HIP ISSN 1120-7000
Hip Int 2015; 25 (2): 120-126 DOI: 10.5301/hipint.5000201
REVIEW
Management of pelvic discontinuity in revision total hip arthroplasty: a review of the literature Mohammad K. Abdelnasser1, Frank M. Klenke2, Patrick Whitlock3, Aly M. Khalil1, Yaser E. Khalifa1, Hassan M. Ali1, Klaus A. Siebenrock2 Orthopaedic Department, Assuit University Hospital, Assuit - Egypt Department of Orthopaedic Surgery, University of Bern, Bern - Switzerland 3 Maurice E. Müller foundation fellow at the Department of Orthopedic Surgery, University of Bern, Bern - Switzerland 1 2
ABSTRACT Pelvic discontinuity is a complex problem in revision total hip arthroplasty. Although rare, the incidence is likely to increase due to the ageing population and the increasing number of total hip arthroplasties being performed. The various surgical options available to solve this problem include plating, massive allografts, reconstruction rings, custom triflanged components and tantalum implants. However, the optimal solution remains controversial. None of the known methods completely solves the major obstacles associated with this problem, such as restoration of massive bone loss, implant failure in the short- and long-term and high complication rates. This review discusses the diagnosis, decision making, and treatment options of pelvic discontinuity in revision total hip arthroplasty. Keywords: Revision total hip arthroplasty, Pelvic discontinuity, Implants, Complications
Introduction Pelvic discontinuity describes the loss of structural bone or fracture between the superior and inferior pelvis resulting in complete separation of the superior pelvis from the inferior pelvis through the acetabulum (1-5). It is considered one of the most challenging aspects of acetabular revision surgery. Pelvic discontinuity is a rare condition usually due to progressive bone resorption secondary to periprosthetic osteolysis and osteopenia with increasing age. Pelvic discontinuity may also occur due to excessive acetabular reaming, trauma, infection, or stress fracture (1, 6-7) (Fig. 1). The incidence of pelvic discontinuity is rare. In published series, the rate of discontinuity encountered in revision total hip arthroplasty ranged from 1% to 8% of all acetabular revisions preformed (1, 3, 5, 8-11). Female sex and rheumatoid arthritis are associated with an increased risk of pelvic discontinuity. Furthermore, a history of radiation therapy of the pelvis has been reported to be a potential risk factor (1). The incidence of pelvic discontinuity is likely to increase due to an aging and more active population and due to the increasing Accepted: September 21, 2014 Published online: November 6, 2014 Corresponding author: Mohammad Kamal Abdelnasser Orthopaedic Department Assuit University Hospital 71516 Assuit, Egypt [email protected]
number of primary and revision total hip arthroplasties performed each year (12-15).
Diagnosis of pelvic discontinuity Successful revision total hip arthroplasty requires careful preoperative evaluation and planning. With respect to pelvic discontinuity, preoperative identification of pelvic discontinuity is of critical importance to surgical planning, and to ensure that the appropriate revision equipment is available in the operating room. Antiprotrusio cages, plates for the posterior column, large quantities of bone graft, large uncemented cups, structural metal wedges, or custom triflange sockets are among the many specialised implants that may be required to treat pelvic discontinuity (1, 5, 8, 10). Suspicion of pelvic discontinuity usually arises from plain radiographs. Computed tomography (CT) is recommended to confirm the diagnosis and to characterise the localisation and the amount of bone loss more precisely. Intraoperatively, pelvic discontinuity features pathologic motion between the superior and inferior portions of the acetabulum after removal of the acetabular components (10). Important intraoperative findings include the amount of host bone present, the location of structural defects, and the location of the discontinuity. It is also important to distinguish between acute and chronic pelvic discontinuity. Acute pelvic discontinuity with potential for healing shows minimal gapping between the superior and inferior hemipelvis such that bony apposition with compression is possible. Chronic discontinuity has a poor potential for healing. It may show large amounts of fibrous tissue between the hemipelves with the bone itself being sclerotic or nonvascularised (10). © 2014 Wichtig Publishing
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Fig. 1 - Female patient, 70 years old, sustained a T-type acetabular fracture on the right side after acute trauma representing acute pelvic discontinuity. The iliopectineal line (white arrow) is interrupted indicating fracture of the anterior column. The posterior column is identified by medial displacement and rotation of the ischial tuberosity (black arrow) and the visible fractures of the greater sciatic notch and inferior pubic ramus (dotted arrows).
Standard radiographs Plain anteroposterior radiographs of the pelvis are used for the initial assessment of pelvic discontinuity. The initial radiographic criterion relates to the superior migration of the hip center. The probability of a pelvic discontinuity is minimal if the hip center has not migrated more than 3 cm above the superior obturator line (16). Berry et al (1) reported the radiographic findings in 29 hips with pelvic discontinuity. These included visible fracture, rotation of the inferior aspect of the pelvis relative to superior aspect, asymmetry of the obturator rings, and a broken Kohler line with medial translation of the inferior hemipelvis (Fig. 2). None of these findings were visible with 100% consistency on preoperative radiographs. This is in line with the findings of Paprosky et al (17) who reported that, in their series of 147 patients, 11% were found intraoperatively to have a pelvic discontinuity that was not detected preoperatively. Oblique (Judet) and lateral views may be used as diagnostic tools to visualise the anterior and posterior column especially when visualisation of the acetabular columns is obscured by the radio-opaque acetabular implants. A cadaveric study (18) showed that oblique radiographs, especially false profile views were more sensitive than standard views in detecting pelvic discontinuities. False profile views achieve a more effective visualisation of the posterior column. Pelvic discontinuities can be detected more reliably because false profile views picture the region posterior to the acetabular component. Based on these findings, the authors recommended false profile views as a reasonable addition to evaluate a patient with acetabular component failure when a pelvic discontinuity is suspected. The visualisation of the posterior © 2014 Wichtig Publishing
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Fig. 2 - Male patient 72 years old with chronic pelvic discontinuity on the left side. Note the marked upward migration of the hip center of rotation, rotation of the inferior hemipelvis (asymmetric obturator foramina) and broken Kohler’s line (white arrow).
