Abstract
Much of the published works assessing the reliability of smartphone goniometer apps
(SG) have poor generalizability since the reliability was assessed in healthy subjects.
No research has established the values for standard error of measurement (SEM) or
minimal detectable change (MDC) which have greater clinical utility to contextualize
the range of motion (ROM) assessed using the SG. This research examined the test–retest
reproducibility, concurrent validity, SEM, and MDC values for the iPhone goniometer
app (i-Goni; June Software Inc., v.1.1, San Francisco, CA) in assessing knee ROM
in patients with knee osteoarthritis or those after total knee replacement. A total
of 60 participants underwent data collection which included the assessment of active
knee ROM using the i-Goni and the universal goniometer (UG; EZ Read Jamar Goniometer,
Patterson Medical, Warrenville, IL), knee muscle strength, and assessment of pain
and lower extremity disability using quadruple numeric pain rating scale (Q-NPRS)
and lower extremity functional scale (LEFS), respectively. Intraclass correlation
coefficients (ICCs) were calculated to assess the reproducibility of the knee ROM
assessed using the i-Goni and UG. Bland and Altman technique examined the agreement
between these knee ROM. The SEM and MDC values were calculated for i-Goni assessed
knee ROM to characterize the error in a single score and the index of true change,
respectively. Pearson correlation coefficient examined concurrent relationships between
the i-Goni and other measures. The ICC values for the knee flexion/extension ROM were
superior for i-Goni (0.97/0.94) compared with the UG (0.95/0.87). The SEM values were
smaller for i-Goni assessed knee flexion/extension (2.72/1.18 degrees) compared with
UG assessed knee flexion/extension (3.41/1.62 degrees). Similarly, the MDC values
were smaller for both these ROM for the i-Goni (6.3 and 2.72 degrees) suggesting smaller
change required to infer true change in knee ROM. The i-Goni assessed knee ROM showed
expected concurrent relationships with UG, knee muscle strength, Q-NPRS, and the LEFS.
In conclusion, the i-Goni demonstrated superior reproducibility with smaller measurement
error compared with UG in assessing knee ROM in the recruited cohort. Future research
can expand the inquiry for assessing the reliability of the i-Goni to other joints.
Keywords
goniometer - reliability - knee range of motion
