Experimental Study On The Effects Of Continuous And Intermittent Mechanical Vibrations On Bone Fracture Healing

Purpose: High frequency and low magnitude mechanical vibration can promotefracture healing, but the study of intermittent mechanical vibration with highfrequency and low magnitude in bone fracture healing is relatively less. In order toavoid nonunion of fracture and the delay, and provide a theoretical basis for clinical,the present macro experiment is to discuss the impact of continuous and intermittentmechanical stimulus with high frequency and low magnitude in fracture healing.Methods: Ninety healthy female Small Tailed Han sheep,12-month-old, wererandomly assigned into10groups in average,9in each group, including control groupand experimental group. The control group included: baseline control group (withoutany treatment, grow normally till the end of the experiment), sham operation group(without fracture, incision subcutaneous tissue and suture bandaging) and simpleinternal fixation group (without fracture, with plate fixation then suture bandaging),fracture control group (fracture treatment and naturally heal till the end of theexperiment); experimental groups includes: continuous vibration group (dailyvibration till the end of the experiment), intermittent vibration groups with1day,3days,5days,7days and14days intervals(vibrate N days then stop N days, thevibration of2N day cycle till the end of the experiment). All the animals inexperimental groups were subjected to surgery for right hind metatarsal fracture. Twoweeks after operation, all the experimental groups were applied magnitude bymechanical vibration (frequency F=35Hz, acceleration a=0.25g, time T=15min,continuous vibration, only the fracture metatarsal with vibration, the other side of thefracture without vibration. The vibration direction is vertical to the transversal crosssection of fracture). Eight weeks after surgery, the metatarsus of all the sheep wereharvested after sacrifice, Roentgen-ray scanning and mechanical compressionexperiment were performed for imaging analysis and biomechanical properties.Results:(1) Macro imaging detection: Semi quantitative assessment of X-ray was performed in the imaging estimation. All the samples were classified from level I tolevel IV. The incidence of the four levels was analyzed. The result showed that mostbone healing belonged to the level III in all the groups, about ninety percent of thetotal; while level II was detected in each group, about ten percent of the total. Contrastthe volume, cross-sectional area and number of callus formed around the site of thefracture: the callus volume, cross-sectional area and the number of experimentalgroups (continuous vibration group and intermittent vibration groups) are larger,wider and more than fracture vibration group. In all groups of experimental group, thecallus volume, cross-sectional area and the number of the intermittent vibrationgroups with7days intervals are larger, wider and more. The parameters of othergroups in experimental group showed no statistical difference in comparison.(2)Macro mechanical properties detection: The mechanical properties of bone, the elasticmodulus of each sample were detected mainly through the mechanical compressexperiment.1, fracture line location: the elastic modulus of fracture control group isslightly larger than that of continuous vibration group and the intermittent vibrationgroup with7days intervals; the elastic modulus of the intermittent vibration groupwith7days intervals slightly less than the continuous vibration group, but there wasno significant difference (p>0.05).2,15mm away from the fracture line: the elasticmodulus of fracture control group is less than continuous vibration group andintermittent vibration group with7days intervals (p<0.05), showing statisticaldifference；Continuous vibration group was less than intermittent vibration group with7days intervals, but no significant difference (p>0.05).3,25mm away from thefracture line: the elastic modulus of fracture control group is less than continuousvibration group and intermittent vibration group with7days intervals (p<0.05),showing statistical difference；Continuous vibration group was less than intermittentvibration group with7days intervals, but no significant difference (p>0.05).Conclusion: Macro imaging detection results showed that in each group, ninetypercent samples were III level, ten percent were II level, the effect was not tooobvious, because the time was short. But from callus volume, cross-sectional area and number，high frequency and low magnitude mechanical vibration promoted callusgrowth and fracture healing, and intermittent vibration group with7days intervalswas best. The detection of macro mechanical properties showed high frequency andlow magnitude mechanical vibration did not significantly improve the elastic modulusof the fracture; but around the fracture, it is conducive to the growth of bone, theelastic modulus of the experimental group was significantly improved, the effect ofthe intermittent vibration group with7days intervals was best.To sum up, in the process of fracture healing, high frequency and low magnitudemechanical vibration promotes bone growth and fracture healing, the effect ofintermittent vibration group with7days intervals was best.