ORIGINAL PAPER

Cementless acetabular revision: past, present, and futureRevision total hip arthroplasty: the acetabular side using cementless implants

Luis Pulido & Sridhar R. Rachala & Miguel E. Cabanela

Received: 20 December 2010 /Accepted: 21 December 2010 /Published online: 14 January 2011# Springer-Verlag 2011

AbstractBackground Acetabular revision is probably the mostdifficult aspect of hip reconstructive surgery. Although themajority of acetabular revisions can be performed using anuncemented hemispherical acetabular device with ancillaryfixation, patients with severe acetabular deficiencies andpoor bone quality require more complex alternatives forrevision. The limitations of traditional cementless acetabu-lar implants has promoted the development of improvedmethods of fixation and revision techniques. Highly porousmetals have been introduced for clinical use in arthroplastysurgery over the last decade. Their higher porosity andsurface friction are ideal for acetabular revision, optimisingbiological fixation. The use of trabecular metal cups inacetabular revision has yielded excellent clinical results.Purpose This review focuses on the use of cementlessimplants for acetabular revision. The use of trabecular metalcups, augments, jumbo cups, oblong cups, cages, andstructural grafting are also discussed.

Introduction

Total hip arthroplasty (THA) ranks as one of the mostsuccessful operations yet devised [1]. It has ruled as the goldstandard treatment for end stage hip disease with excellentclinical results and long-term survivorship. Nonetheless, as

the number of THA increases, and the indications for hipreplacement widen, the number of failures continues to rise.Projection models predict an increase in demand for revisionarthroplasties over the next two decades [2]. The indicationsfor acetabular revision include symptomatic aseptic loosen-ing, failure of fixation, infection, wear, osteolysis, andinstability. Revision may be indicated for an asymptomaticpatient who has progressive osteolysis, severe wear, or boneloss that could compromise a future reconstruction [3].

For the arthroplasty surgeon, acetabular revision is the mostdifficult aspect of hip reconstruction. The achievement of thebasic principles of hip replacement is challenged by the loss ofacetabular bone stock and the condition of the soft tissues.Acetabular bone defects in which the implant has contact withgreater than 50% of the host bone can be addressed using ahemispherical uncemented cup, screw fixation, and morsel-ised bone grafting. The use of an extra large diameter cup issometimes necessary for initial stability. Patients with severecombined segmental and cavitation bone deficiencies, poorbone quality and biology, and pelvic discontinuity, will requiremore complex alternatives for acetabular revision. Trabecularmetal (highly porous metals) cups, augments, oblong cups,reinforcement roof rings, antiprotrusio cages, cup-cages,posterior column plating, structural grafting or combinationsof the above are available for complex acetabular reconstruc-tion. Adequate preoperative planning improves operativeefficiency, and helps identify when more complex alternativesfor reconstruction are needed.

The use of a classification system based on radiographshelps to predict the severity and location of bone loss, andguide treatment options. The Paprosky acetabular classifi-cation system in the failed total hip arthroplasty has provenhelpful in the surgical planning of acetabular revision [4].This system is based on the severity of bone loss and theability to obtain cementless fixation for a given bone losspattern. The evaluation of preoperative radiographs allowsthe surgeon to be prepared and anticipate intraoperativefindings [5] (Table 1).

L. Pulido :M. E. Cabanela (*)Department of Orthopedic Surgery, Mayo Clinic,200 First Street,Rochester, MN 55905, USAe-mail: cabanela.miguel@mayo.edu

S. R. RachalaDepartment of Orthopedic Surgery,State University of New York at Buffalo,100 high Street,Buffalo, NY 14203, USA

International Orthopaedics (SICOT) (2011) 35:289–298DOI 10.1007/s00264-010-1198-y

Cemented acetabular revision

The use of cemented fixation in acetabular revision has beenassociated with unacceptable loosening rates. Kavanagh et al.reviewed 165 cemented revision hip arthroplasties with aminimum follow-up of two years. The probable loosening rateof the revised acetabular component was 25%, and theincidence of symptomatic loosening was almost 50% if therevision was done for acetabular loosening [6]. Callaghan etal. presented similar early results with 34% of acetabularloosening at two to five years follow-up [7]. The long-termresults of cemented acetabular revision are of even moreconcern. Katz et al. reported 65% acetabular loosening orrevision with a minimum of ten years follow-up [8]. Datafrom the Norwegian arthroplasty registry including over4,762 revision hip operations, showed inferior results withthe use of cemented revision techniques [9].

