SPINE Volume 33, Number 16, pp 1789–1792
©2008, Lippincott Williams & Wilkins
The Effect of Obesity on Clinical Outcomes After
Mladen Djurasovic, MD,*† Kelly R. Bratcher, RN,* Steven D. Glassman, MD,*†
John R. Dimar, MD,*† and Leah Y. Carreon, MD, MSc*
Study Design. Retrospective cohort analysis.
Objective. To investigate and compare back and leg
pain, and health-related quality of life measures in obese
patients undergoing lumbar spine fusion, and to compare
the results to nonobese patients.
Summary of Background Data. Obesity is a growing
healthcare crisis in the United States and an increasing
number of patients undergoing spinal surgery are obese.
Obesity is also associated with low back pain. Some obese
patients with significant structural spine problems may be
dismissed as having their pain only coming from their
weight. We compared patient outcomes in obese and nono-
bese patients undergoing lumbar fusion surgery.
Methods. We retrospectively reviewed a single-center
patient database of patients undergoing lumbar fusion
and identified 270 patients with greater than 2-year out-
come data. Body mass index (BMI) was calculated and
patients were classified as obese (BMI ? 30) or nonobese
(BMI ? 30). All patients completed Oswestry Disability
Index (ODI), Short Form (SF)-36 questionnaires, and back
and leg pain numerical rating scores before surgery and
at 2 years. We compared clinical outcomes and compli-
cation rates in the 2 groups.
Results. The overall study group consisted of 109
obese patients and 161 nonobese patients. Both the
obese and nonobese patients demonstrated significant
improvements in back pain, leg pain, SF-36 physical com-
posite summary (PCS), and ODI scores (P ? 0.001) at
2-year follow-up compared with baseline. There was no
significant difference in the mean improvements seen in
obese patients compared with nonobese patients with
respect to back pain, leg pain, or SF-36 PCS or ODI scores.
Both SF-36 PCS (P ? 0.037) and ODI score (P ? 0.028) at
2-year follow-up were better in the nonobese patients
compared with the obese patients. Overall complication
rates were slightly higher in the obese group (P ?
0.045), predominantly because of wound-related com-
Conclusion. Obese patients undergoing lumbar fusion
achieve similar benefits to nonobese patients. Wound-
related complications are more common in obese
patients. Obese patients with otherwise good indications
for lumbar fusion should not be denied this procedure
because of their weight.
Key words: obesity, lumbar spinal fusion, outcomes,
complications. Spine 2008;33:1789–1792
Obesity has reached epidemic proportions in the United
States. Current Centers for Disease Control statistics
show that 67% of the US population is now overweight
and 32% is obese.1These proportions continue to rise.
Obesity has long been associated with a multitude of
health problems, and has been shown to be an indepen-
dent risk factor for low back pain.2Recent studies exam-
ining whether obesity compromises the clinical results of
common orthopedic procedures have shown varying ef-
fects, but have generally shown an increased rate of peri-
There likely exists some degree of surgeon bias among
spinal surgeons against operating on obese patients. Sur-
geons generally perceive that operative times are longer,
exposure of the spine is more challenging and other tech-
nical aspects of the surgery more difficult. In addition, as
obesity has been associated with low back pain, it may
introduce further uncertainty regarding the source of a
particular patient’s symptoms, even in the face of other-
wise acceptable surgical indications. For this reason,
some surgeons may expect inferior clinical results in
obese patients undergoing spinal surgery.
There has been a paucity of studies examining the
effect of obesity on the clinical results of spinal sur-
gery.5,6Existing studies have looked at a mixed group of
health-related quality of life measures. Lumbar fusion is
surgeons, with more than 250,000 procedures per-
formed annually. The purpose of the current study was
to examine the effects of obesity on the clinical results
and complication rates of patients undergoing lumbar
sures and numerical rating scale of back and leg pain of
obese patients to nonobese patients.
