1 Introduction

Post-operative hand-stiffness is a major problem faced by hand surgeons universally. Persistent edema, pain, and immobilization during the immediate postoperative period and subsequent scar formation contribute to stiffness in the long-term.¹ In a series of fractures in hands treated with internal fixation, Page et al. showed stiffness as a complication in 13 % of metacarpal and 64 % of phalangeal fractures.² Prevention of these complications involves hand therapy, which aims to reduce stiffness. The role of a well-trained hand therapist, a cooperative patient, corrective splinting, and mobilization is invaluable in getting satisfactory functional results.^1,3 However, despite adequate therapy, stiffness of the hand may remain and restrict function.

There are currently a variety of research groups developing assistive devices that can help in hand-rehabilitation.^4–6 The clinical benefits observed are improving and maintaining the joint range of motion, preventing adhesions, reducing pain and edema and proprioceptive stimulation. The problems with the existing devices are that they are bulky, expensive and require institutional setup for their functioning.

To address these problems, we developed a wearable, automated, motorized assistive glove (MAG) based on the concept of continuous passive mobilization (CPM). This may influence and help overcome impending hand-stiffness. This device provides repetitive and continuous passive flexion of fingers and thumb.

We aimed to evaluate the effectiveness of MAG and compare it with conventional hand therapy (CHT) under the domains of Total Active Motion (TAM) and Quick-DASH score. We hypothesized that results of CHT would be similar with or without this device.

2 Materials and methods

2.5

2.5 Assistive device

The MAG provides repetitive and continuous passive flexion movement of the fingers. It does not provide passive extension and cannot be used for extensor injuries. It was designed in-house in collaboration with the Department of Biomedical Engineering. We developed a miniaturized version of the large hospital devices used for hand-rehabilitation based on the devices developed in the past. The kit contains a synthetic polymer glove with double filament strings connected to the electric DC motor and powered by a power bank (10,000 mAh) (figure-1A, B). The National Drug Control Authority gave the no objection certificate (NOC) for the assistive device as it is a Class B- low to moderate risk device. The power bank is placed beside the patient's hand and connected to the motor component with a DC jack and micro-USB cables (Fig. 1A and B).

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Figure-1A Power bank connected to the motor component with DC jack and micro-USB cables, 1B: Motor component case secured with velcro straps to the distal forearm, and 1C: a.) Double filament strings from the glove component, b.) Stainless steel coupler, c.) Double filament strings from the motor component.

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The motor component is housed in a 3D printed case secured on the volar aspect of the distal-forearm by velcro straps (Fig. 1A and B). If required, a wrist brace is used to restrict wrist flexion. The weight of the glove is 50 gms, and that of the device is 500 gms. The double filament strings leading out of the glove can easily be connected to the motor component with the help of stainless steel couplers (figure-1A and 1B). During therapy, the flexion speed relaxation cycles can be set to slow-mode (1 cycle/15 s) and fast-mode (1 cycle/6 s), depending on the rehabilitation goal. Slow-mode was selected in all cases in the first two weeks of therapy. Fast-mode is used after the passive range of movement has improved to at least 50 % of the normal. The glove was developed to mimic the normal kinematics of the hand. Hence, it has three degrees of freedom for each finger joint and two for the thumb. The activities performed by the assistive device were to make a fist by closing with flexion at each joint, thumb flexion, and opposition of thumb to the ulnar three fingers (figure-1A and 1B). The device is effective for 48–60 h on a single charge. The glove can be easily applied and removed as required. The glove could be customized for the patient's needs and size. However, in our study, they were stitched in small (S), medium (M), and large (L) sizes.

2.6

2.6 Study group

Patient demographics, including age, sex, occupation, dominant hand, side of injury, and structures involved, were documented. The skin around the surgical site was examined for wounds and painful areas. The investigator supervised the usage of MAG, including explaining various parts of the device, wearing the device, motor, and battery connection, and training the patients. The therapy was provided twice daily for 60 min during admission and later once daily for five days/week on an outpatient basis (Fig. 2). This was done alternatively in addition of twice daily CHT as planned for controls. The activities were.1.50 repetitions of movement, each includinga.Exercises for digital flexion involving all the digits. (15 min)b.Exercises for opposition from thumb to the ulnar three fingers (15 min),c.Opening and closing to make a fist (20 min),2.Twenty repetitions of alternate use of fingers and thumb flexion movements (10 min).

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Figure-2A and 2B Fist opening/closing and thumb-finger opposition movements performed by the assistive device.

