Fractures of the acetabulum

                   Fractures of Acetabulum

                                      Dr KS Dhillon

Anatomy

The acetabulum is a deep, cup-shaped, hemispherical depression, directed downward, lateralward, and forward.Three bones of the pelvis, namely the ilium, ischium and the pubic bone contribute to the formation of the acetabulum. A little less than two-fifths is contributed by the ilium, a little more than two-fifths by the ischium, and the remaining fifth by the pubic bone. The pubic bone lies anteriorly, the ilium superiorly and the ischium posteroinferiorly. It has six principal components, the  anterior column, posterior column, anterior wall,   posterior wall, acetabular dome or roof and the medial wall.

The posterior column is composed of the quadrilateral surface, posterior wall, dome, ischial tuberosity and the greater/lesser sciatic notches. The anterior column is composed of anterior ilium, anterior wall, dome, iliopectineal eminence and the lateral superior pubic ramus.

The roof of the acetabulum is the thick, weight bearing portion and forms a separate fragment in bicolumnar fractures. The thin quadrilateral plate forms the medial wall or the floor of the acetabulum.

The acetabulum is bounded by an uneven rim, which is thick and strong above, and to it is attached the glenoid labrum which deepens the surface for articulation. Below it, there is a deep notch, the acetabular notch, which is continuous with a circular non-articular depression, the acetabular fossa, at the bottom of the cavity. This depression contains a mass of fat. The notch is converted into a foramen by the transverse ligament; through which nutrient vessels and nerves enter the joint. The margins of the notch give attachment to the ligamentum teres. The rest of the acetabulum is covered with a curved articular surface, the lunate surface, for articulation with the head of the femur.
The mean lateral inclination of the acetabulum is between 40 to 48 degrees and the mean anteversion is between 18 to 21 degrees.

Classification of acetabular fractures

The most widely used classification of acetabular fractures is that by Judet and Letournel. According to this classification fractures of the acetabulum are broadly divided into 2 categories: elementary fractures and associated fractures. There are 5 elementary and 5 associated fracture patterns. The associated fractures are composed of a combination of at least two of the elementary fracture patterns.

Elementary fractures involve a single wall, involve a single column, or are purely transverse. The simplest elementary fractures are two-part fractures.

Associated fracture patterns have at least three major fracture fragments and include a posterior column fracture with a posterior wall fracture, a transverse fracture with a posterior wall fracture, an anterior column fracture with a posterior hemitransverse fracture, a T-type transverse fracture, and associated both-column fractures.

The wall fractures can be divided into two types: the anterior wall fractures and the posterior wall fractures. The transverse fractures can be divided into three types: the transverse fracture, the T- shaped fracture and the transverse with posterior wall fracture. The column fractures can be divided into five types: posterior column, anterior column, posterior column with posterior wall, both columns and anterior column with posterior hemitransverse fractures [1].

Out of the 10 fracture patterns, 90% of acetabular fractures that occur are one of following five types: associated both-column, T-type, transverse, transverse with posterior wall, and elementary posterior wall fractures [2,3]. Often the acetabular fractures do not fit perfectly into one of the fracture patterns in the classification scheme [4].

Radiography

An anteroposterior view and left and right Judet views are required for evaluation of acetabular fractures. Judet views are the obturator oblique view (fig 1) which shows profile of obturator foramen and also shows the anterior column and posterior wall, and the iliac oblique view (fig 2) shows profile of involved iliac wing and it shows the posterior column and anterior wall.

The radiographic landmarks of the acetabulum include the iliopectineal line (anterior column), ilioischial line (posterior column), anterior wall, posterior wall, teardrop, weight bearing roof and the Shenton's line.

CT scan 

A CT scan is now considered a gold standard in management of patients with acetabular fractures. It helps in identification of the fracture pattern orientation, and definition of fragment size and orientation. Marginal impaction, articular gaps and step offs can be identified with a CT scan.
Loose bodies in the joint can be seen with CT scan.

