Energy Metabolism ; Humans ; Oxygen Consumption ; Walking ; physiology ; Weight-Bearing ; physiology

OBJECTIVETo investigate the changes of stress distribution in the normal maxillary complex under different conditions and explore the feature of biomechanical reaction.

METHODSA three-dimensional finite element stress analysis has been used to investigate the characters of stress distribution at open-mouth position and in centric occlusion.

RESULTSUnder the same load, the stresses of the same region in the normal maxillary complex were distributed unequally. The limits of stress at open-mouth position (8.969 N) were wider than that in centric occlusion (6.497 N).

CONCLUSIONSThe stress of the whole maxillary complex in centric occlusion was lower than that at open-mouth position because of the different state of masticatory muscle. This indicated that the effect of muscles needed to be considered in the study of maxillary complex biomechanics.

Finite Element Analysis ; Humans ; Maxilla ; physiology ; Stress, Mechanical ; Weight-Bearing

This study was designed to determine the effect of backpack loading on the gait pattern and corresponding compensatory strategy, which is important to the balance control of biped robot and military training. Five healthy subjects were instructed to walk at their preferred speed on level pathway taking three different loads i.e. 6 kg, 12 kg and 25 kg, on their backs. The results showed that the gait pattern was apparently influenced, and the dominant effects were found to be the flexion of hip, knee joints and pitch angle of torso. The stride speed decreased apparently with loading on their backs, but the stride length showed less changes. Besides, the responses to taking loads might be influenced by the strength of body. An apparent multi-joints coordination motor mode was employed to compensate the influences of loading, however, their contributions are different; hip, knee joints and torso pitch made dominant contributions to the compensation while ankle joints made minor. The anterior pitch of upper torso could be employed to adjust the overall center of mass while loading on their backs, the larger the magnitude of loading on their backs, the larger the anterior pitch angle of torso. After the heel touched the ground, the flexion of hip and knee joints were effective for the shock absorption, which means that the stiffness of hip and knee joints can be used to absorb the shock and avoid the trauma of each joints.
Adult ; Ankle Joint ; physiology ; Back ; physiology ; Gait ; physiology ; Hip Joint ; physiology ; Humans ; Knee Joint ; physiology ; Male ; Weight-Bearing ; physiology

The purpose of this study was to investigate the effect of different backpack load on the plantar pressure of people during walking. By using three-dimensional force platform system, we collected the ground reaction force data from 20 college students, who were carrying different loads on their backs, and then we transformed the data into a characteristic two-peak curve. Seven characteristic parameters on the curve were selected and analyzed by using statistical methods. The results indicated that the peak ground reaction forces increased as the loads increased. Furthermore, in consideration of different genders, the amount increased was different. For the male subjects, when backpack load reached 17% body weight, changes in ground reaction force began to take place until the backloads reached 20% body weight changes in ground reaction force induced a significant difference. Por the female subjects, changes in ground reaction force began to take place with loads up to 14% body weight and while it reached 15% body weight it induced a significant difference.
Back ; physiology ; Biomechanical Phenomena ; physiology ; Female ; Foot ; physiology ; Humans ; Male ; Pressure ; Stress, Mechanical ; Walking ; physiology ; Weight-Bearing ; physiology ; Young Adult

OBJECTIVETo investigate the stress distribution and fracture mechanism of proximal femur under impact loads.

METHODSThe image data of one male's femur were collected by the Lightspeed multi-lay spiral computed tomography. A 3D finite element model of the femur was established by employing the finite element software ANSYS, which mainly concentrated on the effects of the directions of the impact loads arising from intense movements and the parenchyma on the hip joint as well as those of the femur material properties on the distribution of the Mises equivalent stress in the femur after impact.

RESULTSThe numerical results about the effects of the angle sigma of the impact loads to the anterior direction and the angle gamma of the impact loads to the femur shaft on the bone fracture were given. The angle sigma had larger effect on the stress distribution than the angle gamma, which mainly represented the fracture of the upper femur including the femoral neck fracture when the posterolateral femur was impacted. This result was consistent with the clinical one. The parenchyma on the hip joint has relatively large relaxation effect on the impact loads.

CONCLUSIONSA 3D finite element analysis model of the femoral hip joint under dynamic loads is successfully established by using the impact dynamic theory.

Femur ; physiology ; Finite Element Analysis ; Humans ; Male ; Models, Biological ; Stress, Mechanical ; Weight-Bearing ; physiology

The tension moduls and compression modulus of Chinese tibia and femur of male in three different directions, namely axial, circumferential and radial directions, were tested in our experiments. The measured compression moduli are 5.8 +/- 0.34, 3.4 +/- 0.17, 2.1 +/- 0.18 GPa respectively for femur, and 6.1 +/- 0.36, 3.5 +/- 0.17, 2.1 +/- 0.18 GPa respectively for tibia; the measured tension moduli are 15.6 +/- 1.21, 9.8 +/- 0.73, 5.4 +/- 0.52 GPa respectively for femur, and 16.7 +/- 1.09, 10.3 +/- 0.70, 5.6 +/- 0.49 GPa respectively for tibia. The tension and compression ultimate strengths of femur and tibia were tested, too. The measured compression ultimate strengths are 150 +/- 9.3, 111 +/- 6.5, 110 +/- 7.1 MPa respectively for femur, and 191 +/- 12.3, 140 +/- 6.3, 123 +/- 8.3 MPa respectively for tibia; the measured tension ultimate strengths are 115 +/- 9.6, 82 +/- 6.8, 78 +/- 7.3 MPa respectively for femur, and 143 +/- 8.7, 110 +/- 8.3, 97 +/- 6.4 MPa respectively for tibia. Furthermore, the stress-relaxation experiments were conducted. The relation between loading and time during the experiments were obtained by the method of curve fitting. They meet the logarithm function: F = A * B(log t); A is the initial load, and B is the fitting material parameter. For femur, B is equal to 0.985; for tibia, B is equal to 0.987.
Anisotropy ; Biomechanical Phenomena ; China ; Elasticity ; Femur ; physiology ; Humans ; Male ; Models, Biological ; Reference Values ; Tibia ; physiology ; Weight-Bearing ; physiology

OBJECTIVETo study the effect of disc degeneration on the structural property distributions in the cervical vertebral endplates.

