Smartphones measure physical performance after lumbar spine surgery

Smartphone-based real-life activity data can be used to track physical performance in patients after lumbar spine surgery for degenerative lumbar disorders (DLD), according to a recent study.

The prospective and observational pilot analysis included eight patients (mean age 45.8 years, 62 percent men), whose physical performance was first measured objectively using validated questionnaires the 6-minute walk distance (6MWD).

Before surgery, patients had a mean 6MWD of 351.56 m, which increased to 555.25 m at 6 weeks after the surgery and to 567.38 m at 12 weeks postoperatively. The increase in time was statistically significant (p=0.03). [Brain Spine 2022;doi:10.1016/j.bas.2022.100881]

Other measures of physical performance likewise improved. Scores in the Core Outcome Measures Index (COMI)-Back improved from a baseline mean of 7.55 to 2.19 and 2.41 at 6 and 12 postoperative weeks, respectively (p=0.002).

The researchers also used the Zurich Claudication Questionnaire to evaluate the patients’ symptoms, function, and satisfaction after their treatment. Scores in the physical function domain dropped significantly from 2.25 at baseline to 1.10 at 6 weeks and 1.20 at 12 weeks (p<0.001), indicative of marked improvement.

A similar effect was reported for the Questionnaire’s symptom severity index, scores for which improved from 3.88 at baseline to 2.16 and 2.06 at 6 and 12 weeks postoperatively, respectively (p=0.018).

Smartphone validation

The researchers then retrieved device data and assessed how well smartphone-based monitoring could match objective measures of physical performance.

Overall, participants provided a total of 286,856 smartphone mile counts, as tracked by the iPhone Health app. Data on cumulative distance covered per day showed that performance varied greatly between patients, and that each patient had a strong effect on the cumulative activity.

Normalizing data revealed a slight downward trend in distance before the surgery, followed by a slight increase postoperatively.

Linear mixed effects model using device data further validated the objectively detected improvements in physical function measures. For 6 months before the procedure, daily distance covered by the patients decreased consistently and significantly, as indicated by a negative slope estimate: –0.094 (95 percent confidence interval [CI], –0.136 to –0.053; p<0.001).

However, in the first 4 months after surgery, smartphone data revealed a positive slope estimate of 0.178 (95 percent CI, 0.087–0.269; p<0.001) which could be suggestive of improving function.

Between 4 and 12 months after surgery, the linear model again yielded a negative slope estimate of –0.076 (95 percent CI, –0.1 to –0.005; p<0.001), which might correspond to worsening or plateauing of physical performance.

Pearson correlation analysis showed that the normalized daily distance as collected by smartphones correlated with 6MWD measures, particularly at the first preoperative month and third postoperative month. A similar effect was detected for patient-reported outcomes, as measured by COMI.

“Although, smartphone-based performance assessment correlated with functional 6MWD scores, daily activity levels decreased again in the further postoperative period exhibiting a discrepancy between patients’ postoperative physical performance and physical capacity,” the researchers said.

“Our finding should consult a more cautious use of physical performance as objective outcome measure in conjunction with existing physical capacity assessments,” they added.