The impact of obesity on complications in spine surgery is not quite clear. Some authors report no difference in complication rates between obese patients and those of normal weight [13
]. Nevertheless, the fact remains that obesity is a problem of significant magnitude in surgery [3
Patel investigated a cohort consisting of 84 patients (60 treated by the open technique and 24 by minimally invasive procedures). This group was confined to patients with symptomatic degenerative conditions in need of an anterior, posterior, or combined antero-posterior fusion [3
]. Patel addressed the probability of significant complications related to BMI (p
= 0.04): the chances of significant complications were 14% in patients with a BMI of 25, 20% in those with a BMI of 30, and 36% in those with a BMI of 40. Telfeian [5
] noted a high complication rate (50%), but good overall outcomes in a small series of morbidly obese patients.
Wound infection rates are believed to be higher in obese patients, but the reported data range from 0 to 33% [5
]. Olsen [18
] showed that obesity as well as the posterior approach was associated with a high risk of spinal surgical site infection in patients undergoing laminectomy and/or spinal fusion. Djurasovic [19
] studied 109 obese patients and 161 non-obese patients undergoing single or multilevel lumbar spinal fusion for a variety of degenerative lumbar spine conditions, such as spondylolisthesis, spinal stenosis, lumbar instability, and degenerative disc disease. He registered higher complication rates in the obese group (p
= 0.045), principally due to wound-related complications (5.5%). Friedman analyzed 41 patients with surgical site infection complicating laminectomy and 82 matched controls [20
]. He found a BMI greater than 35 [OR, 7.1 (95% CI 1.8–28.3); p
= 0.005], and laminectomy at a level other than the cervical spine [OR, 6.7 (95% CI, 1.4–33.3); p
= 0.02] to be independent risk factors for surgical site infection after laminectomy. Gepstein [16
] evaluated 298 patients older than 65 years undergoing decompressive laminectomy, discectomy or a combination of these procedures. He noted that patients with a BMI > 25 had significantly more complications (89 patients with a BMI > 25 versus 33 patients with a BMI ≤ 24.9, p
0.02). Wound infections occurred in 9% of overweight and obese patients.
], using a similar tubular retractor system as in our study, assessed patient outcomes and complication rates after minimally invasive lumbar microdiscectomy in 32 obese patients with a body mass index of 30 or more, and encountered no infectious complications in the study population.
Park evaluated 56 patients with a mean BMI of 31.5 using a minimally invasive tubular retractor system. In cases of fusion, TLIF was used in conjunction with posterolateral fusion via paramedian incisions [12
]. Thirty-one of the 56 patients underwent either discectomy or decompressive laminotomy; the remaining 25 patients underwent single-level or two-level spinal fusion. Again, no infection was encountered.
We observed no severe wound healing disorders in our study sample.
MIS fusion procedures are associated with less blood loss, faster recovery, and less perioperative morbidity while yielding similar results as those after open procedures [6
]. The reason for this is presumably the smaller corridor to the spine, which causes less tissue trauma. Enzymes indicative of muscle damage as well as inflammatory cytokines are lower in patients who have undergone mini-open fusion rather than open procedures [22
]. Nevertheless, the benefits of spinal MIS fusion procedures in obese patients have been poorly investigated.
The most frequent intraoperative complication in our sample was leakage of cerebrospinal fluid (13.9%). Telfeian [5
] reported a durotomy rate of 16.7% for spinal surgery in the morbidly obese. All leakages were closed during the same surgical session as far as possible, and the patients were advised to remain supine for 2.5–5 days. Until completion of the present study no patient experienced an adverse consequence due to leakage. Cole performed minimally invasive lumbar discectomies in 32 obese patients and reported incidental durotomies as the most common complication (9.4%). He attributed this to the greater working distance in overweight patients [21
]. In contrast, we registered no significant difference in the occurrence of dural tears in our 3 BMI groups.
We made a distinction between minor and major postoperative complications, as did Carreon [23
]. Carreon classified the following as major complications: wound infection (10%), pneumonia (5%), renal failure (5%), myocardial infarction (3%), respiratory distress (2%), neurologic deficit (2%), congestive heart failure (2%) and cerebrovascular accident (1%). Minor complications were urinary tract infection, anemia requiring transfusion, confusion, ileus, arrhythmia, transient hypoxia, wound seroma, and leg dysesthesia.
We observed one pulmonary embolism (1.4%), one transient ischemic attack (1.4%) one cardiac ischemia (1.4%), one pneumonia (1.4%), and one patient with a neurogenic deficit (1.4%). These amounted to five major complications (6.9%). Again, no statistical difference was registered between the three BMI groups.
Fever was observed in 15 patients. Of these, 12 had subfebrile temperatures. Subfebrile temperatures ranged between 37.5 and 38.0°C, whereas a body temperature above 38.1°C was defined as fever. Temperature is ultimately regulated in the hypothalamus. A trigger of the fever, called a pyrogen or cytokine, causes the release of prostaglandin E2 (PGE2). PGE2 then, in turn, acts on the hypothalamus, which generates a systemic response to the rest of the body, causing thermic effects to match the new temperature level. Fever is a common phenomenon in the early postoperative period fever, being the consequence of an inflammatory event. As endogenic cytokines (interleukin-1, interleukin-6) are released even after minor trauma, we viewed fewer as no cause of concern among our patients. We found no connection between fever and obesity.
In the published literature, some authors have reported longer operating times for MIS procedures [6
], others an equivalent [8
], and yet others shorter operating times [25
] than those required for open surgery. In our group, mean operating times were 157 min in patients of normal weight and 205 min in the obese. One explanation could be the fact that longer retractor blades are needed to cover the longer distance to the spine and the longer tubes are difficult to handle. Moreover, the more numerous levels require additional laminotomies, which, in turn, prolong the operating time. We registered longer operating times (p
= 0.049) and greater blood loss (p
= 0.039) with advancing age. This may have been due to the fact that elderly patients require laminotomies at more numerous levels in cases of spinal stenosis. However, we did not register greater blood loss in these patients.
Revision surgery was required because of one malpositioned rod and one epidural hematoma (each 1.4%). The frequency of postoperative epidural hematomas has not been extensively reported. In a review of 16 articles, Glotzbecker [26
] found clinically relevant epidural hematomas in no more than 1% of cases. We registered a similar rate in our study.
In conclusion, the frequency of adverse events after MIS spine surgery does not differ from that after open procedures. MIS techniques would seem to benefit obese patients because of the smaller access and less tissue trauma compared to open techniques. The gentler handling of soft tissue may have been the reason for the absence of infections in our sample.