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Reconstruction of Major Segmental Acetabular Defects with an Oblong-Shaped Cementless Prosthesis
The Journal of Arthroplasty Vol. 23 No. 2 2008
Reconstruction of Major Segmental Acetabular Defects with an Oblong-Shaped Cementless Prosthesis A Long-Term Outcomes Study Paul N. Abeyta, MD,* Robert S. Namba, MD,y George V. Janku, MD,z William R. Murray, MD,* and Hubert T. Kim, MD, PhD*
Abstract: A retrospective outcomes study was performed on 25 consecutive acetabular reconstructions of major segmental defects by using an oblong-shaped cementless implant. All patients had combined acetabular defects (type III) as defined by the American Academy of Orthopaedic Surgeons classification of acetabular bone deficiency. Long-term follow-up was performed at an average of 11 years postoperatively. Clinical and radiographic outcomes were measured. Failures were defined by component revision or clear radiographic evidence of loosening. Six patients died before final evaluation, and 4 patients did not have complete radiographic data, leaving 14 patients (15 hips) for final analysis. At final follow-up, only 3 of the implants had failed and were revised. There was 1 case of a well-functioning implant with circumferential radiolucency; otherwise, there was no evidence of loosening among the remaining implants. Key words: acetabular, segmental, defect, oblong, cementless. n 2008 Elsevier Inc. All rights reserved.
joint rotation. The limited anterior-posterior dimension of the pelvis may preclude use of oversized conventional cementless cups in large segmental defects [6], particularly those involving the superolateral region of the acetabulum. For acetabular reconstruction in the presence of large bone deficits, several methods have been advocated. Structural allografting facilitates restoration of bone stock to allow anatomic placement of acetabular implants [7-13]. However, limited contact between the implant’s porous coating and living bone with ingrowth capacity compromises the effectiveness of cementless fixation. Even when the fixation is adequate, subsequent graft resorption and implant loosening have been described [14-18]. Placement of a high hip center for management of deficient supra-acetabular bone requires the use of small cementless acetabular components and special extended-neck femoral
Total hip arthroplasty (THA) in the presence of major segmental acetabular defects remains a difficult surgical challenge. Failed acetabular components with small cavitary bone defects can be revised with particulate bone grafting and conventional hemispherical cementless implants [1-5]. For small cavitary defects, reliable fixation can be achieved with minimal alteration of the center of
From the *Department of Orthopaedic Surgery, University of California, San Francisco; yDepartment of Orthopaedic Surgery, Kaiser Permanente Hospital, Orange County; and zDepartment of Orthopaedic Surgery, Kaiser Permanente Hospital, San Francisco. Submitted April 29, 2006; accepted January 28, 2007. No benefits or funds were received in support of the study. Reprint requests: Paul N. Abeyta, MD, Department of Orthopaedic Surgery, 500 Parnassus Ave, MU-320W, University of California, San Francisco, San Francisco, CA 94143-0728. n 2008 Elsevier Inc. All rights reserved. 0883-5403/08/2302-0015$34.00/0 doi:10.1016/j.arth.2007.01.024
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248 The Journal of Arthroplasty Vol. 23 No. 2 February 2008 components [19,4,20]. Femoral and acetabular component loosening may be associated with high hip centers [21,22]. More recently, trabecular metal implants have been introduced, but longterm data are still lacking [23]. Eccentric or oblong-shaped acetabular implants offer another means of managing large bone deficits and have several advantages [24,25]. These devices allow the surgeon to fill large defects with metal, thus avoiding the potential complications of bone graft fracture and resorption. The eccentric shape permits filling of defects and restoration of the joint center of rotation without bulky anterior and posterior projections. The augmented metallic region increases the area of contact between the porous coating and viable bone, thus enhancing the opportunity for cementless fixation. A recent study has suggested increased failure rates in those cases where the medial wall is not intact, which may be a limitation of the component [26]. The purpose of this study was to assess long-term results of using an oblong-shaped, cementless acetabular component for reconstruction of major acetabular defects and to identify any factors that may influence clinical and radiographic outcomes.
Materials and Methods This series consisted of 25 consecutive cases, performed between October 1992 and October 1993, of complex acetabular reconstructions using a porous-coated oblong-shaped acetabular implant (S-ROM Oblong Cup, Johnson & Johnson, Raynam, Mass) (Fig. 1). The oblong shape is more accurately described as 2 overlapping hemispheres.
Fig. 1. Oblong prosthesis, SROM (Johnson & Johnson, Depuy). Photo courtesy of Johnson & Johnson, Depuy.
