Effect of Model Parameters on the Biomechanical Behavior of the Finite Element Cervical Spine Model.

Finite element (FE) models have frequently been used to analyze spine biomechanics. Material parameters assigned to FE spine models are generally uncertain, and their effect on the characterization of the spinal components is not clear. In this study, we aimed to analyze the effect of model parameters on the range of motion, stress, and strain responses of a FE cervical spine model. To do so, we created a computed tomography-based FE model that consisted of C2-C3 vertebrae, intervertebral disc, facet joints, and ligaments. A total of 32 FE analyses were carried out for two different elastic modulus equations and four different bone layer numbers under four different loading conditions. We evaluated the effects of elastic modulus equations and layer number on the biomechanical behavior of the FE spine model by taking the range of angular motion, stress, and strain responses into account. We found that the angular motions of the one- and two-layer models had a greater variation than those in the models with four and eight layers. The angular motions obtained for the four- and eight-layer models were almost the same, indicating that the use of a four-layer model would be sufficient to achieve a stress value converging to a certain level as the number of layers increases. We also observed that the equation proposed by Gupta and Dan (2004) agreed well with the experimental angular motion data. The outcomes of this study are expected to contribute to the determination of the model parameters used in FE spine models.

Direct Validation of Model-Predicted Muscle Forces in the Cat Hindlimb During Locomotion.

Various methods are available for simulating the movement patterns of musculoskeletal systems and determining individual muscle forces, but the results obtained from these methods have not been rigorously validated against experiment. The aim of this study was to compare model predictions of muscle force derived for a cat hindlimb during locomotion against direct measurements of muscle force obtained in vivo. The cat hindlimb was represented as a 5-segment, 13-degrees-of-freedom (DOF), articulated linkage actuated by 25 Hill-type muscle-tendon units (MTUs). Individual muscle forces were determined by combining gait data with two widely used computational methods-static optimization and computed muscle control (CMC)-available in opensim, an open-source musculoskeletal modeling and simulation environment. The forces developed by the soleus, medial gastrocnemius (MG), and tibialis anterior muscles during free locomotion were measured using buckle transducers attached to the tendons. Muscle electromyographic activity and MTU length changes were also measured and compared against the corresponding data predicted by the model. Model-predicted muscle forces, activation levels, and MTU length changes were consistent with the corresponding quantities obtained from experiment. The calculated values of muscle force obtained from static optimization agreed more closely with experiment than those derived from CMC.

Gait Analysis of Patients Subjected to the Atrophic Mandible Augmentation with Iliac Bone Graft.

In this study, we aimed to quantitatively monitor and describe the gait functions of patients, who underwent iliac crest bone grafting in atrophic jaw augmentation operation, by taking into account the alterations of gait parameters and muscle forces in the early recovery course. To do so, temporospatial and kinematic gait parameters of ten patients during pre- and postoperative periods were recorded, and forces of the gluteus medius, gluteus maximus, and iliacus muscles were calculated. Three postoperative periods were specified as one week (post-op1), two weeks (post-op2), and three weeks (post-op3) after the surgery. Restoring process of the gait patterns was comparatively evaluated by analyzing the gait parameters and muscle forces for pre- and postoperative periods. Temporospatial and kinematic parameters of post-op3 were closer to those obtained in pre-op than those in post-op1 and post-op2 (p < 0.05). Muscle forces calculated in post-op3 showed the best agreement with those in pre-op among the postoperative periods in terms of both magnitude and correlation (p < 0.05). In conclusion, the patients began to regain their preoperative gait characteristics from the second week after surgery, but complete recovery in gait was observed three weeks after the surgery.

EFFECTS OF HIGH-DOSE VITAMIN C AND HYALURONIC ACID ON TENDON HEALING.

OBJECTIVE: To assess the histopathologic and biomechanical effects of hyaluronic acid (HA) and high-dose vitamin C (VC) on rat Achilles tendon healing. METHODS: Forty-eight Sprague-Dawley rats were randomized to HA and VC and control groups with equal numbers. Each group was further divided into two subgroups to be sacrificed on Day 15 (n=8) and Day 30 (n=8). The Achilles tendons were cut and repaired. While the control rats remained untreated, HA and VC were administered after repair. The repaired tendons were removed for biomechanical and histopathologic analyses. In the biomechanical tests, the tendons were stretched to failure and maximum forces were measured. For histopathologic examination, the specimens were interpreted semiquantitatively using Movin's grading scale and Bonar scores. RESULTS: The highest mean forces were obtained in the HA group on Day 15 and in the VC group on Day 30, with a significant difference between HA and VC on Day 15 between control and VC on Day 30 (p<0.05). Histological examination showed both Movin and Bonar scores decreased in all groups on Day 30, with significant improvements in the HA and VC groups (p<0.05). CONCLUSION: Our results demonstrated that both VC and HA had therapeutic effects on tendon healing, especially in the late phase. Level of Evidence I; High quality randomized trial with statistically significant difference.

