Research progress on mechanical performance evaluation of artificial intervertebral disc / 生物医学工程学杂志

The mechanical properties of artificial intervertebral disc (AID) are related to long-term reliability of prosthesis. There are three testing methods involved in the mechanical performance evaluation of AID based on different tools: the testing method using mechanical simulator, specimen testing method and finite element analysis method. In this study, the testing standard, testing equipment and materials of AID were firstly introduced. Then, the present status of AID static mechanical properties test (static axial compression, static axial compression-shear), dynamic mechanical properties test (dynamic axial compression, dynamic axial compression-shear), creep and stress relaxation test, device pushout test, core pushout test, subsidence test, etc. were focused on. The experimental techniques using specimen testing method and testing results of available artificial discs were summarized. The experimental methods and research status of finite element analysis were also summarized. Finally, the research trends of AID mechanical performance evaluation were forecasted. The simulator, load, dynamic cycle, motion mode, specimen and test standard would be important research fields in the future.

Advances in Loading Methods of in vitro Spinal Biomechanical Test / 医用生物力学

The description for load-displacement characteristics of in vitro spinal specimens in three-dimensional (3D) motion is the foundation of spinal biomechanical research. How to simulate the load and movement of spine in vivo as accurately as possible is the difficulty of in vitro spinal biomechanical research. Domestic and foreign scholars have carried out extensive research on theories and equipments of spinal biomechanical test. Currently, the spinal 3D motion test is mainly divided into load control, displacement control and hybrid control according to the control method. Based on different control method, the test equipments are also developing and perfecting constantly. The operation principle for current in vitro spinal loading devices are summarized, and their advantages and disadvantages are also analyzed, so as to provide references for the research on in vitro spinal biomechanical loading devices.

Evaluación biomecánica del efecto de bisfosfonatos y aceite de oliva en un modelo de remodelación óseo en fémur de rata: efectos en la remodelación ósea / Biomechanical evaluation of the effect of bisphosphonates and olive oil in a model of bone remodeling in rat femur: effects on bone remodeling

Estudios han demostrado que el aceite de oliva (O) con sus compuestos fenólicos tienen efectos positivos en diversos biomarcadores fisiológicos. Análisis previos han demostrado que los bisfosfonatos, son potentes inhibidores de la resorción ósea. Estudiar el efecto del tratamiento combinado de alendronato (AL) y pamidronato (PA) y de O sobre la regeneración ósea. Las fórmulas se dosificaron 0,5 mg/kg de peso para AL, y de 0,6 mg/kg de peso para PA. El O se administró en la dieta, 50 g/Kg. Cincuenta y cuatro ratas macho de la línea Wistar se dividieron en 6 grupos. El grupo control (C), recibió semanalmente 0,3 ml/100 g de solución salina vía subcutánea. El grupo (AL) recibió semanalmente por vía subcutánea en el miembro posterior izquierdo. El grupo (PA) se colocó igual que el grupo anterior. El grupo (O) fue tratado en la alimentación y en las áreas de la cirugía recibieron inyección subcutánea con solución fisiológica. El grupo (ALO) recibió tratamiento combinado con AL y O. El grupo (PAO) se trató igual al anterior. Se obtuvieron muestras de fémur en tiempos 15, 30, 60 y 90 días, que se incluyeron en solución fisiológica y mantenidos a -20 C. Los estudios estadísticos se realizaron a través del análisis de la variancia a dos y tres criterios de clasificación. Sólo el factor días influye significativamente sobre los valores. Las diferencias entre drogas no resultaron estadísticamente significativas. Tampoco se verificó interacción significativa entre los factores Droga y etapa. Los valores más elevados de fuerza de ruptura aplicada, se registraron a los 90 días. No se encontraron diferencias significativas en los ensayos biomecánicos, poniendo de manifiesto la acción sistémica de los fármacos. Estas acciones fueron benéficas al aumentar la rigidez.

