Accuracy of visual estimates of joint angle and angular velocity using criterion movements

Physiotherapists could detect changes of 12 degrees or more in single-plane movement when observing forward bending, squat or hand-over-head: A cross-sectional experiment

BACKGROUND

The visual accuracy of physiotherapists to detect changes in dynamic joint angles is currently unknown.

OBJECTIVE

To investigate (i) the smallest detectable change in movement that physiotherapists could visually observe, and (ii) whether visual accuracy was associated with the functional activity observed or characteristics of the physiotherapist.

METHODS

Thirty-four physiotherapists viewed and rated videos of squat, hand-over-head, forward bend functional activities and an artificial test condition (a reference movement followed by subsequent movements showing random differences in peak angle from 0° to 15°, so 18 sets of paired videos per functional activity). They rated each range of movement (same/more/less) relative to the reference movement, while their visual tracking was continuously monitored. Accuracy was calculated (multilevel regression) using two thresholds - two correct out of three viewings (2/3) and three correct out of three viewings (3/3).

RESULTS

More than 80% of physiotherapists were able to detect 9° difference using the 2/3 threshold and 12° using the 3/3 threshold. There was no association (p > 0.05) between visual accuracy and experience, sex, or movement type, except when viewing shoulder abduction compared with knee flexion using the 3/3 threshold. The only association between accuracy and visual tracking characteristics was for assessing lumbar flexion, where use of more visual fixation areas and a shorter fixation time per area were more accurate.

CONCLUSION

Physiotherapists were consistently accurate at detecting changes of ≥12° in single-plane, low-speed functional activities. Visual accuracy was not explained by experience or sex, and rarely associated with functional activity type or visual fixation.