| Acetabular fractures are rapidly increasing recently. Displaced acetabular fractures frequently result from high-energy traumatic events?and may have significant primary organ system associated injuries. Rapid increase in the incidence of acetabular fractures and high expectations of the patients has compelled the orthopaedic surgeons across the world to do more research and study acetabular fractures. Surgery is the gold standard to treat unstable and incongruous acetabular fractures. Joint stability and early mobilization are the main goals of the surgery for acetabular fracture which can be achieved by anatomic reduction and rigid internal fixation. Screw penetration into the hip joint during operation is an unusual but potentially serious complication.Acetabular fractures in the posterior column, particularly involving the danger zone, are the most common form of acetabular fracture. They remain technically challenging to the orthopedic surgeons. Proper screw placement can avoid the complication. Some basic researches are indicated to evaluate the acetabulum characters. The majority of these studies focus on the orientation and morphology of the acetabulum, the transacetabular screw fixation and related vital structures for total hip arthroplasty. There are only a few anatomic studies regarding plate-screw fixation for acetabular fractures. The danger zone of the acetabulum, which was defined by Tile as that part of the posterior wall and column at the mid-acetabulum lying above the ischial spine, is frequently used in the fixation of posterior wall and posterior column. Screws directed perpendicular to posterior column in the danger zone would violate the hip joint. Ebraheim et al determined the exact configuration of the danger zone of the acetabulum, and proposed the safe pathway for screw placement in this zone based upon their study on the parallel cross-sections of cadaveric hemiplevises. After an extensive review of the existed literature, the comprehensive studies on the danger zone of the acetabulum by CT images have been barely reported so far. Therefore,our studies aim was to designed to measure and record the safe angles for screw placement and the thickness of posterior wall for different points in the danger zone of the acetabulum first, using the images of surface shadow display and multiplanar reconstruction of multislice spiral CT scan. Then the model of posterior column fracture of acetabulum was established, and the stability of internal fixation with the plate and lag screw for the posterior column fracture of acetabulum was evaluated. After that the W-shaped acetabular angular plate was designed, and the stability of internal fixation with the W-shaped acetabular angular plate and reconstruction plate for the simulated posterior column fracture of acetabulum was evaluated. Further investigation on the results of reconstruction of posterior wall fractures of the acetabulum by using the W-shaped acetabular angular plate. Finally the effect of early rehabilitation on the hip joint function for patients of the comminuted posterior wall fractures of the acetabulum after internal fixation was investigated.Part 1 Anatomic study of the safe angle for screw placement and the thickness of posterior wall in the danger zone of the adult acetabulumObjective: To evaluate the safe angle for screw placement and the thickness of posterior wall of the danger zone in adult acetabulum, and provide the data for the reconstruction of acetabular fracture.Methods: Thirty-two cadaveric adult bony semipelvic specimens and thirty adult volunteers were obtained to investigate the safe angle for screw placement and the thickness of posterior wall at the different points in the danger zone of acetabulum through analysis of the images of surface shadow display and multiplanar reconstruction of multislice spiral CT scan.Results: In specimens, the safe angles for 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0cm entry points medial to the lateral acetabular brim were( 49.23±11.54 )°, ( 42.48±8.97 )°, ( 29.53±7.86 )°, ( 23.68±6.20 )°,(18.42± 5.41)°, and (15.91±4.37)°respectively in males and those for 0.5, 1.0, 1.5, 2.0, and 2.5cm entry points were (45.02±8.82)°, (35.98±7.60)°, (23.77±6.29)°, (19.96±4.36)°, and (14.68±3.48)°respectively in females. The differences of the safe angle measured between the specimens and the volunteers were not statistically in the same gender ( P > 0.05 ). The safe angles for screw placement were statistically different between males and females for both specimens and volunteers ( P < 0.05 ).In specimens, the thickness of posterior wall for 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0cm entry points medial to the lateral acetabular brim were ( 0.64±0.13)cm, ( 0.97±0.25)cm, (1.46±0.40)cm,(2.14±0.46)cm,(2.61±0.47)cm, and (2.96±0.42)cm respectively in males and those for 0.5, 1.0, 1.5, 2.0, and 2.5cm entry points were (0.51±0.08)cm,(0.93±0.22)cm,(1.45±0.31)cm,(2.02±0.39)cm, and(2.50±0.50)cm respectively in females. The differences of the thickness measured between the specimens and the volunteers were not statistically in the same gender ( P > 0.05 ). The thickness were statistically different between males and females for both specimens and volunteers ( P < 0.05 ).Conclusion: The data derived from the study will be valuable for screw placement during internal fixation of posterior column and posterior wall fractures.Screw insertion at the points of 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0cm medial to the lateral acetabular brim and angled medially no less than 75°, 65°, 50°, 45°, 35°, and 30°in males, and those at the points of 0.5, 1.0, 1.5, 2.0, and 2.5cm angled medially no less than 65°, 55°, 45°, 40°, and 25°in females respectively, could avoid screw penetration of the hip joint.The length of screw at the points of 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0cm medial to the lateral acetabular brim would be less than that of 1/2,1/3,1/3,1/2,1/2 , and 1/2 from entry point to lateral acetabular brim in males , and those for 0.5, 1.0, 1.5, 2.0, and 2.5cm points would be all less than that of 1/2 in females when screw insertion perpendicular to the surface of posterior column. Part 2 Establishing the model of posterior column fracture of acetabulum and biomechanical evaluation of the stability between plate and lag screw internal fixationObjective: To establish the model of posterior column fracture of acetabulum, and evaluate the stability of internal fixation with the plate and lag screw