Two designs are available and are distinguished primarily by the offset of the 2 hemispheres. The smaller (E15) implants have 15 mm of offset and 158 of adduction between the hemispheres. The larger (E25) implants have 25 mm of offset, 208 of adduction, and 158 of anteversion between the hemispheres. The smaller implant (E15 design) was used in 10 cases, and the larger configuration (E25 design) was used in 15 reconstructions. All the surgeries were performed at a single institution by 2 experienced hip surgeons. The average age of the patients (7 men and 16 women) was 59.5 years (range, 31-80 years). Two patients underwent bilateral hip surgeries as staged procedures. The oblong cup was used for revision of aseptically loosened primary THA in 17 cases, for revision of aseptically loosened, previously revised hips in 6 cases, and as a primary prosthesis in 2 cases (Fig. 2A, B). The revisions were performed at an average of 14.7 years (range, 1-23 years) after the prior reconstruction. A revision of the femoral component was performed in 19 cases at the time of oblong cup implantation. The primary THA cases were performed in 1 patient with massive destruction of the acetabulum due to rheumatoid arthritis, and in 1 patient with severe hip dysplasia. A constrained acetabular liner was used in 9 cases for instability determined intraoperatively. The oblong acetabular components were implanted following the manufacturer’s guidelines. In brief, a standard hemispherical reamer was used to create the inferior portion of the socket, reestablishing the native hip center. A special offset reamer was then seated in the inferior portion of the socket such that the cutting component of the reamer would create the superior portion of the socket. An offset reamer is used to prepare the defect cavity to match the contours of the oblong cavity. The amount of bone reamed is dependent on the encountered size and shape of the existing defect. Cup fixation was always supplemented with multiple screws. Bone defects were assessed on preoperative radiographs and intraoperatively in all cases and recorded according to the American Academy of Orthopaedic Surgeons classification of acetabular defects [27]. Postoperative radiographic evaluation included measurement of the height of joint center with respect to the interteardrop line, with values compared with the contralateral hip joint. The horizontal inclination of the true acetabular face on anteroposterior (AP) radiographs was determined with reference to the interteardrop line. Radiolucencies at the prosthetic-bone interface were recorded for immediate postoperative
Reconstruction Oblong Prosthesis ! Abeyta et al 249
and final follow-up AP radiographs. A modification of the Delee and Charnley classification of acetabular demarcations was required to account for the augmented implant. Zone I (lateral third) represented the elliptical extension of the hemisphere. The remaining hemispheric segment was divided in half and designated zones II (middle segment) and III (medial segment). Lack of reproducibility between serial radiographs of Smith-Peterson views precluded adequate analysis of lateral projections. An implant was considered to have failed if acetabular revision was performed or if follow-up radiographs showed definitive evidence of loosening. Clinical assessment included physical examinations and patient questionnaires performed preoperatively and at final follow-up examination. Harris hip scores were calculated based upon these data. Clinical outcomes data were collected prospectively for the first 18 cases. Some clinical data for the final 7 patients in the series were obtained retrospectively from their medical records. Statistical analysis was performed by using Fisher exact test. All data were collected with institutional review board approval.
found the cup to be solidly fixed. The liner was replaced with a new constrained liner and no further dislocations occurred. A second case was complicated by a single posterior dislocation 4 weeks postoperatively and was managed with closed reduction and an abduction brace for 6 weeks. Instability did not recur in this patient. A third case was complicated by a deep infection with Staphylococcus aureus diagnosed 6 weeks postoperatively and was managed with debridement, intravenous antibiotics, placement of antibioticimpregnated methylmethacrylate beads, and implant retention. The implant remained intact without evidence of loosening at final follow-up. Over the entire study period, only 3 of the oblong components failed, requiring revision. The first failed at 3 years postoperatively in a 69-year-old
Results All cases involved major segmental defects of the superior acetabulum. All cases had additional defects in another region (ie, anterior, posterior, or medial segmental defects) and were therefore classified as type III deficiencies [27]. A protrusio (cavitary medial wall defect) was present in 13 cases. There were no cases of pelvic discontinuity. The reconstructed joint center averaged 19 mm (range, 12-32 mm) above the interteardrop line; the mean difference between the reconstructed and contralateral hip was 0.36 mm (SD, 0.626). The average inclination of the true acetabular face was 528 (range, 358-658). With respect to the 11 patients (12 hips) for whom long-term clinical outcome data were available, preoperative Harris hip scores averaged 46 (range, 27-67). At final follow-up, their Harris hip scores averaged 76.5 (range, 25-91). There were no cases of leg-length discrepancy greater than 2 cm. At followup, 7 patients (8 hips) described no or slight pain, 2 patients (2 hips) described mild pain, and 2 patients (2 hips) noted moderate or severe pain. Three complications occurred in the study group. In 1 case, hip dislocation occurred 38 months postoperatively because of failure of a constrained acetabular liner. At time of revision, the surgeons
Fig. 2. (A) Preoperative radiograph of a 68-year-old patient with bilateral failed total hip prosthesis. (B) Follow-up radiograph with bilateral oblong prosthesis 11 years postoperatively.
