key: cord-1054474-ob81cgx0
authors: Van de Kleut, Madeleine L.; Bloomfield, Riley A.; Teeter, Matthew G.; Athwal, George S.
title: Monitoring daily shoulder activity before and after reverse total shoulder arthroplasty using inertial measurement units
date: 2020-08-06
journal: J Shoulder Elbow Surg
DOI: 10.1016/j.jse.2020.07.034
sha: fbc3ab1001b10235bcf538801a92ca88563bd9d3
doc_id: 1054474
cord_uid: ob81cgx0

Abstract Background The purpose of this study was to use at-home, portable, continuous monitoring technologies to record arm motion and activity preoperatively and postoperatively after reverse total shoulder arthroplasty (RTSA). Methods Thirty-three patients indicated for RTSA were monitored preoperatively, three, and 12 months postoperatively. Inertial measurement units were placed on the sternum and upper arm of the operative limb, recording humeral motion relative to the torso for the duration of a waking day. Elevation events (EE)/hour, EE/hour greater than 90°, time spent above 90°, and activity intensity were calculated and compared between time points. Patient-reported outcome measures were also collected at all time points. Results At three (P=0.040) and 12 (P=0.010) months after RTSA, patients demonstrated a significantly greater number of EE/hour greater than 90° compared to preoperatively. There were no significant differences (P≥0.242) in the amount of time spent at different elevation angles at any time point, or in arm activity intensity. Overall, 95% of the day was spent at elevation angles less than 60° and 90% of the day in a low or moderate intensity state. Pearson correlations demonstrated relationships between forward elevation and the number of EE/hour (r=0.395, P=0.001) and the number of EE/hour greater than 90° (r=0.493, P<0.001). Conclusion After RTSA, patients significantly increase the frequency of arm elevation to higher angles. However, no differences were found in the amount of time spent at different elevation angles. Overall, after RTSA, greater than 95% of the day was spent at elevation angles less than 60° and less than 1% of the day was spent above 90° of elevation. Level of Evidence Level IV; Case Series; Treatment Study;

elevation angles. Overall, after RTSA, greater than 95% of the day was spent at elevation angles 23 less than 60° and less than 1% of the day was spent above 90° of elevation. investigating shoulder motion. 18 Real-time Kalman filtering was used to determine orientation. 99

An on-board micro secure digital card enabled real-time data logging at a frequency of 10 Hz. 100

An external power supply was connected to each IMU to increase data logging capacity for the 101 duration of a day of wear. This external power supply was approximately 40 x 15 x 80 mm, and 102 fitted into a separate, snug pocket sewn into the compression shirt so as not to inhibit shoulder 103 range of motion. Prior to patient use, IMUs were charged and time-synchronized via wired 104 connection to a computer. After donning the compression shirt, a research associate ensured 105

IMUs were properly positioned. The patient was asked to assume a normal standing position 106 with the arm of interest as close to their side as possible. The research associate then began 107 simultaneous data logging from both the torso and humerus reference IMUs. At the end of the 108 day, patients were asked to remove the instrumented shirt and return it to the research institute 109 via prepaid expedited parcel. Patients were also asked to complete a daily activity log, record 110 when the garment was removed, and include this in the envelope. 111 logs from each IMU consisted of timestamped quaternions, four-element vectors comprising 114 orientation information in three dimensions. Quaternion representations are more robust than 115

traditionally-used Euler angles as quaternions do not suffer from singularities such as gimbal 116 lock when extracting anatomical joint rotations (in the case of two rotation axes aligning in a 117 parallel configuration creating an indeterminate system) and are more memory efficient than 118 logging raw rotation matrices. 2 In MATLAB (MathWorks, Natick, MA, USA), quaternions from 119 both the torso and humerus IMUs with corresponding time stamps were matched and a rotational 120 difference between sensor pairs was computed with respect to the torso. Knowing the first 121 quaternions were recorded when the patient was in a standing position with their arm at 0° 122 abduction and neutral alignment, subsequent arm positions can be determined by taking the 123 relative difference in orientation of the humerus IMU to that of the torso IMU at matched times. 124

Given a quaternion and rotation sequence, anatomical joint angles can then be determined and 125 the angle of interest isolated -in this case the angle of shoulder elevation. 126 127 Following processing, metrics isolated from the data include: the number of elevation events per 128 hour, the proportion of time spent within different elevation ranges (0-20°, 20-40°, 40-60°, 60-129 80°, 80-100°, >100°), the proportion of elevation events that occur within these elevation ranges, 130 and the intensity of arm activity, rated as low, moderate, or high intensity (defined below). 131

Elevation events were measured as discrete peaks in the timeseries with a minimum peak height 132 of 20° and minimum peak width of one second. Thus, subsequent peaks must be separated by a 133 trough of at least 20° to be considered separate events. Peak height of 20° and width of one 134 second was chosen to highlight arm movements that are deliberate -arm elevation changes of less than 20° and one second are likely normal variations in a static condition that encompass 136 any orientation error from the IMUs and any change in orientation of the IMUs within the 137 compression shirt due to slight body movements. 23 To evaluate the intensity of arm activity, the 138 elevation timeseries was discretized into epochs of 60 seconds. 13 For each epoch, arm activity 139 was classified as low if there were fewer than three elevation events, as moderate if there were 140 more than three but fewer than 10 elevation events, and as high if there were more than 10 141 elevation events. The number of epochs with low, moderate, or high intensity classifications was 142 normalized to the total number of epochs, defining the proportion of the day spent at each 143 activity level. 

