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Posterior Acetabular Wall Fractures

  - See:
      - Associated Transverse and Posterior Wall Frx 
      - Classification and Column Theory 

- Discussion:
    - most common type of acetabular frx (up to 50% of acetabular fractures will contain a posterior
             wall fragment);
    - posterior wall frxs involve the posterior articular surfaces, often w/ retroacetabular surface and
             sometimes entire surface;
    - frx of posterior rim & posterior column may be seen in MVA from posteriorly directed dashboard impact;
    - hips w/ > 40-50% involvement of posterior wall (as per CT scan) or w/ posterior subluxation are unstable and
             require ORIF to restore acetabular wall; 
    - posterior wall and posterior dislocation of hip;
             - reduction needs to be within 6 hours of injury;
             - CT only need be performed following closed hip reduction;
    - work up of acetabular frx and associated injuries:
             - inspection of soft tissues:
             - GYN / urinary / rectal injuries: RUG vs. suprapubic catheter placement;
             - neurologic injury:
                    - w/ this injury, the sciatic nerve may be injured about 30% of patients;
                    - be sure to document even subtle signs of injury;
                    - ref: Somatosensory evoked potential monitoring in the surgical treatment of acute, displaced acetabular fractures. Results of a prospective study.

             - transverse frx (most common);
             - posterior dislocation of hip;
             - posterior dislocation with femoral head fracture:
                    - if femoral head fragment is above the fovea, then attached ligamentum teres prevents reduction of the
                              femoral head fracture;
                    - with small infrafoveal fragments, a posterior approach may allow fixation or debridement of the femoral head fragment;
             - anteroposterior compression fractures;
             - PCL rupture (may occur along w/ posterior wall frx when dashboard injury is the mechanism of injury);

- Radiographic Studies:
    - internal (obturator) oblique view:
             - visualizes iliopubic (anterior) column of pelvis & posterior rim;
             - demostrates the fracture fragment, acetabular defects and degree of displacement;
    - note whether there are intra-articular frx fragments;
    - note degree of comminution:
             - most posterior wall fractures will have some degree of posterior comminution;
             - w/ isolated posterior wall frx, ilioischial line remains intact;
             - note that comminution of the posterior wall fragment is a poor predictor of outcome (3 or more fragments
                      indicates poor prognosis);
             - posterior wall fracture extending into the acetabular roof also indicates negative prognosis;


- CT Scan:
    - hips w/ less than 34% of the remaining posterior wall are generally unstable;
    - hips w/ more than 55% of the remaining posteiror wall are generally stable;
    - note degree of comminution;
           - single posterior fragment is present in 30%;
           - multiple fragment fractures occur in about 30%;
           - osteochondral depression fractures of the posterior wall;
    - references:
           - Computed tomography evaluation of stability in posterior fracture dislocation of the hip.
           - Stability of posterior fracture-dislocations of hip. Quantitative assessment using computed tomography


- Non Operative Treatment:
    - indications:
          - stable fractures (less than 30-50%) which are demonstrated to be stable under flouroscopic evaluation;
          - congruent reduction w/ assurance that incarcerated fracture fragments are not present (as determined from fine cut CT scan); 
          - references:
                  - Computed tomography as a predictor of hip stability status in posterior wall fractures of the acetabulum.
                  - Outcomes of posterior wall fractures of the acetabulum treated nonoperatively after diagnostic screening with dynamic stress examination under anesthesia.
                  - Can experts in acetabular fracture care determine hip stability after posterior wall fractures using plain radiographs and computed tomography?
                  - Nonoperative Treatment of Posterior Wall Acetabular Fractures After Dynamic Stress Examination Under Anesthesia: Revisited.
                  - Examination Under Anesthesia for Evaluation of Hip Stability in Posterior Wall Acetabulum Fractures..