Studies have shown that olive oil (O) with its phenolic compounds have positive effects on various physiological biomarkers. Previous analyzes have shown that bisphosphonates are potent inhibitors of bone resorption. The objective of this work was to study the effect of combined treatment with alendronate (AL) and pamidronate (PA) and O on bone regeneration. Formulas 0.5 mg/kg for AL dosed, and 0.6 mg/kg for PA. O was administered in the diet, 50 g/kg. Fifty-four male Wistar rats were divided into 6 groups. The control group (C) received weekly 0.3 mL/100 g of saline subcutaneously. Group (AL) received weekly subcutaneously in the left posterior limb. Group (PA) was placed as the previous group. Group (O) was treated in food and in the areas of surgery received subcutaneous injection with saline. The (ALO) group received combined treatment with Al and O. The group (PAO) was treated the same as before. Femur samples at times 15, 30, 60 and 90 days, were included in physiological solution and maintained at -20 °C were obtained. Statistical studies were conducted through analysis of variance to two and three classification criteria. The ANOVA showed that only days factor significantly influences the values of the variables (p <0.05). The differences between drugs were not statistically significant (p> 0.05). Nor was there significant drug interaction between factors and stage (p> 0.05) was verified. The highest values of force rupture applied occurred at 90 days. No significant differences were found in the biomechanical testing, demonstrating the systemic action of drugs. These actions were beneficial to increase rigidity.

Effect of three different fixation techniques on stability of greater tuberosity fractures of humerus / 医用生物力学

Objective To compare the stability of greater tuberosity fractures of humerus treated by three different fixation techniques (screws, tension band, locking plate, respectively) through biomechanical testing, so as to provide the biomechanics basis for choosing a better fixation in the clinical treatment for greater tuberosity fractures of humerus. Methods Standardized fracture models of the greater tuberosity from 18 fresh-frozen proximal humeri with intact rotator cuffs were created. The specimens were randomly assigned to 3 groups and treated by screws, tension band and locking plates, respectively. An increasing force was applied to the supraspinatus tendon. The force displacement curve and two parameters: LtYP(Load to 5 mm yield point) and Ltf(load to failure) were recorded. Results LtYP from the screw group, tension band group and locking plate group was (377±86), (499±90), (793±52) N, respectively, with significant differences among the three groups (P0.05). Conclusions Locking plates show more obvious biomechanical stability than screws and tension band, which provides a new and better choice for treatment of isolated greater tuberosity fractures of humerus.

Biomechanical evaluation on dynamic hip screw versus proximal femoral nail fixation for unstable femoral intertrochanteric fractures / 医用生物力学

Objective To investigate the biomechanical stability of both DHS (dynamic hip screw) and PFN (proximal femoral nail) for treating unstable intertrochanteric fractures. Methods A standard 4-part osteotomy was performed in 8 pairs of fresh frozen human cadaver femurs, which were then randomly assigned to two groups: PFN group and DHS group for biomechanical testing. These specimens were applied to a cyclic load up to 200, 400, 600, 800, 1 000, 1 200, 1 400 N, respectively. Fracture displacement was measured during the loading to determine biomechanical stability of the implant. Each specimen was repeatedly loaded for 5 times to calculate the average displacement and draw the load-displacement curve. For failure testing, the initial load and loading rate was set at 1 400 N and 10 N/s, respectively. The applied compressive load was increased by 600 N each time for five cycles. The pressure was gradually increased to its peak force, and sustained for 10 second before it was gradually decreased to 0 N. The highest force value sustained before failure was defined as the maximum strength of the implant. Results The biomechanical testing on all specimens was completed successfully. There was no damage to the internal fixation. The average displacement and stiffness in DHS group were (3.92±2.21) mm and (215.28±58) N/mm, while those in PFN group were (4.22±1.80) mm and (197.06±34.20) N/mm, so no significant difference was found between the DHS and the PFN group (P> 0.05). New fracture occurred at the distal end of nail in PFN group. The DHS was fractured at the distal cortical screw, but no nail was cut out of the femoral head. The average load required for failure was (4 312±560) N in PFN group and (3 954±520) N in DHS group, and no significant difference was found between the two groups(P＞0.05). Conclusions The test shows that the PFN does not appear to offer any distinct biomechanical advantage over the DHS in the treatment of unstable intertrochanteric fractures. The implant chosen for treating intertrochanteric fractures must depend on patient’s fracture geometry, and anatomic reduction should be conducted in clinical treatment. If the anatomic reduction is difficult, trying to recover continuity of the posterior cortical bone would be necessary.

