The Journal of Arthroplasty Vol. 25 No. 2 2010

Successful Performa

From thHospital, IpSurgery, W

SubmitNo benReprint

OrthopaedSuffolk, U

© 20100883-5doi:10.1

nce of the Bi-MetricUncemented Femoral Stem at a MinimumFollow-Up of 13 Years in Young Patients

Howard Davies, MRCS,* Ben Ollivere, MRCS,* Joseph Motha, FRCS,yMatthew Porteous, FRCS,y and Adrian August, FRCSy

Abstract: We report the mean 15.2 year follow-up results for a porous coated version of theBi-Metric (Biomet UK Ltd, Bridgend, UK) uncemented femoral stem in young patients. Sixty-fourhips were implanted into 54 patients (mean age, 54.3 years) and followed up using the Hospital forSpecial Surgery score and regular radiographs. The first 13 patients had a TTAP-ST acetabulum(Biomet UK), the remainder receiving a Universal cup (Biomet UK). At 15.2 years, there were nostem failures or femoral revisions. The mean Hospital for Special Surgery score was 34.7 (20-40), andthere was no evidence of stem loosening radiologically. There were 3 acetabular revisions and 3 linerchanges at 10 years, with a further 5 cup revisions and 9 liner changes at final follow-up.Keywords: uncemented, Bi-Metric, porous coated, TTAP-ST, universal.© 2010 Elsevier Inc. All rights reserved.

Concern over the high rates of aseptic loosening incemented implants [1], particularly in young high-demand patients, has led to the increasing popularity ofcementless total hip arthroplasty (THA). The Bi-Metrichip system (Biomet UK Ltd, Bridgend, UK) consists of anuncemented forged titanium femoral stem with either ahydroxyapatite or an Interlock™ plasma-sprayed porouscoating designed to osseointegrate and provide a barrierto wear debris. It is available in collared or collarlessdesigns, and 1 mm increments in stem size ensureoptimal press fit.Over the last few years, excellent long-term results with

a follow-up of greater than 10 years have becomeavailable for some of the most widely used cementlessimplants [2-8]. Despite this, there is little availablepublished data on the long-term survivorship of the Bi-Metric uncemented femoral stem beyond the Scandina-vian arthroplasty registers [9,10]. Of the remainingstudies, 1 deals exclusively with patients being treatedfor juvenile chronic arthritis [11]; 2 originate fromuniversity hospitals or specialist arthroplasty centers

e *Department of Trauma and Orthopaedic Surgery, Ipswichswich, Suffolk, UK; and yDepartment of Trauma and Orthopaedicest Suffolk Hospital, Bury St Edmunds, Suffolk, UK.ted December 8, 2007; accepted November 26, 2008.efits or funds were received in support of the study.requests: Howard Davies, MRCS, Department of Trauma andic Surgery, Ipswich Hospital, Heath Road, Ipswich, IP4 5PDK.Elsevier Inc. All rights reserved.

403/08/2502-0003$36.00/0016/j.arth.2008.11.105

186

[12,13]; and the final one reports results for a version ofthe stem that has a hydroxyapatite coating [14].The purpose of this study was to prospectively

evaluate the long-term results of a porous coatedversion of the Bi-Metric uncemented stem after it wasimplanted into a cohort of young high-demandpatients with mixed pathology at a nonspecialist districtgeneral hospital.

Materials and MethodsSixty-four uncemented titanium alloy (Ti-6Al-4V) Bi-

Metric femoral stems (Biomet UK Ltd) were implantedconsecutively into 54 patients between August 1988 andApril 1995. Each stem had a plasma-sprayed, closed pore,porous coat (proximal one third), and a collar. The first 13patients received a metal-backed screw-in acetabular cup(TTAP-ST, Biomet UK Ltd) with the remainder receivingmetal-backed press-fit cups (Universal. Biomet UK Ltd).The liners were manufactured from high-density poly-ethylene in all cases.Patients were selected by the senior author (A.A.) on

the basis of their young age and high-demand lifestyles.The surgery was performed by a single surgeon (A.A.)using the posterior approach. Intraoperative femoralpreparation was carefully undertaken with the aim ofsecure press fit and calcar seating of the collar.Patients were followed up annually and assessed using

the Hospital for Special Surgery (HSS) score (10 pointseach for pain, function, movement, and walking; max-imum score 40). If patients were unable to attend thefollow-up appointment for any reason, they were sent a

Fig. 1. Kaplan-Meier curve of survivorship for 64 uncementedTHAs counting revision for any cause.

