Failure of the acetabular component in total hip arthroplasty (THA) frequently is associated with lytic lesions.24 The resulting defects may be a challenge during revision as the stability of the new acetabular socket requires adequate mechanical support.11,13,14,51 The rates of mechanical failure with the use of cemented cups in acetabular revisions have been high, with reported failure rates between 17% and 93% at 2 to 8 years followup in large series (greater than 50 patients).8,19,30,36,37 The results of revision with threaded acetabular components and bipolar implants also have been less than satisfactory.1,2,5,9,12
During the past decade, bone grafting has emerged as a common technique for prosthetic acetabular reconstruction.13,21,23 Structural grafts may be used for rim defects that are not well contained.14 However, cavitary defects and linear lesions associated with intact rims seem to be amenable to impacted morselized bone grafts.45,51 The results for acetabular osteolysis associated with stable components that are left in situ are promising although preliminary.35 To our knowledge, there are no reports specifically addressing the fate of morselized bone grafts in revised cementless acetabular sockets. The purpose of the current study was to evaluate the 5- to 10-year radiographic results of morselized bone grafting of acetabular osteolysis at revision with cementless components. The clinical results and complication rates also were analyzed to determine whether they correlate to the radiographic results.
MATERIALS AND METHODS
A review of our database for all revision hip arthroplasties was used to identify patients who had revision hip arthroplasty with bone grafting. This was incorporated into an Institutional Review Board protocol to review the outcomes of morselized bone grafting in acetabular revisions. From July 1, 1991 to December 31, 1995, 134 acetabular revisions using cementless components and morselized bone grafting were done. Informed consent was obtained from all patients. Clinical data on all patients were recorded before surgery and at regular intervals after the revision surgery by the two senior authors (MAM, DSH). The mean followup was 85 months (range, 60–118 months) after the revision procedure.
At the last followup, 16 patients (19 hips) had died from causes unrelated to the index revision surgery and 15 patients (16 hips) were not available for followup. Ten of these 31 patients (11 hips) had adequate followup to satisfy the minimum 60 months inclusion criterion to be included in the current study. Complete data were available for 108 revision arthroplasties in 99 patients. There were 44 men and 55 women with a mean age of 66 years (range, 39–93 years) at the time of the index revision. The primary diagnoses at the time of the primary hip replacement were osteoarthritis (OA) in 48 hips; osteonecrosis (ON) in 22 hips; rheumatoid arthritis (RA) in 16 hips; developmental dysplasia in 12 hips; posttraumatic degenerative joint disease in seven hips; and ankylosing spondylitis, Gaucher’s disease, and pigmented villonodular synovitis in one hip each.
The Harris hip score was used for evaluation of clinical results. A score between 90 and 100 points was considered excellent. Scores between 80 and 89 points were rated good. Excellent and good clinical results were considered successes. Harris hip scores between 70 and 79 points were classified as fair and scores less than 70 points were poor. Fair and poor results were considered clinical failures. In addition, levels of activities of daily living were recorded. The preoperative Harris hip scores ranged from 12 to 93 points with a mean of 37 points. Seventy hips had Harris hip scores less than 70 points whereas 30 hips had between 70 and 79 points. Seven hips had scores between 80 and 89 points. One patient had a Harris hip score of 93 points. This patient was functional with mild pain. However, the size and progression of the osteolytic lesions were used as indications for surgical intervention in this patient and in the eight patients with scores between 80 and 89 points. At the time of preoperative evaluation, eight patients (eight hips) still participated in some outdoor activities of daily living. Twenty-nine patients (30 hips) were able to do only indoor activities of daily living. Fifty-eight patients (63 hips) were restricted to their self-care activities of daily living, whereas four patients (seven hips) were totally dependent, requiring assistance in all activities of daily living.
