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Prerequisite to a smart spinal needle: Development of a pilot testing model to study spinal needle stiffness and buckling forces
Abstract Number: SAT-29
Abstract Type: Original Research
Introduction: Advancements in spinal needle size and tip design have given clinicians more choices when performing neuraxial procedures based on the patient and clinical scenario. Reducing the needle gauge has reduced the incidence of complications, such as postdural puncture headache, but may cause higher rates of placement failure or needle breakage in older or morbidly obese patients. The primary goal of the study is to design an experimental testing model to evaluate needle stiffness by comparing the forces required to buckle a spinal needle and the associated displacement of the needle from a straight trajectory.
Methods: Four gauges (22G, 24G, 25G, 27G) of ten 127mm IMD/Gertie Marx needles were inserted with increasing vertical force into a 50 mm uniform ballistic gel sample using a MTS servohydraulic test system with a custom designed needle grip fixture made on a 3D-printer. The 11% by mass 250 bloom Knox ballistic gel is composed of collagen and is comparable to human muscle tissue. The critical buckling load (N) was defined as the maximum compressive force sustained by the spinal needle during axial loading before buckling occurs. In addition, buckling displacement (mm), insertion energy (J), insertion stiffness (N/mm), and buckling energy (J) were determined with sensors and camera measurements with p<0.05 considered significant.
Results: The mean critical buckling load (elastic force, N) and the needle stiffness (N/mm) of the 127mm IMD spinal needle differed significantly at each of the four tested gauges (p<0.0001, see Figure). The critical buckling displacement and buckling energy differed significantly in all needles except between the 25G and 27G needles. Needle insertion energy and stiffness were significantly different between all needle gauges (data not shown).
Conclusion: This pilot testing model provides accurate and reproducible measurements of spinal needle stiffness and the forces required to initiate buckling in a human tissue equivalent design. Future studies comparing spinal needles of different lengths, gauges, and manufacturers can be studied at various tissue depths to provide useful clinical data to assist clinicians in appropriate needle choice.
IMD provided the spinal needles. Study supported by WFSM Anesthesia research grant.