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Comparison of the BMI of Hip Replacement Patients in 2000 and 2008

Wegner_A1, Landgraeber_S1, Kauther_MD1, Claßen_T1, von Knoch_M1,2

1 Department of Orthopaedics, University of Duisburg-Essen, Essen, Germany.

²Department of Orthopaedic Surgery and Joint Replacement, Bremerhaven General Hospital, Bremerhaven, Germany.

Address for Correspondence:

Alexander Wegner
Department of Orthopaedics
University of Duisburg-Essen
Pattbergstrasse 1-3
D-45239 Essen, Germany



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


Endoprosthesis; BMI; Hip



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.


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).


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 ()
















Standard deviation





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 ()
















Standard deviation










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.

Reference :

  1. Sun Y, S.T., Günther K et al., Inzidenz und Prävalenz der Cox- und Gonarthrose in der Allgemeinbevölkerung. Z Orthop, 1997. 135: p. 184-192.

  2. von Stein, T., H. Gollwitzer, C. Kruis, and V. Buhren, [Arthrodesis after total knee arthroplasty considering septic loosening as an example]. Orthopade, 2006. 35(9): p. 946, 948-52, 954-5.

  3. Bostman, O.M., Prevalence of obesity among patients admitted for elective orthopaedic surgery. Int J Obes Relat Metab Disord, 1994. 18(10): p. 709-13.

  4. Flugsrud, G.B., et al., The impact of body mass index on later total hip arthroplasty for primary osteoarthritis: a short study in 1.2 million persons. Arthritis Rheum., 2006. 54: p. 802-807.

  5. Changulani, M., Y. Kalairajah, T. Peel, and R.E. Field, The relationship between obesity and the age at which hip and knee replacement is undertaken. J Bone Joint Surg Br, 2008. 90(3): p. 360-3.

  6. Lubbeke, A., K.G. Moons, G. Garavaglia, and P. Hoffmeyer, Outcomes of obese and nonobese patients undergoing revision total hip arthroplasty. Arthritis Rheum, 2008. 59(5): p. 738-45.

  7. Jibodh, S., I. Gurkan, and J. Wenz, In-Hospital Outcome and Resource Use in Hip Arthroplasty: Influence of Body Mass. Orthopedics, 2004. 27(6): p. 594-601.

  8. Hellmeier, W., Adipositas in NRW. Landesinstitut für den Öffentlichen Gesundheitsdienst NRW, 2006.

  9. Liu, B., et al., Relationship of height, weight and body mass index to the risk of hip and knee replacements in middle-aged women. Rheumatology (Oxford), 2007. 46(5): p. 861-7.

  10. Fehring, T.K., S.M. Odum, W.L. Griffin, J.B. Mason, and T.H. McCoy, The obesity epidemic: its effect on total joint arthroplasty. J Arthroplasty, 2007. 22(6 Suppl 2): p. 71-6.

  11. Kaur, H., M.L. Hyder, and W.S. Poston, Childhood overweight: an expanding problem. Treat Endocrinol, 2003. 2(6): p. 375-88.

  12. Kromeyer-Hausschild, K., K. Zellner, U. Jaeger, and H. Hoyer, Prevalence of overweight and obesity among school children in Jena (Germany). International Journal of Obesity, 1999. 23: p. 1143-1150.

  13. Whitaker, R.C., J.A. Wright, M.S. Pepe, K.D. Seidel, and W.H. Dietz, Predicting obesity in young adulthood from childhood and parental obesity. N Engl J Med, 1997. 337(13): p. 869-73.

  14. Mensink, G., T. Lampert, and E. Bergmann, Übergewicht und Adipositas in Deutschland 1984-2003. Bundesgesundheitsblatt Gesundheitsforschung Gesundheitsschutz, 2005. 48: p. 1348-56.

  15. Franklin, J., T. Ingvarsson, M. Englund, and L.S. Lohmander, Sex differences in the association between body mass index and total hip or knee joint replacement due to osteoarthritis. Ann Rheum Dis, 2008.

This is a peer reviewed paper 

Please cite as: Alexander Wegner: Comparison of the BMI of Hip Replacement Patients in 2000 and 2008.

J.Orthopaedics 2009;6(4)e4





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