CRUTCH - LIKE TRANSFER BLOCK

Mohamed Samir Hefzy1,2, Gregory Nemunaitis3, Thomas Jackman4 and Clifford Csulik2 1Dept. of Orthopaedic Surgery, King Faisal Special Hospital & Research Center, Riyadh, Saudi Arabia 2Biomech. Lab., Mech. Eng., Univ. of Toledo 3Dept. of Phys. Med., Med. College of Ohio, Toledo, OH 4South Carolina Vocational Rehab. Dept., Rehab Tech. Program, West Columbia, SC

ABSTRACT

This paper describes the design and development of a pair of crutch-like transfer blocks. A totally different design concept from the typical simple transfer blocks was adopted. The crutch-like transfer blocks are adjustable in height and provide forearm support for people transferring themselves in and out of a wheelchair. Details are provided so that the crutch-like transfer blocks can be duplicated.

BACKGROUND

Patients that are confined to a wheelchair must often move themselves from a chair to an adjacent surface such as a bed. This movement is sometimes difficult due to body morphology. If a patient has short arms or long trunk, transfers from one surface to another is impossible without the use of a transfer block. A transfer block is a device which allows the patient to elevate the body high enough above the surface on which he is seated so that he can then shift his body to an adjacent surface. The problem with the transfer blocks commercially available is that they lack vertical adjustability and forearm support. Patients using these devices may have different arm lengths. A set of transfer blocks that could be adjusted up or down could be thus used by a wide range of patients. A second problem with the typical transfer blocks available is the vulnerable position of the wrist during use. While performing a transfer, the weight is supported by the two hands as the body is elevated. The simple transfer blocks being used do not offer any support for the forearm or the wrist should the blocks become unstable during the maneuver. The purpose of this project was to design and construct a set of transfer blocks that are vertically adjustable in length and provide some degree of forearm support.

STATEMENT OF THE PROBLEM

A pair of height adjustable transfer blocks that provide forearm support are needed to be used by patients to transfer themselves in and out of a wheelchair. This device should satisfy the following requirements:

1. It should be safe. Safety is identified as the most important characteristic of the device because of the physical limitations of the target population.

2. It should be easily adjustable and comfortable to use.

3. It should be affordable.

4. It should be easily built. The device should have as few parts as possible to fasten together. The individual parts would also need to be easily machined.

5. The weight of the transfer blocks should be kept to a minimum. The transferring maneuver involves the patient manipulating the transfer block with one hand. Since this task is often repeated several times a day, the weight of the block must be kept to a minimum such that this does not overly fatigue the patient.

6. The strength and durability of the transfer block must be kept to a maximum.

RATIONALE

The crutch-like transfer blocks were developed because commercially available transfer blocks lack vertical adjustability and forearm support.

DESIGN & DEVELOPMENT

Several designs were considered starting with a simple commercially available transfer block. The original idea was to modify the simple transfer block by adding a leather support strap that wraps around the wrist and additional blocks under the base to allow adjustability in height. However, the addition of blocks to attain a certain height is inconvenient at best. Also, the leather support strap needs to be pulled tight with the teeth and/or requires the assistance of a helper. Another approach that was considered to adjust the height was to include a handle that is capable of sliding up or down steel support tubing. However, none of these modifications promised significant improvement over the existing transfer block. It was thus decided to try a radical departure from the basic shape of a transfer block. The outcome of this route was the development of the crutch-like transfer block shown in Figure 1. Six characteristics including safety, cost, ease of construction, material acquisition, ease of operation and weight were identified as evaluation criteria to compare the new transfer block with the original simple design and slightly modified redesigns. The Pugh method (1) was used to select the optimal redesign.

Fig 1. Crutch - like transfer block.

