Biomechanical stability of single-screw versus two-screw fixation of an unstable slipped capital femoral epiphysis model: effect of screw position in the femoral neck.
OBJECTIVE
To biomechanically evaluate single screw and varying 2 screw fixations for an unstable slipped capital femoral epiphysis (SCFE) model using physiologically relevant loading.


METHODS
In vitro biomechanical study.


METHODS
Twenty-four immature porcine proximal femurs were prepared to simulate a mild-to-moderate unstable SCFE. The femurs were randomized into 4 fixation groups: single screw, 2 screws horizontally placed, 2 screws vertically placed, and 2 oblique screws. Biomechanical testing determined maximum load to failure (N), load (N) at 2, 4, 6, and 8 mm of femoral head displacement, and stiffness (newtons per millimeter) for each group.


RESULTS
No significant differences were found among the 3 different 2 screw configurations. The 2 screw constructs were 66% stiffer and 66% stronger than the single screw construct. In addition, whereas there was no difference at 2 mm of femoral head displacement, each subsequent displacement (4, 6, and 8 mm) demonstrated significantly higher failure loads when 2 screws were used for stabilization.


CONCLUSIONS
Slipped capital femoral epiphysis stabilization with 2 screws leads to increased stability over single screw fixation; however, none of the 3 configurations/placement patterns of the 2 screw constructs seemed to be superior in fixation stability.


CONCLUSIONS
These data support the use of a 2 screw construct in acute/unstable SCFE fixation. The biomechanical benefit of 2 screws needs to be considered in the face of greater potential for inadvertent penetration into the joint with an increased number of screws.
Kishan
Shyam
S
Department of Orthopaedics, Children's Hospital, San Diego, CA, USA.
Upasani
Vidyadhar
V
Mahar
Andrew
A
Oka
Richard
R
Odell
Tim
T
Rohmiller
Michael
M
Newton
Peter
P
Wenger
Dennis
D
D000818:Animals; D001696:Biomechanical Phenomena; D001863:Bone Screws; D004195:Disease Models, Animal; D004839:Epiphyses, Slipped / Q000503:physiopathology / Q000601:surgery*; D005272:Femur Neck; D005471:Fluoroscopy; D006621:Hip Joint / Q000503:physiopathology / Q000601:surgery*; D019637:Orthopedic Procedures / Q000379:methods*; D013552:Swine