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Abstract Number: 1093

Obesity Is Not a Risk Factor for Poor Pain and Function Two Years After Total Knee Replacement

Lisa A. Mandl1, Mark P. Figgie2, Alejandro Gonzalez Della Valle3, Michael Alexiades3 and Susan M. Goodman1, 1Rheumatology, Hospital for Special Surgery, New York, NY, 2Orthopedics, Hospital for Special Surgery, New York, NY, 3Orthopaedics, Hospital for Special Surgery, New York, NY

Meeting: 2012 ACR/ARHP Annual Meeting

Keywords: Arthroplasty, functional status, Knee, obesity and pain

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Session Information

Title: Orthopedics, Low Back Pain, and Rehabilitation

Session Type: Abstract Submissions (ACR)

Background/Purpose: Almost 90% of referring physicians think obesity increases the likelihood of poor outcomes after total knee replacement (TKR).  However, current data are conflicting.  The purpose of this study is to assess of the association of body mass index (BMI) with pain, function and satisfaction 2 years after primary TKR.

Methods:  Institutional TKR Registry patients who had a primary TKR between July 2007 and June 2009 and BMI>18.5 were enrolled. Poor pain and function were defined as WOMAC score <= 60. Data were collected prior to surgery and 2 years post-op. Multivariate regressions were performed to evaluate the association between BMI at baseline and poor pain and function at 2 years, controlling for gender, age, race, Deyo Comorbidity score and educational attainment. Expectations were measured with a validated TKR Expectations Survey.

 Results: 2524 patients were included in the analysis. BMI > 40 were more likely to be non-Caucasian, female, have less education and more co-morbidities.  Pre-operatively, both pain and function were least severe in <25 BMI category, increasing as BMI increased. At 2 years, change in WOMAC pain and function showed a step wise, dose dependant improvement across BMI categories, with BMI > 40 showing the most improvement.  At 2 years, there was a statistically significant trend towards lower BMI categories having the least pain (p-value=0.0003) and best function, (p-value<0.0001), but the differences between groups were not clinically significant.  In the multivariate regressions, there were no statistically significant associations between any BMI category or number of co-morbidities and poor pain or function at 2 years. Being female significantly increased the risk of having poor pain (OR 1.6; 95% CI 1.2-2.2) or poor function (OR 1.5; 95% CI 1.1-2.1) at 2 years.  Being Caucasian decreased the risk of poor pain (OR 0.6; 95% CI 0.4-0.9) or poor function (OR 0.5; 95% CI 0.3-0.7).  Having only high school education also increased the risk of poor pain (OR 1.5; 95% CI   1.1- 2.1) and poor function (OR 1.9; 95% CI 1.4-2.6) at 2 years. Age group 61-70 showed a decreased risk of poor pain compared to age <=60, (OR 0.5; 95% CI 0.4- 0.8). At 2 years, 20.4% of patients lost weight, (mean weight loss 0.6 lbs +/- 2.7), with the greatest loss in BMI >40 (2.7 lbs, +/- 5).  There were no significant differences in expectations or satisfaction between BMI categories. 

Conclusion: Although obese patients have worse pain and function at the time they elect TKR, their outcomes at 2 years are not clinically significantly different than other patients.  However, race and educational attainment were significantly associated with poor outcomes.  Obese patients have similar expectations and are as satisfied as patients with lower BMI.  More research should be done on the effect of race and education on TKR outcomes.   Obesity should not be regarded as a risk factor for poor outcomes after primary TKR.

Patient Characteristics

Average Weight

Overweight

Obese class I

Obese class II

Obese class III

P-value

 

(18.5 ≤ BMI <25)

(25 ≤ BMI <30)

(30 ≤ BMI <35)

(35 ≤ BMI <40)

(40 ≤ BMI)

 

 

N=523

N=902

N=633

N=289

N=177

 

 

 

 

 

 

 

 

Age

71.0 ± 10.0

69.1 ± 9.7

66.7 ± 9.2

64.8 ± 8.9

64.3 ± 7.9

<0.0001

Female

365 (70.3%)

476 (53.0%)

359 (57.2%)

200 (69.4%)

132 (75.4%)

<0.0001

Caucasian

491 (93.9%)

824 (91.4%)

560 (88.5%)

251 (86.9%)

156 (88.1%)

0.0027

High school or less

56 (17.9%)

153 (24.1%)

140 (29.4%)

72 (29.4%)

51 (30.3%)

<0.0001*

 Some college or college graduate

254 (81.2%)

416 (65.5%)

286 (60.0%)

130 (53.2%)

82 (48.8%)

 

 Masters professional or doctorate degrees

207 (66.1%)

323 (50.9%)

203 (42.6%)

86 (35.2%)

42 (25.0%)

 

0 Deyo comorbidities

409 (79.4%)

664 (75.5%)

435 (70.7%)

195 (68.8%)

100 (59.0%)

<0.0001*

 1-2 Deyo comorbidities

103 (20.0%)

214 (24.3%)

178 (28.9%)

86 (30.3%)

67 (39.5%)

 

 >= 3 Deyo comorbidities

7 (1.4%)

20 (2.3%)

15 (2.4%)

7 (2.5%)

8 (4.7%)

 

Pre-Operative WOMAC Pain

59.4 ± 17.1

57.0 ± 17.5

53.6 ± 17.1

51.0 ± 18.3

46.5 ± 16.3

<0.0001

2-Year Post-Operative WOMAC Pain

89.2 ± 15.1

88.9 ± 14.5

86.9 ± 16.2

84.8 ± 17.2

86.0 ± 16.5

0.0001

   Change in WOMAC Pain

29.9 ± 20.0

31.9 ± 19.6

33.3 ± 20.2

34.0 ± 21.6

39.3 ± 21.9

<0.0001

Pre-Operative WOMAC Function

58.7 ± 17.5

57.6 ± 17.2

52.6 ± 17.0

49.7 ± 17.7

43.5 ± 15.9

<0.0001

2-Year Post-Operative WOMAC Function

87.9 ± 15.5

87.3 ± 15.0

84.7 ± 17.0

82.8 ± 18.2

82.2 ± 16.6

<0.0001

   Change in WOMAC Function

29.0 ± 20.1

30.5 ± 18.8

32.4 ± 19.1

34.1 ± 18.6

38.0 ± 20.5

<0.0001

Change in Weight (lbs)

0.2 ± 1.7

-0.3 ± 1.9

-0.8 ± 2.7

-1.3 ± 3.2

-2.7 ± 5.5

<0.0001

Somewhat/Very Satisfied with Relieving Pain

453 (90.2%)

797 (93.1%)

547 (91.0%)

253 (90.7%)

152 (92.7%)

0.333

Somewhat/Very Satisfied with Improving

413 (83.4%)

695 (82.1%)

495 (83.2%)

230 (82.4%)

123 (76.9%)

0.401

ability to do recreational activities

 

 

 

 

 

 

Overall Somewhat/Very Satisfied with TKR

445 (88.3%)

786 (91.5%)

537 (89.2%)

252 (89.7%)

148 (91.4%)

0.333

*= test for trend

 

 

 

 

 

 

 


Disclosure:

L. A. Mandl,
None;

M. P. Figgie,
None;

A. Gonzalez Della Valle,
None;

M. Alexiades,
None;

S. M. Goodman,
None.

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