250 The Journal of Arthroplasty Vol. 23 No. 2 February 2008 woman who had undergone revision of a bipolar prosthesis with protrusio defect to a constrained oblong prosthesis. One month before revision, she had multiple dislocations without trauma. Intraoperatively, a fractured acetabular liner was found. The acetabular prosthetic screws were loosened and there was gross motion of the prosthesis. However, after screws were replaced and supplemental screws added in the previously bone-grafted locations in the medial, posterior, and anterior walls, excellent fixation was obtained and the acetabular prosthesis was retained. This patient had no further complications and was deceased at the time of final followup. The 2 additional failures both occurred 6 years postoperatively. One occurred in a 59-year-old
woman who had previously undergone revision of primary THA for aseptic loosening. She complained of pain and limb shortening and was found to have fractured the acetabular screws and had superior migration and bead pull-off from the prosthesis. She underwent revision with a bulk allograft and cage (Fig. 3A, B). The other failure occurred in an 82-year-old woman who had undergone bilateral oblong revisions for aseptically loosened total hip prostheses. The patient presented with pain and radiographic evidence of loosening. Intraoperatively, the cup was noted to have gross loosening but no screw breakage. She was revised with bulk allograft and a cage with a cemented polyethylene acetabular component. The contralateral oblong prosthesis survived without complication throughout the study period. Overall, there was no association found between implant failure and severity of acetabular defect (all type III), presence of protrusio defect, or use of a constrained liner. At final follow-up, there was a single case of a well-functioning implant with a circumferential radiolucency. Radiographic evidence of stable fixation was noted in all other cases. No migration of implants was observed, and there were no screw failures or shedding of porous coating beads. Progression, or development of 1-mm radiolucencies, was noted in a single case within zone 1. In 3 cases, progression or development of radiolucencies was noted in zones II and III. No association was found between appearance of radiolucencies and severity of acetabular defect, position of joint center, or use of a constrained liner.
Discussion
Fig. 3. (A) Computed tomography reconstruction of a failed oblong prosthesis at 6 years. (B) Revision of the oblong component to bulk allograft with cage, and cemented polyethylene prosthesis.
The current study represents long-term results of a challenging series of hip reconstructions for large segmental acetabular bone defects, managed with a noncustom, cementless oblong cup. To our knowledge, this is the longest follow-up study to date for this type of implant. Fixation was reliably achieved, and only 3 implants failed and were revised during the study period. Although circumferential radiolucency was noted in one additional case, no component migration, bead shedding, or screw breakage was observed among the surviving implants. The complication rate compares favorably with those reported for reconstruction of similar defects using other techniques [1-8]. The overall success of this implant is likely due to a design that places the porous ingrowth surface in direct contact with good host bone. The bone in the
Reconstruction Oblong Prosthesis ! Abeyta et al 251
base of the ileum, in contact with the eccentric portion of the implant, was consistently the best quality structural bone encountered at surgery. Densification of bone supporting the augmented portion of the device in 4 cases may indicate this region to be a major site of load transmission and maximal bone ingrowth. Proponents of high hip center reconstructions also exploit this iliac bone for reliable fixation. Near-anatomic restoration of the hip joint center was achieved in this series of type III acetabular defects. The assortment of sizes and configurations of the oblong-shaped acetabular component facilitated filling of skeletal defects, restoring the joint’s center to within an average 3 mm compared with the contralateral side. An anatomic location of the acetabular component has been associated with lower rates of acetabular and femoral component loosening [21]. Restoration of the joint center allows for more normal function of hip musculature and minimizes leg-length discrepancies, which likely contributes to the excellent clinical function in this series. There was a significantly high use of constrained liners in this series representing 9 of the 25 cases. A posterior approach was used in all cases. The nature of the component design can limit positioning compared with conventional cups thus resulting in less than the desired anteversion and potentially contributing to instability. However, we were not
able to study this possibility in a systematic fashion within this particular series. There was no statistically significant increased risk of failure among patients with a protrusio defect in our series. This result is in contrast to the recent series published by Chen et al [26], where presence of a protrusio defect in the setting of 2 cm of proximal component migration predicted an increased risk of failure with oblong cup revisions. There are no clear explanations for the differences in our patients’ outcomes compared with those reported in this previous study. Although only 3 patients had clinical failures, our study was limited by a significant dropout rate, which includes 3 patients lost to follow-up and 7 patient deaths (Table 1). Our survivorship of 88% drops considerably to 76% if the 3 patients lost to follow-up are considered as failed cases and as low as 48% if the deceased patients are included as failures. Again, in a study of this duration with a population undergoing complex revision hip surgery, this rate of patient loss is not unexpected. The use of the oblong cup precluded the need for structural allografts in these cases. Graft resorption and subsequent loosening of implants has been recognized as a late complication of reconstructions with massive structural allografting [14-18]. Avoiding grafts also eliminates the possibility of structural allograft fracture, which may jeopardize fixation of the acetabular implant [28,29]. Finally, the role of
Table 1. Patient Data for the 25 Consecutive Oblong Hip Revisions Number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Side/DX
Preoperative HHS
Postoperative HHS
Survivorship
Constrained
L DDH L DJD R AVN L RA L DDH R DJD L DDH R DDH L DDH L DJD L after infection R DJD R AVN R trauma R trauma R RA R DJD L trauma L DJD L DJD L DJD L DJD R DDH L DDH L DJD
50 25 50 47 51 54 38 64 31 67 27 43 51 None 27 None 35 36 None None None None None None None
86 72 Deceased Deceased 85 70 77 Deceased Failed Deceased 73 Failed Deceased Lost to follow-up Deceased 25 Lost to follow-up 91 Failed Lost to follow-up Deceased 87 80 96 76
Survived Survived x x Survived Survived Survived x Failed x Survived Failed x x x Survived x Survived Failed x x Survived Survived Survived Survived
No Yes No No Yes No Yes Yes Yes No No No Yes No No No No Yes Yes No No No Yes No No
DDH indicates developmental dysplasia of hip; AVN, avascular necrosis; DJD, degenerative joint disease; RA, rheumatoid arthritis.
