Rotational Stability of Scaphoid Osteosyntheses: An In Vitro Comparison of Small Fragment Cannulated Screws to Novel Bone Screw Sets.
BACKGROUND
The current standard of care for operative repair of scaphoid fractures involves reduction and internal fixation with a single headless compression screw. However, a compression screw in isolation does not necessarily control rotational stability at a fracture or nonunion site. The single screw provides rotational control through friction and bone interdigitation from compression at the fracture site. We hypothesize that osteosyntheses with novel bone screw sets (BSS) equipped with anti-rotational elements provide improved rotational stability.


METHODS
Stability of osteosynthesis under increasing cyclic torsional loading was investigated on osteotomized cadaveric scaphoids. Two novel prototype BSS, oblique type (BSS-obl.) and longitudinal type (BSS-long.) were compared to three conventional screws: Acutrak2®mini, HCS®3.0 and Twinfix®. Biomechanical tests were performed on scaphoids from single donors in paired comparison and analyzed by balanced incomplete random block design. Loading was increased by 50 mNm increments with 1,000 cycles per torque level and repeated until a rotational clearance of 10°. Primary outcome measure was the number of cycles to 10° clearance, secondary outcome measure was the maximum rotational clearance for each torque level.


RESULTS
BSS-obl. performed significantly better than Acutrak2®mini and HCS® (p = 0.015, p<0.0001). BSS-long. performed significantly better than HCS® (p = 0.010). No significant difference in performance between BSS-obl. and BSS-long. (p = 0.361), between BSS obl. and Twinfix® (p = 0.50) and BSS long. and Twinfix® (p = 0.667) was detected. Within the torque range up to 200 mNm, four of 21 (19%) BSS-long. and four of 21 (19%) BSS-obl. preparations showed early failure. The same loading led to early failure in four (29%) Twinfix®, seven (50%) Acutrak2®mini and 10 (71%) HCS® of 14 screw samples, respectively.


CONCLUSIONS
For both BSS and to a lesser extent for Twinfix® (as dual-component screw), higher rotational stabilities were identified in comparison to single component headless compression screws.
Department of Trauma Surgery, Medical University of Vienna, Waehringer Guertel 18-20, A-1090, Vienna, Austria.
Jochen
J
Erhart
Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Waehringer Guertel 18-20, A-1090, Vienna, Austria.
Ewald
E
Unger
Department of Trauma Surgery, Medical University of Vienna, Waehringer Guertel 18-20, A-1090, Vienna, Austria.
Philip
P
Schefzig
AO Research Institute Davos, Clavadelerstrasse 8, CH-7270, Davos, Switzerland.
Peter
P
Varga
Department of Trauma Surgery, Medical University of Vienna, Waehringer Guertel 18-20, A-1090, Vienna, Austria.
Inga
I
Trulson
Department of Trauma Surgery, Medical University of Vienna, Waehringer Guertel 18-20, A-1090, Vienna, Austria.
Anna
A
Gormasz
BG Clinic Tuebingen Schnarrenbergstr. 95, D-72076, Tuebingen, Germany.
Alexander
A
Trulson
Department of Trauma Surgery, Medical University of Vienna, Waehringer Guertel 18-20, A-1090, Vienna, Austria.
Martin
M
Reschl
Section for Medical Statistics, Center for Medical Statistics, Informatics, and Intelligent Systems, Medical University of Vienna, Spitalgasse 23, A-1090, Vienna, Austria.
Michael
M
Hagmann
Department of Trauma Surgery, Medical University of Vienna, Waehringer Guertel 18-20, A-1090, Vienna, Austria.
Vilmos
V
Vecsei
Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Waehringer Guertel 18-20, A-1090, Vienna, Austria.
Winfried
W
Mayr
D001863:Bone Screws; D019245:Compressive Strength; D005593:Fracture Fixation, Internal / Q000379:methods*; D050723:Fractures, Bone / Q000601:surgery*; D006801:Humans; D012399:Rotation; D021361:Scaphoid Bone / Q000293:injuries*