(Poster 10) Anterior Trocar Passage During Midurethral Sling Simulation

Objectives: Passing a retropubic trocar anterior to the suprapubic bone during midurethral sling surgery can cause bleeding and pain, occurring in 27.1% of novice passes in our recent experiment. We introduced teaching instructions mimicking intraoperative guidance to help distinguish anterior from posterior bone surfaces. Our objective was to assess whether this reduced anterior trocar passage, hypothesizing that instruction would decrease anterior errors and improve accuracy.

Methods: Twelve medical students performed 5 bilateral retropubic trocar passes on our midurethral sling simulation platform. All participants were right-handed, and mean participant height and table height were 169.0 and 84.8cm. Each student was given instructions to maintain contact with the suprapubic bone and exit at marked sites 2cm lateral to the midline. The teaching group (TG; n=6) was given additional hands-on instruction about distinguishing anterior and posterior trocar passage that included practice, lasting 10-20 seconds. The control group (CG; n=6) was not given this instruction.

Retroreflective markers placed on the trocar were tracked using an 18-camera OptiTrack Flex 13 motion capture system (Natural Point Inc, Corvallis, OR). Motion data was streamed to MATLAB (MathWorks, Natick, MA), which was used to calculate trocar tip position using marker positions and known trocar geometry, and to evaluate trocar tip proximity to suprapubic bone, bladder, and bowel. Linear mixed modeling was used to compare TG to CG in passage anterior to the bone, time in and out of the correct pathway, and contact with the bladder and bowel.

Results: The percentage of trials with at least one anterior trocar pass did not differ between CG and TG (73.8% vs 68.0%, p=0.71). Post-hoc power calculation revealed that 258 participants per group would be required to demonstrate a difference with 80% power. Mean time anterior to the bone for all anterior passes was 4.3 seconds. The TG spent more time in the correct pathway (19.5 vs 9.6 seconds, p=0.02) and exhibited longer bladder contact time (1.9 vs 0.1 seconds, p=0.02). There was no difference in time outside of the correct pathway while not in contact with a vital organ (10.5 vs 10.6 seconds, p=0.96). Four TG subjects made contact with the bowel.

Conclusions: Despite receiving teaching on anterior vs posterior, TG participants could not consistently distinguish between the anterior and posterior surfaces of the suprapubic bone during retropubic trocar passage, although they spent more time in contact with the bone. In this novice population, anterior trocar passage was common, as was contact with the bladder and bowel. Novice surgeons are at significant risk for injuring the patient and require close supervision, possibly hands-on-hands guidance.