252 The Journal of Arthroplasty Vol. 23 No. 2 February 2008 rejection of structural allografts remains unresolved, but incompatibility of major histocompatibility complex genes has been observed to lead to failure of allogeneic bone graft [30]. Other methods of managing complex acetabular defects with cementless acetabular reconstructions, and their drawbacks, have been described. Large-sized conventional cementless acetabular components may bridge small defects of bone, but the AP dimensions of the pelvis prohibit use of extremely large hemispherical cups. Custom-made acetabular components have been reported to have high rates of loosening due to lack of dedicated instruments for performing the operation [25]. When a custom device fails to fit properly, it may have to be discarded, which adds considerable expense. Placing microminiature implants at a high hip center location has been associated with increased rates of femoral and acetabular loosening [21,22] and precludes maximal thickness of the polyethylene liner. Cemented acetabular reconstruction in the setting of major bone deficits typically includes the use of antiprotrusion cages in conjunction with particulate bone grafting [31-33]. This method of reconstruction is particularly useful in cases of severe osteoporosis and radiation-induced necrosis of pelvic bone, where bone ingrowth is unlikely. However, when viable bone remains, cementless acetabular revisions yield superior results [1-5] compared with cemented reconstructions [34-38] and avoid the filling defects associated with cemented revision procedures. Clear limitations of this study include the relatively small number of patients and the high percentage of patients either lost to follow-up or deceased by the end of the study period. However, this bdropoutQ rate is not unexpected given the nature of the study population and the long followup period. The study could also have been strengthened had all the data been collected prospectively. In fact, most of the data (18 of 25 cases) were collected prospectively; however, it was felt that the benefit of including data on an additional 7 patients outweighed the disadvantage of presenting a retrospective, rather than a prospective, study. Of note, there were no significant differences in the outcomes data collected prospectively and retrospectively. Our experience with the SROM oblong porous coated acetabular component is encouraging. The authors wish to remind the readers that this implant was placed by experienced hip surgeons and its use can be technically demanding especially given its use in difficult cases. However, we believe
reconstruction using this implant provides an excellent option for the management of major segmental acetabular defects. Results are at least comparable with other types of reconstructions for these complex cases. Our data confirm the favorable short-term and intermediate-term results reported by others, and suggest that implants surviving intermediate term will continue to survive long term.
References 1. Hedley AK. Cementless revision of the acetabulum. Tech Orthop 1987;2:41. 2. Engh CA, Glassman AH, Griffin WL. Results of cementless revision for failed cemented total hip arthroplasty. Clin Orthop 1988;235:91. 3. Harris WH, Krushell RJ, Galante JO. Results of cementless revisions of total hip arthroplasties using the Harris-Galante prosthesis. Clin Orthop 1988; 235:120. 4. Tanzer M, Drucker JM. Revision of the acetabular component with an uncemented Harris-Galante porous-coated prosthesis. J Bone Joint Surg 1992; 79A:987. 5. Padgett DE, Kull L, Rosenberg A. Revision of the acetabular component without cement after total hip arthroplasty: three to six-year follow-up. J Bone Joint Surg 1993;75A:663. 6. Emerson RH, Head WC, Berklacich FM, et al. Noncemented acetabular revision arthroplasty using allograft bone. Clin Orthop 1989;249:30. 7. Trancik TM, Stulberg BN, Wilke AH, et al. Allograft reconstruction of the acetabulum during revision total hip arthroplasty. J Bone Joint Surg 1986; 68A:527. 8. Oakeshott RD, Morgan DAF, Zukor DJ, et al. Revision total hip arthroplasty with osseous allograft reconstruction. Clin Orthop 1987;225:37. 9. McGann WA, Welch RB, Picetti GD. Acetabular preparation in cementless revision total hip arthroplasty. Clin Orthop 1988;235:35. 10. Emerson RH, Head WC. Dealing with the deficient acetabulum in revision hip arthroplasty: the importance of implant migration and use of the jumbo cup. Semin Arthroplasty 1993;4:92. 11. Convery FR, Mintzer-Convery M, Devine S, et al. Acetabular augmentation in primary and revision total hip arthroplasty with cementless prostheses. Clin Orthop 1990;252:167. 12. Gross AE, Allan DG, Catre M. Bone grafts in hip replacement surgery: the pelvic side. Orthop Clin North Am 1993;24:679. 13. Paprosky WG, Magnus RE. Principles of bone grafting in revision total hip arthroplasty. Acetabular technique. Clin Orthop 1994;298:147. 14. Jasty M, Harris WH. Salvage total hip reconstruction in patients with major acetabular bone deficiency