column is often obstructed by the presence of metal hardware when using standard Judet views of the pelvis. Giori and Sidki (19) showed that a lateral radiograph of the pelvis and/ or high-angle oblique views (10-20° off of a lateral view) of the pelvis can provide excellent visualisation of the posterior column and aid in the diagnosis of pelvic discontinuity. High angle oblique views can also be helpful if the contralateral side of the pelvis obscures visualisation of the posterior column of interest. Computed tomography CT is the most effective imaging tool in identifying osteolytic lesions, pelvic discontinuity, and column deficiencies (20) (Fig. 3). Metal hardware in the hip can cause substantial scatter of the CT image and may limit one’s ability to judge the bone of interest completely. Nevertheless, CT scans provide the most accurate localisation and characterisation of the pelvic discontinuity and the associated bone loss. Recent CT protocol includes the application of metal artifact suppression improving the assessability of pelvic discontinuity in the proximity of metal implants (21). Precise preoperative characterisation of pelvic discontinuity is essential to choose the best possible surgical strategy. Therefore, the authors recommend to use CT scans for each case of suspected pelvic discontinuity although CT is more expensive than radiography and increases radiation exposure to the patient.
Classification of pelvic discontinuity The most frequently used radiological classifications for acetabular defects are those defined by D’Antonio (also referred to as AAOS classification) (6), Paprosky (17), and Gross (22). The Paprosky classification quantifies the extent of bone loss to guide clinical decision making. However, it does not specifically include category of pelvic discontinuity. The classifications by
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3) Bone-grafting at the site of the discontinuity; 4) Treatment of any associated bone loss; and 5) Placement of a stable acetabular implant. Plates
Fig. 3 - CT scan of a female patient, 46 years old, showing pelvic discontinuity by the presence of a complete vertical fracture line through both columns (white arrows).
the AAOS and Gross categorise the type and location of the bone loss in more detail. These 2 classifications include a category for pelvic discontinuity. The original AAOS classification has been modified by Berry et al (1). (It includes a sub-classification of type IV defects: type IVa (pelvic discontinuity with cavitary or moderate segmental bone loss), type IVb (severe segmental loss or combined segmental and massive cavitary bone loss), and type IVc (previously irradiated bone with or without cavitary or segmental bone loss). Berry’s classification allows for a precise description of pelvic dissociations. Alternatively, Paprosky’s classification may be sub-classified into acetabular defects with and without pelvic discontinuity (e.g. type III A or type III B with and without discontinuity) (23).
Surgical management Management of pelvic discontinuity remains one of the most challenging aspects of hip surgery (1, 24, 25). However, the optimal surgical technique for management of pelvic discontinuity is still controversial. Numerous case series reporting the outcome of the various treatment options, have been published (1, 3-5). Long-term studies involving adequate series of patients treated with a specific surgical procedures are lacking. According to Berry et al (1), the guiding principles for the treatment of pelvic discontinuity are: 1) Identification of the problem; 2) Stabilisation or effective bypass of the discontinuity;
Plates are usually used together with other reconstructive devices. In case of acute pelvic discontinuity, isolated plating may be applied as a first stage acetabular revision to stabilise the discontinuity followed by a second stage cup revision. Stiehl et al (5) reported 10 cases of pelvic discontinuity in patients with an average age of 68 years treated with plating of the anterior and posterior columns, bone defect filling with structural allografts, and cemented cups. In total 8 patients had evidence of healing of the discontinuity. However, 6 patients encountered severe complications requiring revision surgery. Due to the high revision rate the authors concluded that this technique should be avoided in elderly patients. Similarly, Berry et al (1) found that none out of 5 pelvic discontinuities treated with dual plating and a cemented cup showed a satisfactory result. In contrast, 5 out of 8 hips reconstructed with a cementless socket and with 1 (7 hips) or 2 posterior plates (1 hip) had a mechanically stable construct at the time of the latest follow-up. In total, 4 of these 8 hips had a satisfactory result (3 had type IVa and 1 had type IVb) and 4 hips failed (all had type IVb). Due to the excessive motion, pelvic discontinuity compromises the incorporation of bone grafts which may lead to the failure of the reconstructive procedure. The combination of plate osteosynthesis with metal reinforcement cages may reduce this micromotion and improve healing (25). Previously, Eggli et al (26) evaluated the clinical outcome of 7 patients with pelvic discontinuity treated with plating of both columns, implantation of a reinforcement cage (5 with hook, 2 without hook), and transplantation of bone allograft and autograft. One patient had an additional revision surgery due to aseptic implant loosening and another patient required the removal of 2 prominent screws. After a mean follow-up of 96 months all acetabular components were stable and the pelvic discontinuities had healed. Similarly, Rogers et al (25) found that none out of 8 patients treated with compression plating of the posterior column plating and an acetabular shell required revision after a mean follow-up of 34 months. Without the use of posterior plating, Goodman et al (27) observed a failure rate of 50% of 10 cases of pelvic discontinuity treated with a cage alone. Springer et al (28) reported 7 cases of pelvic discontinuity that were diagnosed several months after hip revision arthroplasty performed with tantalum cups. Repeat revision surgery revealed the cups to be well-fixed in spite of the discontinuity, and supplementary fixation of the posterior column with a plate plus bone grafting was done. Only 4 out of the 7 cases healed. Massive structural allograft Filling the defective bone with unsupported massive allo grafts has resulted in early failure because of graft resorption and cup loosening (29). Paprosky and Sekundiak reported 3 failures in 17 patients with Paprosky type 3B defects treated with © 2014 Wichtig Publishing
