1 Principles topenlarge
Definition: Posterior wall
Typically, fractures of the posterior wall involve the rim of the acetabulum, a portion of the retroacetabular surface, and a variable segment of the articular cartilage.
The fracture line leaves undisturbed the major portion of the posterior column. A posterior dislocation is usually associated.
Thus, posterior wall fractures are partial fractures of the posterior column.
Mechanism of the injury
Posterior wall type fractures, including those of the posterior wall and the posterior column, with or without transverse T-configuration, occur in motor vehicle crashes. An unrestrained, seated occupant's flexed knee strikes the dashboard. If the force vector is directed appropriately, the femoral head strikes the posterior wall, resulting in a fracture, the exact location of which depends upon the position of the hip at the time of impact. If the hip is sufficiently adducted, a posterior dislocation may occur without a posterior wall fracture.
Search for associated knee injuries.
When a posterior dislocation is associated with a posterior wall fracture, open reduction and internal fixation is virtually always indicated because the posterior wall defect renders the hip unstable.
Posterior dislocations also increase the risks of sciatic nerve injury and of avascular necrosis of the femoral head.
Comminution of posterior wall
If the posterior wall fragment is comminuted, reduction and fixation will be more difficult, and the prognosis is poorer.
Crushing of the posterior acetabular surface (marginal impaction) creates a condition of incongruity and instability. Reduction requires elevation of the impacted articular surface and bone grafting of the resulting defect.
The reduced femoral head is a helpful template.
If a satisfactory and stable reduction can be achieved, the final outcome may be better. Otherwise, prognosis is be poor. Unreduced impaction, which not only leaves an incongruent area of joint surface but also prevents proper reduction of adjacent displaced wall fragments, adversely affects prognosis.
Femoral head contusion and abrasion
Femoral head contusions and abrasions are both extremely difficult to repair and increase the risk of post-traumatic arthritis.
Loose bodies (intraarticular fracture fragments) produce incongruity and instability. If interposed between the joint surfaces, they cause arthritis. The need to remove such loose bodies is thus an indication for acetabular fractures surgery.
Duration of dislocation
The more time that passes before the hip is relocated, the higher the risk of avascular necrosis.
Greater displacement of the dislocated hip also adversely affects the outcome.
2 Joint distraction topenlarge
Traction on the femur, laterally or distally, increases the joint space.
This will help
- expose the joint
- remove loose fragments and
- reduce some marginal impaction fractures
Traction can be applied in several ways, including
- by hand (the “assistant-distractor”)
- with a femoral distractor
- with a traction table
Traction with a femoral distractor
One way to apply traction is with a large distractor. This avoids both constant pulling and use of the fracture table, but does limit mobility of the hip. Properly placed, the distractor may properly realign the femoral head.
Insert a 5 mm Schanz screw into the sciatic buttress proximally. Place a second Schanz screw into the femur at the level of the lesser trochanter.
Tension on the distractor can be adjusted as needed for visualization or reduction
3 Cleaning of the fracture site topenlarge
Cleaning and irrigation
Clean and irrigate the fracture site in preparation for direct reduction.
The posterior wall fragments with attached capsule must be reflected.
Displacing the posterior wall fragment(s) allows access to the hip joint.
Remove loose bodies
The post-reduction x-ray or CT scan may reveal intraarticular loose bodies. If so, the femoral head must be distracted, or even re-dislocated, for the removal of entrapped loose bodies.
4 Reduction of the femoral head topenlarge
Remember that most posterior wall fractures, elemental and associated, were caused by a posterior dislocation of the femoral head.
This dislocation should have been reduced upon the patient's arrival in hospital, to restore blood flow to the femoral head and minimize additional joint trauma. However, this reduction may be unstable, particularly with a large posterior wall fragment or fracture site impaction. The reduction may need to be repeated or adjusted intraoperatively. The femoral head must be completely reduced before the posterior wall can be reduced anatomically.
This CT scan image shows residual posterior dislocation, posterior wall impaction, and a free bone fragment in the foveal notch.
5 Elevation of impacted zones topenlarge
Look for posterior wall impaction
Posterior wall fractures may be relatively simple with shearing fracture planes.
Fracture impaction is often associated with posterior wall fractures. It causes joint incongruity, and deforms the fracture surfaces so that anatomical reduction is not possible until the impaction is corrected.
Elevate impacted fragments
In case of a circumscribed impaction of the articular surface, carefully elevate and mold the area against the femoral head.
Fill the defect
Fill the defect zone with cancellous autograft or a structurally supportive bone substitute.
Use K-wires, screws, or resorbable pins to hold the reduction of small fragments.
6 Direct fracture reduction topenlarge
Confirm underlying reduction first
After reduction of the marginal impaction, reduction and initial fixation of the posterior wall fragment are the next steps.
Before replacing and fixing the posterior wall fragment, it is important to confirm the reduction of any underlying impaction. Otherwise, anatomical reduction will be impossible.
Use pelvic reduction forceps or a ball-spike pusher
Reduction of a single large posterior wall fragment is usually straightforward, but must be done anatomically.
Insert a pelvic reduction forceps with pointed ball tips into the greater
sciatic notch and reduce the posterior wall fragment into position.
Use the forceps to hold the fragment reduced until definitive fixation.
Alternatively a ball-spike pusher can be used to maintain the reduction until definitive fixation.
When comminution is present, the pieces must be reduced and stabilized independently. The shape and size of the fragments may determine the order of reduction.
7 Definitive fixation topenlarge
Fix fragments with lag screws (large fragments)
Once the posterior wall fragment is reduced satisfactorily, it is stabilized with a clamp as described above, supplemented, if necessary, with K-wires. Now definitive lag screws should be inserted.
Before and after applying fixation, reconfirm the reduction.
Apply an underbent plate
Tightly applying a plate which is slightly less curved than the underlying bone will compress and stabilize the reduction.
Such an "undercontoured" plate is prepared with the aid of a flexible aluminum template.
Apply a 3.5 mm reconstruction plate in buttress mode over the reduced posterior wall. Anchor it first to the ischium. The distal end of the plate is pre-contoured to fit the concavity at the base of the ischium. Next attach the proximal end to the ilium. Tightening the proximal screws completes plate contouring and compresses the fracture fragment(s) against the underlying bone.
At least two or three screws should secure each end of the plate. They must not penetrate the acetabulum. Some screws over the posterior wall may need to be omitted to protect the joint. Each screw should be checked with the image intensifier to ensure that it is outside the joint.
8 Pearl: Spring hook plates topenlarge
Spring hook plates, prepared from small fragment one-third tubular plates, can stabilize posterior wall fragments that are too small or too peripheral for lag screws.
Be careful to ensure that the hooks of the spring plate do not impale the labrum and are far enough away from the edge of the joint not to scratch the femoral head.
Cut off the plate
Take a three or four-hole one-third tubular plate. Cut off the tip through a hole.
Bend the ends into hooks
Bend the newly created prongs downwards to create small hooks.
Overbend the hook
The shape of the hook plate should be more convex than the underlying bone, so that tightening its screw compresses the hooks against the fragment to be stabilized.
Proper alignment is achieved by compressing the fragments against the femoral head.
The hooks should not penetrate the hip joint.
Affix the plates
The spring hook plates should extend medially beyond the posterior wall buttress plate. These supplementary plates provide additional buttress support for the comminuted fragments.
The hooks must press on the bone fragments and not into the labrum.