Measuring the global mechanical properties of the human thorax: Costo-vertebral articulation.

Biomechanical simulation of the human thorax, e.g. for 3D-printed rib implant optimisation, requires an accurate knowledge of the associated articulation and tissue stiffness. The present study is focusing on determining the stiffness of the costo-vertebral articulations. Specimens of rib segments including the adjacent thoracic vertebrae and ligaments were obtained from two human post-mortem bodies at four different rib levels. The rib samples were loaded with a tensile force in the local longitudinal, sagittal and transverse direction and the resulting displacement was continuously measured. The moment-angle response of the rib articulations was also determined by applying a load at the rib end in the cranial - caudal direction and measuring the resulting displacement. The torsional load response of the costo-vertebral articulations at an applied moment between -0.1 Nm and 0.1 Nm corresponded to a median range of motion of 13.2° (6.4° to 20.9°). An almost uniform stiffness was measured in all tensile loading directions. The median displacement at the defined force of 28 N was 1.41 mm in the longitudinal, 1.55 mm in the sagittal, and 1.08 mm in the transverse direction. The measured moment-angle response of the costo-vertebral articulation is in line with the data from literature. On the contrary, larger displacements in longitudinal, sagittal and transverse directions were measured compared to the values found in literature.

Measurement of global mechanical properties of human thorax: Costal cartilage.

Surgical resection of chest wall tumours may lead to a loss of ribcage stability and requires reconstruction to allow for physical thorax functioning. When titanium implants are used especially for larger, lateral defects, they tend to break. Implant failures are mainly due to specific mechanical requirements for chest-wall reconstruction which must mimic the physiological properties and which are not yet met by available implants. In order to develop new implants, the mechanical characteristics of ribs, joints and cartilages are investigated. Rib loading is highly dependent on the global thorax kinematics, making implant development substantially challenging. Costal cartilage contributes vastly to the entire thorax load-deformation behaviour, and also to rib loading patterns. Computational models of the thoracic cage require mechanical properties on the global stiffness, to simulate rib kinematics and evaluate stresses in the ribs and costal cartilage. In this study the mechanical stiffness of human costal cartilage is assessed with bending, torsion and tensile tests. The elastic moduli for the bending in four major directions ranged from 2.2 to 60.8 MPa, shear moduli ranged from 5.7 to 24.7 MPa for torsion, and tensile elastic moduli ranging from 5.6 to 29.6 MPa. This article provides mechanical properties for costal cartilage. The results of these measurements are used for the development of a whole thorax finite element model to investigate ribcage biomechanics and subsequently to design improved rib implants.

Attachment of upper arm prostheses with a subcutaneous osseointegrated implant in transhumeral amputees.

BACKGROUND: The stump-socket interface is of utmost importance for prosthetic function in transhumeral amputees. Stability of this connection may be improved using a newly designed subcutaneous implant. OBJECTIVES: The purpose was to determine the effect of the implant together with customized socket designs on the range of motion of the shoulder and the prosthetic function compared to conventional fitting. STUDY DESIGN: Case series. METHODS: The range of motion was measured with scaled metrics and the prosthetic function evaluated with the Southampton Hand Assessment Procedure and the Box and Block Test. Maximal loading was measured in straight and 90° flexion of the elbow. RESULTS: The restriction of range of motion after conventional fitting was decreased from 42.55% ± 6.56% to 9.23% ± 14.89% in Patient I and from 62.18% ± 15.19% to 2.51% ± 2.49% in Patient II using the implant with customized sockets compared to range of motion without prosthesis. Both patients showed improved prosthetic function with the new system compared to conventional fitting. CONCLUSION: The presented subcutaneous humeral implant, together with customized socket designs without straps and harnesses to the contralateral shoulder, can maintain almost complete range of motion of the shoulder. This resulted in improved prosthetic function and comfort for the patient without constant risk of infection. Clinical relevance Discomfort and limited prosthetic function are the main reasons for abandonment especially in transhumeral amputees. Shoulder straps and harnesses within conventional socket designs may not only lead to pain and skin irritations at the contralateral shoulder but also limit the range of motion of the shoulder joint and therefore prosthetic function.