From 1986 on, our institution has been implanting the described Alloclassic SL and CSF screw cup total hip arthroplasty system in primary and secondary hip surgery.
This is the first study to provide a 30-year follow-up for young patients under 60 years of age treated with an uncemented total hip arthroplasty system consisting of a porous coated straight stem and threaded.
Pursuing our published data for the Alloclassic stem system after 30 years of follow-up, our evaluation in combination with the cementless implanted Alloclassic CSF cup system is the first ultra-longterm-study in young and demanding patients with a mean follow up of 29.5 years[18,19]. During this timespan, a broad variety of complications occurred in our cohort. Reasons for revisions were: wear and change of head and liner (11 patients), septic loosenings (3), aseptic loosening of stem and cup (1), aseptic loosening of stem (1), periprosthetic calcification (2), implant fracture (1), periprosthetic fracture (1), intraoperative fissure of stem (1), total wear of liner including cup (1).
Nevertheless, for a majority of 70.6%, the implantation of the evaluated THA-system was the last surgery needed involving the replaced joint.
Previous data shows, that youth as well as higher activity levels may increase the incidence of mechanical failure of total hip prostheses. Wangen et al. showed a failure rate of 49 percent for the acetabular components (press fit and screw cups) due to mechanical failure in patients younger than 30 years after a mean follow-up of 16 years[20]. The main type of failure in our study did not occur in the interface between cup and bone, but wear of the polyethylene liner was the main reason for revision.
In our population group 29.6% needed revision surgery for any reason, which seems to be on a high level compared to other published cohorts with a long-term follow-up in the third decade. It has to be noted, that in those cases, which needed revision surgery to exchange head and liner, a regular PE-liner had been implanted in primary surgery. As soon as ultra-high cross-linked UHMWPE liners have entered the market in 1998, secondary surgery was performed using this long material, which has proven about 10-times less wear in long-term follow-up cohorts. As a result, a far smaller revision rate due to wear can be expected.[21-23].
It can be assumed, that the known cost-effectiveness of THA gets stronger when the revision rate decreases[24,25].
Regarding the low wear rates of modern materials, the fear of wear-associated complications in younger individual over decades does not seem to be justified.
Most of the radiolucent lines and osteolytic zones were seen in the lateral zone I according to DeLee and Charnley describing changes at the cup. Radiolucent lines around the stem were commonly seen in Gruen-zones 1 and 7, but none of the implanted systems was considered to be at risk[3,26]. The authors were able to show in a previous study, that there may be a positive effect for the reduction of osteolytic zones around the stem caused by wear when performing an exchange of head and liner[27].
The results of this study group are comparable to to previous published cohorts as shown by Delauny, giving survival rates of 99% for aseptic loosening after a timespan of 7 to 8 years[1].
The study group of Pieringer et al. presented 98.4% surviving cups after 157 months for the endpoint of aseptic loosening in 2006[28]. The cohort of Busch et al. gave results of 89% survival rate (revision for any reason; including cup and stem) after 17 years in 2012[4]. Schröder et al. gave a report on their cohort of revision cases with a survival rate of 95% percent for the cup after 6.1 years[2]. Within the czech arthroplasty register, 2677 evaluated stems showed a survival rate of 99.81% after 1 to 11 years[29].
Other stems with excellent long term results in younger patients such as CLS Spotorno (72.8 any reason after 23.8 years)[10,12,11], Bicontact (93.57% at 12 years)[6,5] and Corail (95% at 12 years)[8,9] show good results up to 24 years of follow-up, but none of the mentioned cohorts give results for a period up to the end of the third decade as we do. Published data does sometimes not focus on the long-term problems such as wear of early polyethylene liners, therefore the reason for aseptic loosenings stays unclear in most cases. We observed a high number of worn-out liners, so we assume that the reason for our aseptic loosenings may be the result of wear after a long timespan.
It has to be stated, that the criteria ‚revision for any reason’ increases with the years and usage because of progressive wear and the need for replacing head and liner[30]. Comparison with data from our previous publications shows, that all of the patients, who needed an exchange of head and liner, were not older than 60 years at primary surgery.
Knowing the excellent results for aseptic loosening of the discussed system a successing arthroplasty system needs further benchmarks to prove superiority. Criteria such as bone loss in revision surgery and reproducibility of surgical results are arguments to pursue the development and evaluation of bone sparing, and more anatomically shaped arthroplasty systems[31-33].
Our evaluation is limited by the small number of patients being alive after 30 years. Furthermore, most of the surviving patients are in a bad general medical condition or have moved far away from our institution, which leads to a very small number of clinical evaluations. Nevertheless, our primary aim was not the collection of clinical scores, but the survival rate of the implant and the resulting complications during a 30-year-timespan in younger, more demanding patients. This objective was achieved satisfactorily.
The evaluated system is very reliable in primary and secondary THA, as shown in previous studies as well as in this one. In our institution, it has been the basic implant for many years. It has been our backup-system in cases of failure of spherical pressfit cups for a long period of time.