ABSTRACT
[Introduction] This study compared the effects of joint immobilization and concurrent electroacupuncture stimulation on fracture line appearance, which is indicative of differences in cortical bone structure, in the femurs of young adult rats. [Materials and Methods] Forty-two 7-week-old Wistar rats were divided into three groups: a hindlimb immobilized group (IM), a hindlimb immobilized group with concurrent electroacupuncture stimulation (IMEA), and an untreated control group (CO). IM and IMEA were immobilized for two weeks with a jacket-type immobilization device that immobilized the hip joint in extension and restricted hip joint adduction and abduction. Acupuncture needles were inserted into the femoral region during the immobilization period in the IMEA group, and continuous alternating current was used for stimulation. A low-frequency stimulator was used to generate electrical current (250 μsec, 50 Hz, 0.24 mA, 500 Ω load resistance), and stimulation was performed daily for two weeks at 10 min/day. The extracted femur was fractured from the anterior part of the diaphysis or metaphyseal end by three-point-bending under constant conditions with 10 mm between the fulcrum and a crosshead speed of 10 mm/min. [Results] IM showed significantly lower Stiffness, Deformation, and Strength values than CO. Bone morphometry parameters also showed lower values for IM. A cement line was observed between lamellar and non-lamellar bone in CO and IMEA, but was indistinct in IM. In CO and IMEA, minute bone fragments were formed in the deep diaphysis region sandwiched between the inner and outer circumferential lamellae, but no such fragments were found in IM. IMEA had less resorption than IM, and lamellar bone with a structure similar to CO was maintained. Moreover, cracks observed in CO and IMEA ran longitudinally in the vicinity of the cement line and rest line, but no such cracks were found in IM. [Discussion and Conclusion] These findings suggest that electroacupuncture mitigates bone weakening in immobilized rat femurs, and this affects the appearance of the fracture line.