Background/Purpose: Joint pain is a common issue amongst patients. In the appropriate clinical setting, joint injections or aspirations may benefit the patient. Pain, however, is a known side effect of the procedure. Despite this known risk, the injector’s choice of needle size is based on expert opinion and the historical practices of a training institute. At this time, there are no formal studies justifying the gauge of needle used in intra-articular procedures and how it may alter pain perception. The purpose of this study was to identify if pain perception of a patient during intra-articular procedure was influenced by the gauge of the needle.

Methods: A prospective, double-blinded study on patients receiving bilateral large-joint (namely knee and shoulder) injections or aspirations was conducted at Tibor Rubin VA Medical Center in Long Beach, California. The joints were randomized to undergo injections with either large (22 G or lower, n = 34) or small (25 G or higher, n = 32) needles. Patients were further stratified to receive ethylene chloride (EC) spray as local skin anesthesia at the site of injection prior to needle insertion. All injections were performed by palpation-guidance and in the same approach with 2 mL of 1% lidocaine as subcutaneous and intra-articular anesthesia. Pain perception was assessed by the Visual Analog Scale (VAS) immediately upon needle insertion. After the procedures, patients completed the Short-form McGill Pain Questionnaire 2 (SF-MPQ-2 scaled 0-10) to assess the quality and intensity of pain, and the Somatic Symptom Scale-8 (SSS-8) to measure the impact of somatic symptom burden in pain perception.

Results: Of the 66 joints assessed, 34 joints were injected with large needles and 32 joints were injected with small needles. There was no significant difference in pain perception between large and small needle sizes when EC spray was applied (VAS 1.43 vs 1.42, p = 0.5). In the absence of EC spray, pain was more pronounced when injections were performed with large needles than with small needles (VAS 2.9 vs 1.25, p = 0.0227). All patients had similar somatic symptom burden at a medium level (SSS-8, No EC 8.8 vs EC 10.1, n.s.). There was no correlation between SSS8 and VAS scores with patient preference for EC spray. More patients who did not receive EC spray reported piercing pain (24% vs 10%) and at a higher intensity (SF-MPQ-2, 0.4 vs 0.1, p = 0.05). Notably, freezing and tingling pain were only reported in patients who received EC spray (19.6% and 24%).

Conclusion: Ethylene chloride anesthesia masks pain and affords flexibility in choice of needle size during intra-articular procedures. Patients may report mild post-procedural discomfort from the spray. If planning to forgo the application of ethylene chloride, a smaller needle reduces pain perception.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/a-prospective-study-on-pain-associated-with-injection-of-needles-pain-study/