Acetabular fractures are uncommon but important because they involve a major weight-bearing joint in the lower extremity. Being intraarticular fractures, these fractures require anatomical reduction for good long-term function of the hip joint.
A failure to achieve anatomical reduction could lead to the breakdown of the cartilage surface due to articular incongruity present leading to degenerative changes and arthritis of the hip joint.
Fractures of the acetabulum occur primarily in young adults as a result of high-velocity trauma like motor vehicular accidents or fall from height and are frequently associated with other serious injuries.
The acetabulum is a socket in the innominate bone where the ilium, ischium, and pubis are joined by the triradiate cartilage, which later fuses. A normal relation with the femoral head is essential for the complete development of adult acetabulum.
The acetabulum is enclosed by the anterior and the posterior columns like the two limbs of an inverted Y.
The anterior column comprises the anterior border of the iliac wing, the entire pelvic brim, the anterior wall of the acetabulum, and the superior pubic ramus.
The posterior column is formed by the ischial portion of the bone, including the greater and lesser sciatic notch, the posterior wall of the acetabulum, the majority of the quadrilateral surface, and the ischial tuberosity.
The roof of the acetabulum is the thick, weight-bearing portion and forms a separate fragment in bicolumnar acetabular fractures. The thin quadrilateral plate forms the medial wall or the floor of the acetabulum.
In addition to acetabular anatomy, the anatomy of pelvis and hip including vessels and nerves around needs to be studied for a better understanding of fracture and execution of treatment.
[Read anatomy of pelvis]
[Read anatomy of hip joint]
Mechanism of Injury of Acetabular Fractures
There are two basic mechanisms of injury:
- Direct blow on the acetabulum
- Flexed knee joint strikes the dashboard of a motor vehicle, driving the femur posteriorly on the acetabulum [dashboard injury]
A blow directly upon the greater trochanter usually causes a transverse type acetabular fracture, depending on the degree of abduction and rotation of the femoral head, whereas the dashboard injury causes a posterior wall or posterior column fracture or fracture-dislocation of the hip joint.
Although it is difficult to pinpoint the exact relation between the point of impact and the mechanism of injury in acetabulum fractures, certain relations are well-recognized.
Force Acts on Greater trochanter Along Axis of Femoral Head
The point of impact of the femoral head is decided by the degrees of adduction and abduction and rotation of the femur. Though this oversimplifies the concept, one variable is being considered at a time for simplification
Hip in neutral adduction-abduction
External rotation of the hip predisposes to anterior column injury, and internal rotation predisposes to posterior column injury. The pattern of injury varies with rotation
- Neutral rotation- Central/anterior column
- External rotation (~25°) – Anterior column
- External rotation (~50°) – Anterior lip
- Internal rotation (~25°) – Transverse/T-shaped/bicolumnar, depending upon the degree of force applied
- Internal rotation (~50°, extreme) – Posterior column with transverse element
Hip in neutral rotation
Greater the degree of adduction of the femur, the higher the level of the fracture (greater involvement of the roof). The greater the degree of abduction, the lower (more inferior) is the fracture line.
- Neutral adduction-abduction – Transverse or T-shaped fracture beginning at the inner margin of the roof of the acetabulum
- Increasing adduction – Transverse or T-shaped fracture with increasing involvement of the roof of the acetabulum
- Increasing abduction – Transverse or T-shaped fracture with a progressively inferior shift of the fracture line
Force Acts on Flexed Knee Along Femoral Shaft
With the hip flexed to 90°, positions of the femur and associated fractures are as follows:
- Neutral adduction-abduction – Posterior wall
- Maximum abduction – Posterior column with transverse element
- Mild (~15°) abduction – Posterior column
- Adduction – Posterior dislocation of the hip, with or without posterior-wall fracture
Note: With increasing flexion>90 degrees, a progressively lower involvement of the posterior column occurs whereas on decreasing flexion (<90°) posterosuperior portion of the acetabulum is increasingly involved.
Force applied to Foot with knee Extended
Positions of the femur with associated acetabulum fractures are as follows:
- Hip extended (eg, fall from a height) – Transtectal transverse fracture
- Hip flexed (eg, frontal collision in a vehicle, with force transmitted through the foot pedal) – Depending on the position, similar to the force acting through a flexed knee
Classification of Acetabular Fractures [Letournel and Judet]
Acetabulum consists of four anatomical areas
- Anterior column
- Posterior column
- Anterior wall of lip
- Posterior wall of lip.
All fracture types involve one or a combination of more than one of these.
