Success of Hip Replacement Based on Age and Type of Implant Used
In Finland, information collected about patients with total hip replacements (THRs) is put into the Finnish Arthroplasty Registry. Researchers can draw data from this databank to study various things about THRs. Today, nearly 98 per cent of all Finnish patients with THRs are included in the registry.
In this study, success rates of THR based on age and type of implants used were the main topics. Over a period of nearly 25 years (from 1980 to 2004), there were 50,968 patients in the registry who had their first total hip replacement. Success rates were defined by survival of the implant. Excessive wear and/or loosening of the implant requiring a revision (second) operation was defined as the end-point for survival (failed implant).
To qualify for this particular study, the patients had to be at least 55-years-old at the time of the operation. They all had osteoarthritis (OA) as the main reason for a hip replacement. The choice of implants included in the study was limited. It had to be one that was used in more than 50 hips during that time period. Any implant that had already been shown to have poor results in previous studies was not included.
The patients were divided into three groups by age: 1) 55 to 64 years old, 2) 65 to 74 years old, and 3) 75 and older. They were classified two different ways based on implant type. The first classification method included four groups:
The second classification scheme included three groups:
These classifications were necessary in order to compare results from one implant type to another. There were 135 different stem types and 132 different cup designs used in Finland during the time period specified. About one-third of the patients received a cementless stem or cementless cup.
In order to make comparisons, they chose one implant (known to be successful) as the reference group. The reference group for stems was the loaded-taper cemented stem implant. The reference group for the acetabulum (cup or socket) was the polyethylene, cemented cup. And the reference group for the complete implant was the cemented total hip replacement.
They found that the cementless stem groups had better survival rates and lower revision rates when compared with the loaded-taper cemented stems. The loaded-taper cemented stems did outperform the composite-beam cemented stems after 10- and 15-year marks. Results were equal at the 20-year point. The advantage of the cementless stem was only seen in the groups younger than 75 years old. Patients who were older than 75 showed no difference in outcomes based on stem type.
Comparing the survival of the acetabular cups, there was no overall difference between cemented and cementless cups after 10 years. Based on age, adults less than 75 years old did better with the cementless cups. There were fewer cases of revision because of loosening of the cup. In the older group, cementless, hydroxyapatite-coated press-fit cups were less likely to loosen or need revision.
When problems did occur with the cups, there was one main difference between cemented and cementless cups. Cups with a polyethylene (synthetic or plastic) liner showed excessive wear in the cementless group under age 75. The large number of wear-related revisions of cementless cups points to the need for an improved (wear resistant) design.
When reviewing the overall results of the total hip replacement (both stem and cup components), the cementless implants had the better outcomes. The 10-year survival rate was 90 per cent or better for all total hip groups. When broken down by age, there was no major difference in the risk of revision among the groups.
The authors show how collecting data on all total hip replacement patients can help guide surgeons when choosing the right implant for each patient. Implants that do not hold up 10, 15, and even 20 years should not be used when other, more reliable implants are available. This type of systematic analysis and reporting aids in the development of guidelines for total hip replacements.
Keijo T. Mäkelä, MD, et al. Total Hip Arthroplasty for Primary Osteoarthritis in Patients Fifty-Five Years of Age or Older. In The Journal of Bone & Joint Surgery. October 2008. Vol. 90-A. No. 10. Pp. 2160-2170.