Journal of Back and Musculoskeletal Rehabilitation 18 (2005) 45–49
Terminology used in the analysis of joint
Mirthe de Groot
, Cornelis W. Spoor and Chris J. Snijders
Department of Biomedical Physics and Technology, Erasmus MC, University Medical Center Rotterdam,
Rotterdam, The Netherlands
. Joint function is described by biomechanical parameters like range of motion (ROM), stiffness, laxity and stability.
However, these terms are frequently used ambiguously. Due to the lack in standardisation, it is difficult to compare results of
examinations. A literature survey is performed and an inventory is made about the definitions used for the terms. The final
definition for ROM is the range of translation and rotation through which a joint may be actively or passively moved in a certain
direction. Joint stiffness describes the resistance of the joint to imposed relative movement between two joint surfaces. Laxity
is the normal amount of motion that results from passive forces or moments and stability is the ability to control positions or
movements of joints.
Keywords: Stiffness, laxity, range of motion, stability
A human joint can be viewed as a collection of mov-
able parts whose purpose is to accept, transfer and dis-
sipate loads generated at the lever arms of bones .
The joint should manifest normal biomechanical pa-
rameters such as laxity, stiffness, range of motion and
stability to achieve normal function in daily life. These
terms are closely related to each other.
A lot of articles describe studies of the assessment of
these parameters. However, clinicians and researchers
do not always give a clear description of the joint func-
tion they measured [15,28]. In other cases, descrip-
tions are given, but they are not unambiguous [27,36].
It is hard to communicate and it is also very difficult
to compare measurements when the definitions are not
clear or even not given.
To come to clear terminology, a literature survey is
done. The definitions are studied and compared to
Address for correspondence: Mirthe de Groot, Department of
Biomedical Physics and Technology, Erasmus MC, University Med-
ical Center Rotterdam, P.O. Box 1738, 3000 DR Rotterdam, The
Netherlands. Tel.: +31 10 4087375; Fax: +31 10 4089463; E-mail:
each other. Finally, overall conclusions about the terms
are made. The findings of this literature survey are
considered below and they are summarised in Table 1.
2.1. Range of motion
With the combination of uniaxial, biaxial and mul-
tiaxial joints, the body is able to adopt a multitude of
functional positions. The range of motion (ROM) of
a joint is the range of rotation or translation through
which a joint can be moved between the physiologic
extremes. The ROM can be expressed for each of the
six degrees of freedom. For example, one ROM of
the shoulder joint (Fig. 1) would be the number of de-
grees rotated between the points of full extension and