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Constrained Acetabular Liners Cemented Into Cages During Total Hip Revision Arthroplasty
The Journal of Arthroplasty Vol. 25 No. 6 2010
Constrained Acetabular Liners Cemented Into Cages During Total Hip Revision Arthroplasty John I. Khoury, MD,* Arthur L. Malkani, MD,y Edward M. Adler, MD,z and David C. Markel, MD,*§
Abstract: The combination of acetabular bone loss and hip instability is challenging. Sixteen patients underwent revision total hip arthroplasty using constrained acetabular liners cemented into cages. The average follow-up was 28 months (range, 24-60 months). Clinical evaluation was obtained using the Harris hip score along with radiographic data. At latest follow-up, 13 patients were available for evaluation. Although the average postoperative Harris hip score was 62 points, which was better than the preoperative score of 27 points, the overall radiographic failure rate was 23%. The combination of poor acetabular bone stock and altered stresses from the increased constraint likely led to the poor outcome. We would only recommend use of a cemented, constrained acetabular liner in combination with a protrusio cage as a bail out or salvage procedure. Keywords: revision total hip arthroplasty, cages, constrained liners, acetabulum. © 2010 Elsevier Inc. All rights reserved.
As the life expectancy of the population continues to rise and the indications for total hip arthroplasty expand, the number and complexity of acetabular revisions are expected to increase [1,2]. Current treatment options for massive acetabular defects encountered in revision total hip arthroplasty are numerous but are often associated with inconsistent clinical results and substantial complication rates [3]. Those options are predicated on the amount and type of bone loss present, the ability to achieve a rigid, stable construct that allows for the osteointegration of the chosen implant, and long-term, predictable implant survival [4-8]. A significant challenge in revision surgery is creating a stable construct with long-term stability, despite insufficient acetabular bone stock [1]. With moderate degrees of bone loss, a large cup can achieve peripheral fixation at or near anatomic position. Success with this technique requires an intact posterior column and anterior-inferior
From the *Detroit Medical Center/Providence Hospital Orthopaedic Surgery Residency Program, Detroit, Michigan; yDepartment of Orthopaedic Surgery, NYU Hospital For Joint Disease, New York, New York; zDepartment of Orthopaedic Surgery, Jewish Hospital & St. Mary's Healthcare, Center for Advanced Medicine, Louisville, Kentucky; and §Department of Orthopaedic Surgery, Providence Hospital and Medical Centers, Southfield, Michigan. Submitted September 25, 2008; accepted August 19, 2009. No benefits or funds were received in support of this study. Reprint requests: David C. Markel, MD, Department of Orthopaedic Surgery, Providence Hospital and Medical Centers, 22250 Providence Dr. # 401, Southfield, MI 48075. © 2010 Elsevier Inc. All rights reserved. 0883-5403/2506-0010$36.00/0 doi:10.1016/j.arth.2009.08.012
or anterior-superior bone to obtain a press fit [1]. In situations with significant acetabular bone loss, when an acetabular press fit cannot be achieved, anti-protrusio cages can be useful. Since these devices are usually combined with bone graft for long-term acetabular reconstruction, the ability to bridge ileum to ischium allows creation of a stable acetabular construct. Once the metallic cage is stably fixed, a polyethylene liner or hemispheric component can be cemented into place with version and verticality independent of the cage position. Although this technique has been supplanted in many cases by trabecular metal devices and augments, cages are still widely distributed and used. Unfortunately, despite advances in bony reconstruction, instability remains frequent and problematic in these cases. The instability likely results from concomitant destruction of soft tissues, muscle insufficiency and/ or impingement. As such, instability remains as one of the most common complications of revision surgery [9]. Methods for managing instability include the use of femoral head with a longer neck [9], removal of sources of impingement [9,10], revision and reorientation of the femoral or acetabular component [10-12], trochanteric advancement [13], the use of a femoral head with a larger diameter [14], creation of a tripolar articulation [15], removal of the acetabular component and insertion of a bipolar head [16-17], and use of constrained liners [18-23]. Constrained acetabular liners have been successfully used to treat recurrent instability and the intraoperative instability encountered at the time of revision surgery [24,25]. However, with the increased use of constrained devices, there has been concern with
901
902 The Journal of Arthroplasty Vol. 25 No. 6 September 2010 the effect of increased bony stressors, accelerated wear, component failure, and decreased range of motion [26]. The purpose of this study was to review the results of use of a constrained acetabular liner cemented into cages for complex revision total hip arthroplasty.
