Nine Year Follow-up of a Ceramic-on-Ceramic Bearing Total Hip Arthroplasty Utilizing a Layered Monob

McLaren Regional Medical CenterKettering UniversityNINE YEAR FOLLOW-UP OF A CERAMIC-ON-CERAMICBEARING TOTAL HIP ARTHROPLASTY UTILIZING ALAYERED MONOBLOCK ACETABULAR COMPONENTDavid Mayor, MD1, Savan Patel, MD1, Clayton Perry, MD1,Norman Walter, MD1, Stephen Burton, MD1, Theresa Atkinson, PhD2ABSTRACTIntroduction: Early ceramic bearing systems intotal hip arthoplasty (THA) sought to provide longterm wear improvement over traditional metal onpolyethylene systems. However, previous designsexhibited fractures of the ceramic acetabular liner,leading to the development of the Implex Hedrocelceramic bearing THA system where the ceramicliner was supported on a layer of polyethylene in-tended to transition liner loads to the metal shell,a so-called “sandwich” design. Unfortunately,the device trial was stopped to further enrollmentwhen liner fractures were reported. The currentstudy examines nearly 10-year follow-up on 28devices implanted by two surgeons at one institu-tion in order to document ceramic bearing systemperformance over a longer time period.Methods: Radiographic and patient reportedoutcomes, in the form of Harris Hip Scores (HHS)and 12-Item Short Form Health Sur vey (SF-12),were collected.Results: During the study period two cups werereplaced, one at three years and a second at sevenyears. At the five year follow-up HHS were similarto those reported in the literature for devices withtraditional metal-on-polyethylene bearing surfacesand for other sandwich ceramic bearing designs. Atthe nine year follow-up, the HHS had not changedsignificantly and SF-12 scores measuring overallphysical and mental health were higher than agematched national norms (p0.001). There were nosigns of cup migration, stem subsidence, osteolysisor cup loosening at any time up to the last follow-up in this patient cohort. The 89% sur vivorshiprate and device revisions due to delamination ofthe liner obser ved in this group were similar tothose reported earlier for this device and for other“sandwich design” ceramic bearing systems.1401 S. Ballenger Hwy, Flint, MI 4853221700 University Ave, Flint, MI 48504Phone: 810-762-9949Fax: 810-762-7860Discussion: This cohort did not exhibit newfailure modes and HHS and SF-12 scores indi-cated high functionality for the majority of patients.These data suggest that a focus on preventingceramic liner fracture through design and/or ma-terials improvements may result in a device withlong-term functionality.INTRODUCTIONIn the United States, the majority of total hip arthro-plasty (THA) involves a metal stem, head and acetabularcomponent with a polyethylene liner1. The primary draw-back of this bearing surface is the osteolysis associatedwith wear debris generated by the polyethylene bearingsurface2,3,4. The development of highly cross-linkedpolyethylene (HXPLE) has improved outcomes for totalhip arthroplasty, but is still not seen as the ideal bearingsurface in young active adults5,6. Low wear rates andlonger lasting bearing surfaces are of specific interest inaddressing the needs of young patients with a long lifeexpectancy and a high activity level5,6,7. One alternativeis the use of ceramic-on-ceramic bearing surfaces.Ceramic-on-ceramic bearing surfaces in THA havebeen used in an effort to combat the osteolysis and asep-tic loosening associated with the wear debris generatedby polyethylene2,3,4,8,9,10. Excellent wear and biologicallyinert characteristics of ceramic appear to yield an idealbearing surface, however, the risk of ceramic fracturepresents a unique concern4,7,8,10,11. Since the initial useof ceramics in THA in the 1970s, improvements in itsmechanical proper ties, grain structure, purity, andproof testing have significantly improved the quality ofmodern ceramics7,11,12,13. The improvements in physicalcharacteristics decreased fracture rates4,7,11 but revealedaseptic loosening as another challenge. The mechanismfor loosening was thought to be caused by a mismatchin the modulus of elasticity between the ceramic andbone4,8. “Sandwich” designs utilize a ceramic inlay withpolyethylene interposed between the ceramic inlay andthe metal shell which decreases the stiffness mismatch,thus potentially reducing the rate of fracture and improv-ing bony in-growth4,7.A number of “sandwich” acetabular component designshave been trialed with varying degrees of success. Thefirst commercialized “sandwich” acetabular design was78 The Iowa