Riveting hammer vibration damages mechanosensory nerve endings

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Abstract

Background and Aims

Hand‐arm vibration syndrome (HAVS) is an irreversible neurodegenerative, vasospastic and musculoskeletal occupational disease of workers using powered hand tools. The etiology is poorly understood. Neurological symptoms include numbness, tingling and pain. This study examines impact hammer vibration‐induced injury and recoverability of hair mechanosensory innervation.

Methods

Rat tails were vibrated 12 min/d for 5 wk followed by 5 wk recovery with synchronous non‐vibrated controls. Nerve fibers were PGP9.5 immunostained. Lanceolate complex innervation was compared quantitatively in vibrated vs sham. Vibration peak acceleration magnitudes were characterized by frequency power spectral analysis.

Results

Average magnitude (2515 m/s2, rms) in kHz frequencies was 109 times that (23 m/s2) in low Hz. Percentage of hairs innervated by lanceolate complexes was 69.1% in 5wk sham and 53.4% in 5wk vib generating a denervation difference of 15.7% higher in vibration. Hair innervation was 76.9% in 5wk recovery sham and 62.0% in 5wk recovery vibration producing a denervation difference 14.9% higher in recovery vibration. Lanceolate number per complex (18.4 ± 0.2) after vibration remained near sham (19.3 ± 0.3), but 44.9% of lanceolate complexes were abnormal in 5 wk vibrated compared to 18.8% in sham.

Interpretation

The largest vibration energies are peak kHz accelerations (~ 100 000 m/s2) from shock waves. The existing ISO 5349‐1 standard excludes kHz vibrations, seriously underestimating vibration injury risk. The present study validates the rat‐tail, impact hammer vibration as a model for investigating irreversible nerve damage. Persistence of higher denervation difference after 5‐week recovery suggests repeated vibration injury destroys the capability of lanceolate nerve endings to regenerate.

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