Final answer:
A completely immobilized patient in spinal traction is at risk from shear and pressure forces, with friction also contributing to potential tissue damage.
Step-by-step explanation:
A patient who is completely immobilized in spinal traction is at risk mainly from shear and pressure forces, although friction can also contribute to risk. The shear force is a sliding force that moves the skin in one direction and the underlying bone in another, potentially leading to tissue damage. Pressure force is the constant force exerted on tissues by weight or tension, which can cause pressure injuries, especially in immobilized patients. Friction force, while less implicated than shear and pressure, can also contribute to tissue injury when a patient's skin is rubbed against another surface.