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Hip dislocation and Acetabular fractures

Description

Acetabular fractures are complex injuries associated with intricate, often confusing anatomy, with a recognized potential for long-term disability and progressive joint degeneration. They occur in isolated fashion, or in combination with pelvic ring disruption and/or ipsilateral extremity injuries, including hip dislocations.

Native hip dislocations require an inherently massive force secondary to the intrinsic stability of the hip joint. Timely reduction, assessment of stability, and detection of associated injuries are paramount to achieving an enduring functional result.

Structure and function

The acetabulum is formed from the ilium, ischium, and pubis. Its structure is described via a two-column concept, intrinsically resembling an inverted-Y position. The anterior column consists of iliac and pubic components, while the posterior column incorporates the ischium. The acetabular dome, considered the weight-bearing portion, is formed by the junction of both columns.

The hip is an extremely stable joint. This is conferred via bony, ligamentous, muscular, and soft tissue constraints. Much force is required to cause a native hip dislocation.

Fractures of the acetabulum and/or hip dislocations can lead to an incongruent hip joint and altered weight-bearing characteristics that contribute to pain and dysfunction. This may be manifested through post-traumatic arthritis, avascular necrosis (AVN), and associated gait abnormalities. Treatment options for young adults with hip pathology are evolving, but at present, remain quite limited.

Epidemiology

Acetabular fractures are relatively uncommon injuries, generally affecting the young adult population following motor vehicle collisions.  Significant psychosocial and economic burden may incur, with great potential for long-term functional deficits.

The disease burden of hip dislocations can be quite similar, or incredibly different. Simple dislocations without fracture generally enjoy good long-term results if reduction is timely and concentric. Future consequences can also be exceedingly destructive despite any/all accepted treatment measures.

Clinical presentation

Common mechanisms causing acetabular fractures include motor vehicle collisions, falls from height, and industrial accidents. Full trauma evaluation is required, with many patients arriving unconscious or obtunded in consideration of associated injuries.

The proximal femur is excessively loaded, with the precise fracture pattern determined by position of the hip, magnitude of force, and bone quality. Moreover, if force transmission continues, the femoral head can also be displaced, resulting in dislocation.

Approximately 85-90% of hip dislocations are posterior, occuring secondary to axial loading of a flexed/adducted hip. This leads to a shortened, adducted, and internally rotated extremity. Associated sciatic nerve palsy is present in about 10% of cases, with the peroneal division (ankle dorsiflexion) preferentially affected.

Anterior hip dislocations result from loading a flexed, abducted, and externally rotated extremity, leading to an abducted, and externally rotated limb. The degree of hip flexion will determine whether the dislocation is inferior or superior. 

Following initial trauma management, the position of the affected limb, a complete neurovascular exam, and an assessment of skin integrity should be documented.

Common mechanisms causing acetabular fractures include motor vehicle collisions, falls from height, and industrial accidents. Full trauma evaluation is required, with many patients arriving unconscious or obtunded in consideration of associated injuries.

The proximal femur is excessively loaded, with the precise fracture pattern determined by position of the hip, magnitude of force, and bone quality. Moreover, if force transmission continues, the femoral head can also be displaced, resulting in dislocation.

Approximately 85-90% of hip dislocations are posterior, occuring secondary to axial loading of a flexed/adducted hip. This leads to a shortened, adducted, and internally rotated extremity. Associated sciatic nerve palsy is present in about 10% of cases, with the peroneal division (ankle dorsiflexion) preferentially affected.

Anterior hip dislocations result from loading a flexed, abducted, and externally rotated extremity, leading to an abducted, and externally rotated limb. The degree of hip flexion will determine whether the dislocation is inferior or superior. 

Following initial trauma management, the position of the affected limb, a complete neurovascular exam, and an assessment of skin integrity should be documented.

Figure 1. Right posterior hip dislocation. Note the typical internally rotated position of the leg with flexed hip.

