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Wilmington robotic exoskeleton

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Courtesy of Broadened Horizons
Courtesy of Broadened Horizons

The Wilmington robotic exoskeleton (WREX) is a passive gravity-balanced arm orthosis that was developed at the Nemours/Alfred I. duPont Hospital for Children in Wilmington, Delware. It is designed for people suffering from neuromuscular weakness of the upper limbs by assisting in elevating the upper limbs and improving range of motion by eliminating the effects of gravity.

Contents

Features

The device is a lightweight exoskeleton structure that is arranged parallel to the arm and is fixed to either a wheelchair or back brace for stability.

The WREX consists of two segments.

  • An upper arm link constructed from hollow steel (or 3d printed plastic) rods into the shape of a parallelogram
  • A forearm link that is a single rod.
  • Linear elastic bands as a linkage between two segments provide a balance and assist movements against the effect of the gravity.
WREX configuration showing four degrees of freedom
WREX configuration showing four degrees of freedom

The purpose of the parallelogram linkage is to allow flexion and extension of the shoulder joint while maintaining a vertical reference for the elbow joint. [1] A polyethylene brace is attached to the forearm link to secure the device to the wearer.

The entire device is secured directly above the shoulder to a wheelchair or a back brace.

Each joint is able to rotate in two directions: flexion/extension (up/down) and adduction/abduction (towards/away from body). The joints are not able to rotate about their own axes. The four degrees of freedom obtained from the two joints allow positioning of the arm and hand in 3-D space.

Gravity is eliminated by two sets of rubber bands that are arranged to oppose gravity’s effect of downward motion of the segments. The rubber bands are selected by clinician and adjusted to provide enough lift to eliminate effects of gravity but not so much that it overpowers the wearer’s limited muscular strength.

Clinical applications

The WREX exoskeletal arm has shown promise in assisting patients.

  • Seventeen subjects between the ages of 4-20 suffering from muscular dystrophy were tested with the device. [2] The subjects were able to increase range of motion in their arms and some were able to decrease time in performing tasks in the Jebsen test of hand function when wearing the WREX.
  • Five subjects between the ages of 6-14 with arthrogryposis were fitted to a WREX secured to a back brace. [3] Four of the five subjects were reported to continue to use the WREX at home and school. The WREX was reported to assist the subjects with eating independently.
3D printed WREX attached to a back brace, courtesy of Stratasys
3D printed WREX attached to a back brace, courtesy of Stratasys

Advantages

  • Provides 3-D movements in low-profile exoskeleton structure
  • Increase in range of motion
  • Subjects reported being able to raise hand in class easier

Disadvantages

  • Requires assistance to put on and take off the device
  • Can slow down some hand tasks
  • One of the test subjects reported teasing from her peers and discontinued use of the WREX

Case present

  • A study recruited an ambulatory patient with arthrogryposis multiplex congenita and 2 nonambulatory patients with spinal muscular atrophy. All patients were evaluated by motion analysis with and without the WREX and qualitative questionnaire. Result described that WREX succeed to enhance patients' functional mobility of upper limb, including self-feeding, fine motor control and use of a TV remote control. It also elevated their quality of life by improving functionality.[4]
  • There is a video showing how WREX helps the patient with neuromuscular disability to perform his movement of upper extremity.[5]

Commercial Distributors

  • JAECO Orthopedics Inc. official license[6]
  • Broadened Horizons

References

  1. T Rahman, R Ramanathan, R Seliktar, W Harwin, A simple technique to passively gravity-balance articulated mechanisms. ASME Trans Mech Des. 1995; 117(4):655-658
  2. T Rahman, W Sample, R Seliktar, et al., Design and Testing of a Functional Arm Orthosis in Patients With Neuromuscular Diseases, IEEE Transactions on Neural Systems and Rehabilitation Engineering, 2007; 15(2): 244-251
  3. T Rahman, W Sample, S Jayakumar, et al., Passive exoskeletons for assisting limb movement, Journal of Rehabilitation Research and Developement, 2006; 43(5): 583-590
  4. Haumont T, Rahman T, Sample W, et al., Wilmington robotic exoskeleton: a novel device to maintain arm improvement in muscular disease, Journal of Pediatric Orthopaedics, 2011; 31(5):e44-9
  5. https://www.youtube.com/watch?v=0kGMhBW3p1E
  6. http://jaecoorthopedic.com/products/products/WREX%3A-Wilmington-Robotic-EXoskeleton-Arm.html