Ribcage and Thoracic Spine Model

Ribcage and Thoracic Spine Model#

The present generic ribcage and thoracic model has been published in Shayestehpour, H., Tørholm, S., Damsgaard, M., Lund, M., Wong, C., Rasmussen, J.: A generic detailed multibody thoracic spine and ribcage model. This model extends the state-of-the-art by introducing a kinematically determinate rigid-body model controlled by full spine DOFs, enabling the simulation of activities such as curved spine motions (e.g., scoliosis) with detailed ribcage kinematics. Designed for improved usability in clinical and motion capture applications, the model has a wide Range of Motion (ROM) and accommodates severe deformities without locking, thanks to nonlinear constraints and redundancy handling. The model supports direct and inverse kinematics, offering flexibility in input options.

The new model builds on a previously developed thoracic spine model 1. This thoracic spine model consists of the thoracic vertebral column (12 vertebrae) and the ribcage, including individual ribs (24 ribs) and a two-part sternum. The multiple segments interconnected by joints replicate the physiological connections and load transfer mechanisms.

Here is a full view of the flexible thoracic model together with the new abdominal pressure model.

Kinematics#

The kinematic constraints of the thorax are summarized as follows:

  • Vertebra constraints: The intervertebral joints of the spine, adopted from previous work, are modeled as spherical joints. These joint angles can be adjusted to set the model’s posture.

  • Rib constraints: The costovertebral (CV) connections between the vertebrae and ribs are also defined as spherical joints. For each rib, three rotational Averaging measure (AvgM) constraints were established. Detailed information is provided in the paper.

  • Sternum constraints: A revolute joint was defined between the manubrium and the sternal body, allowing rotation around the mediolateral axis. This DOF enables ribcage movements independent of spinal posture. Additionally, three linear and three rotational AvgM constraints were defined for the entire sternum, with further details provided in the paper.

../_images/Ribcage_Constraints.jpg

Spine rhythms#

To drive the thoracic model, only the thoracic spine needs to be controlled, while the ribcage follows the spine as it is kinematically determinate due to the constraints. However, the thoracic spine consists of 12 vertebrae, each requiring three rotational drivers. To simplify usage, we introduced rhythms, which are constraints that link the rotational DOFs of the intervertebral joints. As a result, all vertebrae are linked with rhythm drivers, requiring input for only three spine rotational DOFs (flexion/extension, lateral bending, and axial rotation). Below is a video demonstrating how the rhythms work.

Example of the model#

Here are some examples of the new thoracic model.

Muscles configurations#

The muscle configuration of the model has been greatly expanded in both the spine and abdominal regions, with a total of 1,222 muscle fascicles for the thoracic spine.

Thoracic Muscle Front Thoracic Muscle Back Thoracic Muscle Iso

Example Configuration#

The detailed thoracic model can be controlled using the BM_* statements like the rest of the body models.

#define BM_TRUNK_THORACIC_MODEL _THORACIC_MODEL_RIGID_
#define BM_TRUNK_THORACIC_MODEL _THORACIC_MODEL_FLEXIBLE_
#define BM_TRUNK_THORACIC_MODEL _THORACIC_MODEL_USERDEFINED_

model

Resources#

References#

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