Materials and Methods This was a 3-center review of 16 revisions performed by 3 experienced surgeons between 1998 and 2005. There were 5 women and 11 men with an average age of 63 years (range, 33-89 years). The clinical outcome was assessed with the use of the Harris hip score [27]. Serial anterior posterior pelvic and lateral radiographs of the involved hip were reviewed to evaluate the position of the prosthesis and to assess for signs of loosening and osteolysis. Radiolucencies around the acetabular shell were evaluated in the three zones of DeLee and Charnley [28] at the time of the index surgery and at the final follow-up evaluation to determine whether there was any progression. All cases employed the use of a constrained liner (Stryker Orthopaedics, Mahwah, NJ) that was cemented into an antiprotrusio cage. The constrained liners used in this study were a tri-polar concept. A bi-polar articulation locked via a locking ring into a specialized polyethylene liner. Infection, dislocation, fracture of the polyethylene liner, aseptic loosening, and failure of the constrained mechanism were end points used to define failure. Table 1 lists the degree of acetabular bone loss based on the Paprosky classification [29] and the reason those patients underwent the revision surgery. Pre- and postoperative Harris hip scores were compared based on a Student paired t test assuming unequal variance, with P b .05 considered significant.
Results At the last follow-up, 3 patients had died leaving 13 patients available for evaluation. There were 3 women Table 1. The Paprosky Classification and the Reason for Acetabular Revision Patients 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Paprosky Classification
Reason for Revision
2 3 3 3 3 2 2 3 2 2 3 2 2 3 2 3
Infection Aseptic loosening Metastatic disease Aseptic loosening Aseptic loosening Aseptic loosening Infection Aseptic loosening, pain, osteolysis Aseptic loosening, dislocation Pain, osteolysis Aseptic loosening Dislocation Aseptic loosening, infection, dislocation Aseptic loosening Aseptic loosening Aseptic loosening
Table 2. The Harris Hip Score Before and After Surgery Patients 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Preoperative Score
Postoperative Score*
27 1 1 17 45 25 21 27 28 44 32 33 42 24 25 40
74 56 54 84 71 47 50 49 71 85 74 70 56 58 45 54
* P b .0001.
and 10 men with an average age of 61 years (range 33–84 years). The average follow-up was 28 months (range 2460 months). Using the Paprosky acetabular classification [29], 6 patients had type II bone loss and 7 patients had type III bone loss. There were 3 failures from the group of 13 patients with 2 years follow-up. The first failure occurred 25 months postoperatively in a patient who underwent the revision for pain and osteolysis. His radiographs showed the acetabular implant to be loose, and the patient is pending revision. The second failure occurred 35 months postoperatively in a patient who underwent the revision due to aseptic loosening and Paprosky 3 bone loss. She eventually developed aseptic loosening again and required removal of implants. The third failure occurred 39 months postoperatively in a patient who underwent the procedure for aseptic loosening with Paprosky 3 bone loss. She had a fracture of the constrained polyethylene liner. As shown in Table 2, the mean pre-operative Harris hip score was 27. A statistically significant increase was observed in the postoperative Harris hip score, which improved postoperatively to 62 at the latest follow-up examination (P b .0001). There were no infections. The overall failure rate was 23 % (3/13).
Discussion As the number of total hip arthroplasties performed continues to rise owing to the increasing age and longevity of the population, the failure of the procedure will become a growing problem [2,30]. Those patients requiring revision are often asymptomatic for many years as osteolysis progresses [31]. By the time they become symptomatic, osteolysis may have resulted in medial migration of the cup and continuous erosion of the acetabulum so that the medial wall is often noted to be deficient in bone stock at the time of surgery [32].
