Validation of a novel knee harness inertial-cum-ultrasound wearable device as a quantitative measure of knee function

Accurate assessment of knee function is essential for diagnosis, monitoring, and rehabilitation of musculoskeletal injuries. Patient-reported outcome measures (PROMs) such as the International Knee Documentation Committee (IKDC) score, although validated, are limited by subjectivity and ceiling effects. This study aimed to validate a novel wearable device, the GATOR system, which integrates inertial measurement units (IMUs) and ultrasound to produce an objective composite knee function score, PRIME.

In a prospective cohort of 90 participants (180 knees), PRIME scores were obtained for healthy, injured, and contralateral knees, with concurrent IKDC scores. Descriptive statistics and non-parametric tests compared groups. Spearman correlation and univariate linear regression assessed the relationship between PRIME and IKDC, with the primary correlation analysis restricted to injured knees. Receiver operating characteristic (ROC) analysis evaluated the ability of PRIME to discriminate injured from healthy knees, and the optimal PRIME cut-off was derived using the Youden index. The minimal detectable change (MDC) of PRIME was estimated from the variability in healthy knees.

PRIME scores were highest in healthy knees, intermediate in contralateral knees, and lowest in injured knees, with statistically significant differences between all groups (p < 0.001). In injured knees, PRIME showed a moderate-to-strong correlation with IKDC (ρ = 0.54, p < 0.001), whereas no significant correlation was observed in healthy knees, likely reflecting ceiling effects. ROC analysis yielded an AUC of 0.846. A PRIME cut-off of 71.2 points optimally discriminated injured from healthy knees (sensitivity 74.5 %, specificity 82.1 %). The MDC for PRIME was 39.1 points, suggesting that changes exceeding this threshold likely represent true change beyond measurement error.

PRIME appears to be a valid, objective measure of knee function that correlates with patient-reported outcomes in pathological knees and demonstrates good discriminatory performance for detecting knee injury.