Therefore, the following fracture types are possible
- Isolated anterior column fracture
- Isolated posterior column fracture
- Anterior column fracture with an anterior lip fracture
- Posterior column fracture with a posterior lip fracture.
Following points should be noted
- If both columns are broken, the injury is called a transverse fracture
- When both columns are broken and separated from each other, it is called a T fracture
- Both of these [ the transverse or T] may be associated with an anterior or posterior lip fracture as well.
- In the transverse type, a portion of the acetabular dome is always attached to the intact ilium.
Letournel and Judet Classification
Letournel and Judet divided acetabular fractures into simple and complex types. Fractures may be of the anterior, posterior, medial, or transverse type associated with anterior, posterior, or medial displacement.
Simple or Elementary Fractures
These have only one fracture line and include the following:
- Posterior-wall fractures
- Posterior-column fractures
- Anterior-wall fractures
- Anterior-column fractures
- Transverse fractures
Complex or Associated Fractures
The five associated patterns are combinations of simple patterns:
- Posterior column + posterior wall fractures
- Transverse + posterior wall fractures
- T-shaped fracture
- anterior wall/column + posterior hemi-transverse fracture
- Bilateral-column fracture
The details of these fractures are described below.
Details of Fracture patterns
Posterior Wall Fractures
These fractures typically involve the rim of the acetabulum, a portion of the retroacetabular surface, and a variable segment of the articular cartilage.
There may be impaction of the articular cartilage requiring elevation at the time of surgery.
Extended posterior-wall fractures can involve the entire retroacetabular surface and include a portion of the greater or lesser sciatic notch, the ischial tuberosity, or both. The ilioischial line, however, remains intact on the anteroposterior view.
Posterior- column Fractures
These include only the ischial portion of the bone. The entire retroacetabular surface is displaced with the posterior column. As the vertical line separating the anterior column from the posterior column traverses inferiorly, it most commonly enters the obturator foramen. An associated fracture of the inferior pubic ramus is present.
Sometimes, the fracture line traverses just posterior to the obturator foramen, splitting the ischial tuberosity. The ilioischial line typically is displaced and disassociated from the teardrop.
These are uncommon injuries and often occur in conjunction with anterior dislocations.
Low Anterior-column Fractures
These fractures involve only the superior ramus and pubic portion of the acetabulum. High anterior-column fractures can involve the entire anterior border of the innominate bone. The pelvic brim and iliopectineal line are displaced. Medial translation of the entire roof or a portion of the roof is typical of displacement of a high or intermediate anterior-column fracture.
These fractures divide the innominate bone into two portions by a fracture line crossing through the acetabulum at a variable level.
The superior part is composed of the iliac wing and a portion of the roof of the acetabulum. The lower part of the bone, the ischiopubic segment, is composed of an intact obturator foramen with the anterior and posterior walls of the acetabulum.
Letournel further divided transverse fractures into the following three subtypes:
- Transtectal, in which a transverse fracture line crosses the superior acetabular articular surface
- Juxtatectal, in which a transverse fracture line crosses at the junction of the superior acetabular articular surface and superior cotyloid fossa
- Infratectal, in which a transverse fracture line crosses through the cotyloid fossa
Anterior with posterior hemitransverse
This acetabular fracture is common in elderly patients. These fractures combine an anterior-wall or anterior-column fracture with a horizontal transverse component, which traverses the posterior column at a low level.
Posterior-column with posterior-wall
The posterior-column with posterior-wall pattern divides the posterior column into a larger posterior-column component and an associated posterior-wall component. The ilioischial line typically is displaced and disassociated from the teardrop.
Transverse with posterior-wall
It is similar to a transverse fracture except for the addition of a vertical split along the quadrilateral surface and acetabular fossa which divides the anterior column from the posterior column. An associated fracture of the inferior pubic ramus typically is present.
Anterior and posterior columns are separated from each other, and all articular segments are detached from the intact portion of the posterior ilium, which remains attached to the sacrum. A fracture of both columns is associated with the spur sign [pathognomonic], in which the fractured edge of the intact posterior iliac wing is seen prominently relative to the medially displaced articular segments on the obturator oblique radiographic view.
The patient is often received as polytrauma patients though isolated fractures of acetabulum do occur. the patient has a history of significant injury and should be examined from head to toe for assessment of likely injuries.
Patients often have multiple injuries about half of the patients do have an associated injury.
Injuries of bowel and urinary tract are specifically looked for as these, and a high likelihood of associated injury exists (in as many as 50% of patients). It is also important to exclude injury to the bowel and the urinary tract, in that such injuries influence decision-making about an open reduction of the acetabular fracture
Often the patient needs resuscitative measures.
