###### Abstract  
The objective of this work is to design a rehabilitation mechanism for the index finger that can replicate the finger's natural movements in the sagittal plane; this mechanism must also be able to adapt to an individual's anthropometric dimensions. The personalization of the mechanism is made through a parametric model assisted by computer-aided design software. An infrared motion capture system is used to validate the natural finger movements, comparing them to the ones generated by the parametric designed mechanism. The replication of natural finger movements with this mechanism is possible due to the use of virtual centers and the employment of two degrees of freedom. One degree of freedom is proximal phalanx flexion-extension, and the other one is the middle-distal phalanges conjoined movement. The replication of natural motions and the use of personalization techniques offer three main advantages: a diverse set of rehabilitation exercises, an increase in the range of motion of the finger compared to other designs in the literature and the short construction time required for the rehabilitation device. finger; rehabilitation; glove; exoskeleton +
Footnote †: journal: Medical  
These single-action designs focus on extension assistance because, in stroke patients, hand function is often lost due to flexor hypertoronia and weakness in finger extensor muscles [15]. [PERSON] et al. [16] show that a critical success factor in rehabilitation therapy is the intensity and complexity of exercises the patient performs during therapy sessions. Complex hand movements in rehabilitation are essential since these allow for task-oriented training, which shows a favorable improvement in the capacity of the subject to carry ADLs [17]. The number of Degrees Of Freedom (DOFs) is directly related to the complexity and variety of movements that the glove can replicate [18]; therefore, at a surface level, more DOFs are equal to better rehabilitation for the patient. However, by increasing the DOFs, the cost of manufacturing and the difficulty of controlling the mechanism increases. For these reasons, it is necessary to find an equilibrium when selecting the number of DOFs [18]. In order to reproduce complex movements, it is also necessary to keep the assisting mechanism as least intrusive as possible, allowing for the ROM during rehabilitation to be the closest to the natural ROM of a healthy human hand. One solution to make a less intrusive mechanism is using virtual centers and cams, which allow the mechanism's hinges to be away from the finger's articulations. A mechanism that uses virtual centers is proposed in studies performed by [PERSON] [19; 20]. Nevertheless, this mechanism only transmits movement to the middle and proximal phalanges while having a limited range of motion, as just one design is made to fit a wide variety of patients. The ROM of the mechanism can be increased if it is designed specifically for each patient [21]. The quick personalization of a rehabilitation glove is possible thanks to the anatomical properties of the human hand. General anatomical studies of the phalanx and metacarpal bones in adults have found statistical ranges of up to 31.71 mm for the second finger's bone lengths [22]. This variation indicates a wide disparity of anthropometric measurements in individuals. Nevertheless, multiple studies have shown constant proportions between metacarpals and phalanges bones [23]. For example, in [24], equations have been proposed to obtain the metacarpals, proximal and middle phalanges lengths as a function of the distal phalanx. Other works study the proportions between the phalanges and metacarpals, and they have found these proportions to be different between each finger [25]. Hence, the best approach is to find individual proportions for each finger, as was found in [PERSON]'s [24] study. This research aims to produce a personalized finger rehabilitation mechanism design for the second human digit that has a broad ROM and is easy to manufacture.