Minimum 13 Year Follow Up of the Bi-Metric Uncemented Hip � Davies et al 187

postal questionnaire and contacted by telephone, allpatients attended for their radiographic evaluation.Each patient had a standard anteroposterior and lateral

radiograph of the hip taken in the immediate post-operative period before discharge. The radiographs wererepeated every 2 to 3 years initially and again at aminimum of 10 years postoperatively.Radiographs were reported by 2 independent obser-

vers (H.D. and B.J.O.). Any conflicting results wererereviewed until agreement was reached. Femoralstems and acetabular components were assessed forsigns of loosening and osseointegration. Migration ofthe femoral stem, which is considered to be a majorsign of instability, was assessed using the methoddescribed by Malchau et al [15]. Radiolucent lines orosteolytic lesions at the bone implant interface wererecorded in 7 zones (Gruen [16]) for the femoralimplant and 3 zones (DeLee and Charnley [17]) for theacetabular component. Radiographic loosening wasdefined according to the criteria of Hodgkinson et al[18] for the acetabular component, and the criteria ofEngh et al [19] for the femoral component. Heterotopicossification was recorded according to the classificationof Brooker et al [20].Statistical analysis was undertaken with Graphpad

Prism (GraphPad Software, San Diego, USA). Contin-uous data was analysed for difference using a 2-tailedStudent t test. Survivorship analysis has been calculatedusing the Kaplan-Meier method [21], with Green-woods method for confidence intervals (CIs). Survivalcurves were tested for difference using the Mantel-Cox(log rank) test. A P value of less than 0.05 was definedas significant in all cases. The primary outcomemeasure was revision for any cause with subsetanalysis performed for liner exchange and the press-fit cup subgroup.

ResultsThe 64 hips were implanted into 43 men and 21

women. The mean average age at surgery was 54.3 years(42-65 years), and the mean body mass index was 27.8(20.9-35.9). The underlying pathology was osteoarthritisin 59 cases, rheumatoid arthritis in 4 cases, andankylosing spondylitis in 1 case.Four patients (6 hips) died of unrelated causes to the

surgery, and 1 patient was lost to follow-up, leaving atotal of 57 hips in 49 patients available for final follow-up. Final review was undertaken at a mean of 15.2years (range, 13-20 years). Patients who had diedduring the period of follow-up had their most recentradiographs reviewed, and their data was included inthe series. All patients had current radiographs availableat final review.To date, there have been no cases of deep infection or

dislocation. There have been no revisions of the Bi-Metricfemoral stem. The mean average HSS score preopera-tively was 14.5 (range, 8-24). This improved to 33.6 (20-

40) at the 13 year follow-up, inclusive of patients whohad already undergone or who were awaiting acetabularrevision or liner exchange. This difference was statisti-cally significant (P b .001 paired Student t test). Nopatients reported experiencing thigh pain at any time inthe postoperative period.The 10-year survival for the THAs defining failure as

further surgery for any cause (Fig. 1) is 90.0% (95% CIs,95.3%-79.6%). The Bi-Metric stem when consideredalone has undergone no revisions to date. The 15.2-yearsurvival is 100% (95% CI, 100%-92.3%).A further subgroup survivorship analysis was per-

formed for all cause revision and is given for the press-fit (Universal) and screw-fit (TTAP-ST) cups in Fig. 2. Thesmall numbers of TTAP-ST cups preclude further mean-ingful analysis.Of the 44 Universal cups, there was 1 revision of the

acetabular shell and 2 liner changes by 10 years. The10-year survivorship for the Universal cup is 93.6%(95% CI, 97.9%-81.5%). There has subsequently been 1further acetabular revision and 9 more liner changes,giving an overall survival rate of 73.7% at a meanfollow-up of 15.2 years. Excluding liner exchange fromrevisions gives a survival rate of 97.7% (95% CI, 84.9%-99.7%) at 10 years, and 92.2% at mean follow-up of15.2 years.Of the 13 screw-fit cups (TTAP-ST), there were 2

revisions and 1 liner change by 10 years. The 10-yearsurvivorship is 83.3% (95% CI, 48.1%-95.5%). Subse-quently, there have been 4 further revisions, giving anoverall failure rate of 58.3% at a mean follow-up of 15.2years. Although a small sample, the TTAP-ST cup has astatistically significant poorer survivorship (P = 0.0022)than the Universal cup.

