An anatomical and biomechanical study of the stabilizing ligaments of the thumb trapeziometacarpal joint was conducted on 32 hand specimens. Five main ligamentous structures could be identified. The mechanical properties (in particular, strength) of the five ligaments using a strain-rate failure test were determined and evaluated quantitatively. The maximum tensile strength of each ligament was correlated with the condition of the trapeziometacarpal articular cartilage. In studying the anterior oblique ligament, maximum strength decreased from Grade 0 to Grade 1 by 51%. With the first intermetacarpal ligament, the drop from Grade 1 to Grade 2 was 53%. With the posterior oblique ligament, the decrease was closely related to the grade of the deterioration of the trapeziometacarpal articular surface. These three ligaments also significantly decreased in strength with age. Our results may suggest that the anterior oblique ligament, intermetacarpal ligament and posterior oblique ligament play a large role in stabilizing the trapeziometacarpal joint and that the decrease in their strength is related to the pathogenesis of trapeziometacarpal osteoarthritis.

A morphometric study has shown that 10% of the fibers of the ulnar nerve should suffice to reinnervate the biceps muscle in brachial plexus palsies. The aim of this study was to evaluate, by a morphometric study using computerized microanalysis, the cross-sectional surface areas of the different collateral and terminal branches of the ulnar nerve. This was expressed in terms of percentage of the cross-sectional surface area of the main trunk of the ulnar nerve. The study revealed that the branch to the flexor digitorum profundus bellies to the ring and little fingers formed 9.5% of the cross-sectional area of the ulnar nerve. Thus use of these fascicles destined for the flexor digitorum profundus, identified by intra-operative nerve stimulation, at the level of the arm would be sufficient for neurotisation of the nerve to the biceps. This has been confirmed by the initial clinical results in patients operated upon using this technique.

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