structural graft4,5. The high rate of failure is believed to be secondary to a lack of superior dome support with subsequent component micromotion and/or superolateral migration. Distal femoral allografts can be used to provide additional component support, and the early results associated with this method of reconstruction have been encouraging6. However, revascularization of the allograft with subsequent resorption has been reported7. The purposes of the present study were to determine the long-term results associated with the use of a porous-coated acetabular component, supported with a distal femoral structural allograft, for revision of a Type-IIIa acetabular defect and to determine if graft resorption leads to late failure.

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Materials and Methods

Following approval from the institutional review board, a retrospective clinical and radiographic review was performed for patients in whom a Type-IIIa defect had been treated with acetabular revision with use of a porous-coated hemispherical acetabular shell along with a structural distal femoral allograft (a so-called number-7 graft) between January 1985 and December 1990 at Central DuPage Hospital by the senior author (W.G.P.). Patients with metabolic bone disease or malignant disease as well as those who had had a primary procedure for the treatment of hip dysplasia were excluded from this review. This cohort represented an unselected series of patients because, during this time-period, the use of a hemispherical shell with structural support was the only surgical treatment performed for patients with Type-IIIa defects.

Between 1985 and 1990, thirty-one hips in thirty-one patients with a Type-IIIa acetabular defect were treated with a porous-coated hemispherical shell and a distal femoral allograft. Of these thirty-one patients, eight died and one was lost to follow-up. One of the patients who died had had a clinical failure at 4.5 years postoperatively and was included in the analysis. The other seven patients who died had a well-functioning implant at the time of death but were excluded from the analysis because they had not been followed for a minimum of seven years. Therefore, twenty-three patients were evaluated at an average of 10.3 years (range, seven to fifteen years) postoperatively. These patients included seven men and sixteen women with an average age of sixty-one years (range, thirty-seven to seventy-seven years) at the time of the index revision procedure. Twenty hips were revised because of aseptic acetabular loosening, and three were revised because of infection. The average size of the revision cup was 64 mm (range, 55 to 75 mm). The average number of previous surgical procedures was 3.2 (range, one to four).

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Surgical Technique

A posterior approach was used for all patients. The distal femoral allograft with the attached metaphysis was cut into the shape of the number 7. The anterior femoral groove and a portion of the metaphysis were positioned outside of the acetabulum, juxtaposed against the ilium. The remainder of the femoral condyle was placed inside the acetabulum to buttress the ilium. The allograft was rigidly fixed with several 6.5-mm cancellous-bone screws and washers (Figs. 1-A, 1-B, and 1-C). The condyles of the allograft were then reamed until the remains of the host anterior and posterior columns were engaged. The acetabular component consisted of a beaded porous-coated hemispherical shell (Solution or Arthropor II; DePuy, Warsaw, Indiana) that was inserted with two, three, or four screws for initial fixation. Postoperatively, all patients were placed in an abduction brace and were allowed only toe-touch weight-bearing on crutches for three months before being advanced to weight-bearing as tolerated.

The annual radiographic review consisted of standard anteroposterior radiographs of the pelvis, anteroposterior radiographs of the femur, and Lowenstein lateral radiographs. Radiographs that had been made preoperatively, immediately postoperatively, and at the time of the most recent follow-up were reviewed, and the findings were consensually agreed upon by two reviewers (S.M.S. and W.G.P.) (Figs. 2-A and 2-B). The preoperative anteroposterior radiographs were graded according to the acetabular defect classification system described by Bradford and Paprosky3. The most recent radiographs were compared with the initial postoperative radiographs. Loosening was defined radiographically as a change in the component abduction angle of >10° or a change in the horizontal or vertical position of >6 mm after correcting for magnification. Graft resorption was classified, according to the percentage of resorption on the final follow-up radiograph as compared with that on the immediate postoperative radiograph, as none (0%), mild (<25%), moderate (25% to 50%), or severe (>50%). Clinical evaluation was performed with use of the functional hip-grading scale described by Merle D'Aubigné and Postel8. This assessment instrument assigns a value ranging from 0 to 6 points in each of two categories (“pain” and “ability to walk”). A combined score of 10 points or greater indicates a good result, whereas a combined score of less than 7 points indicates a poor result.

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Results

Five acetabular components were re-revised because of aseptic loosening at 2.6, 3.0, 4.8, 7.6, and 8.7 years postoperatively. Therefore, the ten-year survival rate with re-revision because of aseptic acetabular loosening as the end point was 78% (95% confidence interval, 74% to 82%). All of the cups that were re-revised because of aseptic loosening demonstrated incorporation of the femoral allograft, and all of the acetabular defects that were present at the time of the re-revision were consistent with Type-II defects that were amenable to treatment with a porous hemispherical shell. The shells that were used at the time of re-revision ranged in size from 68 to 72 mm. Radiographic evidence of osseous ingrowth was observed in association with all of the remaining cups but one; the latter cup was in a hip that demonstrated radiographic signs of failure at the cup-graft interface at 2.6 years postoperatively. Therefore, the ten-year survival rate with radiographic signs of acetabular loosening as the end point was 74% (95% confidence interval, 70% to 78%).

Allograft resorption around intact stable shells was classified as “none” in eleven hips, “mild” in one, “moderate” in four, and “severe” in one. Allograft resorption around shells that were re-revised was classified as “none” in three hips, “mild” in one, and “severe” in one. Although extremely difficult to ascertain on the basis of anteroposterior pelvic radiographs alone, the estimated percentage of host-bone coverage as viewed on the anteroposterior pelvic radiographs averaged 42% for the stable shells and 43% for the shells that failed clinically.

