Results
"How long will it last, doctor?" is a question that many patients will ask their surgeon prior to hip replacement. To give an accurate reply is impossible, but most orthopaedic surgeons will advise that an average of ten years is a realistic estimate. It should be remembered that this is an average and not a guarantee.
Irrespective of the type of replacement performed, more than 95% of patients are highly satisfied with the results of surgery in the immediate postoperative period. As time goes by the components can begin to loosen and so the level of satisfaction declines.
Many factors determine the lifespan of a total hip replacement. The age of the patient is important. The younger the patient, the shorter a hip replacement is likely to last. An American study in 1983 looked at more than 100 patients under the age of 45 years at the time of hip replacement. An average of 4½ years after the procedure only 76% of the replacements were still satisfactory. For this reason, great care is needed if total hip replacements are performed for such young patients.
The failure of hip replacements does appear to increase with time. Some studies suggest that the failure rate at 15 years is more than twice that at 10 years. Also, different parts of the total hip replacement behave in different ways. The femoral component usually lasts longer than the acetabular component. Indeed, it is the problem of failure of the cemented acetabular component that has led orthopaedic surgeons to look at the use of cementless acetabular components.
Surgical technique plays a significant part in the longevity of a total hip replacement. Results for the same design of component, inserted in different orthopaedic centres, show failure rates that vary between 1 and 24%, with some very old-fashioned designs having done well in the long-term, perhaps because of the expertise with which they were inserted.
You would not expect a revision hip replacement to last as long as a primary one and this is indeed the case, though some centres claim that the results of a first revision are as good as the results of a primary replacement. Certainly, the early results of revision surgery can be as good as the results of a primary procedure, but, overall, the failure rate of a revision replacement is higher. For revisions of revisions, the failure rate can be as high as 60%.
When it comes to assessing the result of a total hip replacement it is difficult to know against what the result should be compared. In the United Kingdom, the 'gold standard' prosthesis is the Charnley. As well as advocating the use of bone cement in the late 1950s, John Charnley also realised the importance of following patients up over the years. Only in this way can failures be identified and avoiding action taken before errors are compounded. Consequently it is possible to say that, for patients over the age of 65 years approximately 90% of Charnley components will still be going strong at 15 years after implantation. This is an excellent result, but not necessarily applicable to younger age groups, nor for categories of patient who are heavy users and extremely active.
The problem with predicting results for a hip replacement is the necessity to wait so long before any sense can be made of a prosthesis' performance. Only once a component has been followed through for 15 years can it compete with the Charnley design. In the author's practice, for example, it can be said that only 0.5% of hybrid hip replacements have failed at 10 years. Though this implies a very successful prosthesis, we still have to wait another five years before being able to perform a direct comparison with the Charnley.