Systematic review and meta-analysis of predictive factors for spontaneous regression in lumbar disc herniation

Relatively little evidence exists on predictive factors for the spontaneous regression of lumbar disc herniation (LDH), although it is a well-documented phenomenon. Therefore, current care is not optimized to identify those who would benefit from early surgery versus those who could avoid surgical risks and pursue nonsurgical therapy. In this study, the authors aimed to analyze and summarize all literature to date on predictive factors for spontaneous LDH regression as well as suggest future research strategies to aid in the decision-making for this cohort.A literature search was conducted of the Cochrane, Embase, and MEDLINE databases for articles that described LDH in terms of the North American Spine Society task force definitions: bulging, protruded, extruded, and sequestered disc morphologies. All articles described a nonsurgical primary symptomatic LDH cohort with at least two MR images to assess regression. Those with concomitant spinal disease were excluded. The primary outcome was to assess the probability of disc regression for each disc morphology, with a secondary analysis for any other predictive factors identified. The authors synthesized their results with the only previous review (examining articles published before March 2014) to comprehensively describe the literature. A qualitative analysis of the wider literature was also performed for those studies with differing definitions of LDH but meeting all remaining inclusion criteria.Sixteen articles describing 360 cases of LDH were identified. Participants tended to be younger and male and presented with radiculopathy and L4-5 or L5-S1 LDH. The mean time to follow-up imaging was 11.5 months. The probabilities of spontaneous regression with bulging, protruded, extruded, and sequestered discs were 13.3%, 52.5%, 70.4%, and 93.0%, respectively (χ2 = 126.01, p < 0.001). Extruded and sequestered discs were also significantly more likely to completely regress than smaller morphologies. Other predictors of regression were larger baseline herniation volume (1260.16 vs 1006.71 mm3, p < 0.002), transligamentous herniation (χ2 = 13.321, p < 0.001), and higher Komori types (χ2 = 14.5132, p < 0.001). The authors also found similar trends in qualitative data as well as confirmed that symptom improvement was associated with disc regression.This study shows further evidence of the influence of disc morphology on predicting LDH regression as well as provides the first meta-analysis of data indicating additional predictive factors. Further investigation of predictive factors for early (< 6 months) LDH regression is suggested to optimize clinical use.