Incidence of and risk factors for lumbar disc herniation with radiculopathy in adults: a systematic review

Background: Lumbar disc herniation (LDH) with radiculopathy is associated with greater pain, disability, healthcare use, and costs compared with nonspecific low back pain. Reliable information about its incidence and risk factors were lacking. Questions: (1) What is the incidence of lumbar disc herniation (LDH) with radiculopathy in adults? (2) What are the risk factors for LDH with radiculopathy in adults? Methods: Systematic review. We searched five electronic databases from 1970 to September 2023. Eligible cohort and case–control studies were identified and independently assessed for risk of bias. A qualitative best evidence synthesis of low and moderate risk of bias studies was conducted. Results: We critically reviewed 87 studies and synthesised data from 59 (68%) studies; 12 were of low and 47 of moderate risk of bias. The lower and upper bound limits of the 95% CIs of annual incidence estimates ranged from 0.3 to 2.7 per 1000 persons for surgical case definitions, from 0.04 to 1.5 per 1,000 persons for hospital-based case definitions, and from 0.1 to 298.3 per 1,000 persons for clinical case definitions. Factors associated with the development of LDH with radiculopathy included middle-age (30–50 years), smoking, higher BMI, presence of cardiovascular risk factors (in women), and greater cumulative occupational lumbar load by forward bending postures and manual materials handling, with effect sizes ranging from ranging from 1.1 (1.0–1.3) to 3.7 (2.3–6.0). Conclusions: Incidence of LDH varies in different populations and according to case definition. Risk factors include individual, behavioural, and work-related variables. Our findings support the need to develop standardised case definitions that validly classify the clinical spectrum of LDH and for future low risk of bias studies examining causal relationships for LDH with radiculopathy in adults.