Crossover innervation after digital nerve injury: myth or reality?

Several clinical studies promulgate the concept that some degree of crossover innervation occurs after digital nerve injuries are sustained and that the intact digital nerve might even substitute for the loss of nerve function on the injured side. Other studies strongly dispute the existence of this phenomenon. An excellent model for evaluation of crossover innervation is bilateral sharp digital nerve lacerations because there is no confusion of anomalous innervation from an intact contralateral nerve. This model avoids problems seen with replanted digits such as the inherent ischemia, multistructural injury, and the frequent crush component. The author evaluates the role of crossover innervation after digital nerve injury by comparing recovery of sensibility after unilateral and bilateral epineural neurorrhaphies. A retrospective review of 74 sharp unilateral and bilateral epineural digital nerve repairs in 54 patients using microsurgical techniques was performed by measurement of Weber's two-point discrimination (2PD). Fifty-four unilateral digital nerve repairs were performed in 46 patients who ranged in age from 8 to 54 years (mean age, 30.8 years). Concomitant flexor tendon injuries occurred in 50% of patients. Injury to repair was less than 1 day in 14.3% of patients, 2 to 7 days in 34.7%, 8 to 30 days in 40.8%, and 31 to 300 days in 10.2%. Follow-up ranged from 6 to 68 months (average follow-up, 13.8 months). Twenty bilateral digital nerve repairs were performed in 8 patients who ranged in age from 6 to 37 years (mean age, 27.6 years). Concomitant flexor tendon injuries occurred in 80% of patients. Injury to repair was less than 1 day in 10% of patients, 2 to 7 days in 60%, 8 to 30 days in 20%, and 31 to 300 days in 10%. Follow-up ranged from 6 to 77 months (average follow-up, 15.8 months). In this series, 2PD averaged 7.8 mm after unilateral digital nerve repairs compared with 7.1 mm after bilateral nerve repairs. Recovery of sensibility was also stratified into groups according to modified American Society for Surgery of the Hand guidelines: excellent, <6 mm; good, 6 to 10 mm; fair, 11 to 15 mm; and poor, >15 mm or protective sensation. Unilateral digital nerve repairs produced excellent results in 27.8% of patients, good in 46.3%, and fair in 25.9% compared with bilateral nerve repairs with excellent results in 15% of patients, good in 70%, and fair in 15%. There was no significant difference in recovery of sensibility after unilateral and bilateral digital nerve repairs. Crossover innervation did not appear to influence the long-term outcome after digital neurorrhaphy.