Radiographic evaluation was done by the two senior authors (MAM, DSH) using standard anteroposterior (AP) views obtained preoperatively and at regular intervals during the followup (Table 1). An original analysis also included lateral films, but these radiographs were less reliable for evaluation, and the results were not different for classifying the lesions when the analysis used only AP films. The osteolytic lesions were recorded according to the zonal system of DeLee and Charnley.15 Migration was evaluated by Dorr’s technique,16 and lateral opening was measured by Callaghan’s method.7 Thirty-nine hips (36%) had preoperative migration ranging from 1 to 20 mm with a mean of 7.4 mm. The mean lateral opening was 56° (range, 15° –80°). Thirty-six of the primary acetabulae were inserted with cement fixation. Sixty-three of the 72 cementless primary cups had been press-fit without screws. Adjuvant screw fixation was used in nine hips: four had one screw; three had two screws; and two had three screws. There were 76 cavitary lesions in all three zones, averaging 252.5 mm2 on AP radiographs. There were 49 defects in Zone 1, ranging from 60 to 800 mm2 (mean, 235.6 mm2). Zone 2 had only four cavitary defects (mean, 225 mm2; range, 50–300 mm2). The 23 cavitary defects in Zone 3 averaged 297 mm2 (range, 50–750 mm2). In addition, there were 39 linear radiolucencies in Zone 1, 71 in Zone 2, and 61 in Zone 3. The Zone 1 linear lesions ranged from 5 to 10 mm (mean, 6 mm). The preoperative radiolucencies in Zone 2 had a mean of 7 mm (range, 5–15 mm). Those in Zone 3 ranged from 5 to 20 mm (mean, 8 mm; Table 1). Fifty-eight hips (54%) had complete osteolysis around the cups: 27 had continuous linear lucencies in all three zones; five had continuous lucencies in Zones 1 and 2 combined with cavitary defects in Zone 3; 26 had continuous linear osteolysis in Zones 2 and 3, associated with cavitary lesions in Zone 1. The other 11 hips (10%) were revised because of progressive osteolysis associated with wear and a painful hip.
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Table 1: Radiographic Data
Followup radiographs were evaluated for radiographic incorporation of morselized bone graft by assessing trabecular remodeling and the characterization of radiolucent lines. Cup position and migration also were evaluated.
Operative Procedure
All the acetabular components were revised as an inclusion criterion in this series. All of the revision procedures were done through an anterolateral approach. The reconstructive technique included debridement of soft tissues with removal of granulomata in the lytic lesions. All cement was removed in the cemented primary acetabulae. The acetabulae then were reamed using a technique of underreaming by 1 to 3 mm depending on the quality of the host bone. Morselized cancellous bone graft was obtained from fresh-frozen femoral head allograft using small acetabular reamers to obtain cancellous bone. The defects were addressed by tightly packed placement of morselized bone graft into the acetabulum. Additional impaction was obtained by reverse reaming. None of the hips had uncontained defects or column deficiencies. A trial shell that was 1 mm undersized to the final component was used to evaluate the acetabular preparation. No cement fixation was used in the revised acetabulae. After insertion of the final cup, intrinsic stability was assessed to determine whether adjuvant screw fixation was necessary. Eighteen revised hips had one screw augmenting the fixation; 19 had two screws; and two had three screws. The femoral stem was examined and loose stems were changed, whereas stable ones were preserved. Eighteen femoral components were changed in this series. All of the loose femoral stems were in patients with loose acetabular components. Most femoral heads were exchanged with 87 hips revised to 28-mm heads and 14 hips revised to 22-mm heads. There were seven monoblock femoral components left in situ. The mean operative time, excluding induction of anesthesia, was 2.1 hours (range, 1.5–3 hours). The mean estimated blood loss was 1476 mL (range, 400–3800 mL).
Postoperatively, the patients were allowed 20% weightbearing on the surgically treated extremity for the first 6 weeks using two crutches or a walker. They then were advanced to 50% weightbearing for an additional 6 weeks with a crutch or a cane in the opposite hand. Full weightbearing without ambulatory aids was permitted by 12 weeks.
RESULTS
At the latest followup, the mean Harris hip score was 91 points (range, 31–100 points). The mean improvement in the Harris hip scores was 54 points (range, 6–68 points). Nineteen hips had Harris hip scores greater than 90 points whereas 84 had scores between 80 and 89 points. Therefore, 103 hips (95%) had good or excellent clinical results. Three hips were rated between 70 and 79 points and two patients (two hips) had scores less than 70 points.
