Biomedical Engineering Reference
In-Depth Information
Table 6.2
Different available composite interference screws
Composite materials
Product/manufacturer
Polymeric matrix
Ceramic phase
70% PLDLA
30% BCP
Biocomposite/Arthrex
70% PLLA
30% b -TCP
Biolok/Arthrocare
40% PDLLA
60% b -TCP
Composit/Biomet
75% SR PDLLA
25% b -TCP
Matryx/ConMed Linvatec
70% PLLA
30% b -TCP
Bio-Intra fi x/De Puy Mitek
70% PLGA
30% b -TCP
Milagro/De Puy
75% PLLA
25% HA
Biosure/Smith & Nephew
75% PLLA
25% HA
Biosteon/Stryker
6.2
Interference Screw Classi fi cation and Design
A thorough analysis of the bioresorbable interference screws currently on the
market allowed a classification based on their geometrical specifications and
design:
•
Non-cannulated, cannulated, cannulated and perforated
•
Nonself-tapping, self-tapping
Overall shape:
•
Tapered (conical)
•
Cylindrical
•
Cylindrical + conical
•
Shape of the channel for screwdriver: Hexagonal, triangular, quadrangular, six-
stars, tri-lobe, turbine-like
Number of flutes for tapping: 1, 2, 3, or 4
•
•
Screw head: Round head, tapered head, flat head (headless), hemispherical
•
Single helix thread, double-helix thread
•
Thread pro fi le: Buttress, V-shaped
•
Pitch: Constant, variable
Different types of bioresorbable interference screws are shown in Table
6.3
in
order to illustrate some of the above-mentioned design characteristics and the man-
ner in which the producers leading the market in this field have chosen to adapt the
design to the ACL clinical requirements.
As it can be seen, the designs of these screws do not differ significantly, the varia-
tions being given by the thread shapes and sizes, values of the taper angle, or tip
geometry. Moreover, the producers provide almost the same range of dimensions
for the interference screw.
The usual range of dimensions (length and major diameter) varies between 8 and
10 mm as major diameter (for some interference screw models 7, 11, and 12 mm
diameters are also available) and 25-35 mm in length (screw with lengths of 20 and
23 mm can also be purchased for special indications). Obviously, this range is
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