Risk Factors for Poor Outcomes Following Minimally Invasive Discectomy: A Post Hoc Subgroup Analysis of 2-Year Follow-up Prospective Data

OBJECTIVE: A post hoc subgroup analysis of prospectively collected data from a randomized controlled trial was conducted to identify risk factors related to poor outcomes in patients who underwent minimally invasive discectomy. METHODS: Patients were divided into satisfied and dissatisfied subgroups based on Oswestry Disability Index (ODI), visual analogue scale (VAS) back pain score (VAS-back) and leg pain score (VAS-leg) at short-term and midterm follow-up according to the patient acceptable symptom state threshold. Demographic characteristics, radiographic parameters, and clinical outcomes between the satisfied and dissatisfied subgroups were compared using univariate and multivariate analysis. RESULTS: A total of 222 patients (92.1%) completed 2-year follow-up, and the postoperative ODI, VAS-back, and VAS-leg were significantly improved after surgery as compared to preoperatively. Multivariate analysis indicated older age (p=0.026), lateral recess stenosis (p=0.046), and lower baseline ODI (p=0.027) were related to poor short-term functional improvement. Higher baseline VAS-back (p=0.048) was associated with poor short-term relief of back pain, while absence of decreased sensation (p=0.019) and far-lateral disc herniation (p=0.004) were associated with poorer short-term relief of leg pain. Lumbar facet joint osteoarthritis was identified as a risk factor for poor functional improvement (p=0.003) and relief of back pain (p=0.031). Disc protrusion (p=0.036) predicted poorer relief of back pain at midterm follow-up. CONCLUSION: In this study, several factors were identified to be predictive of poor surgical outcomes following minimally invasive discectomy. (ClinicalTrials.gov number: NCT01997086).