A mechanical evaluation of two fixation methods using cancellous screws for coronal fractures of the lateral condyle of the distal femur (OTA type 33B).
OBJECTIVE
To compare the relative strength and stability of 2 fixation methods for displaced coronal shear fractures of the lateral femoral condyle (Hoffa fractures, OTA Type 33B3).


METHODS
University Biomechanics laboratory.


METHODS
Eight matched pairs of embalmed femurs were divided into 2 groups and simulated Hoffa fractures were created. In each pair, 1 of the fractures was fixed with 2 screws placed in an anteroposterior direction, and in the other, the fracture was fixed with 2 screws placed in a posteroanterior direction.


METHODS
All specimens were cyclically tested with simulated physiologic loading. Displacement of the femoral condyle was continuously measured to 10 cycles. The specimens were then loaded to failure.


RESULTS
Fixation with posterior to anteriorly placed cancellous lag screws was significantly more stable than that with anterior to posteriorly placed screws at 10 cycles (P = 0.05), with 0.67 mm displacement compared to 1.36 mm, respectively. They were also more stable at 10, 100, and 1000 cycles; however, these displacements were not statistically significant. Fixation with posteriorly placed cancellous screws also had significantly higher ultimate strength (P = 0.04), 1700 N compared to 1025 N for anterior placement.


CONCLUSIONS
Lag screws placed posterior to anterior provided more stable fixation of Hoffa fractures in embalmed femurs than anteroposteriorly placed lag screws. This finding may apply in the clinical setting; however, this technique requires that the screw heads be recessed beneath the articular surface. The effects of the cartilage defects so created are not known. The choice of technique is also determined by concomitant fractures and the exposure required for their fixation.
Jarit
Gregg J
GJ
Department of Orthopaedic Surgery, NYU-Hospital for Joint Diseases, New York, NY 10003, USA.
Kummer
Frederick J
FJ
Gibber
Marc J
MJ
Egol
Kenneth A
KA
D000368:Aged; D001696:Biomechanical Phenomena / Q000379:methods*; D001863:Bone Screws; D004548:Elasticity; D019544:Equipment Failure Analysis / Q000379:methods*; D005260:Female; D005264:Femoral Fractures / Q000503:physiopathology* / Q000601:surgery*; D005593:Fracture Fixation, Internal / Q000295:instrumentation*; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008875:Middle Aged; D009038:Motion; D013314:Stress, Mechanical; D016896:Treatment Outcome