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Comparison of Outcome between Obese and Non-Obese Patients after Primary Lumbar Discectomy

Awaiz Ahmed, Muralidharan Venkatesan, Martyn Newey

Awaiz Ahmed, Buckinghamshire Healthcare NHS Trust, Stoke Mandeville Hospital, Aylesbury, HP21 8AL, United Kingdom
Muralidharan Venkatesan, The Centre for Spinal Study and Surgery, Queen’s Medical Centre, Nottingham, United Kingdom
Martyn Newey, University Hospital of Leicester, United Kingdom

Conflict-of-interest statement: The author(s) declare(s) that there is no conflict of interest regarding the publication of this paper.

Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http: //creativecommons.org/licenses/by-nc/4.0/

Correspondence to: Awaiz Ahmed, Buckinghamshire Healthcare NHS Trust, Stoke Mandeville Hospital, Aylesbury, HP21 8AL, United Kingdom.
Email: orthofixer@hotmail.com
Telephone: +44-7738236297

Received: December 25, 2016
Revised: February 12, 2017
Accepted: February 15 2017
Published online: April 28, 2017

ABSTRACT

BACKGROUND AND AIM: Increasing numbers of patients undergoing spinal surgery are overweight or obese. It is unknown if the degree of obesity influences surgical outcomes in patients undergoing primary lumbar discectomy. The purpose of this study was to evaluate the effect of different body mass indices on the surgical experience, perioperative data and clinical outcomes in patients undergoing primary elective lumbar discectomy.

METHODS: A singe-center review of prospective database of patients treated by a single surgeon over an 8-year period was performed. From this we identified 92 consecutive patients who underwent primary lumber discectomy. Visual Analogue Scores (VAS) for leg and back pain and Oswestry Disability Index (ODI) were recorded preoperatively and postoperatively, as were complications, recurrence of disc and subsequent revision surgery. From medical records we also recorded various demographics including height (cm), weight (kg), body mass index (BMI), comorbidities, smoking status, operative time, time to ambulate, length of hospital stay. Patients were stratified into the standard BMI categories: normal (< 25 kg/m2), overweight (25 - 29.9 kg/m2) or obese (≥ 30 kg/m2).

RESULTS: The overall study group consisted of 36 normal patients, 33 overweight and 23 obese patients. Indications for surgery were a uni-lateral disc prolapse in 74 (80%) patients and a central disc prolapse in 18 (20%), and patients underwent a discectomy, decompression or a combination. The three patient groups were comparable in terms of age, sex, and diagnosis. All three patients groups demonstrated significant improvements in leg pain, back pain, and ODI scores (p < 0.001) at 2-months and 6-months following surgery compared to baseline. There was no significant difference in the mean improvements observed in obese or overweight patients compared to patients of normal weight with respect to leg pain (p = 0.69), back pain (p = 0.14), and ODI (p = 0.3). Operative time was significantly longer for the obese group. Time to ambulate and length of hospital stay were comparable. The incidence of wound infections was also comparable while the incidence of a dural tear was higher in the non-obese group. There was no difference in the revision rate between the groups.

CONCLUSION: Obese patients undergoing lumbar discectomy achieve similar benefits to non-obese patients.

Key words: Butyrate; Endophytic bacterial fermentation/identification; Anti-inflammation

© 2017 The Author(s). Published by ACT Publishing Group Ltd. All rights reserved.

Ahmed A, Venkatesan M, Newey M. Comparison of Outcome between Obese and Non-Obese Patients after Primary Lumbar Discectomy. International Journal of Orthopaedics 2017; 4(2): 714-718 Available from: URL: http: //www.ghrnet.org/index.php/ijo/article/view/1949

INTRODUCTION

The prevalence of overweight and obese individuals in the Western World has reached epidemic proportions[1-5]. Recent survey conducted in 2009 and 2010 by Centers for Disease Control statistics report that 69.2% of adults older than 20 years are now overweight and 35.9% are obese[6]. Obesity has long been linked to a multitude of health problems, and has been shown to be an independent risk factor for lumbar spine related disorders[7-11]. Consequently, the number of overweight and obese patients requiring spinal surgery is on the rise.

Much has changed the face of modern spine surgery especially over the last two decades. There may still exists some degree of subconscious bias among spinal surgeons against operating on obese patients. Surgeons often perceive spinal surgery in obese patients to be associated with increased operative times, perioperative complications and inferior clinical outcomes.

