Background: Traction is presumed to be the mechanism of injury to
the superficial peroneal nerve in an inversion ankle sprain, but it is not
known whether the amount of strain caused by nerve traction is sufficient to
cause nerve injury. We hypothesized that the superficial peroneal nerve would
experience significant excursion and strain during a simulated inversion
sprain, that sectioning of the anterior talofibular ligament would increase
excursion and strain, and that an impact force would produce strain in a range
that can structurally alter the nerve.
Methods: Differential reluctance transducers were placed in the
superficial peroneal nerve in sixteen lower-extremity cadaver specimens to
measure excursion and strain in situ. Static weight was applied to the foot in
increments starting at 0.454 kg and ending at 4.54 kg. The anterior
talofibular ligament was sectioned, and the measurements were repeated. A
final impact force of 4.54 kg was applied to each specimen. Two-way
repeated-measures analysis of variance was used to evaluate differences in
excursion and strain.
Results: The mean excursion and strain of the superficial peroneal
nerve increased with increases in the applied weight in both the group with
the intact anterior talofibular ligament and the group in which it had been
sectioned. Nerve excursion was greater in the sectioned-ligament group than in
the intact-ligament group with all applied weights (p < 0.05). The mean
nerve strain was greater in the sectioned-ligament group (range, 5.5% to
12.9%) than in the intact-ligament group (range, 3.0% to 11.6%) with
application of the 0.454, 0.908, 1.362, and 1.816-kg weights (p < 0.05).
With the ligament sectioned, the 4.54-kg impact force produced significantly
higher mean nerve excursion and strain than did the 4.54-kg static weight (p
Conclusions: The magnitude of strain with the impact force was in
the lower range of values that have been shown to structurally alter
peripheral nerves. The superficial peroneal nerve is at risk for traction
injury during an ankle inversion sprain and is at additional risk with more
severe sprains or with an insufficient anterior talofibular ligament.
Clinical Relevance: Nerve injury may contribute to the high rate of
residual morbidity after inversion ankle sprains.