Abstract
Elucidating whether there is a correlation between biomechanical functions and histomorphometric data in the rat sciatic nerve crush injury model would contribute to an accurate evaluation of the regeneration state without sacrificing animals. The gold standard for functional evaluation is the sciatic functional index (SFI) despite there being intrinsic shortcomings. Kinematic analysis is considered a reliable and sensitive approach for functional evaluation, most commonly assessed as ankle angle at various phases of a gait cycle. Studies utilizing the toe angle for functional evaluation are scarce, and changes in the toe angle following surgery remain unknown. The present study assessed correlations of ankle angle, toe angle and SFI with histomorphometric data, aiming to determine which parameters most accurately reflect changes in histomorphometric data over time. Six Lewis rats were designated as the control group. 30 animals received surgery, six of them were randomly selected on the first, second, third, fourth, and sixth week after surgery for measurements of ankle and toe angles in the “toe-off” phase, and for evaluation of SFI. Histomorphometric analysis were also performed, to determine the number of myelinated nerve fibers, diameters of myelinated nerve fibers, axon diameters, and myelin sheath thicknesses. Furthermore, we investigated changes in ankle angle, toe angle, SFI, and histomorphometric data over time, as well as correlations between ankle angle, toe angle, and SFI with histomorphometric data. The results revealed that changes in SFI, ankle angle, and toe angle highly correlate with histomorphometric data in the rat sciatic nerve crush injury model. Toe angle reflected changes in histomorphometric data with time more precisely than ankle angle or SFI did, and ankle angle was a better prognostic parameter than SFI.
Highlights
The sciatic nerve is likely to undergo varying extent of crush injury in situations such as the fracture of pelvis, swelling resulting from muscle strains, or even prolonged sitting or lying with pressure on the buttocks [1]
We aimed to determine whether correlations exist between ankle angle, toe angle, and sciatic functional index (SFI), and histomorphometric data
Functional evaluation consisted of both SFI and kinematic analysis, and histomorphometric analysis included four parameters, including the number of myelinated nerve fibers, the diameter of myelinated nerve fibers, axon diameter, and myelin sheath thickness
Summary
The sciatic nerve is likely to undergo varying extent of crush injury in situations such as the fracture of pelvis, swelling resulting from muscle strains, or even prolonged sitting or lying with pressure on the buttocks [1]. The outcome of a crush injury can be improved by axonal regeneration and re-myelination in humans and rodents, due to intrinsic regenerative abilities of a peripheral nerve. The sciatic nerve generally undergoes three main processes after crush injury: Wallerian degeneration, axonal regeneration, and end-organ reinnervation[2]. Wallerian degeneration occurs within the first week after injury; the required time for axonal regeneration and end-organ reinnervation primarily depends on the distance from the distal stump to the organ. Identification of a correlation between function and histomorphometric data would be useful for evaluating the degree of sciatic nerve regeneration accurately while allowing for reductions in the number of experimental animals that are sacrificed. Previous studies suggested a lack of correlation between functional evaluation and histomorphometric data [3],[4]. Recent research provided evidence to the contrary, with findings indicating support a reliable correlation between function and histomorphometric data [5,6,7]
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