Objective  To evaluate the stability of 4 different methods of plate internal fixation for simulated posterior column fracture of the acetabulum.   Methods  Twenty preserved cadaveric semipelvic specimens were divided into 4 groups randomly. Models of isolated posterior column fractures of acetabulum were established and then fixed with 1 of following 4 methods of plate internal fixation: 2 screws at the each end of plate (group A)

3 screws at the each end of plate (group B)

1 screw each side in the closest allowable hole to the fracture and 2 screws at the each end of plate (group C)

and 4 screws on each side of the fracture (group D). Under vertical compression load of 3 times’ body weight

the displacements of the fracture site were measured and the shear rigidity of different internal fixation methods were compared.   Results  The displacements of the fracture site in Group A

B

C

and D were 4.68±0.35

2.80±0.25

2.12±0.11 and 1.58±0.17 mm respectively

with a decreasing trend from Group A to D. The shear rigidity of internal fixation methods in Group A

B

C

and D were 129.42±9.60

228.91±12.05

285.21±26.16 and 414.71±34.29 N/mm respectively

with an increasing trend from Group A to D. The differences of both displacements and shear rigidity between each 2 groups were significant (P0.05). The stability of fixation methods in different groups was  reached its maximum in Group D.    Conclusion  Under the prerequisite of safe angle of screw placement

holes on the plate in the danger zone of acetabulum

especially the ones being closest to either side of the fracture line

should be fixed in order to attain rigid internal fixation for posterior column fractures of the acetabulum.