Abstract
The aim of the study was to investigate, firstly, the force distribution between scaphoid/radius and lunate/radius in the normal wrist and in the presence of a scaphoid fracture, secondly, how stresses and strains at the fractured area change during the healing process and thirdly, how the direction of the applied forces affects load transmission.
A 3D finite element model of the normal wrist was initially developed. Two typical scaphoid fractures B2 and B3 according to Herbert’s classification, were investigated. The fractured areas were modeled with a range of modulus of elasticity to resemble the various stages of the healing process. Furthermore, three different directions of the externally applied loads were examined.
The applied compressive vertical load in the normal joint was transmitted to the radius through the radioscaphoid and the radiolunate articular surfaces at a ratio equal to 56:46 respectively. The ratio was equal to 54:48 and 53:49 for the B2 and the B3 fracture respectively. The load direction resembling an ulnary deviated wrist caused the appearance of a significantly higher strain field at the fractured area. The maximum developed stresses at the fractured area for scaphoid fracture B2 were approximately 37%–58% higher than those of B3, for all three loading directions.
Based on our results, the onset of osteoarthritic changes in a wrist with a scaphoid fracture is due to carpal collapse and scaphoid deformity. The recorded maximum developed strains for both B2 and B3 scaphoid fractures suggested intense bone remodeling activity. Among the examined three different load directions, the one simulating an ulnary deviated wrist corresponded to the most severe effects.
Correspondence should be addressed to Anastasia C. Tilentzoglou MD, General Secretary of the Board of Directors of HAOST, 20 A. Fleming Str. (N.Filothei), Gr. 15123 Maroussi, Athens Greece. E-mail: info@eexot.gr
