- See:
-
Classification and Column Theory
-
Posterior Wall Fractures:
- Discussion:
- posterior column extends from obturator foramen thru posterior aspect of the wt bearing dome of acetabulum & then obliquely thru
greater sciatic notch;
- frx of posterior rim & posterior column arise from MVA, most likely as
result of dashboard impact;
-
associated injuries:
-
posterior dislocation of the femur;
-
AP compression frx
- Radiographs:
-
posterior column fractures involve not only posterior articular surfaces, but also the ilioischial line;
- AP view:
- medial displacement of the femoral head and sciatic buttress;
- ilioishial line is disrupted;
-
external (iliac) oblique view:
- visualizes ilioischial (posterior) column & anterior acetabular rim;
- often reveals the internal and superior boundaries of the displaced fragment;
- radiographic technique: pt is supine w/ uninvolved side rotated anteriorly 45 deg and central beam directed vertically toward the affected hip
- assesment of stability:
- in the study by Vrahas et al 1999, a cadaveric biomechanical study was performed to determine the relative stability of anterior column, posterior column, and transverse fractures;
- they noted that posterior column fractures with a posterior
roof-arc angle (iliac oblique radiograph) of 70 degrees or less were unstable and required ORIF;
- ref: The Effects of Simulated Transverse, Anterior Column, and Posterior Column Fractures of the Acetabulum on the Stability of the Hip Joint* MS Vrahas MD et al.
JBJS Vol 81-A. July 1999.
- PreOp Planning: 
-
work up of acetabular frx:
- w/ posterior injury, the
sciatic nerve may be injured in 40% of patients;
- Surigical Approach:
-
Kocher-Langenback incision is used w/ pt in prone position;
- Reduction:
-
sciatic notch is useful landmark to help reconstruct posteror column;
- posterior column is strong & triangular, w/ extremely thick bone at greater trochanter sciatic notch;
- medial surface forms posterior aspect of quadrilateral plate;
- reduction may achieved w/ direct visualization of quadrilateral surface thru distraction of femur if needed, & thru palpation of
quadrilateral surface thru the greater sciatic notch (thru
posterior approach);
-
insertion of Schanz screw:
- w/ the posterior approach, reduction can be facilitated by inserting a Schanz screw into the ischium just inferior to the subcotyloid gutter;
- a T chuck is applied over the the Schanz screw, which is then used to rotate a displaced posterior column frx into a reduced position;
- the surgeon's other hand can guide the reduction by palpating the quadrilateral surface;
- additionally a Schanz screw may be placed into the greater trochanter for additional traction;
- frx lines may be distracted using lamina spreader or
AO femoral distractor;
- frx lines may be compressed using Farabeuf clamps;
- blood clot & granulation tissue are removed, as are any free fragments that might impede
reduction;
- identify & reduce marginally
impacted frx of
posterior wall;
- Reconstruction:
- posterior column is reconstructed using lag screws or
pelvic recon plates;
- initial fixation is w/ lag screw, placed from posterior to anterior & followed by a curved plate on the retroacetabular surface;
- small reconstruction plate applied from the ischial tuberosity to the lateral ilium along the retroacetabular surfaces.
- Screw Placement in the Ischial Tuberosity:
-
anatomical hazards:
- the internal pudendal bundle usually lies 1.5 cm from the medial posterior margin of the ischial tuberosity;
- internal pudendal bundle passes out of
greater sciatic foramen, passes around sacrospinous ligament,
over the
internal obturator muscle (just medial to the tuberosity) and then into lesser foramen;
- excessively medially angulated screws may injure the internal pudendal;
- at 2 cm below the inferior acetabular margin, hamstring origin is encountered (and therefore dissection below this point is avoided);
-
technique of insertion:
- maximal purchase is achieved w/ entry into the tuberosity 5 or 10 mm medial to the lateral margin of the tuberosity and are directed inferiorly;
- at the level of the inferior acetabular margin, direct the screw 35-40 deg caudally;
- at 1 cm below the inferior acetabular margin, direct screws 45-50 deg caudally;
- at 2 cm below the inferior acetabular margin, direct screws 50-55 deg caudally;
