The sensory function of the hand provides feedback to the brain for object recognition and protection as the hand interacts with its environment. A sense of having contact with an object and the quality of contact is important to the effective use of the hand.
By providing signals from the brain to the hand, the peripheral nerves provide the arm and hand with the senses of touch, pressure, temperature and pain. When the peripheral nerves are lost, the effect is partial loss of the feedback system of the body. A person may no longer be able to tell the difference between objects in the hand, to recognize an object with eyes closed or feel (search) for an object to pick up or manipulate. If no longer able to be sure he has hold of an object, a person squeezes harder to be certain that there is contact. There is no limit on when to stop applying pressure. Without modulation control, the use of the affected hand in normal activities for work and play results in excessively high pressures on the hand. If not immediately damaging, over time even moderate pressures can be damaging to the skin and bones of the hand from repetitive stress on the tissues.
The skin and soft tissues of the hand serve as an impact covering for the bones and are intended to absorb and accept certain amounts of pressure during use. Some stress on these tissues is actually needed to maintain healthy tissue. If the hand is not used, the result is muscle wasting and skin atrophy (loss of substance tissue) . It is when pressures on the skin become excessive that injury occurs. Injury to skin and soft tissues (including tendons which cross and operate joints and ligaments and maintain bony structure) , can result in permanent deformity and disability of the fingers and hand. In hands with normal peripheral nerves and sensation, pain from abnormally high stress on the skin and soft tissue usually prevents injury. If nerve damage is severe enough that there is a "loss of protective sensation", the pressures on the skin can be excessive. There is often continual bruising and scaring of the skin. With scar and callus, the normally soft and pliable tissue becomes hard and brittle. Cracks in the skin can develop which easily become infected and result in tissue damage.
Even individuals who recognize pain may still have a significant enough loss that they lose "protective sensation" (enough feedback that they can detect an object about to injure them in time to protectively react). Individuals who have lost protective sensation are important to identify and counsel regarding protective techniques to prevent injury, deformity and resultant disability.
NOTE: Not all patients with sensory impairment will develop deformity. Much can be done to use vision as a substitute for sensory feedback. The patient's understanding of the role insensitivity plays in deformity is paramount for any individual with any degree of sensory loss, but is critical where sensory loss is severe.