Uncemented acetabular revision

Porous coated hip implants were introduced almost 30 yearsago in an attempt to improve the durability of hip replacement.Initially the cementless implant metallurgy included: cobalt–chrome sintered beads, diffusion bonded fibre metal mesh,cancellous-structured titanium, and titanium plasma spray.Their biological method of fixation allows bone ingrowth or

ongrowth and remodelling in the metal-bone interface, andlonger rigid fixation. However, in the setting of acetabularrevision surgery these traditional materials have inherentlimitations, particularly when the surface of native boneavailable for osteointegration was minimal.

The limitations of traditional cementless acetabularimplants encouraged further work toward improved fixationmethods, alternative techniques and implants for acetabularrevision, especially in cases with major bone loss. Highlyporous metals (HPM) were developed to improve upon thebiomaterial properties of uncemented implants. The open-cellstructure of these HPMs is ideal for acetabular revision surgerydue to the high volumetric porosity, low modulus of elasticity,and high frictional characteristics. These characteristics offerthe potential of better osseointegration and biological fixationwith increased depth of bone ingrowth and improved initialstability [10, 11]. The manufacturing process involves thecreation of a reticulated skeleton with deposition of a metalonto the surface. Polyurethane foam, reticulated vitreouscarbon, and other organic substrates can be designed intovarious shapes and sizes for use in orthopaedics. Once ascaffold is created, a metallic coating can be applied using achemical or arc vapour deposition process. Histologicalanalyses of the bone and fibrous ingrowth responses tovarious implants in animals have indicated a propensity forrapid infiltration with healing tissue and rapid rates ofmechanical attachment and osteointegration.

Table 1 Paprosky classification of acetabular defects

Type of defect Radiographic and intraoperative findings

Type-I Acetabular rim, anterior-posterior column intactImplies near primary situation with >90% host bone support of cup

Type-II Less than 3 cm superior migrationDistorted acetabular rim. Intact anterior and posterior columnsAdequate stability with Trial. Greater than 50% contact surface

IIA Superior and medial cavitation defect. Intact rim

IIB Segmental supero-lateral defect (less than 1/3 of circumference)

IIC Medial defect with cup medial to Kohler’s line (Protrusio)

Type-III Greater than 3 cm superior migrationNon-supportive acetabular rim for biological fixation

IIIA “Up and Out” Lateral to Kohler’s line. Intact medial supportModerate ischial lysis (<15 mm below superior obturator line)Medial limb of teardrop is intactSuperior and lateral migration “up and out”Contact of trial with bone over 40–60%Intact ilioischial and iliopubic

IIIB “Up and In” Broken Kohler’s line. No medial or superior supportnExtensive ischial osteolysis (>15 mm below superior obturator line)Complete destruction of tear dropSuperior and medial migration “up and in”Under 40% contact surface. High risk of occult pelvic discontinuity

Pelvic discontinuity Fracture line through columnsBroken Kohler’s line or obturator foramen asymmetry on AP pelvisSuperior and inferior hemipelvis separation

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Several orthopaedic manufacturers have introduced theirproducts of highly porous metals for arthroplasty over the lastdecade. These include: Trabecular Metal (Tantalum, Zimmer,Warsaw, IN), Tritanium (Titanium, Stryker, Mahwah, NJ),Regenerex (Titanium, Biomet, Warsaw, IN), Stiktite (Titanium,Smith and Nephew, Memphis, TN) and Gription (Titanium,DePuy, Warsaw, IN). Trabecular Metal (TM) has been theleader in development and use of this technology, with themostrobust basic and clinical data. They are currently available foruse in reconstructive surgery with promising clinical results inacetabular revision surgery (Table 2).