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total acetabular allografts and cemented cups but without reconstruction cages after a mean follow-up of 31 months. One of the failures was attributable to aseptic loosening whereas the other 2 were attributable to recurrent infection (30). Paprosky’s unsatisfying experience with the use of total acetabular transplants and allografts with cage reconstructions has led him to encourage the use of alternative reconstructive measures with porous ingrowth implants (3). Non-custom reconstruction rings and cages Reconstruction rings and cages are the major alternative devices used in cases with major periacetabular bone loss. They are usually used to bridge an area of major acetabular bone loss or pelvic discontinuity by obtaining fixation from both the ischuim and ilium. Furthermore, they protect extensive acetabular bone graft by transferring the load from the acetabulum to the ilium and the ischium. They also help to restore the centre of rotation of the hip joint (27). Although cage reconstructions provide good initial stability, the inability for biologic fixation at the cage-bone interface may compromise long-term success (27, 31, 32). As such, a high failure rate at an average follow-up of 5 years has been shown by Paprosky et al (3) in 16 acetabular revisions for pelvic discontinuity using ilioischial acetabular cages, which were combined with posterior column plate, supporting structural allograft, or cancellous allograft. In total, 4 hips were revised because of aseptic loosening while another 3 cages were loose. In 10 cases of pelvic discontinuity with extensive cavitary and structural bone loss managed with antiprotrusio cages, Goodman et al (27) reported 8 patients had complications requiring reoperation. A total of 5 out of 10 reconstructions were successful after a mean follow-up of 41 months, i.e. they were stable without further revision of the antiprotrusio cage. Conversely, satisfactory outcome in the treatment of pelvic discontinuity using antiprotrusio cages was described by Berry et al (1) in 11 of 13 hips at a mean of 3 years postoperatively, and by Symeonides et al (33) in a small series of 7 cases. As stated above, Eggli et al (26), in a small case series of 7 patients treated with plating of both columns and reinforcement cages, showed that in 6 out of 7 patients the pelvic discontinuities healed with stable acetabular components and no further interventions. Regis et al (34) followed 18 patients revised with antiprotrusio cages and bulk bone graft. At a mean follow up of 13.5 years, no general complications were reported in this series and only 3 cases (16.7%) required revision (1 due to infection and 2 due to aseptic loosening). An extensive resorption of the bone graft occurred in 2 hips. The stability of the cage was confirmed in 13 cases. They concluded that the use of antiprotrusio cages and bulk allografts are a reliable option to manage pelvic discontinuities with acetabular deficiencies and appear to be able to restore vital bone stock. Custom triflange components Custom made triflange components have shown promising short- and mid-term results. They seem to provide a valuable alternative to non-custom reconstruction rings and cages. However, the number of studies available is limited. © 2014 Wichtig Publishing
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DeBoer et al (8) evaluated the outcome of revision total hip arthroplasty with a custom-made porous coated triflange acetabular cage in 20 patients with pelvic discontinuity at a mean of 10 years. Definitive healing of the pelvic discontinuity was found in 18 hips (90%), with the remaining 2 implants appearing radiographically stable. However, the overall dislocation rate in this population was 30%. Taunton et al (35) retrospectively reviewed 57 patients with pelvic discontinuity treated with revision THA using a custom triflange acetabular component. At a mean follow up of 65 months, there were 3 failures (5.3%) of the triflange acetabular component defined as revision or resection of the acetabular component. Two of these failures were due to deep infection and 1 was due to aseptic loosening. In total, 46 out of the 57 patients (81%) were judged to have a stable triflange acetabular components with a healed pelvic discontinuity. They concluded that in a group of patients with osteolytic pelvic discontinuity, triflange implants provided predictable midterm fixation. Holt and Dennis (36) also reported on the use of the custom triflange device in 26 hips. However, only 3 of the 26 hips had a pelvic discontinuity. Two of these 3 pelvic discontinuities failed secondary to loss of inferior fixation in the ischium. The authors recommended caution in the use of the device without additional column plating. The major drawback of custom made triflange components is the complexity of the preoperative templating process. The custom design process takes several weeks to complete and involves the surgeon working closely with the engineer. However, this disadvantage is compensated for by a relatively uncomplicated surgical technique without the need to shape, fit and fix the structural allograft nor to bend and fix the antiprotrosio cage. Trabecular Metal™ In recent years, the use of tantalum or Trabecular Metal™ for pelvic discontinuity has been recommened by many authors (9, 10, 16, 25). In contrast to approaches aiming at the healing of the pelvic discontinuity, Trabecular Metal™ implants are designed to bridge the area of pelvic discontinuity. Kosashvili et al (9) revised pelvic discontinuity using the so-called cup-cage technique viz. the combination of antiprotrusio cages, Trabecular Metal™ acetabular components, and morselised bone. No clinical or radiologic evidence of loosening was observed in 23 hips (88.5%) out of a consecutive series of 26 patients after a mean follow-up of 45 months. In the largest reported series so far, Rogers et al (25) evaluated 62 patient treated for chronic pelvic discontinuity after a mean follow up of 35 months (24-93 months). The reconstructive techniques used consisted in antiprotrusio cages or cup-cage reconstructions. Cup-cage reconstructions required revision in 9.5% (4/42 cases) whereas antiprotrusio cages had to be revised in 29% (6/20). The study demonstrated that cupcage acetabular reconstructions were superior to antiprotrusio cages in successfully reconstructing chronic pelvic discontinuity due to the inherent beneficial biologic and biomechanical properties of porous tantalum metal. Similarly, Sporer et al (16) reported on 20 chronic pelvic discontinuity cases treated with acetabular reconstruction using acetabular distraction.
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A porous tantalum elliptical acetabular component was used alone or together with a modular porous tantalum augment. The superior and inferior aspects of the hemipelvis were distracted through by using a tantalum acetabular component 6 to 8 mm larger than the last reamer. The porous acetabular component was initially placed against the remaining ischuim followed by bringing the implant to the desired position while continuously placing an inferiorly directed stress thus achieving distraction. The press fit created by this distraction porvided the initial stability of the cup until multiple cancellous screws were placed into the remaining ilium and ischuim. A total of 3 patients died and 5 were lost to follow-up before 2 years. After a minimum of 2 years (average 4.5 years; range 2-7 years) only 1 of the 20 patients required revision for aseptic loosening. In total, 4 patients had early migration of their acetabular component but remained clinically asymptomatic and radiographically stable thereafter. A total of 15 patients showed no signs of loosening or implant migration until the last follow up. They concluded that acetabular distraction for chronic pelvic discontinuity is promising to obtaining reliable and durable fixation. However, both the superior and inferior portions of the pelvis must achieve independent growth into the porous tantalum components for this method to be successful.
