The dynamic locking screw (DLS) can increase interfragmentary motion on the near cortex of locked plating constructs by reducing the axial stiffness.
BACKGROUND
The plate-screw interface of an angular stable plate osteosynthesis is very rigid. So far, all attempts to decrease the stiffness of locked plating construct, e.g. the bridged plate technique, decrease primarily the bending stiffness. Thus, the interfragmentary motion increases only on the far cortical side by bending the plate. To solve this problem, the dynamic locking screw (DLS) was developed.


METHODS
Comparison tests were performed with locking screws (LS) and DLS. Axial stiffness, bending stiffness and interfragmentary motion were compared. For measurements, we used a simplified transverse fracture model, consisting of POM C and an 11-hole LCP3.5 with a fracture gap of 3 mm. Three-dimensional fracture motion was detected using an optical measurement device (PONTOS 5 M/GOM) consisting of two CCD cameras (2,448 x 2,048 pixel) observing passive markers.


RESULTS
The DLS reduced the axial stiffness by approximately 16% while increasing the interfragmentary motion at the near cortical side significantly from 282 microm (LS) to 423 microm (DLS) applying an axial load of 150 N.


CONCLUSIONS
The use of DLS reduces the stiffness of the plate-screw interface and thus increases the interfragmentary motion at the near cortical side without altering the advantages of angular stability and the strength.
Döbele
Stefan
S
Klinik für Orthopädie und Unfallchirurgie, Abteilung für Unfallchirurgie, Klinikum rechts der Isar, Technische Universität München, Ismaninger Str. 22, 81675, München, Germany. doebele@tum.de
Horn
Carsten
C
Eichhorn
Stefan
S
Buchholtz
Arne
A
Lenich
Andreas
A
Burgkart
Rainer
R
Nüssler
Andreas K
AK
Lucke
Martin
M
Andermatt
Daniel
D
Koch
Rudolf
R
Stöckle
Ulrich
U
D001696:Biomechanical Phenomena; D001860:Bone Plates; D001863:Bone Screws; D005593:Fracture Fixation, Internal / Q000295:instrumentation*; D017102:Fracture Healing; D050723:Fractures, Bone / Q000601:surgery*; D006801:Humans; D008954:Models, Biological; D013978:Tibial Fractures / Q000601:surgery*