Some authors have evaluated the effect of obesity on the complication rates and clinical results of spine surgery[12-16]. Existing studies have focused mainly on lumbar fusion and a mixed group of surgical procedures (discectomies, laminectomies, and fusions). None has specifically looked at the direct relationship between obesity and primary lumbar discectomy. Lumbar discectomy is the most common procedure performed by spinal surgeons.

The purpose of the current study was to determine if different body mass indices has an impact on the surgical experience, perioperative data and clinical outcomes in patients undergoing primary elective open lumbar discectomy.

MATERIALS AND METHODS

We analysed a prospectively maintained single spine surgeon’s database at our institution containing patient demographics, procedure details, and pre-and postoperative outcome scores.

We searched this database for patients undergoing elective primary lumbar open discectomy for herniated nucleus pulposus (HNP) between October 2001 and September 2009. Exclusion criteria included age younger than 18 years and those patients undergoing emergent lumbar discectomy for traumatic herniation or cauda equina syndrome (CES). Current review of this database identified 92 consecutive patients undergoing primary lumbar discectomy with a minimum of 6-months follow-up and complete functional outcomes data, and this group comprised the subjects for the current study. All patients were operated by our senior author (MLN). Institutional review board approved the review of the prospective database for this study.

In addition, medical notes, anaesthetic charts, operative notes, and clinic letters were reviewed. Patient demographics included gender, age, height (cm), weight (kg), body mass index (BMI), smoking habitus, associated comorbidities, and American Society of Anesthesiologists (ASA) scores. Comorbidities that were considered included: hypertension, diabetes mellitus, heart disease, and pulmonary disease. Operative variables included type of procedure, operative time, estimated blood loss (EBL), length of time to ambulate, and length of stay (LOS). Complication variables that were assessed included dural tears, wound infection, recurrence of disc, and re-operations. Any technical difficulties in relation to intubation and positioning were also collated. Our spine database collects visual Analogue Scores (VAS) for leg and back pain and Oswestry Disability Index (ODI) outcome measures in a standard written format during scheduled clinic visits preoperatively and postoperatively at 2 months and 6 months.

Body mass index (BMI) was calculated for each individual patients as the weight in kilograms divided by height in meters squared. Patients were then grouped according to National Institutes of Heath criteria[17]. These criteria define a BMI of less than 25 kg/m2 as normal weight, 25.0 to 29.9 kg/m2 as being overweight, and greater than 30.0 kg/m2 as obese. To assess the effect of different body mass indices on the outcome of lumbar discectomy, we stratified patients into normal (< 25 kg/m2), overweight (25-29.9 kg/m2) or obese (≥ 30 kg/m2) groups. Demographics, operative variables, complication rates, and patient outcomes were compared between these 3 groups.

Statistical Analysis

Normality of data was evaluated with Shapiro-Wilk test. Normally distributed continuous data relating to the three groups (normal, overweight and obese) was compared using analysis of variance (ANOVA). Tukey’s post hoc test was performed to determine which differences were significant. Non-normal data was analysed with Kruksall Wallis test. Categorical data was compared using Chi-squared test. P-values of less than 0.025 were deemed to be clinically significant. Statistical tests were performed with PASW 18 statistical software package (PASW © Chicago IBM).

RESULTS

There were 92 patients with a mean age was 44.3 years (range, 20-72 yrs). Of these, 47 (51%) were women For the whole group the mean BMI was 26.4 kg/m2, the mean height was 171.2 cm, and the mean weight was 77.8 kg/m2.

When categorised by BMI, 39% of patients were normal-weight or underweight (BMI, < 25), 36% were overweight (BMI, 25-29.9), and 25% were obese (BMI, > 30). Co-morbidities were noted in 48% of obese patients, 24% of overweight and 17% of normal-weight patients. All patients with diabetes were overweight or obese. Table 1 shows the clinical characteristics of the study population. Groups were similar with respect to age, gender, diagnosis, and surgical level.

