Comparison of Two Anatomic Landmarks With Ultrasonography in Spinal Anesthesia

Phase IV Study of Landmarks for Spinal Anesthesia

The most used anatomical landmark for application of spinal anesthesia is Tuffier's line. Other alternative landmark is tenth rib. However there is no trial that compare these landmarks based on using ultrasonography.

The investigators aim to compare two landmarks (Tuffier's line and tenth rib line) for accuracy by using ultrasonography. 40 patients will be included in each groups. all of them will be assessed by ultrasonography during application of spinal anesthesia. And the investigators will examine the percentage of successful estimation of correct vertebral space.

Inclusion Criteria:

• knee arthroscopic surgery

Exclusion Criteria:

• BMI>30
• anatomical anomaly of vertebrae