The Journal of Arthroplasty Vol. 25 No. 1 2010

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© 20100883-5doi:10.1

Coated Hip Prosthesis vsthe Charnley Cemented Hip Prosthesis

Prakash Chandran, MS, AFRCS,* Mohamed Azzabi, MRCS, Jeremy Miles, PhD,yMark Andrews, FRCS Ortho,z and John Bradley, FRCSz

Abstract: We report the results of a prospective trial comparing uncemented Furlonghydroxyapatite-coated total hip arthroplasty and cemented Charnley total hip arthroplasty. Onehundred ninety-one patients were allocated into 2 groups depending on their year of birth. Onegroup received a Furlong hydroxyapatite-coated total hip arthroplasty and the other group receiveda cemented Charnley total hip arthroplasty. At a mean follow-up of 14 years (12-16 years), Harriship scores showed no difference between the 2 groups. The longitudinal multilevel model analysisshows that the mean slope of the change in the Harris hip score was −0.02 for the Furlong group and−0.05 for the Charnley group; the difference is 0.03 (P = .002). The survival analysis using Kaplan-Meier regression analysis (the log-rank test λ21 = 0.031, P = .58) does not show a significantdifference between the 2 groups. Overall survival was 93.6% in the Furlong group and 94.8% in theCharnley group. Keywords: total hip arthroplasty, prospective randomized, Furlong hydroxyapa-tite-coated, Charnley cemented prosthesis.© 2010 Elsevier Inc. All rights reserved.

The national joint registry for England and Walesreported a total of 44 262 primary hip arthroplastiesbetween January 2004 and December 2004 [1]. Bothcemented and uncemented prostheses are in regular use.Debate continues over the relative merits of cementedand uncemented fixation of the prosthesis. Changes inthe implant design and cementation technique havefurther improved the results of cemented hip arthroplasty[2], and long-term clinical results at 25 to 30 years [3-9]show a survival rate between 68% and 88%. Survival ofthe implant further depends on the age of the patient andlevel of activity. Wear debris, osteolysis, and asepticloosening still remain areas of concern. Most revisions inpatients with cemented total hip arthroplasty are due toaseptic loosening [9]. In the mid 1980s, the introductionof calcium hydroxyapatite ceramic (HAC) coating pro-vided an alternative method of fixation of the prosthesis.Hydroxyapatite (HA) ceramic stimulates bone growthonto the prosthesis and achieves osseointegration leadingto biologic fixation [10-12], and mineralized continuity is

e *Trauma and Orthopaedics, Scarborough General Hospital,h, West Yorkshire, United Kingdom; yDepartment of Healthniversity of York, York, United Kingdom; and zScarboroughspital, Scarborough, West Yorkshire, United Kingdom.ted January 31, 2007; accepted October 20, 2008.efits or funds were received in support of the study.al support to setup data collection was provided by theundation during the first 2 years of the study.requests: Prakash Chandran, MS, AFRCS, 15, Cresswell

llands, Warrington, North Cheshire, WA5 9UA, United

Elsevier Inc. All rights reserved.403/08/2501-0011$36.00/0016/j.arth.2008.10.009

52

established around the prosthesis [13,14]. An HAC-coated implant also allows constant bone remodelingaround the prosthesis resulting in adaptive stress transferat the prosthesis-bone interface. Early clinical results ofHAC-coated implants show good survival rates of theimplant [13,15-18]. We report the results of a compara-tive study with follow-up for 16 years of the Hydro-xyapatite-coated Furlong coated uncemented hipprosthesis and the Charnley cemented total hipprosthesis.

Patients and MethodDemographicsBetween 1988 and 1993, patients, in the age range of

45 to 75 years, diagnosed with primary osteoarthritis ofthe hip requiring total hip arthroplasty were invited totake part in the study.The patients were divided into 2 groups according to their

year of birth. Patients whose year of birth was an evennumber received an uncemented Furlong hydroxyapatiteceramic-coated total hip arthroplasty, and patients whoseyear of birth was an odd number received a Charnleycemented total hip arthroplasty. The2groupshadequivalentdemographics and were suitable for comparison.The demographics are displayed in Table 1, and there

was no statistical difference between any of the demo-graphic characteristics in the 2 groups.

