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Abstract:
Obesity is one of the major topics in politics today. It is
known that overweight is related to co-morbidities which shorten
life expectancy and that it is more difficult to perform surgery
on an obese patient. The aim of this study was to compare the
preoperative body mass index (BMI) of patients who underwent
joint replacement surgery in 2000 with that of patients in the
year 2008 in one academic institution.
In both groups the mean BMI was 27, ranging from 18 to 35 in
2000 and from 18 to 39 in 2008. There was no significant
difference between the BMI values in these two groups.
In this study on patients treated in one academic institution
there was no significant change in BMI during the last eight
years in hip replacement surgery.
J.Orthopaedics 2009;6(4)e4
Keywords:
Endoprosthesis; BMI; Hip
Introduction:
Twenty to forty percent of the population over sixty years of
age suffer from arthritis (1). As a result, 150,000 hip
replacements are implanted every year in Germany and one third
of these are revision procedures. Worldwide, the annual figure
amounts to 800,000 hip replacements and the trend is increasing
(2). We know from the literature that 24-36% of patients who
have undergone joint arthroplasty are overweight and that
overweight persons have a risk of hip arthritis which is 3.4
times higher than that of people of normal weight. Furthermore,
obese patients are on average ten years younger at the time of
total joint replacement than people of normal weight (3-5). It
is also known that there is a correlation between co-morbidities
such as deep vein thrombosis, cardiovascular disease or surgical
site infections and obesity (6) and that the duration of surgery
is longer and the intraoperative blood loss is higher in obese
patients (7). In industrialized countries the number of obese
people is continually increasing (8), making obesity an economic
factor. A study published in 2007 showed that 27% to 69% of hip
and knee replacements are necessary because of obesity (9). The
aim of this study was to compare the preoperative body mass
index (BMI) of patients who underwent hip joint surgery in 2000
with that of patients who received hip replacements in 2008.
Materials
and Methods:
The data for our retrospective study was obtained from the
patients’ medical records, operation reports and anaesthesia
protocols.
The study was approved by the university ethics committee and
the local authorities according to the official guidelines of
the Declaration of Helsinki 1996.
Patients
We evaluated a total of 150 patients, with 76 consecutive
patients who underwent surgery in 2008 and 74 consecutive
patients from the year 2000. Of these, 46 were excluded from the
study because they had revision total hip arthroplasty or their
available data was not complete. The patient population included
in the study was therefore 104, with 49 consecutive patients
from 2000 and 55 consecutive patients from 2008. Forty-four
replacements were implanted on the left side and 60 on the right
side. The mean age of our patients was 68 years, ranging from 37
to 86. Seventy-two were female and 32 male. The body mass index
(BMI) was calculated by dividing the patients’ weight in
kilograms (kg) by their size in square meters (m²). Overweight
was defined as a BMI of ≥25 and obesity as a BMI of ≥30 (10).
Statistics:
We used the Kolmogorov-Smirnov-Test to test for normal
distribution of the data (p≤ 0.05 => not normally distributed).
Because all of our data was normally distributed we used the
t-test to test for significant differences. A gender-related
sub-analysis of our data was also performed with the t-test
because the data was distributed normally. A p-value of 0.05 was
considered as statistically significant.
Results :
The mean, minimum, maximum and standard deviations are
summarized in Tables 1 and 2. There was no significant
difference between the size, weight or BMI of the patients who
underwent surgery in 2000 and those who were treated in 2008.