Mean age at the time of surgery was 71 ± 8 years, 58% male, and 70% for whom their dominant 170 arm was that undergoing RTSA. Full patient demographics are reported in Table I.  171 172 Inertial Measurement Unit data: 173 hours (range = 4.2-13.2 hours; 72% > 6 hours). Three months postoperatively, 27 patients 176 donned the garment for an average of 6.6 hours (range = 1.8-11.2 hours, 74% > 6 hours), and one 177

year postoperatively 19 patients wore the garment for an average of 5.9 hours (range = 3.7-9.8 178 hours, 79% > 6 hours). Preoperatively, four patients were not instrumented because their visit to 179 the clinic coincided with further same-day preoperative assessment, for which application of the 180

IMUs would hinder appropriate examination. Three months postoperatively, six patients were not instrumented due to an unavailability of study IMU devices which were all currently 182 deployed due to a sudden surge in recruitment. One year postoperatively, three patients were not 183

instrumented as a result of contralateral arthroplasty, preventing donning of the over-the-head 184 garment; two patients refused further follow-up; and the remainder (n = 9) were not assessed due 185 to the transition from in-person to remote follow-up resulting from the COVID-19 pandemic. (Table II) (Table III) proportion of elevation events greater than 100° at three months (mean difference = 5, P = 0.043; 213 mean difference = 2.6%, P = 0.034, respectively) and one year (mean difference = 5, P = 0.031; 214 mean difference = 1.6%, P = 0.045, respectively) compared to preoperatively (Table V) . There 215 were no significant differences between time points for any IMU metric within the non-dominant 216 cohort (all P ≥ 0.200) (Table VI) . Interestingly, there were no significant differences in shoulder activity intensity after reverse 255 total shoulder arthroplasty as compared to preoperatively. One would theorize that after 256 undergoing surgery designed to alleviate pain and improve range of motion, patients would 257 increase their intensity of activity. This finding of no difference may be a reflection of the 258 relatively elderly and obese patient population with limited functional demands, and the large 259 standard deviations observed within the group. This may also explain why no differences were 260 observed with respect to the proportion of the day spent at different elevation angles -both 261 preoperatively and one year postoperatively, 95% of the day was spent at elevation angles less 262 than 60°. A previous study assessing shoulder biomechanics in the healthy elderly population 263 found similar results, with 97% of the day spent at elevation angles less than 90°, suggesting that 264 even if the elderly population has the capacity to perform activities with a large range of motion, 265 they seldom do. 4 It is also noteworthy, that while no differences were observed with time, 266 significantly more elevation events occurred at ranges greater than 100° three months 267 postoperatively compared to preoperatively, though not one year compared to preoperatively. Overall, it appears that the increased elevation events to obtain motion at 3 months are transient, 276

and that patients settle back to their original preoperative movement event frequency. both three months and one year postoperatively, without an observed increase in time spent 319 above 90°. Another explanation for this apparent incongruence is that patients may use their arm 320 more efficiently as a result of both increased range of motion and reduction in pain. 321

Postoperatively, it may take less time to complete overhead tasks than preoperatively, and 322 therefore more events may take place in the same amount of time. 323

To ensure there was sufficient space on the on-board secure digital card to record all data, 325

quaternions were logged at a frequency of 10 Hz. Though a higher logging rate would provide a 326 smoother timeseries, as the study cohort was elderly, it was proposed that activities would likely 327 not be of very high intensity. This assumption was reflected in the results, where approximately 328 90% of the day was spent in low or moderate activity phases, with less than ten elevation events 329 per minute. After reverse shoulder arthroplasty, patients significantly increase the frequency of arm elevation 368 events to higher elevation angles. However, no differences were found in the amount of time 369 spent at different elevation angles when comparing preoperative to postoperative. Overall, after 370 reverse total shoulder arthroplasty, greater than 95% of the day was spent at elevation angles less 371 than 60° and less than 1% of the day was spent above 90° of elevation. J o u r n a l P r e -p r o o f Table III Proportion of day (%) spent at varying arm elevation angles (mean ± SD). Note:

percentages may not add up to 100% due to rounding.

Preoperative 3 months postop 1 year postop P-value 0-20 52 ± 14 55 ± 16 50 ± 15 0.496 20-40 31 ± 12 29 ± 11 33 ± 7 0.334 40-60 12 ± 8 10 ± 7 13 ± 10 0.515 60-80 3 ± 4 4 ± 4 3 ± 3 0.890 80-100 1 ± 1 2 ± 3 1 ± 1 0.282 > 100 0.5 ± 1 1 ± 1 0.5 ± 1 0.242 J o u r n a l P r e -p r o o f Table IV Proportion of elevation events (%) at varying arm elevation angles (mean ± SD).

Note: percentages may not add up to 100% due to rounding. 

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