Constrained Acetabular Liners Cemented into Cages Khoury et al
Moreover, revision arthroplasty has a higher incidence of complications than the initial procedure, including infection, deep venous thrombosis, dislocation and nerve damage [33]. Paprosky et al [29] introduced a classification system that reported bone loss from the perspective of acetabular component failure and includes the following variables: A, superior cup migration greater than 2 cm; B, lysis of the ischium (posterior column involvement); C, integrity of Kohler's line; and D, teardrop presence. Three types of defects are also part of the classification system. In type I defects, there is sufficient support from the host bone to provide initial stability so that most patients can be reconstructed with an uncemented hemispherical cup with screws with or without morselized bone graft [1]. The difficulty arises in type II and III defects where the remaining acetabular rim will not provide adequate initial component stability to achieve reliable biologic fixation. Severe acetabular defects might require a structural graft, a bilobed cup, or a cup\cage construct [34]. Acetabular protrusio cages span the acetabular defect, obtaining support from the ilium superiorly and the pubis and ischium inferiorly. This mechanical bridge can decrease the forces across the bone graft and allow more time for potential integration [1]. A disadvantage is an unacceptable midterm failure if support from the bone graft or host bone is not adequate [1]. The current generation of cages does not provide biologic fixation and, with time, may loosen or fracture if the bone graft does not incorporate. Cages may also migrate or fracture when there is inadequate contact as a result of bone loss between the superior rim of the cage and the weightbearing dome area of the host acetabulum. The chance of loosening appears to increase as the size of the bony defect increases [35]. Boscainos et al. [34] reported a 76% survivorship at 4.6 years with the use of a large structural graft supporting greater than 50% of the cup when protected by a cage. They attributed failures to the fact that cages do not have a surface that permits stabilization by ongrowth or ingrowth. They now use a trabecular metal cup when contact with bleeding host bone is less then 50% [34]. The trabecular metal appears to provide a better environment for bone graft remodeling [36]. A cage protects the metal until the cup is stabilized, at which time the stress is relieved from the cage, and the midterm cage failures should not occur [34,36]. Udomkiat et al [35] reported loosening and migration of the cage in 9 out of 11 hips when the superior weight-bearing dome defect was N50%. He concluded that the cage alone could not withstand the load across the hip joint without a superior bone buttress. Morcellized allograft was not felt to be strong enough when there was a defect greater than 40% [35]. To reduce the loosening rate of the cage, the superior rim of the metal should be placed against host bone for 60% of its support. If the bony defect is too large to permit stable bony support, a structural allograft may
903
be required for reconstruction [35]. Other authors have confirmed this finding reporting 0% to 2.7% loosening rates at 7 to 8 years when using structural grafts to reconstruct defects N50 % of the superior acetabulum [36-38]. Alternative treatments for a type III defect include high hip center [39], the oblong cups method [40,41] and more recently modular augments. Placing the cup at a high hip center may avoid the need for a structural graft. This strategy does not however restore bone stock and may significantly shorten the extremity and risk impingement and instability [42]. The high hip center has also been associated with a higher rate of acetabular loosening [43]. Despite improvements in techniques for bony reconstruction and acetabular fixation, instability remains one of the most challenging issues facing the revision surgeon. There is extensive literature detailing the potential causes of instability. These include component malposition, impingement, inadequate soft tissue tension, deficient abductor musculature, neuromuscular disorders, and patient noncompliance [44-47]. Revision surgery appears to make any or all of these factors more common. The quality of the soft tissue deteriorates with every revision operation. In a revision situation, inadequate soft tissue and bone stock contribute to a dislocation rate of as much as 15% to 30% [10,48,49]. Constrained acetabular liners are useful in the complex revision for achieving hip stability. These components are designed to hold the femoral head captive via a secure locking mechanism [44]. Goetz et al [21,50] reported no additional dislocations in 54 (96%) of 56 hips treated for recurrent instability using a constrained liner. The liners are usually easily applied and can be combined with a secondary procedure to achieve stability, such as trochanteric advancement [44]. Unfortunately, constrained liners may decrease range of motion. Increased transmission of stress to the implant-bone and implant-cement interface may lead to impingement and early loosening [51]. Component failure may occur by dissociation of the liner from the shell or the disruption of the locking mechanism. Unfortunately, if dislocation occurs in the presence of a cemented liner, open reduction or revision is usually required. In this study, the combination of significant bone loss and instability necessitated the use of an acetabular reconstruction cage combined with a constrained liner. Although this combination was effective for the immediate remedy of the pathology, there was significant failure rate (23%) at a mean follow-up of only 28 months. When we conducted a limited extended follow-up (6 patients), which increased our mean follow-up to 47 months, the failure rate increased (31%) due to a failure in a female patient secondary to aseptic loosing. She went on to revision with tantalum cup with a constrained liner due to an incompetent abductor mechanism. It is likely that the combination of poor acetabular bone stock and the increased stresses imparted to the construct through the constrained liner led to the early failure. Newer reconstruction devices, like trabecular metal
904 The Journal of Arthroplasty Vol. 25 No. 6 September 2010 revision systems and modular augments, may provide more viable options for these reconstructions. The increased porosity of the 3-D ingrowth materials combined with augments that can bridge acetabular defects appear to create a more biologic reconstruction option. These newer components also have the ability to employ very large femoral heads, which may obviate the need for a constrained liner. Nevertheless, cages are still used today, despite the availability of these newer devices. Thus, it is our recommendation that the combination of an acetabular reconstruction cage not be combined with a cemented constrained acetabular liner except as a salvage procedure.
Conclusion This series reviewed 16 cases of acetabular reconstruction using a protrusio acetabular cage combined with a cemented constrained liner. While the reconstructions were successful in terms of improvement of the Harris hip scores, there was a 23% (3/13) failure rate at mean follow-up of 28 months. Although this construct was found to be effective for reconstruction of severe acetabular bone loss complicated by instability, due to the high failure rate, this combination should be reserved for the salvage situation.