Materials and Methods
Adult patients at a single tertiary care spine center, undergoing
lumbar fusion for degenerative conditions, were prospectively
enrolled in a surgical database from January 2001 to January
a minimum of 2-year follow-up and complete outcomes data,
and this group comprised the subjects for the current study.
From the *Kenton D. Leatherman Spine Center, and the †Department
of Orthopaedic Surgery, University of Louisville School of Medicine,
Acknowledgment date: November 13, 2007. Acceptance date: Febru-
ary 18, 2008.
The manuscript submitted does not contain information about medical
Institutional funds were received in support of this work. Although one
or more of the author(s) has/have received or will receive benefits for
personal or professional use from a commercial party related directly
or indirectly to the subject of this manuscript, benefits will be directed
solely to a research fund, foundation, educational institution, or other
nonprofit organization which the author(s) has/have been associated.
Address correspondence and reprint requests to Leah Y. Carreon, MD,
MSc, Kenton D. Leatherman Spine Center, 210 East Gray Street, Suite
900, Louisville, KY 40202; E-mail: email@example.com
Inclusion criteria included patients undergoing single or multi-
level lumbar spinal fusion for a variety of degenerative lumbar
spine conditions, such as spondylolisthesis, spinal stenosis,
lumbar instability, and degenerative disc disease. Patients un-
derwent concomitant decompression of neural compressive le-
sions as indicated by preoperative imaging studies. Patients
undergoing fusion for trauma, infection, neoplasm, or severe
spinal deformity (scoliosis greater than 30 degree, flatback syn-
drome) were excluded. The study protocol was approved by
the Institutional Review Board at the University of Louisville.
Body mass index (BMI) was calculated for each individual
patient as the weight in kilograms divided by height in meters
squared. Patients were then grouped according to National Insti-
kg/m2as normal weight, 25.0 to 30.0 kg/m2as overweight, and
greater than 30.0 kg/m2as obese. For the purposes of statistical
analysis, we categorized patients in this study as either nonobese
(BMI ?30) or obese (BMI ?30). This yielded a group of 161
Primary comparisons were made between these 2 groups.
and at 1 and 2 years postsurgery. Patients were asked to rate low
back pain and leg pain independently on a 10-point numerical
rating scale, ranging from 0 (no pain) to 10 (worst pain). The
questionnaires also included the Short Form-36 (SF-36) General
Health Instrument8and Oswestry Disability Index (ODI).9The
SF-36 is a self-administered short-form health status survey that
cause of physical health, mental health, vitality, bodily pain, and
composite summary score and a mental composite summary
a 10-item scale with 6 response categories each. Each item scores
from 0 to 5, which is transformed into a 0–100 scale. Demo-
of office and hospital charts.
Statistical analysis was performed using SPSS software (SPSS
Inc., Chicago, IL). Mean differences from baseline measures to
2-year postoperative values were compared for the obese patients
and nonobese patients with respect to back pain numerical rating
scale, leg pain numerical rating scale, physical component sum-
mary score of the SF-36 (SF-36 PCS), and the ODI. Continuous
variables were compared using the Student t test. Dichotomous
data such as preoperative diagnoses and incidence of complica-
ing on the frequency of outcomes. A 2-tailed P value of less than
0.05 was considered statistically significant.
Baseline characteristics of the 2 groups were similar with
respect to demographic characteristics and surgical indica-
tions (Tables 1 and 2). The average age of study subjects
was 57.1 years in the nonobese patients and 56.2 years in
the obese patients. Women comprised 60% of the subjects
near the cutoff between normal and overweight at 25.7
difference (P ? 0.359) in the distribution of preoperative
diagnoses between the 2 groups. Revision surgeries ac-
counted for 31.7% of the cases in the nonobese group and
37.6% of the obese group.
Back pain and leg pain showed similar improvements
from preoperative to postoperative values in the obese
subjects when compared with the nonobese subjects (Ta-
ble 3). Both groups showed significant improvement in
back and leg pain after surgery (P ? 0.001), and the
degree of improvement after surgery was not different in
the 2 groups. The obese patients had slightly higher
2-year leg pain scores (P ? 0.043), but because their
preoperative leg pain showed a nonsignificant trend to-
wards higher leg pain, the amount of improvement with
surgery was similar in the 2 groups.
