Acetabulum fractures

FRACTURES OF THE ACETABULUM
Letournel and Judet Classification
• Letournel and Judet devised the column concept where the anterior column was formed by the iliopectineal component and the posterior column was formed by the ilioischial component.
• The acetabular dome is formed the junction of the two columns.
• Both the columns have an inverted Y shaped construct
• Based on degree of columnar damage, 10 fracture patterns occur-
5 “elementary” and 5 “associated”.

Elementary Patterns
1. Posterior wall #
2. Posterior column #
3. Anterior wall #
4. Anterior column #
5. Transverse #

Associated Patterns
1. T-shaped #
2. Posterior column and posterior wall #
3. Transverse and posterior wall #
4. Anterior column/Posterior hemitransverse #
5. Both columns #

Mechanism of Injury:
a) Direct trauma:
Direct impact to the greater trochanter forms a transverse fracture when the hip is in neutral position
Direct impact to the greater trochanter forms an anterior column fracture when the hip is externally rotated.
Direct impact to the greater trochanter forms a posterior column fracture when the hip is internally rotated.
b) Indirect trauma:
As in a dash type of injury with a flexed knee.

Clinical Features:• Airway, breathing and circulation should be assessed.
• Look for sciatic nerve injury (common peroneal nerve component) especially in posterior column fractures.
• Morel-Lavallée lesion: It is a localised area of subcutaneous fat necrosis over the lateral aspect of the hip caused by the same trauma that causes the acetabular fracture.

X-ray • AP view
• The obturator oblique view evaluates the anterior column (iliopectineal line) and posterior wall of the acetabulum. The obturator oblique view is obtained when the pelvis is rotated 45 degrees with the inured side up
• The iliac oblique radiograph – posterior column (ilioischial line or Kohler’s line), anterior wall of the acetabulum.
• Roof arc angle of Matta is calculated by drawing 2 lines, one vertical line along the geometric centre of the acetabulum and the other from the fracture line to the geometric centre. The medial, anterior and posterior roof arcs are calculated.


CT scans including 3-D CT:
• 3D CT helps in a better understanding of the fracture but may not clearly identify fractures with minimal displacement due to “averaging” phenomena

Treatment

Non-operative Treatment (Indications)
1. Minimally displaced fractures (<2 mm) in the weight-bearing dome.
2. Roof arc angle> 45 degrees.
3. Secondary congruence in both column fractures where the ball and socket configuration of hip is maintained.
4. No femoral head subluxation on three x-rays, taken out of traction
5. For posterior wall fractures: less than 40% of width of wall on CT

Roof arc angles are not used in posterior wall fractures.

Operative Treatment (Indications)
1. Mainly for displaced fractures in the weight bearing area.
2. Matta’s roof arc angle <45 degrees.
3. Inability to maintain a congruent joint out of traction
4. Cranial 10 mm of the acetabulum on the CT scan corresponds to the area defined as the weight-bearing dome by roof arcs. Fractures involving area in the upper 10 mm of acetabulum are treated operatively.

Applied anatomy:
• Corona mortis: is a vascular communication between external iliac and deep inferior epigastric artery and the obturator artery. May extend over the superior pubic ramus; average distance from the symphysis to corona, 6 cm
• The ascending branch of MCFA contributes to vascularity of femoral head; hence preservation of this artery while dissecting near the quadratus femoris is important.
• The superior gluteal neurovascular bundle exists through the greater sciatic notch, damage of this bundle can occur when the fracture line exits the greater sciatic notch.

Factors predicting a good outcome in acetabular fracture fixation:

• Injury to cartilage or bone of femoral head
Damage: 60% good/excellent result
No damage: 80% good/excellent result
• Anatomic reduction
• Age of patient: predictive of the ability to achieve an anatomic reduction


Posterior wall fracture:•
- Maybe single or multifragmentary
• Marginal impactions maybe present: This is a rotated and impacted osteochondral fragment that is displaced as the femoral head dislocates and the wall fractures
• CT scan helps to evaluate marginal impaction, loose fragments in the joint, evaluation of joint concentricity and estimation of size of posterior wall fragment.
• Kocher Langenback approach is used for fixation

Posterior column fracture:• Usually fractures the greater sciatic notch at or above the location of the superior gluteal neurovascular bundle, extends inferiorly through the roof of the weight bearing dome and exists through the obturator foramen
• Neurovascular bundle maybe entrapped in the fracture if the posterior column is widely displaced. It should be extracted prior to reduction of the fracture dislocation
• Letournel’s gull sign: the articular cartilage accompanying the displaced posterior acetabular segment hinges inward creating an image with the intact portion of the roof that looks like a bird in flight.
• Kocher Langenback approach is used for fixation

Anterior wall fractures:• May be associated with “thinning” or reduplication of the ilioischial line
• The teardrop is often displaced medially with respect to the ilioischial line.
• Ilioinguinal approach is used for fixation

Anterior column fracture:
• High anterior column fractures exit the iliac crest, intermediate fractures exit the anterior superior iliac spine (ASIS), low fractures exit the psoas gutter just below the AIIS, and very low anterior column fractures exit the bone at the iliopectineal eminence
• The roof or portion of it can be displaced medially as seen in high or intermediate anterior column fractures. This pattern may also be seen in anterior column-posterior hemitransverse fractures or both column fractures of the acetabulum.
• The more superiorly the fracture line ascends, the greater the involvement of the weight-bearing aspect of the acetabulum.
• Ilioinguinal approach is used for fixation

Transverse fractures:• breaks both the anterior and posterior border of the innominate bone
• separates the innominate bone into two pieces: the upper iliac piece and the lower ischiopubic segment

subdivided by where the fracture crosses the articular surface:
 Transtectal fractures cross the weight bearing dome of the acetabulum.
 Juxtatectal fractures cross the articular surface at the level of the top of the cotyloid fossa.
 Infratectal fractures cross the cotyloid fossa
• Transtectal fractures maybe fixed with extended iliofemoral approach or Kocher langenback approach
• Infratectal or Juxtatectal fractures are approached through the Kocher Langenback approach

Complications:
1. Nerve injury: Sciatic nerve injury is associated with posterior column fractures.
2. Surgical wound infection: abdominal and pelvic visceral injuries predispose to increased incidence of surgical wound infection.
3. Heterotopic ossification: the incidence is highest with the extended iliofemoral approach and second highest with the Kocher-Langenback. indomethacin or low-dose radiation are sued for prophylaxis
4. Avascular Necrosis
5. Chondrolysis