Roentgen stereophotogrammetric analysis (RSA) can be utilize
d to accurately
describe joint kinematics, but even when measuring small
displacements within ra
diographically
discernible structures, stan
dar
dize
d reference frames are imperative for useful comparison across patients an
d across stu
dies. In the current paper, accurately controlle
d laboratory mo
dels
demonstrate
d the consi
derable influence that a mere 1.9-cm offset of the origin of the coor
dinate system from the rotation axes coul
d exert on translation measures when rotations were occurring. In a
ddition, the use of two
different coor
dinate systems to gauge translation on a ra
diographic anterior–posterior (A–P) knee laxity exam resulte
d in a significant correlation (
decoration:none; color:black"" href=""/science?_ob=MathURL&_method=retrieve&_udi=B6T82-4K7NHSN-5&_mathId=mml3&_user=10&_cdi=5074&_rdoc=30&_acct=C000050221&_version=1&_userid=10&md5=a7f287145b07dcc159a3716a77c1dbb3"" title=""Click to view the MathML source"">R2=0.562) between the two systems; however,
differences of up 9.28 mm were foun
d between correspon
ding measurements. This implies that clinical conclusions can potentially be uphel
d or refute
d, base
d on the same
data set, subject to coor
dinate system
definition. Although the
data analyze
d presently involve
d the knee joint, similar issues surroun
d the RSA motion analysis of other joints as well.