Table 1 Clinical Characteristics of the Study Population
DemographicAllBMI <24.9BMI 25-29.9BMI >30p Value
Number of Patients9236 (39%)33 (36%)23 (25%) 
Mean Age (years)44.342.545.545.4P=0.52
Gender    P=0.39
Women47 (51%)22 (61%)15 (45%)10 (43%) 
Men45 (49%)14 (39%)15 (55%)13 (57%) 
BMI26.421.82732.9 
ASA1.51.31.481.82 
14825185 
242111417 
32011 
Smoking Status     
Yes44 (48%)24 (67%)8 (24%)12 (52%) 
No48 (52%)12 (33%)25 (76%)11 (48%) 
Diagnosis    P=0.127
Uni - HNP74 (80%)32 (89%)23 (70%)19 (83%) 
Central HNP18 (20%)4 (11%)10 (30%)4 (17%) 
Surgical Level     
Single Level83 (90%)35 (97%)28 (85%)20 (87%) 
L4-53013107 
L5-S153221813 
Multilevel9 (10%)1(3%)5 (15%)3 (13%) 
L2-31 1  
L3-51  1 
L4-S17142 

Smoking habitus was noted in 67% of normal weight patients and 52% of obese patients as compared to 24% in overweight patients. All patients with diabetes were overweight or obese reflecting the higher ASA.

Table 2 compares the perioperative parameters of all three BMI classifications. A positive impact of increased BMI on the operating time was observed. There was a statistically significant difference between the operating time for the obese and those of normal weight (p < 0.025). While the operative time for the overweight cohort was greater for than that for those of normal weight and less than the obese cohort, this difference did not reach statistical significance. A similar pattern was observed with regard to estimated blood loss. Obese patients suffered a greater degree of blood loss compared to the overweight who in turned endured greater loss than the normal-weight cohort. However, a statistical significant difference only existed in the estimated blood loss between the obese and normal weight cohort (p < 0.01). The length of time to ambulation and length of hospital stay was not influenced by the BMI (p = 0.32 and p = 0.69 respectively). There were 3 cases of prolonged intubation in the obese group. No positioning-related issues were noted in the study groups.

Table 2 Comparison of peri-operative parameters
Examined ParameterAll (n=92)BMI <25 (n=36)BMI 25-29.9 (n=33)BMI >30 (n=23)
Operating Time (min)92.7(51-190)85.7(52-135)94.3(57-190)101.3(51-158)(p<0.025)
Estimated Blood Loss (mL)293(100-1000)248(150-500)300(100-1000)353(200-500)(p<0.01)
Length of time to ambulate (hrs)1.2(1-5)1.1(1-3)1.2(1-5)1.23(1-2)(p<0.32)
Lenghth of hospitilization (d)2.8(2-10)2.7(2-5)3(2-10)2.7(2-5)(p<0.69)

All three patients groups demonstrated significant improvements in leg pain, back pain, and ODI scores (p < 0.001) at 2-months and 6-months following surgery compared to baseline Table 3. There was no significant difference in the mean improvements between the three groups at six months with respect to leg pain (p = 0.69), back pain (p = 0.14), and ODI (p = 0.3).

Table 3 Baseline and post-operative outcome measures
OutcomeNormalOverweightObesep Value
Number of patients36(39%)33(36%)23(25%) 
VAS (Leg Pain)    
Baseline7074.675.4 
2 month26.42431.7<0.001
6 month24.122.527.1<0.001
VAS (Back Pain)    
Baseline52.244.349.9 
2 month18.820.131.5<0.001
6 month17.72131.7<0.001
ODI    
Baseline52.650.154.1 
2 month23.522.630.4<0.001
6 month20.817.929.2<0.001

Table 4 discusses the Surgical complications, which occurred in 14 patients with an overall complication rate of 15%. Intraoperative complications included six dural tears (6.5%), the symptoms from which resolved without the need for additional operative interventions. However, no case of inadvertent durotomy occurred in the obese group. There were eight cases of superficial wound infection with two cases requiring washout in addition to antibiotic therapy. Three of them were stitch abscess and we coded them under infection category as these were treated by General Practitioner as “presumptive” wound infection without a positive culture. One case of paralytic ileus occurred in an overweight patient for 2 days post-operatively. One obese patient had lung collapse post-operatively requiring prolonged high dependency support. No cases of post operative symptomatic deep vein thrombosis were seen. Eight late recurrent disc herniations occurred (8.6%) necessitating additional operative interventions. The incidence of infection, dural tear or reoperation was not influenced by BMI (p = 0.76, p = 0.24 and p =0.92 respectively). The same was observed with regard to the overall complication rate (p = 0.14).

Table 4 Surgical Complications
Adverse EventALLBMI <25BMI 25-29.9BMI >30p Value
Number of patients9236(39%)33(36%)23(25%) 
SSI8422p=0.76
Dural Tear6420p=0.24
Reoperation10442p=0.92
Indication     
Infection2110 
Recurrent Disc8332 

DISCUSSION

The primary finding of this report is that degree of body habitus measured by BMI does not appear to significantly affect self-reported outcome after open primary lumbar discectomy. Although there was a trend for obese patients to have a slightly lower general health and higher back-specific outcome scores before surgery and after surgery, the degree of improvement with surgery was similar to non-obese controls.

