Factors Affecting Aseptic Loosening of 4750 Total Hip Arthroplasties: Multivariate Survival Analysis

Barbara Bordini; Susanna Stea; Manuela De Clerico; Sergio Strazzari; Antonio Sasdelli; Aldo Toni

Disclosures

BMC Musculoskelet Disord 

In This Article

Discussion

To determine the factors that influence component survival we followed a large number of consecutive primary total hip arthroplasties performed in the same Institute. The cohort was large enough to be analysed by age, gender, diagnosis, Charnley score, side, skill of surgeon, and type of component. Distribution of frequencies of some variables (ie age at surgery, surgeon experience) is clearly different among types of implants. Multivariate analysis applied to test the influence of single factors can limit this bias. By analysing prostheses implanted between 1995 - 2000, we were able to include designs that are still modern, and at the same time have a long enough follow-up to highlight any failures.

Since the register was started at Rizzoli Institute in 1990, all patients have been monitored; if patients fail to attend scheduled clinical exams, they are contacted by phone or asked to fill in a questionnaire. This was acceptable as the recorded end-point (revision) was independent of clinical examination. The chosen end-point is undoubtedly a raw parameter, which does not take into account the quality of life and restoration of function in the treated limb, but its strength lies precisely in its objectivity.

Some of the results obtained from this analysis support data reported by other authors in comparable series. In agreement with the literature, the risk of failure is increased by male gender, young age, and certain diseases.[17,18,20] These variables, which constitute the patient's characteristics, are unchangeable. However, knowing the influence they can have enables a correct statistical interpretation. The interesting finding that has emerged from this study is that among the factors that influence the risk of failure are the surgeon's skill, and the type of prosthesis-to-bone fixation used.

The surgeon's skill is an extremely delicate aspect, which might depend on the reliability of the hospital where the operation is performed rather than the experience of the single surgeon. High-risk patients, who are often admitted to hospitals not necessarily near home, might be treated more safely in highly specialised centres. It should be remembered that the data presented in this study come from operations performed at a highly specialised hospital and includes very complex cases, which, on the other hand, have been treated by highly specialised surgeons.

Another important factor that can be modified is the prosthetic component. Uncemented components are generally much less likely to fail than cemented ones. However, our results appear to be in contrast with those of other registers.[11] Nevertheless, reading the data more carefully reveals that as experience using uncemented components increases, the difference in results between the two types of prostheses decreases, and the efficacy of uncemented prostheses is highlighted especially with regards to young[12,17] or middle-aged patients.[13]

An interesting finding that emerged from our study was that the more expensive the prosthesis, the longer its survival was.

With regards to the cup, all other variables being equal, compared to the monoblock polyethylene cup the failure rate of the press-fit cup with a polyethylene liner, which costs four times more than the monoblock cup, was reduced by half, and reduced by 2/3 when using the press-fit cup with a ceramic liner, which costs five times more than the monoblock cup.

Concerning the stem, there were no significant differences in the failure rate between the straight cemented stem and the anatomical cemented stem, which costs 10% more. Conversely, compared to the cemented straight stem, the failure rate of the uncemented straight stem, which costs 90% more than the cemented one, is 60% less. The reduction in the failure rate is 60% also when using uncemented modular stems, which cost 150% more than the cemented straight stem.

Finally, coated and/or anatomical uncemented stems cost 110% more than cemented straight stems but the failure rate is reduced by 80%.

All the conclusions drawn from these data have intrinsic and unavoidable limits due to the low rate of revision (less than 3%) that affect primary Total Hip Arthroplasty. The revision rate is fortunately lower than the 10% suggested as the maximum acceptable by NICE.[1] For this reason a non-parametric statistical method of analysis was used, which can handle correctly this kind of data.

This analysis provides the basis for a cost-benefit assessment, which aims at determining whether a certain clinical result can be achieved while reducing the resources used. From a strictly ethical point of view the results give a clear indication of the choice, but the availability of economic resources can only be determined by healthcare policy. Undoubtedly, subsequent cost-benefit analysis should take into account that this type of operation is performed on elderly people who need a long recovery period. Therefore, there is also a need for rehabilitation centres, which are often lacking, and so elderly people often have to rely on the help of their families.

Besides social aspects, also technical difficulties should not be underestimated. Sometimes surgeons are faced with difficult operations and have to make bold choices. However, cost-benefit analysis is not within the scope of this paper, which is limited to providing data to enable correct elaboration.[21,22] We reiterate that the data presented come from a series of patients and include the use of cemented and uncemented components, unlike those based on large databanks of northern European registers, which show that cemented components perform better[23,24] or at least as well as[25] uncemented ones. Since cemented prostheses are cheaper, they are more advantageous from a cost-benefit point of view. The data we have presented, which do not include only the cost of materials[26] will enable a cost-benefit analysis that is closer to reality in countries where the use of uncemented prostheses is more widespread.

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