Orthopaedic Surgery - Traumatic Hip Dislocation

Basics

Traumatic hip dislocation is an orthopaedic emergency in which the femoral head is completely displaced from the acetabulum.

These injuries usually result from high-energy trauma and may occur as an isolated dislocation or as a fracture-dislocation involving the acetabulum, femoral head, or femoral neck.

Because the mechanism is often severe, a complete trauma assessment is essential.

Associated Trauma

Up to approximately 50% of patients may have additional fractures or other major injuries at the time of presentation.

Associated acetabular, femoral head, femoral neck, knee, foot, spinal, thoracic, and abdominal injuries should be actively sought.

Classification

Traumatic hip dislocations are classified primarily according to the direction of displacement.

They may be:

Posterior or anterior, with further description according to associated fractures of the femoral head, femoral neck, or acetabulum.

Prevention

Seat-belt use together with appropriate air-bag protection reduces the risk and severity of injuries sustained in motor vehicle collisions.

Epidemiology

Traumatic hip dislocation is most commonly encountered in young adults exposed to high-energy trauma.

Males are affected more frequently than females.

Posterior Dislocation

Posterior dislocations account for approximately 85–90% of traumatic hip dislocations.

Anterior Dislocation

Anterior dislocations represent approximately 10–15% of cases.

Risk Factors

Major risk factors include:

Motor vehicle collisions, falls from substantial height, pedestrian-versus-vehicle injuries, industrial trauma, and high-energy sports accidents.

Etiology

Approximately 70–90% of traumatic hip dislocations have historically been associated with motor vehicle collisions.

Dashboard Injury

A classic mechanism for posterior dislocation occurs when the patient is seated with the hip and knee flexed.

During rapid deceleration, the knee strikes the dashboard, transmitting an axial force through the femur.

This drives the femoral head posteriorly out of the acetabulum.

Other Mechanisms

Other causes include:

Falls from height, industrial accidents, pedestrian injuries, motorcycle trauma, and sporting injuries.

The direction of force and position of the hip at impact determine whether the femoral head dislocates anteriorly or posteriorly.

Associated Conditions

Because traumatic hip dislocations usually result from high-energy injury, associated abnormalities are common.

Sciatic Nerve Injury

The sciatic nerve is particularly vulnerable in posterior dislocation.

Sciatic nerve dysfunction has been reported in approximately 10–20% of posterior dislocations.

The peroneal division is affected most commonly.

Relationship to Reduction Delay

Prolonged dislocation may increase the likelihood of neurologic injury and other complications.

Musculoskeletal Injuries

Common associated injuries include:

Femoral head fracture, femoral neck fracture, acetabular fracture, ipsilateral knee injury, and foot or ankle injury.

Other Trauma

Chest, abdominal, spinal, and head injuries may also occur and can take priority during initial resuscitation.

Diagnosis

Signs and Symptoms

Patients usually have severe hip pain and inability to move or bear weight on the affected extremity.

Numbness or paresthesias may occur when the sciatic nerve is injured.

Posterior Dislocation Position

The classic posture of a posteriorly dislocated hip is:

Flexion, adduction, and internal rotation.

The affected extremity also typically appears shortened.

Anterior Dislocation Position

An anteriorly dislocated hip usually rests in:

Abduction and marked external rotation, often with some degree of flexion or extension depending on the subtype.

Altered Mental Status

Some patients are obtunded or unconscious because of associated trauma, intoxication, or head injury.

The diagnosis therefore cannot depend solely on patient-reported symptoms.

Careful inspection of limb position and systematic trauma imaging are essential.

Physical Examination

Trauma Survey

A full primary and secondary trauma survey should be performed because associated injuries are common and may be life-threatening.

Limb Position

The position, shortening, and rotational alignment of the lower extremity should be documented before reduction.

Neurovascular Examination

Motor, sensory, and vascular findings should be documented before and after reduction.

Sciatic Nerve

Particular attention should be given to sciatic nerve function.

Motor testing should include:

Ankle dorsiflexion, plantarflexion, great-toe extension, and ankle eversion.

Sensory testing should include the dorsum and plantar aspects of the foot according to tibial and peroneal nerve distribution.

Vascular Status

Distal pulses, capillary refill, skin temperature, and overall limb perfusion should be assessed.

Laboratory Tests

Laboratory studies are directed by the overall trauma evaluation rather than the hip dislocation itself.

A standard trauma panel may be obtained according to injury severity and anticipated operative management.