Red flags

Any patient presenting with an acetabular fracture and/or hip dislocation must be evaluated for a femoral neck fracture. The long-term consequences of missing this injury may dramatically alter treatment, heighten the risk of AVN and/or cause associated life-altering consequences.

AVN is commonly associated with hip dislocations, as the dominant blood supply to the femoral head, the medial femoral circumflex artery, can be stretched or occluded. The risk of AVN increases the longer the hip remains dislocated, and the rate is slightly higher when there is an associated femoral head fracture. The overall rate of AVN following hip dislocation is approximately 15%, but increases to 20% with an associated femoral head fracture.

Sciatic nerve palsy is also a common complication of acetabular fractures and/or hip dislocations. Documentation of function should proceed any attempts at reduction. Appropriate consent including the risks of sedation,  fracture, loss or diminished sciatic nerve function, and the potential of an unsuccessful result with the need for open reduction must be initiated.

Differential diagnosis

Based upon loading mechanism, associated ipsilateral injuries can involve the entire extremity. Posterior wall fractures, the most common isolated acetabular fracture pattern, are frequently associated with posterior hip dislocations and/or ipsilateral knee injuries. This can include patellar fractures and rupture of the posterior cruciate ligament (PCL). These structures comprise the so-called “dashboard injury,” whereby a flexed knee contacts the dashboard as force is transmitted to the hip joint.

Pelvic ring and spinal injuries are frequent associated injuries, with disruption of adjacent organ systems also a common consequence.

Objective evidence

Secondary to its high energy mechanism, a full trauma evaluation should be obtained. This includes an AP chest, AP pelvis, and lateral cervical spine films. Judet views are required if an acetabular fracture is discovered, while an AP/cross-table lateral view of the hip, and a full-length femur film that includes the knee should be considered depending upon associated pathology and/or treatment expectations. Likewise, if a pelvic ring injury is suspected, inlet and outlet views should be obtained. They demonstrate anterior/posterior and vertical displacement of the pelvis respectively.

There are six radiographic landmarks that should be identified on an AP Pelvic x-ray:

  1. Anterior column - delineated by the iliopectineal line.
  2. Posterior column - delineated by the ilioischial line.
  3. Anterior wall - located medially relative to the convex posterior wall.
  4. Posterior wall - larger and more lateral than the anterior wall.
  5. Acetabular roof - also referred to as the “sourcil” (eyebrow) and found cranial to the femoral head
  6. Teardrop - radiographic structure created by confluence of medial obturator neurovascular sulcus, the quadrilateral surface of the pelvis, and the lateral cortical boundary of the acetabular fossa.

Figure 2. Anteroposterior (AP) x-ray of the pelvis.

Acetabular fracture classification is divided into five elementary patterns with a single fracture plane and five associated fracture patterns that combines elementary patterns. 

Elementary Patterns

Pattern

Description

Anterior Column                                            

AP Pelvis-Iliopectineal line disruptedàfurther identify on Obturator Oblique Judet view

Posterior Column

AP Pelvis-ilioischial line disruptedàfurther identify on Iliac Oblique Judet view.

Anterior Wall

Best seen on Iliac Oblique Judet view. The “teardrop” is usually displaced medially with respect to the ilioischial line.

Posterior Wall

Best seen on Obturator Oblique Judet view. Most common isolated acetabular fracture.

Transverse

AP Pelvis-iliopectineal and ilioischial lines disrupted. Ilioischial line and teardrop maintain normal relationship.

Associated Patterns

Pattern

Description

Posterior Column / Posterior Wall

AP Pelvis-PC-ilioischial line disrupted, also seen on Iliac Oblique view. PW best seen on Obturator Oblique view.

Transverse / Posterior Wall

AP Pelvis-Iliopectineal and ilioischial line disrupted, PW best seen on Obturator Oblique view.

Anterior Column / Posterior Hemi-transverse

AP Pelvis-iliopectineal and ilioischial lines disrupted. Ant column fracture also seen on Obturator Oblique view.

