Verification of the usefulness of shape acquisition using plastic casts during fabrication of a metal strut ankle-foot orthosis.
Shinnosuke Sato, Koutaro Ishikawa, Kousuke Yajima and 2 others
PMID 39092413WHAT IT FOUND
Plastic casts save significant time compared to plaster bandages but add thickness due to stockinette layers.
Trace methods are fastest but produce smaller, less accurate dimensions. Plaster remains most reproducible for shape. Choose the method based on whether time efficiency or dimensional accuracy is the priority for the specific patient.
Key findings
01The plastic cast method significantly reduced the total work time until just before metal strut bending compared to the plaster of Paris bandage method (median 275.5 s vs 5,521 s).
02Shape acquisition using plastic casts resulted in a significantly larger circumferential diameter (median +7.5 mm) compared to 3D scan references, likely due to the thickness of the stockinette and cast.
03The trace method produced significantly smaller circumferential diameters (median -15 mm) and widths compared to reference dimensions, attributed to differences in body position during measurement.
STILL TO COME
How it was doneWhat they foundWhat it means for OTs
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What it does not show
The study used healthy undergraduate students, not patients with ankle deformities. The findings may not apply to clinical populations with significant varus/valgus deformities where three-dimensional support is critical. The comparison involved only three methods; it does not account for all possible fabrication techniques or materials. The 'trace' method results were affected by body position (supine vs sitting), which may introduce variability in real-world clinical settings where positioning is less controlled. The study did not evaluate patient comfort or skin integrity over time, only the fabrication process and immediate dimensional accuracy.
Declared interests
The authors declare no conflicts of interest. No specific grant funding was received.
The easy way to misread this
Do not assume plastic casts provide a perfect one-to-one shape match. They consistently add thickness to the model, which can lead to a loose orthosis if not corrected during fabrication. Also, do not generalize these timing and accuracy results to patients with severe ankle deformities, as the study only used healthy legs.