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 107

The current development of resorbable biomaterials provided the support for
improvement of these implants. Bioresorbable screws became a golden standard,
with growing use in additional sports medicine and traumatology techniques as
patella stabilization, or different tenodesis including shoulder and ankle surgery.
Experimental and clinical papers have shown that direct graft fixation achieved
with bioresorbable interference screws provides immediate stable fixation and pro-
motes good healing by applying compressive forces to the cancellous bone within
the bony tunnels [ 14- 17 ] .
Faster rehabilitation protocols, currently in use, are developed due to permission
for early postoperative weight bearing. Graft fixation is considered to be the weak
link in early and aggressive postoperative rehabilitation of ACL reconstruction.
What makes such screws suitable for so many applications with various require-
ments? One can only remind some of the required properties: the screws should
provide enough strength until the surrounding tissue has healed and must not induce
inflammatory, toxic, or carcinogenic response, being metabolized after performing
the mechanical stability purpose, ideally leaving no debris. The surgical technique
should be consistently reproducible, not leading to damage to the graft or surround-
ing tissues. The screw should also demonstrate good shelf life, as well as easy ster-
ilization. The mechanical properties depend primarily on the structural aspects of
the materials and processing technology.
An ideal biodegradable material for interference screw must initially provide
secure fixation of the graft and assure a gradual degradation as biologic fixation is
established, should have appropriate mechanical properties, would not cause
inflammation or other toxic response, would be metabolized once it was destroyed
completely, and should be sterilized and easily processed into a final product that
has an acceptable shelf life.
On the other hand, some papers reveal possible disadvantages for the use of bio-
absorbable fi xation including in fl ammatory reactions, osteolysis with cyst formation,
sterile sinus tract formation, and a time dependent deterioration of the mechanical
properties. Common complications described in literature include early screw
breakage during insertion or late fracture due to mechanical constraints, with even-
tual migration of biopolymer fragments [ 18, 19 ]. As observed, such cases are rare
compared to the wide usage of implants and may be more related to the surgical
technique than to the properties of the biomaterial (e.g., a low implant diameter or a
smaller screw which does not provide adequate stability).
In general, most commercially available biodegradable interference screws used
in clinical practice are chemically based on polylactide (or polylactic acid (PLA))
and polyglycolide (or polyglycolic acid (PGA)), but others include polycaprolac-
tone (PCL), polydioxanone (PDO), and poly(trimethylene carbonate) (TCM). For
decades, these polymers have been used for clinical applications as sutures, osteo-
synthesis implants (plates, screws), and drug delivery devices [ 20, 21 ] .
There is also a number of biodegradable polymers derived from a natural source
such as polysaccharides (cellulose, chitin, dextrin) or modified proteins that can be
used as raw materials for interference screw, but synthetic polymers have some
advantages over these [ 20 ] .