Imaging

Initial Trauma Radiographs

Imaging commonly includes an AP pelvis as part of the initial trauma evaluation.

Additional imaging is determined by associated injuries.

Hip Radiographs

Dedicated radiographs may include AP and cross-table lateral views.

A cross-table lateral can help establish whether the dislocation is anterior or posterior.

Radiographic Appearance

In a posterior dislocation, projection may make the displaced femoral head appear relatively smaller than the opposite side.

In an anterior dislocation, it may appear somewhat larger.

These findings are secondary to projection and should not replace assessment of the actual displacement pattern.

Associated Acetabular Injury

The acetabulum should be inspected carefully for fracture fragments, wall disruption, or joint incongruity.

When an acetabular fracture is suspected, Judet oblique views may provide additional information, although CT now plays the major role in defining fracture anatomy.

Femoral Neck

The femoral neck must be scrutinized for associated fracture.

An unrecognized femoral neck fracture can be displaced or worsened by forceful reduction.

Intra-Articular Fragments

The joint should be evaluated for:

Osteochondral fragments, femoral-head fractures, acetabular fragments, and asymmetric joint-space widening suggesting an incarcerated fragment.

CT

CT is routinely obtained after reduction in many modern trauma protocols, particularly when there is concern for associated fracture or nonconcentric reduction.

Post-Reduction CT

CT can demonstrate:

Small intra-articular fragments, femoral-head fractures, acetabular fractures, subtle femoral-neck injury, joint congruity, and incarcerated osteochondral material.

Before Open Reduction

If closed reduction fails and open reduction is required, CT may help define fracture anatomy when this can be obtained without creating an unsafe delay.

MRI

MRI is not routinely required during the acute reduction phase.

It may later be useful for evaluating:

Osteonecrosis, cartilage injury, labral injury, occult fracture, or persistent unexplained symptoms.

Differential Diagnosis

Important competing or associated diagnoses include:

Femoral neck fracture, femoral head fracture, acetabular fracture, pelvic fracture, and severe proximal femoral trauma without dislocation.

Treatment

Initial Stabilization

Initial management follows standard trauma principles.

Life-threatening injuries are addressed first.

Once the patient is sufficiently stable, the dislocated hip should be reduced urgently.

Orthopaedic Emergency

Traumatic hip dislocation requires emergent orthopaedic reduction because prolonged displacement increases the risk of femoral-head osteonecrosis and other complications.

Timing

Reduction should be performed as soon as safely possible, ideally within approximately 6 hours of injury when circumstances permit.

Closed Reduction

Closed reduction is the preferred initial treatment when there is no contraindication.

Sedation or Anesthesia

Adequate muscle relaxation is essential.

Reduction may be performed under:

Procedural sedation, regional anesthesia in selected circumstances, or general anesthesia with muscle relaxation.

Reduction Technique

Most techniques use longitudinal or inline traction combined with controlled manipulation of the hip.

The specific maneuver depends on the direction of dislocation and surgeon preference.

Forceful repeated attempts should be avoided.

Contraindications to Forceful Closed Reduction

Reduction should be approached cautiously when there is concern for:

Associated femoral neck fracture, large displaced fracture fragment, or other injury in which manipulation could worsen the fracture.

Stability Assessment

After reduction, the hip should be gently assessed for stability through a safe range of motion.

Instability may suggest an associated acetabular wall fracture, capsular injury, or intra-articular fragment.

Post-Reduction Examination

The neurovascular examination must be repeated immediately after reduction.

Any new deficit should be documented and urgently evaluated.

Post-Reduction Radiographs

Plain radiographs should confirm:

Reduction of the femoral head, restoration of joint congruity, and absence of obvious new fracture displacement.

Post-Reduction CT

CT is then used to assess the congruity of the reduction and to identify occult fracture fragments or intra-articular debris.

Traction

Routine prolonged traction is not required for most simple, stable hip dislocations after successful concentric reduction.

Temporary traction may be considered in selected unstable injuries, painful fracture-dislocations, or situations awaiting definitive fixation.

Definitive Management

After the hip is reduced, management becomes focused on:

Associated fractures, joint stability, intra-articular fragments, cartilage injury, and the patient’s overall trauma condition.

Indications for Surgery

Operative treatment may be required for:

Irreducible dislocation, nonconcentric reduction, incarcerated intra-articular fragments, associated femoral-head fracture requiring fixation or excision, acetabular fracture requiring stabilization, femoral-neck fracture, or persistent post-reduction instability.

Open Reduction

If a satisfactory closed reduction cannot be achieved, open reduction is indicated.

