An update on phantom hand and wrist movements in upper limb amputees
People often experience pain after limb amputation with a vivid perception of the presence of the missing limb known as phantom limb pain. Apart from the pain sensations, patient with phantom limb may experience other phantom sensations including voluntary movements.
Recently a randomized study was conducted to quantify the phantom movement kinematics and relate these to intact limb kinematics and to the time elapsed since amputation. Phantom finger, hand and wrist movements at self-chosen comfortable velocities were performed by six upper arm and two forearm amputees with various delays of 6 months to 32 years.
Cyberglove® was used for measuring finger movements and an inertial measurement unit for wrist movements. The kinematics of the phantom movements was indirectly obtained through the intact limb that synchronously copied the phantom limb movements.
The results indicated that the execution of phantom movements is perceived as “natural” but effortful. The different phantom movements were found to be varying from one patient to another. However, thumb flexion/extension and global hand opening/closure was performed by all the patients. Finger extension movements were found to be 24% more faster than finger flexion movements. The number of types of phantom movements that can be executed and kinematic characteristics were not linked to the elapsed time since amputation, which emphasize the existence of post-amputation neural adaptation.
This study summarizes that the perceived slowness of phantom movements is connected to altered proprioceptive feedback that cannot be recalibrated by lack of visual feedback during phantom movement execution.