Nerve damage: Medical literature reports damage to nerves in the wrist following police use of metallic handcuffs - particularly ratchet handcuffs of the rigid 'quickcuff' type design.
Damage appears to be associated with overtightening of the cuffs or twisting of the cuff once applied. Most frequent damage is to the superficial radial nerve in the wrist, which can result in temporary or lasting loss of sensation in specific areas of the hand (like the numbness when a dentist gives you a lignocaine injection).
Cuffs should be 'tight enough to touch the skin' but not 'tight enough to dig into the skin' - if it's causing indentation as you apply it, it's too tight. Double lock the cuffs immediately to prevent accidental tightening. Ratchet cuffs may be inappropriate where the sub may roll onto them or where tension is put on the chain, resulting in twisting. Rigid cuffs or hinged cuffs may present a higher risk of twisting. Smooth, barrel type cuffs (such as the historic Hyatts models) may present less risk of digging in.
Typical Medical Reference....
Grant, A.C., Cook, A.A. (2000) 'A prospective study of handcuff neuropathies.' Muscle And Nerve 23(6): 933-8