Hip Dislocation

Traumatic hip dislocation is displacement of the femoral head from the acetabulum and is usually a high energy injury.

Because the native hip is intrinsically very stable, dislocation implies substantial soft tissue disruption and frequently associated fracture.

This is an orthopaedic emergency.

The femoral head should be reduced as rapidly as possible, ideally within approximately 6 hours, because delayed reduction increases the risk of osteonecrosis and post traumatic arthritis.

Direction classification

Posterior dislocation

Approximately 85% to 90% of traumatic dislocations.

Mechanism:

Axial force through a flexed, adducted hip, classically a dashboard injury.

Position:

• Hip flexed
• Adducted
• Internally rotated

Sciatic nerve is at risk.

Anterior dislocation

Less common.

Occurs with forced abduction and external rotation.

Can be:

• Superior, pubic type
• Inferior, obturator type

The limb is generally abducted and externally rotated.

Simple versus complex

Simple

Dislocation without associated fracture.

Complex

Dislocation with:

• Acetabular fracture
• Femoral head fracture
• Femoral neck fracture

Thompson Epstein classification of posterior fracture dislocation

Type I

Simple posterior dislocation with no fracture or only a minor posterior wall fragment.

Type II

Dislocation with a single large posterior acetabular wall fragment.

Type III

Dislocation with a comminuted posterior wall fracture.

Type IV

Dislocation with acetabular floor fracture.

Type V

Dislocation with femoral head fracture.

Pipkin classification

Used for femoral head fracture associated with hip dislocation.

Pipkin I

Femoral head fracture inferior to the fovea capitis.

The fragment is outside the main superior weight bearing surface.

Pipkin II

Femoral head fracture superior to the fovea.

Involves weight bearing articular surface.

Pipkin III

Type I or II femoral head fracture plus femoral neck fracture.

Carries very high risk of osteonecrosis.

Pipkin IV

Type I or II femoral head fracture plus acetabular fracture, usually posterior wall.

Posterior dislocation typically produces a shortened, flexed, adducted and internally rotated limb.

Anterior dislocation usually produces abduction and external rotation.

Do not assume an abnormal limb position is simply a dislocation. Associated femoral neck or acetabular fracture may alter the posture.

Document sciatic nerve function before reduction.

Particularly assess the peroneal division:

• Ankle dorsiflexion
• Great toe extension
• Dorsal foot sensation

Also assess distal pulses.

The sciatic nerve is injured in a significant minority of posterior fracture dislocations.

Obtain an AP pelvis rapidly if this does not meaningfully delay reduction.

A clearly dislocated hip in a stable trauma patient should be reduced urgently.

If femoral neck fracture is suspected, excessive closed manipulation can worsen the injury and operative reduction may be necessary.

Post reduction CT should be performed after traumatic hip dislocation to identify:

• Femoral head fracture
• Acetabular fracture
• Intra articular loose bodies
• Incongruent reduction.

Immediate reduction

Provide procedural sedation or general anaesthesia with adequate muscle relaxation.

Perform controlled closed reduction.

Common posterior reduction techniques include:

• Allis
• Stimson
• Captain Morgan

The specific manoeuvre is less important than controlled axial traction with avoidance of excessive force.

After reduction:

• Repeat sciatic nerve examination
• Repeat vascular examination
• Confirm concentric reduction radiographically
• Obtain CT

Open reduction indications

Proceed to open reduction when:

• Closed reduction fails
• Dislocation is irreducible
• Femoral head or acetabular fragment blocks reduction
• Reduction remains nonconcentric
• Associated femoral neck fracture makes closed manipulation unsafe

Simple dislocation

After concentric reduction without fracture:

• Begin early controlled hip motion
• Protected weight bearing initially
• Avoid extreme flexion and adduction after posterior injury during early healing

Prolonged traction is not routinely required.

Pipkin I

A small non weight bearing femoral head fragment can sometimes be excised when it remains displaced or loose.

Larger reconstructable fragments should be fixed.

Pipkin II

Because the fracture involves the weight bearing femoral head, aim for anatomical reduction and internal fixation.

Pipkin III

Young patients require urgent anatomical femoral neck and head reconstruction when feasible.

In older patients, arthroplasty may provide more reliable treatment because the combined neck and head injury has a very high osteonecrosis and fixation failure risk.

Pipkin IV

Treat both:

• Femoral head injury
• Acetabular fracture

Posterior wall stability frequently determines whether acetabular fixation is required.

Osteonecrosis

Reduction timing is critical but does not eliminate the risk entirely.

Follow patients clinically and radiographically.

Persistent or progressive hip pain months after injury should trigger investigation for:

• Osteonecrosis
• Post traumatic arthritis
• Loose body
• Heterotopic ossification

Major complications include:

• Osteonecrosis
• Sciatic nerve palsy
• Post traumatic osteoarthritis
• Heterotopic ossification
• Recurrent instability, uncommon after simple traumatic dislocation
• Femoral head chondral injury