References 1. Paprosky WG, Sporer SS, Murphy BP. Addressing severe bone deficiency: what a cage will not do. J Arthroplasty 2007;22:111. 2. Lawrence JM, Engh CA, Macalino GE, et al. Outcome of revision hip arthroplasty done without cement. J Bone Joint Surg Am 1994;76:965. 3. Holt GE, Dennis DA. Use of custom triflanged acetabular components in revision total hip arthroplasty. Clin Orthop Relat Res 2004;429:209. 4. Whaley AL, Berry DJ, Harmsen WS. Extra-large uncemented hemispherical acetabular components for revision total hip arthroplasty. J Bone Joint Surg Am 2001;83-A:1352. 5. Rosenberg WJ, Schreurs BW, Waal MC, et al. Impacted morselized bone grafting and cemented primary total hip arthroplasty for acetabular protrusion in patients with rheumatoid arthritis. Acta Orthop Scand 2000;71:143. 6. Saleh KJ, Jaroszynski G, Woodgate I, et al. Revision total hip arthroplasty with the use of structural acetabular allograft and reconstruction ring: a case series with 10year average follow-up. J Arthroplasty 2000;15:951. 7. Welten MLM, Schreurs BW, Buma P, et al. Acetabular reconstruction with impacted morselized cancellous autograft and cemented total hip arthroplasty. J Arthroplasty 2000;15:819. 8. Shinar AA, Harris WH. Bulk structural autogenous grafts and allografts for reconstruction of the acetabulum in total hip arthroplasty: sixteen-year-average follow-up. J Bone Joint Surg Am 1997;79:159. 9. Toomey SD, Hopper Jr RH, McAuley JP, et al. Modular component exchange for treatment of recurrent dislocation of a total hip replacement in selected patients. J Bone Joint Surg Am 2001;83:1529.
10. Kavanagh BF, Fitzgerald Jr RH. Multiple revisions for failed total hip arthroplasty not associated with infection. J Bone Joint Surg Am 1987;69A:1144. 11. Daly PJ, Morrey BF. Operative correction of an unstable total hip arthroplasty. J Bone Joint Surg Am 1992;74:1334. 12. Eftekhar NS. Dislocation and instability complicating low friction arthroplasty of the hip joint. Clin Orthop Relat Res 1976;121:120. 13. Kaplan SJ, Thomas WH, Poss R. Trochanteric advancement for recurrent dislocation after total hip arthroplasty. J Arthroplasty 1987;2:119. 14. Beaule PE, Schmalzried TP, Udomkiat P, et al. Jumbo femoral head for the treatment of recurrent dislocation following total hip replacement. J Bone Joint Surg Am 2002;84:256. 15. Grigoris P, Grecula MJ, Amstutz HC. Tripolar hip replacement for recurrent prosthetic dislocation. Clin Orthop Relat Res 1994;304:148. 16. Ries MD, Wiedel JD. Bipolar hip arthroplasty for recurrent dislocation after total hip arthroplasty. A report of three cases. Clin Orthop Relat Res 1992;278:121. 17. Parvizi J, Morrey BF. Bipolar hip arthroplasty as a salvage treatment for instability of the hip. J Bone Joint Surg Am 2000;82:1132. 18. Anderson MJ, Murray WR, Skinner HB. Constrained acetabular components. J Arthroplasty 1994;9:17. 19. Bremner BR, Goetz DD, Callaghan JJ, et al. Use of constrained acetabular components for hip instability: an average 10-year follow-up study. J Arthroplasty 2003; 18:131. 20. Goetz DD, Capello WN, Callaghan JJ, et al. Salvage of total hip instability with a constrained acetabular component. Clin Orthop Relat Res 1998;355:171. 21. Goetz DD, Capello WN, Callaghan JJ, et al. Salvage of a recurrently dislocating total hip prosthesis with use of a constrained acetabular component. A retrospective analysis of fifty-six cases. J Bone Joint Surg Am 1998;80:502. 22. Kaper BP, Bernini PM. Failure of constrained acetabular prosthesis of a total hip arthroplasty. A report of four cases. J Bone Joint Surg Am 1998;80:561. 23. Lombardi Jr AV, Mallory TH, Kraus TJ, et al. Preliminary report on the S-ROM constraining acetabular insert: a retrospective clinical experience. Orthopedics 1991;14:297. 24. Callaghan JJ, Parvizi J, Novak CC, et al. A constrained liner cemented into a secure cementless acetabular shell. J Bone Joint Surg Am 2004;86-A:2206. 25. McCarthy JC, Lee J, Hanssen AD. Constrained acetabular components in complex revision total hip arthroplasty. Clin Orthop Relat Res 2005;441:210. 