The local site should be examined for wounds, swelling, and associated injuries. The position of a lower limb would indicate the type of dislocation. In a posterior dislocation, the lower limb is adducted, flexed, and internally rotated. In an anterior dislocation, it is abducted.
If the anterior superior iliac spine on the affected side is more laterally placed and it may indicate a central dislocation.
The neurovascular examination should be done.
The patient needs hemoglobin and hematocrit levels during the phase of resuscitation along with blood group typing and crossmatching.
The required investigation for surgical fitness are done before the patient is planned for surgery.
Radiographic examination of the pelvis should include the anteroposterior view, the inlet view, and the outlet view to allow visualization of pelvic injuries.
Pelvis with both hips
This is an essential radiograph and may depict the following:
- Associated pelvic-ring fractures and dislocation through or disruption of one or more joints in the pelvic ring
- Bone quality
- The acetabular fracture itself
In this view, the affected hips are raised by 45° with the appropriate foam wedge under the affected and the beam is centered over a point one fingerbreadth below and medial to the anterior superior iliac spine.
In this view, the iliac crest is seen perpendicular to its normal plane, so displacement of the iliac wing in the coronal plane is best noticed here. This view also best shows the anterior column and the posterior lip of the acetabulum.
Pelvic brim is visualized and the junction of the anterior and posterior columns is seen as a line just above the roof
The uninjured hip is elevated to 45°. The injured part rests on the table and a foam wedge is inserted under the opposite hip of the patient. The beam is centered one fingerbreadth below the level of the anterior superior iliac spine and at the midpoint of a transverse line from the anterior superior iliac spine to the midline.
It depicts well
- Anterior lip of the acetabulum
- Posterior column and posterior border of the iliac bone
- Iliac wing
CT has revolutionized the imaging acetabular fractures, especially with 3D reconstruction. It is able to tell better about the fracture anatomy, the degree of comminution, and associated fracture patterns, intra-articular/incarcerated fragments.
Associated injuries such as to femoral head are better noted. It is a better investigation to visualize sacroiliac joint integrity, pelvic hematoma, and minimally displaced iliac fractures.
Treatment of Acetabular Fractures
In acute stage, the patient needs to be managed by
- Resuscitation of the patient – Basic and advanced life support
- Treatment of associated life-threatening head, chest, abdominal, or other injuries
- Urgent reduction of dislocations
After the patient has been stabilized, the treatment for acetabular fractures should follow.
Nonoperative or Operative – The Decision Making
The treatment options for acetabular fracture include both nonoperative and operative options.
Nonoperative methods include
- Early mobilization, limited and progressive weight bearing
Operative Care includes
- Open reduction, internal fixation
- Primary total hip arthroplasty
Decision-making requires a careful assessment of both fracture factors and patient factors.
The stability of the hip and/ or the fracture is of prime importance.
In general, nonoperative care is indicated when the joint is stable in all anatomical positions and congruity is acceptable
Undisplaced fractures, minimally displaced fractures, (low anterior column, low transverse), Fractures with secondary congruence (both- column) are candidates for non-operative treatment.
Thus, nonoperative treatment should be considered in the following circumstances:
- Undisplaced fractures
- Displaced fractures when
- A large portion of the acetabulum remains intact and the femoral head remains congruous
- a secondary congruence is present – 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
- Minimally displaced or nondisplaced posterior wall fracture
- Contraindication to surgery
- Severe osteopenia
- Severe systemic illness
- Local infection
- Severe comminution
- Preexisting degenerative changes in the joint
Non- Operative Treatment
Once the main form of treatment, today skeletal traction has only a limited role in definitive management. Its role is in the emergency phase to keep the femoral head away from the acetabular fracture fragments.
It is not necessary for stable minimally displaced fractures, it is unnecessary, and in displaced fractures, operative treatment is required.
Early Ambulation, Limited and Progressive Weight Bearing
In stable and minimally displaced fractures, nonoperative care consists of early mobilization, with limited and progressive weight bearing as fracture healing progresses. The weight bearing initially involves toe to touching for the first 4–6 weeks followed by progression to full weight bearing at 8–12 weeks.
The patient must be followed closely with serial X-rays and examinations.
