Development of the pencil point needle

37 years after Whitacre developed the pencil point needle, Sprotte published a paper on the improvement of Whitacre needles. The initial problem with the Whitacre needle is still obvious. Sprotte improves the needle by increasing the size of the distal orifice to solve the problems of slow cerebrospinal fluid flow, difficulty in inhaling, and resistance to injection of local anesthetic solution. The wider hole also allows the local anesthetic solution to better mix with the cerebrospinal fluid, so that the local anesthetic solution is more evenly distributed in the subarachnoid space. The tip of the Sprotte needle is elongated to try to separate the dural fibers more gradually, thereby reducing CSF leakage and reducing the incidence of PDPH (Figure 21). Although Sprotte has a large case series, his needle design has been criticized. The size of the side hole sometimes causes the orifice to cross the dura mater, resulting in partial loss of the local anesthetic solution and incomplete blockade. The width of the hole also makes the distal portion of the tip relatively vulnerable to damage, including rupture. Aglan & Stansby conducted a flow study on the Sprotte needle in 1992 and concluded that the needle hole area can be reduced to the cross-sectional area of the cannula without affecting the flow rate. Sprotte strongly refutes these claims, but the manufacturer made the recommended modifications, and by the early 1990s, the Sprotte needle had been modified to the needle commonly used today.

Figure 21

Pencil point needle.

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