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Finite element (FE) simulations can be utilized to predict contact pressures at the bone/implant interface as well as to identify the position and shape of the contact region. However, the accuracy and reliability of FE models of the bone/implant interface reconstructed from tomographic images may be affected by a number of factors such as the presence of image artifacts, the magnitude of geometric errors made in the reconstruction process, the type of boundary and loading conditions hypothesized in the model, the nonlinear solver utilized for computing the contact pressure distribution, and the element type. This paper attempts to estimate the global effect of the aforementioned factors. For this purpose, a cylindrical contact problem — pin/muff — portraying a simplified model of the bone/implant interface is considered. The accuracy of numerical predictions is estimated by comparing contact pressures predicted by an FE model reconstructed from computed tomography (CT) scan images and by an "ideal", experimentally validated FE model. Two different couplings, i.e. chromium-cobalt alloy and titanium implants, are considered. In the former case, image artifacts complicate the reconstruction process of model geometry and lead to less accurate predictions on contact pressure distribution; conversely, the limited streaking effects occurring in the titanium pin case allow us to precisely reconstruct coupling geometry. Finally, a rather clear correlation between errors on contact pressure and geometric errors made in the reconstruction process is found only for the titanium pin.

Background: The use of volar locking plate in distal radius fracture can lead to extensor tendon rupture due to dorsal screw penetration. The aim of our study was to investigate the occurrence of dorsal and intra-articular screw penetration using CT scan after volar distal radius osteosynthesis for distal radius fractures.

Methods: Thirty patients who underwent distal volar locking plate for distal radius fracture were included in a retrospective study. In all 30 patients no dorsal and intra-articular screw penetration were detected on standard AP and lateral views of a plain radiograph. CT scan of the operated wrist was performed to determine the number of intra-articular and dorsal screw penetrations. Clinical examination was performed to determine the wrist functions in comparison to the normal wrist.

Results: Nineteen wrists were noted to have screw penetration either dorsally or intraarticularly. The highest incidence is in the 2nd extensor compartment where 13 screws had penetrated with a mean of 2.46 mm. Six screws penetrated into the distal radial ulnar joint and five screws into the wrist joint with a mean of 2.83 mm and 2.6 mm, respectively. However, there was no incidence of tendon irritation or rupture.

Conclusions: This study demonstrated a high incidence of dorsal and intra-articular screw penetration detected by CT scan which was not apparent in plain radiograph. We recommend that surgeons adhere to the principle of only near cortex fixation and downsizing the locking screw length by 2 mm.

Background: Anatomical structure affects function. The morphology of articulations dictates the way forces will travel through the joint. A better understanding of the structure and function of the wrist will enhance our ability to diagnose and treat wrist conditions. Two wrist types have been described based on the morphology of the midcarpal joint. Biomechanically it is important to see if these 2-dimensional (2D) observations reflect articular contact areas. Our purpose was to assess the correlation between measurements performed on wrist radiographs (2D) to measurements performed on 3-dimensional (3D) computed tomography (CT).

Methods: Retrospective review of a database of normal wrist radiographs and corresponding normal CT scans. Only imaging pairs with normal carpal alignment and technically optimal imaging were included. Evaluations included lunate, capitate and wrist type, capitate circumference, percent capitate circumference and volume that articulates with the lunate, scapholunate ligament, scaphoid, hamate, trapezoid, base of the index and middle and ring metacarpal bones.

Results: Midcarpal joint radiographic measurements were positively correlated with measurements on CT scans. Correlations were 0.51 for capitate type and 0.71 for lunate type with both p < 0.001. Percent contact of the lunate with the hamate: r was 0.74 p < 0.001. Using logistic regression analysis, percent lunate-hamate contact on CT was a significant predictor of radiographic lunate type 2 p < 0.001. Percent contact area between lunate and hamate > 7.8% on CT scan achieved a sensitivity of 100% and specificity 79.4% for a type 2 lunate.

Conclusions: 1) Good correlations found between CT and plain radiographs in lunate type, capitate type, and midcarpal joint contact support the use of plain radiographs to describe contact between the carpal bones in the clinical setting. 2) The retrospective nature of this study limited the technical quality of the measurements. Volumetric analysis may aid in a more exact evaluation of surface contact area.