Similarly both SF-36 PCS and ODI scores showed sig-
bese subjects (P ? 0.001), and the degree of improvement
was similar in both groups (Table 3). Two-year SF-36 PCS
scores were lower in the obese patients (P ? 0.037); how-
ever, as they started slightly lower, the degree of change
from preoperative to postoperative was the same as in the
nonobese patients. Obese patients had worse ODI scores
before surgery (P ? 0.017) and after surgery (P ? 0.028),
Table 1. Demographic Characteristics of Study Subjects
Nonobese (161)Obese (109)P
Gender (% male)
Mean follow-up (mo)
25.74 ? 2.41
57.11 ? 14.40
26.73 ? 13.08
34.78 ? 4.80
56.18 ? 12.24
25.86 ? 12.08
Table 2. Pre-Operative Diagnosis
Preoperative Diagnosis NonobeseObese
Adjacent level degeneration
Table 3. Baseline and Two-Year Outcomes Measures
Leg pain NRS
Mean baseline score
Mean 2-yr score
Mean change in score
Back pain NRS
Mean baseline score
Mean 2-yr score
Mean change in score
Mean baseline score
Mean 2-yr score
Mean change in score
Mean baseline score
Mean 2-yr score
Mean change in score
6.71 ? 2.67
4.29 ? 3.20
2.38 ? 3.75
7.18 ? 2.60
5.10 ? 3.18
2.13 ? 3.60
7.82 ? 1.97
4.91 ? 2.95
2.86 ? 3.06
7.85 ? 1.96
5.47 ? 2.83
2.43 ? 3.13
28.63 ? 6.46
34.72 ? 10.18
6.17 ? 9.11
27.68 ? 5.35
32.07 ? 9.77
4.22 ? 12.59
51.42 ? 15.80
36.07 ? 21.70
15.35 ? 20.56
55.83 ? 13.17
41.80 ? 19.65
14.03 ? 20.09
1790 Spine•Volume 33•Number 16•2008
but again, the degree of improvement with surgery was the
same as for the nonobese patients.
Overall complication rates were slightly higher in the
obese group, with 17.4% of nonobese patients having
perioperative complications, compared with 28.4% for
the obese subjects (P ? 0.045) (Table 4). This was pre-
dominantly because of wound-related complications (in-
fection, persistent wound drainage), which were signifi-
cantly more common in the obese subjects (5.5% vs.
0.6%) (P ? 0.018). The odds ratio of perioperative com-
plications was 1.88 (95% confidence interval, 1.05–
3.38), and the odds ratio for wound-related complica-
tions was 9.3 (95% confidence interval, 1.11–78.5).
Approximately 13% of the subjects in both groups re-
quired revision surgery during the follow-up period,
with the development of adjacent level degeneration as
the most common cause for revision (Table 5).
otherwise meet acceptable criteria and indications for
lumbar fusion, obtain similar degrees of improvement
with lumbar fusion as nonobese patients. Although there
was a trend for obese patients to have a slightly lower
general health and back-specific outcomes scores both
before surgery and after surgery, the degree of improve-
ment with surgery was similar to nonobese controls.
Obese patients did have a higher incidence of wound-
Our data suggest that obese patients can be expected to
derive the same benefits from lumbar fusion as the general
population. It is likely that some surgeons have had signif-
icant reluctance to recommend fusion to obese patients.
From the surgeon’s perspective, the exposure is more diffi-
cult and time consuming, and the deep soft tissue envelope
could make certain technical aspects of the surgery more
ing spinal implants such as pedicle screws. In addition, the
source of back and/or leg pain in any given patient can be
difficult to identify, and in an obese patient whose lumbar
extensor muscles must work even harder to support their
higher trunk body mass, the issue of the “pain generator”
with a spondylolisthesis, there is no objective test, which
can tell a surgeon how much of their mechanical back pain
is from segmental instability, and how much is from
paraspinal muscle fatigue. Given this uncertainty, it would
be reasonable to expect that the presence of obesity may
compromise the clinical results of fusion.