Cementless acetabular designs

The high failure rates of cemented cups encouraged theevolution of uncemented fixation. As the outcomes ofacetabular revision were better with cementless fixationthan with cement, uncemented fixation became the methodof choice in acetabular primary and revision arthroplasty.The early cup models used different ingrowth surfacetechnologies for cementless fixation. In the mid 1980s theuse of the Mecron (Johnson and Johnson, New Brunswick,New Jersey) threaded metal screw-in cups was undertaken.The initial enthusiasm was tempered by high early failurerates. Engh et al. report their experience after 54 revisioncups and showed an overall 42% loosening rate at anaverage of 4.4 years [12].

The porous-coated anatomic ingrowth cup (PCA) long-term results showed a 23% failure rate at 15 years inprimary THA [13]. The PCA cup in revision surgeryshowed good early clinical results. Hedley et al. performed61 acetabular revisions for infection and mechanicalloosening. After 20 months, there was a 6.6% looseningrate (4 of 64) [14]. The Anatomic Medullary Lockingprosthesis (AML) (De Puy, Warsaw, Indiana) porous-surfaced hemispheric acetabular design with either spikesor threads showed good mid-term results. Engh et al.presented one failure of 34 acetabular revisions at 4.4 yearsfollow-up [12].

The Harris-Galante prosthesis (HGP I and HGP II,Zimmer, Warzaw, Indiana) in uncemented acetabularrevision showed excellent early-, mid- and long-termresults. The HGP is a titanium mesh ingrowth prosthesisfixed with supplemental acetabular screws (Fig. 1a, b).

Tanzer and Harris published their early results after 140acetabular revisions [15]. There were two failures (1.4%) at41 month follow-up. Both cases were young patients withpelvic discontinuity, and their cups had migrated.Lachiewicz et al. [16] published his mid-term results atfive to 12 years of 57 cementless acetabular revisions usingHGP I or II implants. Despite varying degrees of bone loss,no acetabular component showed evidence of loosening atthe latest follow-up. Long-term results of the HGPacetabular components for revision were published byHallstrom et al. [17]. The authors studied 122 patients withan average follow-up of 12.5 years. The rate of survival ofthe shell, with aseptic loosening as the end point, was 96%at 12 years. The survival rate with revision surgery as theendpoint was 88% at 12 years. A series by Templeton et al.,including 64 acetabular revisions using the HGP-I, showedoutstanding long-term results at ten to 14 years follow-up[18]. With failure defined as repeat revision of theacetabular component because of aseptic loosening, therate of survival was 100% at ten years after the indexrevision. With an end point of definite or probableloosening of the acetabular component, the probability ofsurvival at ten years was 98%.

Hydroxyapatite (HA) coated shells should not be usedfor acetabular revision. Manley et al. [19] published a

Fig. 1 a Failed PCA acetabular component with severe polyethylenewear. b Same patient 11 years after revision with uncementedacetabular component

Biomaterial properties Trabecular metal Tritanium Regenerex Stiktite Gription

Metal coatings Tantalum Titaniuim Titanium Titanium Titanium

Modulus of elasticity (GPa) 2.5–3.9 106–115 1.6 NA NA

Average pore size 550 μm 616 μm 300 μm 200 μm 300 μm

Porosity 75% 60% 67% 60% 63%

Coefficient of friction 0.88 0.65 NA 96–100 1.2

Table 2 General characteristicsof highly porous metal coatingsfor acetabular revision

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multicentre study comparing three different surfaces in 377patients for uncemented acetabular fixation in total hiparthroplasty. At a minimum of one year follow-up, one(1%) of the 131 hydroxyapatite-coated threaded cups, two(2%) of the 109 porous-coated pressfit cups, and 21 (11%)of the 188 hydroxyapatite-coated pressfit cups were revisedfor aseptic loosening. The probability of revision for asepticloosening was significantly greater for the hydroxyapatitecoated pressfit cups than it was for the hydroxyapatitecoated threaded cups or the porous-coated pressfit cups.Lazarinis et al. [20] studied 8,043 THAs using uncementedacetabular fixation with and without HA coated implantsfrom the Swedish arthroplasty registry. They found that HAcoating was a risk factor for cup revision for asepticloosening. Others however have shown satisfactory long-term results with HA coated cups.

