Spontaneous Recovery of Radial Nerve Function Following Axonamonosis Caused by Impingement from Distal Locking Screws during Humeral Nailing

A 39-year-old man developed a radial nerve palsy following repair of a left segmental humerus fracture with a rigid interlocking intramedullary nail and screws. His palsy manifested as a wrist and finger drop, associated with numbness in the distribution of the radial nerve. This was managed conservatively with a wrist brace and passive extension exercises. The fracture repair was surgically explored again 9 months later because of a lack of recovery of the radial nerve palsy and fracture non-union leading to localized pressure and pain. During this period, there was no recordable recovery of the nerve; objective clinical assessments were regularly made and the findings were confirmed by neurophysiological studies. During the operation, it was found that the two distal locking screws were impinging on the radial nerve, trapping the epineurium and part of the perineurium. Careful neurolysis was performed and the screws were removed. The fracture was then reduced and fixed without further incident. Immediately following the operation, the patient almost immediately regained complete function in his left wrist and hand. The sensation was restored to normal and the power of his wrist and finger extension returned to Medical Research Council grade 4. As a result of the rapid rate of recovery, we have concluded that impingement by the screws on the patient's radial nerve had resulted in axonamonosis, an uncommon nerve lesion in which pressure on a nerve results in mechanical demyelinization of a length of nerve with interruption of conduction. On release of the pressure, early recovery follows the return of the myelin insulation.