Complications Despite the many methods available for the treatment of pelvic discontinuity none of them completely solve the major obstacles associated with this problem such as restoration of massive bone loss, implant failure in the short- and long-term, and high complication rates. Complication rates of 25-80% have been reported (24, 26, 27). As such, authors often distinguish between reoperation (caused by any complication) and revision (because of failure of the reconstruction). The most frequent complications are those associated with any total hip arthroplasty revision surgery including dislocation, nerve injury, and infection. Dislocations Hip arthroplasty dislocations remain the most common complication associated with revision arthroplasty in the presence of pelvic discontinuity. The incidence of dislocation varies from 0% (16) to 40% (5). The high incidence of dislocation may be attributed to several factors including the high number of previous operations with resultant tissue scars and defects, abductor weakness, and extensive approaches. Furthermore, cup orientation is a key factor influencing the risk of dislocation (37). The possibility of a high degree of freedom for cup and/ or liner orientation is essential to adapt the orientation to the individual needs. Modular cup systems with a fixed connection of the metal shell and the liner may be limited in the ability to choose cup orientation freely. In contrast, cemented low profile cups used together with antiprotrusio cages allow the surgeon to adapt the cup orientation without substantial limitations. The same is true for large diameter Trabecular Metal™ shells into which a low profile cup may be cemented. Due to the high rate of dislocation, some authors recommend the use of constrained liners in those patients at risk for
Management of pelvic discontinuity in revision total hip arthroplasty
dislocation. These include patients with severe abductor insufficiency due to superior gluteal nerve injuries or extensive soft tissue scarring, proximal femoral deficiency, non union of the greater trochanter, or a history of recurrent dislocation (24, 38, 39). However, the routine use of constrained liners is not recommended because these implants were shown to increase stresses on the reconstruction which again may result in premature failure (40). More recently, dual mobility cups have been used to decrease the risk of dislocation (41, 42). Due to their design providing a large range of motion they are less associated with increased stresses on the acetabular reconstruction. The major concern of dual mobility cups is increased volumetric wear due to the large diameter of the outer bearing surface (43). However, long-term survival rates of dual mobility cups were shown to be as high as 81.5% after 20 years with respect cup or liner revision (44). Nerve injuries The sciatic nerve can be injured during ischial dissection when positioning the ischial flange. As such, some authors prefer to slot the ischial flange into the ischium. Other causes for sciatic nerve injury include inadvertent use of retractors, excessive limb lengthening and extensive soft tissue dissection. Similarly, the superior gluteal nerve is vulnerable to injury during dissection of the proximal ilium leading to abductor weakness and Trendelenberg gait. Deep infections Deep infection often requiring implant removal have been reported to occur in 0% (26) to 30% (5). Increased operative time, extensive tissue dissection, recurrent operations and poor general patient health contribute to these observed infections. Aseptic loosening Asceptic loosening ranges from 0% (8) to 44% (3). Paprosky et al (3) found an overall incidence of 44% aseptic loosening using reconstruction cages. Improved results regarding aseptic loosening have been obtained using custom triflanged (8, 35) and trabecular metal components (16, 25).
Own approach In acute pelvic discontinuities or chronic discontinuities in patients with good potential for osseous healing the authors usually aim for a solution obtaining osseous consolidation and restoration of the continuity of the pelvic ring. In such cases the authors most often perform plating of the anterior and/or posterior column, bone defect filling with allograft bone, and implantation of an antiprotrusio cage such as the Ganz reinforcement ring. In cases with a high risk of dislocation the authors use a dual mobility cup system that can be cemented into the antiprotrusio cage. In chronic discontinuities in patients with a high risk of non-union following reconstruction of the pelvis we prefer “non-biologic” solutions with the application of Trabecular © 2014 Wichtig Publishing
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Metal™ implants. Several factors including age, local bone stock, history of irradiation, presence of osteoporosis, rheumatoid arthritis, or diabetes, smoking, and chronic treatment with cortisone or other immunosuppressants are taken into account for the decision making. In the authors experience Trabecular Metal™ implants show a reliable integration into the host bone even in cases with severely altered local bone biology e.g. osteoporosis and chronic cortisone use.
Summary Pelvic discontinuity is a complex problem in revision total hip arthroplasty and its incidence is likely to increase with the increasing number of total hip arthroplasties performed each year. Accurate preoperative planning based on plain radiographs and computed tomography is essential for successful and durable reconstructions of the acetabulum. The surgical approach and the choice of implants depend on whether osseous consolidation of the pelvic ring or “nonbiologic” bridging of the acetabular defect with osseo-integratable implants such as Trabecular Metal™ is the primary goal. Today, the optimal surgical solution is still controversial. The treatment strategy should be individualised to the patients’ needs, the local bone and soft tissue quality and general health status of each patient to optimise treatment outcomes.
Disclosures Financial support: None. Conflct of interest: None.
