Electromagnetic simulation for diagnosing damage to femoral neck vasculature: A feasibility study

Abstract

Background: Femoral neck fractures are common injuries managed by orthopedic surgeons across the world. From pediatrics to geriatrics, disruption of the blood supply to the femoral neck is a well-recognized source of morbidity and mortality, oftentimes resulting in avascular necrosis of the femoral head. This devastating complication occurs in 10-45% of femoral neck fractures. Therefore, it is vital for orthopedic surgeons provide efficient treatment of this injury, in order to optimize the patient's potential outcome and prevent long-term sequelae.

Methods: In this study, the anatomy of the proximal femur, including femoral metaphysis, femoral neck, vasculature, and femoral head, were simulated in COMSOL Finite Element Analysis (FEA) software. Electric fields were generated in a fashion that exploited disruptions within the vasculature of the femoral neck. This study was aimed at developing an alternative imaging modality for narrowing or disrupting the femoral neck's vasculature. The variables used for investigation included: frequency, penetration depth, and magnitude of the electrical energy. These variables, when combined, allowed for enhanced simulated visualization of the vasculature of the femoral neck and theoretically expedited diagnosis of obvious, or occult, femoral neck injury.

Results: Simulated blood vessels were developed in two-dimensions: the phi direction (circular), and z-direction. Two different frequencies, 3 GHz, and 5 GHz were considered, with 100-J energy pulses within blood vessels of 2.54 mm in diameter. The fat surrounding the bone to the outside surface body was simulated at 0.25 inch (0.65 cm). An additional model, with layered fat and skin above the vessels, was simulated at 2000J and successfully able to visualize the femoral neck's blood vessels. Results showed a distinguished E field across the blood boundary of nearly 170 V/M.

Conclusions: The electric field simulation data within the Phi and Z directions promises the feasibility of a subsequent practical model.

Fig. 1

The z and phi Blood Vessels Used for the Simulation: (a) for the z-direction, and (b) for the phi direction.

Fig. 2

The Femur with compoents and blood vessels: (a) the COMSOL Model, (b) the Femur components.

Fig. 3

Blood Vessels showing rapture in the femur.

Fig. 4

2D simulation for the 3 Ghz and 5 GHz field response.

Fig. 5

2D simulation for the 5 GHz Field response.

Fig. 6

3D Field response in the Phi direction for two different frequencies and two different energy levels with fat depth of nearly 0.6 cm.

Fig. 7

3D Field response in the Z-direction for two different frequencies (3 GHz and 5 GHz) and two different energy levels; 1000 J and 2000J with fat depth of nearly 0.6 cm.

Fig. 8

Narrowing arteries at 3 GHz and 5 GHz.

Fig. 9

Closed (or blocked) at 3 Ghz and 5 Ghz

Fig. 10

The concept of comparator circuits for generating the output voltages given at different frequencies for both the Z- and Phi directions.

Fig. 11

The proposed electronic circuits for the practical model of the proposed system:(a) The top circuit is the comparator circuit for generating the digitized output, the bottom circuit (b) is the sample and hold off circuit to store the data within the capacitance.

Fig. 12

Proposed sensor array in 2D (a) and 1D array (b).

Fig. 13

Proposed 3D holder system with 1D array that may rotate to track the field distribution inside the Femur.