Journal of Robotics, Networking and Artificial Life, Vol. 4, No. 3 (December 2017) 243–247___________________________________________________________________________________________________________A Piston Finger Device for Restoring the Motor Function of Chronic Plegic Fingers:
Analysis of the Piston Finger TechniqueMengsu Wang

Department of Electrical and Mechanical Engineering, Nagoya Institute of Technology,
Gokiso-cho, Syouwa-ku, Nagoya, Aichi 466-8555, Japan
Hirofumi Tanabe

Department of Health Sciences, Shonan University of Medical Sciences,
16-48 Kamishinano, Totsuka-ku, Yokohama, Kanagawa 244-0806, JapanKenji Ooka

Department of Electrical and Mechanical Engineering, Nagoya Institute of Technology,Gokiso-cho, Syouwa-ku, Nagoya, Aichi 466-8555, Japan
Yoshifumi Morita

Department of Electrical and Mechanical Engineering, Nagoya Institute of Technology,
Gokiso-cho, Syouwa-ku, Nagoya, Aichi 466-8555, Japan
E-mail: m.wang.188@nitech.jp, hirofumi.tanabe@sums.ac.jp, k.oooka.446@nitech.jp, morita@nitech.ac.jp
http://www.nitech.ac.jp/eng/index.html

Abstract
A piston finger technique (PFT) was developed for restoring the motor function of chronic plegic fingers, withgood treatment outcomes, including reduced spasticity and improved muscle shortening. Before developing a piston
finger device (PFD) simulating the PFT, we analyzed the PFT by using a motion capture system. The motion of achronic plegic index finger was investigated after administering two types of PFT-based treatment. The ranges ofmotion of the proximal interphalangeal and metacarpophalangeal joints of the index finger, and the vibration widthand frequency during treatment were measured. These results will be useful for developing a PFD.
Keywords: Piston finger technique, Plegic finger, Spasticity, Motion analysis, Piston finger device

and many patients are forced to give up self-sustaining
living.
In hand rehabilitation therapy, the therapist performs
treatment by moving the patient’s fingers passively.
However, because of the lack of therapists, many
patients do not receive adequate treatment. In view ofthis situation, we aimed to develop a rehabilitation
device to support therapists.

1. Introduction
The number of patients with cerebrovascular disease inJapan in 2014 has reached 1.179 million.1 The main
sequelae of cerebrovascular disease is hemiplegia, andapproximately 80% of patients with chronic hemiplegia
have chronic finger paralysis. Among the symptoms ofhemiplegia, the decreased motor function of the fingers
is the most difficult to recover. Owing to hand paralysis,
nursing care is needed in many situations in daily life

Copyright © 2017, the Authors. Published by Atlantis Press.
This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/).
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Journal of Robotics, Networking and Artificial Life, Vol. 4, No. 3 (December 2017) 243–247___________________________________________________________________________________________________________Currently, in Japan, a treatment method has beenused for therapeutic stimulation and motion
reconstruction of paralyzed limb according to uppermotor neuron disorders such as stroke and spinal cord
injury by therapeutic electrical stimulation andfunctional electrical stimulation.2 The hybrid assistive
neuromuscular dynamic stimulation (HANDS) therapy3
has been devised to encourage brain plastic change inchronic stroke hemiplegia patients and to improve upper
limb motor function and the quality of daily life. In thedevelopment of equipment supporting finger
rehabilitation, a perception support system has beendeveloped that allows biofeedback transfer from theparalyzed side motion to the non-paralyzed side so thatawareness can be directed to the paralyzed side
movement sensation through the non-paralyzed side.4 Inaddition, a new spasticity suppression method named
direct application of vibratory stimuli (DAVS)5 using
vibration stimulation has been devised, which has antispastic effects in the hemiplegic upper limbs of poststroke patients.
In other countries, the constraint-induced movement
therapy (CIMT)6 has been developed, to increase thefunctional use of the neurologically weaker upperextremity through massed practice while restraining thelesser involved upper extremity. A robotic interface fortraining hand and finger functions has been developed.
It is a cable-actuated rehabilitation system where eachfinger is attached to an instrumented cable loop thatallows force control and a predominantly linear
displacement.7
However, only a few studies have been conductedon the validation and motion analysis of manual
treatment methods. Moreover, only few research studies
have been conducted to develop rehabilitation devices
simulating the treatment method.