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126 31. Paprosky WG, Sporer SS, Murphy BP. Addressing severe bone deficiency: what a cage will not do. J Arthroplasty. 2007;22(4) (Suppl 1):111-115. 32. Berry DJ. Antiprotrusio cages for acetabular revision. Clin Orthop Relat Res. 2004;420:106-112. 33. Symeonides PP, Petsatodes GE, Pournaras JD, Kapetanos GA, Christodoulou AG, Marougiannis DJ. The Effectiveness of the Burch-Schneider antiprotrusio cage for acetabular bone deficiency: five to twenty-one years’ follow-up. J Arthroplasty. 2009;24(2):168-174. 34. Regis D, Sandri A, Bonetti I, Bortolami O, Bartolozzi P. A minimum of 10-year follow-up of the Burch-Schneider cage and bulk allografts for the revision of pelvic discontinuity. J Arthroplasty. 2012;27(6):1057-1063, e1. 35. Taunton MJ, Fehring TK, Edwards P, Bernasek T, Holt GE, Christie MJ. Pelvic discontinuity treated with custom triflange component: a reliable option. Clin Orthop Relat Res. 2012; 470(2):428-434. 36. Holt GE, Dennis DA. Use of custom triflanged acetabular components in revision total hip arthroplasty. Clin Orthop Relat Res. 2004;429:209-214. 37. Elkins JM, Callaghan JJ, Brown TD. The 2014 Frank Stinchfield Award: The ‘Landing Zone’ for Wear and Stability in Total Hip
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Hip Int 2015; 25 (2): 120-126 DOI: 10.5301/hipint.5000201
REVIEW
Management of pelvic discontinuity in revision total hip arthroplasty: a review of the literature Mohammad K. Abdelnasser1, Frank M. Klenke2, Patrick Whitlock3, Aly M. Khalil1, Yaser E. Khalifa1, Hassan M. Ali1, Klaus A. Siebenrock2 Orthopaedic Department, Assuit University Hospital, Assuit - Egypt Department of Orthopaedic Surgery, University of Bern, Bern - Switzerland 3 Maurice E. Müller foundation fellow at the Department of Orthopedic Surgery, University of Bern, Bern - Switzerland 1 2
ABSTRACT Pelvic discontinuity is a complex problem in revision total hip arthroplasty. Although rare, the incidence is likely to increase due to the ageing population and the increasing number of total hip arthroplasties being performed. The various surgical options available to solve this problem include plating, massive allografts, reconstruction rings, custom triflanged components and tantalum implants. However, the optimal solution remains controversial. None of the known methods completely solves the major obstacles associated with this problem, such as restoration of massive bone loss, implant failure in the short- and long-term and high complication rates. This review discusses the diagnosis, decision making, and treatment options of pelvic discontinuity in revision total hip arthroplasty. Keywords: Revision total hip arthroplasty, Pelvic discontinuity, Implants, Complications
Introduction Pelvic discontinuity describes the loss of structural bone or fracture between the superior and inferior pelvis resulting in complete separation of the superior pelvis from the inferior pelvis through the acetabulum (1-5). It is considered one of the most challenging aspects of acetabular revision surgery. Pelvic discontinuity is a rare condition usually due to progressive bone resorption secondary to periprosthetic osteolysis and osteopenia with increasing age. Pelvic discontinuity may also occur due to excessive acetabular reaming, trauma, infection, or stress fracture (1, 6-7) (Fig. 1). The incidence of pelvic discontinuity is rare. In published series, the rate of discontinuity encountered in revision total hip arthroplasty ranged from 1% to 8% of all acetabular revisions preformed (1, 3, 5, 8-11). Female sex and rheumatoid arthritis are associated with an increased risk of pelvic discontinuity. Furthermore, a history of radiation therapy of the pelvis has been reported to be a potential risk factor (1). The incidence of pelvic discontinuity is likely to increase due to an aging and more active population and due to the increasing Accepted: September 21, 2014 Published online: November 6, 2014 Corresponding author: Mohammad Kamal Abdelnasser Orthopaedic Department Assuit University Hospital 71516 Assuit, Egypt [email protected]
number of primary and revision total hip arthroplasties performed each year (12-15).
Diagnosis of pelvic discontinuity Successful revision total hip arthroplasty requires careful preoperative evaluation and planning. With respect to pelvic discontinuity, preoperative identification of pelvic discontinuity is of critical importance to surgical planning, and to ensure that the appropriate revision equipment is available in the operating room. Antiprotrusio cages, plates for the posterior column, large quantities of bone graft, large uncemented cups, structural metal wedges, or custom triflange sockets are among the many specialised implants that may be required to treat pelvic discontinuity (1, 5, 8, 10). Suspicion of pelvic discontinuity usually arises from plain radiographs. Computed tomography (CT) is recommended to confirm the diagnosis and to characterise the localisation and the amount of bone loss more precisely. Intraoperatively, pelvic discontinuity features pathologic motion between the superior and inferior portions of the acetabulum after removal of the acetabular components (10). Important intraoperative findings include the amount of host bone present, the location of structural defects, and the location of the discontinuity. It is also important to distinguish between acute and chronic pelvic discontinuity. Acute pelvic discontinuity with potential for healing shows minimal gapping between the superior and inferior hemipelvis such that bony apposition with compression is possible. Chronic discontinuity has a poor potential for healing. It may show large amounts of fibrous tissue between the hemipelves with the bone itself being sclerotic or nonvascularised (10). © 2014 Wichtig Publishing
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Fig. 1 - Female patient, 70 years old, sustained a T-type acetabular fracture on the right side after acute trauma representing acute pelvic discontinuity. The iliopectineal line (white arrow) is interrupted indicating fracture of the anterior column. The posterior column is identified by medial displacement and rotation of the ischial tuberosity (black arrow) and the visible fractures of the greater sciatic notch and inferior pubic ramus (dotted arrows).