Treatment of acetabular fractures

Nonoperative treatment

Indications for nonoperative treatment include:

• Undisplaced fractures and minimally displaced fractures (<2mm displacement).
• Displaced fractures where a large portion of the acetabulum remains intact and the femoral head remains congruent with the acetabulum.
• Moderate displacement of a both-column fracture and the patient presents late (>3 weeks after injury).
• Small posterosuperior-wall fractures with a stable hip joint and a congruent reduction.
• A posterior-wall injury that is minimally displaced or nondisplaced.
• If surgery is contraindicated

Surgery would be contraindicated in patients with:

• Severe systemic illness or secondary multiorgan failure due to polytrauma
• Systemic infections or sepsis
• Local infection
• Extreme  osteoporosis
• Severe comminution with preexisting arthrosis would be a relative contraindication.

Nonoperative treatment includes:

• Resuscitation of the patient - Basic or advanced life support where necessary.
• Diagnosis - After patient has been stabilized a clinical and radiologic diagnosis is established.
• Treatment of other life-threatening injuries such as head, chest, abdominal, or other injuries.
• Urgent reduction of associated dislocation is carried out. Posterior dislocations are managed by gentle close reduction on an emergency basis. Central fracture-dislocations are treated by skeletal traction applied to an upper tibial or lower femoral pin. 

For patients with undisplaced and minimally displaced fractures, protected weight bearing for 6-8 weeks is usually recommended.  DVT prophylaxis is usually recommended in patients who are immobilized or are slow to slow to mobilize.

Indications for open reduction and internal fixation include [5,6] :

• Injury less than 3 weeks old
• Patient physiologically stable
• Good soft-tissue coverage
• no local infection
• More than 2 mm displacement of roof 
• Unstable fracture pattern 
• Marginal impaction
• Intra-articular loose bodies
• Irreducible fracture-dislocation
• Intact roof-arc angle less than 30°
• Fractures that have a medial roof-arc angle of 45° or less
• Anterior roof-arc angle of 25° or less
• Posterior roof-arc angle of 70° or less across the weight bearing part of the acetabulum. 
• Vascular injury or sciatic palsy after a closed reduction

The fractures can be approach anteriorly by the ilioinguinal, iliofemoral or the modified stoppa approach. The Kocher-Langenbeck approach can be used for posterior fractures and an extended iliofemoral combined approach for both anterior and posterior fractures.

Outcome of management of acetabular fracture

The outcome after undisplaced and minimally displaced fractures treated conservatively is invariably good. The outcome of treatment of significantly displaced fractures which require open reduction and internal fixation can vary widely. There is a strong correlation between the accuracy of reduction
and the clinical outcome. Accurate reduction with restoration of articular congruence is associated with good clinical outcome [7]. Incongruent reduction correlates strongly with a poor outcome [8]. Excellent results can be achieved even when the reduction is poor, provided that the step or gap is outside the weight-bearing region [9].

A significant negative impact on outcome is seen in patients with simple posterior column fractures and T-shaped fractures. Patients with a combined posterior wall traumatic dislocation and sciatic nerve palsy also fare badly. The outcome is also poor when the acetabular fracture are associated with injury to the femoral head  [10-13].

Deo et al [14] reported good to excellent results in 74% of 79 patients they treated who had acetabular fractures. Early operation and an anatomical reduction was associated with good outcome and poor outcome was seen in patients who had delayed surgery, and in patients where there was failure to achieve or maintain reduction, and in patients who had femoral head damage at the time of injury.

Matta JM [15] published the outcome of treatment of 262 displaced acetabular fractures in 259 patients. The patients were treated with open reduction and internal fixation (ORIF) within 3 weeks after injury. This review was carried out at a mean follow-up of 6 years. Anatomical reduction was achieved in 71% of cases. Greater fracture complexity, age > 40 years, and a longer interval between injury and surgical reduction were  bad prognostic factors which were significantly associated with a decreased rate of anatomical reduction and poorer outcome. The results were excellent in 40%, good in 36%, fair in 8%, and poor in 16% of the patients.The overall clinical results were excellent / good for 76% of patients.

There was neurological injury (2 sciatic nerve injury and 1 femoral nerve injury and 6 peroneal nerve injury) in 3% of the cases. Wound infection occurred in 13 hips (5%), extraarticular in 5 hips and intraarticular in 8 hips. Progressive femoral head wear was seen 13 cases (5%). Osteonecrosis of the femoral head occurred in 8 hips (3%). Subsequent operations included a total hip replacement in 6% of the cases and an arthrodesis in 2% of the patients.

