Hip and Knee Arthroplasty - Surface Hippy Guide to Hip Resurfacing

knee increased from 29.4% in 2003 to 32.1% in
2007 (Figure KG2).
Diagnosis
The indication for almost all primary knee
replacement procedures is osteoarthritis (partial
resurfacing 90%, unispacer 100%,
patella/trochlear 98.9%, uni-compartmental
98.8%, bicompartmental 100% and primary total
96.8%). The principal cause for revision knee
replacement is loosening (36.5%).
Use of different Categories of Knee
Replacement
The most common knee procedure is a primary
total knee replacement (78.7% of all knee
procedures recorded by the Registry). The
proportion of other knee procedures is 12.2% for
unicompartmental, 0.5% for patella/trochlear and
8.5% for revision procedures. There is a small
number of procedures recorded for the other
types of primary knee replacement, partial
resurfacing (90), unispacer (39) and
bicompartmental (42) (Table KG1).
The proportion of all knee replacements that are
primary total knee replacements has increased
each year from 77.2% in 2003 to 82.0% in 2007.
The proportion of unicompartmental knees has
decreased from a high of 14.6% in 2003 to 9.7%
in 2007. The proportion of knee replacements
that are revision procedures is the same in 2007
as it was in 2003 (8.2%) (Figure KG3).
State and Territory Variation in Use
There is some regional variation in the
proportional use of the different knee
procedures. All states however have shown a
decrease in the use of unicompartmental knee
procedures since 2003. Tasmania is the only
state to show a small increase in the use of this
type of prosthesis in 2007 compared to 2006
(Figure KG3).
Bilateral Primary Knee Replacement
The Registry definition of a bilateral procedure is
when an individual has undergone primary knee
replacement on both knees regardless of the type
of primary knee replacement or the timing of the
second knee operation. Within five years 21.2%
of patients have undergone bilateral knee
replacement.
The Registry has recorded 32,695 individuals
with bilateral knee procedures, 25.5% of these
were performed on the same day. The most
common same day bilateral knee replacement is
bilateral primary total knee replacement. This
combination of knee replacement accounts for
77.8% of all same day bilateral procedures. Of
the remaining same day bilateral procedures
18.5% are bilateral unicompartmental knee
replacements (Table KG3).
General Comparison of Outcomes
The main outcome of the Registry is the time to
first revision of a primary joint replacement. The
outcomes of procedures are measured in two
ways, using the number of revisions per 100
observed component years and using the
cumulative percent revision at specified time
points (see Appendix 1 for the full definition).
Primary total knee replacement has the lowest
rate of revisions per 100 observed component
years when comparing all primary knee
procedures (primary total 0.8, unicompartmental
1.9, patella/trochlear 3.1, and unispacer 36.0).
The two new categories of primary knee
replacement reported this year are partial
resurfacing and bicompartmental primary knee
replacement. Both have higher rates of revision
per 100 observed component years compared to
all other primary procedures other than the
unispacer (partial resurfacing 7.5 and
bicompartmental 21.7) (Table KG4).
Comparison of the cumulative percent revision
further highlights the difference in the risk of
revision for each of these procedures. At seven
years the cumulative percent revision of primary
total knee procedures is 4.3% and
unicompartmental is 12.1%. The other
procedures do not have seven year follow up,
however the five year cumulative percent revision
for patella/trochlear procedures is 13.8%, three
year cumulative percent revision for unispacer
procedures is 66.7% and for the two newly
reported primary procedures, partial resurfacing
is 16.5% at two years and bicompartmental is
10.2% at one year (Table KG5).
Outcome by Diagnosis
As with primary hip replacement, the Registry is
presenting outcomes related to primary diagnosis
for the first time. Only primary total knee
replacement has been included in this analysis as
primary partial knee replacement is almost
entirely performed for osteoarthritis.
The outcomes of the four most common
diagnoses for primary total knee replacement
were compared using osteoarthritis as the
comparator diagnosis. Rheumatoid arthritis had
the lowest revision rate and the risk of revision is
significantly less than for osteoarthritis. There is
no difference in the risk of revision for avascular
necrosis and other inflammatory arthritis
compared to osteoarthritis (Tables KG6 and KG7
and Figure KG4).
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