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Effects of hypertonia on contracture development in rat spinal cord injury


Study design

Experimental animal study.


Spastic hypertonia is originally believed to cause contractures from clinical observations. Botulinum toxin is effective for the treatment of spasticity and is widely used in patients who have joints with contractures. Using an established rat model with knee contractures after spinal cord injuries, we aimed to verify whether hypertonia contributes to contracture development, and the botulinum toxin improves structural changes in muscles and joint components responsible for contractures.


University laboratory in Japan.


To evaluate the effect of hypertonia on contracture development, the rats received botulinum toxin injections after spinal cord injuries. Knee extension motion was measured with a goniometer applying a standardized torque under anesthesia, and the contribution by muscle or non-muscle structures to contractures were calculated by measuring joint motion before and after the myotomies. We quantitatively measured the muscle atrophy, muscle fibrosis, and synovial intima length.


Botulinum toxin injections significantly improved contractures, whereas did not completely prevent contracture development. Botulinum toxin was effective in improving the muscular factor, but little difference in the articular factor. Spinal cord injuries induced muscle atrophy, and botulinum toxin significantly accelerated muscle atrophy and fibrosis. The synovial intima length decreased significantly after spinal cord injuries, and botulinum toxin did not improve this shortening.


This animal study provides new evidence that hypertonia is not the sole cause rather is the partial contributor of contractures after spinal cord injuries. Furthermore, botulinum toxin has adverse effects in the muscle.

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Data archiving

All data generated or analyzed during this study are included in this published article and its supplementary information files.


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We thank Naoyoshi Sakitani, Shin Ogasawara, Ryota Suzuki, Eriko Mizuno, and Masato Nomura for their skilled technical assistance.


This work was supported in part by the Japan Society for the Promotion of Science (JSPS) KAKENHI Grant no. 17K19908.

Author information

HM was responsible for designing and directing the protocol, interpreting results, and writing the manuscript. JO was responsible for designing and directing the protocol, interpreting results, and revising the manuscript. TY, SI, and TW was responsible for conducting the experiment, extracting and analyzing data, and revising the manuscript. NK, YS, and TA was responsible for designing the protocol, interpreting results, and revising the manuscript.

Correspondence to Hideki Moriyama.

Ethics declarations


This study was approved by the Institutional Animal Care and Use Committee (Permission number: P130408) and carried out according to the Kobe University Animal Experimentation Regulations.

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The authors declare that they have no conflict of interest.

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