Prevalence of Anatomic Impediments to Interlaminar Lumbar Epidural Steroid Injection

Hameed F, Hunter DJ, Rainville J, Li L, Suri P. Prevalence of anatomic impediments to interlaminar lumbar epidural steroid injection. Arch Phys. Med Rehabil 2012;93:339-43. Objective: To determine the prevalence of anatomic impediments to interlaminar lumbar epidural steroid injection (LEST) in a community-based population. Design: Cross-sectional observational study. Setting: Community-based. Participants: Older adults (N=333) sampled irrespective of back pain status. Interventions: Not applicable. Main Outcome Measures: Computed tomography evaluation of 5 potential anatomic impediments to interlaminar LEST at the L2-S1 spinal levels, including (1) ligamentum flavum (LF) calcification, (2) interspinous ligament (ISL) calcification, (3) spinous process (SP) contact, (4) the absence of epidural fat in the posterior epidural space, and (5) the presence of fat density superficial to the LF in the midsagittal plane. Independent variables included age, sex, body mass index (BMI), and current smoking. Results: LF and ISL calcifications were prevalent in 3% to 7% and 2% to 3% of spinal levels, respectively, without significant differences by spinal level. SP contact was most common at the L4-5 level (22%). Absence of posterior epidural fat was very common at L5-S1 (65%), but infrequent at other levels. The presence of midline fat density superficial to LF was most common at L5-S1 (55%). The prevalence of LF calcification, ISL calcification, and SP contact increased with age, but the prevalence of absence of posterior epidural fat and the presence of a midline fat density superficial to LF did not. Sex and smoking status were not associated with the prevalence of anatomic impediments, but higher BMI was associated with a lower prevalence of absence of posterior epidural fat. Conclusions: Anatomic impediments to interlaminar LEST were common in this community-based population, particularly at the L5-S1 spinal level. Because of the high overall prevalence of anatomic impediments, and differences in prevalence by spinal level, knowledge of the distribution and frequency of these impediments may aid in aspects of decision-making for the interventional spine physician.