26. Williams Jr JT, Ragland PS, Clarke S. Constrained components for the unstable hip following total hip arthroplasty: a literature review. Int Orthop 2007;31. 27. Harris WH. Traumatic arthritis of the hip after dislocation and acetabular fractures: treatment by mold arthroplasty. An end-result study using a new method of result evaluation. J Bone Joint Surg Am 1969;51:737. 28. DeLee JG, Charnley J. Radiological demarcation of cemented sockets in total hip replacement. Clin Orthop Relat Res 1976;121:20. 29. Paprosky WG, Perona PG, Lawrence JM. Acetabular defect classification and surgical reconstruction in revision
Constrained Acetabular Liners Cemented into Cages Khoury et al
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arthroplasty: a six-year follow-up evaluation. J Arthroplasty 1994;9:33. Kurtz S, Ong K, Lau E, et al. Projections of primary and revision hip and knee arthroplasty in the United States from 2005 to 2030. J Arthroplasty 2007;89:780. Dorr LD, Wan Z. Ten years of experience with porous acetabular components for revision surgery. Clin Orthop Relat Res 1995;319:191. Harkess JW. Arthroplasty of hip. In: Crenshaw AH, editor. Campbell's operative orthopaedics, vol. 1. St. Louis (Mo): Mosby Year Book; 1992. p. 536. Emerson RH, Head WC, Berklacich FM, et al. Noncemented acetabular revision arthroplasty using allograft bone. Clin Orthop Relat Res 1989;249:30. Boscainos PJ, Kellett CF, Maury AC, et al. Management of periacetabular bone loss in revision hip arthroplasty. Clin Orthop Relat Res 2007;465:159. Udomkiat P, Dorr LD, Won YY, et al. Technical factors for success with metal ring acetabular reconstruction. J Arthroplasty 2001;16:961. Gross AE. Revision arthroplasty of the acetabulum with restoration of bone stock. Clin Orthop Relat Res 1999; 369:198. Gill TJ, Sledge JB, Muller ME. The management of severe acetabular reinforcement devices. J Arthroplasty 2000;15:1. Garbuz D, Morsi E, Gross AE. Revision of the acetabular component of a total hip arthroplasty with a massive structural allograft: study with a minimum five-year followup. J Bone Joint Surg Am 1996;78:693. Harris WH. Reconstruction at a high hip center in acetabular revision surgery using a cementless acetabular component. Orthopedics 1998;21:991. DeBoer DK, Christie MJ. Reconstruction of the deficient acetabulum with an oblong prosthesis: three- to sevenyears results. J Arthroplasty 1998;13:674.
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41. Koster G, Willert HG, Kohler HP, et al. An oblong revision cup for large acetabular defects: design rationale and two to seven year follow-up. J Arthroplasty 1998; 13:559. 42. Gross AE, Goodman S. The current role of structural grafts and cages in revision arthroplasty of the hip. Clin Orthop Relat Res 2004;429:193. 43. Kelley SS. High hip center in revision arthroplasty. J Arthroplasty 1994;9:503. 44. Su EP, Pellicci PM. The role of constrained liners in total hip arthroplasty. Clin Orthop Relat Res 2004;420:122. 45. Ali Khan MA, Brakenbury PH, Reynolds IS. Dislocation following total hip replacement. J Bone Joint Surg Br 1981; 63B:214. 46. Berry DJ. Unstable total hip arthroplasty: detailed overview. Instr Course Lect 2001;50:265. 47. Morrey BF. Instability after total hip arthroplasty. Orthop Clin North Am 1992;23:237. 48. Phillips CB, Barrett JA, Losina E, et al. Incidence rates of dislocation, pulmonary embolism, and deep infection during the first six months after elective total hip replacement. J Bone Joint Surg Am 2003; 85-A:20. 49. Williams JF, Gottesman MJ, Mallory TH. Dislocation after total hip arthroplasty: treatment with an above-knee hip spica cast. Clin Orthop Relat Res 1982;171:53. 50. Goetz DD, Bremner BR, Callaghan JJ, et al. Salvage of a recurrently dislocating total hip prosthesis with use of a constrained acetabular component: a concise followup of a previous report. J Bone Joint Surg Am 2004; 86-A:2419. 51. Tanzer M, Drucker D, Jasty M, et al. Revision of acetabular components with an un-cemented HarrisGalante porous-coated prosthesis. J Bone Joint Surg Am 1994;74:987.