- Surgical Considerations:
    - indications for ORIF:
           - irreducible fracture dislocation;
           - incarcerated osteochondral fragments:
                  - in some cases, small fragments which lie in the lower half of the acetabulum do not require removal; 
                  - ref: Intra-articular Fragments in Acetabular Fracture-Dislocation
           - hip instability;
           - defect in the posterior wall of more than 50% (associated w/ instability even if instability is not apparent on
                  static radiographs);
                  - defects of between 30-50% may or may not be stable;
                  - often the status of the posterior capsule determines whether the hip is stable; 
          - elderly patients:
                  - fractures in elderly patients and those with extensive comminution are more likely to have a poor clinical result;
                  - ref: Results of Operative Treatment of Fractures of the Posterior Wall of the Acetabulum 
    - other considerations:
          - references;
                 - Outcomes of posterior wall fractures of the acetabulum treated nonoperatively after diagnostic screening with dynamic stress examination under anesthesia.
                 - Does Early Fixation of Posterior Wall Acetabular Fractures Lead to Increased Blood Loss?

- Surgical Technique:
   - prone positioning:
           - posterior wall fractures that extend from the greater and or lesser sciatic notch are usually best operated on w/ prone
           - w/ posterior instability, prone position ensures hip reduction;
           - prone position keeps the hip in extension which reduces sciatic nerve tension;
           - be sure that the patient is placed on a flouro table and be sure to run through all of the important flouroscopic views prior to
                   prepping the patient; 
     - implants and tools for posterior wall fracture:
           - 3.5 mm cortical screws4.0 mm cancellous bone screws3.5 mm reconstructed plate, curved,
           - spiked ball pusher, T handle chuck and schanz half pin, flouro OR table; 
           - synthes spring plates
    - bone grafting: indicated for comminuted posterior wall fractures; 

- Surgical Exposure:
    - Kocher Langenback incision:
           - a sliding trochanteric osteotomy may be required if there is cranial extension of the wall fragment;
           - releasing 1 cm of the gluteus insertion onto the femur widens the posterior exposure; 
           - knee should be flexed to protect the sciatic nerve;
    - dislocation of femoral head:
           - Surgical Hip Dislocation for Exposure of the Posterior Column
           - Patients undergoing surgical hip dislocation for the treatment of acetabular fractures show favourable long-term outcome.
    - deep exposure:
           - schanz screw (w/ T chuck handle) can be inserted into the greater trochanter, inorder to distract the femoral head for
                     improved exposure;
           - joint is debrided & irrigated to remove all loose fragments;
           - articular surfaces are inspected & impactions of articular surface are elevated;
           - in some cases, the posterior wall fragment may be displaced anteriorly and held tethered by the anterior capsule
                     (ligament of Bigelow); 
           - small fragments may be discarded, but save & reduce all fragments since significant posterior wall defects may lead
                     to hip instability; 
           - capsular attachment to the posterior wall fragment should be preserved to maintain circulation;  
           - superior fracture extension of the posterior wall:
                   - consider trochanteric slide osteotomy in order to
                            - avoid stretch on the superior gluteal neurovascular bundle;
                            - avoid direct damage to the medius and minimus muscles; 
           - references:
                   - Modified Kocher-Langenbeck approach for the stabilization of posterior wall fractures of the acetabulum.
                   - Modified "2-portal" kocher-langenbeck approach: a minimally-invasive procedure protecting the short external rotator 
                   - Management of acetabular fractures with modified posterior approach to spare external hip rotators.

    - fixation w/ lag screws:
           - fixation w/ lag screws is inferior to fixation w/ lag screws and a contoured plate;
           - best indication for lag screw fixation is large non comminuted posterior wall fragment;
           - two synthes 3.5 mm cortical screws are inserted after the outer cortex has been over-drilled w/ a 3.5 mm drill bit;
           - it is important to aim the drill bit perpendicular to the fracture site (rather than perpendicular to the cortex site);


           - hazards:
                   - danger zone of the acetabulum (screw penetration of joint): 
                   - consider role of hip arthroscopy;
                   - note: its easy for screws inserted into retroacetabular space to enter joint;
                   - screws are normally directed away from the joint, oblique to the retroacetabular surface;
                   - retrograde drilling of frx frag may avoid joint penetration, however, requires stripping fragment from hip capsule,
                              (removing its blood supply);
                   - radiographic methods to determine articular penetration:
                          - multiple flourscopic views including cross table lateral view and the Judet iliac view are often the most useful views;
                          - flouroscopy w/ intra-articular contrast dye and moving the hip w/o crepitus are other methods to avoid joint
                          - using flouroscopy to achieve "end on" view of lag screws;
                   - reference:
                          - Radiographic diagnosis of screw penetration of the hip joint in acetabular fracture reconstruction
                          - Danger Zone of the Acetabulum.    