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2.7

2.7 Control group

Patients visited the therapist twice daily for 60 min during admission and followed the exact instructions at home with weekly outpatient visits to the therapist (Fig. 3). The hand therapist provided active-assisted and passive-mobilization of the affected hand). The activities in serial order were.1.Moist heat (5 min).2.Ultrasound scar message (5 min),3.Electrical stimulation of muscles (5 min),4.Flexion and extension of the digits and wrist (15 min),5.Adduction and abduction of the fingers (15 min),6.Thumb opposition with the other fingers (15 min),

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Figure-3 Passive mobilization of MCP joints and opposition.

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The patients followed the regime at home from the sixth week till its completion at three-months. The home program was the same except for the ultrasound and electrical stimulation which was used only during first admission.

3 Results

The study recruited 120 patients who presented with post-operative hand-stiffness three weeks after index hand surgery, of which twenty patients were excluded (Table 1). Among them, in eight patients, there were associated extensor tendon injuries; in six, there was an associated crush element with composite tissue loss; in four, persistent ulcers over the hand and wrist did not permit wearing the assistive glove. Two patients refused to participate. One hundred patients were categorized into two groups by computer-generated randomization. We randomized 59 patients to the assistive glove and 41 to the CHT groups. We did not observe any harm or adverse effects as all the patients completed the therapy program without any loss of follow-up. We followed the CONSORT guidelines, as shown in the flow diagram of the study in Fig. 4.

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Fig. 4 CONSORT flow diagram of the study.

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4 Discussion

This study aimed to evaluate the effectiveness of a portable MAG in the management of post-traumatic hand-stiffness based on the concept of continuous passive motion (CPM). The RCT showed that hand therapy with MAG with addition of standard therapy showed better TAM when compared to CHT at a short follow up of three-months.

The benefit of CPM to joints was initially proposed by Salter et al. He suggested that this procedure improved the healing of surrounding soft tissues.⁹ CPM will also help in stretching and elongating the scar tissue which improves the range of movement.

Currently, most therapists still rely on manual methods which is an easy, adaptable but time-consuming and labour-intensive.

In collaboration with Springer, Salter introduced a CPM machine in 1979 for their patients.⁹ Machine-based CPM devices essentially allow the patient's hand to be moved through some movement while the patient supplies no input forces. In this way, early treatment of stiffness and other complications can be addressed to improve recovery time. They advocated this device following MCP joint arthroplasty, intra-articular fractures, synovectomy, and arthrolysis.⁹ It can also be used after tendon repair, ligament reconstructions, and other intra-articular procedures.⁹

Ketchum et al. introduced an electrically driven splint (EDS) for the hand. The device consisted of nylon lines attached to adjustable thimbles on the fingertips.¹⁰ Gentle, rhythmic, passive motions of 2.3 kg force at varying frequencies could be applied in both extension and flexion of the fingers. They reported a statistically significant improvement in TAM and passive motion in the group treated by EDS after one month compared to the group treated by the hand therapist.¹⁰ The time taken to use the EDS for the hand was half that of the time needed by a hand therapist to treat a patient by passive mobilization. Bunker et al. reported a trial of CPM following flexor tendon repairs with the Toronto Mobilimb for four and a half weeks after tendon repair.¹¹ The results were 85 % excellent or good and 15 % fair or poor using the Buck-Gramcko criteria.¹¹ The older generation CPM devices were large and were mounted on the back of the hand and fingers. These devices are only capable of operating on one finger at a time. They were heavy dorsal-mounted linkages that could cause patient fatigue.

There has also been recent interest in using robotic assistive devices to perform CPM. Such machines are ideal for tasks that require repetitive, accurate, monitored, and highly controlled motion. In a randomized control study involving 27 patients with sub-acute hemiplegia, Vanoglio et al. showed significantly better results in the treatment group than the control group in the nine-hole peg test, grip and pinch strength, and Quick-DASH scores.⁶ They observed that robot-assisted hand-rehabilitation is effective in recovering strength and decreasing disability in patients.⁶ We believe that The current randomized study shows that the results of using a similar portable device are effective even in post-traumatic injuries of the hand. In both the scenarios the benefit could be due to improved circulation, stretchability of muscles and joints. In post-traumatic injuries when used as a prophylactic device the rehabilitation becomes much more effective as the spasticity element is absent.

