Predicting tibiotalar and subtalar joint angles from skin-marker data with dual-fluoroscopy as a reference standard.
Jennifer A Nichols, Koren E Roach, Niccolo M Fiorentino and 1 others
PMID 27414041WHAT IT FOUND
A model allowing 1 rotation per joint predicted average tibiotalar motion more consistently than a model allowing 3 rotations, but neither gave reliable per-person tibiotalar or subtalar angles; errors exceeded 10° in 9 of 10 subjects.
Key findings
01The 1 DOF model predicted average tibiotalar motion more consistently than the 3 DOF model, with significantly smaller errors for inversion/eversion and internal/external rotation during all activities.
02Neither model consistently predicted subtalar joint angles during stance, and per-subject prediction error exceeded 10° for 9 of 10 subjects during at least one activity.
03The study considered limits of agreement below 5° acceptable because that is within goniometer measurement error, but per-subject error exceeded 10° for 9 of 10 subjects.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
The sample was small and included only ten control subjects with no history of foot or ankle disorders. Only one foot per subject was imaged, with 6 right feet and 4 left feet, and four trials were excluded for missing data. The dual-fluoroscopy field of view could not capture an entire stance phase, so heel-strike and toe-off were analyzed separately. The models used generic bone geometry and joint axes based on cadaveric experiments, not subject-specific anatomy. The study tested treadmill walking events and heel-rise, not a clinical population or a treatment outcome. Per-subject prediction error exceeded 10° for 9 of 10 subjects, which is larger than the 5° limit the authors considered acceptable.
The easy way to misread this
Do not conclude that skin-marker inverse kinematics can accurately estimate individual tibiotalar or subtalar joint angles. The study found average model trends, but per-subject error exceeded 10° for 9 of 10 subjects, so these outputs should not be treated as reliable patient-specific measurements.