Background: The use of ultrasound guidance during knee arthrocentesis has proven to increase operator confidence and accuracy, particularly in novice healthcare providers. Realistic and practical means of teaching this procedure to medical trainees are needed. This study is intended to assess the feasibility and efficacy of using formalin-embalmed human cadavers in the instruction of ultrasound-guided knee arthrocentesis to medical trainees. Methods: Twenty participants received a 30-minute didactic orientation detailing the principles of ultrasound-guided knee arthrocentesis, followed by a training practicum performed on human cadavers. The practicum included a 25-minute training period, followed by a 15-minute assessment period. Participants were objectively assessed on their ability to independently aspirate synovial fluid from the suprapatellar bursa using ultrasound guidance. Digital pretraining and posttraining questionnaires were administered to evaluate each participant’s confidence in their ability to independently locate the site of optimal needle placement and successfully aspirate synovial fluid with the guidance of ultrasound imaging. Results: An analysis via the Wilcoxon rank sum testing revealed that participant self-confidence increased significantly after training across all assessment items (p < 0.0001). Fifteen participants (75%) successfully aspirated 1 mL of synovial fluid on their first attempt, whereas 3 participants (15%) were successful on their second attempt. Two participants (10%) failed to perform a successful aspiration within the 15-minute time limit. The average time required to aspirate 1 mL of synovial fluid was 41 seconds. Conclusions: Ultrasound images of the formalin-embalmed suprapatellar bursa are of sufficient quality to use in the instruction of arthrocentesis to medical trainees. Brief instruction using formalin-embalmed cadaver models significantly increases trainee confidence and prepares first-year medical students to successfully and independently perform ultrasound-guided knee arthrocentesis.