Lewallen et al. reported the long-term survivorship of 2,443acetabular revisions performed at the Mayo Clinic between1984 and 1998 [21]. They showed that survivorship of themajority of uncemented acetabular designs (HG-I, HG-II,PCA, PSL [Peripheral self locking], Spherical, and Trilogy)dropped consistently below 90% after ten years follow-up,with a dramatic increase in their failure rate and revisionsurgery. Despite variability in the results by acetabular design,there was a uniform fall-off in results into the second decadeafter surgery. There was a positive correlation betweenacetabular bone stock and implant failure.

Jumbo cups

The use of cementless extra large “jumbo cups” foracetabular revision has shown favourable results in patientswith moderate, but not severe bone loss. The advantages ofextra-large sockets are that (1) the acetabulum is preparedby reaming to a large hemisphere, a method that istechnically straightforward; (2) most bone deficiencies arefilled by the socket itself, thereby obviating the need forextensive bone-grafting; (3) there is increased contact areabetween the implant and the host bone; and (4) the centre ofhip rotation is translated to a more lateral and inferiorposition, allowing restoration of hip biomechanics closer tonormal. The disadvantages are that (1) extra-large socketslimit bone-stock restoration, and (2) large, oblong bonedeficiencies cannot be filled in an inferior-to-superiordirection without extensive reaming of the anterior orposterior column or superior placement of the cup.

Whaley et al. reported the Mayo clinic mid-term results.Eighty-nine extra-large uncemented hemispherical acetabu-lar components were used for revision after aseptic failureof a total hip arthroplasty [22]. The revision implant (HGP-Ior II cup fixed with screws) had an outside diameter greateror equal to 66 mm in men, and greater or equal to 62 mm inwomen. The probability of survival of the acetabular

component at eight years was 93% with removal for anyreason as the end point, 98% with revision for asepticloosening as the end point, and 95% with radiographicevidence of loosening or revision for aseptic loosening asthe end point.

Oblong cups

Bilobed oblong cups are an alternative for large superiorsegmental acetabular bone deficiencies (Paprosky typeIIIA). Oblong cups can restore hip centre of rotation andincrease implant contact on host bone by matching deviceto the defect. Disadvantages include the high cost andtechnical difficulties with incomplete contact, componentmalposition, and excess bone removal to achieve fit. Berryet al. [23] published a multicentre series including 34oblong cups. They reported good clinical results andstability at three years follow-up for most patients. Therewas only one failure in their series that required revision foracetabular loosening. This patient had the oblong cup restedon a previous structural bone graft. The mid-term results ofChen et al. [24] were less favourable. They reported a 24%failure rate in 37 hips followed for an average of41 months.

The series of Civinini et al. included 53 hips withencouraging mid-term results using uncemented bilobedcomponents for acetabular revision for Paprosky type II andIII acetabular defects [25]. At an average of 7.2 yearsfollow-up, only one socket was revised for asepticloosening (1/53). Another patient was operated upon forlate polyethylene liner dissociation. Although Oblong cupsremain as an alternative for acetabular revision, the use ofthis technique seems impractical in modern revisionsurgery.

Structural bone allograft

Structural bone grafting is a treatment option for uncon-tained or segmental acetabular defects (Paprosky IIB, IIIAand IIIB). The size and complexity of the graft can rangefrom using a femoral head to reinforce the medial wall orsuperolateral segmental defect, to the use of total acetabularallograft in the case of massive defects. Advantages includerestoration of the hip centre of rotation, and the potential torestore bone stock for future revisions. Nonetheless, theresults are unpredictable. These procedures are technicallydemanding and are associated with numerous complica-tions. The failure rate is related to the excessive loadbearing requirements being placed on the dead allograftbone, as the graft tends to weaken over time duringrevascularisation, leading to failure [26]. The actual long-term restoration of viable and mechanically competent boneby graft remains controversial. A series by Jasty and Harris

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included 38 hip reconstructions using femoral head allo-graft to augment severe acetabular defects. The extent ofcover provided by the allograft and the severity of graftresorption both correlated with acetabular loosening. Theirfailure rate increased from 0% at four years to 32% at sixyears [26].

