移乗介助動作の計測と腰部負担の評価

抄録

Daily living care for severely disabled people, transferring them between wheelchair and bed for example, is very hard work for a caregiver. Actually, over 80% of professional caregivers had experience of lower-back pain. Many types of lifting devices are available for transferring disabled people, but hanging the person in the sling requires a large moment around the lumbar joint of the caregiver. The most practical solution to reducing the risk of lower-back disorder, therefore, should be to select the most suitable method for transferring.
The lumbar joint moment is a reasonable biomechanical evaluation index for workload because it relates directly to the worker’s backmuscle tension and lumbar disk pressure. The joint moment is calculated from posture data and applied force data during care motions using a rigid-link model of the human body. In the case of two-person transfers, the caregivers stand sufficiently far away from each other that a standard motion measurement system of force plates and opto-electric cameras can be used. The measurement of one-person transfer motion is difficult, however, because many external forces caused by a patient’s body weight are applied on the caregiver’s contact points, and the body parts of the caregiver are extensively covered by the patient’s body.
In this study, a new measurement method was developed. The contact forces were measured with a fluid pressure sensor jointed to a thin rubber tube sandwiched between curved plastic plates. The absolute angles of body segments were measured with twelve small tiltmeters. These sensors had been sewn on a plain jacket beforehand to reduce preparatory time for the measurement.
Hold-type transferring and carry-type transferring by one person, and front- and back-type transferring by two persons were measured for beginners and for specialists. In hold-type transfers, the caregiver holds the patient’s head under one arm and grasps the patient’s waist belt, pulling up around the knee joints as a fulcrum utilizing the caregiver’s body weight. The carry-type transfer is the ordinary carrying method on one’s shoulder. The front caregiver in a two-person transfer supports the patient’s knees and calves, and the back caregiver pulls up the patient’s upper body.
Calculated results of lumbar load in each type of transferring show that the hold-type transfer by one person is the least risky method regardless of caregiver’s skill level and body physics. The worst case is a carry-type transfer by a tall caregiver. In this case, the lumbar load reaches three times that of a hold-type transfer by a short caregiver. The load of a two-person transfer is as great as that of a one-person transfer. The load can be reduced to 80% by raising the bed surface about twenty centimeters above the wheelchair seat.
In conclusion, the hold-type transfer by one person is a suitable transfer method for avoiding caregiver’s lower-back pain. The portable measurement system developed and used in this study will be applicable to analysis of other kinds of care motions.