Numerical approximation of the solutions to continuum mechanics boundary value problems, by means of finite element analysis, has proven to be of incalculable benefit to the field of musculoskeletal biomechanics. This article briefly outlines the conceptual basis of finite element analysis and discusses a number of the key technical considerations involved, specifically from the standpoint of effective modeling of musculoskeletal structures. The process of conceiving, developing, validating, parametrically exercising, and interpreting the results of musculoskeletal finite element models is described. Pertinent case study examples are presented from two series of finite element models, one involving total hip implant dislocation and the other involving femoral head osteonecrosis.
Thomas D. Brown
Shawn S. Kao, Richard W. Sellens and Joan M. Stevenson
A wind tunnel test was conducted to empirically determine the relationship between the Magnus force (M), spin rate (ω), and linear velocity (V) of a spiked volleyball. This relationship was applied in a two-dimensional mathematical model for the trajectory of the spiked volleyball. After being validated mathematically and empirically, the model was used to analyze three facets of play that a coach must address: the importance of topspin, possibility of overblock spiking, and optimum spiking points. It was found that topspin can increase the spiking effectiveness dramatically in many ways. It was also found that a shot spiked from about 2 m behind the net has the least possibility of being blocked.
This article presents the validation of a technique to assess the appropriateness of a 2 degree-of-freedom model for the human knee, and, in which case, the dominant axes of flexion/extension and internal/external longitudinal rotation are estimated. The technique relies on the use of an instrumented spatial linkage for the accurate detection of passive knee kinematics, and it is based on the assumption that points on the longitudinal rotation axis describe nearly circular and planar trajectories, whereas the flexion/extension axis is perpendicular to those trajectories through their centers of rotation. By manually enforcing a tibia rotation while bending the knee in flexion, a standard optimization algorithm is used to estimate the approximate axis of longitudinal rotation, and the axis of flexion is estimated consequently. The proposed technique is validated through simulated data and experimentally applied on a 2 degree-of-freedom mechanical joint. A procedure is proposed to verify the fixed axes assumption for the knee model. The suggested methodology could be possibly valuable in understanding knee kinematics, and in particular for the design and implant of customized hinged external fixators, which have shown to be effective in knee dislocation treatment and rehabilitation.
Rebecca J. Giorcelli, Richard E. Hughes, Richard S. Current and John R. Myers
This paper describes a procedure developed and validated to assess the accuracy of an infrared-based motion measurement system used to perform a kinematic analysis of the torso with respect to the pelvis during simulated lifting tasks. Two rigid reflective marker triads were designed and fabricated for attachment to the thorax over the 6th thoracic vertebra and the pelvis. System accuracy was assessed for planar rotation as well as rotations about multiple orthogonal axes. A test fixture was used to validate known triad orientations. The spatial coordinates of these triads were collected at 120 Hz using a ProReflex motion measurement system. Single value decomposition was used to estimate a rotation matrix describing the rigid body motion of the thorax triad relative to the sacral triad at each point in time. Euler angles corresponding to flexion, lateral bending, and twisting were computed from the rotation matrix. All measurement error residuals for flexion, lateral bending, and twisting were below 1.75°. The estimated mean measurement errors were less than 1° in all three planes. These results suggest that the motion measurement system is reliable and accurate to within approximately 1.5° for the angles examined.
David B. Berry, Ana E. Rodríguez-Soto, Jana R. Tokunaga, Sara P. Gombatto and Samuel R. Ward
Vertebral level-dependent, angular, and linear translations of the spine have been measured in 2D and 3D using several imaging methods to quantify postural changes due to loading conditions and tasks. Here, we propose and validate a semiautomated method for measuring lumbar intervertebral angles and translations from upright MRI images using an endplate-based, joint coordinate system (JCS). This method was validated using 3D printed structures, representing intervertebral discs (IVD) at predetermined angles and heights, which were positioned between adjacent cadaveric vertebrae as a gold standard. Excellent agreement between our measurements and the gold standard was found for intervertebral angles in all anatomical planes (ICC > .997) and intervertebral distance measurements (ICC > .949). The proposed endplate-based JCS was compared with the vertebral body-based JCS proposed by the International Society of Biomechanics (ISB) using the 3D printed structures placed between 3 adjacent vertebrae from a cadaver with scoliosis. The endplate-based method was found to have better agreement with angles in the sagittal plane (ICC = 0.985) compared with the vertebral body-based method (ICC = .280). Thus, this method is accurate for measuring 3D intervertebral angles in the healthy and diseased lumbar spine.
