Defining and evaluating wrapping surfaces for MRI-derived spinal muscle paths.

Area of Science:

• Biomechanics
• Musculoskeletal Modeling
• Spinal Anatomy

Background:

• Approximating muscle paths in biomechanical models often involves wrapping paths around geometric surfaces.
• Current methods for selecting and evaluating these wrapping surface parameters, particularly for spinal muscles, lack clear definition.
• Accurate muscle path representation is essential for reliable biomechanical analysis.

Purpose of the Study:

• To establish objective methods for selecting the shape, orientation, size, and location of muscle wrapping surfaces.
• To evaluate wrapping surfaces using a defined error metric based on magnetic resonance imaging (MRI) data.
• To optimize wrapping surface placement and assess their utility across different postures for neck musculature.

Main Methods:

• Developed objective criteria for defining wrapping surface parameters (shape, orientation, size, location).
• Utilized an error metric quantifying the distance between modeled muscle paths and MRI-derived centroid paths.
• Applied methods to a neck musculature model, optimizing vertebral level placement and evaluating neutral posture parameters in various postures.

Main Results:

• For the sternocleidomastoid, wrapping surface placement level had minimal impact on path error; neutral posture surfaces improved representation versus straight lines in most postures.
• For the semispinalis capitis, wrapping surfaces at C3 or C4 yielded lower errors, significantly enhancing muscle path representation across all tested postures.
• The developed methods demonstrate a quantifiable improvement in modeling complex spinal muscle paths.

Conclusions:

• Objective methods for defining and evaluating muscle wrapping surfaces enhance biomechanical model accuracy.
• Optimized wrapping surfaces improve the representation of spinal muscle paths in various postural conditions.
• These advancements are critical for refining estimates of muscle length, moment arm, and force-generating capacity in biomechanical studies.