T-Type

AP Pelvis-iliopectineal and ilioischial lines disrupted.

Both Column

AP Pelvis-iliopectineal and ilioischial lines disrupted. "Spur" sign on Obturator oblique formed by intact ilium.

Acetabular Fracture Classification System:

ELEMENTARY FX PATTERNS-top row), ASSOCIATED FRACTURE PATTERNS (bottom row)

JUDET VIEWS: Obturator Oblique better delineates anterior column and posterior wall fractures, also scrutinizing the posterior acetabular surface for posterior hip joint subluxation.

RIGHT OBTURATOR OBLIQUE TECHNIQUE/X-RAY            

(Both Column Fx-Iliopectineal line disrupted/”Spur sign”)

In contrast, the iliac oblique film provides detailed imaging of the posterior column and anterior wall.


RIGHT ILIAC OBLIQUE TECHNIQUE/X-RAY

(Both Column Fx-Ilioischial line disrupted/Intact Ant Wall)

CT can provide further information regarding size and position of column fractures, impacted patterns, incarcerated bony fragments, and level of comminution. It is usually substituted for lateral C-spine radiographs, and can also help better identify associated traumatic and occult injuries.

Hip dislocations follow a similar pattern, with a cross-table lateral key to defining location of the femoral head with respect to the acetabulum.  The femoral heads will appear of different size with a dislocation, smaller in a posterior dislocation and larger if anterior with respect to the concentric hip joint.


CROSS-TABLE LATERAL OF HIP

**ISCHIAL TUBEROSITY CAN PROVIDE ANT/POST ORIENTATION

Risk factors and prevention

In younger individuals, preventable risk factors include wearing a seatbelt and associated safety precautions with respect to potential for high energy/velocity injuries. Regarding older individuals and/or those persons with gait abnormalities, detailed fall precautions, visual/auditory testing, and monitoring of medication effects may help to decrease events.

Treatment options

Non-operative management of an acetabular fracture requires a congruent, stable hip joint, with an intact weight-bearing dome. In addition, the orthopaedic surgeon must take into account associated injuries, functional demands and expectations of the patient, and consider his or her own experience treating the injury pattern. Elderly, non-ambulatory patients with multiple co-morbidities may be considered for non-operative management regardless of fracture pattern.

The goals of surgical intervention should be to maintain a painless and functional hip joint, restore the articular surface to prevent post-traumatic arthritis, and help diminish the risk of development of future complications (AVN, HO).

Early referral to an appropriate institution with an experienced acetabular surgeon can positively affect outcomes. It diminishes the need for more extensile exposures and allows for manipulation of more mobile fracture fragments. This can lead to a more accurate reduction, improving chances for better long-term results.

Hip arthroscopy is an alternative to open arthrotomy, and is indicated in select circumstance. This includes removal of residual joint debris and incarcerated fragments. Its less invasive nature however is generally offset by its heightened skill level requirement.

The most important parameter regarding treatment of a native hip dislocation involves time to reduction. Likewise, assessment of neurovascular function, specifically the sciatic nerve, must be evaluated before and after attempted reduction.

Reduction of a posterior dislocation involves traction/counter-traction, stabilizing the patients’ pelvis, along with gentle rotation motions, and perhaps slight adduction. Successful reduction is usually signalled by an palpable/audible “clunk”, with the return of appropriate leg length and rotation.

Stability should then be assessed regarding maintenance of concentric reduction. If determined stable, a knee-immobilizer should be protect against excessive flexion, adduction, and internal rotation.

Post-reduction radiographs should confirm concentric reduction and a pelvic CT can further evaluate for residual bony fragments and/or “marginal impaction.” Otherwise, protected weight bearing is implemented, and continued until evidence of healing on x-ray is present with an associated fracture.