The surgical approach depends on the direction of dislocation, associated fracture pattern, and surgeon preference.

Associated Acetabular Fracture

Acetabular fractures are treated according to displacement, stability, articular congruity, and fracture pattern.

Some require open reduction and internal fixation.

Associated Femoral-Head Fracture

Treatment depends on fragment size, location, displacement, and whether the fragment contributes to the weight-bearing surface.

Options may include:

Fixation, excision of a small nonessential fragment, or more extensive reconstruction.

Activity

Weight-bearing recommendations depend on whether the injury is a simple dislocation or a fracture-dislocation.

Simple Stable Dislocation

After a concentric stable reduction without significant fracture, early protected mobilization and range of motion are generally encouraged.

Weight bearing may be advanced according to the injury pattern and treating surgeon’s protocol.

Fracture-Dislocation

Associated femoral-head or acetabular fractures often require more prolonged protected or restricted weight bearing.

Physical Therapy

Physical therapy commonly includes:

Gait training, protected weight bearing when required, progressive hip range of motion, and later strengthening.

Early controlled motion helps reduce stiffness.

Medication

Analgesics are required during the acute phase.

Opioid medications may be necessary initially because traumatic hip dislocation is extremely painful.

Venous thromboembolism prophylaxis should be considered according to the patient’s overall trauma burden, mobility, and associated injuries.

Follow-Up

Prognosis of Simple Posterior Dislocation

Approximately 70–80% of uncomplicated posterior hip dislocations without associated fracture have historically achieved good or excellent long-term outcomes.

Fracture-Dislocation

Outcome is less favorable when posterior dislocation is associated with acetabular or femoral-head fracture because cartilage injury, instability, and post-traumatic arthritis are more common.

Anterior Dislocation

Anterior dislocations may be associated with substantial femoral-head impaction or cartilage injury.

Long-term outcome depends largely on the degree of articular damage and associated fracture.

Effect of Delayed Reduction

Prognosis worsens as the duration of dislocation increases.

Reduction delayed beyond several hours, particularly beyond approximately 6–12 hours, is associated with greater concern for femoral-head osteonecrosis.

Complications

Post-Traumatic Arthritis

Post-traumatic osteoarthritis is the most common major long-term complication.

Risk is highest in patients with:

Acetabular fractures, femoral-head fractures, chondral injury, nonconcentric reduction, or osteonecrosis.

Osteonecrosis

Avascular necrosis of the femoral head may occur because the injury disrupts its blood supply.

Reported rates vary widely, historically ranging from approximately 1–17% or more depending on injury severity and delay to reduction.

Timing of Reduction

The risk of osteonecrosis increases with prolonged dislocation.

Even prompt reduction cannot eliminate the risk completely because vascular damage may occur at the moment of injury.

Sciatic Nerve Injury

Sciatic nerve palsy occurs most often with posterior dislocation.

Reported rates are approximately 8–20%.

Peroneal Division

The common peroneal component of the sciatic nerve is affected more frequently than the tibial component.

Patients may develop weakness of ankle dorsiflexion and great-toe extension together with sensory loss over the dorsum of the foot.

Electrodiagnostic Testing

If neurologic deficits persist, electromyography and nerve-conduction studies may be obtained after several weeks, often around 3–4 weeks or later, to establish a baseline and aid prognosis.

Recovery

Neurologic recovery is variable.

Some patients recover completely, whereas others have persistent weakness or sensory loss.

Recurrent Dislocation

Recurrent traumatic hip dislocation is uncommon, historically occurring in fewer than approximately 2% of patients.

Heterotopic Ossification

Heterotopic ossification may develop after severe hip trauma or surgery, although it is less common after uncomplicated dislocation alone.

Chondral and Labral Injury

Damage to the acetabular labrum and articular cartilage may occur at the time of dislocation and can contribute to persistent pain and later arthritis even after successful reduction.

Patient Monitoring

Patients require long-term follow-up because osteonecrosis and post-traumatic arthritis may appear months or years after the original injury.

First Year

Clinical examination and serial radiographs may be obtained approximately every 3–4 months during the first year, depending on injury severity.

MRI for Osteonecrosis

MRI is more sensitive than radiographs for early detection of femoral-head osteonecrosis and may be used when symptoms, examination, or radiographs raise concern.

Long-Term Surveillance

Follow-up should assess:

Pain, gait, hip range of motion, neurologic function, femoral-head contour, joint congruity, osteonecrosis, and development of post-traumatic arthritis.