Screw pullout strength: a biomechanical comparison of large-fragment and small-fragment fixation in the tibial plateau.
OBJECTIVE
To compare the pullout strengths of 6.5-millimeter diameter partially threaded cancellous screws and 4.5-millimeter diameter fully-threaded cortical screws versus 3.5-millimeter diameter cortical screws in the proximal tibia.


METHODS
Three screws were inserted in the lateral tibial plateau of each leg of fifteen paired cadaveric tibias. In one tibia, large-fragment fixation was used, consisting of a unicortical 6.5-millimeter screw in the subchondral bone, and bicortical 4.5-millimeter screws in the metadiaphyseal and diaphyseal bone. In the contralateral tibia, small-fragment fixation consisting of three 3.5-millimeter screws was used, placing the screws in the same positions as described above.


METHODS
A materials-testing machine was used to determine axial pullout strengths of each screw. The mean pullout strengths of large-fragment and small-fragment screws in each position were compared.


RESULTS
No significant difference in pullout strengths was found between the large-fragment and small-fragment screws in subchondral and metadiaphyseal bone. A statistically significant difference was found between pullout strengths of large-fragment and small-fragment screws in diaphyseal bone.


CONCLUSIONS
In human proximal tibial bone, the data from this study do not suggest that the pullout strength of 3.5-millimeter screws differs from that of 6.5-millimeter screws in subchondral bone, or that the pullout strength of 3.5-millimeter screws differs from that of 4.5-millimeter screws in metadiaphyseal bone. However, the pullout strength of 3.5-millimeter screws is significantly less than that of 4.5-millimeter screws in diaphyseal bone. The authors of the present study believe this supports the use of small-fragment fixation in the treatment of tibial plateau fractures.
Westmoreland
Greg L
GL
South Austin Orthopaedic Clinic, Austin, Texas, USA.
McLaurin
Toni M
TM
Hutton
William C
WC
D001696:Biomechanical Phenomena; D001863:Bone Screws; D002102:Cadaver; D005593:Fracture Fixation, Internal / Q000379:methods*; D006801:Humans; D013977:Tibia / Q000502:physiology*; D013978:Tibial Fractures / Q000601:surgery