Constrained Acetabular Liners Cemented Into Cages During Total Hip Revision Arthroplasty John I. Khoury, MD,* Arthur L. Malkani, MD,y Edward M. Adler, MD,z and David C. Markel, MD,*§
Abstract: The combination of acetabular bone loss and hip instability is challenging. Sixteen patients underwent revision total hip arthroplasty using constrained acetabular liners cemented into cages. The average follow-up was 28 months (range, 24-60 months). Clinical evaluation was obtained using the Harris hip score along with radiographic data. At latest follow-up, 13 patients were available for evaluation. Although the average postoperative Harris hip score was 62 points, which was better than the preoperative score of 27 points, the overall radiographic failure rate was 23%. The combination of poor acetabular bone stock and altered stresses from the increased constraint likely led to the poor outcome. We would only recommend use of a cemented, constrained acetabular liner in combination with a protrusio cage as a bail out or salvage procedure. Keywords: revision total hip arthroplasty, cages, constrained liners, acetabulum. © 2010 Elsevier Inc. All rights reserved.
As the life expectancy of the population continues to rise and the indications for total hip arthroplasty expand, the number and complexity of acetabular revisions are expected to increase [1,2]. Current treatment options for massive acetabular defects encountered in revision total hip arthroplasty are numerous but are often associated with inconsistent clinical results and substantial complication rates [3]. Those options are predicated on the amount and type of bone loss present, the ability to achieve a rigid, stable construct that allows for the osteointegration of the chosen implant, and long-term, predictable implant survival [4-8]. A significant challenge in revision surgery is creating a stable construct with long-term stability, despite insufficient acetabular bone stock [1]. With moderate degrees of bone loss, a large cup can achieve peripheral fixation at or near anatomic position. Success with this technique requires an intact posterior column and anterior-inferior
From the *Detroit Medical Center/Providence Hospital Orthopaedic Surgery Residency Program, Detroit, Michigan; yDepartment of Orthopaedic Surgery, NYU Hospital For Joint Disease, New York, New York; zDepartment of Orthopaedic Surgery, Jewish Hospital & St. Mary's Healthcare, Center for Advanced Medicine, Louisville, Kentucky; and §Department of Orthopaedic Surgery, Providence Hospital and Medical Centers, Southfield, Michigan. Submitted September 25, 2008; accepted August 19, 2009. No benefits or funds were received in support of this study. Reprint requests: David C. Markel, MD, Department of Orthopaedic Surgery, Providence Hospital and Medical Centers, 22250 Providence Dr. # 401, Southfield, MI 48075. © 2010 Elsevier Inc. All rights reserved. 0883-5403/2506-0010$36.00/0 doi:10.1016/j.arth.2009.08.012
or anterior-superior bone to obtain a press fit [1]. In situations with significant acetabular bone loss, when an acetabular press fit cannot be achieved, anti-protrusio cages can be useful. Since these devices are usually combined with bone graft for long-term acetabular reconstruction, the ability to bridge ileum to ischium allows creation of a stable acetabular construct. Once the metallic cage is stably fixed, a polyethylene liner or hemispheric component can be cemented into place with version and verticality independent of the cage position. Although this technique has been supplanted in many cases by trabecular metal devices and augments, cages are still widely distributed and used. Unfortunately, despite advances in bony reconstruction, instability remains frequent and problematic in these cases. The instability likely results from concomitant destruction of soft tissues, muscle insufficiency and/ or impingement. As such, instability remains as one of the most common complications of revision surgery [9]. Methods for managing instability include the use of femoral head with a longer neck [9], removal of sources of impingement [9,10], revision and reorientation of the femoral or acetabular component [10-12], trochanteric advancement [13], the use of a femoral head with a larger diameter [14], creation of a tripolar articulation [15], removal of the acetabular component and insertion of a bipolar head [16-17], and use of constrained liners [18-23]. Constrained acetabular liners have been successfully used to treat recurrent instability and the intraoperative instability encountered at the time of revision surgery [24,25]. However, with the increased use of constrained devices, there has been concern with
901
902 The Journal of Arthroplasty Vol. 25 No. 6 September 2010 the effect of increased bony stressors, accelerated wear, component failure, and decreased range of motion [26]. The purpose of this study was to review the results of use of a constrained acetabular liner cemented into cages for complex revision total hip arthroplasty.