Table 1. Radiological Features of the Femoral Stems on theAnteroposterior Radiograph at 10-Year Follow-Up

Radiological feature All hips (57) Revised hips (20)

Radiolucency 1× zone 3,4,5 1× zone 3,4,51× zone 3 1× zone 3

Osteolysis 1× zone 7 1× zone 7Pedestal sign 17 (29.8%) 8 (40%)Calcar atrophy 11 (19.3%) 5 (25%)Distal cortical hypertrophy 8 (14.0%) 3 (15%)

The revised hips category includes all hips that had either undergoneor would subsequently undergo an acetabular revision or a liner changeduring the course of the study.

Fig. 2. Kaplan-Meier curve of survivorship of 2 differentacetabular shells in 64 uncemented THAs.

188 The Journal of Arthroplasty Vol. 25 No. 2 February 2010

Radiological AssessmentFifty-six femoral stems were in neutral alignment ±4°,

with 1 stem in 4.5° varus. None of the femoral stems hadmigrated more than 5 mm from the immediate pre-operative radiograph and so were all considered to bestable [15].At 10 years, 3 of the 57 femoral stems had

radiolucent lines at the bone-implant interface, with 1stem showing signs of osteolysis in zone 7. None ofthese were definitely loose [19]. All 3 of these stemswere in the group that had undergone acetabularrevision, and notably, 2 of these were the poorlyperforming screw-fix cups. Despite this, the stems hadnot migrated and showed no other signs of loosening orinstability (Table 1).Heterotopic ossification was seen in 22 (38.6%) of the

57 hips. These were classified according to the criteria ofBrooker as class I (7 hips), class II (6 hips), and class III(9 hips).

DiscussionThis series demonstrates the excellent performance of

the Bi-Metric stem with 100% survival at a minimumof 13 years and a mean of 15.2 years. Most of the hipsare performing well as indicated by high HSS scores.We selected the collared version of the Bi-Metric stem

due to its proposed ability to load the proximal femurand prevent stress shielding. When compared withreports of collared porous-coated Bi-Metric stems [12],our series has a similar incidence of distal corticalhypertrophy and pedestal formation but with less calcaratrophy (Table 1). In contrast, collarless Bi-Metric stems[13] have much higher rates of pedestal formation(47%), calcar atrophy (70%), and distal hypertrophy(83%), all signs of proximal stress shielding. These

findings support the fact that collared prostheses resultin proximal axial femoral loading [22] and integrationinto the metaphyseal bone and therefore avoid theproblems associated with proximal femoral resorption[23,24].There have been no incidences of thigh pain, a

recognized complication of uncemented femoral stemsof this generation [25,26], although more recent designsare not reported as suffering from this problem [27].This finding is likely to be the result of the taper fitdesign of the Bi-Metric stem coupled with a collarproviding proximal femoral loading and intrinsic stabi-lity at the femoral-implant interface before bonyintegration [22].The incidence of heterotopic ossification is directly

comparable with a series on the same stem [12] but lowerthan results previously published for uncemented hips of47% to 77% [25,28,29].Most of the revisions seen in this series are

accounted for by acetabular liner changes. At a meanof 15.2 years, 26% (n = 14) of patients had undergonerevision surgery; however, only 2 Universal acetabularshells needed revision. Although it may be argued thatany further surgery constitutes a failure, liner exchangeis often a smaller procedure with less associated morbi-dity than acetabular revision. All modular uncementedacetabular components suffer from the requirement forliner exchange, and this is particularly the case for theUniversal cup. In our series, we replaced 11 of 44 linerswith rates similar to this reported throughout theliterature [30,31]. It is felt that thin polyethylene ispartially to blame for the failures [30].The TTAP cup performed very badly with a failure rate

of 58.3% at 15 years. The Finnish arthroplasty registerreports a 9-year survival of only 58% for the TTAP-ST cup[32], and both these figures are comparable. The TTAP-STcup has subsequently been withdrawn from the market.Given that the degree of osteolysis in a THA is directly

related to the number of wear particles [33], the Bi-Metric stem is remarkable in its ability to withstandloosening given the environment it has had to coexistwith the Universal cup. In our series, there is only a singlecase of stem osteolysis in zone 7. This also demonstrates

