Veiranto M and Törmälä P (PhD, MDHs), Tampere University of Technology, Suokas E (Dr.Tech.), Bionx Implants Ltd. Niemelä S-M, Ikäheimo I (MD, PhD), Koskela M (MD, PhD), Syrjälä H (MD, PhD), Waris T (MD, PhD), Ashammakhi N (MD, PhD, FRCSEd)

Oulu University Science Day, 18 Feb 2003, Oulu, Finland.


MATERIALS AND METHODS
The bioabsorbable matrix polymer in studied screws was poly(lactide-co-glycolide) (PLGA 80:20) (Purac) and the antibiotic was ciprofloxacin. Components were extruded into billets and then die-drawn into self-reinforced rods. Screws with the same geometry as that of BioSorbPDX® 1.5 Screws (Bionx Implants, Ltd.) and length of 4.0 mm were machined from self-reinforced rods. The finished screws were gamma sterilized. The released ciprofloxacin concentrations were measured using a UV-spectrophotometer (wavelength=270.5 nm) and mechanical properties using an Instron 4411 materials testing machine. Screws were tested for their bacterial inhibitory effect by embedding in agar dishes containing ca. 107 cfu/ml S. epidermidis ATCC 35989 and inhibition areas were measured.

INTRODUCTION
Bone infections are serious clinical complications associated with surgical trauma and procedures. Antibiotics are the basic treatment for bone infections. Our group has recently developed antibiotic- releasing SR-PLGA bone fixation screws for CMF surgery. Studied screws progressively release the contained antibiotic during the degradation in vitro and have sufficient initial mechanical properties.

RESULTS
After 140 days all loaded ciprofloxacin was released from the screws. During that time measured average concentration of released antibiotic per day was between 0.8 and 11.5 µg/ml after the start-up burst peak. Initial shear strength of the studied screws was 104 MPa. Torsion strength of the screws was 65 MPa. Antibiotic releasing screws inhibited bacteria on average areas of 30 mm in diameter. No inhibition was seen with control screws (non-antibiotic containing bioabsorbable or titanium screws).

CONCLUSIONS
Ciprofloxacin releasing CMF-fixation screws based on SR-PLGA have sufficient drug release properties in vitro, good initial mechanical strengths and bacterial inhibitory effect. They may be useful for clinical use in infection prophylaxis or therapy.