Survival analysis of cementless grit-blasted titanium total hip arthroplasties

Survival analysis of cementless grit-blasted titanium total hip arthroplasties

Delaunay, C

Although about 200 000 cementless Zweymuller-Alloclassic total hip arthroplasties

(THAs) were carried out worldwide in the last decade, the survival analysis of these prostheses was not available in the 2000 report of the Swedish national hip arthroplasty registry. We report a prospective survivorship analysis of 200 consecutive grit-blasted cementless Alloclassic primary THAs carried out since 1988.

Using surgical, clinical and radiological endpoints for the stem and the threaded cup the ten-year survivorship was 91.5% for reoperation for any cause, 96.4% for hip pain (Merle d’Aubigne score

J Bone Joint Surg [Br] 2001;83-B:408-13.

Received 15 March 2000; Accepted after revision 9 October 2000

Multicentre clinical trials of total hip arthroplasty (THA) are invaluable1,2 and can change practices either at individual,3 institutional or national levels.5,6 The impact of the Swedish national hip arthroplasty register, which started in 1978, on THA practice worldwide has been dramatic over the last ten years. Since the late 1980s, the data of the Swedish Arthroplasty Register (SAR) have been strongly influenced by second-generation cementing techniques. Because most orthopaedic units in Sweden have since adopted these methods, a second study period (1988 to 1998) was recently reported.8 Of the 107 825 primary THAs analysed over that decade, 91.8% were cemented, 4.6% were ‘hybrids’ and 3.6% were cementless. Of the 3929 cementless THAs, only 33 were carried out using a Zweymuller prosthesis, being 0.8% of the cementless implants and 0.03% of the total hips from 1988 to 1998. Worldwide, however, more than 200 000 ZweymUller hip prostheses have been used, mainly in western Europe. Although very popular in Europe, data on the outcome of this cementless THA have not been available from the SAR. We have therefore carried out a prospective survey of consecutive Zweymuller-Alloclassic THAs from a personal registry during the same period.

Patients and Methods

From January 1988 to December 1998, we performed 451 consecutive primary THAs. In all but eight hips (1.7%), a Zweymuller grit-blasted threaded cup forged in pure titanium (Protasul-Ti; Sulzermedica, Winterthur, Switzerland) was used. In 47 hips the femoral components were cemented because of poor femoral bone stock (39 hybrid combinations). A cementless grit-blasted Zweymuller-Alloclassic straight tapered femoral component, forged in niobium containing titanium alloy (Protasul-100; Sulzermedica), was used in 404 hips. The usual bearing surfaces were alumina ceramic (Biolox heads; CeramTec AG, ex Cerasiv, Plochingen, Germany) on polyethylene (PE), but an optional proximal hydroxyapatite (HA) femoral coating and/or metal-on-metal bearings were available from 1991 and 1994, respectively. We excluded THAs performed using these last two components (189 hips) or with a potential follow-up of less than two years (15 hips) from the study.

Thus, the 185 patients in this series included 200 Alloclassic (Sulzer Orthopedics Ltd, Baar, Switzerland) cementless primary THAs which used only grit-blasted titanium components and 28 mm alumina-ceramic on PE bearings. Because of the design criteria for inclusion, only the first 140 THAs were consecutive and the oldest cases represented the first experiences and learning curve of both surgeons with the Alloclassic stem. Table I gives the details of the patients. Their mean age was 65.9 years (32 to 91), with 47% of THAs being performed in patients less than 65 years of age and 12.5% in those over 80 years.

Patient outcome and survival analysis. Postoperative clinical and radiological reviews were undertaken at two, six and 12 months, and then annually. The THA register started in 1987 with the use of a personal database. Statistical survivorship analysis was undertaken by the construction of life tables and calculation of annual cumulative rates.9,10 The 95% confidence intervals were calculated according to the Wilson quadratic method.11

Clinical results were graded according to the Merle d’Aubigne scoring system12 as modified by Charnley.13 Three clinical endpoints were studied: a pain level less than 5 points counted at the annual interval when first noted;14 hip reoperation for any cause such as infection, recurrent dislocation and aseptic loosening; and revision of a component for aseptic loosening only. We contacted 18 patients (20 hips) by phone or mail for this clinical survival analysis.

