The Wrist Joint - Computational Biomechanics of the Wrist Joint - page 8

the ligaments structure including the histology, shape and the composition. The
general nomenclature was also identified; where the names of the ligaments were
given based on the bones they connect, from proximal-to-distal and radial-to-ulnar
paths. Potential biomechanical functions have also been considered to summarise
the ligaments of the wrist [ 5 , 20 ].
Significantly, previous studies have showed variability in sizes and structures of
the ligaments in the wrist joint. In a study by Nowalk et al. [ 21 ] revealed that the
cross-sectional area of 12 investigated radiocapitate ligaments was 8 mm 2 (stan-
dard deviation of 1.3 mm 2 ) and the length was 10 mm (standard deviation of
1 mm). In a study on 90 cadaveric wrists, it was demonstrated that the ligaments
seem to have large range of size [ 22 ]. For instance, the dorsal radiocarpal liga-
ments range in width at the proximal end between 5.5 and 17.8 mm and in length
between 13.8 and 29.4 mm. They also addressed three distinct shape categories for
the dorsal intercarpal ligament and four distinct shape categories for the dorsal
radiocarpal ligament [ 22 ]. Thus, these findings induced a noteworthy conclusion,
where there should be no standardisation to define the kinematics of the wrist joint
due to huge existing variability found in the ligamentous structure.
1.5 Kinematics
In comparison with other common joints like the knee and the hip, the wrist is an
extremely mobile organ. Two main factors lead to its great mobility; multi-planar
geometry of the articulation surfaces and complex ligamentous interactions [ 5 ].
The principle of ''variable geometry'' is naturally implemented which enable the
great range of motion of the wrist joint. This concept caused the multi-directional
relative motion between individual carpal bones. Kinematic behaviour of both
static and dynamic postures through planar (in both sagittal and coronal planes)
and non-planar motions has been thoroughly examined in previous reports.
As far as the kinematics of the wrist joint was concerned, it was vital to identify
of the center of rotation for the primary axes of flexion-extension or radial-ulnar
deviation. There were studies attempted to tackle this issue, however, to date, none
of them have successfully established the exact location, thus came with several
assumptions. The head of the capitate was assumed to be the center of rotation, the
axis connecting the styloid process of the radial and ulnar was assumed as the axis
of flexion-extension whereas for the radial-ulnar deviation, the axis was assumed
to be oriented orthogonal to the flexion-extension axis [ 23 - 28 ]. Out of these
complete ranges, its lesser functional range of motions has also been suggested to
range from 40 o extension to 40 o flexion in the sagittal plane, and the arc of motion
for radioulnar deviation in the coronal plane of 40 o [ 7 ].
There were studies performed on the nature and direction of the carpal bones.
One of the findings was that a single functional model of the wrist was not likely to
be determined [ 29 , 30 ]. There were also no significant differences found in a
gender-based analysis performed in a study by Wolfe et al. [ 31 ]. This finding was