The 3D-printed temporal bone helps the consultant and burdens the trainee

Design

randomised controlled trial, level II, analysed with linear mixed-effects models

Population

40 consecutive adult primary cochlear implant operations performed by seven attending and five trainee surgeons at a large implant centre

Primary outcome

intraoperative cognitive load measured by the Surgery Task Load Index

Effect

attendings 3.8 vs 5.5 (P<0.01) favouring the model; residents 7.2 vs 4.8 (P=0.02) against it; fellows 8.2 vs 8.0 (P=0.88)

Patient-specific 3D-printed models are usually justified as a training aid, and this randomised trial tested them somewhere more demanding - in theatre, during cochlear implantation, as a supplement to imaging. Forty consecutive adult primary implant operations by seven attending and five trainee surgeons were randomised 1:1 to standard imaging-based planning or standard planning plus intraoperative inspection of a printed model, with cognitive load measured by the Surgery Task Load Index and analysed in linear mixed-effects models.

The effect depended entirely on who was holding the model. Attending surgeons had lower overall cognitive load with it (3.8 vs 5.5, P<0.01), driven by reduced physical fatigue. Residents had higher load (7.2 vs 4.8, P=0.02), with both mental effort and physical fatigue increased. Fellows sat between: no difference in overall load (8.2 vs 8.0), lower rated case complexity (P=0.02) offset by higher physical fatigue (P=0.04). Everyone rated the models accurate and useful, particularly for anticipating difficulty and anatomical boundaries.

The interpretation the authors offer is convincing. For someone with a fully formed mental model of the anatomy, the printed bone is a reference that offloads working memory. For someone still building that model, it is another source of information to integrate under time pressure - which is more cognitive work, not less. That has a general lesson beyond cochlear implants: an aid that reduces expert load can increase novice load, and the two should not be introduced with the same expectation. Cognitive load is also a process measure, and this trial did not measure surgical outcomes.

• Offer the model to experienced surgeons as a reference and to trainees as preoperative preparation, not as an intraoperative addition.
• Do not assume a training aid helps trainees in theatre; here it measurably did not.
• The outcome measured is cognitive load, not operative time, complications or hearing results.
• Forty cases across twelve surgeons - the experience-level interaction is the finding, and it rests on small subgroups.
• Where models are printed anyway, the cheapest use is preoperative planning and teaching outside the operating room.

The statistics, in plain English

Forty operations split across seven attendings, five trainees and a fellow group means each experience stratum contains very few cases, so these subgroup comparisons are underpowered and the interaction was not formally tested against a prespecified hypothesis. Linear mixed-effects modelling is the right approach because it accounts for the same surgeon contributing several cases, which a simple comparison would not. The Surgery Task Load Index is a self-reported instrument, and surgeons were necessarily aware of which arm they were in - so expectation effects cannot be excluded in either direction. Level II evidence, and a process outcome rather than a patient one.

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