Jeffrey D. Holmes, David M. Andrews, Jennifer L. Durkin and James J. Dowling
The purpose of this study was to derive and validate regression equations for the prediction of fat mass (FM), lean mass (LM), wobbling mass (WM), and bone mineral content (BMC) of the thigh, leg, and leg + foot segments of living people from easily measured segmental anthropometric measures. The segment masses of 68 university-age participants (26 M, 42 F) were obtained from full-body dual photon x-ray absorptiometry (DXA) scans, and were used as the criterion values against which predicted masses were compared. Comprehensive anthropometric measures (6 lengths, 6 circumferences, 8 breadths, 4 skinfolds) were taken bilaterally for the thigh and leg for each person. Stepwise multiple linear regression was used to derive a prediction equation for each mass type and segment. Prediction equations exhibited high adjusted R 2 values in general (0.673 to 0.925), with higher correlations evident for the LM and WM equations than for FM and BMC. Predicted (equations) and measured (DXA) segment LM and WM were also found to be highly correlated (R 2 = 0.85 to 0.96), and FM and BMC to a lesser extent (R 2 = 0.49 to 0.78). Relative errors between predicted and measured masses ranged between 0.7% and –11.3% for all those in the validation sample (n = 16). These results on university-age men and women are encouraging and suggest that in vivo estimates of the soft tissue masses of the lower extremity can be made fairly accurately from simple segmental anthropometric measures.
Ching-Chao Chan, Chou-Ching K. Lin and Ming-Shaung Ju
The steady-state passive joint moment was considered as a nonlinear elasticity in the past. However, we found that it was path dependent and the estimation error could be large if the commonly used path-independent functions were adopted. The aim of this study was to develop a model to describe the movement history-dependent passive moment in the steady state. The steady-state passive ankle moments of the rabbit were measured by a series of ramp-and-hold angle changes (stairway angle trajectory). A customized discrete Preisach model was constructed and a commonly adopted double-exponential function was also implemented. Two sets of data with different angle paths (major loop and inward loop trajectories) were acquired for model validation. The performance of the two models was compared. The results showed that the proposed model could accurately estimate the steady-state passive moment for both sets of validation data. The estimated error of the proposed model was approximately 50% smaller than that of the double-exponential function approach. It is expected that this new approach, by reducing the error of estimating passive joint moment, may contribute to the active control of joint moments.
The transtheoretical model has been widely used in the investigation of how people adapt to new behaviors; however, the literature appears to be lacking documentation of any assessment/s administered to injured athletes to determine their readiness for rehabilitation, which depending on the severity of the injury, could possibly represent a behavior change for that individual.
To validate the application of the transtheoretical model to injury rehabilitation and assess the impact of stages of change on athletes’ adherence and compliance rates.
Large Mid Atlantic Division I institution.
Seventy injured athletes.
Main Outcome Measures:
Readiness was assessed using the Transtheoretical Model. Adherence was assessed using the percentage of rehabilitation attendance and compliance was assessed using the Sport Injury Rehabilitation Scale.
Participants who were advanced in their stages of change generally reported an increase in self efficacy, utilization of pros versus cons, and the use of behavioral processes instead of experiential processes of change. No significant relationships were found between stages of change and athletes’ adherence and compliance.
Although no statistical significance was found between stages of change and adherence and compliance the results did validate the application of the transtheoretical model to injury rehabilitation.
Ahlem Arfaoui, Catalin Viorel Popa, Redha Taïar, Guillaume Polidori and Stéphane Fohanno
The objective of this article is to perform a numerical modeling on the flow dynamics around a competitive female swimmer during the underwater swimming phase for a velocity of 2.2 m/s corresponding to national swimming levels. Flow around the swimmer is assumed turbulent and simulated with a computational fluid dynamics method based on a volume control approach. The 3D numerical simulations have been carried out with the code ANSYS FLUENT and are presented using the standard k-ω turbulence model for a Reynolds number of 6.4 × 106. To validate the streamline patterns produced by the simulation, experiments were performed in the swimming pools of the National Institute of Sports and Physical Education in Paris (INSEP) by using the tufts method.
Julien Morlier, Michel Mesnard and Mariano Cid
The development of composite material poles since 1960 has played a prominent part in performance improvement in pole-vaulting. Previous studies devoted to pole-vaulting models were based on constant mechanical characteristics. It is thus necessary to identify the local bending rigidities of the pole to build realistic pole-vaulting models. Updating methods developed for dynamic structure studies allow us to describe local mechanical characteristics. These methods are based on the comparison between experimental results and those determined numerically by finite element models. This study presents an adaptation of these methods to determine the local bending rigidities of the pole. The updating technique is validated by a deflection test of a homogeneous beam. Then, a study of the model sensitivity is carried out to investigate the procedure robustness. Finally, the updating method is applied to an old design pole and to a recent one. The results obtained vary greatly from one pole to the other; they highlight the evolutions in pole design.