for the posterior column fracture of acetabulum.Methods: A total of 20 preserved cadaveric semipelvic specimens were randomly divided into two groups. Models of isolated posterior column fracture of acetabulum were established. The models were fixed with plate or lag screw. Under vertical compression load of 3 times body weight, the horizontal displacements of the fracture site were measured and the shear rigidity of two fixation conditions was compared.Results: The horizontal displacements of the fracture site fixed with plate and lag screw were (1.64±0.17) mm and (1.70±0.20) mm. The shear rigidity fixed with plate and lag screw were (392.40±41.22) N/mm and (386.33±50.07) N/mm. The differences of both horizontal displacements and shear rigidity between the two groups were not significant (P > 0.05).Conclusions: The fracture model provides an ideal tool for biomechanical evaluation of the stability of internal fixation for the posterior column fracture of acetabulum. There was no significant difference in the stability of internal fixation with the plate and lag screw for the posterior column fracture of acetabulum.Part 3 Biomechanical evaluation on the W-shaped acetabular angular plate internal fixation of the fractures of acetabular posterior columnObjective: To evaluate the stability of internal fixation with the W-shaped acetabular angular plate and reconstruction plate for the simulated posterior column fracture of acetabulum.Methods: Twenty preserved cadaveric semipelvic specimens were divided into four groups randomly. Models of isolated posterior column fractures of acetabulum were established. Group A was fixed with the W-shaped acetabular angular plate. Group B, C, and D were fixed with one of the three methods of reconstruction plate:four screws on each side of the fracture (group B); four screws on each side of the fracture , but the screw closest to the fractrue on each side malplaced into the acetabulum primarily and correct placement finally(group C); two screws at the each end of plate(group D). Under vertical compression load of 3 times body weight, the horizontal displacements of the fracture site were measured and the shear rigidity of different internal fixation methods were compared.Results: The horizontal displacements of the fracture site in Group A, B, C, and D were (1.58±0.17) mm, (1.62±0.14) mm, (2.66±0.26) mm, and (4.68±0.35) mm respectively. The shear rigidity of internal fixation methods in Group A, B, C, and D were (414.71±34.29) N/mm, (394.75±32.52) N/mm, (219.93±22.04) N/mm, and (129.42±9.60) N/mm respectively. The differences of both horizontal displacements and shear rigidity between Group A and B were not statistically different ( P > 0.05 ). The horizontal displacements and shear rigidity in both Group A and B were statistically different from those of the?Group C or D ( P < 0.05 ). The differences of both horizontal displacements and shear rigidity between Group C and D were statistically different ( P < 0.05 ).Conclusion: The W-shaped acetabular angular plate can improve the internal fixation stability of posterior column fracture of acetabulum.Part 4 Application of the W-shaped acetabular angular plate in treatment of posterior wall fracture of acetabulumObjective: To assess the results of reconstruction of posterior wall fractures of the acetabulum by using the W-shaped acetabular angular plate.Methods: Twenty-two patients ( 20 men, 2 women, mean age 35.7 years, range 18–61 years ) with posterior wall fracture of the acetabulum underwent reconstruction of the posterior wall were randomly divided into study group ( 10 cases ) and control group ( 12 cases ) during the period of July 2009 to February 2010. The patients of study group was fixed by using the W-shaped acetabular angular plate and control group by pelvic reconstruction plate. The results of the intraoperative fluoroscopic images,radiographic evaluation of the quality of reduction,the duration of operation, and the loss of blood were compared. Radiographic evaluation of the quality of reduction was according to criteria developed by Matta.Results: The intraoperative fluoroscopic images confirmed extra-articular screw placement in all cases in study group. In the control group, no intra-articular screw was noted in 6 patients, intra-articular screw placement was seen in 2 patients, and definitive location of periarticular hardware could not be determined in 4 patients. The differences between the two groups were statistically significant ( P < 0.05 ). Radiographic evaluations of the quality of reduction were not significantly different between the two groups. There were significant differences in both the duration of operation and the loss of blood between the two groups ( P < 0.05 ).Conclusion: Reconstruction of posterior wall fractures of the acetabulum via the W-shaped acetabular angular plate could avoid screw penetration of the hip joint , reduce the duration of operation and the loss of blood during surgery.Part 5 Effect of early rehabilitation on the hip joint function in patients of comminuted posterior wall fractures of the acetabulum after internal fixationObjective: To investigate the effect of early rehabilitation on the hip joint function for patients of the comminuted posterior wall fractures of the acetabulum after internal fixation.Methods: Forty patients of comminuted posterior wall fractures of the acetabulum were divided into rehabilitation group ( n = 20 ) and control group ( n = 20 ) randomly.All the patients were fixed with reconstruction plate, the patients in rehabilitation group received early standard rehabilitation exercises intervention and those in control group received usual care. The clinical result was evaluated with the score of Merle d'Aubigne and Postel.The fracture reductions were judged according to the criteria of Matta.Results: The scores of Merle d'Aubigne and Postel for 3, 6 , and 12 month after operation were ( 13.10±2.05 ), ( 14.50±1.32 ), and ( 15.80±1.36 ) respectively in rehabilitation group and those were ( 11.20±2.80 ), ( 13.00±2.10 ) , and ( 14.25±1.74 ) respectively in control group. The differences of the scores between the two groups were significant ( P < 0.05 ). In regard of fracture reductions, there was insignificant statistical difference between the two groups ( P > 0.05 ).Conclusion: The early rehabilitation exercises may improve the hip joint function for patients of the comminuted posterior wall fractures of the acetabulum after surgery.
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