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using structural femoral head allografts. J Bone Joint Surg 1990;72B:63. Mulroy Jr RD, Harris WH. Failure of acetabular autogenous grafts in total hip arthroplasty. Increasing incidence: a follow-up note. J Bone Joint Surg 1990;72A:1536. Pollock FH, Whiteside LA. The fate of massive allografts in total hip acetabular revision surgery. J Arthroplasty 1992;7:271. Kwong LM, Jasty M, Harris WH. High failure rate of bulk femoral head allografts in total hip reconstructions at ten years. J Arthroplasty 1993;8:341. Hooten Jr JP, Engh Jr CA, Engh CA. Failure of structural acetabular allografts in cementless revision hip arthroplasty. J Bone Joint Surg 1994; 76B:419. Russotti GM, Harris WH. Proximal placement of the acetabular component in total hip arthroplasty. J Bone Joint Surg 1991;73A:587. Schutzer SF, Harris WH. High placement of porouscoated acetabular components in complex total hip arthroplasty. J Arthroplasty 1994;9:359. Yoder SA, Brand R, Pedersen DR, et al. Total hip acetabular component position affects component loosening rate. Clin Orthop 1988;288:79. Kelley SS. High hip center in revision arthroplasty. J Arthroplasty 1994;9:503. Unger AS, Lewis RJ, Gruen T. Evaluation of porous tantalum uncemented acetabular cup revision total hip arthroplasty: clinical and radiographical results of 60 hips. J Arthroplasty 2005;20. Miyanga Y, Tagawa H, Ninomiya S, et al. A new socket design for the dysplastic acetabulum in total hip replacement. Clin Orthop 1980;149:194. Sutherland CJ. Early experience with eccentric acetabular components in revision total hip arthroplasty. Amer J Orthop 1996;25:284. Chen W, et al. Acetabular revision with use of a bilobed component inserted without cement in
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Reconstruction of Major Segmental Acetabular Defects with an Oblong-Shaped Cementless Prosthesis A Long-Term Outcomes Study Paul N. Abeyta, MD,* Robert S. Namba, MD,y George V. Janku, MD,z William R. Murray, MD,* and Hubert T. Kim, MD, PhD*
Abstract: A retrospective outcomes study was performed on 25 consecutive acetabular reconstructions of major segmental defects by using an oblong-shaped cementless implant. All patients had combined acetabular defects (type III) as defined by the American Academy of Orthopaedic Surgeons classification of acetabular bone deficiency. Long-term follow-up was performed at an average of 11 years postoperatively. Clinical and radiographic outcomes were measured. Failures were defined by component revision or clear radiographic evidence of loosening. Six patients died before final evaluation, and 4 patients did not have complete radiographic data, leaving 14 patients (15 hips) for final analysis. At final follow-up, only 3 of the implants had failed and were revised. There was 1 case of a well-functioning implant with circumferential radiolucency; otherwise, there was no evidence of loosening among the remaining implants. Key words: acetabular, segmental, defect, oblong, cementless. n 2008 Elsevier Inc. All rights reserved.
joint rotation. The limited anterior-posterior dimension of the pelvis may preclude use of oversized conventional cementless cups in large segmental defects [6], particularly those involving the superolateral region of the acetabulum. For acetabular reconstruction in the presence of large bone deficits, several methods have been advocated. Structural allografting facilitates restoration of bone stock to allow anatomic placement of acetabular implants [7-13]. However, limited contact between the implant’s porous coating and living bone with ingrowth capacity compromises the effectiveness of cementless fixation. Even when the fixation is adequate, subsequent graft resorption and implant loosening have been described [14-18]. Placement of a high hip center for management of deficient supra-acetabular bone requires the use of small cementless acetabular components and special extended-neck femoral
Total hip arthroplasty (THA) in the presence of major segmental acetabular defects remains a difficult surgical challenge. Failed acetabular components with small cavitary bone defects can be revised with particulate bone grafting and conventional hemispherical cementless implants [1-5]. For small cavitary defects, reliable fixation can be achieved with minimal alteration of the center of
From the *Department of Orthopaedic Surgery, University of California, San Francisco; yDepartment of Orthopaedic Surgery, Kaiser Permanente Hospital, Orange County; and zDepartment of Orthopaedic Surgery, Kaiser Permanente Hospital, San Francisco. Submitted April 29, 2006; accepted January 28, 2007. No benefits or funds were received in support of the study. Reprint requests: Paul N. Abeyta, MD, Department of Orthopaedic Surgery, 500 Parnassus Ave, MU-320W, University of California, San Francisco, San Francisco, CA 94143-0728. n 2008 Elsevier Inc. All rights reserved. 0883-5403/08/2302-0015$34.00/0 doi:10.1016/j.arth.2007.01.024
247
248 The Journal of Arthroplasty Vol. 23 No. 2 February 2008 components [19,4,20]. Femoral and acetabular component loosening may be associated with high hip centers [21,22]. More recently, trabecular metal implants have been introduced, but longterm data are still lacking [23]. Eccentric or oblong-shaped acetabular implants offer another means of managing large bone deficits and have several advantages [24,25]. These devices allow the surgeon to fill large defects with metal, thus avoiding the potential complications of bone graft fracture and resorption. The eccentric shape permits filling of defects and restoration of the joint center of rotation without bulky anterior and posterior projections. The augmented metallic region increases the area of contact between the porous coating and viable bone, thus enhancing the opportunity for cementless fixation. A recent study has suggested increased failure rates in those cases where the medial wall is not intact, which may be a limitation of the component [26]. The purpose of this study was to assess long-term results of using an oblong-shaped, cementless acetabular component for reconstruction of major acetabular defects and to identify any factors that may influence clinical and radiographic outcomes.
