Reliability of a smartphone app to objectively monitor performance outcomes in degenerative cervical myelopathy: an observational study

Objectives To assess the reliability of the MoveMed battery of performance outcome measures. Design Prospective observational study. Setting Decentralised secondary care in England, United Kingdom. Participants Seven adults aged 59.5 (SD 12.4) who live with degenerative cervical myelopathy (DCM) and possess an approved smartphone. Primary and secondary outcome measures The primary outcome was to determine the test-retest reliability of the MoveMed performance outcomes using the intra-class correlation of agreement (ICC agreement ). The secondary outcome was to determine the measurement error of the MoveMed performance outcomes using both the standard error of agreement of the mean (SEM agreement ) and the smallest detectable change of agreement (SDC agreement ). Criteria from the Consensus-based Standards for the selection of health Measurement Instruments (COSMIN) manual were used to determine adequate reliability (i.e., ICC agreement ≥ 0.7) and risk of bias. Disease stability was controlled for using two minimum clinically important difference (MCID) thresholds obtained from the literature on the patient-derived modified Japanese Orthopaedic Association (P-mJOA): namely, MCID ≤1 point and MCID ≤2 points. Results All tests demonstrated moderate-to-excellent test-retest coefficients and low measurement errors. In the MCID ≤1 group, ICC agreement values ranged from: 0.84–0.94 in the Fast Tap Test, 0.89–0.95 in the Hold Test, 0.95 in the Typing Test, and 0.98 in the Stand and Walk Test. SEM agreement values ranged from ±1 tap, ±1–3% stability score points, ±0.06 keys per second, and ±10 steps per minute, respectively. SDC agreement values were ±3 taps, ±4–7% stability score points, ±0.2 keys per second, and ±27 steps per minute. In the MCID ≤2 group, ICC agreement values ranged from: 0.61–0.91, 0.75–0.77, 0.98, and 0.62, respectively; SEM agreement values from: ±1 tap, ±2–4% stability score points, ±0.06 keys per second, and ±10 steps per minute; and SDC agreement values from: ±3–7 taps, ±7–10% stability score points, ±0.2 keys per second, and ±27 steps per minute. Furthermore, the Fast Tap, Hold, and Typing Tests obtained sufficient ratings (ICC agreement ≥ 0.7) in both MCID≤1 and MCID≤2 groups. No risk of bias factors from the COSMIN Risk of Bias checklist were recorded. Overall, ‘very good’ quality evidence of sufficient reliability was found for the MoveMed battery in DCM. Conclusions Criteria from COSMIN provide ‘very good’ quality evidence of the reliability of the MoveMed tests in an adult population living with DCM. Strengths and limitations of this study Criteria from the COSMIN manual support the reliability of MoveMed’s battery of performance outcome measures. Criteria from the COSMIN manual rate the methodological quality of the evidence at ‘very good’. Self-reported outcome measures and data elements were used in a decentralised secondary setting. Primary and secondary outcomes were used to assess reliability. Study design and analyses were performed by individuals formally trained in clinimetrics.