Validation of a Novel Smartphone Accelerometer-Based
Knee Goniometer

Ockendon M & Gilbert RE.  J Knee Surg. 2012 Sep;25(4):341-5. 

knee range of motion (ROM) is a common clinical practice among most healthcare
professionals, especially when monitoring ROM to track post-surgical outcomes.  Goniometers, accelerometers, and
inclinometers are some examples of instruments that have been used to assess
knee ROM.  Smartphones have built in accelerometers
for various uses; therefore, the purpose of this study was to evaluate the
reliability of a Smartphone knee goniometry application for assessing knee
ROM.   The authors designed an application
for the iPhone (“Knee Goniometer”) that estimates knee ROM by utilizing tibial
incline measurements and basic trigonometry when placing the phone on the
mid-shaft of the tibia.  Two independent
and blinded clinicians measured 3 simulated joint angles bilaterally in 5
healthy males utilizing the iPhone application as well as a goniometer.  The intra- and inter-observer reliability of a
traditional goniometer were excellent with correlations of 0.93 and 0.95 and
standard errors of ± 9.6 degrees and ±
8.4 degrees, respectively.  In
comparison, the intra-and inter-observer reliability of the iPhone application
were mildly better with correlations of 0.98 and 0.99 and standard errors of ±
4.6 degrees and ± 2.7 degrees,
respectively.  The authors found there
was a high correlation between instruments (r = 0.95) and a mean difference of
only -0.04 degrees.           

the athletic trainer may have a valid and reliable application readily
available in their pockets for clinical ROM knee measurements.  Truthfully, the smartphone may take out some
of the ambiguity and user error often associated with the use of a traditional
goniometer, potentially providing a more accurate and universally accepted
method to measure ROM.   The possible
implications of an application like this could mean more accurate interobserver
results.  Furthermore, this method for
measuring ROM could have implications on the compliance and monitoring of ROM
during home exercise programs. Athletes may be able to track and report their
ROM to the clinician daily, or even multiple times throughout the day. However,
there results should be interpreted with mild caution.  Interestingly, the authors of the paper are
the creators of the application “Knee Goniometer.” Curiosity led me to the App
Store for independent investigation of this potentially useful
application.  Much to my surprise, the
application could be purchased for $4.99. 
While the authors did demonstrate that this application was valid and
reliable in comparison to currently utilized clinical knee ROM measures, they
have a bias in conducting this research as it has a financial implication to
them personally.  It would have been more
interesting to see a third party, independent group investigate the clinical
usefulness of this application.  Does
anyone have any experience with an application like this?  Furthermore, does anyone have any smartphone
applications that they find clinically useful?  

by: Nicole Cattano 
by: Stephen Thomas


Ockendon M, & Gilbert RE (2012). Validation of a novel smartphone accelerometer-based knee goniometer. The Journal of Knee Surgery, 25 (4), 341-5 PMID: 23150162