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
Christopher D. Brown, Christine A. lauber and Thomas Cappaert
Iontophoresis is a method of local transfer of ionized medicated and nonmedicated substances through the skin and into the target tissues using magnetic polarization. The anti-inflammatory properties exhibited by dexamethasone sodium phosphate (DEX) combined with iontophoresis make it a potentially desirable treatment for clinicians wishing to administer a noninvasive localized drug concentration without having a large systemic concentration of that drug. Since concurrent treatments are commonly used in clinical practice, many of the published studies that included the use of DEX also used concurrent treatments. However, this may make it difficult for clinicians to determine the individual effectiveness of DEX iontophoresis in treating musculoskeletal conditions.
Focused Clinical Question:
Does DEX iontophoresis, alone, decrease pain and improve function in patients with musculoskeletal conditions when compared with placebo or control?
Donald D. Anderson, Krishna S. Iyer, Neil A. Segal, John A. Lynch and Thomas D. Brown
There exist no large-series human data linking contact stress exposure to an articular joint’s propensity for developing osteoarthritis because contact stress analysis for large numbers of subjects remains impractical. The speed and simplicity of discrete element analysis (DEA) for estimating contact stresses makes its application to this problem highly attractive, but to date DEA has been used to study only a small numbers of cases. This is because substantial issues regarding its use in population-wide studies have not been addressed. Chief among them are developing fast and robust methods for model derivation and the selection of boundary conditions, establishing accuracy of computed contact stresses, and including capabilities for modeling in-series structural elements (e.g., a meniscus). This article describes an implementation of DEA that makes it feasible to perform subject-specific modeling in articular joints in large population-based studies.
Bhupinder Singh, Thomas D. Brown, John J. Callaghan and H. John Yack
During seated forward reaching tasks in obese individuals, excessive abdominal tissue can come into contact with the anterior thigh. This soft tissue apposition acts as a mechanical restriction, altering functional biomechanics at the hip, and causing difficulty in certain daily activities such as bending down, or picking up objects from the floor. The purpose of the study was to investigate the contact forces and associated moments exerted by the abdomen on the thigh during seated forward-reaching tasks in adult obese individuals. Ten healthy subjects (age 58.1 ± 4.4) with elevated BMI (39.04 ± 5.02) participated in the study. Contact pressures between the abdomen and thigh were measured using a Tekscan Conformat pressure-mapping sensor during forward-reaching tasks. Kinematic and force plate data were obtained using an infrared motion capture system. The mean abdomen-thigh contact force was 10.17 ± 5.18% of body weight, ranging from 57.8 N to 200 N. Net extensor moment at the hip decreased by mean 16.5 ± 6.44% after accounting for the moment generated by abdomen-thigh tissue contact. In obese individuals, abdomen-thigh contact decreases the net moment at the hip joint during seated forward-reaching activities. This phenomenon should be taken into consideration for accurate biomechanical modeling in these individuals.