Minimum 13 Year Follow Up of the Bi-Metric Uncemented Hip � Davies et al 189

the success of the Universal hemispherical plasma-sprayed acetabular shells with only 2 cases of asepticloosening at 15.2 years. Radiologically, the number ofacetabulae with radiolucent lines at 10 years (35%) iscomparable to other studies in the literature (33%) [34]and demonstrates stability of the remaining cups. Duringsurgery for 4 liner changes, small areas of osteolysis werenoted behind the cup around the area of the screw holes.In each case, this was treated with curettage and bonegrafting. Radiographic review demonstrates graft incor-poration in all 4 cases.This series represents a small-sized cohort of patients,

but the prospective collection of data and long-termfollow-up add weight to the findings. However, althoughthe data were prospectively collected, it was analysed inretrospect. Although radiographs were reviewed accord-ing to standardized criteria, we have not performedformal wear analysis, and thus, the rate of wear of theacetabular component cannot be determined, only theend point of liner exchange due to wear.The Bi-Metric stem demonstrates excellent survivor-

ship over a minimum follow-up of 13 years in a cohortof young high-demand users. The universal cup demon-strates similarly high survivorship of the acetabular shellbut suffers from liner wear and subsequent revisions.Our results support the use of porous-coated collaredfemoral stems.

AcknowledgmentWe would like to thank Mrs Verna Hamilton for her

help in following up the patients and collecting andaccessing the data.

References1. Eftekhar NS, Nercessian O. Incidence and mechanism of

failure of cemented acetabular component in total hiparthroplasty. Orthop Clin North Am 1988;19:557.

2. Duffy GP, Papa B, Rowland CM, et al. Primary uncementedHarris-Galante acetabular components in patients 50 yearsold or younger: results at 10 to 12 years. Clin Orthop RelatRes 2004;427:157.

3. Clohisy JC, Harris WH. The Harris-Galante uncementedfemoral component in primary total hip replacement at10 years. J Arthroplasty 1999;14:915.

4. Kim YH, Kim JS, Cho SH. Primary total hip arthroplastywith the AML total hip prosthesis. Clin Orthop Relat Res1999;360:147.

5. McLaughlin JR, Lee KR. Total hip arthroplasty in youngpatients 8 to 13 year results using an uncemented stem. ClinOrthop Relat Res 2000;373:153.

6. Delaunay C, Kapandji AL. 10-year survival of Zweymullertotal prostheses in primary uncemented arthroplasty of thehip. Rev Chir Orthop Reparatrice Appar Mot 1998;84:421.

7. Aldinger PR, Breusch SJ, Lukoschek M, et al. A ten to15 year follow-up of the cementless Sportorno stem. J BoneJoint Surg [Br] 2003;85:209.

8. McNally SA, Shepperd JAN, Mann CV, et al. The results atnine to twelve years of the use of a hydroxyapatite-coatedfemoral stem. J Bone Joint Surg [Br] 2000;82:378.

9. Eskelinen A, Remes V, Helenius I, et al. Uncemented totalhip arthroplasty for primary osteoarthritis in youngpatients. A mid to long term follow-up study from theFinnish Arthroplasty Register. Acta Orthop Scand 2006;77:57.

10. Eskelinen A, Remes V, Helenius I, et al. Total hiparthroplasty for primary osteoarthrosis in youngerpatients in the Finnish arthroplasty register. 4661 primaryreplacements followed for 0-22 years. Acta Orthop 2005;76:28.

11. Lyback CC, Lyback CO, Kyro A, et al. Survival of Bi-Metricfemoral stems in 77 total hip arthroplasties for juvenilechronic arthritis. Int Orthop 2004;28:357.

12. Jacobsen S, Jensen FK, Poulsen K, et al. Good performanceof a titanium femoral component in cementless hiparthroplasty in younger patients. Acta Orthop Scand 2003;74:375.

13. Meding JB, Keating EM, Ritter MA, et al. Minimumten-year follow-up of a straight stemmed, plasma-sprayed,titanium-alloy, uncemented femoral component in pri-mary total hip arthroplasty. J Bone Joint Surg [Am] 2004;86:92.

14. Boden H, Salemyr M, Skoldenberg O, et al. Total hiparthroplasty with an uncemented hydroxyapatite-coatedtapered titanium stem: results at a minimum of 10 years'follow-up in 104 hips. J Orthop Sci 2006;11:175.

