Effect of Subject-Specific Vertebral Position and Head and Neck Size on Calculation of Spine Musculoskeletal Moments

• Published in: Annals of biomedical engineering Vol. 46; no. 11; pp. 1844 - 1856
• Main Authors: Vasavada, Anita N., Hughes, Ellis, Nevins, Derek D., Monda, Steven M., Lin, David C.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.11.2018; Springer Nature B.V
• Subjects: Adult; Biochemistry; Biological and Medical Physics; Biomedical and Life Sciences; Biomedical Engineering and Bioengineering; Biomedicine; Biophysics; Body measurements; Cervical Vertebrae - diagnostic imaging; Cervical Vertebrae - physiopathology; Classical Mechanics; Computer simulation; Computers; Female; Gender aspects; Gender differences; Gravitation; Gravity; Head - diagnostic imaging; Head - physiopathology; Head and neck; Humans; Male; Mathematical models; Middle Aged; Models, Biological; Muscle strength; Muscle, Skeletal - diagnostic imaging; Muscle, Skeletal - physiopathology; Musculoskeletal diseases; Parameters; Posture; Sex; Sex Characteristics; Sex differences; Spine; Tablet computers; Tomography, X-Ray Computed; Vertebrae; Cervical spine kinematics; Musculoskeletal modeling; Neck loads; Anthropometry
• ISSN: 0090-6964; 1573-9686
• DOI: 10.1007/s10439-018-2084-9

Spine musculoskeletal models used to estimate loads and displacements require many simplifying assumptions. We examined how assumptions about subject size and vertebral positions can affect the model outcomes. Head and neck models were developed to represent 30 subjects (15 males and 15 females) in neutral posture and in forward head postures adopted while using tablet computers. We examined the effects of (1) subject size-specific parameters for head mass and muscle strength; and (2) vertebral positions obtained either directly from X-ray or estimated from photographs. The outcome metrics were maximum neck extensor muscle moment, gravitational moment of the head, and gravitational demand, the ratio between gravitational moment and maximum muscle moment. The estimates of maximum muscle moment, gravitational moment and gravitational demand were significantly different when models included subject-specific vertebral positions. Outcome metrics of models that included subject-specific head and neck size were not significantly different from generic models on average, but they had significant sex differences. This work suggests that developing models from X-rays rather than photographs has a large effect on model predictions. Moreover, size-specific model parameters may be important to evaluate sex differences in neck musculoskeletal disorders.