Background Epidural steroid injections are a common method used for the treatment of patients with sciatica. They are usually performed without imaging guidance using anatomical landmarks. However, injections are sometimes challenging resulting in prolonged procedure times, multiple needle passes and significant pain. Ultrasonography (US) is mainly used by rheumatologist for the guidance of peripheral joint injections. However, some studies have shown that US examination of the spine was useful before epidural anesthesia to predict which patients were at risk for a difficult procedure (1).
Objectives The aim of our study was to evaluate the feasibility of a pre-procedure ultrasound examination of the spine before epidural steroid injections.
Methods US examination of the lumbar spine was performed in 21 patients referred to our unit for the treatment of sciatica due to lumbar disc herniation. The scanning was performed with an Esaote My lab 70 unit using a curved-array, low-frequency (1–8 MHz) probe on a patient seated. L5-S1 intervertebral space was first located on a sagittal view, and the probe was then moved cranially. At each intervertebral level, we recorded our ability to depict the epidural space. We rated the visibility as ‘absent’, ‘poor’, ‘moderate’, ‘good’ with assigned numerical values of 0, 1, 2 and 3, respectively. We measured distance between spinous processes and depth of the epidural space in L3-L4, L4-L5 and L5-S1. Each measurement was performed 3 times and the mean was used for statistical analysis. Data are given as the median (+/- interquartile range). Differences between measurements at each lumbar levels was assessed with a Friedman’s Test and correlations between age, gender and Body mass index (BMI) and epidural visibility with a Pearson’s test.
Results 21 patients (11 men and 10 women), mean age 46 years (38-60.5) were included in our study. Median weight was 73 kg (59-85) and median BMI 24.8 (20.85-27.05). Median depth of the epidural space was 44.5 mm (41.60-48.45) in L3-L4, 43.80 mm (41.35-45.85) in L4-L5 and 40.8 mm (39.2-46.9) in L5-S1. Median distance between spinous processes was 17.9 mm (12.95-20.75), 15.9 mm (13.15-17.8) and 16.4 mm (15.30-17.7) in L3-L4, L4-L5 and L5-S1, respectively. Visibility of the epidural space was significantly lower in L5-S1 (p<0.01). We found a negative correlation between age and the distance between spinous processes and visibility of the epidural space at all levels (p<0.01). No significant correlation was found between the visibility of the epidural space and the BMI.
Conclusions We accurately identified each intervertebral level, estimated depth to the epidural space, and located the most appropriate interspinous space for needle insertion. As expected, the distance between spinous processes and epidural accessibility was reduced in older patients. US might help us to predict which patients are at risk for a difficult epidural injection and help the physician to identify the optimal site of injection. Overall, US of the lumbar spine represents a new imaging modality available for the rheumatology to treat patients with lumbar conditions.
Weed JT, Taenzer AH, Finkel KJ, Sites BD. Evaluation of pre-procedure ultrasound examination as a screening tool for difficult spinal anaesthesia. Anaesthesia. 2011 Oct;66(10):925-30.
Disclosure of Interest None Declared