The levels of activities of daily living improved for 26 patients (28 hips) participating in some sports with little stress on the hip such as golf or bowling. Sixty-three patients (66 hips) improved from limited self-care and/or indoor activities of daily living to outdoor activities of daily living. Five patients (nine hips) were restricted to indoor activities of daily living whereas four patients (four hips) only could do self-care activities of daily living comfortably. One patient (one hip) was wheelchair-bound and totally dependent secondary to a cerebrovascular accident.
No cup was observed to have migrated at the latest followup. The mean lateral opening was 50° (range, 15°–65°). There were only three osteolytic defects at final followup: two in Zone 1 and one in Zone 3. The two lesions in Zone 1 (16 mm2 and 100 mm2) resulted from failure of the graft to incorporate. The Zone 3 defect (25 mm2) was new and already visible on the 2-year followup radiographs. In addition, there were 35 linear radiolucencies measuring 0.5 to 3 mm (mean, 1.2 mm). The zonal distributions were as follows: 11 radiolucent lines in Zone 1 (range, 0.5–2 mm; mean, 0.9 mm); eight radiolucent lines in Zone 2 (range, 0.5–3 mm; mean, 1 mm); and 16 radiolucent lines in Zone 3 (range, 0.5–2 mm; mean, 1.6 mm). All of these radiolucent lines were seen on the immediate postoperative radiographs, and they were not progressive at periodic radiographic examinations. There were no cups with complete radiolucencies in all three zones (Table 1). Heterotopic ossification was a common finding. Although no surgical treatment was required, 26 hips had radiographic evidence of heterotopic ossification.6 Nine hips were graded as having heterotopic ossification Grade 1; 13 were classified as having heterotopic ossification Grade 2; and four had heterotopic ossification Grade 3. Ten patients had preoperative heterotopic ossification that was treated with prophylactic radiotherapy with a single dose of 700 rad.
There were four dislocations, of which two occurred within 12 weeks of the index revision and were treated nonoperatively with an abduction brace after reduction. The other two hips dislocated after 2 years (27 and 31 months) and were treated with locked liners after failure of nonoperative therapy. At the time or revision, the cups were stable with apparent reconstitution of bone stock as checked through screw holes. Histologic analysis was not done. The bone grafts were fully incorporated radiographically in all four acetabulae at the latest followup. All four patients currently do outdoor activities of daily living and had Harris hip scores of 86, 87, 90, and 93 points at 5-, 5-, 7-, and 8 years followup, respectively. There were three late hematogenous infections at 73, 80, and 90 months after the index revision. These infections were treated by a two-stage approach. No additional bone grafting was necessary at the reimplantation stage. The incorporated grafts provided better support than that found at the index revision in all of these cases. One of these three patients reported constant moderate to severe pain at rest resulting in a Harris hip score of 31 points at 3 years followup. The other two patients were functioning well with Harris hip scores of 88 and 90 points at 3 and 4 years after reimplantation. An intraoperative femur fracture occurred during a femoral stem revision. This was treated with a strut graft and cables and healed uneventfully. The patient currently is doing well with a Harris hip score of 89 points 8 years after the revision surgery.
No revision of the acetabular components was done because of aseptic loosening after the index surgery. One patient had a traumatic medial wall fracture secondary to a motor vehicle accident. She had revision surgery at another institution.
