RESUMO
BACKGROUND: Intra-articular knee injections are routinely performed in clinical practice without documenting intra-articular placement. HYPOTHESIS: A small amount of air to an intra-articular knee injection produces an audible "squishing" sound with range of motion. STUDY DESIGN: Prospective nonrandomized clinical trial. METHODS: The study group (20 knees from 20 patients) received an intra-articular injection with a mixture of local anesthetic, corticosteroid, contrast dye, and 1 to 2 cc of air. The control group (10 knees from 5 patients) received extra-articular injections of a mixture of local anesthetic, contrast dye, and 2 cc of air. All knees were examined immediately after injection for a squishing sound with range of motion. Postinjection arthrographic radiographs were taken to verify the actual placement. RESULT: All study group knees and no control group knees had intra-articular contrast by radiograph. Clearly audible squishing sounds were heard in 17 of 20 study knees (sensitivity of 85%). Squishing sounds were audible in none of the control knees (specificity of 100%). CONCLUSION: Adding 1 to 2 cc of air to knee injections provides a no-cost, reliable, sensitive, and specific method of confirming accurate placement. CLINICAL RELEVANCE: This simple method is easily reproduced, can confirm accurate placement, and can eliminate extra-articular injection as the reason for clinical response failure.
