Clinical Results of Ceramic on Ceramic Systems 109
f European Experience with Ceramic Systems
A. Ton! and F. Traina
Introduction
Medical applications of alumina followed its use in mechanical engineering and electronics, which started in the 1950s.
The application of ceramics for joint replacements is going back to early 70s, after that the first successful bio-inert Alumina material (Degusit AL 23) was propose and patented in England for dental implants (Sandhaus, 1965).
In Europe, Boutin (France, 1970) was the first to introduce Alumina (AI2O3, Ceraver) for hip arthroplasty bearing surfaces [1], Germans followed: Mittelmeier in 1974 [2], Heimke in 1977 [3], than Salzer in 1976 in Austria [4].
In Italy, the first experience with a ceramic prosthesis followed the first European Society of Biomaterials in 1975 in which, by a cooperation between the istituti Ortopedici Rizzoli and Prof. Chiari from Austria, a prosthesis with ceramic surfaces was devised [5].
In these early experience, only monolithic ceramic cups were used. They were fixed without cement and presented only large diameters (more than 58mm).
Monolithic cups were not successful because of their poor osseointegration potential that lead to early failure [6].
To avoid this problem, in 1985 we proposed and clinically introduced a cup made of dense alumina, coated by 3-D porous alumina beads on the dome, and contoured by a self cutting screw thread made of titanium [7]. The first series of this prosthesis was made of Ostalox, a ceramic that showed poor biomechanical properties, the second series presented a Biolox head and a Ostalox cup, finally the third series was a Biolox-Biolox coupling with a 32mm head. Notwithstanding the evolution of the ceramic material the prosthesis showed a early high failure rate [8], major problems were related to the design of the cup and to the coating of the first series of the stem [9,10].
Since 1994, we started to use a new hemispheric press-fit cup made of titanium alloy with a modular Biolox Forte liner that at the beginning was coupled with a 28mm Biolox head, and then with a 28mm Biolox Forte head.
It is the purpose of thisstudy to present our experience with ceramic bearing surfaces for total hip arthro plasty. In the first part of the study a comparative analysis of our experience with ceramic-ceramic versus metal-polyethylene coupling will be presented. To collect a statistically significant amount of data, a long-term survival analysis comparison of the 2 cohorts was inferred from Rizzoli's Register of Orthopaedic Prosthetic Implants (RlPO) [11]. In the second part of this study our experience with a modern cementless prosthesis with Biolox Forte coupling will be reported.
1 10 SESSION 3.4
Materials and Methods
Parti
At the time of this retrospective study, 8177 primary hip arthroplasties were collected in the RlPO; of these, 3465 metal on polyethylene and 3018 ceramic on ceramic couplings were recorded. Threaded cup prostheses included solely in the ceramic on ceramic cohort were excluded from the comparison, because of a statistically significant low long-term survival [11]. Excluding cases that did not have a proper follow-up, the survival of 3357 metal on polyethylene prostheses was compared with the survival of 1935 ceramic on ceramic prostheses. The cumulative probability of revision was estimated by Cox's proportional hazards regression [12]. Cox's proportional hazards model selects the variables to be included in the regression, and estimates the hazard rate, considering the fact that all of the variables can influence this rate. Definition of failure was revision for any reason for at least one prosthetic component. Log-rank and Wilcoxon tests were used to compare the two cohorts.
Part 2
From August 1995 to August 2003, 1752 primary hip replacement were consecutively performed in our Division.
The prosthesis (An.C.A. Fit, Wright-Cremascoli) presents an anatomic titanium alloy stem (Ti6A14V), proximally coated with 80|j high crystalline plasma sprayed hydroxyapatite.
In all the surgeries a 28 millimetres ceramic head and a ceramic liner (Biolox®
Forte, Ceramtec, Stuttgart, Germany) were used.