DISCUSSION
The treatment of acetabular defects during revision THR is a challenge. Based on multiple reports, it has been determined that cemented components are not the optimal treatment method for acetabular osteolysis at revision.4,8,19,22,36,37,46,47 The lack of good mechanical support and the sclerotic or nontrabecular nature of the defects are not satisfactory conditions for cement fixation. Kavanagh et al30 reported a 53% loosening rate in 166 hips at an average 4.5 years followup. The failure rate was 100% for patients who had multiple revisions. Others have reported equally disappointing results ranging from 17% to 93% failure rates at 2 to 14 years8,19,36,37,46,47 (Table 2). The use of threaded cups also has multiple reports of high failure rates1,9,12,26,39,56 (Table 3). Bipolar prostheses yielded equally poor results at short-term followup5,8,10,55 (Table 3). The rationale for bipolar acetabular components is to preserve the acetabulum with motion occurring within the bipolar femoral head.31,34,38,54 A proposed additional benefit is the lower tendency to dislocate. Although the bipolar implant has gained popularity in fracture treatment,2 the results in revision situations have been unsatisfactory. Studies by Scott et al,55 Oakeshott et al,42 Wilson et al,59 and Emerson et al18 suggest that morselized bone grafts behave poorly with a bipolar implant. Mechanisms for graft failure in association with bipolar implants have included fragmentation, mechanical graft failure, and erosion of the outer shell.18 Numerous authors have concluded that bipolar implants are the last choice and only should be considered as a salvage procedure for cases with deficient abductors and adequate bony support.5,9,18,36,41,43,50
Table 2: Results of Cemented Acetabular Revisions
Table 3: Results of Threaded Cups and Bipolar Endoprostheses
Cementless revision was popularized to avoid the abnormal tissue reaction to the cement.28 Hedley et al27 evaluated 61 cementless acetabular revisions done for infection and mechanical failure. Although 67.4% of these cases had radiolucencies at the bone-implant interface, they reported 91.8% excellent or good results at a mean of 21 months followup (range, 15–30 months). Engh et al20 reviewed 34 cementless acetabular revisions and, at a mean of 4.4 years, one cup was considered loose. Similarly, low loosening rates (2–8%) were duplicated by numerous authors in series of 40 to 200 patients followed up for 4 to 8 years (Table 4).17,25–27,29,32,33,36,40,44,57,58 All of the aforementioned reports included sockets revised without bone graft. Therefore, they did not specifically address the fate of morselized bone graft. Maloney et al35 reported on stable cementless acetabular components that were left in situ. Their study differs from the current study in which all the failed acetabulae were revised and there were significant bone defects to warrant the use of morselized allografts in all cases.
Table 4: Results of Cementless Acetabular Revisions
Numerous authors have described the use of morselized bone grafting in revision hip replacement (Table 5).3,4,48,52,53,60 Some surgeons have combined structural grafts with antiprotrusio ring reinforcements with cemented liners in addition to the morselized allograft.3,52 Only two of the reports3,60 had small subsets of patients (n = 38 and 26) treated with morselized bone grafts and cementless cups. These two reports were favorable for this treatment approach and compared similarly with the 98% clinical and radiographic success rate in the current study. We are encouraged by this treatment method for contained acetabular defects at revision hip surgery.
Table 5: Reports Addressing the Fate of Bone Graft
An assessment of interobserver and intraobserver reliability was made to reduce the possibility of error in radiographic interpretation. The intraobserver reliability of the two surgeons (DSH, MAM) was excellent, with agreement in all cases. The interobserver agreement was an exact match in 95% of cases. Both authors independently evaluated the radiographs to minimize interobserver and intraobserver variability. If there was a discrepancy, a third author (GE) interpreted the radiographs until a unanimous decision was made concerning the radiographic interpretation.
A limitation of this study includes the limited ability of standard radiographs to assess size of osteolytic lesions. The size and location of these lesions can better be delineated by CT scanning49 which was not used in our study. However, all of the lesions were treated successfully with morselized bone graft and did not require structural allografts. Patients who required structural allografts or other methods of treatment (protrusio rings) with large, noncavitary defects or unstable acetabulae were not included in this study.
Only two of the 108 cavitary defects had failure of incorporation of the grafts. This represents a 98% incorporation rate for the cavitary lesions. Thirty-five radiolucent lines, seen in the immediate postoperative period, still were present at the latest followup. However, they all decreased in size owing to at least partial incorporation. These radiolucent lines measured an average of 1.2 mm at followup versus 7 mm on the preoperative radiographs. No cups had complete radiolucencies around the entire prostheses at the latest followup. Furthermore, the revisions were not done because of failure of radiographic graft incorporation. All the grafts were fully incorporated in the six hips that had revision.
The results of this study confirmed the success of morselized bone grafting in the treatment of acetabular lesions at revision surgery. As more primary hip arthroplasties are being done, the number of revision hip arthroplasties will continue to increase. Periprosthetic bone loss as the result of osteolysis remains a challenge to the revision hip surgeon. Morselized bone graft may be a useful adjunct in cementless acetabular revisions as a means of dealing with cavitary bone loss.
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