A vibration injury can cause sensory, vascular and muscular problems. Often there is a very troublesome cold-intolerance, which is not necessarily associated with white fingers. Life quality and the ability to perform daily physical activities may also suffer.
Impaired sensory-motor functions of the hand may have a number of various causes. It is important to perform relevant clinical tests and laboratory investigations to clarify the underlying reasons for impaired hand function. A vibrometry test can confirm whether the ability to perceive vibrations in the hand is impaired, but this test is not enough for a conclusive diagnosis, or to identify the true reason for the sensory impairment.
Sensory problems in the hand can be caused by cervical rhizopathy or entrapment of nerve trunks in the arm or hand, for instance carpal tunnel syndrome or ulnar nerve entrapment. Polyneuropathy, for instance diabetes, can be an alternative explanation. If a patient has been subjected to vibrations via hand-held vibrating tools, the vibrations may certainly offer a plausible explanation.
The patient’s own story is very important for the diagnosis. When did the symptoms first appear? Do the symptoms come and go during the day? Which fingers and which parts of the hand feel numb? Is the numbness associated with pain? Is the patient exposed to vibrations at work or through some leisure activity? These are important questions in order to make a diagnosis.
A clinical investigation can usually confirm or exclude carpal tunnel syndrome or ulnar nerve entrapment at the elbow or wrist level, but sometimes it is necessary to conduct a neurophysiological investigation to confirm the diagnosis.
When there is a vibration injury, the perception of touch applied to the finger pulp is often impaired at an early stage. To assess the capacity to perceive pressure, Semmes-Weinstein’s monofilaments of various thicknesses should be used. Another important test is the two-point (2 PD) discrimination test, which measures the capacity to differentiate between two close pressure points applied to the skin. Normally, the two-point discrimination capacity in the finger pulp is 4-5 mm. In the case of vibration injury, the ability to perceive pressure is impaired before the two-point discrimination capacity is impaired.
The fine motor dexterity is tested by the Purdue Pegboard test, which is an assessment of manual ability to manipulate and move small items.
A neurophysiologic investigation is sometimes be needed in order to confirm or exclude vibration injury. A sensory nerve conduction test implies assessment of the conduction velocity of sensory impulses in the nerve. Assessment of sensory conduction velocity over the carpal tunnel segment is sometimes mandated to confirm carpal tunnel syndrome.
An common component of vibration injury is damage to the thin nerve fibres transmitting temperature stimuli. There are various tests available to assess the ability to perceive heat and cold stimuli respectively, and to perceive changes in temperature of a test element applied to the fingers.
The patient’s own account is important in order to evaluate vasospastic problems in the fingers (”white fingers”). Various tests are available at departments of physiology at major hospitals. These include the assessment of finger systolic blood pressure (FSBP) and critical opening pressure (COP) after cold provocation.
Sometimes there is impairment of the handgrip force as well as the power in the pinch grip and key grip. The handgrip force should be assessed using a JAMAR-dynamometer. The force in the pinch grip and key grip should be assessed using a standardized instrument, a so-called pinch gauge.