So why did some papers, e.g. by Callaghan et al in 2000 (also Kavanagh, Wroblewski, Older, etc.), show that the probability of reoperation for a cemented joint is only 77% after 25 years?
The answer is very simple: Patients who had surgery 25 years ago were already relatively old at that time, i.e. older than 70 in most cases. In addition, they were barely able to be physically active before surgery due to their ailment and after surgery, their mobility reduced even further. As a result, the implanted joints experienced only little load and wear.
For years, most of these patients had already been in a home for senior citizens. During the follow-up exam after 25 years it wasn’t even checked whether they were still able to walk. The records only show that the patient had no further hip surgery until that point. Because of this, most of these cement studies are completely useless and cannot be applied to today’s situation.
If we look at the results of cemented shafts and plastic cups in young, active patients, they are dramatically worse and sometimes don’t even last for 10 years! Why is that?
Very simple: Young patients and even some of today’s older patients are much more active than previous generations. As early as 1998, the American Tom Schmalzried published in JBJS that the average patient receiving a hip prosthesis in San Francisco produces about one million loading cycles (steps) per year. In 2002, only four years later, the same group published that the patients were producing an average of as many as two million loading cycles – twice as much after just four years. Today, active patients even take four to five million steps per year. But why is this so important?
The original plastic hip sockets were designed for about 10 million loading cycles. If a patient takes one million steps a year, it can be assumed that the plastic socket will last about 10 years. With two million steps per year, the lifespan decreases to five years and goes down further with even more cycles. Even though the plastic was improved somewhat, the plastic sockets were simply not suitable for young, active patients since they were never developed for that kind of stress.