Orthopaedic JournalNine Year Follow-Up of a Ceramic-On-Ceramic Bearing Total Hip ArthroplastyImage 1: Cross sectional diagram of Hedrocel Implex Acetabularcomponent (a: porous shell, b: polyethylene, c: ceramic)produced in 1993 and consisted of polyethylene sand-wiched between an alumina ceramic inlay and a titaniumshell3. Viste et al.3 studied the long term results of thiscup and found a fracture rate of 3.3% (5 of 151) at anaverage of 9.9 years due to failure. Evidence of impinge-ment of the femoral neck on the rim of the ceramic linerwas also noted and thought to be involved in the failure3.Iwakiri et al.13 utilized a unique alumina ceramic insert ona polyethylene shell that was directly cemented to bonewith no metal backing. At an average of 5.6 years theyreported a 5.6% (4 of 72) alumina fracture rate. Notchingwas again noted on the femoral neck, which suggestedthat impingement likely played a role in the ceramicfailure13. Park et al.7 reviewed 357 hips at an average of3.9 years with a ceramic liner embedded in polyethylenewhich then had a Morris taper fit into a titanium shell.They reported an alumina fracture rate of 1.7% (6 of357) (two alumina heads, four alumina liners). Based onmicroscopic and gross analysis of the fractured liner atrevision, impingement of the femoral stem on the rimof the ceramic was seen as a primary cause of fracture7.A “sandwich” design with the goal of decreasing theimpact of femoral stem impingement on the rim of theacetabular liner was developed. The Hedrocel ceramicbearing cup (Implex, Allendale, New Jersey) consists ofa Trabecular Metal tantalum shell, compression-moldedpolyethylene, and a press fit ceramic inlay (Image 1). Thealumina ceramic inlay was recessed so any femoral stemimpingement would result in polyethylene contact, asopposed to ceramic contact, thus decreasing the risk ofdelamination of the alumina component and subsequentdislocation and/or fracture. A multicenter prospectiverandomized clinical study under the supervision of theUnited States Food and Drug Administration (FDA) wasinitiated in 1999 to evaluate this device. In 2003 enroll-ment in the study was suspended due to failures of theceramic liner8. Two measures of patient outcomes wereused in the Hedrocel Ceramic Bearing Cup trial: the Har-ris Hip Score (HHS) and the 12-Item Short Form HealthSurvey (SF-12). The Harris Hip score is a well-known andoften utilized measure of hip function that was initiallydescribed by William H. Harris in 196914. The SF-12 is ashortened version of the 36-Item Health Survey (SF-36)which generates a mental component score (MCS) andphysical component score (PCS). These scores reflectoverall health-related quality of life15,16. The SF-12 providesa generic measure of health that is not related to a specificdisease or condition. The score is scaled from zero, beingthe lowest level of health, to 100, representing the highestlevel of health16. As patients age, the PCS component ofthe score tends to trend down while the MCS componentof the score tends to trend up, thus any score must becompared to an age-matched control to be of any meaning.The SF-12 was utilized to provide a tool by which we cancompare the patients with the ceramic total hip againstthe general population.The current study examines 5 and 10 year functionaloutcomes and radiographic appearance of the Hedrocelceramic bearing cup at our institution. Though this systemis part of an investigational device trial and will never becommercialized, many patients received it as their THAand their long-term results are of interest.METHODSThe Implex Hedrocel system is an investigationaldevice implanted in 315 patients as part of a FDA moni-tored, randomized multicenter prospective trial from1999 to 2003. The current study examines data collectedfrom one site where a total of 28 experimental deviceswere implanted in 25 patients by two surgeons (NW,SB) between March 2001 and December 2002 with anaverage of 9.2 year follow-up. The control group wascompleted but was not required to be followed whenthe long term follow up was initiated. Average follow-up after exclusion of patients who died or underwentrevision procedure (six patients) is 9.8 years (6.1-10.5).The device studied is a “sandwich” monoblock acetabu-lar component consisting of an alumina ceramic inlay(BIOLOX forte; CeramTec, Stuttgart, Germany) pressfit into a direct-compression-molded ultra-high molecularweight polyethylene backed by a porous tantalum shell.The cup and femoral stem were press fit. The