Fig 1.
Within the carpal bones of the wrist are the scaphoid and lunate bones. The scaphoid and lunate are held together by a the interosseous scapholunate ligament. A three-dimensional rendering of the scapholunate interosseous ligament is presented (top right). Removing the scaphoid reveals the dorsal (blue), proximal (yellow), and volar (green) regions of the the interosseous scapholunate ligament.
Fig 2.
Design of multiphasic bone-ligament-bone scaffold.
(a) A schematic 2D view and (b) 3D rendering of the scaffold design, and (c) an example fabricated scaffold.
Fig 3.
Schematic overview of the computational framework.
Fig 4.
The 3D anatomical model created from computed tomography scan.
The model consists of capitate (grey), scaphoid (green), lunate (yellow), and radius (grey) bones. Bone positions in dorsal view of anatomical model correspond to maximum wrist flexion. The attachment sites of the dorsal SLIL are depicted with green dotted lines on both scaphoid and lunate. The dorsal SLIL attachment sites are derived from MRI scan of intact native SLIL with the wrist at neutral position and projected onto the anatomical model created from computed tomography scan. The BLB scaffold is placed at a position proximal to the native attachment sites.
Fig 5.
(a) The 28 fibres represent the ligament-scaffold where red and black nodes are prescribed boundary conditions. Rigid bones demonstrate (b) distal, (c) intermediate and (d) proximal ligament-scaffold installation sites for FEA.
Fig 6.
Geometry of rectangular sample.
A 3D schematic of the rectangular sample used for uniaxial tensile and cyclic testings that consists of bone plugs and 10 mm length ligament-scaffold with 28 fibers and 350 μm in diameter each.
Fig 7.
The hexahedral mesh of a single fibre (left) used for iFEA, and two close-ups for the top two and bottom two element layers. The top surface nodes (red) feature a prescribed z-displacement and a zero x, and y displacement constraint. The bottom surface nodes (black) are fully constrained from moving.
Fig 8.
The Cauchy stress-stretch curves.
(a) The 3D-printed samples. The zoom in (b) locates the elastic-plastic region from Cauchy stress-stretch curves depicted in (a).
Fig 9.
Experimental and simulated force-displacement curves.
This is the force-displacement curve using the material constants from the optimisation of the elastic properties. The area between minimum and maximum force-displacement experimental curves are shaded grey.
Fig 10.
Experimental and simulated force-time curves.
This is the force-time curve using the material constants from the optimisation of the viscoelastic properties. The area between minimum and maximum force-time experimental curves are shaded grey.
Table 1.
Optimised material parameters for finite element models.
Fig 11.
Filtered motion of wrist, scaphoid, and lunate for flexion (first frame) acquired from tri-planar video-radiography [41].
Times 0; 1.11; 2.355; 3.42; 3.67 and 4.485 seconds correspond to flexion (red), extension (purple), radial deviation (green), neutral (yellow), ulnar deviation (cyan) and radial deviation again (green), respectively.
Fig 12.
The 10-, 7-, 5- and 3-mm ligament-scaffold inserted at distal (Fig 5b), intermediate (Fig 5c), and proximal (Fig 5d) surgical sites. The von Mises stress depicted maximum values of stress distribution in ligament-scaffold. The percentage of mesh elements exceeding critical stress (σy = 17 MPa) for 3 mm ligament-scaffold length was calculated at times 0; 1.11; 2.355; 3.42; 3.67 and 4.485 seconds, which correspond to flexion (red), extension (purple), radial deviation (green), neutral (yellow), ulnar deviation (cyan) and radial deviation (green), respectively.
Fig 13.
Von Mises stress distribution on the 3 mm ligament-scaffold at three surgical installation sites.
(a) The distal (Fig 5b); (b) intermediate (Fig 5c); (c) proximal (Fig 5d) in the dorsal view of the wrist being in positions of extension, neutral, ulnar deviation, and radial deviation. The von Mises stress scale bar is from 1 to 18 MPa.
Fig 14.
Von Mises stress distribution on the 7 mm ligament-scaffold at three surgical installation sites.
(a) The distal (Fig 5b); (b) intermediate (Fig 5c); (c) proximal (Fig 5d) in the dorsal view of the wrist being in positions of extension, neutral, ulnar deviation, and radial deviation. The von Mises stress scale bar is from 1 to 18 MPa.
Fig 15.
Von Mises stress distribution on the 3 mm ligament-scaffold at three installation surgical sites.
Chosen time corresponds to maximum peaks in von Mises stress (Fig 13). (a) The distal (Fig 5b); (b) intermediate (Fig 5c); (c) proximal (Fig 5d) in the dorsal view of the wrist.
Fig 16.
Closest point distance (mm) from an optimised scaffold to scaphoid and lunate.
The length of the ligament-scaffold is 7 mm. The scaffold is placed at the proximal site according to Fig 5d. The scale bar is in the range from 0 to 2 mm.