Abstract
This study investigated how the posture of the thumb while performing common pinch movements and the levels of pinch force applied by the thumb affect the arthrokinematics of the trapeziometacarpal joint in vivo. Fifteen subjects performed the pinch tasks at the distal phalange (DP), proximal interphalangeal (PIP) joint, and metacarpophalangeal (MP) joint of the index finger with 0%, 50%, and 80% of maximal pinch forces by a single-axis load cell. 3D images of the thumb were obtained using the computed tomography. The results show that the reference points moved from the central region to the dorsal-radial region when changing from pinching the DP to the MP joint without pinching force being applied. Pinching with 80% of the maximum pinching force resulted in reference points being the closest to the volar-ulnar direction. Significant differences were seen between 0% and 50% of maximum pinch force, as well as between 0% and 80%, when pinching the MP joint in the distal-proximal direction. The effects of posture of the thumb and applied pinch force on the arthrokinematics of the joint were investigated with a 3D model of the trapeziometacarpal joint. Pinching with more than 50% of maximum pinch force might subject this joint to extreme displacement.
Highlights
Human hands play an important role in performing various daily activities, most of which involve grasping and pinching actions
When the MP joint is pinched, the reference points seem to move towards the dorsal-radial direction from the resting position and glide towards the volar direction when there is an increase in force
Efforts were made to find the contact patterns of joint gliding by simulating functional pinching in Gliding ratio radial(+)/ulnar(−) (%)
Summary
Human hands play an important role in performing various daily activities, most of which involve grasping and pinching actions. Sufficient muscular strength, and appropriate hand sensations are required to accomplish coordinated thumb-finger interactions [1, 2], and a well-integrated thumb-finger relationship is regarded as a crucial element in a variety of tasks which are based on power grip or precision pinch performance [3,4,5]. Among the numerous factors that contribute to such performance, a proper thumb, with either structural or functional integrity, is one indispensable component. The multidirectional and wide motion ranges of the thumb are essential elements in activities requiring grasp and pinch functions. The results indicate that the average range of motion of the TMC joint is from 41∘ to 47∘ in flexion-extension, from 53∘
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