Clinical and Radiographic EvaluationAll patients were seen preoperatively by the senior

surgeon (JB) and a nurse practitioner (KL). Medical andradiographic assessment was made. Pain, function, and

Table 1. Comparative Demographic Details Between Furlongand Charnley Groups

DemographicsCharnley

(86 Patients/97 Hips)Furlong

(105 Patients/125 Hips) P

Age 65.5 (48-75) * 64.5 (45-75) * .26Sex 68.6% (59), y females 67.6% (71), y female .61Body mass

index22.6 (18.3-28.5) * 23.9 (19.4-30) * .12

Diagnosis Primary osteoarthritis Primary osteoarthritis –

Pre operativeHarris hipscore

23.4 (13-42) * 22.34 (14-38) * .33

No statistical difference was observed between the 2 groups.*Minimum value and maximum value.†Number of patients.

Fig. 1. Hydroxyapatite ceramic–coated furlong total hip arthro-plasty stem.

Furlong Hydroxyapatite-Coated Hip Prosthesis vs the Charnley Cemented Hip Prosthesis � Chandran et al 53

range of motion of the hips were recorded using amodified Harris hip score.After surgery, all patients were allowed to mobilize

partial weight bearing beginning at 48 hours andcontinuing for 6 weeks. Each patient was reviewedpostoperatively at 6 weeks, 3 months, 6 months, andthen annually. The senior author and the research nursereviewed all patients at a follow-up clinic or by homevisits. In the last 5 years, all patients were reviewed in thehospital. Clinical and radiologic assessment was per-formed at every visit. Patients reviewed at home attendedhospital for check x-ray. A modified Harris hip score [19]was recorded without access to the radiograph, followedby detailed clinical assessment. The patients were scoredblind (radiographs were not available for review whilerecording the scores) after clinical evaluation, and radio-graphs were taken and further reviewed. The Harris hipscore was modified by omitting out the elements of publictransport and sitting in a chair, because for most patientsin our area, the ability to use public transport was not anoption, and sitting on a chair was not considered a normalpractice in everyday life. Radiographs were reviewed atevery visit for radiolucent lines, loosening, osteolyticareas, and migration of the prosthesis

Surgical Technique and Implants UsedAmodified Watson-Jones anterolateral approach to the

hip was used in all patients. Two senior surgeonsperformed all the surgeries; the same surgical techniquewas used in all the patients.In the cemented hip arthroplasty group, the implant

used was a monoblock Charnley flanged 45 Ortron stemwith a 22.25-mm head and the Charnley (ultra highmolecular weight polyethylene) cup, which was either along posterior wall or Ogee type (Depuy, heeds, UK).Palacos® with gentamicin cement was used adopting asecond-generation cementation technique. The techni-que involved exhaust mixing of cement, preparation ofthe femoral canal initially by an awl, and followed bybroaching the canal to appropriate size. Scraping andwashing were performed to remove all loose cancellousbone. A vent was used and the cement inserted into the

canal manually and pressurized using orthograde digitalpressure.The Furlong stem had HA coating applied by plasma

spray with thickness of 200 μm and bond strength of 40MPa (Fig. 1). The modular head diameter is 28 mm andwas made of ceramic alumina; the head was availablewith 3 different neck lengths. The cup was a FurlongHAC-coated threaded cup, except in 3 patients whoreceived a hemispherical cancellous screw fixation cupwith 3 or 4 screws (available from 1991). (Both cupswere manufactured by Joint Replacement Instrumenta-tion Limited [JRI], London, UK.) An ultra highmolecular weight polyethylene liner was used, whichwas sterilized by γ radiation in air.

Statistical AnalysisThree methods were used to analyze the data: first,

analysis of covariance to compare the Harris hip scores ofCharnley and Furlong groups at individual time points,controlling for preoperative scores for all continuousvariables; second, a longitudinal multilevel model toexamine the rate of change of the Harris hip scores overtime; and finally, to look at the time to failure of theimplant, we did a Kaplan-Meier regression analysis. Thevalue .05 was used as the significance level cutoff.

Fig. 2. Diagram showing Kaplan-Meier survival analysis.The 95% CIs at 5 years was 0.36 to 2.11; at 10 years, 0.12 to2.88; and at 15 years, 0.24 to 2.44. The numbers of hips studiedat 5, 10, and 15 years were 81, 71, and 59 in the Charnley groupand 103, 90, and 78 in the Furlong group, respectively.

54 The Journal of Arthroplasty Vol. 25 No. 1 January 2010

ResultsResults at 12 to 16 years are presented with a mean

follow-up of 14 years. At latest follow-up, 76 (72%) of105 hips were available for review in the Furlong group(27 deaths and 2 cases lost to follow-up). In patients inthe Charnley group 55 (64%) of 86 hips were availablefor review (27 deaths and 4 patients lost to follow-up). Atthe time of death, all patients in both groups hadsatisfactory hip joint function. The radiographs showed5 cases of osteolysis and loosening with Charnley stems,which were revised, and in the Furlong group, there wereno cases of osteolysis; however, 2 stems had asepticloosening, which were subsequently revised.

