AUSTRALIAN ORTHOPAEDIC ASSOCIATION – NATIONAL JOINT REPLACEMENT REGISTRY
2008 ANNUAL REPORT
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Highlights of report by Patricia Walter 9/29/08

The analysis for this Report is based on 135,799 primary total hip replacements reported to the Registry up to and
including 31st December 2007. This is an increase of 22,472 primary total hip procedures reported in the 2007 Annual Report. In this category of hip replacement there are 125,004 conventional total hip replacements, 10,623 total resurfacing hip replacements and 172 thrust plate hip replacements.

Primary Total Resurfacing Hip Replacement

For the second consecutive year the number of total resurfacing hip replacements has not only declined as a proportion of all hip procedures but also in terms of the absolute number. There was no change in the number of different types of total resurfacing prostheses used in 2007compared to 2006. The 10 most frequently used total resurfacing prostheses were used in 99.7%of all procedures in 2007.

The BHR remains the most used prosthesis accounting for 54.5% of all total resurfacing procedures in 2007. The number of procedures using this prosthesis has declined in recent years as a consequence of increased use of other total resurfacing systems. The Mitch TRH is now the second most used total resurfacing system and is one of the few that has increased in usage.

The ASR, Durom and Adept total resurfacing systems make up the top five in 2007 and have all declined in use since 2006 (Table HT10).

Gender and Age

The use of primary total resurfacing procedures in females declined from 28.8% of all total resurfacing procedures in 2003 to 23.6% in 2007 (Table HT3). Most total resurfacing procedures are undertaken in patients less than 65 years of age (91.9% in 2007) (Table H5).

Fixation

In 2007, 95.1% of total resurfacing procedures used hybrid fixation, this has declined from 97.5% in 2003.

Cementless fixation, although uncommon has increased from 2.3% to 4.7% over the same period.

Outcome

Total resurfacing hip replacement has a significantly higher revision rate compared to conventional total hip replacement (hazard ratio (adjusted for sex and age) (Adj HR)= 1.42; 95% CI (1.24, 1.63) p<0.001). At seven years the cumulative percent revision is 4.6% for total resurfacing hip replacement compared to 3.4% for conventional total hip replacement (Tables HT13 and HT14 ).

Effect of Age and Gender

The cumulative percentage revision for resurfacing hip replacement increases with increasing age (Figure HT28).
At five years the cumulative percent revision for patients aged <55 years is 3.1%, 55-64 years is 4.1%, 65-74 years is 5.0% and ≥75 years is 9.9% (Table HT36). At five years the cumulative percent revision for females (6.5%) is two and half times higher than males (2.6%) (Table HT38). As there are only a small number of total resurfacing procedures in the older age group the Registry has combined those aged 65 and older into one age group (≥65) to analyse differences between age and gender. Both genders demonstrate an increased revision rate with age. Males have a lower risk of revision per 100 observed component years compared to females in each of the three age groups (Table HT39). The five year cumulative percent revision for females aged <55 years is 5.2% increasing to 9.2% for females ≥65 years. Males <55 years of age have a five year cumulative percent revision of 2.2% increasing to 4.7% for males ≥65 years (Table HT40).

Effect of Fixation

No comparative data are presented for the outcome of total resurfacing hip replacement by fixation as most procedures use hybrid fixation. There are a number of prostheses that utilize cementless femoral component
fixation, the outcomes of the individual resurfacing systems are listed in Tables HT45 and HT46. The most commonly used cementless resurfacing system is the Cormet, which has three varieties, one of which is no longer used. The other major cementless resurfacing system is the Bionik.

Gender

The effect of femoral component head size is evident in both males and females. There is no significant difference in the risk of revision between males and females after adjusting for femoral component head size. Males and females with a femoral component head size greater than 50mm have a similar seven year cumulative percent revision (2.1% and 2.0% respectively). The same is seen for males and females with a femoral component head size less than 50mm (seven year cumulative percent revision is 5.5% and 7.3% respectively). The risk of revision for females with a femoral component head size less than 50mm is significantly higher than for females with a femoral component head size greater than 50mm ((age adjusted) HR=3.22; 95% CI (2.47, 4.21) p<0.001). A similar situation applies to males with a femoral component head size less than 50mm having a significantly higher revision rate compared to males with a femoral component head size greater than 50mm ((age adjusted) HR=2.69; 95% CI (1.91, 3.79) p<0.001).

Total Resurfacing Hip Replacement

In the 2007 Annual Report the Registry identified the ASR, Cormet 2000 HAP and the Durom as having a higher than anticipated rate of revision. The same three prostheses have been reidentified this year. The Cormet 2000 HAP is no longer used, however the ASR and Durom continue to be used, although the number is declining. All three prostheses have more than twice the risk of revision compared to all other total resurfacing prostheses combined (Tables HT50-HT52).

Prosthesis Specific Outcomes

The three total resurfacing systems with over 1,000 observed component years are the BHR, ASR and Durom. The
number of revisions per 100 observed component years for BHR is 0.8, for ASR is 2.6 and for Durom is 2.3. The three year cumulative percent revision for BHR is 2.5% and for ASR is 6.0% and for Durom is 5.8%. This year the Registry is able to report a seven year cumulative percent revision for the BHR (4.6%) (Table HT46).

Tables listed below: