Background: Traditionally, knee arthrocentesis has been guided by anatomic landmarks, but ultrasound (US) has also been used for guidance. Studies have shown similar rates of aspiration success with both approaches, though provider confidence and patient comfort has been found to be more favorable under US guidance. There is need for further study comparing safety between the two approaches and amount of training required for competence with an US-guided approach. We hypothesize that US use will reduce inadvertent bone contacts, need for repeat attempts, and increase comfort with the procedure, after a brief training session.
Methods: This was a prospective observational crossover study. There were 61 participants (medical students and emergency medicine providers), who were recruited to volunteer by email. Participants completed a 20-minute training session covering both landmark and US-guided knee arthrocentesis, after which they performed each procedure on embalmed cadavers with simulated joint effusions. The primary outcomes were occurrence of bone contact, first attempt success, user confidence, and user preference.
Results: All 61 participants successfully completed knee arthrocentesis under US guidance, and 60/61 participants successfully completed the procedure using landmark guidance. There were fewer bone contact events in the US group, with 5% (3/61) of participants contacting bone, versus 30% (18/61) when landmark guidance was used (p<.001). There was a trend towards increased first attempt success in the US group, with repeat attempts required in 11% (7/61) of participants, compared to 21% (13/61) when landmark guidance was used (p=0.110). Using a visual analog scale from 1 to 100, there was an increase in the median level of confidence for both landmark and US upon completion of both techniques. The median value was 14 points higher in the US group (83 ), compared to the landmark group (69 ). US was preferred by 89% (54/61) of participants upon completion of both techniques.
Conclusion: Both US and landmark techniques had similar rates of successful knee arthrocentesis. US use resulted in less frequent bone contact. Users were more confident with and preferred US guidance over the landmark technique. A 20-minute educational session appears adequate to teach both techniques. Use of US may be associated with greater first attempt success.