The Journal of Arthroplasty Vol. 24 No. 1 2009

Hydroxyapatite Coated Femoral Stems in PrimaryTotal Hip Arthroplasty

A Meta-Analysis

Rajiv Gandhi, MD, J. Roderick Davey, MD, and Nizar N. Mahomed, MD

Abstract: We conducted meta-analysis of clinical studies of HA coated femoral stemsin hip arthroplasty. After an exhaustive literature search, we abstracted relevant dataon the outcomes of stem survival from aseptic loosening and Harris Hip scores. Therisk ratios and mean differences with 95% confidence intervals (CI) are reported.9 studies met our inclusion criteria for the analysis. The cumulative risk ratio forfemoral stem survival from aseptic loosening was 1.0 (95% CI: 0.995 to 1.005) P =.98. The pooled mean difference for the Harris Hip scores (HHS) was 0.072 (95% CI:−0.062 to 0.206), P = .293. The results of this study demonstrate that there are noclinical benefits in the use of HA/porous coating over porous coating alone in primaryhip arthroplasty. Key words: hip arthroplasty, hydroxyapatite, survivorship, clinicaloutcomes, meta-analysis.© 2009 Elsevier Inc. All rights reserved.

Proponents of hydroxyapatite(HA) coating on pri-mary uncemented femoral stems have suggestedthere may be a benefit to improved quality andtiming of bone ingrowth [1-3]. The potentialdisadvantages are cost and delamination of thecoating which may lead to increased third-bodypolyethylene wear with subsequent periprostheticbone loss and implant loosening [4,5].Many authors have looked at bone remodelling

around HA coated stems by examining radiographsfor distal cortical hypertrophy and cancellouscondensations and have shown conflicting results[3,7-10]. A potential limitation of these studies isthat under certain conditions, a 30% change in

From the Division of Orthopedic Surgery, University of Toronto,Toronto, Ontario, Canada.

Submitted November 7, 2007; accepted January 14, 2008.No benefits or funds were received in support of the study.Reprint requests: Rajiv Gandhi, MD, Toronto Western

Hospital, East Wing 1-435, 399 Bathurst St, Toronto, Ontario,Canada M5T 2S8.

© 2009 Elsevier Inc. All rights reserved.0883-5403/08/2401-0007$36.00/0doi:10.1016/j.arth.2008.01.299

38

calcification is necessary before a change in bonemineral density (BMD) can be seen on standardradiographs [6]. We therefore chose to examineonly those studies which report patient centeredclinical outcomes.

We hypothesized a priori that HA/porous coatedfemoral stems would show no clinical benefit overporous coated femoral stems in clinical follow up. Asystematic review of the literature was performed toevaluate our hypothesis.

Materials and Methods

Eligibility Criteria

We included articles relevant to 1) those patientsundergoing primary uncemented total hip replace-ment 2) the comparison was between a proximallyporous coated/HA femoral stem and a proximallyporous coated stem [3] the outcome measures weresurvival from aseptic loosening and post-operativeHarris hip scores [4] the study was a published orunpublished randomized controlled trial or compar-ison observational study.

Fig. 1. Search results and study selection procedure.

A Meta-Analysis of HA Coated Stems in Hip Arthroplasty � Gandhi et al 39

Study Identification. Two of the authors inde-pendently completed a computerized search of theelectronic databases PubMed MEDLINE and OVIDMEDLINE (1966 to July 2007) EMBASE (1980 to2007) with the following search terms (hydroxya-patite OR HA) AND (hip arthroplasty OR jointreplacement OR arthroplasty). We also searched theCochrane Database of Systematic Reviews, theCochrane Central Register of Controlled Trialsand Clinicaltrials.gov. After reviewing the title ofthe study we retrieved the abstract if we felt itwas appropriate. We independently reviewedthese abstracts and chose those studies that werepotentially relevant. Bibliographies of each articlethat met our inclusion criteria were reviewed for

Table 1. Summary data of stu

Study NMean f/u(years)

Mean age(years)

%men

StemFail

Dorr et al-1988 HA 15 6.5 (5-7.9) 55 (38-71) 67% 0No HA 15 0

McPherson et al1995

HA 42 3 55 57% 1No HA 42 56.5 57% 0

Tanzer et al2001

HA 17 2 66 (54-80) 68% 0No HA 22 64 (43-78) 65% 0

Kim et al 2003 HA 50 6.6 45.3 72% 0No HA 50 45.3 72% 0

Camazzola et al2004

HA 35 13 48.2 74% 0No HA 27 50.4 54% 0

Parvizi et al2004

HA 43 9.8 66.8 50% 0No HA 43 65.7 0

Sanchez-Sotoloet al 2004

HA 68 7 54 59% 2No HA 68 56 59% 6

Rorabeck 2006 HA 69 4 61(19-90) 56% 0No HA 1083 2

Yoon et al 2007 HA 37 10 6 45.3 78% 0No HA 38 46.0 1

NR – Not reported.

any further relevant studies. Furthermore, wesearched the archives of orthopedic meetings forpotential abstracts.

Assessment of Study Quality. Each publishedrandomized study was independently assessed bytwo of the authors to grade the quality of the studydesign with use of a 21-point scale [11]. Theobservational studies were graded on an 11 pointscale based on the following criteria: well definedeligibility criteria that would limit the potential forconfounding by indication, quality of outcomemeasures and statistical analysis. Conflicts wereresolved through consensus. We also assessed thestudies for number of patients lost to follow-up.Kappa calculations were performed to assess thelevel of agreement between reviewers.

Data Extraction. For each eligible study, one ofus extracted relevant data for both the interventionand control groups. This includes demographic data,post operative femoral stem survival and HHS, theintervention protocol, duration of the study, loss tofollow-up, and sources of funding.