Clinical ResultsThe Harris hip score in patients with Furlong hips was a

mean of 94.16 ± 2.12 at 1 year postoperatively and was94.87 ± 1.84 at 5 years and then gradually declined to88.54 ± 1.78 at final follow-up. In patients with Charnleyhips, the mean Harris hip scores was 93.62 ± 1.98 at 1year postoperatively and was 92.97 ± 1.84 at 5 years andthen gradually declined to 89.13 ± 1.18 at final follow-up.The mean pain score improved from 13.83 ± 0.8preoperatively to 43.7 ± 2.1 at 1 year postsurgery. At 5years postoperatively, the pain score in 103 patients withthe Furlong stem was a mean of 43.5 ± 1.9 and in 81patients with the Charnley stem was 42.8 ± 1.6; at 10years in 90 patients, it was 43 ± 0.9 in the Furlong group,and in 71 patients with the Charnley, it was 42.5± 0.8;and at 15 years in 78 patients, the mean was 43.5 ± 1.1,and in 59 patients, it was 42.5 ± 1.4 (difference = 2.5;95% confidence interval [CI], −0.17 to 0.45, P = .596). Bythe Harris hip score, there was no statistical difference inthe function scores. It was observed that in both groups,there was a slow decline in walking distance over theyears from a score of 10.19 ± 0.8 at 1 year postoperativelyto 7.66 ± 0.6 at latest follow-up (difference = 2.5; 95% CI,1.7-3.36; Pb .001). In no case in either group was theinability to walk for less than 1 mile due to the total hiparthroplasty.

Radiologic resultsAll patients had radiologic evaluation at each annual

follow-up. At final review excluding patients who hadfailures and had revisions, no patient had any progressiveradiolucent lies around the prosthesis nor did any bodyhave obvious loosening, significant osteolysis, or migra-tion of the prosthesis in both the groups.

ComplicationsIn patients with the Furlong stem, 12 (9.6%) of 124

hips had complications. Four (3.2%) had intraoperativefractures of the calcar, which were stabilized withcerclage wires and had no adverse consequence. At 6weeks postoperatively, there was a fractured ceramichead that required revision. There were 4 revisionsbecause of severe wear at a mean of 114 months (60-164 months). Two acetabular cups were also

exchanged at these revisions for wear of the linerbecause the rim of the cups was damaged because ofimpingement. A third cup was revised for recurrentsubluxation. Two stems (1.6%) had aseptic loosening at4 and 12 years postoperatively.In patients with the Charnley stem, 5 (5.2%) of 97 hips

had aseptic stem loosening with osteolysis requiringrevision. There was no aseptic loosening of the cup ineither group.

Survival AnalysisAt an average of 14 years, the overall survival was

93.6% in the Furlong group and 94.8% in the Charnleygroup. Kaplan-Meier regression analysis (the log-ranktest λ21 = 0.031, P = .58) did not show a significantdifference in survival between the 2 groups at 12 to 16years of follow-up (Fig. 2).

DiscussionWith revision as the end point, we observed an implant

survival rate of 93.6% and 94.8% in the Furlonguncemented and the Charnley cemented group, respec-tively. Pain, functional, and survival analysis showed nodifference between the 2 groups. Most of the revisions inthe Furlong group were due to excessive polyethylenewear, and in the Charnley group, they were due toaseptic stem loosening.The primary limitation to this study is the method of

allocation into different groups. Although this is not arandomized study, there is no statistical differencebetween the demographics (Table 1), and therefore,the 2 groups are considered to be comparable. Thesecond limitation is the lack of report on wearmeasurements. In long-term studies, wear measure-ments are of vital importance to understand theexpected further prognosis with the implant system.The third limitation is the absence of measurementspertaining to offset and leg lengths, which can be ofimportance when the neck-shaft angle of the prosthesisis 140°. There is also no data on inclination and

