Anatomical factors predisposing to focal dystonia in the musician's hand--principles, theoretical examples, clinical significance.

In this paper, anatomical interconnections between tendons, between tendons and their environment, and anatomical constraints on joint mobility are considered as possible causes of focal dystonia in the hand of the musician. By hypothesis, focal dystonias arise when the constraints on movement resulting from these anatomic limitations impede playing movements with sufficiently low energy expenditure. This hypothesis is modelled for connections between the deep finger flexors. The displacements, forces, stresses, and work per volume in the finger motors in some common piano playing movements are calculated. The results indicate that with mentioned connections, in certain movements the extensor and lumbrical, and in others the lumbrical and interossei are most strained, while the interossei may become the main power source in loaded instrumental movements. Also discussed are compensatory movements. The biomechanical principles of surgical and conservative treatment are summarised.