Standard radiographs Plain anteroposterior radiographs of the pelvis are used for the initial assessment of pelvic discontinuity. The initial radiographic criterion relates to the superior migration of the hip center. The probability of a pelvic discontinuity is minimal if the hip center has not migrated more than 3 cm above the superior obturator line (16). Berry et al (1) reported the radiographic findings in 29 hips with pelvic discontinuity. These included visible fracture, rotation of the inferior aspect of the pelvis relative to superior aspect, asymmetry of the obturator rings, and a broken Kohler line with medial translation of the inferior hemipelvis (Fig. 2). None of these findings were visible with 100% consistency on preoperative radiographs. This is in line with the findings of Paprosky et al (17) who reported that, in their series of 147 patients, 11% were found intraoperatively to have a pelvic discontinuity that was not detected preoperatively. Oblique (Judet) and lateral views may be used as diagnostic tools to visualise the anterior and posterior column especially when visualisation of the acetabular columns is obscured by the radio-opaque acetabular implants. A cadaveric study (18) showed that oblique radiographs, especially false profile views were more sensitive than standard views in detecting pelvic discontinuities. False profile views achieve a more effective visualisation of the posterior column. Pelvic discontinuities can be detected more reliably because false profile views picture the region posterior to the acetabular component. Based on these findings, the authors recommended false profile views as a reasonable addition to evaluate a patient with acetabular component failure when a pelvic discontinuity is suspected. The visualisation of the posterior © 2014 Wichtig Publishing
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Fig. 2 - Male patient 72 years old with chronic pelvic discontinuity on the left side. Note the marked upward migration of the hip center of rotation, rotation of the inferior hemipelvis (asymmetric obturator foramina) and broken Kohler’s line (white arrow).
column is often obstructed by the presence of metal hardware when using standard Judet views of the pelvis. Giori and Sidki (19) showed that a lateral radiograph of the pelvis and/ or high-angle oblique views (10-20° off of a lateral view) of the pelvis can provide excellent visualisation of the posterior column and aid in the diagnosis of pelvic discontinuity. High angle oblique views can also be helpful if the contralateral side of the pelvis obscures visualisation of the posterior column of interest. Computed tomography CT is the most effective imaging tool in identifying osteolytic lesions, pelvic discontinuity, and column deficiencies (20) (Fig. 3). Metal hardware in the hip can cause substantial scatter of the CT image and may limit one’s ability to judge the bone of interest completely. Nevertheless, CT scans provide the most accurate localisation and characterisation of the pelvic discontinuity and the associated bone loss. Recent CT protocol includes the application of metal artifact suppression improving the assessability of pelvic discontinuity in the proximity of metal implants (21). Precise preoperative characterisation of pelvic discontinuity is essential to choose the best possible surgical strategy. Therefore, the authors recommend to use CT scans for each case of suspected pelvic discontinuity although CT is more expensive than radiography and increases radiation exposure to the patient.
Classification of pelvic discontinuity The most frequently used radiological classifications for acetabular defects are those defined by D’Antonio (also referred to as AAOS classification) (6), Paprosky (17), and Gross (22). The Paprosky classification quantifies the extent of bone loss to guide clinical decision making. However, it does not specifically include category of pelvic discontinuity. The classifications by
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3) Bone-grafting at the site of the discontinuity; 4) Treatment of any associated bone loss; and 5) Placement of a stable acetabular implant. Plates
Fig. 3 - CT scan of a female patient, 46 years old, showing pelvic discontinuity by the presence of a complete vertical fracture line through both columns (white arrows).
the AAOS and Gross categorise the type and location of the bone loss in more detail. These 2 classifications include a category for pelvic discontinuity. The original AAOS classification has been modified by Berry et al (1). (It includes a sub-classification of type IV defects: type IVa (pelvic discontinuity with cavitary or moderate segmental bone loss), type IVb (severe segmental loss or combined segmental and massive cavitary bone loss), and type IVc (previously irradiated bone with or without cavitary or segmental bone loss). Berry’s classification allows for a precise description of pelvic dissociations. Alternatively, Paprosky’s classification may be sub-classified into acetabular defects with and without pelvic discontinuity (e.g. type III A or type III B with and without discontinuity) (23).
Surgical management Management of pelvic discontinuity remains one of the most challenging aspects of hip surgery (1, 24, 25). However, the optimal surgical technique for management of pelvic discontinuity is still controversial. Numerous case series reporting the outcome of the various treatment options, have been published (1, 3-5). Long-term studies involving adequate series of patients treated with a specific surgical procedures are lacking. According to Berry et al (1), the guiding principles for the treatment of pelvic discontinuity are: 1) Identification of the problem; 2) Stabilisation or effective bypass of the discontinuity;
Plates are usually used together with other reconstructive devices. In case of acute pelvic discontinuity, isolated plating may be applied as a first stage acetabular revision to stabilise the discontinuity followed by a second stage cup revision. Stiehl et al (5) reported 10 cases of pelvic discontinuity in patients with an average age of 68 years treated with plating of the anterior and posterior columns, bone defect filling with structural allografts, and cemented cups. In total 8 patients had evidence of healing of the discontinuity. However, 6 patients encountered severe complications requiring revision surgery. Due to the high revision rate the authors concluded that this technique should be avoided in elderly patients. Similarly, Berry et al (1) found that none out of 5 pelvic discontinuities treated with dual plating and a cemented cup showed a satisfactory result. In contrast, 5 out of 8 hips reconstructed with a cementless socket and with 1 (7 hips) or 2 posterior plates (1 hip) had a mechanically stable construct at the time of the latest follow-up. In total, 4 of these 8 hips had a satisfactory result (3 had type IVa and 1 had type IVb) and 4 hips failed (all had type IVb). Due to the excessive motion, pelvic discontinuity compromises the incorporation of bone grafts which may lead to the failure of the reconstructive procedure. The combination of plate osteosynthesis with metal reinforcement cages may reduce this micromotion and improve healing (25). Previously, Eggli et al (26) evaluated the clinical outcome of 7 patients with pelvic discontinuity treated with plating of both columns, implantation of a reinforcement cage (5 with hook, 2 without hook), and transplantation of bone allograft and autograft. One patient had an additional revision surgery due to aseptic implant loosening and another patient required the removal of 2 prominent screws. After a mean follow-up of 96 months all acetabular components were stable and the pelvic discontinuities had healed. Similarly, Rogers et al (25) found that none out of 8 patients treated with compression plating of the posterior column plating and an acetabular shell required revision after a mean follow-up of 34 months. Without the use of posterior plating, Goodman et al (27) observed a failure rate of 50% of 10 cases of pelvic discontinuity treated with a cage alone. Springer et al (28) reported 7 cases of pelvic discontinuity that were diagnosed several months after hip revision arthroplasty performed with tantalum cups. Repeat revision surgery revealed the cups to be well-fixed in spite of the discontinuity, and supplementary fixation of the posterior column with a plate plus bone grafting was done. Only 4 out of the 7 cases healed. Massive structural allograft Filling the defective bone with unsupported massive allo grafts has resulted in early failure because of graft resorption and cup loosening (29). Paprosky and Sekundiak reported 3 failures in 17 patients with Paprosky type 3B defects treated with © 2014 Wichtig Publishing