- Displaced fractures with >2 mm articular step)
- Vascular injury or sciatic palsy develops after a closed reduction
- Instability – when hip dislocation associated with
- Posterior wall or column displacement
- Anterior wall or column displacement
- Fractures through the roof of the dome
- Displaced dome fragment
- Transverse or T types (transtectal)
- Both-column types with incongruity(displaced posterior column)
- Fractures through the roof of the dome
- Incarcerated intra-articular fragments
- Impaction of the articular surface
- Displaced fractures of the femoral head
- Soft tissue interposition
- Fracture of the ipsilateral femur
Timing of Surgery
The patient should be operated as early as is feasible, usually on the fourth to seventh day after trauma.
There might be certain conditions requiring immediate or urgent surgery. These are
- An irreducible dislocation
- An unstable hip following reduction
- An increased neurological deficit following reduction or an increasing neurological deficit with CT evidence of pressure on the nerve
- An associated vascular injury
- An open fracture
The choice of surgical approach is determined by the type of fracture. Several approaches are available to the surgeon and may be summarized as follows:
- Posterior Kocher-Langenbeck
- Posterior transtrochanteric
- Triradiate transtrochanteric
- Extended iliofemoral
- Combined approaches
Posterior wall fractures require posterior approaches and major anterior column displacements anterior approaches. Extensile approaches cause more complications than simple ones and are less preferred.
Internal Fixation Techniques
Implants used are
- Cancellous lag screws
- 4.0-mm cancellous screws
- 3.5 mm cortical screws
- Reconstruction plate
- 3.5 mm
- 4.5-mm [used less commonly]
[Read more on Bone Screws]
Adequate contouring of the plates is essential.
In postop period, a longer period of immobilization may be indicated if the fixation is not deemed stable at the time of surgery. A longer period of immobilization may also be indicated in extensile approaches.
Otherwise, the patient can start exercises on day 1 of the postoperative period, starting with ankle dorsiflexion, followed by static quadriceps and other exercises for limb as the patient becomes comfortable.
If there is concern about the quality of the bone, about gross comminution, especially of the medial wall of the acetabulum, or about inadequate stability, traction should be continued for 6 weeks until some healing of the fragments has occurred. Ambulation may then begin with crutches, followed by progressive weight bearing at approximately 12 weeks.
Total hip replacement
Early total hip arthroplasty is being recommended in patients in whom operative open fixation will yield poor results, such as the older patient with severe comminution, especially with a fractured femoral head.
Delayed total hip arthroplasty remains the mainstay of treatment if methods of internal fixation fail.
Complications of Acetabular Fractures
Complications are divided into early and late.
Predisposing factors are
- Poor skin condition
- Open fractures
- Presence of wounds/friction abrasions near the operative site or at a distance
- Extensive exposure
- Prolonged surgery
Early recognition, vigorous antibiotic therapy, wound cleaning are the measures to control infection. If infection communicates with the joint, cleaning and draining the joint is essential.
Sciatic nerve damage is caused by the injury and trauma at the time of surgery.
Injury to the lateral cutaneous nerve of the thigh usually occurs as an iatrogenic injury in the ilioinguinal or extensile approaches.
Injury to the femoral nerve is extremely rare and occurs due to traction on the iliopsoas compartment in an ilioinguinal approach.
The superior gluteal nerve is at risk in fractures that exit high in the greater sciatic notch and during the posterior approach.
The pudendal nerve may be injured because of pressure from the perineal post of the traction table.
The superior gluteal artery is the vessel most commonly involved. The injury may be due to the injury itself or result from iatrogenic damage during dissection in the region of the roof of the greater sciatic notch.
The femoral artery may be damaged by a misplaced screw or excessive manipulation.
Thromboembolism is one of the most significant complications of acetabular fractures. The emboli usually originate from the proximal large veins of the lower limb
Therefore, some form of anticoagulant prophylaxis is often recommended, especially in high-risk patients.
Fixation related Issues
- Fixation failure
- Intra-articular hardware
- Avascular necrosis
- Posttraumatic osteoarthrosis
- Heterotopic new bone formation
- Male sex, associated head injury, T-shaped fractures, and extensile approaches increase the risk
Prognosis of Acetabular Fractures
Prognostic Factors are
- The degree of initial displacement
- The damage to the superior weight-bearing surface of the acetabulum or the femoral head
- The degree of hip joint instability caused by a posterior wall fracture
- The adequacy of reduction, either open or closed
- The late complications of:
- Avascular necrosis of the femoral head
- Heterotopic ossification
- Sciatic or femoral nerve injury
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- Maini L, Kumar S, Batra S, Gupta R, Arora S. Evaluation of the muscle morphology of the obturator externus and piriformis as the predictors of avascular necrosis of the femoral head in acetabular fractures. Strategies Trauma Limb Reconstr. 2016 Apr 26.
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