Recent studies in other areas of orthopaedic surgery have examined whether the presence of obesity adversely affects patient outcomes after surgery. Foran et al[18] reported inferior knee society scores at 8-year follow-up in obese patients undergoing total knee arthroplasty, when compared with a matched group of non-obese patients. Amin et al[19] reported that morbidly obese patients demonstrated inferior Knee Society scores, more complications, and worse implant survival. Namba et al[20] found a 6-fold higher infection rate for obese patients undergoing total knee arthroplasty, and a 4-fold higher infection rate for total hip arthroplasty. However, several other studies have shown equivalent outcomes for obese patients undergoing hip and knee arthroplasty[21-25].

In the area of spinal surgery, there has been a paucity of studies examining the influence of obesity on clinical outcomes. Glassman et al[26] categorised 497 open lumbar fusion patients as normal weight, overweight, and obese using BMI. Their analysis did not demonstrate a difference between the groups in the pre-and postoperative change in SF-36 and ODI. Andreshak et al[13] reported, in a mixed group of surgeries (discectomies, laminectomies, and fusion), equivalent clinical results in obese and non-obese patients. They concluded that proper surgical indications are the predominant factor affecting surgical results and the patient weight should not influence surgical decision-making. Gepstein et al[14] recently reported their results in elderly obese patients undergoing decompressive procedures for lumbar stenosis, and found similar degrees of improvement and subjective satisfaction rates in their obese and non-obese patients.

Djurasovic et al[27] similarly reported that obese patients undergoing lumbar fusion achieve similar benefits to non-obese patients. The addition of patient-directed quality of life measure SF-36 in their study confirms the equivalence of outcomes from a patient perspective as well.

Our findings are consistent with the limited previous data on the relationship between body habitus and spine surgery.

Several studies have demonstrated increased complication rates in overweight or obese patients in the setting of elective spinal fusion[12,28,29]. The present study in contrast found no impact of increasing body habitus on the peri-operative complications in a cohort of patients undergoing primary lumbar discectomy.

In the published literature, rates of surgical site infection (SSI) after spinal surgery reported from individual institutions have ranged from 0% to 15%, depending on the indication for the operation, the site, the approach, and the use of instrumentation[30-35]. In this present series it was 8.6%. The incidence of SSI in our cohort without instrumentation is rather high since we used generous criteria to include the presumptive wound infection cases treated in the community by general practitioner. Nevertheless we did not find any difference in terms of wound complications among various body habitus groups.

The incidence for unindented postdiscectomy dural tears also varies from as low as 1% to 7.1%[36-38] and as high as 16.7% for spinal surgery in the obese[16]. In our study it was 6.5%. We noted no case of inadvertent dural tear in obese patients. We registered no significant difference in the occurrence of dural tears in our 3 BMI groups.

We observed symptomatic re-herniation needing revision discectomy in 8.6% of our patients and this correlates with published data[39-41]. We also found no significant difference in the occurrence of disc recurrence in our 3 BMI groups.

Although this study found no significant difference of peri-operative complications, recurrence, reoperation rate or functional outcomes of surgery between non-obese, overweight and the obese group, we do not suggest that obesity should be ignored. This current study showed a positive impact of the degree of obesity on blood loss and operative time. It should be recognised that the obese patient is more difficult to position for surgery and surgery is relatively more difficult, although this by itself should not be a contraindication for this procedure in obese patients. Our analysis also showed that obese patients had similar faster rehabilitation potential and length of hospital stay as non-obese patients. There have not been many studies comparing outcomes of minimally invasive discectomies, however Mae et al reports in selected obese patients endoscopic lumbar discectomy can be a safe effective as it can reduce perioperative morbidity and allow early rehabilitation and return to work [42].

In summary, this study found equivalent degrees of improvement with respect to back and leg pain, and low back specific quality of life measures in obese patients undergoing lumbar discectomy. Our findings also suggest that increasing BMI has no impact on hospital stay, peri-operative complications, disc reherniation, and functional outcome after primary lumbar discectomy. Obese population should not be denied surgery based on their BMI values alone and patient selection continues to be the most important factor in terms of operative success.

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Peer reviewer: Chi Heon Kim

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