Biomechanical Properties and Behaviours of the Wrist Joint - Computational Biomechanics of the Wrist Joint - page 16

Fig. 2.2 The mechanical
sequence for the scapholunate
ligament [ 14 ]
Investigation on the effect of preconditioning routine has also been performed in
previous studies. It was found that the preconditioning routine by stretching the
ligaments enables averaging approach to the measurements [ 17 - 19 ]. This finding
was proven to be logical as in the first ten load cycles, the restraint force of ligament
for a given strain will decrease continually [ 19 ]. There was also a study with no
preconditioning performed, which resulted in high variability of the results
obtained [ 20 ]. Repeatable comparable data was one of the aims of these experi-
ments. Out of these experimental studies, it was addressed that many difficulties
faced due to the complexity of the carpal ligaments (the dimensions and shapes as
well as the structures of the bones and articulations), and also the results obtained
were incomparable with findings from knee ligaments experimental works [ 17 - 19 ].
Stiffness as one of the critical parameters has been addressed and its elastic
modulus was found possible to be calculated once the physical dimensions of the
ligaments were obtained. The stiffness of the extrinsic carpal ligaments has been
discovered in previous works. It was found that the magnitude for the corre-
sponding ligaments range from 10.9 to 46.4 N/mm [ 17 ]. It was also discovered that
in neutral posture of the wrist, some of the ligaments were actually in tension [ 19 ].
Despite of the complex structure of the intrinsic ligaments which has thus far
received little attention, their mechanical properties as found in several studies
were profound and sufficient to be utilised in future studies. The stiffness of these
intrinsic ligaments which range from 40 to 350 N/mm was obviously higher as
compared to the extrinsic carpal ligaments. This difference was therefore showed
that the mechanical properties of ligaments were highly dependent on its physi-
ological location.
Overall, previous studies have progressively investigated the behaviour and
properties of the ligaments associated with the wrist joint. A wide range of vari-
ability was reported, not only among different studies, but also among specimens
within a given study comparing the same ligament. Despite these inconsistencies,
the reported works significantly provide constructive fundamentals for specifying
ligament behaviours, assisting better understanding on the static and kinematics of
the wrist joint.