Australian Orthopaedic Association – National Joint Replacement Registry 2009 Annual Report2009 ANNUAL REPORT – View Full Report by Clicking HereHighlights of report by Patricia Walter 10/2/09
This report is based on the analysis of 224,390 primary and revision hip replacements received by the Registry with a procedure date up to and including 31st December 2008. This is an additional 32,717 hip procedures compared to the Annual Report released in 2008. In this category of hip replacement there are 147,422 conventional total hip replacements representing 92.3% of all hip replacements and 12,093 total resurfacing hip replacements representing 7.6% of all hip replacements.
Total resurfacing continues to decline and in 2008 accounted for 6.1% of all primary total hip replacement, a reduction from 8.8% in 2005.
The use of primary total resurfacing hip replacement has declined for the third year in a row. Analysis on a variety of factors affecting outcome has again been presented. These include primary diagnosis, type of prosthesis, gender and age. Patients having a total resurfacing for osteoarthritis are revised less frequently than patients with developmental dysplasia of the hip. Females have a significantly higher rate of revision compared to males and the risk of revision increases with age. Males have an age related risk of revision which is significantly higher after the age of 65 years.
As reported last year, the difference in outcome related to gender is largely due to the size of the femoral component. There is an inverse relationship between risk of revision and size of the femoral head component. Increased revision with increasing age and the relationship to femoral component head size indicate that both bone volume and quality are factors that may impact on the outcome of this procedure.
As with primary conventional total hip replacement outcome is also determined by the prosthesis used. The ASR and Durom, reported last year as having a higher than anticipated rate of revision, continue to demonstrate more than twice the risk of revision compared to other resurfacing prostheses. In addition, the Recap resurfacing prosthesis has been identified this year as having more than twice the rate of revision compared to other resurfacing prostheses. It is not uncommon for orthopaedic manufacturers to attribute these differences to surgeon learning curve. This approach however does not explain why most new prostheses are not identified as having a higher than anticipated rate of revision.
Primary Total Resurfacing Hip Replacement
The number of total resurfacing hip procedures has continued to decline as a proportion of all hip 47 procedures and also in terms of absolute numbers. The BHR remains the most used prosthesis accounting for 50.9% of all total resurfacings in 2008. The Mitch TRH was the second most used prosthesis and showed a small increase in 2008. The ASR and Durom showed a small decline in use and the Cormet HAP BiCoat showed an increase in usage from 71 in 2007 to 84 in 2008. The ten most frequently used total resurfacing prostheses accounted for 99.9% of all procedures implanted in 2008.
Age And Gender
Age has a significant effect on the risk of revision for primary total resurfacing and the risk of revision increases with increasing age. At seven years the cumulative percent revision for patients aged less than 55 years is 4.7%, 55-64 and 65-74 are both 5.6%. At seven years females have more than twice the cumulative percent revision than males, 8.7% compared to 3.8%. The effect of increasing age on the risk of revision is evident for both males and females.
Almost all total resurfacing procedures utilise hybrid fixation with a cemented femoral component and cementless acetabular component. There has been an increase in cementless total resurfacing procedures (i.e. cementless femoral component) in 2008. No comparative outcome data by fixation are presented. The principal cementless femoral components are the Biomet, Cormet 2000 HAP and Cormet HAP BiCoat.
Femoral Component Head Size
As reported for the first time last year there is a relationship between femoral component head size and the risk of revision for total resurfacing hip replacement. Further data confirms an inverse 49 relationship between the femoral component head size and the risk of revision. At seven years patients with a femoral head size component 44mm or less have over four times the risk of revision of patients with a component head size 55mm or more, with a five year cumulative percent revision of 9.2% and 2.3% respectively (Adj HR=4.30; 95%CI (2.21, 8.37) p<0.001)
The effect of femoral component head size is evident in both males and females. Gender difference in outcome for total resurfacing procedures is largely due to differences in femoral head size. There is no significant difference between gender in the risk of revision after adjusting for femoral component head size. Males and females with femoral component head size less than 50mm have a similar cumulative percent revision at seven years (8.4% and 9.5% respectively) and males and females with head sizes 50mm or greater also have a similar five year cumulative percent revision (2.3% and 2.0% respectively).
Devices with Higher than Expected Revision Rate
The same three prostheses previously identified by the Registry have again been identified as having a higher than anticipated rate of revision. These are the Cormet 2000 HAP which is no longer used and has a 9.5% cumulative percent revision at five years. Both the ASR/ASR and Durom/Durom are still used and have a five year cumulative percent revision of 8.7% and 6.7% respectively. Newly identified this year is the Recap/Recap, of which there have been 137 implanted. The one year cumulative percent revision is 5.0% and this combination has over two and half times the risk of revision compared to all other total resurfacing procedures (Adj HR=2.59; 95%CI(1.29, 5.22) p=0.007)