Finite Element Analysis of the Wrist Joint Affected by Rheumatoid Arthritis - Computational Biomechanics of the Wrist Joint - page 50

insertion of the tendons (abductor pollicis longus muscle, flexor carpi radialis
muscle, flexor carpi ulnaris muscle, extensor carpi ulnaris muscle, extensor carpi
radialis brevis muscle, extensor carpi radialis longus muscle) were fixed prohib-
iting motion at the x and y directions, to enable movements of all bones (excluding
the proximal ends of the radius and ulna) in the direction of the applied loading
[ 19 ]. All these settings worked as input of the FE analyses using Marc. Mentat
(MSC.Software, Santa Ana, CA) software.
5.3 Biomechanical Behaviours of the Rheumatic Wrist Joint
5.3.1 Comparative Analysis
As far as the reliability of the results and model created were concerned, com-
parison was made between literatures and findings from our study. Results from
finite element analyses were used (Fig. 5.11 ). It was addressed that all of the five
aspects of stress transfer emphasized in the previous studies were in agreement
with our investigation [ 18 , 20 , 29 - 33 ]. One of them was the percentage of load
transmission through the radiocarpal and midcarpal joints as reported by Patterson
et al. They have found that the scaphoid sustained 60.0 % of the load and the other
40.0 % by the lunate [ 29 ]. The same finding was observed in our study where the
scaphoid was subjected with the higher load as compared to the lunate, 63.4 and
65.3 % for the healthy and RA models, respectively.
In their cadaveric studies, Macleod et al. [ 30 ] have revealed that 68.0 % of the
load through the forearm was transferred to the radius, whereas Gislason et al. [ 18 ]
have came out with a range of 78.7-92.8 % from his simulation studies. These
studies notably addressed the role of the radius as a major load bearer in the wrist
joint. Our study presents similar findings where 77.8 % of the load was transferred
to the radius and the remaining to the ulna. For the RA model, a higher percentage
of 87.3 % of the load was transferred to the radius thus leads to imbalance of stress
distribution.
This study revealed that the load was transferred radially throughout the wrist
joint, similar to the simulation studies by Gislason et al. [ 20 ] and experimental
work by Givissis et al. [ 31 ]. In comparison with the RA model, higher stress
concentration was found at the radial side of the healthy model (63.34 %), whereas
a lower percentage of loads (60.99 %) were found at the RA model.
Comparison was also made on the strain magnitude of the radius bone. Bosisio
et al. [ 32 ] have addressed an ultimate strain value for the cortical radius
(e u = 1.5 ± 0.1 %) as well as the yield strain (e y = 0.9 ± 0.2 %). Another study
by Kerin et al. [ 33 ] have reported a failure strain value of the cartilage under
compression to be 30 %. In this study, analyses at the diaphysis of the distal radius
showed that the strain value of the cartilage of the healthy model was on average
e = 1.4 %. The corresponding value for the cortical bone of the healthy and RA