In-vitro comparison of biomechanical efficiency of three cannulated screws for arthrodesis of the hindfoot.
BACKGROUND
Sufficient inter-fragmentary compression is helpful to achieve successful bony fusion in hindfoot arthrodesis using internal fixation by screws. Beside bone quality, the design of a screw influences inter-fragmentary compression. Compressive force is achievable for any kind of screw system; however, the primary deformation of the bone is different for the different screw systems. The work necessary to achieve compressive force for primary stability was measured for different screw systems and compared to an AO screw with washer.


METHODS
The compressive force was determined as a function of screw advancement for 3 different cannulated screw types (7.3-mm AO screw with and without washer, the 6.5-mm Herbert screw and the 6.5-mm Ideal Compression Screw (I.CO.S) using different synthetic bone density (0.16, 0.24, 0.48 g/ccm). Compressive force was measured indirectly, via screw tension measurement with strain gauges.


RESULTS
We calculated the work to reach a limit of 60 N and the corresponding ratios to the value of the golden standard: I.CO.S (35.2%), Herbert (89.0%), AO screw without washer (116%).


CONCLUSIONS
All screw systems yielded acceptable results but the ICOS did produce greater compression. The essential differences were the primary deformation of the bone before reaching the sufficient compressive force for primary stability.
Huber
Wolfgang O
WO
Medical University Vienna, Orthopaedic Department, General Hospital Vienna, F. Schillerstr. 45, 2340 Mödling, Austria. dr.wolfgang.huber@aon.at
Reihsner
Roland
R
Trieb
Klemens
K
Wanivenhaus
Axel Hugo
AH
Beer
Rudolf
R
D001174:Arthrodesis / Q000295:instrumentation*; D001863:Bone Screws; D018786:Bone Substitutes; D019245:Compressive Strength; D004867:Equipment Design; D019544:Equipment Failure Analysis; D033023:Foot Joints / Q000601:surgery*; D006801:Humans; D008954:Models, Biological; D016474:Weight-Bearing
D018786:Bone Substitutes