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. 2017 Dec;4(1):16.
doi: 10.1186/s40634-017-0091-7. Epub 2017 May 12.

The effect of repetitive flexion and extension fatigue loading on the young porcine lumbar spine, a feasibility study of MRI and histological analyses

Olof Thoreson  1   2 , Lars Ekström  3 , Hans-Arne Hansson  4 , Carl Todd  3   5 , Wisam Witwit  6 , Anna Swärd Aminoff  3 , Pall Jonasson  7 , Adad Baranto  3
Affiliations

The effect of repetitive flexion and extension fatigue loading on the young porcine lumbar spine, a feasibility study of MRI and histological analyses

Olof Thoreson et al. J Exp Orthop. 2017 Dec.

Abstract

Background: The biomechanical mechanisms of failure of FSUs have been studied but the correlation of repetitive flexion and extension loadings to the initial phase of fatigue in young FSUs are still not known. The purpose of the study was to examine the fatigue results of low magnitude repetitive flexion and extension loading on porcine lumbar Functional Spinal Units (FSUs) with Magnetic Resonance Imaging (MRI) and histology.

Methods: Eight FSUs were subject to repetitive pivot flexion and eight to extension loading by a protocol of 20 000 cycles at 1 Hz with a load of 700 N. All loaded FSUs (N = 16) were examined with MRI and histology post loading. Three FSUs were examined with MRI as controls. Further three FSUs were non loaded histology controls.

Results: Fifteen (94%) of the loaded FSUs have decreased MRI signal in the growth zone of the superior vertebra and 12 (75%) in the inferior vertebrae. Fourteen (88%) FSUs have increased signal in the superior vertebral body. Fourteen (88%) FSUs have a reduced signal in all or any endplate. The histology morphometry displayed that the unstained parts of the epiphyseal growth zone were larger among the loaded FSUs (mean 29% vs 4%) and that the chondrocytes in the endplate and growth zones had abnormal structure and deformed extracellular matrix.

Conclusion: Repetitive loading of young porcine FSUs in both extension and flexion causes concurrent MRI and histological changes in the growth zones and endplates, which could be a first sign of fatigue and an explanation for the disc, apophyseal and growth zone injuries seen among adolescent athletes.

Keywords: Animal experimentation; End plate histology; Fatigue; Growth zone injury; In vitro; Intervertebral disc; MRI; Repetitive loading; Spine.

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Figures

Fig. 1
Fig. 1
Schematic view of the experimental set up in the MTS testing machine
Fig. 2
Fig. 2
Sagittal location of pivot point according to flexion (a) and extension (c) in relation to the most dorsal point of vertebrae (b)
Fig. 3
Fig. 3
Un-loaded control (a) and FSU after repetitive flexion (b). Decreased signal in both the superior (1) and inferior growth zones (2) and endplates in the flexed FSU. Un-loaded control (c) and FSU after repetitive extension (d). Reduced signal in the superior growth zone (1) and in inferior end plate (2) in the extended FSU
Fig. 4
Fig. 4
Histological overview of a flexed FSU. Highlighted are the cranial-anterior growth zone (1) and the caudal-posterior growth zone (2). Sizebar in cm. Haematoxylin-eosin and Alcian blue solution stain
Fig. 5
Fig. 5
Visualization of the histological results. Control (a), flexion (b) and extension (c) FSUs, where the reduction of intracellular content (1) and extracellular matrix (2) are highlighted with white arrows. Sizebar in mm. Haematoxylin-eosin and Alcian blue solution stain
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