Sonographically Guided Semimembranosus Bursa Injection: Technique and Validation

Objectives: To describe and validate a sonographically guided (SG) semimembranosus (SM) bursa injection technique in an unembalmed cadaveric model. Design: Prospective, cadaveric laboratory investigation. Setting: Academic institution procedural skills laboratory. Subjects: Ten unembalmed cadaveric thigh-knee-ankle-foot specimens from 4 male and 6 female donors ages 55-92 years (mean 76.2 years) with body mass indices of 15.4-31.8 kg/m² (mean 21.9 kg/m²). Methods: A single, experienced operator completed SG SM bursa injections in 10 unembalmed cadaveric knees using 3 mL of diluted colored latex. At a minimum of 2 days after the injection, co-investigators dissected the specimens to assess the distribution of latex with respect to the SM bursa. Main Outcome: Injections were graded for accuracy as follows: accurate (all latex contained within the SM bursa), accurate with overflow (latex within the SM bursa and extending into regions other than the needle track), or inaccurate (no latex within the SM bursa). Results: All 10 injections (100%) accurately placed latex within the SM bursa and resulted in proximal spread to at least the level of the knee joint. Eight of 10 injections (80%) demonstrated minimal (< 1 mL) extrabursal flow without extension into the intra-articular space. No neurovascular injury occurred in any specimen. Conclusions: SG SM injections are feasible and accurate and may be considered for diagnostic and therapeutic injections in patients with suspected distal SM disorders. Injection volumes less than 3 mL should be considered to reduce extrabursal spread as clinically indicated.