15. Malchau H, Karrholm J, Wang YX, et al. Accuracy ofmigration analysis in hip arthroplasty. Digitized andconventional radiography compared to radiostereometryin 51 patients. Acta Orthop Scand 1995;66:418.

16. Gruen TA. Modes of failure of cemented stem-type femoralcomponents. Clin Orthop 1979;141:17.

17. DeLee JG, Charnley J. Radiological demarcation of cemen-ted sockets in total hip replacement. Clin Orthop 1976;121:20.

18. Hodgkinson JP, Shelley P, Wroblewski BM. The correlationbetween the roentgenographic appearance and operativefindings at the bone-cement junction of the socket in theCharnley low friction arthroplasty. Clin Orthop Rel Res1988;228:105.

19. Engh CA, Massin P, Suthers MEA. Roentgenographicassessment of the biologic fixation of porous-surfacedfemoral components. Clin Orthop Relat Res 1990;257:107.

20. Brooker AF, Bowerman JW, Robinson RA, et al. Ectopicossification following total hip replacement. Incidence andmethod of classification. J Bone Joint Surg [Am] 1973;55:1629.

21. Murray DW, Carr AJ, Bulstrode C. Survival analysis of jointreplacements. J Bone Joint Surg Br 1993;75:697.

22. Whiteside LA, Easley JC. The effect of collar and distalstem fixation on micromotion of the femoral stem inuncemented total hip arthroplasty. Clin Orthop Relat Res1989;239:145.

23. Meding JB, Ritter MA, Keating EM, et al. Comparisonof collared and collarless components in primaryuncemented total hip arthroplasty. J Arthroplasty 1997;12:273.

24. Kelley SS, Fitzgerald Jr RH, Rand JA, et al. A prospectiverandomised study of a collar versus a collarless femoralprosthesis. Clin Orthop Relat Res 1993;294:114.

25. Bourne RB, Rorabeck CH, Ghazal ME, et al. Pain in thethigh following total hip replacement with a porous

190 The Journal of Arthroplasty Vol. 25 No. 2 February 2010

coated anatomic prosthesis for osteoarthritis. A five yearfollow-up study. J Bone Joint Surg [Am] 1994;76:1464.

26. Lavernia C, D'Apuzzo M, Hernandez V, et al. Thigh pain inprimary total hip arthroplasty: the effects of elastic moduli. JArthroplasty 2004;19(7 supp12):10.

27. Strom H, Kolstad K, Mallmin H, et al. Comparison of theuncemented Cone and the Bi-Metric hip prosthesis inyoung patients with osteoarthritis: an RSA, clinical andradiographic study. Acta Orthop 2006;77:71.

28. Grubel A, Chiari C, Gruber M, et al. Cementless total hiparthroplasty with a tapered, rectangular titanium stem anda threaded cup. A minimum ten-year follow up. J BoneJoint Surg [Am] 2002;84-A:425.

29. Archibeck M, Berger R, Jacobs J, et al. Second-generationcementless total hip arthroplasty. Eight to eleven yearresults. J Bone Joint Surg [Am] 2001;83-A:1666.

30. Puolakka TJ, Laine HJ, Moilanen TP, et al. Alarming wear ofthe first-generation polyethylene liner of the cementless

porous coated Biomet Universal cup: 107 hips followed fora mean 6 years. Acta Orthop Scand 2001;72:1.

31. Llewellyn-Isaac D, Forder J, Skyrme A, et al. The Biomet Bi-Metric total hip arthroplasty and Universal Acetabular cup.J Arthroplasty 2007;22:697.

32. Puolakka TJ, Pajamaki KJ, Pulkkinen PO, et al. Poorsurvival of cementless Biomet total hip: a report on 1047hips from the Finnish arthroplasty register. Acta OrthopScand 1999;70:425.

33. Orishimo KF, Claus AM, Sycterz CJ, et al. Relationshipbetween polyethylene wear and osteoysis in hips with asecond-generation porous coated cementless cup after7 years of follow-up. J Bone Joint Surg [Am] 2003;85-A:1095.

34. Kawamura H, Dunbar MJ, Murray P, et al. The porouscoated anatomic total hip replacement. A ten to fourteenyear follow-up study of a cementless total hip arthroplasty.J Bone Joint Surg [Am] 2001;83-A:1333.