Furlong Hydroxyapatite-Coated Hip Prosthesis vs the Charnley Cemented Hip Prosthesis � Chandran et al 55

anteversion angles of the cup, which can be used toevaluate impingement, which could be a cause offailure with Charnley prosthesis after 20 years. Absenceof all these radiologic data presents a limitation, makingthis primarily a clinical study. Difference in the implantdesigns compared, particularly with relation to theneck-shaft angles, which can change the mating of thecup and stem, could be a further limitation. The Furlongstem and threaded cup both provide excellent primarystability, and it is recognized that HA coating promotesrapid osseointegration [11] and reduces early implantmigration [20-22], whereas the Charnley stem and cupachieve good stability after cementing. It is not possibleto assess the relative merits of component geometry,materials, or coating from this study, but we believethat all are important for each particular prosthesis. Thestandard Furlong stem has a 140° neck-shaft anglecompared with the mean (129° in male and 133° infemales [23]) in the native hip joint, which will tend todecrease offset when leg lengths are equal. Reducedoffset increases load across the hip joint and polyethy-lene wear rate [24]. A 5-mm increased offset Furlongstem is now available and may help reduce polyethy-lene wear. Reducing the neck-shaft angle could alsoproduce better wear performance.The performance of Charnley hip prosthesis has been

widely published; the reported survival is 82% to 94%at 10 to 15 years [25-28]. Our results at 93.6% in theCharnley group are comparable with these publishedresults. In the flanged design, the exact mechanicaleffects of the dorsal flange on the host bone are still notcompletely understood. Comparative studies with non-flanged prosthesis have shown a significant decrease inprosthesis fracture rates, but the flat-back stems had ahigher rate of stem-cement radiolucency, and the cobra(flanged) stems had a higher rate of bone-cementradiolucency. Sangiorgio et al [29] reported increasedaseptic loosening with the flanged designs due to theirhigher stiffness. However, Ebramzadeh et al [30] foundno significant difference in the failure rates between thestainless steel Charnley cobra and straight-narrowCharnley stems. The differences in the risk of develop-ing radiolucent lines, cement fracture, and progressiveloosening among these stems were dependent on therelative rigidity of the femoral stems, differences in stemsurface finish, femoral ball size, and material used.The uncemented Furlong prosthesis is fully HA coated,

and studies have shown 100% stem survival at 10 years[16] and 99% survival at 13 to 15 years [31]. Comparingthe HA-coated implants with the noncoated implants,Palm et al [32], in a prospective randomized clinicalstudy, reported 90% failure of noncoated stems at 8 to 10years. Second-generation cementless femoral compo-nents were developed to provide more reliable ingrowthand to limit distal osteolysis by incorporating ingrowthsurfaces either circumferential proximally or to cover the

whole surface of the prosthesis. Non–HA-coated stemswith modified surfaces such as the Lord prosthesis(Benoist Girard, Bagneux, France) or the anatomicmedullary locking (DePuy) have a porous coating,which has shown to provide osseous anchorage in bothclinical and animal studies [33]. Although Palm et al [32]have shown that HA coating significantly improves thesurvival of the prosthesis, comparative clinical studieshave not shown any superiority in comparison withporous-coated or grit-blasted stems (including Zweymül-ler stems) [34-39].Aseptic loosening is the major cause of revision after

Charnley total hip arthroplasty [6]. Newer cementingtechnique and meticulous positioning of the prosthesismay improve the long-term outcome [40,41].With the uncemented HA-coated implants, improved

results can be obtained by attention to appropriatesizing of the prosthesis to avoid a mismatch betweenthe implant and the bone. Engh study [42] highlightedthat a smaller-sized implant in a stiffer bone generatesa mechanical mismatch, which may lead to loosening.Although overall revision rates are equivalent, the

trend seems to favor survival of the stem in the Furlonguncemented group and of the cup in the Charnleycemented group. This trend was also observed byEbramzadeh et al [30]. In the Furlong group, fixation isreliably achieved, but despite the ceramic head, poly-ethylene wear continues to present a problem. In anattempt to reduce acetabular revisions due to polyethy-lene wear in the future, we now routinely template forthe “offset” stem and consider alternative (ceramic-ceramic or metal-metal) bearings or smaller femoralheads in young or active individuals.In conclusion, Charnley cemented and Furlong HAC-

coated uncemented total hip prostheses had similarsurvival rates at 12 to 16 years of follow-up in thisstudy. The commonest cause of revision in the Furlonggroup was severe polyethylene wear, and all revisions inthe Charnley group were due to aseptic loosening of thestem. Polyethylene wear may be addressed by insertingthicker polyethylene (smaller head or bigger cup), bytemplating the offset to reduce leg length discrepancy andwear, and by alternative bearings in young/activepatients. Increased use of high offset stems or redesigningthe Furlong stems with a better neck-shaft angle may alsohelp to address polyethylene wear.

AcknowledgmentsWe are very grateful to Mrs Kathleen Lee and Mrs

Caroline Scott for collecting the clinical data and to MrDouglas Shaw for maintaining and analyzing the data.

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