Soft tissue artifact causes significant errors in the calculation of joint angles and range of motion at the hip.
Niccolo M Fiorentino, Penny R Atkins, Michael J Kutschke and 3 others
PMID 28475981WHAT IT FOUND
Skin markers on the hip and thigh gave large movement errors and underestimated hip range of motion compared with X-ray bone tracking in 11 healthy adults.
The tested model changes did not consistently fix the angles.
Key findings
01The greater trochanter marker moved the most relative to the bone, with 5.2 cm of movement in the front-to-back direction during hip rotation.
02Skin-marker hip range of motion was smaller than bone-tracking range of motion by 21.8° during rotation.
03Changing model constraints or marker configuration did not universally reduce hip angle errors.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
Read the rest of this summary
You get three full summaries a month, free, and we do not ask for a card. Search, the TL;DRs and your library stay unlimited either way.
What it does not show
Only 11 healthy young adults were studied, and they had low BMI and no hip pain, surgery, dysplasia, impingement, or osteoarthritis, so the results may not apply to patients with hip problems or more soft tissue. Two participants did not have abduction trials analyzed because the allowed radiation exposure time had expired. The study used one marker set and three specific models, so it does not show how all clinical motion-capture marker placements or models behave. Joint-angle comparisons were offset by the static trial, so individual bony anatomy differences were partly removed before the error was assessed. The reference method used 10.72 mSv of radiation exposure.
Declared interests
The corresponding author and co-authors declared no financial or other conflict of interest.
The easy way to misread this
Do not conclude that hip range of motion measured with skin markers equals true bone motion. In this study, skin-marker measurements underestimated hip rotation range by 21.8° during the rotation activity, and tested model changes did not universally reduce errors.