Effect of low-intensity pulsed ultrasound stimulation on maturation of regenerate bone / 中南大学学报(医学版)

Objective To explore the effect of low intensity pulsed ultrasound stimulation (LI-PUS) on the maturation of regenerate bone in a rabbit limb lengthening model. Methods Sixty skeletal mature female New Zealand white rabbits were randomly divided into an LIPUS treatment group and a control group. All rabbits were underwent mid-diaphyseal tibial osteotomy and immobilized in an Orthofix M103 Mini lengther. Gradual distraction at 0. 5 mm every 12 h for 10 d was performed at day 7 postoperatively. A 4-week course of LIPUS treatment group was applied over the distraction site for 20 min daily starting immediately after the completion of the distraction only for the treatment group. Rabbits were euthanized and the mid-diaphyseal tibia was harvested for evaluation at 4, 8, and 12 wk after the completion of the bone lengthening protocol. Radiographic analysis was performed to study the formation of bone callus using the ImageJ software at 12 wk after the completion of the bone lengthening protocol. Bone mineral density (BMD) of regenerate bone was measured by Dual energy X-ray absorptiometry (DEXA) . Torsional testing to failure was performed on the tibia specimens at 8 and 12 wk after the completion of the bone lengthening protocol. Results Radio-graphic measurement showed higher relative gray scale of bone callus in the LIPUS group than that in the control group at 12 wk (P ＜ 0. 05) . BMD in the LIPUS group was significantly higher than that in control group at 8 and 12 wk (P ＜ 0. 05). Biomechanical testing showed that the ultimate torque, ultimate torsional stiffness, and energy absorption at failure of regenerated bone at 8 and 12 wk in the LIPUS treatment group were better than those in the control group (P ＜ 0. 05) Conclusion LIPUS as a biophysical stimulation may accelerate the formation and maturation of regenerate bone in rabbit tibia lengthening model.

A Biomechanical Comparison among Three Surgical Methods in Bilateral Subaxial Cervical Facet Dislocation

OBJECTIVE: The biomechanical stabilities between the anterior plate fixation after anterior discectomy and fusion (ACDFP) and the posterior transpedicular fixation after ACDF(ACDFTP) have not been compared using human cadaver in bilateral cervical facet dislocation. The purpose of this study is to compare the stability of ACDFP, a posterior wiring procedure after ACDFP(ACDFPW), and ACDFTP for treatment of bilateral cervical facet dislocation. METHODS: Ten human spines(C3-T1) were tested in the following sequence: the intact state, after ACDFP(Group 1), ACDFPW(Group 2), and ACDFTP(Group 3). Intervertebral motions were measured by a video-based motion capture system. The range of motion(ROM) and neutral zone(NZ) were compared for each loading mode to a maximum of 2.0Nm. RESULTS: ROMs for Group 1 were below that of the intact spine in all loading modes, with statistical significance in flexion and extension, but NZs were decreased in flexion and extension and slightly increased in bending and axial rotation without significances. Group 2 produced additional stability in axial rotation of ROM and in flexion of NZ than Group 1 with significance. Group 3 provided better stability than Group 1 in bending and axial rotation, and better stability than Group 2 in bending of both ROM and NZ. There was no significant difference in extension modes for the three Groups. CONCLUSION: ACDFTP(Group 3) demonstrates the most effective stabilization followed by ACDFPW(Group 2), and ACDFP(Group 1). ACDFP provides sufficient strength in most loading modes, ACDFP can provide an effective stabilization for bilateral cervical facet dislocation with a brace.