Benjamin Dourthe

Quantifying thumb opposition kinematics using dynamic computed tomography

Current motion capture techniques all have shortcomings when applied to the 3D quantitative evaluation of thumb base motion. Dynamic CT might overcome these shortcomings but, so far, robustness of this technique in more than one specimen has not yet been demonstrated. The aim of the current study is to further evaluate the use of dynamic CT for quantification of thumb motion in a larger cadaveric study using a protocol which is feasible in a clinical context. A dynamic CT scan was acquired from six cadaveric human forearms, while a motion simulator imposed thumb opposition. After image acquisition and segmentation, carpal bone motion was quantified using helical axes. To enable comparisons between specimens, intersection points of the instantaneous helical axis with an anatomically defined plane were determined. Precision of the dynamic CT method, measured as variation in distances between silicon nitride beads between frames of a dynamic scan, was 0.43mm (+/-0.09mm) when fixed to the skin and 0.13mm (+/-0.04mm) when embedded into the bone. Absolute deviation between known and measured distances were not larger than 0.34mm. We could demonstrate and quantify that thumb opposition is associated with motion at the trapeziometacarpal and scaphotrapezotrapezoidal joints. High consistency in motion patterns between specimen were found, while the radiation dose was limited. We conclude that dynamic CT can be used to visualize and quantify 3D thumb kinematics, making it a promising method to explore kinematics in vivo.

In vivo kinematics of the thumb during flexion and adduction motion: Evidence for a screw‐home mechanism

The thumb plays a crucial role in basic hand function. However, the kinematics of its entire articular chain have not yet been quantified. Such investigation is essential to improve our understanding of thumb function and to develop better strategies to treat thumb joint pathologies. The primary objective of this study is to quantify the in vivo kinematics of the trapeziometacarpal (TMC) and scaphotrapezial (ST) joints during flexion and adduction of the thumb. In addition, we want to evaluate the potential coupling between the TMC and ST joints during these tasks. The hand of 16 asymptomatic women without signs of thumb osteoarthritis were CT scanned in positions of maximal thumb extension, flexion, abduction, and adduction. The CT images were segmented and three‐dimensional surface models of the radius, scaphoid, trapezium, and the first metacarpal were created for each thumb motion. The corresponding rotations angles, translations, and helical axes were calculated for each sequence. The analysis shows that flexion and adduction of the thumb result in a three‐dimensional rotation and translation of the entire articular chain, including the trapezium and scaphoid. A wider range of motion is observed for the first metacarpal, which displays a clear axial rotation. The coupling of axial rotation of the first metacarpal with flexion and abduction during thumb flexion supports the existence of a screw‐home mechanism in the TMC joint. In addition, our results point to a potential motion coupling between the TMC and ST joints and underline the complexity of thumb kinematics.

In vivo contact biomechanics in the trapeziometacarpal joint using finite deformation biphasic theory and mathematical modelling

The assessment of the contact biomechanics in the trapeziometacarpal (TMC) joint during functional tasks represents a relevant way to obtain a better understanding of the onset of osteoarthritis (OA). CT scans of the hand region of 20 female volunteers were taken in relaxed neutral, lateral key pinch and power grasp configuration. 3D models of the first metacarpal (MC1) and the trapezium were created. The articular area of each bone was quantified and a mathematical model was developed in Matlab to evaluate the projected contact area and stress distribution of each bone. The articular areas of the MC1 and the trapezium presented no significant difference. A slightly smaller projected contact area was calculated for the trapezium compared to the MC1. Similar amounts of stress were reported in the neutral and lateral pinch configurations. The highest stress levels were observed during power grasp. Very consistent results for high stress location on the volar/radial articular sub-region were found in the neutral and power grasp configurations. More variation was reported during lateral pinch. The mathematical model presented in this paper offers the possibility to predict contact patterns within the TMC joint based on in vivo CT images.

In vivo biomechanical behavior of the trapeziometacarpal joint in healthy and osteoarthritic subjects

Background: The contact biomechanics of the trapeziometacarpal joint have been investigated in several studies. However, these led to conflicting results and were mostly performed in vitro. The purpose of this study was to provide further insight on the contact biomechanics of the trapeziometacarpal joint by in vivo assessment of healthy and osteoarthritic subjects. Methods: The hands of 16 healthy women and 6 women with trapeziometacarpal osteoarthritis were scanned in positions of maximal thumb extension, flexion, abduction and adduction during three isometric tasks (lateral key pinch, power grasp and jar twist) and in thumb rest posture (relaxed neutral). Three‐dimensional surface models of the trapezium and first metacarpal were created for each thumb configuration. The articular surface of each bone was measured in the neutral posture. A computed tomography‐based proximity mapping algorithm was developed to calculate the distance between opposing joint surfaces, which was used as a surrogate for intra‐articular stress. Findings: Distinct proximity patterns were observed across tasks with a recurrent pattern reported on the volar aspect of the first metacarpal. The comparison between healthy and arthritic subjects showed a significantly larger articular area, in parallel with a significant joint space narrowing and an increase in proximity area in arthritic subjects. We also observed severe articular deformations in subjects with late stage osteoarthritis. Interpretation: This study has increased our insight in the contact biomechanics of the trapeziometacarpal joint during tasks and positions of daily life in healthy and arthritic subjects, which might contribute to a better understanding of the occurrence mechanisms of degenerative diseases such as osteoarthritis. HIGHLIGHTSAn approach based on joint proximity is proposed to assess the contact biomechanics of the thumb.Proximity patterns of healthy and late stage osteoarthritic subjects were compared.Healthy group: distinct proximity patterns were observed between tasks.Osteoarthritic group: severe morphological changes were observed.Findings suggest an association between proximity patterns and osteoarthritis development.