The main parts of the crutch-like transfer block are the base, a base plate, support posts, an axillary support and a handle. The base of the transfer block is constructed of oak. The angled shape of the base allows it to be slid slightly under the patients leg during the transfer movement. The top, flat portion of the base has two 7/8" holes in diameter drilled in it to accept the steel tubing. A non-slip base covering is attached to the bottom of the base. A steel plate that covers the flat top portion of the base, provides support for the steel tubing. This plate is attached to the base with eight wood screws. The plate has two steel collars welded to its surface through which the steel tubing passes. The steel tubing is silver brazed to the collars for support and firm anchoring. Two different diameters of steel tubing are used as support posts. The posts, which are inserted into the base, are 7/8" in diameter and 10" in length and penetrate one inch into the base. The posts used for telescoping axillary support are ¾" in diameter and 11" in length. The axillary support is also constructed from oak. It has two holes drilled into it to accept the telescoping posts. The axillary support is covered with a rubber cushion similar to those found on commercially available crutches. The handle is constructed of a wooden dowel 4" in length and ¾" in diameter. It has a 13/32" hole drilled through its longitudinal axis to accept a 3/8" 16 UNC SAE grade 8 steel bolt. This bolt passes through the tubing and handle to secure the handle in place. Wooden knobs were used to secure the bolts to the handles which are covered with commercially available handle pads. The major concern for the telescoping tubing was buckling. A 1020 DOM steel tubing with a yield strength of 60 kpsi was selected for the telescoping tubing. This allowed for a factor of safety of 2 against buckling when a compressive load of 400 lbs is applied to one transfer block. The factor of safety was calculated using the secant column formula. Also, stress analysis was performed on the handle. The wooden doll part of the handle was neglected in this analysis, and it was assumed that the load is carried only by the steel bolt. The 3/8" 16 UNC SAE grade 8 steel bolt was found to sustain a point load of 400 lbs applied at its mid point with a factor of safety of 2.

EVALUATION

The transfer block prototypes were evaluated by the staff at Lake Park Rehabilitation. Three staff physical therapists, two aides, and one physical therapy assistant participated in the evaluation process. Each of the evaluator was asked to use a rating system from 1 to 10, with 10 being excellent, to evaluate the prototype in each of the following categories: adjustability, ease of use, weight, sturdiness of construction, safety, stability and durability. The overall evaluation indicates that the prototype transfer blocks provided adjustability, ease of use, sturdiness of construction, safety, stability and durability. The staff indicated that the weight of the prototype transfer blocks was their only concern. In order to reduce the weight of the transfer blocks, it is suggested to replace the wooden base with a plastic or composite base. Also, and in order to provide a better non-slip surface for the bottom of the base, it is suggested to use a rubber base instead of the non-slip base covering that was utilized. The final cost of the pair of transfer block prototypes was about $250.00.

DISCUSSION

A pair of height adjustable transfer blocks have been designed and built to provide forearm support for people transferring themselves in and out of a wheelchair. The crutch-like design represents a totally different design concept from the typical simple transfer blocks which lack vertical adjustability and do not offer any support for the forearm or the wrist should the blocks become unstable during usage. The population identified as being most likely to benefit from this transfer block design has the following characteristics: a) temporarily or permanently confined to a wheelchair, b) have an arm length to trunk length ratio at an unacceptable range to allow buttocks clearance during transfers, c) possess sufficient upper body strength to elevate and support their body weight on their arms, d) have adequate balance and body awareness to perform the transfer maneuver, e) have adequate mental capabilities to understand the use and/or adjustment of the transfer blocks.

REFERENCES:

1. Lumsdaine, E. and Lumsdaine, M., Creative Problem Solving, 2nd ed., McGraw-Hill, Inc., 1993.

ACKNOWLEDGEMENTS

This work was supported in part by grant BCS-9308700 from Aiding the Disabled Program of the Bioengineering Division of the National Science Foundation.

Mohamed Samir Hefzy, Ph.D., P.E Department of Orthopaedic Surgery King Faisal Specialist Hospital and Research Center P.O. Box 3354, Dept. MBC 77, Riyadh 11211 Kingdom of Saudi Arabia Tel: 9-011-966-1-442-7591 Fax: 9-011-966-1-442-7597

Presently, Dr. Hefzy is on sabbatical from: Biomechanics Laboratories Dept. of Mech., Ind. and Mfg. Engineering The University of Toledo Toledo, Ohio, 43606 Tel: 419-530-8234 fax: 419-530-8206 E-mail: mhefzy@uoft02.utoledo.edu