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SM-BOSS study

Sleeve has fewer complications than bypass

Tailored approach allows the bariatric surgeon to take into account the patients’ preoperative risk profile and will optimise the long-term results of bariatric surgery

The early results from the Swiss Multicentre Bypass or Sleeve Study (SM-BOSS) have shown that laparoscopic sleeve gastrectomy was associated with shorter operation time and a trend toward fewer complications than with laparoscopic Roux-en-Y gastric bypass (LRYGB), however, the difference was not statistically significant. The outcomes were published in the journal Annals of Surgery.

Importantly, both procedures were almost equally efficient regarding weight loss, improvement of comorbidities, and quality of life one year after surgery. However, the study authors from Claraspital, Basel, Inselspital, Bern, Kantonsspital St Gallen, St Gallen, and University Hospital Zürich, Zurich, Switzerland, added that the long-term follow-up data are needed to confirm the results

The researchers write that they undertook the randomised clinical trial to assess the effectiveness and safety of the two procedures as ‘prospective data comparing both procedures are rare’. Indeed, they note that there have been three (two from the same institution) randomised clinical trials published comparing LSG and LRYGB with small patient numbers (16–30per group) and limited follow-up (12–35 months).


A total of 217patients were randomised at four bariatric centres in Switzerland. One hundred seven patients underwent LSG using a 35-F bougie with suturing of the stapler line, and 110 patients underwent LRYGB with a 150-cm antecolic alimentary and a 50-cm biliopancreatic limb. The mean body mass index of all patients was 44±11.1, the mean age was 43 ± 5.3 years, and 72% were female.

The groups were similar in terms of body mass index, age, sex, comorbidities, and eating behaviour. In addition, there were no significant differences with regards to comorbidities (diabetes, hypertension, dyslipidema etc) between the two procedural groups.

The primary end point of the study was weight loss, which was defined by excessive BMI loss (EBMIL), over a period of five years. To detect a 10% difference, we calculated a study size of 200 patients to reach a 94% power. Secondary end points were the rate of perioperative morbidity and mortality, the remission rates of the associated comorbidities, and the change in quality of life (QOL) in the two patient groups.


All patients presented for follow-up at 12 months, 112 patients completed follow-up at two years and 70 patients the three-year follow-up at the time of analysis (median follow-up of two years).

The mean operative time was less for LSG than for LRYGB (87±52.3 minutes vs 108±42.3 minutes; p=0.003). Complications (<30 days) occurred more often in LRYGB than in LSG (17.2%vs 8.4%; p=0.067), although the difference in severe complications did not reach statistical significance.

The rate of severe complications requiring a reoperation was 4.5% (5/110) in the LRYGB group versus 0.9% (1/107) in the LSG group (P = 0.21). The reason for the reoperation in the LSG group was obstruction of the gastric sleeve. The reasons for the five revisions in the LRYGB group were as follows: one leakage at the gastrojejunostomy, one obstruction of the biliopancreatic limb, two intra-abdominal abscesses, and one pleural empyema. Except for gastroesophageal reflux disease (GERD), which showed a higher resolution rate after LRYGB, the comorbidities and quality of life were significantly improved after both procedures.

Excessive body mass index loss at one year was similar between the two groups (72.3%±22% for LSG and 76.6%±21% for LRYGB; p=0.2). There was no difference regarding weight loss or EBMIL between the 2 groups after 1 year (Figures 1A, B), and there was no further weight loss in patients who completed the follow-up at two and three years.

Figure 1: A, Change in BMI (means ± standard error). B, EBMIL (means).


The rate of comorbidities improved in both groups (Figure 2). Except for the remission of GERD, there was no difference between the LSG group and the LRYGB group regarding the remission of comorbidities or improvement rate. Patients undergoing LSG experienced a slightly higher rate of new-onset GERD (12.5% vs 4%; p=0.12), and among those who already presented with GERD before the operation, the rate of improvement was significantly lower than those who underwent LRYGB (50% vs 75%; p=0.008).

Patients from both groups experienced a significant improvement in quality of life, compared with baseline (p<0.0001) and even exceeded that of healthy individuals who reach a score of 121 points (p<0.01).

Figure 2: Reduction in comorbidity one year after surgery. No significant difference in cure or improvement of comorbidities between LSG and LRYGB except for GERD (*P = 0.008). GERD indicates gastro oesophageal reflux disease; OSAS, obstructive sleep apnea syndrome; T2DM, type 2 diabetes.

In the LRYGB group, there was one anastomotic ulcer at the gastroenterostomy and one stricture that needed endoscopic dilatation. Up to one year postoperatively, no patient had to be re-operated on for either insufficient weight loss or internal hernia in both groups.

Two patients of the LSG group experienced severe GERD symptoms, but until one year after the operation, none of them agreed to have undergone conversion to LRYGB.

“Strictures or torsions of the gastric sleeve are complications that are difficult to treat and often result in the resection of the gastric sleeve at the end of the treatment line,” the authors warn. “Therefore, it is utmost important that this procedure is performed with the best standardised technique by experienced bariatric surgeons.”

The incidence of micronutrient deficiency was equal in both groups (LSG: n=28 patients; LRYGB: n= 27 patients), with vitamin D deficiency being the most frequent deficiency, followed by vitamin B12 deficiency (LSG: n=7; LRYGB: n=15; p<0.12). 


They authors state that LSG is best suited for patients with pre-existing GERD are at a risk of deterioration after LSG and should rather undergo LRYGB, for patients who expected major adhesions, who need a staged concept or suffer from Crohn disease. The researchers believe that this tailored approach allows the bariatric surgeon to take into account the patients’ preoperative risk profile and will optimise the long-term results of bariatric surgery.

“We could show that LSG and LRYGB are equally efficient regarding weight loss, reduction in comorbidities, and increase in quality of life at one year,” the authors conclude. “Therefore, we believe that LSG is a valuable surgical alternative for selected patients with morbid obesity.”

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