Wearable device tracks recovery after total knee replacement

A novel wearable device can accurately measure range of motion (ROM) and gait in patients who had undergone total knee replacement (TKR), according to a recent study. This proposed system could facilitate portable progress monitoring in this population.

“We developed a portable and wearable inertial measurement unit (IMU) software and hardware platform and designed a systematic monitoring and evaluation program to address the clinical needs of TKR patients after surgery,” the researchers said. “Through dynamic and static flexion and extension activities, the accuracy and practicability of the system are verified.”

Ten TKR patients and 10 healthy controls participated in the study and were given the wearable device, consisting of two IMUs worn on the thigh and the shank. As a reference, the researchers compared the performance of their novel device to the Baltimore Therapeutic Equipment (BTE) Primus RS, a sophisticated equipment that integrates assessment, training, and rehabilitation, and is widely used in hospitals.

When patients were asked to perform passive flexion-extension experiment at an angular velocity of 15°/s, the wearable IMU device measured knee ROM with an average error of 3.22° as compared with BTE Primus RS. At angular velocities of 30°/s and 45°/s, the corresponding mean errors were 4.94° and 4.34°. [Front Neurobot 2022;16:836184]

Meanwhile, errors between the novel system and BTE Primus RS were smaller in control, with values of 0.76°, 0.63°, and 0.16° at angular velocities of 15°/s, 30°/s, and 45°/s, respectively.

Of note, Bland-Altman plots of all flexion-extension measurements showed that most flexion and extension activities occurred within 10°, suggesting good agreement with the BTE Primus RS reference. In particular, knee ROM of patients ranged from 45°–90°, reflecting the differing degrees to which patients have already recovered from surgery at the time of assessment.

This finding was confirmed during the gait flexion-extension experiments, which showed great variance in knee ROM among TKR patients. For example, four patients had an average ROM of <60°, indicative of poor recovery. ROM between 60°–70°, on the other hand, as experienced by three patients, could suggest good recovery.

Meanwhile, three patients achieved ROM between 70°–80°. This was almost comparable to measurements in healthy controls, who showed ROM between 70°–90°, suggesting that normal walking should not see ROM drop below 70°.

“Due to its simple operation and high execution efficiency, the system has strong clinical application value, which can provide assessment for patients and provide assistant to physical therapists,” the researchers said. “We anticipate the system proposed in this paper can be used for long-term monitoring and evaluation of many symptoms, such as TKR, anterior cruciate ligament, and fractures.”

“Although we have made rich comparisons between healthy people and patients, and the knee replacement and nonreplacement side of the patient, there is still a lack of comparisons between patients on the surgical site in different periods,” they added.

Future research is needed to address this shortcoming and additionally assess other parameters of knee functional recovery, according to the researchers.