Assessing effects of exoskeleton misalignment on knee joint load during swing using an instrumented leg simulator.
Jule Bessler-Etten, Leendert Schaake, Gerdienke B Prange-Lasonder and 1 others
PMID 35090501WHAT IT FOUND
Misaligning a knee brace on a leg simulator increased joint loads.
Rotational misalignment caused the largest spikes in force and torque, exceeding effects from simple position shifts. This suggests checking rotational alignment is critical for safety, even if the brace looks centered.
Key findings
01Rotational misalignment of the knee joint axis relative to the brace joint axis led to significantly higher forces and torques on the simulator leg.
02Rotational misalignments of approximately 10 degrees resulted in much higher peak forces and torques than translational misalignments of 10 mm in any direction.
03The amount of misalignment often reduced during the first flexion cycle, suggesting the device or soft tissue shifted to accommodate the load.
STILL TO COME
How it was doneWhat they foundWhat it means for PTsWhat it means for OTs
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What it does not show
The study used a mechanical dummy leg, not human participants, so it does not account for real-time pain feedback or muscle activation. The simulator leg weighed 4.2 kg, which is lighter than an average human leg, potentially affecting force magnitudes. The brace was moved manually by an experimenter, which may not perfectly replicate the controlled motion of an active exoskeleton. The study focused on the swing phase of gait, not weight-bearing activities like standing or walking, where loads are typically higher.
Declared interests
The study was supported by non-US government funding. The authors declared no conflicts of interest.
The easy way to misread this
Do not assume these force values apply directly to human patients or active exoskeletons. The study used a passive brace on a lightweight dummy leg during manual flexion. Real-world devices and human tissue dynamics differ significantly, so these findings indicate a risk direction, not a specific safety threshold.