Validation of Activity Tracking Procedures in Elderly Patients after Operative Treatment of Proximal Femur Fractures

Abstract

Background Early postoperative physical activity in elderly patients suffering from proximal femoral fractures may reduce mortality. We hypothesized that activity trackers can reliably and objectively monitor the in-hospital mobilization, correlating with functional independence and quality of life. Methods Three different tracker types (Fitbit™ flex, Misfit™ Shine, and Axivity AX3) at three locations (wrist, ankle, and femur) recorded steps and signal vector magnitudes (SVM) in 22 patients. They were 81 ± 8 years old, were equally distributed between the sexes, and had an ASA score of 2.5 ± 0.6. Single protocoled activity events (n = 191) were clinically categorized into 4 levels and correlated with the monitored signals. Additionally, 2 ± 1 and 8 ± 3 days after the operation, the EuroQol-5D and the Barthel-20 index supplemented this data. Results All measurements at the wrist (Fitbit, Misfit) resulted in unacceptable accuracy; however, sensitivity and specificity reached around 90% using the Misfit at the ankle. Applying this combination, the correlation between real and measured steps (R2 = 0.99) and the category discrimination were statistically significant (p < 0.002). A discriminant analysis featured the calculation of four activity levels based on SVM measurements using the Axivity tracker at the femur. A cluster analysis showed a 100% agreement between the clinically observed and the calculated activity levels. The amount of active minutes or periods and both the EuroQol-5D and the Barthel-20 indices significantly increased between the analyzed time points after the operation. However, only the Barthel-20 was associated with the measured activity levels (p < 0.01). Conclusion The Misfit and the Axivity trackers can reliably monitor activity in elderly patients after operative treatment of proximal femur fractures. However, the wear location is decisive. Objectively measured activity correlated with functional independence and quality of life.

Objectively Measured Physical Activity and Its Association with Functional Independence, Quality of Life and In-Hospital Course of Recovery in Elderly Patients with Proximal Femur Fractures: A Prospective Cohort Study

“…Although patients operated for proximal femur fractures move differently and walk slowly compared to a young and healthy population [28], their physical activity could be measured reliably using a specific algorithm developed for this purpose [20]. Hereby, the very low activity levels found in this cohort was consistent with earlier findings [10,18,[29][30][31], although the absolute values were higher in this study caused by the recently adapted threshold [20]. e need for these adjusted algorithms and appropriate tracker devices is in accordance with studies, showing distinctive validity for different wearables and intensities [32,33].…”

“…Parameters. Physical activity was measured as recently described [20]. Briefly, patients were tracked continuously by the skin-taped Axivity™ AX3 tracker (Newcastle upon Tyne, UK), which was placed at the nonoperated antero-lateral femur.…”

“…Serum levels of C-reactive protein (CRP), albumin, and hemoglobin were registered at admission (baseline), TP 1 and 2. Based on the preliminary results of the pilot study [20] we could assume a clinical relevant 25% increased activity from TP 1 to TP 2. Taking this and 20% dropouts into account, an 80% power for paired statistical analysis required the inclusion of 48 hip fracture patients to reach statistical significance.…”

“…By this, two separate constructs are being measured and compared, patients' functional capacity (what they CAN do) vs. their actual activity (what they ACTUALLY do). Our study is based on a reliable accelerometer (Axivity AX3) [19] and recently validated algorithms for measurement of PA in this fragile population [20].…”

The effect of a heel-unloading orthosis in short-term treatment of calcaneus fractures on physical function, quality of life and return to work – study protocol for a randomized controlled trial

“…Regarding the Axivity™ AX3, the portion of highly active periods per day and the number of active minutes, correlating with walking activity, have shown to be most discriminating in the validation study (11). Therefore, these parameters are selected.…”