Impact of Obesity Severity on Achieving a Minimum Clinically Important Difference Following Minimally Invasive Transforaminal Lumbar Interbody Fusion

This was a retrospective cohort study.

The objective of this study was to determine the impact of obesity on postoperative outcomes and minimum clinically important difference (MCID) achievement following minimally invasive transforaminal lumbar interbody fusion (MIS TLIF).

Obesity is a proven risk factor for poorer outcomes in MIS TLIF patients. However, few studies have investigated the impact of body mass index (BMI) on achievement of a MCID for Patient-Reported Outcome Measurement Information System Physical Function (PROMIS PF).

A prospective surgical database was retrospectively reviewed for primary, elective, single level MIS TLIF patients. Patients were categorized into BMI groups: nonobese (<30 kg/m2); obese I (≥30 and <35 kg/m2); severe (≥35 and <40 kg/m2); and morbid (≥40 kg/m2). Demographic, perioperative information, and complication rates were compared between groups. Visual Analog Scale (VAS) back and leg, Oswestry Disability Index (ODI), 12-Item Short Form-12 Physical Composite Score (SF-12 PCS), and PROMIS PF were collected preoperatively and up to 2-year postoperatively. Impact of BMI on outcome measures and MCID achievement at all timepoints was evaluated.

A total of 162 patients were included with 88 patients categorized as normal weight, 37 obese I, 25 severe, and 12 morbid. SF-12 PCS, and PROMIS PF significantly differed by BMI at all timepoints, but only at 6- and 12-week for VAS back, preoperatively and 12 weeks for VAS leg, and preoperatively to 1-year for ODI. MCID achievement only differed for PROMIS PF and VAS back at 2 years, but did not for overall MCID achievement.

BMI is a significant predictor of ODI, SF-12 PCS, and PROMIS PF preoperatively to 1-year postoperatively, but only through 12-week for VAS scores. MCID achievement varied for PROMIS PF and VAS back, suggesting that though BMI may affect postoperative outcome values, obesity may impact a patient's perception of meaningful improvements in pain and physical function.