Materials and Methods This was a 3-center review of 16 revisions performed by 3 experienced surgeons between 1998 and 2005. There were 5 women and 11 men with an average age of 63 years (range, 33-89 years). The clinical outcome was assessed with the use of the Harris hip score [27]. Serial anterior posterior pelvic and lateral radiographs of the involved hip were reviewed to evaluate the position of the prosthesis and to assess for signs of loosening and osteolysis. Radiolucencies around the acetabular shell were evaluated in the three zones of DeLee and Charnley [28] at the time of the index surgery and at the final follow-up evaluation to determine whether there was any progression. All cases employed the use of a constrained liner (Stryker Orthopaedics, Mahwah, NJ) that was cemented into an antiprotrusio cage. The constrained liners used in this study were a tri-polar concept. A bi-polar articulation locked via a locking ring into a specialized polyethylene liner. Infection, dislocation, fracture of the polyethylene liner, aseptic loosening, and failure of the constrained mechanism were end points used to define failure. Table 1 lists the degree of acetabular bone loss based on the Paprosky classification [29] and the reason those patients underwent the revision surgery. Pre- and postoperative Harris hip scores were compared based on a Student paired t test assuming unequal variance, with P b .05 considered significant.
Results At the last follow-up, 3 patients had died leaving 13 patients available for evaluation. There were 3 women Table 1. The Paprosky Classification and the Reason for Acetabular Revision Patients 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Paprosky Classification
Reason for Revision
2 3 3 3 3 2 2 3 2 2 3 2 2 3 2 3
Infection Aseptic loosening Metastatic disease Aseptic loosening Aseptic loosening Aseptic loosening Infection Aseptic loosening, pain, osteolysis Aseptic loosening, dislocation Pain, osteolysis Aseptic loosening Dislocation Aseptic loosening, infection, dislocation Aseptic loosening Aseptic loosening Aseptic loosening
Table 2. The Harris Hip Score Before and After Surgery Patients 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Preoperative Score
Postoperative Score*
27 1 1 17 45 25 21 27 28 44 32 33 42 24 25 40
74 56 54 84 71 47 50 49 71 85 74 70 56 58 45 54
* P b .0001.
and 10 men with an average age of 61 years (range 33–84 years). The average follow-up was 28 months (range 2460 months). Using the Paprosky acetabular classification [29], 6 patients had type II bone loss and 7 patients had type III bone loss. There were 3 failures from the group of 13 patients with 2 years follow-up. The first failure occurred 25 months postoperatively in a patient who underwent the revision for pain and osteolysis. His radiographs showed the acetabular implant to be loose, and the patient is pending revision. The second failure occurred 35 months postoperatively in a patient who underwent the revision due to aseptic loosening and Paprosky 3 bone loss. She eventually developed aseptic loosening again and required removal of implants. The third failure occurred 39 months postoperatively in a patient who underwent the procedure for aseptic loosening with Paprosky 3 bone loss. She had a fracture of the constrained polyethylene liner. As shown in Table 2, the mean pre-operative Harris hip score was 27. A statistically significant increase was observed in the postoperative Harris hip score, which improved postoperatively to 62 at the latest follow-up examination (P b .0001). There were no infections. The overall failure rate was 23 % (3/13).
Discussion As the number of total hip arthroplasties performed continues to rise owing to the increasing age and longevity of the population, the failure of the procedure will become a growing problem [2,30]. Those patients requiring revision are often asymptomatic for many years as osteolysis progresses [31]. By the time they become symptomatic, osteolysis may have resulted in medial migration of the cup and continuous erosion of the acetabulum so that the medial wall is often noted to be deficient in bone stock at the time of surgery [32].