If the hip is irreducible, or dislocates upon dynamic testing (70-90 degrees of flexion, neutral rotation, posterior-directed force), there may be a block to reduction, or it may be too unstable with respect to associated injuries (PW fx). In the former case, surgical intervention is required, while in the latter case, traction pin placement in the distal femur to temporarily maintain reduction may be entertained. However, this modality must be considered with respect to patient age (contraindicated in pediatric population/questionable in elderly osteoporotic patients), as well as in patients with associated injuries (ipsilateral extremity fractures).

A CT scan should then also be obtained to check for subtle joint incongruity, residual bony fragments in the joint, and “marginal impaction. Moreover, it can also aid in pre-operative planning if open reduction and/or surgical management is required.

Outcomes

Outcome of patients with acetabular fractures are based upon numerous factors, including fracture pattern, bone quality, extent of articular injury, associated injuries (hip dislocation, proximal femur fracture, neurovascular complications, etc.), presence/absence of surgical complications, and co-morbid conditions.

Post-traumatic arthritis following acetabular fractures and/or hip dislocation can result from an incongruent hip joint, bony defects of the femur/acetabulum, and articular defects. These conditions may all lead to alterations in weight-bearing biomechanics manifested by pain, stiffness, and overall decreased function.

Heterotopic Ossification (HO), ectopic bone formation, can also disrupt joint motion/function. The highest surgical risk follows a posterior surgical approach, while male patients and/or those with a traumatic brain injury carry the highest overall risk. Prophylaxis should be considered following acetabular surgery, with indomethacin or low dose local radiation the two recommended protocols.

Regarding hip dislocations, time to relocation is extremely important, and directly affects outcomes. Every effort should be made to minimize temporal issues that can lead to AVN because there are no reliable treatment options for its consequences, most notably in the younger population.

Simple posterior dislocations enjoy 70-80% excellent outcomes with early concentric reduction versus those with an associated fracture or delayed reduction (>12 hours). In the latter case, the associated fractures dominate outcome parameters, with the incidence of post-traumatic arthritis much lower in simple hip dislocations versus injuries that involve fractures.

Holistic medicine

The long-term impact faced by the young population with hip pathology can be overwhelming. Unfortunately, there are no good treatment options at present. Conservative treatment (non-narcotic analgesics, physical therapy, weight loss, etc.) generally only provides transient relief, while surgical intervention is a highly debated long-term solution. Hip arthroscopy, associated resurfacing, and/or joint replacement may initially be beneficial, but will all likely require revision/alternative intervention at a later date.
 

Miscellany

Mnemonic for Judet views: “PIC and POW”

PIC: Iliac oblique-Posterior Column/Anterior wall

POW: Obturator Oblique-Anterior Column/Posterior Wall

-Posterior wall fractures are often combined with “marginal impaction.” This refers to articular cartilage being impacted into the underlying cancellous bone. It is best assessed on CT scan and requires surgical management.


RIGHT HIP "MARGINAL IMPACTION"

-In Both Column fracture patterns (“floating acetabulum”), there is no connection of the articular surface to the intact hemipelvis. However, based upon the principle of “secondary congruency,” it may be considered stable and potentially treated non-operatively.

-Corona Mortis-vascular communication between the external iliac artery or inferior epigastric artery and the obturator artery. Found in approximately 85% of the population. Has a large potential for bleeding complications if disrupted.

-Morel-Lavalle lesion: classic skin degloving injury associated with acetabular fractures that requires extensive debridement.
MOREL-LAVALLE LESION

-“Classic” injury presentations can be dramatically altered with accompanying pathology, hence a high level of suspicion must exist in patients unable to provide a history of injury events. Time is of the essence in native hip dislocation, with the risk of avascular necrosis increased with a delay in management.

Key terms


Acetabulum, Hip, Hip Dislocation, Elementary/Associated fracture pattern, Sciatic Nerve, Avascular Necrosis, Post-Traumatic Arthritis, Heterotopic Ossification.

Skills

Radiographic Analysis, Recognition/Treatment of Emergent Orthopaedic Conditions (Hip Dislocation), Extremity Neurovascular Examination (sciatic nerve)

Content

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