Scaling and kinematics optimisation of the scapula and thorax in upper limb musculoskeletal models

Abstract

Accurate representation of individual scapula kinematics and subject geometries is vital in musculoskeletal models applied to upper limb pathology and performance. In applying individual kinematics to a model׳s cadaveric geometry, model constraints are commonly prescriptive. These rely on thorax scaling to effectively define the scapula׳s path but do not consider the area underneath the scapula in scaling, and assume a fixed conoid ligament length. These constraints may not allow continuous solutions or close agreement with directly measured kinematics.A novel method is presented to scale the thorax based on palpated scapula landmarks. The scapula and clavicle kinematics are optimised with the constraint that the scapula medial border does not penetrate the thorax. Conoid ligament length is not used as a constraint. This method is simulated in the UK National Shoulder Model and compared to four other methods, including the standard technique, during three pull-up techniques (n=11). These are high-performance activities covering a large range of motion.Model solutions without substantial jumps in the joint kinematics data were improved from 23% of trials with the standard method, to 100% of trials with the new method. Agreement with measured kinematics was significantly improved (more than 10° closer at p<0.001) when compared to standard methods. The removal of the conoid ligament constraint and the novel thorax scaling correction factor were shown to be key. Separation of the medial border of the scapula from the thorax was large, although this may be physiologically correct due to the high loads and high arm elevation angles.

Scapular kinematic reconstruction – segmental optimization, multibody optimization with open-loop or closed-loop chains: which one should be preferred?

“…not perform as well. For instance, Prinold and Bull (2014) reported reconstruction errors lower than 5° versus 30° in the current paper. Several reasons can explain this substantial difference.…”

“…Furthermore, a scapula palpator, adjusted on the geometry of each participant's scapula, was used to measure the reference scapula kinematics (silver standard; Figure 1). First, the participants were asked to maintain several postures for a few seconds: an anatomical posture and three arm attitudes described in Prinold and Bull (2014) as (1) at rest with the arms by the side, (2) arms horizontal at 45° to the coronal plane and (3) arms at subject's maximal elevation. Then, they were asked to perform dedicated movements in line with Begon et al (2007) recommendations to functionally locate of the pelvothoracic and wrist joint centres as well as the elbow joint axis.…”

Kinematic models of the upper limb joints for multibody kinematics optimisation: An overview

“…Subjects' anthropometry fitting can easily be performed by adjusting each segment length based on geometrical measurements for simple upper limb models. For more complex models, medical images might be needed, to adjust the humeral head and glenoid radii for instance (El Habachi et al, 2015), to find the ellipsoid best fitting the thorax (Prinold and Bull, 2014) or accurately locate joint centres (Michaud et al, 2016). This requirement is somehow a limitation since it can only be afforded in a clinical context.…”

A New Neurocognitive Interpretation of Shoulder Position Sense during Reaching: Unexpected Competence in the Measurement of Extracorporeal Space

“…Thus, the scapula is a strategic joint during anteposition movements of the shoulder regarding lateral-medial displacement and counterbalance of the trunk through changes in its center of rotation. The organization of the center of rotation of the scapula is necessary, allowing the glenoid to move into the most suitable position to effect movements of the humerus space [7, 8]. …”