Sporer et al. [27] presented their results of distal femoralallografts for reconstruction of acetabular defects (PaproskyType IIIA). Twenty-three cases were followed up forten years. The cup survivorship was 78% with re-revisionfor aseptic loosening as the endpoint. Lee et al. [28]published the long-term results of 74 patients undergoingcup revision, using minor column allografts for uncontainedbone defects sized between 30% and 50% of the acetabu-lum. The authors excluded patients with bone defectssmaller than 30% of the acetabulum (did not need structuralgrafting) and greater than 50% of the acetabulum whichneeded a major column allograft and a protective ilioischialantiprotrusio cage or reinforcement roof ring. The 15- and20-year survivorships for cups were 61% and 55%, with theend point defined as re-revision for any cause. The long-term survivorship for grafts was 78%. The authors reportthat they continue to use femoral head structural allograftsfor this selective group of younger patients who are morelikely to require further revision surgery in the future [28].

Trabecular metal cups and augments

Trabecular metal acetabular implants can be used for simpleacetabular revisions, and are the implant of choice for morecomplex situations including poor bone biology, uncon-tained or combined acetabular bone deficiencies, and pelvicdiscontinuity. The high porosity, high frictional character-istics, and low modulus of elasticity offer better biologicalfixation with increased depth of bone ingrowth andimproved initial stability [10, 11, 29]. Although we lacklong-term clinical results, we believe that TM cups are thepresent and may represent the future of acetabular revisionsurgery due to their optimal biomechanical properties,excellent biocompatibility, good capacity to avoid boneloss from stress shielding (due to material modulus ofelasticity similar to cancellous bone) and excellent earlyclinical results.

TM shells are being used more frequently for acetabularrevisions. When reasonable primary stability is obtained,the need for more than 50% host bone contact may bechallenged and reduced with the use of TM cups [30, 31].As a technical point, the cup should be seated against nativebone as close as possible to the hip centre of rotation.Ancillary screw fixation should always be used in revision.Because of the high porosity of the cup, extra screw holescan be made with a high speed burr in the area of the cup incontact with native bone. This technique allows increasing

the number of screws, oblique screw placement, andenhances initial cup stability. Once the implant has beensecured, the polyethylene insert is cemented into the TMrevision shell. Cementation of the liner eliminates backsidemotion and provides a secure bond between the porousshell and the backside of the insert (Fig. 2).

Contained defects rarely require structural support in theform of metal augments or structural bone grafts. Morsel-ised bone graft is used to fill these contained defects(Fig. 3). Lakstein et al. [31] published the early results of53 acetabular revision using TM revision shells foracetabular defects with less than 50% host bone contact.All the cups were reinforced with at least two screws, andmorselised bone graft was used to fill the acetabulardefects. There were two failures at a minimum follow-upof 24 months, accounting for a mechanical failure rate of4%. The authors suggest that TM cups are a reasonableoption for the treatment of major contained acetabulardefects. More extensive cavitation defects for which noinitial stability can be achieved can be protected by a cage“cup cage construct”. TM augments can also be used formedial cup support, in the setting of intact rim and largecontained medial defects. But management of largesegmental bone defects usually requires structural support,such as structural bone grafts or trabecular metal augments.The versatility of TM cups and augments allows adjunctivescrew fixation and fill of acetabular defects at the time ofrevision. The size, location, and orientation of the augmentsare dictated by the acetabular bone defects. The junctionbetween the acetabular augment and revision shell issecured using bone cement. A modular acetabular augmentsystem provides stable support for hemispherical cupswhen a critical segmental defect exists, increases thecontact area against bone, and permits biological fixationrather than purely mechanical fixation.

Nehme et al. reviewed the early results using a modularacetabular augment system [32]. Sixteen patients (16 hips)with severe acetabular bone defects were studied with anaverage follow-up of 32 months. There was no evidence ofimplant migration or loosening in their short-term results.Sporer and Paprosky’s early results using a tantalum cupsupported with a modular tantalum augment for Paproskytype IIIA defects showed similar findings [33]. At anaverage of 3.1 years follow-up, only one patient requiredacetabular revision to a constrained liner for instability. Theremaining hips were stable. Van Kleunen et al. [34]presented 97 cases of acetabular failures with PaproskyIIA defects or higher, treated with a TM revision acetabularcomponent with or without modular augments. There wereno aseptic failures in their series with an average follow-upof 45 months. Acetabular component failures were second-ary to deep periprosthetic joint infection (eight cases) and,in one case, due to instability.

