Development of Bioabsorbable Interference Screws: How Biomaterials Composition and Clinical and Retrieval Studies Influence the Innovative Screw Design and Manufacturing Processes - Biologically Responsive Biomaterials for Tissue Engineering - page 121

Fig. 6.6 SEM aspect of retrieved PLLA screw surface—progressive cracking of the surface
Fig. 6.7 SEM aspect of retrieved PLLA screw surface—deep fissure of the thread due to excessive
torque during insertion
findings (the fragmentation of the screw allows the bone to heal inside the gaps), but
the same progressive cracking of the surface could present a slight parallel orientation
(slippage direction) ( Fig. 6.8 ).
Screw degradation process occurs as a natural biodegradability delamination
associated with the device within the tissue, after a while. Also, it should be noted
that the screws were still present in the body in 9-12 months after implantation,
even with visible signs of degradation. This is possible because the polymer will not
degrade fast enough and still be influenced by mechanical degradation movements
of the grafts inside the bone tunnels. MRI investigations detected no inflammatory
response, but incomplete bone block incorporation was noticed at 6 months in
observed patients (Fig. 6.9 ).
Also, all analyzed interference screws showed signs of degradation which were
still clearly visible even 12 months after ACL reconstruction (Fig. 6.10 ).