On the other hand, the second author developed apiston finger technique (PFT) for restoring the motor
function of chronic plegic fingers and has achieved
good treatment outcomes, including reduced spasticity
and improved muscle shortening.8 The PFT is treatment
for the purpose of temporary reduction of spastic
paralysis, which is used as a preparatory movement
before motor function restoration training.
In this study, we performed myoelectricmeasurement to demonstrate the effectiveness of PFT
for a paralyzed index finger. We also analyzed thefinger motion with the PFT by using a motion capturesystem to clarify the finger joint angles and thefrequency during the repeated motion by PFT. Based on
the analysis results, the specification of piston finger
device (PFD) was determined.
2. PFT and Its Treatment Effect2.1. What is PFT?
In general, when stretching treatment is applied tofingers with spasticity, the spastic muscle is temporarilyimproved. However, the spasticity often occurs again
when the patient bends the affected finger. This is oneof the troubles of many therapists engaged in thetreatment of hemiplegia.
PFT is a technique for improving adhesion of soft
tissues and spasticity. In the PFT, the therapist quickly
repeats flexion and extension of the patient’s finger
joints. The PFT can decrease flexor spasticity in a shorttime and improve muscle contraction. The effect lasts
longer than that by stretching treatment. Treatment withthe PFT by the second author is shown in Fig.1. and thePFT has two patterns which is shown in Fig. 2.8
In Pattern 1, the therapist, with one hand, holds and(a) Pattern 1(b) Pattern 2Fig. 2. Finger motion by piston finger technique8.

Fig. 1. Treatment with piston finger technique.

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Journal of Robotics, Networking and Artificial Life, Vol. 4, No. 3 (December 2017) 243–247___________________________________________________________________________________________________________After treatment, the Modified Ashworth Scale(MAS) scores of the extension of the patient’s plegicindex finger increased from 1 to 4. This means thatspastic paralysis was reduced. Electromyograms of theflexor digitorum superficialis muscle of the patient’splegic index finger before and after treatment are shownin Fig. 3. Figure 3 shows that the abnormal muscle toneof the paralyzed finger during MAS testing by thetherapist. The abnormal muscle tone was markedly
reduced after PFT treatment. This means that spasticity
was reduced by PFT and that the therapeutic effect wasconfirmed.

fixes the patient’s plegic thumb with full abduction, andwith the other hand, holds and moves the distal
phalange of the patient’s index finger. From the start
positions, the metacarpophalangeal (MP) and proximal
interphalangeal (PIP) joints are bended and extended,respectively. Then, the metacarpophalangeal (MP) joint
is bended and extended quickly and repeatedly, while
the proximal interphalangeal (PIP) joint is extended andbended quickly and repeatedly. PFT treatment is applied
to the index, middle, and ring fingers individually ortogether. After PFT treatment with Pattern 1, the flexor
spasticity of the four fingers diminishes.
In Pattern 2, the start positions of the MP, PIP, anddistal interphalangeal (DIP) joints are extended fully.
Then, the MP joint is bended and extended quickly andrepeatedly, while keeping the DIP and PIP joints in theextended position. After PFT treatment with Pattern 2the MP joints of four fingers can bend to the vicinity ofthe end feel within the range without feeling pain.

3. Analysis of the PFT
We analyzed the patient’s finger motion during PFT
treatment by using the VICON motion capture system(Vicon Motion Systems Ltd.).
3.1. Motion measurement

2.2. Treatment effect of PFTIn Pattern 1, as the DIP joint was kept fully extended,
we measured the PIP and MP joint angles of the index
finger as shown in Fig. 4(a). Six markers consisting of
two markers between the DIP and PIP joints, twomarkers between the PIP and MP joints, and twomarkers between the MP joint and the wrist wereattached on the center line of the middle phalanges,
proximal phalanges, and metacarpals of the index finger,respectively. Vectors v11, v12, v13, and v14 were defined
as shown in Fig. 4(a).

To verify the therapeutic effect of the PFT treatment,
the therapist applied the PFT treatment to the paralyzed
index finger of a male adult in his forties. The paralyticside was the left. Nine years had passed since the onsetof stroke.

(a) Before PFT treatment.

(b) After PFT treatment.
Fig. 3. Electromyograms of the flexor digitorum
superficialis muscle of a plegic index finger.

(a) Pattern 1(b) Pattern 2Fig. 4. Marker attachment positions and vectors defined forcomputation of joint angles.

