Pain Perception During Intra-Articular Knee Joint Injection: What is the Effect of Needle Gauge and the Use of Ethyl Chloride?

Hypotheses to be tested:

Hypothesis 1): Patients who receive an ultrasound-guided intra-articular knee steroid injection with a 25G needle will report less pain from the procedure at the time of the procedure and less procedure-related pain 24-48 hours after the procedure

Hypothesis 2) Patients who receive an ultrasound-guided intra-articular knee steroid injection with use of ethyl chloride with a given needle gauge will report less pain from the procedure at the time of the procedure and 24-48 hours after the procedure

Hypothesis 3) Higher thigh circumference and fear of needles will be associated with higher levels of pain from the procedure at the time of the procedure and 24-48 hours after the procedure

Hypothesis 4) Higher levels of patient pain during the injection procedure will be associated with lower improvements in knee osteoarthritis pain and knee functional scores at 6 weeks.

There is evidence to suggest that by effectively altering certain parameters and techniques such as needle gauge diameter, speed of administration, and angle of needle during subcutaneous injection of local anesthetic, one can effectively improve the subjective experience of the patient. Evidence also suggests that choice of needle gauge size - which is at the discretion of the practitioner - may be inversely proportional to patient's perception of pain during an injection procedure. Topical anesthesia, such as via the use of ethyl chloride spray (which is also at the discretion of the practitioner), may also modify procedural pain. Furthermore, some studies suggest a correlation between patients' pain during a procedure and their clinical outcomes from the injection.

However, the current research is primarily composed of studies investigating subcutaneous injections (e.g. insulin or vaccination injections) using relatively small needle gauges, or of anesthetic injections in the spine. As such, there is very limited research on factors which may impact peripheral joint injections. Furthermore, there is a paucity of information regarding the effect of patient factors such as age, sex, limb size, anxiety, and fear of needles on the perception of pain during peripheral intra-articular injections.

Additional knowledge regarding the use of different needle gauge and/or the use of local anesthetic may help guide physician treatment patterns with the goal of optimizing patient satisfaction. Additionally, by obtaining subjective data at multiple time points, including 6 weeks post-injection, investigators hope to determine if differences in patient experience with the procedure is associated with patient outcomes.

Inclusion criteria

• age ≥ 40 years
• fulfillment of the American College of Rheumatology criteria for knee OA
• confirmation of knee-related pain and/or functional loss by clinical examination.
• Patients with either

• bilateral knee OA/injections, or
• unilateral knee OA/injections.
• Agreed to an intra-articular knee joint injection with steroids
• Naive to use of ethyl chloride

Exclusion criteria

• Arthroscopy of the index knee(s) within the prior 6 months
• Steroid injection of the knee(s) within the prior 3 months
• Hyaluronic acid or platelet-rich plasma injection of the knee within the prior 6 months
• Patient reported prior injection of any type with ethyl chloride spray
• Knee effusion requiring aspiration at the time of the procedure
• Cognitively impaired individuals