Serial radiological analysis, conducted by the first author, utilised the scales of DeLee and Charnley for the acetabulum,15 of Gruen, McNeice and Amstutz16 for the femoral zones and of Engh, Massin and Suthers17 for bone ongrowth. The radiological endpoint was aseptic loosening, accounted at the annual interval when first noted. Radiological failure was defined as progressive lucency at the bone-implant interface, stem subsidence > 2 mm and cup tilt or migration (> 2 deg or 2 mm) which was still continuing after the second postoperative year. This two-year period before assessment of definite loosening was proposed both for femoral ‘s and acetabular components.19

To allow accurate comparison with the data from the SAR, we also calculated the ten-year survival rate of THA carried out for primary osteoarthritis only (157 hips; 78.5% of the cohort), with revision for aseptic loosening as the endpoint, using the usual criteria of the SAR.2,5,8 For each edpoint a ‘worse-case’ scenario was established,20 considering the hips in patients who were lost to follow-up before the two-year minimum deadline as failures.

Results

Table II gives the details of the outcome. A two-year minimum, complete clinical and radiological follow-up, was achieved for 169 hips (84.5% of the index series) including the results of 14 hips in patients who died after the second postoperative year; six hips were in patients who died within the first two years. Only three patients (1.5%) were lost to follow-up within the first two years; two of these had a good result at one year. At the six-year mean follow-up (1 to 136 months), six hips (3%) did not achieve an overall Merle d’Aubigne-Charnley score of at least 15 points and five of these did not have a pain score greater than four points. These figures included the last clinical score of the one loose hip before its revision.

Two patients (two hips) died in the immediate postoperative recovery period, one from probable pulmonary embolism and one from cerebral ischaemia. Over the 11-year study period, a total of 19 reoperations was undertaken on 13 hips (Table III). Eight prostheses (4%) dislocated before the third postoperative month, one in a patient who died of cerebral ischaemia. There was no recurrence after closed reduction in two hips; the other five dislocated twice and required ten combined surgical procedures to achieve stability.

Overall, six of the initial components (four stems and two cups) in four hips (2%) were removed. One stem and cup were removed for deep infection, with a two-stage revision using a new Alloclassic cementless THA. Two stems were changed for larger stems with increased offset in two hips because of recurrent dislocation. One stem was revised at 2.4 years for a cemented one, because of an intraoperative femoral fracture, which led to early failure and progressive subsidence. This last case was not counted as femoral aseptic loosening in the survival analysis, but the corresponding cup of the same hip was later revised for aseptic loosening at 5.2 years.

Survivorship data. Table IV gives the details. For both components, the nine-to-ten-year interval survivorships for three endpoints, hip reoperation for any cause, hip pain graded

Discussion

The concept and material properties of the original Zwey muller femoral component were introduced 20 years ago.21 At that time, excellent results for osseo-integration in titanium implants had already been demonstrated in dentistry.22 After seven years of experience and four evolutions of design, the Alloclassic-Stufenlos femoral taper was promoted in 1987.23 We always use this grit-blasted titanium alloy femoral component.

Mechanical testing,24 animal experiments,25 and retrieval studies26,27 have supported the use of this component. In this series, only one stem subsided because of an intraoperative fracture of the femoral shaft which was insufficiently fixed. We have not observed that any solidly fixed femoral component failed to achieve osseo-integration. We have previously described the improvement observed after the introduction of the Alloclassic Stufenlos stem in place of the former Zweymuller-Hochgezogen design, with nearly three times less subsidence and proximal reactive and lucent lines.28 In 1995, the Norwegian arthroplasty register reported early multicentre results of the Alloclassic Stufenlos stem at 4.5 years which showed a cumulative survival rate of 99.1% (95% CI, 97.9% to 100%) and 100% in patients aged less than 50 years.29

We have used the ZweymUller metal-backed threaded cup, made of pure titanium and designed in 1985, since January 1986. In this series one cup (0.5%) failed to achieve long-lasting osseo-integration, after an initial period with no detected early migration. The rationale for use of grit-blasted titanium threaded cups has been published previously.30,31