Materials and Methods This series consisted of 25 consecutive cases, performed between October 1992 and October 1993, of complex acetabular reconstructions using a porous-coated oblong-shaped acetabular implant (S-ROM Oblong Cup, Johnson & Johnson, Raynam, Mass) (Fig. 1). The oblong shape is more accurately described as 2 overlapping hemispheres.
Fig. 1. Oblong prosthesis, SROM (Johnson & Johnson, Depuy). Photo courtesy of Johnson & Johnson, Depuy.
Two designs are available and are distinguished primarily by the offset of the 2 hemispheres. The smaller (E15) implants have 15 mm of offset and 158 of adduction between the hemispheres. The larger (E25) implants have 25 mm of offset, 208 of adduction, and 158 of anteversion between the hemispheres. The smaller implant (E15 design) was used in 10 cases, and the larger configuration (E25 design) was used in 15 reconstructions. All the surgeries were performed at a single institution by 2 experienced hip surgeons. The average age of the patients (7 men and 16 women) was 59.5 years (range, 31-80 years). Two patients underwent bilateral hip surgeries as staged procedures. The oblong cup was used for revision of aseptically loosened primary THA in 17 cases, for revision of aseptically loosened, previously revised hips in 6 cases, and as a primary prosthesis in 2 cases (Fig. 2A, B). The revisions were performed at an average of 14.7 years (range, 1-23 years) after the prior reconstruction. A revision of the femoral component was performed in 19 cases at the time of oblong cup implantation. The primary THA cases were performed in 1 patient with massive destruction of the acetabulum due to rheumatoid arthritis, and in 1 patient with severe hip dysplasia. A constrained acetabular liner was used in 9 cases for instability determined intraoperatively. The oblong acetabular components were implanted following the manufacturer’s guidelines. In brief, a standard hemispherical reamer was used to create the inferior portion of the socket, reestablishing the native hip center. A special offset reamer was then seated in the inferior portion of the socket such that the cutting component of the reamer would create the superior portion of the socket. An offset reamer is used to prepare the defect cavity to match the contours of the oblong cavity. The amount of bone reamed is dependent on the encountered size and shape of the existing defect. Cup fixation was always supplemented with multiple screws. Bone defects were assessed on preoperative radiographs and intraoperatively in all cases and recorded according to the American Academy of Orthopaedic Surgeons classification of acetabular defects [27]. Postoperative radiographic evaluation included measurement of the height of joint center with respect to the interteardrop line, with values compared with the contralateral hip joint. The horizontal inclination of the true acetabular face on anteroposterior (AP) radiographs was determined with reference to the interteardrop line. Radiolucencies at the prosthetic-bone interface were recorded for immediate postoperative
Reconstruction Oblong Prosthesis ! Abeyta et al 249
and final follow-up AP radiographs. A modification of the Delee and Charnley classification of acetabular demarcations was required to account for the augmented implant. Zone I (lateral third) represented the elliptical extension of the hemisphere. The remaining hemispheric segment was divided in half and designated zones II (middle segment) and III (medial segment). Lack of reproducibility between serial radiographs of Smith-Peterson views precluded adequate analysis of lateral projections. An implant was considered to have failed if acetabular revision was performed or if follow-up radiographs showed definitive evidence of loosening. Clinical assessment included physical examinations and patient questionnaires performed preoperatively and at final follow-up examination. Harris hip scores were calculated based upon these data. Clinical outcomes data were collected prospectively for the first 18 cases. Some clinical data for the final 7 patients in the series were obtained retrospectively from their medical records. Statistical analysis was performed by using Fisher exact test. All data were collected with institutional review board approval.