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total acetabular allografts and cemented cups but without reconstruction cages after a mean follow-up of 31 months. One of the failures was attributable to aseptic loosening whereas the other 2 were attributable to recurrent infection (30). Paprosky’s unsatisfying experience with the use of total acetabular transplants and allografts with cage reconstructions has led him to encourage the use of alternative reconstructive measures with porous ingrowth implants (3). Non-custom reconstruction rings and cages Reconstruction rings and cages are the major alternative devices used in cases with major periacetabular bone loss. They are usually used to bridge an area of major acetabular bone loss or pelvic discontinuity by obtaining fixation from both the ischuim and ilium. Furthermore, they protect extensive acetabular bone graft by transferring the load from the acetabulum to the ilium and the ischium. They also help to restore the centre of rotation of the hip joint (27). Although cage reconstructions provide good initial stability, the inability for biologic fixation at the cage-bone interface may compromise long-term success (27, 31, 32). As such, a high failure rate at an average follow-up of 5 years has been shown by Paprosky et al (3) in 16 acetabular revisions for pelvic discontinuity using ilioischial acetabular cages, which were combined with posterior column plate, supporting structural allograft, or cancellous allograft. In total, 4 hips were revised because of aseptic loosening while another 3 cages were loose. In 10 cases of pelvic discontinuity with extensive cavitary and structural bone loss managed with antiprotrusio cages, Goodman et al (27) reported 8 patients had complications requiring reoperation. A total of 5 out of 10 reconstructions were successful after a mean follow-up of 41 months, i.e. they were stable without further revision of the antiprotrusio cage. Conversely, satisfactory outcome in the treatment of pelvic discontinuity using antiprotrusio cages was described by Berry et al (1) in 11 of 13 hips at a mean of 3 years postoperatively, and by Symeonides et al (33) in a small series of 7 cases. As stated above, Eggli et al (26), in a small case series of 7 patients treated with plating of both columns and reinforcement cages, showed that in 6 out of 7 patients the pelvic discontinuities healed with stable acetabular components and no further interventions. Regis et al (34) followed 18 patients revised with antiprotrusio cages and bulk bone graft. At a mean follow up of 13.5 years, no general complications were reported in this series and only 3 cases (16.7%) required revision (1 due to infection and 2 due to aseptic loosening). An extensive resorption of the bone graft occurred in 2 hips. The stability of the cage was confirmed in 13 cases. They concluded that the use of antiprotrusio cages and bulk allografts are a reliable option to manage pelvic discontinuities with acetabular deficiencies and appear to be able to restore vital bone stock. Custom triflange components Custom made triflange components have shown promising short- and mid-term results. They seem to provide a valuable alternative to non-custom reconstruction rings and cages. However, the number of studies available is limited. © 2014 Wichtig Publishing
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DeBoer et al (8) evaluated the outcome of revision total hip arthroplasty with a custom-made porous coated triflange acetabular cage in 20 patients with pelvic discontinuity at a mean of 10 years. Definitive healing of the pelvic discontinuity was found in 18 hips (90%), with the remaining 2 implants appearing radiographically stable. However, the overall dislocation rate in this population was 30%. Taunton et al (35) retrospectively reviewed 57 patients with pelvic discontinuity treated with revision THA using a custom triflange acetabular component. At a mean follow up of 65 months, there were 3 failures (5.3%) of the triflange acetabular component defined as revision or resection of the acetabular component. Two of these failures were due to deep infection and 1 was due to aseptic loosening. In total, 46 out of the 57 patients (81%) were judged to have a stable triflange acetabular components with a healed pelvic discontinuity. They concluded that in a group of patients with osteolytic pelvic discontinuity, triflange implants provided predictable midterm fixation. Holt and Dennis (36) also reported on the use of the custom triflange device in 26 hips. However, only 3 of the 26 hips had a pelvic discontinuity. Two of these 3 pelvic discontinuities failed secondary to loss of inferior fixation in the ischium. The authors recommended caution in the use of the device without additional column plating. The major drawback of custom made triflange components is the complexity of the preoperative templating process. The custom design process takes several weeks to complete and involves the surgeon working closely with the engineer. However, this disadvantage is compensated for by a relatively uncomplicated surgical technique without the need to shape, fit and fix the structural allograft nor to bend and fix the antiprotrosio cage. Trabecular Metal™ In recent years, the use of tantalum or Trabecular Metal™ for pelvic discontinuity has been recommened by many authors (9, 10, 16, 25). In contrast to approaches aiming at the healing of the pelvic discontinuity, Trabecular Metal™ implants are designed to bridge the area of pelvic discontinuity. Kosashvili et al (9) revised pelvic discontinuity using the so-called cup-cage technique viz. the combination of antiprotrusio cages, Trabecular Metal™ acetabular components, and morselised bone. No clinical or radiologic evidence of loosening was observed in 23 hips (88.5%) out of a consecutive series of 26 patients after a mean follow-up of 45 months. In the largest reported series so far, Rogers et al (25) evaluated 62 patient treated for chronic pelvic discontinuity after a mean follow up of 35 months (24-93 months). The reconstructive techniques used consisted in antiprotrusio cages or cup-cage reconstructions. Cup-cage reconstructions required revision in 9.5% (4/42 cases) whereas antiprotrusio cages had to be revised in 29% (6/20). The study demonstrated that cupcage acetabular reconstructions were superior to antiprotrusio cages in successfully reconstructing chronic pelvic discontinuity due to the inherent beneficial biologic and biomechanical properties of porous tantalum metal. Similarly, Sporer et al (16) reported on 20 chronic pelvic discontinuity cases treated with acetabular reconstruction using acetabular distraction.
