Percutaneous placement of pedicle screws in overweight and obese patients

Abstract

In obese patients, placing pedicle screws percutaneously is a particular challenge. As the bulky and thick configuration of obese patients may produce fuzzier fluoroscopic view and longer passage of surgical instruments, the chances of misplacement might increase. This study was designed to evaluate the effect of patient's body habitus on the incidence of percutaneous pedicle screw misplacements. A retrospective study with prospectively collecting data. Three hundred seventy percutaneous pedicle screws for minimally invasive lumbar spinal fusion surgery were noted in 89 consecutive patients. The position and direction of screws to pedicle were evaluated using the findings in computed tomography (CT) scan with the following grading method: Grade A, completely in the range without pedicle cortex violation; Grade B, pedicle wall violation <2 mm; Grade C, pedicle wall violation 2 to 4 mm; and Grade D, pedicle wall violation >4 mm. The direction of violation was grouped as medial, lateral, cranial, and caudal. Two independent observers retrospectively examined all of the postoperative CT images. All screws were assigned into one of the following three groups along with patient's body mass index (BMI): 157 screws (38 patients) in normal weight (BMI<25) group; 124 (29) in overweight (25≤BMI<30) group; and 89 (22) in obese (BMI≥30) group. A pedicle screw was considered misplaced if the grade was defined as B, C, and D. Multivariate logistic regression analyses were performed to evaluate the association between screw misplacements and BMI. Sixty-two screws (16.8%) were misplaced with the majority of Grade B (72.6%, 45/62) and lateral direction (72.6%, 45/62). Twenty-eight screws (22.6%, 28/124) were misplaced in overweight group, 12 (13.5%, 12/89) in obese group, and 22 (14.0%, 22/157) in normal weight group. Two symptomatic pedicle violations were noted with Grade D: a caudal violation was found in overweight group, which happened in the third case of surgeon's series; a medial misplacement, which was occurred in the 29th case, was noticed in obese group. There was no statistically significant association of pedicle violations along with patient's BMI (odds ratio [OR]=1.00, 95% confidence interval [CI]=0.94-1.07, p=.99). Moreover, no other factors, such as patient's age, gender, preoperative diagnosis, number of the fused segments, and year of the surgery, had a statistically significant relationship with pedicle violations. On the contrary, pedicle violations observed approximately five times more frequently at the level of L3 (47.1%, 8/17) and L4 (28.8%, 36/125) rather than L5 (10.1%, 16/158) and S1 (2.9%, 2/70) (OR=4.95, 95% CI=2.62-9.33, p<.0001). Although symptomatic pedicle violations were noted in the earlier period of surgeon's learning curve and in overweight and obese patients, no statistical evidence could be found between patient's body habitus and percutaneous pedicle screw misplacement. Our data also suggest that greater caution should be exercised to avoid pedicle violations especially at L3 and L4.