There was also no significant difference between the age or
gender distribution (32.7% men in 2000 and 29.1% men in 2008) of
the patients from 2000 and 2008. The percentage of overweight
and obese patients in 2000 was 63.3% and 22.4% respectively, and
in 2008 65.5% and 25.5%. A sub-analysis between male and female
patients also yielded no significant results.
|
|
Age (years) |
Size (m) |
Weight (kg) |
BMI ( ) |
|
Mean |
69 |
1.67 |
75.28 |
27 |
|
Minimum |
38 |
1.54 |
53.00 |
18 |
|
Maximum |
86 |
1.87 |
115.30 |
35 |
|
Standard deviation |
11.35 |
0.09 |
14.91 |
4.16 |
Table 1:
Patients from 2000. Size is given in meters (m), weight is given
in kilograms (kg), BMI is given as
|
|
Age (years) |
Size (m) |
Weight (kg) |
BMI () |
|
Mean |
67 |
1.68 |
77.12 |
27 |
|
Minimum |
45 |
1.52 |
48.00 |
18 |
|
Maximum |
86 |
1.92 |
122.00 |
39 |
|
Standard deviation |
9.57 |
0.08 |
16.84 |
4.63 |
|
p-Value |
0.509 |
0.387 |
0.559 |
0.854 |
Table 2:
Patients from 2008. Size is given in meters (m), weight is given
in kilograms (kg), BMI is given as
.
The p-values were determined using the t-test, comparing the
patients from 2000 with those from 2008.
Discussion :
Recently published studies show that the number of obese people
has increased over the last few years (8). The percentage of
obese children, in particular, has grown over the last few
decades (11, 12). From the literature we know that obesity in
childhood is correlated with obesity in adulthood (13). The
consequence is that there is a higher percentage of obese adults
in our population today than ever before (12). As already
mentioned, obesity is correlated to a large extent with
arthritis and other diseases (3, 4, 6). As a result, joint
replacement surgery on obese patients is more resource-consuming
and involves a much greater risk (7). Another problem is that
the dislocation rate of artificial hips is higher in obese
patients than in patients with a normal BMI (6).
However, our findings contrast with the increase in obesity
generally observed in the population. The BMI of our artificial
joint patients in the past and today has remained almost the
same (Tables 1 and 2). One of the reasons for our result could
be that the number of cases in our study was too small. Kromeyer
et al., for example, investigated 5,700 patients, but did not
focus on joint replacement surgery. In contrast, we had only 150
patients. Another point is that we could only evaluate patients
from one hospital and the geographic region of the Ruhr. As a
result, our group of patients may not be representative for the
whole population of Germany or North Rhine Westphalia (NRW) as
was the population in the study of Hellmeier et al. which
evaluated data from the whole population of NRW. A further
reason could be that our hospital is a university clinic and
therefore treats more difficult cases than other hospitals. Many
overweight patients were already treated in 2000, leaving less
opportunity for a rise in the number of patients in the period
up to 2008.
Finally, we compared patients over a period of only eight years
which is perhaps not long enough to reveal any effect. In the
Kromeyer et al. study the period between the questionnaires was
twenty years, and yet they still observed an increase of only
6.3% in the number of obese boys, and 9% in the number of obese
girls. However, a disadvantage of that study is that it
investigated children in only one German city.
It is possible that our study did not reveal a significant trend
because of the disadvantages described above.
Fehring et al. performed a study on obesity in patients with
total joint arthroplasty from 1990 to 2005 in the USA (10). They
showed that the percentage of obese patients increased from
30.4% in 1990 to 52.1% in 2005. However, they also observed that
the BMI from 2000 to 2005 remained almost constant (29.4 and
29.2), which again corresponds to what we observed in our
patients.
In 2006 the German Society of Nutrition published a report
stating that approximately 60% of the German population are
overweight and that about 20% are obese (14). These are
approximately the values we observed in our patients with total
hip arthoplasty (65.5% and 25.5%) despite the fact that our
group of patients may not be representative of the population of
Germany as a whole.
Our sub-analysis between women and men revealed no significant
differences. A recently published study showed that men have a
significantly greater relative risk of suffering osteoarthritis
of the hip than women (15).
In conclusion, there have been no significant changes in the BMI
of patients undergoing joint replacement surgery during the last
eight years at one academic orthopaedic institution.
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