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Journal of Robotics, Networking and Artificial Life, Vol. 4, No. 3 (December 2017) 243–247___________________________________________________________________________________________________________

4. Analysis of the Results of the PFTIn Pattern 2, as the DIP and PIP joints were kept
fully extended, we measured only the MP joint angle ofthe index finger as shown in the Fig. 4(b). Four markers
consisting of one marker between the DIP and PIPjoints, one marker between the PIP and MP joints, andtwo markers between the MP joint and the wrist wereattached on the center line of the middle phalanges,
proximal phalanges, and metacarpals of the index finger,
respectively. Vectors v22 and v23 were defined as shownin Fig. 4(b).

We analyzed the patient’s finger motion during
treatment by the therapist for 10 seconds. The time
histories of the PIP and MP joint angles during
treatment of Patterns 1 and 2 are shown in Figs. 6 to 8.
The summaries of the mean, maximum, and minimum
values of the joint angles at the start and end positionsof Patterns 1 and 2 are shown in Table 1.
In Pattern 1, we analyzed the joint angles in Figs. 6
and 7 from 2 to 10 sec. We found that the PIP joint
angle was moved by the therapist between 86.7° and155.4°, and the MP joint angle was moved between
140.4° and 172.6°. Moreover, the frequency of therepeated motion was found to be 4.3 Hz. From theresults of three dimensional motion analysis of flexionand extension of MP and PIP joints, we found that themotion of the fingertip can be approximated as linear
motion. The mean value of the vibration width of thefingertip was 30 mm.
In Pattern 2, we analyzed the joint angle in Fig. 8
from 0 to 10 sec. We found that the MP joint angle wasmoved between 109.5° and 141.4°. Moreover, thefrequency was found to be 3.6 Hz. From the results ofthree dimensional motion analysis of flexion andextension of MP joint, we found that the motion of thefingertip can be approximated as linear motion. The

3.2. Computation of joint angles
We computed the joint angles of the index finger duringtreatment. For this purpose, we measured the threedimensional coordinates of the markers with VICON
and computed the joint angles from the vectors shownin Fig. 4 (a) and (b). The PIP and MP joint angles weredefined as shown in Fig. 5.
In Pattern 1, the PIP and MP joint angles weredenoted by θPIP1 and θΜP1, respectively. The angles werecomputed by applying vectors v11, v12, v13, and v14 to thefollowing equations:v ⋅vv ⋅v(1)θ PIP1 = cos −1 11 12 , θ MP1 = cos −1 13 14 .
v11 v12v13 v14
In Pattern 2, the MP joint angle was denoted by θMP2.
The angle was computed by applying vectors v22 and v23
to the following equation:v ⋅v(2)
θ MP2 = cos −1 21 22 .
v21 v22

Table 1. Summaries of the joint angles in Patterns
1 and 2. (Start and End: start and end positions of
the repeated motions, Diff.: difference between
Start and End, x (y − z), x: mean value, y: maximumvalue, z: minimum value)
Pattern 1 (degrees)

Pattern 2 (degrees)

PIP
jointangleStart

155.4 (135–178)

End

86.7 (73–96)

Diff.

68.7 (39–105)

MP
jointangleStart

172.6 (168–177)

141.4 (136–148)End

140.4 (135–145)

109.5 (102–119)

Diff.

32.2 (23–42)

31.9 (17–46)

Table 2. Required specifications of PFD.
Pattern 1
Pattern 2
Stroke (mm)3046
Frequency (Hz)
4.3
3.6Fig. 5. MP and PIP joint angles.

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Journal of Robotics, Networking and Artificial Life, Vol. 4, No. 3 (December 2017) 243–247___________________________________________________________________________________________________________joint angles and frequencies of finger motion during
PFT treatment. Future studies are needed to develop thespecifications of a PFT treatment apparatus.
References1.

2.

Fig. 6. Time history of PIP joint angle in Pattern 1.

3.

4.

Fig. 7. Time history of MP joint angle in Pattern 1.

5.

6.

Fig. 8. Time history of MP joint angle in Pattern 2.
mean value of the vibration width of the fingertip was46 mm.
Based on the analysis results, we determined thespecifications of PFD as shown in Table 2.

7.

8.

5. Conclusion
The therapeutic effect of PFT was confirmed by thecomparison of MAS scores and electromyograms beforeand after treatment. The motion analysis revealed the247

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