Samuel Landsberger, Sc.D Julie Shaperman, MSPH Vicente Vargas, BSME Ernest Meadows, BS, OTR Margaret Mitani, BS, OTR Donald R. McNeil, Ph.D.


Mobile arm supports (MAS) are wheelchair-mounted mechanical linkages designed to support the weight of the arm and facilitate shoulder and arm motions. They enable individuals with flaccid paralysis or paresis of the shoulder and elbow muscles to function independently in many daily tasks. However, problems with commercially available designs have limited their use in spite of their low cost and functional benefits. This project aims to create a new MAS design to address these deficiencies.


Child in wheel chair with multi link-arm

The well-designed Jaeco MAS system, which is the medical standard, can be configured to assist arm function in many activities for a patient population with a wide range of strengths. The system offers so much adjustability and choice of componentry that with proper setup it can help most anyone. But the hidden price for such versatility is that many therapists and caregivers find difficulty and time constraints in properly configuring and then aligning the MAS. Further drawbacks are that the Jaeco elbow joint often impedes chair mobility, and the system '50s vintage clinical appearance discourages many who might benefit from the "zero gravity" plane of motion the MAS provides.


The new Rancho arm and mount system are not intended to replace the versatile Jaeco, but rather to offer a simpler option appropriate in some circumstances. It should provide adequate performance in a useful but limited set of activities such as desktop writing and keyboard work for a patient group with a reasonably wide range of neuromuscular capabilities. By aiming to offer fewer options for an "average" population, the design objectives are to create a simpler MAS system that: (i) is relatively easy to mount and balance so that a caregiver can re-adjust as needed, (ii) that does not obstruct passage through doorways, and (iii) that looks good without costing too much. Our expectation is that more patients will then use and benefit from a MAS.


A survey of 28 MAS users identified problems and helped to establish design goals. Additional information was gathered from experienced clinicians and by direct observation of patients by research staff. These goals emphasize ease of adjustment and a low profile and attractive cosmesis along with the requisite ease of motion.

The Arm: A multi-link articulated arm for the MAS has been developed and shows promise. It protrudes less and is more flexible in configuration than the commercial model, and it should therefore offer less interference to passage through doorways and around tables. Children who tested the arm were pleased with the appearance and multi-link design. The Clamp / Mount: Several prototype wheelchair mounts to facilitate arm balance adjustments have been designed and are under evaluation. The ease of chair attachment and of adjustment are being evaluated in both the research laboratory and clinics at Rancho.

Clinical trials: A MAS User Group was recruited in 1997 to test and advise staff members about the MAS design. Most group members are teenagers with muscle diseases or children with arthrogryposis. The ready availability of this knowledgeable group of children and their parents enables prompt testing of various design features and quick feedback to help the design team refine the system to best meet their needs.

Wheel chair mount

The clinical trial protocol for the new MAS systems includes reach measurements and functional activities such as eating, typing (computer keyboard), playing games and writing. The new design is compared to the commercially available unit. Clinicians report any problems encountered with setup and adjustment and document the time required for both. User trials of the new MAS and mounts are providing valuable insights into both benefits and drawbacks of the design. Link geometry, segment lengths, and joint range of motion are important factors in allowing both full range of motion and avoiding interference with the pivoting trough that supports the forearm. Appropriate bearing selection is crucial in providing low-friction motion while maintaining reasonable cost.

Initial feedback from the clinical trials has been encouraging. Industry has expressed interest in producing an improved MAS, and therapists have shown a desire to try it when it becomes available.


A new mounting system will be selected from among several candidates. The design must prove itself satisfactory for clinicians, children and their caregivers and provide easy attachment to the wheelchair and quick adjustment of the MAS. Expanded clinical trials of both the mount and the new MAS arm will then be initiated. After the basic arm and mount have been tested and refined to demonstrate a reliable, commercially feasible system, the new MAS system may be augmented to provide more functionality for a wider patient group. The ability to quickly relocate the MAS from the wheelchair to a preadjusted mount on a desk or table will be investigated as a useful option, as well as a lift assist unit and a lock-down for chair driving. Our goal is to achieve good performance, while designing for low-cost manufacture of all components remains a priority.


Hays N. (1977) Up in arms. Teamrehab Report, June, pp 35-38.




This work is supported by Grant #H133E50006 from the National Institute for Disability and Rehabilitation Research (NIDRR), US Department of Education for a RERC on Technology for Children.