Task Leader(s): Michael Boninger, MD

Co-Investigator: Dan Ding, Ph.D.

Other participants: Annmarie Kelleher, MS (clinical coordinator) and Brad Impink MS (mechanical engineer, Bioengineering Masters student) Michelle Oyster (MSE, clinical coordinator), Erica Authier (MSE, SHRS PhD student); Jennifer Collinger (BSE, Bioengineering PhD student).

Specific Aims

Aim 1: Determine differences in EMG and metabolic responses for wheelchair propulsion with: standard handrims, the Natural-Fit Handrim (NFH) and the FlexRim (FR).

Hypothesis 1a: EMG activity in the forearm and upper arm muscles for propulsion with both the NFH and the FR will be significantly lower than with the standard handrims.

Hypothesis 1b: Metabolic activity for propulsion with both the NFH and the FR will be significantly lower than with the standard handrims.

Note: These tests will also enable determination for any differences between the NFH and FR.

Aim 2: Determine differences in the acute response of the median nerve for wheelchair propulsion with standard handrims, NFH and FR.

Hypothesis 2a: The median nerve cross-sectional area (CSA) will be significantly less and the flattening ratio will be significantly greater for propulsion with the standard handrim than for propulsion with NFR and FR.

Hypothesis 2b: Any changes resulting from propulsion with the ergonomic handrims will return to baseline values faster than changes resulting from propulsion with the standard handrim.

Aim 3: Determine differences in the acute responses of the rotator cuff tendons for propulsion with: standard handrim, NFH and FR.

Hypothesis 3a: Echogenicity will be significantly less and the diameter will be significantly greater for the tendons of the supraspinatus, infraspinatus and long head of the biceps after propulsion with the standard handrim than propulsion with NFR and FR.

Hypothesis 3b: Any changes resulting from propulsion with the NFH or FR will return to baseline values faster than changes due to propulsion with the standard handrim.

Background and Rationale

Ergonomics literature has defined tasks involving high forces, high repetition and large joint excursions as risk factors for musculoskeletal injuries. Manual wheelchair propulsion is such a task. The prevalence of wrist and shoulder pain has been observed to be as high as 73% among manual wheelchair users (MWUs). The development of an ergonomic handrim that eases the stress on the arms and decreases the likelihood of pain and secondary upper extremity injuries would be very beneficial for MWUs. Wrist and shoulder pain decreased for a group of MSUs following their use of the Natural-Fit Handrim (NFH) for six months in place of standard wheelchair handrims. The FlexRim (FR), another ergonomic handrim has been shown to require less forearm muscle activity compared to a standard handrim.

Cumulative trauma disorders (CTDs) typically result from repetitive micro trauma that damages local tissue. A determination of differences in metabolic responses of the upper extremities when using the respective handrims may provide relevant information on the acute responses of nerves and tendons to micro trauma and provide insight on CTDs and the benefits of ergonomic handrims. Ultrasound has been used to measure acute shape and size changes in nerves and tendons after a provocative activity.

We shall determine differences for muscle activity, metabolic activity, and nerve and tendon responses for wheelchair propulsion with standard handrims, the Natural-Fit Handrim and the FlexRim.

The Natural-Fit Handrim (NFH)
The Natural-Fit (www.thenaturalfit.com) consists of a smooth oval surface for the palm of the hand and a higher friction contoured slot for the thumb (Figure 1). These components combine to provide an ergonomic grip and separate surfaces for propulsion and braking. The Natural-Fit is designed to eliminate the pinch grip associated with a standard handrim and to ease stress on the hands and wrists during propulsion. The Natural-Fit has been commercially available since 2003.

The FlexRim
The FlexRim (www.flexrim.com) consists of a high friction rubber surface that connects a standard aluminum handrim to the wheel (Figure 2). The rubber connecting surface is flexible and conforms to the thumb and thenar eminence when gripped. The FlexRim's compliant rubber surface is designed to ease stress during propulsion by creating "give" in the connection point between the handrim and the wheel to absorb propulsion impact forces. The FlexRim is produced by Spinergy and is slated for market entry in the near future.

Figure 2 - The FlexRim