Excursion and strain of superficial peroneal nerve during inversion ankle sprain

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J Bone Joint Surg Am. 2007 May;89(5):979-86.

Excursion and strain of the superficial peroneal nerve during

inversion ankle sprain.

O'Neill PJ, Parks BG, Walsh R, LM, SD.

Union Memorial Orthopaedics, The ston Professional Building,

#400, 3333 North Calvert Street, Baltimore, MD 21218, USA.

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 < 0.05).

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.