found the cup to be solidly fixed. The liner was replaced with a new constrained liner and no further dislocations occurred. A second case was complicated by a single posterior dislocation 4 weeks postoperatively and was managed with closed reduction and an abduction brace for 6 weeks. Instability did not recur in this patient. A third case was complicated by a deep infection with Staphylococcus aureus diagnosed 6 weeks postoperatively and was managed with debridement, intravenous antibiotics, placement of antibioticimpregnated methylmethacrylate beads, and implant retention. The implant remained intact without evidence of loosening at final follow-up. Over the entire study period, only 3 of the oblong components failed, requiring revision. The first failed at 3 years postoperatively in a 69-year-old
Results All cases involved major segmental defects of the superior acetabulum. All cases had additional defects in another region (ie, anterior, posterior, or medial segmental defects) and were therefore classified as type III deficiencies [27]. A protrusio (cavitary medial wall defect) was present in 13 cases. There were no cases of pelvic discontinuity. The reconstructed joint center averaged 19 mm (range, 12-32 mm) above the interteardrop line; the mean difference between the reconstructed and contralateral hip was 0.36 mm (SD, 0.626). The average inclination of the true acetabular face was 528 (range, 358-658). With respect to the 11 patients (12 hips) for whom long-term clinical outcome data were available, preoperative Harris hip scores averaged 46 (range, 27-67). At final follow-up, their Harris hip scores averaged 76.5 (range, 25-91). There were no cases of leg-length discrepancy greater than 2 cm. At followup, 7 patients (8 hips) described no or slight pain, 2 patients (2 hips) described mild pain, and 2 patients (2 hips) noted moderate or severe pain. Three complications occurred in the study group. In 1 case, hip dislocation occurred 38 months postoperatively because of failure of a constrained acetabular liner. At time of revision, the surgeons
Fig. 2. (A) Preoperative radiograph of a 68-year-old patient with bilateral failed total hip prosthesis. (B) Follow-up radiograph with bilateral oblong prosthesis 11 years postoperatively.
250 The Journal of Arthroplasty Vol. 23 No. 2 February 2008 woman who had undergone revision of a bipolar prosthesis with protrusio defect to a constrained oblong prosthesis. One month before revision, she had multiple dislocations without trauma. Intraoperatively, a fractured acetabular liner was found. The acetabular prosthetic screws were loosened and there was gross motion of the prosthesis. However, after screws were replaced and supplemental screws added in the previously bone-grafted locations in the medial, posterior, and anterior walls, excellent fixation was obtained and the acetabular prosthesis was retained. This patient had no further complications and was deceased at the time of final followup. The 2 additional failures both occurred 6 years postoperatively. One occurred in a 59-year-old
woman who had previously undergone revision of primary THA for aseptic loosening. She complained of pain and limb shortening and was found to have fractured the acetabular screws and had superior migration and bead pull-off from the prosthesis. She underwent revision with a bulk allograft and cage (Fig. 3A, B). The other failure occurred in an 82-year-old woman who had undergone bilateral oblong revisions for aseptically loosened total hip prostheses. The patient presented with pain and radiographic evidence of loosening. Intraoperatively, the cup was noted to have gross loosening but no screw breakage. She was revised with bulk allograft and a cage with a cemented polyethylene acetabular component. The contralateral oblong prosthesis survived without complication throughout the study period. Overall, there was no association found between implant failure and severity of acetabular defect (all type III), presence of protrusio defect, or use of a constrained liner. At final follow-up, there was a single case of a well-functioning implant with a circumferential radiolucency. Radiographic evidence of stable fixation was noted in all other cases. No migration of implants was observed, and there were no screw failures or shedding of porous coating beads. Progression, or development of 1-mm radiolucencies, was noted in a single case within zone 1. In 3 cases, progression or development of radiolucencies was noted in zones II and III. No association was found between appearance of radiolucencies and severity of acetabular defect, position of joint center, or use of a constrained liner.
Discussion
Fig. 3. (A) Computed tomography reconstruction of a failed oblong prosthesis at 6 years. (B) Revision of the oblong component to bulk allograft with cage, and cemented polyethylene prosthesis.
