RESULTS OF CONVENTIONAL THR
AND SOME COMPARISONS.
Details of Berry's et al. 2002 report.
In the 1969 the Orthopaedic Department of the Mayo Clinic and doctor Mark Coventry personally received as the first person in the USA the license (from FDA) to use bone cement in total hip surgery. When FDA provided license to Mark Coventry, the bureau knew that these first patients would be followed very carefully. Mayo Clinic is famous for the precise and reliable statistics about the results of patients treated there. With its colleagues, Doctor Coventry's started in 1969 the Registry of all operated on total hip patients. The first 2000 total hip operations are still followed up since then. After 25 years it is a steadily dwindling troop of patients.
There were originally 1689 patients with 2000 total hip operations done between the years 1969 to 1971. During the 25 years of follow- up period 1228 patients died.
The statistic must take into account also the dead patients, who did not survive the whole 25 year period. The results of the dead patients are, of course, not known. The statisticians thus calculate the so- called "survivorship probability". This is the percentage of patients who survived the successive follow up periods with their total hip devices intact.
I
n the following Table 1 are assembled the results of the first 2000 operations as appeared 25 years after the surgery. These results were published by doctor Berry and his colleagues from the Mayo Clinic (Berry 2002).Table 1
Age at operation Percentage of patients who survived 25 years without any revision operation
Age at operation (years)< 40 years 64 % 40-49 years 62 % 50-59 years 76 % 60-69 years 87 % 70-79 years 93 % >=80 years 96 %
Some explanations to the Table 1
The rate of survival of the total hip replacement depends strongly on the patient age at the operation. You see that in the the young, more active patients the total hip device fails more often; actually 34% of all total hips failed during the 25 year follow up in patients < 40 years old at operation. In the older people the majority of TH devices survive the patients; in patients who were 80 years or more old at operation (!), only 4% of all total hips failed during the 25 year follow-up!
One cautious word. You cannot just look at the figures in the Table and say: "I am 75 years old so that I have a 96% chance that my total hip will last 25 years." You are unique, and probably not like the patients who were operated on 25 years ago at the Mayo Clinic. Yet, this Table gives a good perspective what result you can expect 25 years after the surgery with a conventional (cemented polyethylene-on-metal) total hip prosthesis.
Remember also that statistics can always be embellished, unfortunately this method is used often.
In many statistics the surgeons report rates of failure for only one cause, most often for aseptic loosening. These rates are then lower.
Another embellishing: the surgeon reports the failure of only one component, rate of femoral stem loosening only, e.g. These statistics may demonstrate very low failure rate (say 2% in ten years). Yet, the cup component of these total hip models has often had tremendously high failure rate, 30 % are no exception, during the same time. Be careful when you read a report about the results of total hip replacement. What kind of failure the author actually records?
Remember the proverb: I will tell you the truth, but not the whole truth.
Do the risk of failure accelerates as the time goes?
Total hip devices as all man made devices decay with age and fail successively. Does this decay accelerates successively as time goes? Are the risks of failure higher say 20 years after surgery than during the first postoperative years?
Look at this curve (from Doctor Berrys 25 year statistics) that shows the percentages of all patients still having their total hip in place and use. The patients were observed and counted repeatedly during the successive 25 postoperative years. You see that the percentages of the patients with intact total hip diminish slowly, continually, and without any sudden drops. At the end of the 25 years period 81% of all patients still have their total hip device intact. The conclusion is thus that (at least for these patients) the risk of failure of their total hip did not increase as they grew older. (Click on the icon for a full size picture)
It is, however, important to note that the causes of failure of TH change with time since operation. During the first years after surgery three most frequent causes of TH failures are: deep infection, repeated dislocation of the TH, and technical error. Later on, the single most frequent cause of failure is the loosening of the total hip from its bond with the skeleton (aseptic loosening).
Loosening of the total hip is the most frequent failure of this device. The absolute majority of these loosenings occur without action of bacteria, so this complication is also called aseptic loosening.
Are modern total hip results better than the "old" results?
The modern results have usually shorter follow up times, 5 or 10 years only. Are the modern results better then these "old" old operation results (operated on by Marc Coventry and his colleagues?
You will be probably surprised as I was when comparing Dr Berry's statistics with the modern data from the Swedish National Hip Register (Malchau 2002) the percentage of failures by aseptic loosening within ten years after operation.
The Swedish results are divided according to the cemented and cementless models.
PERCENTAGE OF ASEPTIC LOOSENING DURING 10 YEARS AFTER SURGERY
OLD AND MODERN MODELS COMPARED
MODERN TOTAL HIPS
Swedish National Hip Registry
1990 - 2000
OLD CEMENTED MODEL
(Barry 1969 -1972)
CEMENTED CEMENTLESS 5.2 % 12.2% 3 % The modern cemented total hip models used in Sweden between 1990 and 2000 produced clearly worse results than the cemented models in use 30 years ago at Mayo clinic in the USA. And they cost a lot more.
On the other hand, the Swedish "bad percentage" is an average calculated from data for all Swedish hospitals; the quality of surgery varied between individual hospitals and different TH models. Thus the Swedish result reflect a mix of good and bad results. The Doctor Barry's result was achieved on only one Clinic with a known high standard of orthopaedic care and using only one proven total hip model..
Modern cementless total hip models produced bad results in this Swedish statistics, their aseptic loosening was more than twice as high as loosening of cemented models. And these cementless models are really expensive!
However, the patients operated on with the cementless models were younger than the patients operated on with the cemented models. Was it the young age or the cementless model that produced the bad results?
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References:
Berry DJ et al.: J Bone Joint Surg-Am 2002; 84-A: 171-7
Malchau H et al.: Prognosis of total hip replacement. Scientific Exhibition at the 69th Annual Meeting of AAOS, February 2002, Dallas
Revised February 2007
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