To evaluate the influence of the learning curve on ceramic coupling, the series was divided in two cohorts. The first 864 consecutive surgeries performed from August 1995 to December 2000 were included in the first cohort, of these patient
16 were lost to follow-up leaving under observation 848 prostheses. The following 888 consecutive surgeries performed between January 2001 and August 2003 were included in the second cohort: in this group 2 patients were lost to follow-up leaving 886 prostheses under control. Summarizing 18 patients (1.02%) out of 1752 were lost to follow-up, the remaining 1734 patients were investigated. The stem survival was estimated by the Kaplan-Meier method [12].
Results
Parti
A total of 26 ceramic on ceramic and 17S metal on polyethylene prostheses were replaced. A 94.1% survivorship for ceramic on ceramic and 88.3%
survivorship for metal on polyethylene were calculated at 11 years follow-up, the difference between the 2 cohorts being statistically significant (p<0.05).
Part 2
Dislocation rate of the 1734 prostheses, with a ceramic coupling without a liner lip, was 1.4% (25 patients), 6 of them required a revision surgery (0.3%). Eighteen implants failed, 6 for recurrent dislocation, 5 for late aseptic loosening, 3 for early failure (2 cases for intra-operative cracks leading to femoral fractures, 1 for stem undersizing), and 3 for septic loosening. The sun/ival rate of the prosthesis, without
Clinical Results of Ceramic on Ceramic Systems
septic loosening, was 97.5% (C.I. 94.9-100%) at 8 years. None of the revisions was due to cerannic tailure. The two cohorts did not differ for long ternn implant survival.
Discussion
The choice of the best possible prosthetic-bearing coupling for hip arthroplasty is still a topic open to debate [13].
This study shows that ceramic on ceramic coupling presents a lower removal rate than metal on polyethylene coupling. Major criticism against the use of ceramic on ceramic coupling is mainly based on its brittleness [14]. In our experience with 3018 ceramic on ceramic prostheses, 3 alumina head fractures were recorded. Fractures occurred only when a 28mm Biolox®, head was used.
Despite this, no fractures occurred when 32mm Biolox®, or 28mm Biolox® Forte, were chosen. These results revealing a low fracture rate ore comparable with those reported by Homadouche et Al. at a minimum of 18.5 years follow-up [15].
Another concern regarding alumina coupling is the higher rate of dislocations due to the lack of an antidislocation lip on the liner. In the first series, ceramic on ceramic prostheses dislocated more than metal on polyethylene prostheses, the difference between the two being statistically significant (p=0.03). But instead of 17S revisions as was the case with metal on polyethylene, the alumina coupling accounts for only 26 replacements; this higher survival rate is probably enough to justify more cases of dislocation. Besides, with the new prosthesis with modular necks, the dislocation rate was considerably low (1.4%), and only in 0.3% of the cases a revision surgery was needed.
Furthermore ceramic is known to need a particularly precise and careful surgical technique, because surgeon errors could lead to catastrophic ceramic failures [16]. During surgery, we usually careful clean the Morse taper joints of the prosthesis before the coupling with the ceramic head and liner, and we also avoid contact between ceramic surfaces and hard metallic surgical instruments.
Finally, before reduction, a careful checking of the coupling is performed to ovoid malalignment of the components. Following these simple advises from the beginning of our experience, we do not have recorded on influence of the learning curve on ceramic hip survival.
Finally, the over costs of alumina coupling versus metal on polyethylene coupling was compared; if at the time of surgery alumina over costs amount 590 Euro per prosthesis, at 10 years, considering the higher revision rate of metal on polyethylene coupling, the savings drop to 26 Euro and the trend is negative. A balanced budget is thus almost reached after 10 years for metal on polyethylene versus alumina, even without taking into account other unquantifiable costs, such as those related to patients' needs, and to avoidable revision surgery.
Furthermore, there is a higher incidence of surgical complications, longer in- staying, a higher risk of death, and longer rehabilitation time in revision surgery.
By this considerations, we are confident to consider our experience with alumina coupling successful, and to consider ceramic a valuable alternative to polyethylene.
1 1 2 SESSION 3.4
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