The role of ultrasonography in accurately determining the spinal level in orthopedic patients

Orthopedic patients can be a challenging group for neuroaxial block procedures compared to other patient populations, due to factors such as chronic orthopedic disorders, chronic pain, or difficulties in positioning. Pre-procedural ultrasonography provides reliable and accurate information for successful neuroaxial placement, including midline identification and determining the optimal intervertebral level. The objective of this study was to assess whether the target intervertebral space identified using the Tuffier line differs from that determined via ultrasound evaluation. This prospective observational study included 83 patients who underwent orthopedic surgery with spinal and/or epidural anesthesia. Patients were positioned optimally in a sitting posture. An anesthesia assistant identified the intended puncture level (L3-L4 or L4-L5 interspace) using the Tuffier line. Spinal intervertebral spaces were then marked by a senior anesthesiologist proficient in spinal ultrasound, who was blinded to the palpation-based identification of the intervertebral space. The actual intervertebral level corresponding to the target identified by the Tuffier line was recorded. The study also aimed to investigate whether the difference between the target and actual intervertebral space was influenced by factors such as age, height, weight, body mass index (BMI), neck circumference, waist circumference, and the years of experience of the examiner. We found that the accuracy of the lumbar intervertebral space identified by palpation, compared to ultrasound, was 60.24%. Furthermore, we identified that factors related to the patient, including increased weight, BMI, and waist circumference, negatively impacted the accuracy of the Tuffier line in identifying the correct lumbar interspace. Specifically, increases in weight (p=0.025), BMI (p=0.001), and waist circumference (p=0.002) were associated with a decrease in accuracy. The most significant factor influencing the accuracy of the Tuffier line in identifying the correct intervertebral level was the years of experience of the examiner. Our findings demonstrated that accuracy improved in parallel with the examiner's experience, particularly after 3 years of practice. In conclusion, our study suggests that spinal procedures based on the Tuffier line may not reliably correspond to the intended intervertebral level. Therefore, we recommend the use of ultrasound guidance in patients undergoing spinal and/or epidural anesthesia. Keywords: Spinal anesthesia, ultrasonography, Tuffier's line, orthopedic anesthesia.