Validity of remote systems
Cervical rotation measurement by the CV-aided system was moderately correlated to a clinician assessment in the axSpA group and weakly correlated in the non-back pain groups (Table 4); in the axSpA group, the CV-aided system demonstrated a –2.6cm bias compared to the reference physiotherapist measurement with a positive regression slope (Figure 2). Lumbar forward flexion and hip internal rotation were strongly correlated in both the axSpA and non-back pain groups; both demonstrated a postive bias (+0.4cm and +3.7cm, respectively) with one outlier beyond the limits of agreement. Shoulder flexion and lumbar side flexion showed a strong to very strong correlation in axSpA group and moderate to weak correlation in non-back pain group. Shoulder flexion demonstrated a negative bias (right –3.0 degrees, left –1.4 degrees) with a slightly negative slope, and lumbar side flexion demonstrated minimal bias (right –0.6cm, left 0cm). Hip abduction was moderately correlated in axSpA group and demonstrated moderate to strong correlation in the non-back pain group. Metrics for posture showed strong correlation for tragus-to-wall distance (TWD) and thoracic kyphosis measurement in the axSpA group, yet very weak (TWD) to moderate (kyphosis) correlation in the non-back pain group; lumbar lordosis was not significantly correlated in either group (Table 4). All measurements showed agreement in the axSpA group with minimal bias (TWD –0.9, kyphosis +0.4, lordosis +0.2); TWD has a positive slope and kyphosis and lordosis have negative slopes, all with few outliers (Figure 3).