Traction is often applied to part of the body to negate the effect of the forces causing the deformity. To be an effective traction the traction should act on the deformity and not whole body. To counter the effect on the whole body we need another force that acts in opposite direction.
Let us understand this with an example. Suppose that there is a fracture of shaft of femur bone. Shaft femur fracture would produce a deformity because of pull of the muscles and broken bone. To straighten it one requires to put a pulling force distal to the fracture site. Let us say on holds the foot and pulls the limb so as to correct the deformity. Some of deformity would be corrected but the force of the pull would also pull the body towards the person who is pulling.
We need to cancel this force to avoid dragging of the body. Let us say that another person is holding the shoulders of the person and is able to resist the drag exerted by pull. If he exerts a force equal to the pull, there would be two forces that would act on body and body would not move. At the same time both the forces would also be exerted on the fracture and thereforecorrection of the deformity results.
Try to pull a persons hand. If there is no resistance when you would resultin pulling of person toward you. However if a person holds him from elbow, all your force is transferred to forearm only. This is anoyther exmple of traction and countertraction forces,
In orthopaedic practice,countertraction may be obtained by altering the angle of the body-weight force in relation to the pull of traction, such as by elevating the foot of the bed with blocks to enable body weight to act as counter force.
Countertraction is an important aspect of traction treatment.
Absence of countretraction not only results in ineffective traction but also in discomfort of the patient.
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