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Fernandez et al. [35] presented a large series ofacetabular revisions from multiple centres in Spain. Theyreviewed 263 consecutive patients with failed acetabularcomponents after total hip arthroplasty that were revisedusing porous tantalum acetabular components and aug-ments. The mean follow-up was 73.6 months. An unce-mented press-fitted TM Monoblock Acetabular Cup wasused in 78 of 263 cases (29.6%). The 78 cases using thiscup included 18 type I acetabular defects and 60 type IIacetabular defects. A TM Revision Shell allowing screwaugmentation and with a polyethylene liner was used in 136

of 214 cases, including the remaining type I and II casesand in all 49 patients with type III defects. A combinationof TM Revision Cup and porous tantalum modular aug-ments was used in 34 cases (12.9%), three type II-B defects(3/82; 3.6%), 22 type III-A defects (22/40; 55%), and in thenine hips with type III-B defects. Morsellised bone allograftwas added to repair bone defects in 126 cases (48%), andstructural bone graft was not used. At the most recentfollow-up, all acetabular components were radiographicallystable and none required revision for loosening. There wereeight cases of hip dislocation (3%) and two cases of deep

Fig. 3 a Preoperative left hipAP and lateral radiographs of a54-year-old male with obviousacetabular migration and failure.A type IIIB deficiency wasanticipated with the evaluationof the radiographs and con-firmed intraoperatively. b Post-operative AP and lateralradiographs. The acetabularcomponent was revised with a“jumbo” trabecular metal shellsize of 74 mm. The medialcavitary defect required massiveintraacetabular bone grafting

Fig. 2 The porous tantalum—Trabecular Metal (TM)—revi-sion acetabular shell is a two-piece design that allows screwaugmentation. Once good bonequality has been localised, ahigh speed burr is used to createextra holes in the TM shell,increasing the number of screwsand enhancing initial cup fixa-tion into the ilium dome andposterior column. Cementationof the liner into the shell elimi-nates backside motion and pro-vides a secure bond between theporous shell and the backside ofthe insert

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periprosthetic infection which required further surgery.They did not find a correlation between the various degreesof acetabular bony defect and the quality of the clinicalresults. Their mid-term results using tantalum implants foracetabular revision were reliable in creating a durablecomposite without loosening for a minimum of five years.

Pelvic discontinuity

Pelvic discontinuity is an uncommon and unique form ofsevere acetabular bone defect where the superior andinferior aspects of the pelvis are separated by loss of hostbone and/or a fracture through the acetabular columns.The radiographic findings include a visible fracture linethrough both columns, or indirectly a medial shift orrotation of the inferior hemipelvis in relation to thesuperior hemipelvis that can be observed as an interrup-tion of the continuity of the Köhler line, or anasymmetry of the obturator foramen on a true antero-posterior pelvis radiograph [36].

Pelvic discontinuity represents the most difficult chal-lenge in acetabular revision [36]. Treating pelvic disconti-nuity involves the difficulty of simultaneously addressing apelvic fracture and a hip revision arthroplasty in the settingof massive bone loss. The principles for the treatmentshould be (1) identification of the problem, (2) stabilisationor effective bypass of the discontinuity, (3) bone grafting atthe site of the discontinuity, (4) treatment of any associatedbone loss, and (5) placement of a stable acetabular implant[36]. The treatment options available depend on the qualityand quantity of the remaining bone stock. The alternativesfor reconstruction range from the use of plates, grafts anduncemented cups, to the use of acetabular cages (standardantiprotrusio cages, custom triflanged cages, or modular“cup cage” constructs) with morselised or massive struc-tural bone grafts. And the choice depends on the back-ground diagnosis, the amount of bone loss, the quality ofthe residual bone (previous irradiation carries a particularlybad prognosis), and the type of the discontinuity (stiff vs.mobile).

Berry et al. [36] identified 31 patients with pelvicdiscontinuity (0.9%) of 3,505 acetabular revisions per-formed between 1969 and 1995. Two patients died withintwo years after the revision. Two had a resection arthro-plasty for the treatment of the pelvic discontinuity. Twenty-seven hips were reconstructed. Nine of the 27 hips neededfurther surgery after two years follow-up. The reasons forfailure included four cases of aseptic loosening, fourpatients with recurrent instability and one case of deepperiprosthetic infection. Only 16 patients (59%) hadsatisfactory results. Patients with good remaining pelvicbone stock had a higher likelihood of successful treatmentthan did those who had severe segmental bone loss or

history of previous irradiation to the pelvis. Insertion of acementless socket in combination with stabilisation of thediscontinuity with a plate was successful in patients whohad pelvic discontinuity and cavitary bone loss. Patientswith large segmental defects or irradiated bone had betterearly results with reconstruction using an antiprotrusiocage.

