Study Finds Body Location Determines Activity Tracking Device Accuracy in Total Knee and Hip Arthroplasty Patients

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Wearable technology is seemingly ubiquitous. Devices that are placed on a certain part of the body and used to track fitness and activity data have been on the rise in both the fashion and fitness industries, but it doesn’t stop there. Research is beginning to show the benefits associated with wearables in the healthcare industry as well. A recent study published in the Journal of the American Academy of Orthopaedic Surgeons found that body location determines activity tracking device accuracy in total knee and hip arthroplasty patients.

The researchers found that step counts measured by activity monitoring devices (AMDs) and smartphones (SPs) can objectively measure a patient’s activity levels after total hip and knee arthroplasty (total joint arthroplasty [TJA]). The study investigated the use and optimal body location of AMDs and SPs to measure step counts in the postoperative period.

The researchers conducted a two-armed, prospective, observational study of TJA inpatients (n = 24) and 2-week status after TJA (n = 25) completing a 100-ft walk. Observer-counted steps were compared with those measured by AMDs (wrist and ankle) and SPs (hip and neck). Acceptable error was defined as <30%. Error rates were treated as both dichotomous and continuous variables.

The researchers found that AMD and SP step counts had an overall unacceptable error in TJA inpatients. AMDs on the contralateral ankle and SPs on the contralateral hip had error rates less than 30% at 2 weeks postoperatively. Two-week postoperative patients required lower levels of assist (11/25 walker; 4/25 no assist), and significant improvements in stride length (total hip arthroplasty 1.27 versus 1.83 ft/step; total knee arthroplasty 1.42 versus 1.83 ft/step) and cadence (total hip arthroplasty 74.6 versus 166.0 steps/min; total knee arthroplasty 73.5 versus 144.4 steps/min) were seen between inpatient and postoperative patients. Regression analysis found that increases in postoperative day and cadence led to a decrease in device error.

The researchers concluded that in inpatients with TJA, AMDs and SPs have unacceptable variability and limited utility for step counting when using a walker. As gait normalizes and the level of ambulatory assist decreases, AMDs on the contralateral ankle and SPs on the contralateral hip demonstrated low error rates. These devices offer a novel method for measurement of objective outcomes and potential for remote monitoring of patient progress after TJA.

As the need for an objective method of data capture in the healthcare industry continues to increase, new technology is being developed with just that in mind. The TracPatch Surface Sensor Technology takes the idea of activity monitoring devices and smartphones a step further as it simply pairs them together. The TracPatch Surface Sensors are activity monitoring devices that adhere to a patient’s leg following TJA. The devices pair with the patient’s smartphone, collect important activity data in real-time and send it to the patient’s TracPatch app. The data is then sent to the patient’s healthcare provider in real-time through a healthcare provider app and portal.

It’s reassuring to know that activity monitoring devices and smartphones are already showing promise when it comes to a method for objective data capture in TJA patients. TracPatch is already assisting healthcare providers across the country to remotely access accurate and objective patient data. The devices are incredibly beneficial as they measure step count more accurately due to direct lower leg placement as opposed to being worn on the wrist or ankle. For more information about TracPatch contact us today.


Goel, R., Danoff, J. R., Petrera, M., Blevins, K., Purtill, J. J., & Chen, A. F. (2020). A Step in the Right Direction. Journal of the American Academy of Orthopaedic Surgeons28(2). doi: 10.5435/jaaos-d-18-00319

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