METHODSA 2 mm-diameter hemispherical indenter was used to perform indentation tests at 0.03 mm/s to the depth of 2 mm at 20 normalized locations in 50 bony endplates of intact human cervical vertebrae (C2 approximately C7). The resulting load-displacement curves were used to extract the failure load and stiffness of each test site. Grade of disc degeneration was determined using Nachemson's grading scale. One-way ANOVA, factorial analyses, SNK tests and correlate analyses were used to analyze the result data.

RESULTSBoth the failure load and stiffness decreased with disc degeneration in the cervical endplates (P <0.001, both), and correlated significantly with the disc degeneration (rs=-0.429 and rs=-0.244, respectively). Only the distribution of superior cervical endplate changed with disc degeneration, but that of inferior cervical endplate changed little.

CONCLUSIONSThe structural property distributions in the cervical vertebral endplates change significantly in the degenerated discs. It suggests that disc degeneration is an important factor to evaluate the intervertebral implant subsidence in anterior cervical fusion.

Biomechanical Phenomena ; Cervical Vertebrae ; physiopathology ; Compressive Strength ; physiology ; Humans ; Intervertebral Disc ; physiology ; Intervertebral Disc Displacement ; physiopathology ; Weight-Bearing ; physiology

The purpose of this study was to examine and analyze the distribution of pressure under the feet School Children who were carrying different loads on their backs and were walking through the Footscan plantar pressure distribution analytical system. The result showed that the maximum force on the second and third metatarsus increased and the contact phase of walking delayed while walking with a bag weighing 4 kilograms. The variation of center of sure (COP) in mediolateral (M/L) direction was larger. The children must move limb to maintain balance. The proportion of foot pronation and supination enhanced the cause of an ankle sprain. The findings of this study suggest that, for prevention of abnormal corpus callosum and for the normal development of the arch, attention should be given to restricting the weight of children's schoolbags and to avoiding their overloaded walking or standing for a long time.
Biomechanical Phenomena ; Child ; Female ; Foot ; physiology ; Humans ; Lifting ; adverse effects ; Male ; Pressure ; Walking ; physiology ; Weight-Bearing ; physiology

Fins incorporated into the design of a dynamic cervical spine implant have been employed to enhance axial load- bearing ability, yet their true biomechanical advantages, if any, have not been defined. Therefore, the goal of this study was to assess the biomechanical and axial load-bearing contributions of the fin components of the DOC ventral cervical stabilization system. Eighteen fresh cadaveric thoracic vertebrae (T1-T3) were obtained. Three test conditions were devised and studied: Condition A (DOC implants with fins were placed against the superior endplate and bone screws were not inserted) ; Condition B (DOC implant without fins was placed and bone screws were inserted) ; and Condition C (DOC implant with fins were placed against the superior endplate and bone screws were inserted). Specimens were tested by applying a pure axial compressive load to the superior platform of the DOC construct, and load-displacement data were collected. Condition C specimens had the greatest stiffness (459 +/- 80N/mm) and yield load (526 +/- 168N). Condition A specimens were the least stiff (266 +/- 53N/mm), and had the smallest yield loads (180 +/- 54N). The yield load of condition A plus condition B was approximately equal to that of condition C, with condition A contributing about one-third and condition B contributing two-thirds of the overall load-bearing capacity. Although the screws alone contributed to a substantial portion of axial load-bearing ability, the addition of the fins further increased load-bearing capabilities.
*Bone Plates ; Bone Screws ; Humans ; In Vitro ; Spinal Fusion/*instrumentation ; Thoracic Vertebrae/*physiology/*surgery ; *Weight-Bearing

For the past few decades, the repair of rotator cuff tears has evolved significantly with advances in arthroscopy techniques, suture anchors and instrumentation. From the biomechanical perspective, the focus in arthroscopic repair has been on increasing fixation strength and restoration of the footprint contact characteristics to provide early rehabilitation and improve healing. To accomplish these objectives, various repair strategies and construct configurations have been developed for rotator cuff repair with the understanding that many factors contribute to the structural integrity of the repaired construct. These include repaired rotator cuff tendon-footprint motion, increased tendon-footprint contact area and pressure, and tissue quality of tendon and bone. In addition, the healing response may be compromised by intrinsic factors such as decreased vascularity, hypoxia, and fibrocartilaginous changes or aforementioned extrinsic compression factors. Furthermore, it is well documented that torn rotator cuff muscles have a tendency to atrophy and become subject to fatty infiltration which may affect the longevity of the repair. Despite all the aforementioned factors, initial fixation strength is an essential consideration in optimizing rotator cuff repair. Therefore, numerous biomechanical studies have focused on elucidating the strongest devices, knots, and repair configurations to improve contact characteristics for rotator cuff repair. In this review, the biomechanical concepts behind current rotator cuff repair techniques will be reviewed and discussed.
Arthroscopy/*methods ; Biomechanical Phenomena ; Humans ; Models, Biological ; Rotator Cuff/injuries/*physiology/*surgery ; Weight-Bearing