Accelerometers can correctly count orthopaedic patients' early post-operative steps while using walking aids

Purpose

Effective rehabilitation after orthopaedic surgery is critical. The early post-operative phase is increasingly managed in outpatient settings, necessitating objective measures such as step counts to monitor rehabilitation progress. However, it remains unclear if commercially available wearables or accelerometers using simple algorithms can accurately count steps in early post-operative conditions. We hypothesised that only accelerometers could accurately determine the number of steps under these conditions.

Methods

This case series involved 20 healthy subjects, 7 female and 13 males, walking in a circle at varying speeds under partial loading with three different walking aids (forearm crutches, walking frame and rolling walker) and four wearables (Vivofit 4, Fenix 3HR, Fitbit Charge 3 and Omron HJ-325) and one accelerometer (AX6) worn on the wrist, hip and ankle. The two-point and modified three-point gait patterns commonly used post-operatively were simulated. The primary end point was the relative error (RE), defined as RE = (manual count − automated count)/manual count, of each wearable measurement compared to visual and video step counting, the gold standard.

Results

The RE of AX6 and Fitbit was less than 0.1 for all walking aids except the rolling walker, with AX6 showing the lowest standard deviation (SD) compared to other wearables. Other wearables had significantly higher RE. Increased gait speed generally improved accuracy, reducing RE in most devices, except for the AX6, which showed the opposite trend. At 0.6 m/s, only AX6 achieved an RE below 0.1. The ankle was identified as the best measuring location.

Conclusion

During the early post-operative period, commercial wearables can only accurately count steps under specific conditions and should be used cautiously for monitoring steps in the early post-operative phase. However, accelerometers with appropriate coding appear suitable for this purpose.

Level of Evidence

Level III diagnostic study.