Constrained Acetabular Liners Cemented into Cages Khoury et al
Moreover, revision arthroplasty has a higher incidence of complications than the initial procedure, including infection, deep venous thrombosis, dislocation and nerve damage [33]. Paprosky et al [29] introduced a classification system that reported bone loss from the perspective of acetabular component failure and includes the following variables: A, superior cup migration greater than 2 cm; B, lysis of the ischium (posterior column involvement); C, integrity of Kohler's line; and D, teardrop presence. Three types of defects are also part of the classification system. In type I defects, there is sufficient support from the host bone to provide initial stability so that most patients can be reconstructed with an uncemented hemispherical cup with screws with or without morselized bone graft [1]. The difficulty arises in type II and III defects where the remaining acetabular rim will not provide adequate initial component stability to achieve reliable biologic fixation. Severe acetabular defects might require a structural graft, a bilobed cup, or a cup\cage construct [34]. Acetabular protrusio cages span the acetabular defect, obtaining support from the ilium superiorly and the pubis and ischium inferiorly. This mechanical bridge can decrease the forces across the bone graft and allow more time for potential integration [1]. A disadvantage is an unacceptable midterm failure if support from the bone graft or host bone is not adequate [1]. The current generation of cages does not provide biologic fixation and, with time, may loosen or fracture if the bone graft does not incorporate. Cages may also migrate or fracture when there is inadequate contact as a result of bone loss between the superior rim of the cage and the weightbearing dome area of the host acetabulum. The chance of loosening appears to increase as the size of the bony defect increases [35]. Boscainos et al. [34] reported a 76% survivorship at 4.6 years with the use of a large structural graft supporting greater than 50% of the cup when protected by a cage. They attributed failures to the fact that cages do not have a surface that permits stabilization by ongrowth or ingrowth. They now use a trabecular metal cup when contact with bleeding host bone is less then 50% [34]. The trabecular metal appears to provide a better environment for bone graft remodeling [36]. A cage protects the metal until the cup is stabilized, at which time the stress is relieved from the cage, and the midterm cage failures should not occur [34,36]. Udomkiat et al [35] reported loosening and migration of the cage in 9 out of 11 hips when the superior weight-bearing dome defect was N50%. He concluded that the cage alone could not withstand the load across the hip joint without a superior bone buttress. Morcellized allograft was not felt to be strong enough when there was a defect greater than 40% [35]. To reduce the loosening rate of the cage, the superior rim of the metal should be placed against host bone for 60% of its support. If the bony defect is too large to permit stable bony support, a structural allograft may
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be required for reconstruction [35]. Other authors have confirmed this finding reporting 0% to 2.7% loosening rates at 7 to 8 years when using structural grafts to reconstruct defects N50 % of the superior acetabulum [36-38]. Alternative treatments for a type III defect include high hip center [39], the oblong cups method [40,41] and more recently modular augments. Placing the cup at a high hip center may avoid the need for a structural graft. This strategy does not however restore bone stock and may significantly shorten the extremity and risk impingement and instability [42]. The high hip center has also been associated with a higher rate of acetabular loosening [43]. Despite improvements in techniques for bony reconstruction and acetabular fixation, instability remains one of the most challenging issues facing the revision surgeon. There is extensive literature detailing the potential causes of instability. These include component malposition, impingement, inadequate soft tissue tension, deficient abductor musculature, neuromuscular disorders, and patient noncompliance [44-47]. Revision surgery appears to make any or all of these factors more common. The quality of the soft tissue deteriorates with every revision operation. In a revision situation, inadequate soft tissue and bone stock contribute to a dislocation rate of as much as 15% to 30% [10,48,49]. Constrained acetabular liners are useful in the complex revision for achieving hip stability. These components are designed to hold the femoral head captive via a secure locking mechanism [44]. Goetz et al [21,50] reported no additional dislocations in 54 (96%) of 56 hips treated for recurrent instability using a constrained liner. The liners are usually easily applied and can be combined with a secondary procedure to achieve stability, such as trochanteric advancement [44]. Unfortunately, constrained liners may decrease range of motion. Increased transmission of stress to the implant-bone and implant-cement interface may lead to impingement and early loosening [51]. Component failure may occur by dissociation of the liner from the shell or the disruption of the locking mechanism. Unfortunately, if dislocation occurs in the presence of a cemented liner, open reduction or revision is usually required. In this study, the combination of significant bone loss and instability necessitated the use of an acetabular reconstruction cage combined with a constrained liner. Although this combination was effective for the immediate remedy of the pathology, there was significant failure rate (23%) at a mean follow-up of only 28 months. When we conducted a limited extended follow-up (6 patients), which increased our mean follow-up to 47 months, the failure rate increased (31%) due to a failure in a female patient secondary to aseptic loosing. She went on to revision with tantalum cup with a constrained liner due to an incompetent abductor mechanism. It is likely that the combination of poor acetabular bone stock and the increased stresses imparted to the construct through the constrained liner led to the early failure. Newer reconstruction devices, like trabecular metal
904 The Journal of Arthroplasty Vol. 25 No. 6 September 2010 revision systems and modular augments, may provide more viable options for these reconstructions. The increased porosity of the 3-D ingrowth materials combined with augments that can bridge acetabular defects appear to create a more biologic reconstruction option. These newer components also have the ability to employ very large femoral heads, which may obviate the need for a constrained liner. Nevertheless, cages are still used today, despite the availability of these newer devices. Thus, it is our recommendation that the combination of an acetabular reconstruction cage not be combined with a cemented constrained acetabular liner except as a salvage procedure.
Conclusion This series reviewed 16 cases of acetabular reconstruction using a protrusio acetabular cage combined with a cemented constrained liner. While the reconstructions were successful in terms of improvement of the Harris hip scores, there was a 23% (3/13) failure rate at mean follow-up of 28 months. Although this construct was found to be effective for reconstruction of severe acetabular bone loss complicated by instability, due to the high failure rate, this combination should be reserved for the salvage situation.
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