Hand-arm-vi­bra­tion syndrome

Long-term use of hand-held vibrating tools may result in a hand-arm vibration syndrome characterized by white fingers (VWF), sensorineural dysfunction, muscle weakness, and pain. We are currently developing refined protocols to evaluate these patients, aiming at increased understanding of the pathophysiology and symptomatology of the lesion and developing improved methods for early diagnosis. In an extended long-term study these patients have been meticulously followed and assessed with reference to the development and nature of clinical symptoms. Three distinct categories of symptoms can be defined: 1) isolated white fingers 2) isolated sensorineural problems; 3) combined white fingers and sensorineural symptoms.In addition several patients suffer from decreased muscle strength and impaired hand grip in spite of well preserved muscle volume.

The long-term effects of vibration on hand function are poorly understood. Extensive experimental and clinical research is being performed to analyse the pathophysiology, epidemiology, symptomatolgy and diagnosis as related to vibration-induced problems and three theses have been presented on various aspects of the problem. Disturbances in hand function in vibration-exposed patients have been analysed, and a battery of tests for dexterity and manual skills has been developed. Focus has been on hand function and effects on ADL functions and life quality. The motor dysfunction which is often seen in vibration exposed patients has been especially addressed with reference to forearm muscles and intrinsic muscles of the hand.

Central nervous effects of vibration
It is well known from primate experiments that monotonous, iterated sensory stimuli applied to various parts of the hand simultaneously may affect the cortical projection so that boundaries between finger projection are dissolved and the map in generally is distorted. There are reasons to believe that the same phenomenon occurs also in vibration-exposed patients, and that this may play an important role for the neuromuscular dysfunction which is often seen is vibration-exposed patients. We have therefore initiated an fMRI study aiming at analysis of the cortical hand map in vibration-exposed patient. Preliminary studies indicate that a cortical reorganisation in fact takes place in patients subjected to long-term vibration by hand-held tools.

The EU directive
Currently there exists an EU directive (2002/44/EG) stating that some kind of screening will be necessary from July 6, 2005 for group of employees which are at some potential risks at work. Vibration exposure is a well known cause of hand problems where treatment is lacking and where prevention is essential. The VibroSense Meter is an essential tool for easy detection of beginning vibration injury.

Diagnosis
Diagnosis of vibration injury in the hand is complex and must be based on multiple factors such as extent of exposure, subjective complaints and objective findings in clinical investigation and laboratory testing. We have focused on early changes in sensory perception of the hand which is a consistent finding in hand-arm-vibration syndrome. Of special interest is analysis of vibration thresholds in various frequency bands. For this purpose we have been using tactilometry (vibrometry), implying analysis of vibration thresholds within seven frequencies ranging from 8-500 Hz. Sensibility Index (SI) is used as a reliable index for pathology based on comparison with a large normal population. Several years of developmental work has now resulted in a new and refined type of vibrometer, designed to fulfil the requirements set up by EU.