Biomechanical Studies on Hand Function in Rehabilitation

Hand function requires interaction of muscles, tendons, bones, joints and nerves. The unique construction of the hand provides a wide range of important functions such as manipulation, sense of touch, communication and grip strength (Schieber and Santello 2004). The hand is used in many ways, and in many different situations in our daily lives; so injuries, diseases or deformities of the hand can affect our quality of life. Several of our most common injuries and diseases affect hand function. Therefore, it is very important to understand how healthy and diseased hands work in order to be able to design optimal rehabilitation strategies pursuant to hand injury or disease. There are many different methods used today for evaluating hand and finger functions. One widely accepted method that provides an objective index of the hand and finger functions is hand force measurement (Balogun, Akomolafe et al. 1991; Innes 1999; Incel, Ceceli et al. 2002). There is also a potential for using modern non-invasive methods such as ultrasound and finger extension force measurements, but these have not been completely explored so far. An important factor in developing grip force is the synergy between the flexor and extensor muscles. The extensor muscles are active when opening the hand, which is necessary for managing daily activities (Fransson and Winkel 1991). Even though the extensor muscles are important for optimal hand function, surprisingly little attention has been focused on these muscles. It has, however, been difficult to evaluate hand extension force, since there is no commercially available measurement instrument for finger extension force. In addition, because of the lack of a device to assess extension force, there is limited basic knowledge concerning different injuries and how diseases affect the static and dynamic forearm muscle architecture or/and muscle interaction. Impaired grip ability in certain diseases such as Rheumatoid Arthritis (RA) could be caused by dysfunctional extensor muscles leading to inability to open the hand (Neurath and Stofft 1993; Vliet Vlieland, van der Wijk et al. 1996; Bielefeld and Neumann 2005; Fischer, Stubblefield et al. 2007). Deformities of the MCP-joints are common, and may lead to flexion contractures and ulnar drift of the fingers. Weak extensor muscles may play a role in the development of these hand deformities. Furthermore, knowledge concerning how the muscles are influenced by RA and the mechanism of muscle force impairments is not fully understood for RA patients. This group of patients would benefit from further hand/finger