OBJETIVO: Avaliar os efeitos histopatológicos e biomecânicos do ácido hialurônico (AH) e altas doses de vitamina C (VC) na cicatrização do tendão do calcâneo em ratos. MÉTODOS: Quarenta e oito ratos Sprague-Dawley foram randomizados em grupo AH, grupo VC e grupo controle, iguais em número. Cada grupo foi dividido em dois subgrupos a serem sacrificados no Dia 15 (n = 8) e no Dia 30 (n = 8). Os tendões do calcâneo foram cortados e reparados. Enquanto os ratos do grupo controle permaneceram não tratados, os do grupo AH/VC receberam AH e VC após o reparo. Os tendões reparados foram removidos para análises biomecânicas e histopatológicas. Nos testes biomecânicos, os tendões foram estirados até a falha e as forças máximas foram medidas. No exame histopatológico, as amostras foram interpretadas semiquantitativamente usando os escores de Movin e de Bonar. RESULTADOS: As forças médias mais altas foram obtidas no grupo AH no Dia 15 e no grupo VC, no Dia 30, com diferença significativa entre os grupos HA e VC no Dia 15 e entre os grupos controle e VC (p < 0,05). No exame histológico, os escores de Movin e Bonar diminuíram em todos os grupos no dia 30, com melhora significativas nos grupos AH e VC (p < 0,05). CONCLUSÕES: Nossos resultados demonstraram que tanto a VC quanto o AH tiveram efeitos terapêuticos sobre cicatrização do tendão, especialmente na fase tardia. Nível de Evidência I; Estudo clínico randomizado de alta qualidade com ou sem diferença estatisticamente significante.

Biomechanical, histological, and radiological effects of different phosphodiesterase inhibitors on femoral fracture healing in rats.

PURPOSE: To investigate the biomechanical, histological, and radiological effects of sildenafil and pentoxifylline on femoral fracture healing in rats. METHODS: Forty-eight Sprague-Dawley rats were divided into three groups equally according to the pharmacological agents to be investigated. Femoral shaft fractures were formed in the left side. Group 1 (control group), group 2, and group 3 were administered with saline, sildenafil, and pentoxifylline during the fracture healing process, respectively. Eight rats from each group were euthanized on days 15 and 30. X-ray images of the rats were taken after euthanasia for radiographical examination. Femur samples were subjected to histopathological and biomechanical (three-point bending) examinations. RESULTS: Radiologically, no difference between the Goldberg scores of the groups was found for day 15 ( p > 0.05), while higher Goldberg scores were obtained from group 2 than that of group 1 ( p > 0.05) and group 3 ( p < 0.05) for day 30. In the biomechanical analysis, higher mean breaking forces were found both for day 15 and day 30 from group 2 than those obtained from group 1 (for day 15 p > 0.05 and day 30 p > 0.05) and group 3 (for day 15 p < 0.05 and day 30 p < 0.01). Higher mean absorbed energy values were obtained from group 2 than those obtained from group 1 (for day 15 p > 0.05 and day 30 p < 0.05) and group 3 (for day 15 p < 0.01 and day 30 p < 0.01). A significant difference was not found between the histological scores of all groups ( p > 0.05) for day 15, while the histological score of group 1 on day 30 was found to be significantly lower than that of sildenafil and pentoxifylline groups ( p < 0.05). CONCLUSION: Sildenafil had a positive effect on fracture healing, while pentoxifylline did not provide consistent positive effect.

Effects of high-dose vitamin c and hyaluronic acid on tendon healing / Efeitos de altas doses de vitamina c e ácido hialurônico sobre a cicatrização do tendão

ABSTRACT Objective: To assess the histopathologic and biomechanical effects of hyaluronic acid (HA) and high-dose vitamin C (VC) on rat Achilles tendon healing. Methods: Forty-eight Sprague-Dawley rats were randomized to HA and VC and control groups with equal numbers. Each group was further divided into two subgroups to be sacrificed on Day 15 (n=8) and Day 30 (n=8). The Achilles tendons were cut and repaired. While the control rats remained untreated, HA and VC were administered after repair. The repaired tendons were removed for biomechanical and histopathologic analyses. In the biomechanical tests, the tendons were stretched to failure and maximum forces were measured. For histopathologic examination, the specimens were interpreted semiquantitatively using Movin's grading scale and Bonar scores. Results: The highest mean forces were obtained in the HA group on Day 15 and in the VC group on Day 30, with a significant difference between HA and VC on Day 15 between control and VC on Day 30 (p<0.05). Histological examination showed both Movin and Bonar scores decreased in all groups on Day 30, with significant improvements in the HA and VC groups (p<0.05). Conclusion: Our results demonstrated that both VC and HA had therapeutic effects on tendon healing, especially in the late phase. Level of Evidence I; High quality randomized trial with statistically significant difference.

RESUMO Objetivo: Avaliar os efeitos histopatológicos e biomecânicos do ácido hialurônico (AH) e altas doses de vitamina C (VC) na cicatrização do tendão do calcâneo em ratos. Métodos: Quarenta e oito ratos Sprague-Dawley foram randomizados em grupo AH, grupo VC e grupo controle, iguais em número. Cada grupo foi dividido em dois subgrupos a serem sacrificados no Dia 15 (n = 8) e no Dia 30 (n = 8). Os tendões do calcâneo foram cortados e reparados. Enquanto os ratos do grupo controle permaneceram não tratados, os do grupo AH/VC receberam AH e VC após o reparo. Os tendões reparados foram removidos para análises biomecânicas e histopatológicas. Nos testes biomecânicos, os tendões foram estirados até a falha e as forças máximas foram medidas. No exame histopatológico, as amostras foram interpretadas semiquantitativamente usando os escores de Movin e de Bonar. Resultados: As forças médias mais altas foram obtidas no grupo AH no Dia 15 e no grupo VC, no Dia 30, com diferença significativa entre os grupos HA e VC no Dia 15 e entre os grupos controle e VC (p < 0,05). No exame histológico, os escores de Movin e Bonar diminuíram em todos os grupos no dia 30, com melhora significativas nos grupos AH e VC (p < 0,05). Conclusões: Nossos resultados demonstraram que tanto a VC quanto o AH tiveram efeitos terapêuticos sobre cicatrização do tendão, especialmente na fase tardia. Nível de Evidência I; Estudo clínico randomizado de alta qualidade com ou sem diferença estatisticamente significante.