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A porous tantalum elliptical acetabular component was used alone or together with a modular porous tantalum augment. The superior and inferior aspects of the hemipelvis were distracted through by using a tantalum acetabular component 6 to 8 mm larger than the last reamer. The porous acetabular component was initially placed against the remaining ischuim followed by bringing the implant to the desired position while continuously placing an inferiorly directed stress thus achieving distraction. The press fit created by this distraction porvided the initial stability of the cup until multiple cancellous screws were placed into the remaining ilium and ischuim. A total of 3 patients died and 5 were lost to follow-up before 2 years. After a minimum of 2 years (average 4.5 years; range 2-7 years) only 1 of the 20 patients required revision for aseptic loosening. In total, 4 patients had early migration of their acetabular component but remained clinically asymptomatic and radiographically stable thereafter. A total of 15 patients showed no signs of loosening or implant migration until the last follow up. They concluded that acetabular distraction for chronic pelvic discontinuity is promising to obtaining reliable and durable fixation. However, both the superior and inferior portions of the pelvis must achieve independent growth into the porous tantalum components for this method to be successful.
Complications Despite the many methods available for the treatment of pelvic discontinuity none of them completely solve the major obstacles associated with this problem such as restoration of massive bone loss, implant failure in the short- and long-term, and high complication rates. Complication rates of 25-80% have been reported (24, 26, 27). As such, authors often distinguish between reoperation (caused by any complication) and revision (because of failure of the reconstruction). The most frequent complications are those associated with any total hip arthroplasty revision surgery including dislocation, nerve injury, and infection. Dislocations Hip arthroplasty dislocations remain the most common complication associated with revision arthroplasty in the presence of pelvic discontinuity. The incidence of dislocation varies from 0% (16) to 40% (5). The high incidence of dislocation may be attributed to several factors including the high number of previous operations with resultant tissue scars and defects, abductor weakness, and extensive approaches. Furthermore, cup orientation is a key factor influencing the risk of dislocation (37). The possibility of a high degree of freedom for cup and/ or liner orientation is essential to adapt the orientation to the individual needs. Modular cup systems with a fixed connection of the metal shell and the liner may be limited in the ability to choose cup orientation freely. In contrast, cemented low profile cups used together with antiprotrusio cages allow the surgeon to adapt the cup orientation without substantial limitations. The same is true for large diameter Trabecular Metal™ shells into which a low profile cup may be cemented. Due to the high rate of dislocation, some authors recommend the use of constrained liners in those patients at risk for
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dislocation. These include patients with severe abductor insufficiency due to superior gluteal nerve injuries or extensive soft tissue scarring, proximal femoral deficiency, non union of the greater trochanter, or a history of recurrent dislocation (24, 38, 39). However, the routine use of constrained liners is not recommended because these implants were shown to increase stresses on the reconstruction which again may result in premature failure (40). More recently, dual mobility cups have been used to decrease the risk of dislocation (41, 42). Due to their design providing a large range of motion they are less associated with increased stresses on the acetabular reconstruction. The major concern of dual mobility cups is increased volumetric wear due to the large diameter of the outer bearing surface (43). However, long-term survival rates of dual mobility cups were shown to be as high as 81.5% after 20 years with respect cup or liner revision (44). Nerve injuries The sciatic nerve can be injured during ischial dissection when positioning the ischial flange. As such, some authors prefer to slot the ischial flange into the ischium. Other causes for sciatic nerve injury include inadvertent use of retractors, excessive limb lengthening and extensive soft tissue dissection. Similarly, the superior gluteal nerve is vulnerable to injury during dissection of the proximal ilium leading to abductor weakness and Trendelenberg gait. Deep infections Deep infection often requiring implant removal have been reported to occur in 0% (26) to 30% (5). Increased operative time, extensive tissue dissection, recurrent operations and poor general patient health contribute to these observed infections. Aseptic loosening Asceptic loosening ranges from 0% (8) to 44% (3). Paprosky et al (3) found an overall incidence of 44% aseptic loosening using reconstruction cages. Improved results regarding aseptic loosening have been obtained using custom triflanged (8, 35) and trabecular metal components (16, 25).
Own approach In acute pelvic discontinuities or chronic discontinuities in patients with good potential for osseous healing the authors usually aim for a solution obtaining osseous consolidation and restoration of the continuity of the pelvic ring. In such cases the authors most often perform plating of the anterior and/or posterior column, bone defect filling with allograft bone, and implantation of an antiprotrusio cage such as the Ganz reinforcement ring. In cases with a high risk of dislocation the authors use a dual mobility cup system that can be cemented into the antiprotrusio cage. In chronic discontinuities in patients with a high risk of non-union following reconstruction of the pelvis we prefer “non-biologic” solutions with the application of Trabecular © 2014 Wichtig Publishing
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Metal™ implants. Several factors including age, local bone stock, history of irradiation, presence of osteoporosis, rheumatoid arthritis, or diabetes, smoking, and chronic treatment with cortisone or other immunosuppressants are taken into account for the decision making. In the authors experience Trabecular Metal™ implants show a reliable integration into the host bone even in cases with severely altered local bone biology e.g. osteoporosis and chronic cortisone use.
Summary Pelvic discontinuity is a complex problem in revision total hip arthroplasty and its incidence is likely to increase with the increasing number of total hip arthroplasties performed each year. Accurate preoperative planning based on plain radiographs and computed tomography is essential for successful and durable reconstructions of the acetabulum. The surgical approach and the choice of implants depend on whether osseous consolidation of the pelvic ring or “nonbiologic” bridging of the acetabular defect with osseo-integratable implants such as Trabecular Metal™ is the primary goal. Today, the optimal surgical solution is still controversial. The treatment strategy should be individualised to the patients’ needs, the local bone and soft tissue quality and general health status of each patient to optimise treatment outcomes.
Disclosures Financial support: None. Conflct of interest: None.
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