Statistical Analysis. Baseline demographic datawas collected with variance-weighted means. Studyheterogeneity was assessed and a P value b .1 wasconsidered suggestive of statistical heterogeneity.We used two strategies to assess heterogeneity.Firstly, we analysed the data using both random andfixed effects models. Secondly, we evaluated forpublication bias using funnel plots. Publication biaswas assessed with funnel plots, which demonstratethe relationship between the sample size of thestudies and the precision in estimating the treatment

dies including in analysis

ures Femoral ImplantMean PreopHHS

Mean Postop HHS P-value

Omnifit (Osteonics) NR 93.5 .4595.5

APRI Intermedics NR 95.1 .995.8

Multilock (Zimmer) 47 96 .9148 95

IPS (Depuy) 39 (6-54) 94 (80-100) .8441( 12-56) 92 (85-100)

Mallory Head(Biomet)

34.5 89 .5446.6 91

Taperloc(Biomet) NR 93.2 .56891.7

Omniflex(Osteonics)

55 98 .2159 92

Synergy (Smith andNephew)

NR 96 .3594

Multilock (Zimmer) 47.6 (39-60) 91 .7845.3 (38-57) 90

Fig. 2. Funnel plot demonstrating no publication bias.

40 The Journal of Arthroplasty Vol. 24 No. 1 January 2009

effect. Bias can be seen if the plots are widelyskewed versus a plot resembling an inverted trianglewhich represents no bias [12].For categorical variables we used the rate ratio

as the summary statistic. This ratio represents therate of survival of the HA coated stems over therate of survival of the non-HA coated stems. Arisk ratio of less than one favours the non-HA(control) group, and the point estimate of the rateratio is considered statistically significant at the P= .05 level if the 95% confidence interval doesnot include the value 1. We used the Mantel-Haenszel method to combine the rate ratios forthe outcome of interest. For continuous variables,we calculated weighted mean difference. Weused both random effects and fixed effectsmodels for this analysis. Analysis was carried outby using Comprehensive Meta-analysis version 2.0(Englewood, NJ, US).

Fig. 3. Forrest plot for over

Results

We identified 630 studies from our searches andafter applying our eligibility criteria we had 9manuscripts for systematic review and data synth-esis [13-21]. We excluded 1 study because they onlyreported on stem subsidence between the twogroups, 5 studies involved comparisons betweenstems that were not porous coated , and 30 studiesdid not have comparison groups but were case-series. The details of the search is depicted in Fig. 1.

All papers were published in English. Four studieswere prospective randomized controlled studies[14,15,20,21] while 5 were comparison observa-tional studies. All studies reported aminimum2 yearfollow up (mean 6.5 years, range 2- 13). Two studieswere a further follow up of a previous publishedreport and only the most recent publication wasincluded [17,20]. Few studies provided details on theinstitutional review board and sample size calcula-tions. The details of the studies are shown in Table 1.

The reviewers achieved excellent agreement, andthe assessment of the quality of the studies was good(intraclass correlation, 0.66; 95% confidence inter-val, -12.4 to 0.99).

Fig. 2 shows a funnel plot for these studiesreporting Harris hip scores. The studies are distrib-uted within the 95% confidence interval axis.

The combined risk ratio for femoral stem survivalfrom aseptic loosening was 1.0 (95% CI: 0.995 to1.005) P = .946. There was no evidence of statisticalheterogeneity between studies, P = .901. Fig. 3shows a forrest plot of the combined data from the9 studies.

all stem survivorship.

Fig. 4. Forrest plot for Harris Hip Scores.

A Meta-Analysis of HA Coated Stems in Hip Arthroplasty � Gandhi et al 41

The pooledmean difference for the Harris Hip scores(HHS) was 0.072 (95% CI: −0.062 to 0.206), P = .293.There was no evidence of statistical heterogeneitybetween studies, P = .947. Fig. 4 shows a forrest plot ofthe cumulative data from the 9 studies.Seven studies commented on surgical complica-

tions while two studies did not. No study reportedsignificantly more complications in one groupversus the other.

Discussion

The addition of HA coating to femoral implants istheorized to produce bidirectional closure of gapsbetween bone and implant and potential improvedfixation [22]. Whether this theory translates intoimproved clinical outcomes was the question ourstudy was designed to answer.Our data shows that overall femoral stem survival

from aseptic loosening was no different between thetwo groups at a mean follow-up of 6.5 years.Moreover, the mean post operative Harris hip scoresbetween groups showed no difference.The potential for delamination of the HA coating

raises the concerns of accelerated polyethylene wearand osteolysis [23]. Crystallinity is believed to be animportant factor in the efficacy of the HA coatingwhereby amorphous or less crystalline materialshave been found to be more resorbable and arebelieved to be more beneficial for early boneingrowth than coatings with high crystallinity [24].Greater biologic activity of the low crystallinecoating may be explained by the release of morecalcium and phosphate ions into the local micro-environment. An in vivo study by Overgaard et al

showed that low crystalline HA accelerated earlymechanical fixation but there was no difference by32 weeks [25]. In our review, one study describedthe use of low crystallinity HA coating and con-cluded no difference in clinical outcomes betweenHA and non-HA stems [15].

It is likely that the most important factors inobtaining stable bony fixation is the initial fit of thefemoral component in the bone [26], a circumfer-ential proximal porous coating [27], and a tapered,titanium stem design [28-30].

Our systematic review of the literature andpooling of the best available data indicates thatthere is no clinically beneficial effect to the additionof HA to porous coating alone in primary uncemen-ted hip arthroplasty.

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