femoralstem was a porous-coated cobalt-chromium-alloy implant(Implex ProxiLock design). Patients with clinical indica-tions for a total hip replacement, age between 18 and 75Volume 34 79ATable 1. Demographics of patients enrolledbetween this study and similar components described in the literature(1,2)D. Mayor, S. Patel, C. Perry, N. Walter, S. Burton, T. Atkinsonyears, and having a body massindex (BMI) less than 40were included in the study. Patients with bilateral hipsreplacements received the same implant on both sides.The protocol was approved by the sites investigationalreview board. All study participants provided informedconsent prior to participation.The study group included 16 females and 9 males(Table 1). All prostheses were implanted using a lateralapproach. The standard limited incision muscle-sparinganterolateral Watson-Jones approach for THA, as de-scribed by Kenneth Gustke M.D.17, was used with oneexception: the leg, when dislocated, was placed overthe anterior edge of the table, not the posterior edge.Briefly, the incision was made anterior and proximal tothe greater trochanter and the joint exposed through asmall opening created along the intermuscular intervalbetween the gluteus medius and tensor fascia lata.Patients were seen pre-operatively, post-operatively at2 weeks, 6 weeks, 3 months, 6 months, 1 year and an-nually thereafter. At each visit HHS and SF-12 data wascollected. Radiographs obtained at 2 weeks, 3 months,6 months, 1 year and at subsequent yearly visits wereexamined for evidence of osteolysis in the seven femoralGruen Zones18 and three acetabular zones19. The cupinclination was also measured using a transischial lineand the inferior and superior cup margins.Harris hip score and improvement in score (HHS atfollow-up preoperative score) for the study device werecompared to those reported in the literature for similardesigns using student T-test statistics. Rates of revisionand osteolysis were compared using the chi-square test.The post-op SF-12 data was compared to pre-operativedata using the T-test statistic and compared to nationalnorms by age group using both the Wilcoxon SignedRank test and a 95th percentile confidence interval testbased on the standard error of measure16.RESULTSThe average age at the time of surgery was 63 years(standard deviation (SD) 8.9, range 4275). The averageBMI at the time of surgery was 29.68 (SD 4.5, range 23-39). The average pre-operative HHS and the SF-12 PCSwere indicative of reduced joint function and quality oflife (Table 1). Two patients underwent revision (7.1%,2 of 28) during the course of study: one at 3.2 yrs dueto perceived imminent failure (female, 63 yrs, BMI 25revised to metal on polyethylene) and the other at sevenyears due to liner displacement (female, 68 yrs, BMI23, revised to metal on polyethylene). The short-termrevision case was excluded from the five year follow-upgroup, as the revision occurred outside of the five yearwindow (as determined using Chauvenets criterion),while the longer term case was included in both the 5and 10 year groups. Two patients died during the courseof the study: 5.3 yrs and 7.9 yrs, of unrelated causes.Both patients were retained in the 5 year group and thelatter was included in the 10 year group.At the five year follow-up (4.9 yrs, SD 0.5, range3.9-6.0) the HHS were significantly improved over thepre-operative scores at 88.7 (SD 13.6, range 50-100,p0.001). The SF-12 PCS increased significantly fromthe pre-operative level to 46.7 (Table 2, p0.001), whilethe MCS remained relatively high at 55.4. The averageangle of inclination for the cup was 47.3 (SD 5.7, range46.8-59). There were no clinically significant findings ineither stem or cup radiographs.At the 10 year follow-up (9.15 yrs, SD 1.19, 6.04-10.48)the average HHS, PCS and MCS scores remained high.Harris Hip Scores and SF-12 PCS increased significantlyfrom the pre-operative state to the longest post-operativefollow-up (p0.001), but the scores did not significantlydiffer from those at the five year time point. The largestincrease in the Harris Hip Score was 69.0 while lowestTable 2. Comparison of outcome measures (average, standard deviation and range)80The Iowa Orthopaedic JournalDemographics Men WomenNumber (patients/hips) 6/9 16/16Average Age (yrs) 63.2 64.6Average BMI 30.1 29.4Pre-operative 5 years 9 yearsSF-12 Mental Component 54.4 (SD 10.9, 31.5-66.5) 55.4 (SD 6.6, 36.1-64.7) 58.6 (SD 3.1, 47-64)SF-12 Physical Component 26.6 (SD 4.5, 18.9-37.5) 46.7 (SD 10.1, 26.1-56.2) 47.9 (SD 7.3, 30.6-55.5)HHS: Current Study 43.5 (SD 9.0; 24-61.5) 88.7 (SD 13.6, 50-100). 