The potential role of sciatic nerve stiffness in the limitation of maximal ankle range of motion

Ricardo J Andrade,Sandro R Freitas,Lilian Lacourpaille,Peter Mcnair,François Hug,Antoine Nordez,Guillaume Le Sant,Raphäel Gross

doi:10.1038/s41598-018-32873-6

Abstract

It is a long held belief that maximal joint range of motion (ROM) is restricted by muscle tension. However, it exists indirect evidence suggesting that this assumption may not hold true for some joint configurations where non-muscular structures, such as the peripheral nerves, are stretched. Direct evidences are lacking. This study aimed to determine whether a static stretching aiming to load the sciatic nerve without stretch within plantar flexors is effective to: (i) alter nerve stiffness; and (ii) increase the ankle’s maximal ROM. Passive maximal ankle ROM in dorsiflexion was assessed with the hip flexed at 90° (HIP-flexed) or neutral (HIP-neutral, 0°). Sciatic nerve stiffness was estimated using shear wave elastography. Sciatic nerve stretching induced both a 13.3 ± 7.9% (P < 0.001) decrease in the nerve stiffness and a 6.4 ± 2.6° increase in the maximal dorsiflexion ROM assessed in HIP-flexed. In addition, the decrease in sciatic nerve stiffness was significantly correlated with the change in maximal ROM in dorsiflexion (r = −0.571, P = 0.026). These effects occurred in the absence of any change in gastrocnemius medialis and biceps femoris stiffness, and ankle passive torque. These results demonstrate that maximal dorsiflexion ROM can be acutely increased by stretching the sciatic nerve, without altering the muscle stiffness.

Highlights

The maximal range of motion (ROM) of a joint is an important functional parameter to estimate the maximal muscle length or muscle extensibility that is widely used in clinical practice, sport training and research[1]
The effects of nerve stretching on ankle torque and sciatic nerve, gastrocnemius medialis (GM) and biceps femoris (BF) shear wave velocity are summarized in Table 1 and Fig. 1
This study provides the first in vivo experimental evidence that stretching peripheral nerves is efficient to improve the maximal ROM at a joint

Summary

Introduction

The maximal range of motion (ROM) of a joint is an important functional parameter to estimate the maximal muscle length or muscle extensibility that is widely used in clinical practice, sport training and research[1]. Two previous studies observed a remarkable decrease in the maximal ankle ROM in dorsiflexion when the hip was flexed from the neutral position to 90°7,8 This change occurred in the absence of any changes in the gastrocnemius medialis (GM) local stiffness and ankle torque[8]. A sciatic nerve stretch may decrease the stiffness of the neural tissue and improve the maximal ankle dorsiflexion ROM. To test this hypothesis non-invasively, it is necessary to assess the sciatic nerve stiffness during passive ankle rotations. Post hoc p-values for the before to after intervention changes in sciatic nerve shear-wave velocity (SWV) are presented for both Stretch and Control sessions. A better understanding of the biomechanical properties of peripheral nerves in vivo would have strong clinical importance, in particular to the management of nerves in the context of entrapment neuropathy or chronic neuropathies where both nerve’s stiffness and maximal joint ROM might be affected[16,17,18]

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