The current study represents long-term results of a challenging series of hip reconstructions for large segmental acetabular bone defects, managed with a noncustom, cementless oblong cup. To our knowledge, this is the longest follow-up study to date for this type of implant. Fixation was reliably achieved, and only 3 implants failed and were revised during the study period. Although circumferential radiolucency was noted in one additional case, no component migration, bead shedding, or screw breakage was observed among the surviving implants. The complication rate compares favorably with those reported for reconstruction of similar defects using other techniques [1-8]. The overall success of this implant is likely due to a design that places the porous ingrowth surface in direct contact with good host bone. The bone in the
Reconstruction Oblong Prosthesis ! Abeyta et al 251
base of the ileum, in contact with the eccentric portion of the implant, was consistently the best quality structural bone encountered at surgery. Densification of bone supporting the augmented portion of the device in 4 cases may indicate this region to be a major site of load transmission and maximal bone ingrowth. Proponents of high hip center reconstructions also exploit this iliac bone for reliable fixation. Near-anatomic restoration of the hip joint center was achieved in this series of type III acetabular defects. The assortment of sizes and configurations of the oblong-shaped acetabular component facilitated filling of skeletal defects, restoring the joint’s center to within an average 3 mm compared with the contralateral side. An anatomic location of the acetabular component has been associated with lower rates of acetabular and femoral component loosening [21]. Restoration of the joint center allows for more normal function of hip musculature and minimizes leg-length discrepancies, which likely contributes to the excellent clinical function in this series. There was a significantly high use of constrained liners in this series representing 9 of the 25 cases. A posterior approach was used in all cases. The nature of the component design can limit positioning compared with conventional cups thus resulting in less than the desired anteversion and potentially contributing to instability. However, we were not
able to study this possibility in a systematic fashion within this particular series. There was no statistically significant increased risk of failure among patients with a protrusio defect in our series. This result is in contrast to the recent series published by Chen et al [26], where presence of a protrusio defect in the setting of 2 cm of proximal component migration predicted an increased risk of failure with oblong cup revisions. There are no clear explanations for the differences in our patients’ outcomes compared with those reported in this previous study. Although only 3 patients had clinical failures, our study was limited by a significant dropout rate, which includes 3 patients lost to follow-up and 7 patient deaths (Table 1). Our survivorship of 88% drops considerably to 76% if the 3 patients lost to follow-up are considered as failed cases and as low as 48% if the deceased patients are included as failures. Again, in a study of this duration with a population undergoing complex revision hip surgery, this rate of patient loss is not unexpected. The use of the oblong cup precluded the need for structural allografts in these cases. Graft resorption and subsequent loosening of implants has been recognized as a late complication of reconstructions with massive structural allografting [14-18]. Avoiding grafts also eliminates the possibility of structural allograft fracture, which may jeopardize fixation of the acetabular implant [28,29]. Finally, the role of
Table 1. Patient Data for the 25 Consecutive Oblong Hip Revisions Number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Side/DX
Preoperative HHS
Postoperative HHS
Survivorship
Constrained
L DDH L DJD R AVN L RA L DDH R DJD L DDH R DDH L DDH L DJD L after infection R DJD R AVN R trauma R trauma R RA R DJD L trauma L DJD L DJD L DJD L DJD R DDH L DDH L DJD
50 25 50 47 51 54 38 64 31 67 27 43 51 None 27 None 35 36 None None None None None None None
86 72 Deceased Deceased 85 70 77 Deceased Failed Deceased 73 Failed Deceased Lost to follow-up Deceased 25 Lost to follow-up 91 Failed Lost to follow-up Deceased 87 80 96 76
Survived Survived x x Survived Survived Survived x Failed x Survived Failed x x x Survived x Survived Failed x x Survived Survived Survived Survived
No Yes No No Yes No Yes Yes Yes No No No Yes No No No No Yes Yes No No No Yes No No
DDH indicates developmental dysplasia of hip; AVN, avascular necrosis; DJD, degenerative joint disease; RA, rheumatoid arthritis.
252 The Journal of Arthroplasty Vol. 23 No. 2 February 2008 rejection of structural allografts remains unresolved, but incompatibility of major histocompatibility complex genes has been observed to lead to failure of allogeneic bone graft [30]. Other methods of managing complex acetabular defects with cementless acetabular reconstructions, and their drawbacks, have been described. Large-sized conventional cementless acetabular components may bridge small defects of bone, but the AP dimensions of the pelvis prohibit use of extremely large hemispherical cups. Custom-made acetabular components have been reported to have high rates of loosening due to lack of dedicated instruments for performing the operation [25]. When a custom device fails to fit properly, it may have to be discarded, which adds considerable expense. Placing microminiature implants at a high hip center location has been associated with increased rates of femoral and acetabular loosening [21,22] and precludes maximal thickness of the polyethylene liner. Cemented acetabular reconstruction in the setting of major bone deficits typically includes the use of antiprotrusion cages in conjunction with particulate bone grafting [31-33]. This method of reconstruction is particularly useful in cases of severe osteoporosis and radiation-induced necrosis of pelvic bone, where bone ingrowth is unlikely. However, when viable bone remains, cementless acetabular revisions yield superior results [1-5] compared with cemented reconstructions [34-38] and avoid the filling defects associated with cemented revision procedures. Clear limitations of this study include the relatively small number of patients and the high percentage of patients either lost to follow-up or deceased by the end of the study period. However, this bdropoutQ rate is not unexpected given the nature of the study population and the long followup period. The study could also have been strengthened had all the data been collected prospectively. In fact, most of the data (18 of 25 cases) were collected prospectively; however, it was felt that the benefit of including data on an additional 7 patients outweighed the disadvantage of presenting a retrospective, rather than a prospective, study. Of note, there were no significant differences in the outcomes data collected prospectively and retrospectively. Our experience with the SROM oblong porous coated acetabular component is encouraging. The authors wish to remind the readers that this implant was placed by experienced hip surgeons and its use can be technically demanding especially given its use in difficult cases. However, we believe
reconstruction using this implant provides an excellent option for the management of major segmental acetabular defects. Results are at least comparable with other types of reconstructions for these complex cases. Our data confirm the favorable short-term and intermediate-term results reported by others, and suggest that implants surviving intermediate term will continue to survive long term.
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