The role of greater tuberosity healing in reverse shoulder arthroplasty: a finite element analysis.

BACKGROUND: The lack of greater tuberosity (GT) healing in proximal humerus fractures has been negatively correlated with outcomes for hemiarthroplasty; however, there is still debate regarding the effects of GT healing in reverse shoulder arthroplasty (RSA). Our goal was to examine the effects of GT healing using a kinematic finite element analysis (FEA) model. MATERIAL AND METHODS: Computer-aided design models of a medialized glenoid with a lateralized humerus (MGLH) RSA design were uploaded into an FEA shoulder model in 2 different configurations: healed greater tuberosity (HGT) and nonunion greater tuberosity (NGT). Deltoid muscle forces and joint reaction forces (JRFs) on the shoulder were calculated during abduction (ABD), forward flexion (FF), and external rotation (ER). RESULTS: Force magnitude of the anterior, middle, and posterior deltoid muscle as well as JRFs modeled in both GT scenarios were similar for ABD (muscle forces P = .91, P = .75, P = .71, respectively; and JRF P = .93) and for FF (muscle forces P = .89, P = .83, P = .99, respectively; and JRF P = .90). For ER, the force magnitude between 2 GT settings showed statistically significant differences (HGT: 9.51 N vs. NGT: 6.13 N) (P < .001). Likewise, during ER, JRFs were different, and the NGT group showed a steep drop in JRF after 10° of ER (HGT: 28.4 N vs. NGT: 18.38 N) (P < .001). CONCLUSION: GT healing does not seem to impact RSA biomechanics during abduction or forward flexion; however, it does affect biomechanics during external rotation. Overall orthopedic surgeons can expect good results for patients after RSA even with poor GT healing.

Modeling of high sodium intake effects on left ventricular hypertrophy.

Many clinical studies suggest that chronic high sodium intake contributes to the development of essential hypertension and left ventricular (LV) hypertrophy. In the present study, a system-level computer model has been developed to simulate the long-term effects of increased sodium intake on the LV mechanical functions and the body-fluid homeostasis. The new model couples a cardiovascular hemodynamics function model with an explicit account of the LV wall thickness variation and a long-term renal system model. The present model is validated with published results of clinical studies. The results suggest that, with increased sodium intake, the renal system function, the plasma hormone concentrations, and the blood pressure adapt to new levels of equilibrium. The LV work output and the relative wall thickness increase due to the increase of sodium intake. The results of the present model match well with the patient data.

Analytical modeling of capillary flow in tubes of nonuniform cross section.

The interface rise for the flow in a capillary with a nonuniform cross section distribution along a straight center axis is investigated analytically in this paper. Starting from the Navier-Stokes equations, we derive a model equation for the time-dependent rise of the capillary interface by using an approximated three-dimensional flow velocity profiles. The derived nonlinear, second-order differential equation can be solved numerically using the Runge-Kutta method. The nonuniformity effect is included in the inertial and viscous terms of the proposed model. The present model is validated by comparing the solutions for a circular cylindrical tube, rectangular cylindrical microchannels, and convergent-divergent and divergent-convergent capillaries. The validated model has been applied to capillaries with parabolic varying wall, sinusoidal wall, and divergent sinusoidal wall. The inertial and viscous effects on the dynamic capillary rise and the equilibrium height are investigated in detail.