A study by Murray, Carr and Bulstrode32 reported a comprehensive review of 62 designs of THA available in the UK in 1994. It noted that the Zweymuller-Alloclassic THA was introduced in the UK in 1993, seven years after its release in Europe. However, it represented less than 5% of the UK market share and was one of the most expensive. In addition, no clinical results had been published in peerreviewed British journals although Zweymuller implants had already been the subject of papers published before 1994, but not in the English language. These papers had dealt with the evolution and biological fixation of the femoral design23,33 and the clinical results.34,35 Since 1995, independent studies of the Zweymuller system have been published internationally, providing detailed clinical and radiological results of the Alloclassic stem,29,36 the threaded cup,19,30,31 or both.28,37,38 There is also information about the femoral implantation technique,39 efficient prevention of heterotopic ossification without a deleterious effect on osseo-integration,40 and immediate proximal, but non-progressive, loss of bone mineral density using dualenergy x-ray analysis.41

Table VI lists the ten-year survival rates provided in the SAR report, with primary osteoarthritis and revision for aseptic loosening as the endpoint.8 The corresponding tenyear survivorship of 99.1% (95% Wilson CI, 87.3% to 99.9%) from our registry limited to primary osteoarthritis (157 hips) with the same endpoint, compares favourably with the 94.6% survival rate of all THAs cemented with modem techniques in Sweden, of which only three types of prosthesis (Lubinus SP, Exeter polished and MUller straight) achieved a ten-year survival rate greater than 95%.

The limitation of the Swedish national study to primary osteoarthritis led to the exclusion of underlying major hip diseases such as ischaemic necrosis, dysplasia or rheumatoid arthritis. These diagnoses are well known to occur in groups of patients at high risk for loosening of a THA, related to younger age, higher level of activity, longer life expectancy or poor bone stock. Our series of 200 primary Alloclassic THAs included 20 hips with necrosis of the femoral head, and 17 dysplastic hips (Table I). The prospective survival analysis for both components with aseptic loosening (radiological failure) as the endpoint and with a ten-year survivorship of 99.4% is a good predictor for the successful long-term outcome in primary THA.

Nevertheless, in a personal registry such as this, data can be incomplete when patients move home without providing new addresses or do not attend for review. Calculating a `worst-case’ scenario, based on the presumption that patients lost to follow-up are unhappy with their hip replacement and are thus unwilling to co-operate further with their surgeon,20 is a crude way of accounting for this lack of information. Our `worst-case’ scenario for primary osteoarthritis and aseptic loosening as the endpoint was 98.3% at the nine-to-ten-year interval, which remains in the range of the best results of modern cemented THAs reported from the Swedish registry.8

However, this hip system will have to face the same consequences of wear of PE, osteolysis and possible secondary loosening, as any other cemented or cementless THA. Two hips in our series (1%) already show some osteolysis in the area of radiologically well osseo-integrated implants in young patients. Prospective and systematic follow-up has led to early diagnosis of impending failures and, combined with component modularity, could be the key to avoiding extensive and difficult revision surgery.

An outcome survey of THA is crucial in providing useful information for the benefit of patients, surgeons and the community. Our study highlights the fact that conducting a personal prospective follow-up study of a particular THA is essential when corresponding information is not available from a multicentre registry. Expensive prosthetic components cannot be justified if they do not provide a better, or at least as good an outcome as cheaper and proven satisfactory prostheses at an equivalent follow-up. In our hands cementless Alloclassic THA components have provided at least as satisfactory result as the best-performing second-generation cemented THAs reported in the Swedish Arthroplasty Registry. The information from our study supports our continuing use, and data collection, of this particular prosthesis for primary total hip arthroplasty.

One or more of the authors have received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this article. In addition benefits have also been or will be directed to a research fund, foundation, educational institution, or other non-profit institution with which one or more of the authors is associated.

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C. Delaunay, A. I. Kapandji

From the Clinique de l’Yvette, Longjumeau, France

C. Delaunay, MD

A. I. Kapandji, MD

Orthopaedic Surgery Unit, Clinique de l’Yvette, 43 route de Corbeil, 91160-Longjumeau, France.

Correspondence should be sent to Dr C. Delaunay.

Copyright British Editorial Society of Bone & Joint Surgery Apr 2001

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