Normalization technique to build patient specific muscle model in finite element head neck spine

Finite element models of the head and neck are widely used in automotive and clinical fields to understand spinal biomechanics. These models are developed based on CT and MRI scans of the subjects, but historically the muscle data are obtained from cadaveric specimen. The cadaver data is often obtained from older specimens which commonly have undergone degenerative changes resulting in reduction in muscle cross section area. The objective of the current study is to compare the muscle cross-section area used by various finite element models of neck muscles used in the literature and to develop a normalization technique to scale the MRI muscle cross-section area with those available in the literature. Four male and seven female healthy asymptomatic young adult volunteers enrolled in the study after obtaining necessary approval from Institutional Review Board. T1 and T2 weighted magnetic resonance imaging was performed in neutral upright sitting position wearing military helmet. Muscle cross sectional area was obtained for multifidus muscles from the MRI images. Data was compared with those in the literature. Based on the literature review of prior studies, the cross-sectional area of cadaver specimens was smaller than the MRI obtained muscle area. Multifidus muscle scaling factor was obtained by ratio of sum of MRI cross section area with that of cadaver data. Based on the analysis, the scaling factor for male data is 1.6 and for female data is 1.3. the cadaver data can be multiplied by the scaling factor to obtain the MRI specific cross-sectional area. A Normalization technique was developed for scaling MRI data into finite element model. This technique can be used in developing subject specific finite element model of spine which has applications in clinical, automotive, and military environment.