There are now several new electrical portable devices marketed for hand CPM. One of the most notable is the Kinetic Maestra.¹² The device moves the finger from a 0-degree position to 270° (90° in the MCP, PIP, and DIP). The problems with the existing devices are that they are still large, bulky, and expensive, requiring vigorous training. The primary benefit of our device is that it is portable, lightweight, and made of synthetic polymer, which can be customized and mainly used as a home-based tool for therapy.

There is a need to develop customizable and lightweight assistive devices that are practical and accessible for daily and prolonged application. We devised a miniaturized version of the large hospital devices used for hand-rehabilitation. During therapy, the flexion speed-relaxation cycles can be set to slow mode (1 cycle/15 s) and fast mode (1 cycle/6 s), depending on the finger's necessity and from the investigator's point of view, the first two days required more time for education and training to wear the glove correctly and get acclimatized. The investigator initially adapted the MAG to the patient's hand size to ensure that exercises were done correctly. Once the correct positioning of MAG was found, therapy was straightforward and took minimal time.

Assistive devices like MAG can achieve the same action as often as desired without deviating from the desired trajectory. In this way, a patient can be comfortable that the device will repeat the same motion without worrying about further movement on any given iteration. It also lets the patient feel in control of the activity as they know what to expect and can stop the assistive device at any given time. Multiple safety checks can ensure the safety of the assistive device. Finally, the ability to record data allows the therapist to review past data and search for trends or inconsistencies relevant to the patient's recovery and rehabilitation program.

Unlike other studies where devices were tested for problems related to stroke and hemiplegia, we selected patients with injury of multiple structures as the regime for therapy was similar in all groups after three weeks of immobilization. Incidentally, those sets of patients would have received a similar protocol for CHT. All patients required three weeks of immobilization for adequate soft tissue healing. The assessment was done with TAM and Quick-DASH scores as they have become well accepted and extensively used to evaluate the range of motion and disability following hand.^13,14

5 Strengths and Limitations

The study's strengths are a longer follow-up than the available literature studies. The sample size was large, and attrition was not observed. We observed a few problems associated with the glove. The double filament cables in the glove ruptured after three days of usage in one patient and were changed immediately. We observed that the patient had difficulty applying the glove during the initial three weeks due to pain and edema.

The study was done on a limited number of subjects in one center, and hence, our findings must be confirmed in a more extensive and multicenter RCT. Samples were heterogeneous and included fractures, flexor tendon injuries, fractures with flexor tendon injuries, and fractures with tendons with neurovascular injuries. Due to the smaller sample size, individual conditions could not be matched with the control. Since the compliance of the therapy regime performed at home was not checked for controls, the possibility of this influence may not be ruled out. Given the subjective nature of the outcome measures of Quick-DASH and lack of patient blinding may likely introduce an element of bias in the results, however these methods of assessment were one of the most reliable and frequently used tools currently available for comparison. The follow-up period was kept at three-months because we wanted to evaluate the influence of the therapy regime. In our practice, such injuries generally require around three-months of therapy, so we decided to limit our study-period to three-months. In the study-group, the MAG could not be used for extensor tendon injuries and associated fractures. The glove was designed with the motors aligned for only flexion movement in this study. The design can be changed for extensors by housing the motors on the dorsum. This can be proposed for planned later studies.

6 Conclusion

The novel MAG improves the TAM in patients with immediate post-operative hand-stiffness compared to CHT. There is a potential for the assistive device to assist or augment activities at home by providing safe human-device interactions in the future.

Guardian/patient's consent

Informed Consent was taken from all the patients who participated in this Randomized control Trial. The figures shown in the manuscript does not reveal the identity of the patients and hence a separate consent was not taken for the images.

Author contributions

AKB - Conceptualization; Data curation; Formal analysis; Investigation; Methodology; Project administration; Supervision; Writing – review & editing, final draft. VA - Data curation; Formal analysis; Investigation; Methodology; Writing – original and final draft. AMA - Data curation; Formal analysis; Investigation; Methodology; Project administration; Supervision; Writing – review & editing, final draft.

Funding

The assistive device is designed and provided by the Department of Biomedical engineering, Manipal Institute of Technology, Manipal, and under Manipal Universal Technology Business Incubator (MUTBI), India. Biotechnology Industry Research Assistance Council (BIRAC), Small Business Innovation Research Initiative, (SBIRI) India was the funding agency for developing the device.

The Study was approved by the Kasturba Medical College and Kasturba Hospital Institute Ethics Committee (IEC No. 597/2018)

The study was registered under Clinical Trial Registry of India (ctri.nic.in) (CTRI No: CTRI/2019/01/016821)