Gänsslen et al [16] in a study 135 patients with both column fractures of the acetabulum found that 69.8% of those with anatomically reconstructed hip joints had no or mild postoperative pain and a good or excellent result at a mean follow up of 54.6 months. Arthritic changes were seen in 17.5% of the patients and joint failure in a further 25.4% of the patients. Joint failure was usually seen in patients with concomitant femoral head lesion and significant preoperative articular fragment displacement.

Briffa et al [7] reported the outcome of treatment of 161 of the 257 patients who had surgical fixation of acetabular fractures at a minimum of 10 years follow up. The result were excellent in 47%, good in 25%, fair in 7% and poor in 20% of the patients.

They had a high infection rate of 11%, of which 6% were deep infection, despite the use of prophylactic antibiotics. They had a 12.5% incidence of sciatic nerve palsy, a 1.8% obturator and a 14.3% incidence of lateral femoral cutaneous nerve palsy.

There were no cases with pulmonary embolism and no cases with deep vein thrombosis. There was a 10.5% incidence of heterotopic ossification. The incidence of posttraumatic osteoarthritis was 38% in this series, which is higher than the  26.6% reported by Giannoudis et al [17] in their 2005 meta analysis.

The incidence of AVN of the femoral head was 11.8% and the incidence of total hip replacement was 16% in the Briffa et al series.

The 10 years survivorship of total hip replacement (THR) in patients with prior acetabular fracture is markedly inferior and is more frequently associated with serious complications when compared with patients undergoing THR for primary osteoarthritis or AVN. Morison et al [18] carried out a retrospective case-control study which compared the outcome of THR in patients with previous acetabular fractures, with the outcome in patients who received a THR for primary osteoarthritis or AVN. They found that the average time to revision of the THR in patients with previous acetabular fractures was 8 years as compared to 13 years in patients without acetabular fracture who had THR. The primary cause for revision in both cohorts was loosening of the acetabular component. There was no difference in revision rates in patients who had conservative or surgical treatment for the acetabular fractures. The primary cause for revision in both cohorts was loosening of the acetabular component.

Patients undergoing THR who had previous acetabular fractures were more likely to develop serious complications such as infection, dislocation, and acetabular loosening and heterotopic ossification. The infection rates were 7% in patients with previous acetabular fractures as compared to 0% in the cohort without previous acetabular fractures. The dislocation rates were 11% in patients with previous acetabular fracture as compared to 3% in the other cohort and heterotopic ossification was seen in 43% and 16% of the patients respectively, in the two cohorts.

Romness and Lewallen [19] did a retrospective study of 55 primary total hip arthroplasties, in 53 patients with a history of previous acetabular fracture, with a mean follow up of 7.5 years and they found radiographic loosening of the acetabular component in 52.9% of the patients and symptomatic loosening in 27.5% of the patients. The revision rates at a mean follow up of 7.5 years was 13.7%.
Weber et al [20] reported revision rates of 22% for aseptic loosening at 10 years follow up, in patients who had a THR for arthrosis from previous acetabular fractures.

Conclusion

Standard AP and oblique obturator and iliac views of the acetabulum are necessary when an acetabular fracture is suspected. CT scan is now gold standard for a workup in the management of acetabular fractures.

Good long term results can be expected for undisplaced and minimally displaced acetabular fractures treated nonoperatively.

The clinical outcome for operatively treated patients are generally good, with acceptable complication rates. Good to excellent results have been reported in about 76% of the patient.
Loss of joint congruency with an intraarticular step-off of more than 2mm leads to increased rates of secondary osteoarthritis. Post traumatic osteoarthritis has been reported in 26% to 38% of the patients. The reported incidence of AVN of the femoral head is about 11.8% and the incidence of total hip replacement in patients with acetabular fractures is about 16%. The survivorship of THR in patients with acetabular fractures is lower than in patients who have THR for primary OA or AVN by about 5 years at 10 years follow up. Revision rates of 22% for aseptic loosening at 10 years follow up have been reported in patients who had a THR following acetabular fractures.

 References

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