    - fixation w/ reconstruction plate (and lag screws or sping plate):
            - most indicated for comminuted posterior wall frx;
            - butress plate (8 hole 3.5 mm recon plate) is placed along posterior rim of acetabulum (placed from superior pole of ischium
                   to inferior iliac wing);
                   - plate is curved so that it roughly parallels rim of acetabulum (it should be precontoured on a model preoperatively);
                   - undercontouring of the plate helps butress the fragment;
                   - generally two screws are placed above and below acetabulum;
            - generally two lag screws are inserted midway between the reconstruction plate and the edge of the posterior wall;
            - note: its easy for screws inserted into retroacetabular space to enter joint;
            - see: danger zone of the acetabulum:
            - screws are normally directed away from the joint, oblique to the retroacetabular surface; 
            - referencs:
                   - Fixation of marginal posterior acetabular wall fractures using locking reconstruction plates and monocortical screws.
                   - The Use of Cervical Vertebrae Plates for Cortical Substitution in Posterior Wall Acetabular Fractures
                   - Fractures of the posterior wall of the acetabulum: treatment using internal fixation of two parallel reconstruction plates.

            - spring plate: (synthes spring plates)
                   - indicated for comminution;
                   - use a four hole one third tubular plate;
                   - one end of the plate holes is cut out and bent 90 deg;
                   - the plates are contoured to fit the bone;
                   - the two prongs are inserted into the acetabulum 5 mm from its edge;
                   - the plates are secured to the pelvis at the most posterior hole;
                   - following application of the plate, the 3.5 recon plate is placed over the spring plate;
                   - there is some controversy as to whether spring plates offer any significant stability; 
                   - spring plates create a special risk of intra-articular compromise of the joint surface;
                   - if the "hooks" of the plate are too long or malpositioned, the femoral head may be at risk for damage;
                  - ref:
                        - The Use of a T-Plate as "Spring Plates" for Small Comminuted Posterior Wall Fragments.
                        - Use of Spring Plates in Fixation of Comminuted Posterior Wall Acetabular Fractures
                        - Supplemental Superior Buttress Plating for the Treatment of Posterosuperior Wall Acetabulum Fractures

            - bone grafting:
                   - bone grafting is often required to support impacted articular fragments; 
                   - articular impaction is managed with elevation and application cancellous bone graft;
                   - large free fragments are reattached and small fragments removed;
                   - avoid fracture gaps;

- Post Op: 
    - postoperative CT scan allows optimal evaluation of surgical reconstruction;
    - need to limit postoperative hip flexion inorder to limit stress on the posterior wall fragment;
    - references: Computed tomographic assessment of fractures of the posterior wall of the acetabulum after operative treatment

- Complications:
    - this fracture type is associated w/ a high complication rate;
    - iatrogenic sciatic nerve injury may occur and may be prevented by constant knee flexion during the case and by intraoperative
                SSEP monitoring;
    - loss of fracture fixation is a common complication;
    - after ORIF of posterior wall frx, post traumatic osteoarthitis may occur in up to 20% of patients
    - non union:
            - ref: Indomethacin prophylaxis for heterotopic ossification after acetabular fracture surgery increases the risk for nonunion of the posterior wall.

Percutaneous retrograde posterior column acetabular fixation: is the sciatic nerve safe? A cadaveric study.
Biomechanical consequences of fracture and repair of the posterior wall of the acetabulum.
Comminuted Fractures of the Posterior Wall of the Acetabulum. A biomechanical evaluation of fixation methods
Posterior Acetabular Wall Fractures: a technique for screw placement.    
Hip Arthroscopy to Remove Loose Bodies After Traumatic Dislocation. 
Determinants of functional outcome after simple and complex acetabular fractures involving the posterior wall.
Surgical techniques-How do I do it? Open reduction and internal fixation of posterior wall fractures of the acetabulum