91.9 (SD 5.3; 74.9-100)1HHS: Ceramic Comparable I 50.6 (SD 11.4; 26.95-78.03) not reported 96.86 (SD 8.0; 48.95-100)1HHS: Ceramic Comparable II 47.89 (SD 10.7; 28.85-75.23) not reported 96.176 (SD 5.9; 74-100)2HHS: Ceramic Non-Sandwiched 56 (SD not avail; 17-89) not reported 94 (SD not avail; 57-100)1HHS: Metal-on-Poly Comparable 49.83 (SD 12.6; 21.35-87.25) not reported 96.49 (SD 5.6; 74-100)data of other ceramic-on-ceramic sandwich design devicesAnational population16 (p0.001 and p=0.001, respectively). CNine Year Follow-Up of a Ceramic-On-Ceramic Bearing Total Hip ArthroplastyTable 3. Ceramic liner fracture rates compared to publishedincrease was 25.3. The MCS and PCS scores for thestudy group were significantly higher than those of theBThe greatest differences were exhibited in the mentalhealth component with an average difference of 8.5points (2.25 points greater than the 95th percentile) and88% of patients showing improved mental health. No cupmigration or stem subsidence was observed at any time.There were no signs of osteolysis or cup loosening atlast follow-up in February of 2013.DISCUSSIONThe mid-term follow-up data, with the exception ofthe failed ceramic liner, was excellent for patients withthe Hedrocel ceramic-on-ceramic bearing THA. Theseresults are similar to other studies of ceramic bearingTHA systems8,9,10,11,12. The functionality and pain reliefas measured by the HHS were similar to that of othertraditional and ceramic bearing surfaces and the SF-12scores were above average for age-matched controls.The acetabular component showed no signs of migra-tion in the time frame studied. In addition, no evidenceof osteolysis was observed, similar to findings in otherceramic on ceramic designs11,9,12. Perhaps the mostsignificant finding, however, was that no new failuremode was observed and the rate of device failure didnot appear to be increasing.Delamination of the ceramic liner from the polyeth-ylene was the mode of failure identified in this study.This mode has been described in earlier reports forthis design8 and in other similar designs3,13. While nopatient experienced ceramic liner fracture during thedata collection period of the current study, following theconclusion of the study period, an atraumatic ceramicfracture was identified in one patient at 10.8 yrs. Againthe failure mode appeared to be partial delamination andfracture of the ceramic liner. Revision surgery revealedwell-fixed acetabular and femoral components. The im-plant was revised to a ceramic head on HXPLE implantto decrease the effect of third-body wear.Two failure mechanisms for ceramic bearing surfaceshave been proposed in the literature: impingement andphysical property differences between the ceramic andpolyethylene. The Hedrocel device design sought todecrease the incidence of device failures by eliminatingthe direct contact of the femoral stem with the ceramicedge by recessing the ceramic inlay and creating a“bumper” of polyethylene around the rim (Image 1).Physical property differences between the hydrophilicand absorbent ceramic on the hydrophobic polyethylenein a moist environment has been raised as a contributingmechanism of failure2,20.The revision rate for this study is similar to otherstudies of sandwich design acetabular components(Table 3)3,4,7,8,10,20. Though the revision rate is higher thansome comparable studies, the study period is longerallowing time for more device failures. These findingsmay discourage further development of polyethylenesandwich ceramic-on-ceramic designs. Indeed, the 8%revision rate for the study group exceeded the 3% normfor traditional metal-on-polyethylene systems based ondata from the National Joint Registry of England andWales21. However, while the “sandwich” design appearssensitive to non-traumatic failures, those patients whodid not experience the failure demonstrate the potentialfor long-term success. A recent report finds that a non-sandwich design ceramic cup provides long-term func-tion without osteolysis or ceramic fracture 11. Sugano etal.11 conclude “cementless THA with the third-generationalumina COC hip bearings provided an excellent survi-vorship of 95.7% at 14 years and eliminated periprostheticosteolysis for 11 to 14 years”. These data suggest thatthis bearing surface merits further consideration.In the SF-12 data collected in the course of this studyour patient group reported a more positive mental stateas compared wi