Column plating

Column plating can be used in certain pelvic discontinuitieswith cavitary defects, combined with trabecular metalrevision sockets and in our experience this technique canoffer predictable results, especially if the bone loss is mildor moderate and the discontinuity stiff (Fig. 4a–c). It canalso be used as a supplement for cage reconstruction inmassive defects or in the treatment of late stress fractures inthe presence of a well fixed cup [36]. Springer et al. [37]reported seven cases of pelvic discontinuity that werediagnosed as a postoperative complication several monthsafter hip revision arthroplasty performed with TM cups.Five patients were symptomatic with a new displacedtransverse acetabular fracture and underwent reoperation.The other two patients were asymptomatic with nondisplaced fractures and were treated non-operatively.Revision surgery revealed the cups to be well fixed in spiteof the discontinuity. Supplementary fixation of the posteriorcolumn with a plate plus bone grafting was performed infour patients. In the remaining patient, a reconstruction cagewas placed into the well-fixed cup to bridge the fracture. Atthe latest follow-up four of the five patients had radio-graphic evidence of a healed pelvic fracture and a stable,well-fixed cup. If the residual bone stock is adequate, andgood screw fixation is obtained, posterior column plating isan excellent method of dealing with the problem.

Standard ilioischial antiprotrusio cages

Antiprotrusio cages have been used for the more complexacetabular reconstructions. The cage allows bone grafting,bridging areas of bone loss, and provides support to the cupliner in acetabular revisions with severe combined defectsor pelvic discontinuity. Non biological fixation is achievedto the ischium and ilium with screws, enhancing mechan-ical stability into the patient's native bone [38]. Thereported results of cages are mostly mid-term results andinclude a very mixed group of patients with variablepathology and bone loss.

Sembrano and Cheng reported the midterm survivorshipof 72 standard antiprotrusio cage reconstructions performedin 68 patients [39]. They included ten primary hips and 62acetabular revisions, including 19 pelvic discontinuities. Atfive years they reported an overall 87.8% cage revision-free

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survivorship in their study group. The pelvic discontinuitysubgroup had no reoperations at five years. Two had a loosecage on radiographs. Paprosky et al. [40] reviewed 15patients (16 hips) after acetabular cage reconstruction forthe treatment of pelvic discontinuity. Five hips (31%) wererevised or resected for aseptic loosening (four hips) andsepsis (one hip) at an average 46 months. Three additionalhips were loose.In pelvic discontinuity antiprotrusio cageswere associated with a high failure rate at theirintermediate-term follow-up.

Peters et al. [41] presented the early results after 63modular traditional porous-coated anti-protrusio devicesfor failed hips with marked acetabular deficiencies(Paprosky II and III). The revision rate for asepticloosening was 5% (3/63) and the mechanical failure ratewas 8% (5/63) at 29 months follow-up. Four componentswere removed for infection, three for loosening, and onefor malposition. The dislocation rate was 12.7% (eight of63 cases).

A series of Goodman et al. included 61 ilioischialreconstruction cages performed by the senior author [42].Structural allografts were used in 48 cases (79%). Theyreport a 76% success rate at an average follow-up of46 months. Pelvic discontinuity was noted in ten cases. Aposterior plate was not used in any of these cases. They hadan overall 50% success rate in this subgroup of challengingpatients. Eight cases presented at least one complication,including three cases of dislocation, three cases of asepticloosening, and two cases of unresolved pelvic dissociation.There was one case of deep periprosthetic infection thatresulted in resection arthroplasty. The main disadvantagesof standard ilioischial cages are the wide exposure withincreased risks to neurovascular structures. The lack of

biological fixation and the dependence on multiple screwsfor mechanical stability and fixation lead to late failures.

