Finite Element Analysis of the Wrist Arthroplasty in Rheumatoid Arthritis - Computational Biomechanics of the Wrist Joint - page 60

date [ 8 ]. Similarly, the total knee replacement (TKR) procedure possessed sub-
stantially high success rates due to the existence of sufficient bony support to
provide stability [ 9 ]. In total wrist arthroplasty (TWA) procedure, despite of
resecting all the affected regions at the bones as observed in THA and TKR, the
TWA requires several bones to be remained assuring sufficient bony support
(Fig. 6.1 ). The existing bony support which consists of small bones of carpus;
normally the distal row is likely to experience micromotion [ 10 ]. This explains why
solid bony supports at the carpal regions of the joint become extremely problematic.
Consequently, a study to investigate the behaviour of this motion is prudent, par-
ticularly during pre (RA) and post surgery (after TWA). Therefore, this chapter was
presented to highlight the efforts performed to investigate the biomechanical
behaviours of the rheumatic wrist during pre and post surgery, using finite element
analysis.
6.2 Finite Element Modelling of the Total Wrist Arthroplasty
In this simulation, the latest wrist joint replacement, ReMotion TM produced by
Small Bone Innovations, was occupied [ 11 ]. CAD software, Solidworks 2009
was used to model the implant, whereas MARC.MENTAT software used to
convert the model into surface triangular elements. Similar to the real surgical
procedure, the scaphoid, lunate and some parts of the capitate and triquetrum were
resected, and followed by the installation of the implant component to their
respective bones. All parts were then converted into solid tetrahedral mesh with
1,305,415 elements and 277,070 nodes. These steps are illustrated in Fig. 6.2 .
6.3 Finite Element Analysis: Pre-Processing Procedures
For contact modelling, articulating surfaces were established with deformable-to-
deformable contact. Surface roughness at the carpal plate component was set at 0.8
simulating its rough surface to support osseointegration [ 15 ]. The effect of screw
thread in preventing any slippage at the contacting surfaces was simulated [ 16 ].
Physiological movements are allowed for the remaining contacting bodies.
Bones of the wrist in the TWA were modelled as having the same properties as
the RA model (the cortical bone; E = 12 GPa, m = 0.2 and the cancellous bone;
E = 33 MPa, m = 0.25). They were modelled to incorporate linear elastic, iso-
tropic and homogenous properties. Implant components (radius component, carpal
plate, central peg and screws) were assigned with properties simulating CoCrMo
alloys (E = 210 GPa, m = 0.3) [ 17 ], whereas the carpal ball was assigned with
UHMWPE properties (E = 1.4 GPa, m = 0.3 [ 18 ]). The bone graft modulus was
varied (E = 0.1, 1 and 5 GPa, m = 0.2 [ 19 ]) to analyse their effects in performing
intercarpal fusion. These parameters are summarised in Table 6.1 .