1. Structure and Function of Wheelchairs
The structure of a common wheelchair generally consists of four parts: the wheelchair frame, wheels, braking device, and seatback, as shown in Figure 3-7-7. Below is a brief description of the main components' functions.
1. Large Wheels - Carry the primary weight. The diameter varies in several sizes such as 51cm, 56cm, 61cm, and 66cm. Except for some specific environments that require solid tires, most use pneumatic tires.
2. Small Wheels - The diameters vary in sizes like 12cm, 15cm, 18cm, and 20cm. Larger small wheels are easier to cross small obstacles and special carpets. However, too large a diameter increases the space occupied by the entire wheelchair, making it inconvenient to move. Normally, small wheels are in front of the large ones. But for wheelchairs used by people with lower limb paralysis, the small wheels are often placed behind the large ones. It should be noted during operation that the direction of the small wheels is preferably perpendicular to the large wheels; otherwise, they may easily tip over.
3. Handrims - Unique to wheelchairs, the diameter is usually 5cm smaller than the large wheel. For hemiplegic patients using one hand to drive, another smaller option can be added. Handrims are generally pushed directly by the patient. If the function is poor, the following changes can make driving easier:
(1) Adding rubber or other materials on the surface of the handrim to increase friction.
(2) Increasing push handles (knobs) around the handrim. There are different types of push handles:
① Horizontal push handle - Used for C5 spinal cord injury where the biceps are intact, allowing the elbow to flex and push the wheelchair forward.
② Vertical push handle - Used for rheumatoid arthritis when shoulder and hand joint movements are restricted.
③ Thickened push handle - Used for patients with severely restricted finger movement who cannot easily form a fist, also suitable for osteoarthritis, heart disease, or elderly patients.
4. Tires - Come in three types: solid, pneumatic with inner tubes, and pneumatic without inner tubes. Solid tires are faster and less prone to bursting on flat surfaces but cause more vibrations on uneven roads and are hard to remove from grooves. Pneumatic tires with inner tubes are harder to push and puncture easily but have less vibration compared to solid ones. Pneumatic tires without inner tubes do not puncture because there is no inner tube, but they are harder to push than solid ones.
5. Brakes - Each large wheel should have its own brake. When only one hand can be used, as in hemiplegia, single-hand brakes are available, sometimes with an extension rod to control both sides. There are two types of brakes:
(1) Notched brakes - Safe and reliable but require more effort. After adjustment, they can hold on slopes. If adjusted to level 1 and cannot hold on flat ground, they are considered ineffective.
(2) Elbow brakes - Utilize the lever principle through several joints to provide better mechanics than notched brakes but wear out faster. To increase the patient's braking power, an extension rod is often added to the brake, but this rod can be easily damaged, so regular checks are necessary for safety.
6. Seat - The height, depth, and width depend on the patient’s body type, and the material quality depends on the condition. Generally, the depth is 41cm or 43cm, the width is 40cm or 46cm, and the height is 45cm or 50cm.
7. Cushion - To avoid pressure ulcers, attention must be paid to the cushion. Egg-crate type or Roto cushions are preferred. These cushions consist of a large plastic block with numerous hollow cylindrical plastic columns about 5cm in diameter, each being soft and movable. When the patient sits down, the pressure area becomes multiple pressure points, and slight movements change these points, preventing constant pressure on the same area and reducing the risk of pressure ulcers. If such cushions are unavailable, layered foam plastics can be used, with a thickness of 10cm, the top layer being 0.5cm thick high-density polyurethane foam, and the bottom layer being medium-density foam. High-density foam provides strong support while medium-density foam offers comfort. When sitting, the ischial tuberosities bear significant pressure, often exceeding normal capillary end pressure by 1~16 times, leading to easy ischemia and pressure ulcers. To reduce this pressure, a section of the cushion corresponding to the ischial tuberosities can be removed, creating a hollow space. The cutout should be 2.5cm in front and 2.5cm to the side of the ischial tuberosity, with a depth of about 7.5cm, forming a concave shape. This method, combined with the aforementioned cushion, effectively prevents pressure ulcers.
8. Footrests and Legrests - Legrests can be either across both sides or separated on each side. Ideally, they should be able to swing to one side and be detachable. Attention must be paid to the height of the footrests. If the footrests are too high, it increases the hip flexion angle, adding more weight to the ischial tuberosities, increasing the risk of pressure ulcers.
9. Backrest - Backrests come in different heights and tilting options. If the patient has good balance and trunk control, a low backrest wheelchair can be chosen for greater mobility. Otherwise, a high backrest wheelchair is recommended.
10. Armrests or Arm Supports - Generally, armrests are 22.5~25cm above the seat surface, and some are adjustable in height. A lap board can be mounted on the armrest for reading or eating.
2. Electric Wheelchairs
After World War II, the demand for wheelchairs surged. Due to disabled individuals' desire to return to society and live independently, wheelchairs' performance and quality have continuously improved and enhanced. Electric wheelchairs are a typical example, with advanced models incorporating high technology. Electric wheelchairs are used when the patient's hand function is very weak and unable to drive a regular wheelchair, or if they can drive it but the distance is far and physically demanding, or if they are too frail to operate it. The structure of electric wheelchairs is much more complex than regular wheelchairs. They mainly include the following mechanisms:
1. Drive Mechanism - Powered by 12V or 24V batteries, with front-wheel and rear-wheel drive options. Front-wheel drives are better at crossing obstacles.
2. Speed Change Mechanism - Available in geared and gearless options.
3. Brake Mechanism - Mostly uses the motor's reverse action.
4. Battery - Uses a 24V car battery that can last for continuous use of 3~6 hours after one charge.
5. Control Mechanism - Includes hand control, head control, tongue control, cheek control, chin control, air control, and voice control. Except for hand control, all others are used by quadriplegics. For C4 and below injuries where respiratory muscles still function, air control is preferable. For C4 and above injuries with poor respiratory function, head, tongue, cheek, chin, and voice controls can be selected, with chin control being the most common.
3. Indications for Using a Wheelchair
1. Those with reduced or lost walking ability, such as paraplegics, unhealed lower limb fractures, amputees, bilateral lower limb paralysis caused by other neuromuscular diseases, severe lower limb joint inflammation or diseases.
2. Non-musculoskeletal system diseases where walking is detrimental to overall health, such as heart failure or systemic exhaustion caused by other diseases.
3. Central nervous system diseases that make independent walking dangerous, such as dementia, spatial agnosia, intellectual and cognitive impairments, severe Parkinson's disease, or cerebral palsy.
4. Elderly individuals with difficulty walking and prone to accidents.
4. Selection of Wheelchairs
The most important consideration when selecting a wheelchair is its size. The main areas bearing the user's weight are around the buttocks, the ischial tuberosities, the femur area, the popliteal fossa, and the scapular region. Whether the dimensions of the wheelchair, particularly the width and depth of the seat, the height of the backrest, and the distance between the footrest and the seat cushion, are appropriate will affect the circulation in relevant pressure-bearing areas of the user, causing skin wear or even pressure ulcers. Additionally, factors such as the patient's safety, operational ability, wheelchair weight, usage location, and appearance should be considered.