Custom triflange cages

The use of custom porous-coated triflange devices hasyielded good results for difficult acetabular reconstructions.DeBoer et al. [43] reviewed 28 patients (30 hips) withpelvic discontinuity treated using a custom triflange cup.Two patients were lost to follow-up and eight died, leaving18 patients (20 hips) followed up for a mean of ten years.Definite healing of pelvic discontinuity was present in 18hips. Six hips underwent another operation related to theacetabular component, with five of the six treated fordislocation. A series by Holt and Dennis included 26triflange reconstructions for complex acetabular revision,including three cases of pelvic discontinuity [44]. Theoverall success rate was 88.5% at a mean 54-month follow-up. Two of the three hips with discontinuity preoperativelyfailed from loss of ischial fixation. In contrast to Deboer’sseries, the authors recommend the use with caution inpatients’ pelvic discontinuity, unless additional columnplating is done. The primary disadvantage of the triflangecup is that it must be fabricated on a custom basis whichcauses manufacturing delays and is also expensive.

Ingrowth cup plus cage: “Cup cage technique”

The combination of a trabecular metal socket and a cage totreat very large combined deficiencies or pelvic disconti-nuity was first described by Lewallen, and the Mayo Clinicexperience with this technique was reported at the AAOSAnnual Meeting in 2008.

Fig. 4 a, b Oblique radiographs of the hip of a 78-year-old womanwith multiple previous operations. Pelvic discontinuity is obvious. cRadiograph of same patient three years after surgical treatment with

posterior column plating and trabecular metal revision socket. Notethat discontinuity appears healed and socket seems osteointegrated

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The Toronto arthroplasty group published a series of 26cases of acetabular revisions in 24 patients that were treatedusing a modular ilioischial cage and trabecular metalacetabular component for severe acetabular bone lossassociated with pelvic discontinuity [45]. The meanfollow-up was 44.6 months (range 24–68). In 23 hips(88.5%) there was no clinical or radiological evidence ofloosening at the last follow-up. The complications includedtwo dislocations, one infection and one peroneal nervepalsy. Although longer follow-up is required, the prelimi-nary results indicate that the treatment of severe acetabulardefects associated with pelvic discontinuity by this tech-nique is a viable and promising option.

Distraction method of treatment

The use of a trabecular metal cup with or without augmentsfor the treatment of acetabular defects of type IIIB with anassociated pelvic discontinuity was published by Sporerand Paprosky.

The idea here is not to attempt bony union, but toachieve stability by distracting both aspects of the ununitedpelvis. Thirteen hips were followed up for an average of2.6 years. The TM cup was used to bridge the acetabulardefect and obtain fixation proximal and distal to thediscontinuity. There were no reoperations in their short-term follow-up. One patient had radiographic signs ofpossible loosening [46].

Final considerations

In acetabular revision surgery today, the advent of porousmetals represents a significant step forward. Acetabularrevision with cement is of historical interest only in NorthAmerica. Virtually all revision is done without using cement.

For simple revision without bone loss a standarduncemented socket suffices. When bone quality is impairedor there is bone loss, the use of the newer porous metalsincreases the chances of obtaining stable and durablefixation. Some revision components can be made highlyporous (improved early osteointegration) and highly elastic(less chance of bone loss by stress shielding). Theseproperties increase their desirability. In fact, in our practicetoday the majority of the acetabular revisions are doneusing a tantalum revision shell.

Cavitation bone loss can be easily handled with morcel-lised cancellous allograft. Segmental deficiencies can bealso handled successfully with block allografts, and theearly and predictable osteointegration achieved with theporous metal places the block graft in a favourableenvironment for healing. An alternative to block allograftsis the use of metal augments which are more popular today.

Metal augments have the advantages of not resorbing andthe ability to osteointegrate.

The vast majority of acetabular reconstructions can beperformed as discussed. Massive cavitary and segmentaldeficiencies and pelvic discontinuity are encountered lessthan 5% of the time. We have discussed the concepts ofcup-cage, plating of the posterior column, and bridging thediscontinuity with metal, among the most frequently usedmethods, but the need for these techniques is rare.

The development of integrated modular acetabular sys-tems using off-the-shelf implants based on the new porousmetals is the current fashion. Great strides have been made inthe last ten years. In these days of medical costs containment,compromises will have to occur so that these expensivedevelopments can become generally available.

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