Biomedical Engineering Reference
In-Depth Information
Fig. 7.13
Constructed soft elements of the cervical functional unit: (
a
) vertebral artery, (
b
) spinal
cord, (
c
) intervertebral disc, (
d
) interspinous ligament, (
e
) transversal facet joint
The highlighted areas represent the functional surfaces which are designed to join
with the anatomical soft elements.
In addition to the mentioned features, each vertebral body received two threaded
holes designed to join with the bone screws while assembling the functional unit.
Threaded holes design is considered as secondary preparatory operation.
The soft tissues which connect the vertebral bodies were modeled by positive
extrusion method (
boss extrusion
) of various primitive sketches. Excepting the
intervertebral disc, each soft element (vertebral artery, spinal cord, interspinous
ligament, and transversal facet joint) is represented by single one component having
its proper shape (see Fig.
7.13a
, b, d, e) and features.
The intervertebral disc is an exception due to its different properties in external
and internal regions. The
annulus fi brosus
structure was modeled as an ellipsoidal
ring grew linear in the
Z
direction, while the
nucleus pulposus
structure as an ellip-
soid body. The two disc's elements were assembled using both coincidence and
concentricity mates (see Fig.
7.13c
).
Traumatic cervical spine injuries are successfully stabilized with bone plates
applied to the anterior vertebral bodies. Various anterior cervical plate systems are
currently available on the market, such as Caspar Plate and ABC (Aesculap),
Synthes Plate, Codman Plate (Slim Lock) (Johnson and Johnson), Atlantis plate
(Sofamor Danek) [
23,
62
] , SC-AcuFix
®
Anterior Cervical Plates [
69
] , MaxAn
®
Anterior Cervical Plate System, C-Tek
®
Anterior Cervical Plate System [
6
] ,
Reflex Hybrid ACP Implant [
52
], Cervical Spine Locking Plate (CSLP), and
Vectra-Vectra T [
57
] .
The implant was designed to offer anterior fixation possibilities for varying anat-
omies and pathologies. The modeled bone plate is a small implant designed to join
two consecutive vertebrae. There are also many other types of bone plates designed
for three or more vertebrae stabilization.
The mechanical purpose of the stabilization implant is to create a rigid fixation
between the C2 and C3 vertebrae. The stabilization system integrates the following
elements: one bone plate coded CP1, four bone screws of three types coded
Sr1
,
Sr2,
and
Sr3
, and four identical locking screws.
The cervical bone plate was designed using
feature design
module. The primitive
sketch was constructed in the top plane of the working environment. The basic
bone
shape
of the plate was achieved by filleting all corners and using circle arches.
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