Characterization of Spinal Needle Buckling Behavior

Abstract

Abstract The use of large gauge (G) spinal anesthesia needles can increase complications due to buckling. The purpose of this study was to quantify the behavior of spinal needles in buckling using a repeatable laboratory model. A spinal anesthesia procedure and buckling complication was reproduced in vitro using a custom test fixture designed to match the boundary conditions of needle insertion as performed by an anesthesiologist and a uniaxial servohydraulic material testing machine (MTS, Eden Prairie, MN). Buckling tests were performed with 22 G Whitacre (Medline Industries, Inc., Northfield IL), SPROTTE® (Pajunk, Norcross, GA), and Gertie Marx (International Medical Development, Huntsville, UT) needles (n = 30) in a ballistics gelatin tissue surrogate (Clear Ballistics, Fort Smith, AR). In analyzing axial force results, critical buckling load results were 27.65 ± 0.92 N, signifying that needle fragility is not why buckling is challenging to detect. Force feedback during needle insertion increased linearly due to frictional forces from the tissue surrogate on the needle. The differential between the resultant insertion force and the critical buckling force is more important to the detection of needle buckling than the critical buckling force alone. A very small difference in these two forces could feel like expected resistance increase as the needle is further inserted into the multiple tissue layers. Comparison of the differential between the resultant insertion force and the critical buckling force should be considered when choosing a needle to best detect and prevent a buckling complication.