A biomechanical analysis of the healthy and the pathological index finger during pinch function

In this work, a biomechanical model of the index finger is used to get an insight into the mechanism that controls the index musculoskeletal system. Our simulation is intended to determine how different muscles groups are acting on different joints in producing adequate static maximal fingertip forces and moments. The model is then modified to simulate injured fingers with extensor mechanism loss. We investigated two common pathologies that affect the extensor mechanism, i.e., Mallet and Boutonniere lacerations. We used a biomechanical model based on robotic principles and an optimization technique to solve the muscular redundant problem over the 3 joints of the forefinger system. The role of each tendon was quantified in the case of the healthy finger as well as in the pathological one. We showed, in particular, that the loss of strength in the finger can be regained by an increase of the tension in the interosseous tendons; however, this increase can be a source of instability in the pinch task.