Clinical evaluation of the patients who had an intact acetabular component demonstrated improvement of the average Merle D'Aubigne and Postel hip score from 5 points preoperatively to 10 points at the time of the latest follow-up. Ten patients required no assistive devices for walking, five patients used a cane for long walks, and two patients used a cane full time. Thirteen of the patients with a stable component had no pain, while the remaining four had mild exertional pain. The one patient with radiographic signs of loosening had a postoperative dislocation that required closed reduction. This patient had not had any additional episodes of instability at the time of the most recent follow-up.

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Discussion

Acetabular revision in the presence of extensive bone loss is challenging and technically demanding. Successful long-term results depend heavily on the achievement of intraoperative stability of the acetabular shell. Most acetabular revisions are associated with some degree of bone loss. The extent of bone loss and osteolysis often is underestimated on plain radiographs. Therefore, the surgeon must be comfortable with alternative surgical options when unexpected amounts of bone loss are encountered.

The acetabular classification system described by Bradford and Paprosky can be used to categorize the acetabulum into one of three different types in order to assist preoperative planning, to guide treatment options, and to standardize patient reporting3. Defects associated with minimal loss of bone and structural support (Paprosky Type-I and II defects) can be reconstructed with use of a hemispherical acetabular component with or without the use of nonstructural cancellous bone graft. Excellent long-term results have been reported in association with such treatment2,9.

Type-IIIa defects are characterized by severe bone loss with superior migration of the femoral component by >3 cm cephalad to the superior obturator line. Typically, osteolysis involving the teardrop and the ischium is moderate and the Kohler line remains intact. Poor results have been observed when a cementless hemispherical shell alone has been used to reconstruct this type of defect2,10. Options to provide initial stability for bone ingrowth include the use of a hemispherical shell augmented with a structural graft, the use of an implant that accommodates the deficient superior dome (a bilobed cup or a trabecular metal cup with augmentation), or the placement of the prosthesis in a high hip center9,11. We believe that restoration of bone stock is preferable, especially in a younger patient, if complications such as graft loosening, resorption, and infection can be minimized.

The senior author (W.G.P.) previously reported excellent intermediate-term results following acetabular reconstruction of Type-IIIa defects with the use of a distal femoral allograft and a porous hemispherical shell12. In that study, forty-eight patients were reviewed at an average of 6.1 years postoperatively and the survival rate was 94% with aseptic acetabular loosening as the end point. All of the radiographically stable implants demonstrated osseous ingrowth, with no evidence of resorption of the allograft. The current study documents the continued successful results for patients in this cohort at an average of ten years postoperatively. The five components that required revision because of aseptic loosening were converted to a hemispherical shell without the need for additional structural allograft support. Therefore, we believe that our grafting technique restores acetabular bone stock and can allow conversion of a Type-IIIa defect to a Type-II defect if subsequent revision is necessary.

Other authors have reported that the use of structural allograft provides reliable results when >50% host-bone support is present. Morsi et al. reported an 86% survival rate at seven years postoperatively in a study of twenty-nine patients who had been managed with a “shelf allograft” for the treatment of superolateral deficiency13. Woodgate et al. reported an 80.4% survival rate at ten years postoperatively in a study of fifty-one hips and concluded that good results can be achieved in association with the use of structural allograft, especially if there is restoration of nearly normal hip biomechanics14.

Poorer long-term results have been reported when bulk allografts have been used in patients with <50% host-bone support. Chandler et al., in a study of twenty-four hips that had been followed for an average of more than twelve years, reported a 26% rate of revision for aseptic loosening and a 41% rate of radiographic loosening and concluded that structural allografts are rarely indicated15. Similarly, Garbuz et al., in a study of thirty-three hips in which a structural allograft supported >50% of a cementless acetabular component, reported a clinical and radiographic success rate of 55% after an average duration of follow-up of seven years16. The authors concluded that the only clinically important factor was the method of fixation and recommended the use of a roof-reinforcement ring.

Alternatives for acetabular revision in patients with a deficient dome and superior migration (a Type-IIIa defect) include either the use of a bilobed implant or a trabecular metal acetabular component with a superiorly placed trabecular metal augment. The long-term clinical results of acetabular reconstruction performed with use of trabecular metal are currently unavailable, to our knowledge. However, this material appears to allow extensive bone ingrowth with high initial frictional resistance. These material properties ultimately may change the indications for the use of a monoblock acetabular component. In contrast, the intermediate-term results associated with bilobed acetabular components have been disappointing. These implants are used in an attempt to lower the hip center of rotation and to obtain fixation in both the true acetabulum and the ilium. Chen et al., in a study of thirty-seven hips, reported a 24% failure rate at an average of forty-one months postoperatively17. Because of these poor results, they have abandoned the use of this implant. On the basis of the successful results in the present series, the senior author (W.G.P.) continues to use a structural distal femoral allograft and a porous-coated acetabular component for the treatment of Type-IIIa acetabular defects in young patients who have associated bone loss involving the superior dome. ▪

A video supplement to this article is available from the Video Journal of Orthopaedics. A video clip is available at the JBJS web site, . The Video Journal of Orthopaedics can be contacted at (805) 962-3410, web site: .

The authors did not receive grants or outside funding in support of their research or preparation of this manuscript. One or more of the authors received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity (Zimmer). In addition, a commercial entity (Zimmer) paid or directed, or agreed to pay or direct, benefits to a research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

Investigation performed at Central DuPage Hospital, Winfield, Illinois

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