Recent studies in other areas of orthopedic surgery have
examined whether the presence of obesity adversely affects
patient outcomes with surgery. The bulk of this research
recently found inferior Knee Society scores at 8-year fol-
low-up in obese patients undergoing total knee arthro-
plasty, when compared with a matched group of nonobese
patients. A negative impact of morbid obesity on knee ar-
throplasty was also seen in a study by Amin et al11which
showed that at 4-year follow-up, morbidly obese patients
demonstrated inferior Knee Society scores, more complica-
implant survivorship. Namba et al12found a 6-fold higher
infection rate for obese patients undergoing total knee ar-
throplasty, and a 4-fold higher infection rate for total hip
arthroplasty. However, several other studies have shown
knee arthroplasty.13–15A clear consensus has not yet
emerged regarding the influence of obesity in total joint
In the area of spinal surgery, there has been a paucity
of studies examining the influence of obesity on clinical
outcomes. Andreshak et al5found, in a mixed group of
surgeries (discectomies, laminectomies, and fusions),
equivalent clinical results in obese and nonobese pa-
loss, and hospital length of stay. They concluded that
proper surgical indications are the predominant factor
affecting surgical results and that patient weight should
not influence surgical decision-making. Gepstein et al6
recently examined their results in elderly obese patients
undergoing decompressive procedures for lumbar steno-
sis, and found similar degrees of improvement and sub-
jective satisfaction rates in their obese and nonobese pa-
tients. Our findings confirm the results of these previous
studies. The addition of patient-directed quality of life
outcomes from a patient perspective as well. Several
studies have shown higher complication rates with spine
surgery in obese patients,16–18particularly with respect
to wound complications. Although our data did show a
cations in the obese group, this rate was still acceptable
at 5.5%, and by itself would not contraindicate this pro-
cedure in obese patients.
Table 4. Complications
28 (17.4%) 31 (28.4%)
Table 5. Need for Subsequent Surgery
Adjacent level degeneration
Removal of instrumentation
21 (13.0%)14 (12.8%)
1791Effect of Obesity on Clinical Outcomes After Lumbar Fusion•Djurasovic et al
Limitations of the study include the potential for selec-
tion bias. Although baseline demographics and surgical in-
dications were equivalent for the obese and nonobese pa-
tients, it is possible that surgeons unconsciously applied
more stringent criteria (e.g., patient motivation, compli-
ance with therapy, etc.) when selecting obese patients for
surgery. The relatively short-term follow-up period does
not preclude the possibility that obese patients may have
nonobese patients, although we did not see any indication
that this was the case. Also obese patients likely had other
confounding factors affecting their general quality of life
measures. However, we focused on changes in pain scores
and outcome measures from before to after surgery, thus
these confounding factors should not be reflected in the
differences seen with surgery.
In conclusion, this study found equivalent degrees of im-
provement with respect to back and leg pain, general
health, and low back specific quality of life measures in
obese patients undergoing lumbar fusion. Overall compli-
wound-related issues. Our findings suggest that obese pa-
tients with appropriate indications for lumbar fusion
Preoperative counseling on weight loss and careful consid-
eration of comorbidities remain important principles when
treating this challenging patient population.
● Obese patients, who meet acceptable criteria
and indications for lumbar fusion, achieve simi-
lar benefits with lumbar fusion as nonobese pa-
tients. Although obese patients to have slightly
lower general health and back-specific outcomes
scores both before surgery and after surgery, the
degree of improvement with surgery was similar
to nonobese patients.
common in obese patients, the incidence is still ac-
ceptable at 5.5%, and by itself would not contra-
indicate this procedure in obese patients.
● Obese patients with otherwise good indications
for lumbar fusion should not be denied this proce-
dure because of their weight.
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1792 Spine•Volume 33•Number 16•2008