Effects of Rat Hind Limb Unweighting on the Extensibility of the Soleus and Skin around a Joint Contracture

Abstract

Purpose] The purpose of this study was to clarify the effects of unweighting the lower limbs on the extensibilities of the skin and soleus muscle around a contracted joint. [Subjects and Methods] Twelve wistar rats were divided into two experimental groups. The right ankle joints of the first experimental group were fixed in full plantar flexion (F). The hind limbs of the second experimental group were suspended, and their right ankle joints were fixed in full plantar flexion (FS). The period of fixation was one week. On the last day, the extensibilities of the soleus muscles and skin of the right ankle joint were measured.[Results] The extensibility of the soleus muscle of the FS group decreased more than that of the F group. [Conclusion] Our results indicate that unweighting the hind limbs of rats may cause severe joint contractures by decreasing muscle extensibility.

Study on change of rat soleus extensibility caused by reduction in joint movement with unweighting of the hind limbs

“…On the last day of this study, the ankle dorsiflexion angles in the FS group were significantly less than that in the F group. The results of the ankle dorsiflexion angle in this study were the same as in previous studies 15 , 16 ) . Therefore, also in this study, it was clarified that unweighting the lower limbs caused severe joint contractures induced by joint fixation.…”

“…When ankles were immobilized in full plantar flexion for one week, the ankle dorsiflexion angles were severely decreased by unweighting the lower limbs 15 , 16 ) . In the joint contractures caused by joint fixation for one week, the skeletal muscle composed approximately 80.5% of the proportion 17 ) .…”

“…Next, we considered the soleus extensibility in the 10 mm lengthened position. Generally, skeletal muscle extensibility is assessed by obtaining the length-tension curve when the muscle is stretched passively by using an Autograph 3 , 16 , 19 , 22 , 23 , 24 ) . The tension torque of the soleus muscle of normal rats in the length-tension curve gradually increased, but did not increase until the 10 mm lengthened position.…”

“…Unweighting the lower limbs from the microgravity environment of the universe may cause joint contractures in the human body 8 ) . Furthermore, joint movement decreases with hind limb suspension 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ) during an animal experiment model that reproduces the unweighting of the lower limbs 9 ) . From this, it is considered that unweighting the lower limbs might cause joint contracture in humans as well.…”

“…From this, it is considered that unweighting the lower limbs might cause joint contracture in humans as well. Therefore, in a previous study 15 , 16 ) , we performed a combination of hind limb suspension and joint fixation 3 , 4 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 ) , an animal experiment model that reproduces the reduction of joint movement. As a result, it was shown that the occurrence of joint contracture when performing joint fixation and hind limb suspension was more pronounced than when compared with only joint fixation.…”