Knee Dislocation

Developmental dysplasia of the hip describes a spectrum of abnormal development of the acetabulum and femoral head relationship.

The spectrum includes:

• Mild acetabular dysplasia with a centred femoral head
• Hip instability
• Subluxation
• Complete dislocation

The term developmental is preferred because the hip may be abnormal at birth or progressively become dysplastic during infancy.

Normal acetabular development depends on a concentrically reduced femoral head stimulating acetabular growth.

The earlier stable reduction is achieved, the greater the potential for normal acetabular remodelling.

Major risk factors include:

• Female sex
• Breech presentation
• Positive family history
• First pregnancy
• Oligohydramnios
• Tight lower limb swaddling
• Associated congenital torticollis
• Metatarsus adductus

Left hip involvement is particularly common.

Clinical spectrum

Dysplastic hip

Femoral head remains centred but acetabulum is shallow.

Subluxatable hip

Femoral head can partially translate from the acetabulum.

Dislocatable hip

A reduced hip can be completely displaced.

Dislocated but reducible hip

Femoral head is out of the socket but can be reduced.

Fixed dislocation

Hip cannot be reduced by simple examination manoeuvres.

Graf ultrasound classification

Graf classification is based mainly on:

• Alpha angle measuring bony acetabular roof
• Beta angle reflecting cartilaginous roof and labrum

Type I

Mature normal hip.

• Alpha angle at least 60°

Type IIa

Physiological immaturity in an infant below approximately 3 months.

• Alpha 50° to 59°

It may mature spontaneously but requires appropriate surveillance.

Type IIb

Persistent dysplasia after approximately 3 months.

• Alpha 50° to 59°

Type IIc

Critical dysplasia.

• Alpha approximately 43° to 49°

Femoral head remains centred but coverage is poor.

Type D

Decentred unstable hip.

The bony roof is severely deficient and the femoral head is beginning to displace.

Type III

Dislocated hip with substantial acetabular deficiency.

• Alpha below approximately 43°

Type IV

Severe dislocation with major displacement of the femoral head and distorted cartilaginous roof.

Graf type III and IV hips require active reduction rather than observation.

Tönnis radiographic classification

Used when the femoral head ossific nucleus is visible.

Grade I

Ossification centre is medial to Perkins line.

Grade II

Ossification centre is lateral to Perkins line but below the superior acetabular margin.

Grade III

Ossification centre is approximately level with the superior acetabular margin.

Grade IV

Ossification centre lies above the superior acetabular margin.

International Hip Dysplasia Institute classification

Useful because it does not require a visible femoral head ossific nucleus.

It uses:

• Hilgenreiner line
• Perkins line
• 45° diagonal line
• H point at the midpoint of the proximal femoral metaphysis

Grade I

H point is at or medial to Perkins line.

Grade II

H point is lateral to Perkins line but at or medial to the diagonal line.

Grade III

H point lies lateral to the diagonal line and at or below Hilgenreiner line.

Grade IV

H point lies above Hilgenreiner line.

Increasing grade indicates increasing displacement.

Newborn

Perform both:

Barlow manoeuvre

Tests whether a reduced hip can be dislocated.

With the hip flexed, gentle posteriorly directed pressure is applied while adducting.

A positive test indicates a dislocatable unstable hip.

Ortolani manoeuvre

Tests whether a dislocated hip can be reduced.

With the hip flexed, gentle abduction with anterior pressure over the greater trochanter reduces the femoral head.

A true positive Ortolani produces a palpable clunk, not merely a soft click.

Older infant

As soft tissue contracture develops, instability manoeuvres become less reliable.

Look for:

• Limited hip abduction
• Asymmetric thigh or gluteal folds
• Apparent limb shortening

Galeazzi sign

With hips and knees flexed, the knee on the affected side appears lower because of proximal femoral displacement.

Walking child

Unilateral dislocation can produce:

• Limp
• Apparent leg shortening
• Positive Trendelenburg sign
• Increased lumbar lordosis

Bilateral dislocation can produce:

• Waddling gait
• Hyperlordosis
• Less obvious limb length asymmetry

Pain is usually absent in young children.

Untreated dysplasia later produces early hip osteoarthritis.

Ultrasound

Use ultrasound in young infants before reliable ossification of the femoral head.

It provides:

• Dynamic stability assessment
• Femoral head coverage
• Graf classification

Ultrasound is particularly important in high risk infants and abnormal examination.

Radiographs

After approximately 4 to 6 months, AP pelvis radiography becomes increasingly useful.

Assess:

Hilgenreiner line

Horizontal through both triradiate cartilages.

Perkins line

Vertical from lateral acetabular edge.

Acetabular index

Angle between Hilgenreiner line and acetabular roof.

Normally decreases with growth.

Shenton line

Smooth curved line along inferior femoral neck and superior obturator foramen.

Disruption suggests subluxation or dislocation.

The treatment principle is:

Achieve a concentric stable reduction early, then maintain it while avoiding femoral head osteonecrosis.

Birth to approximately 6 months

The main treatment for a reducible dislocated or unstable hip is a Pavlik harness.

The harness maintains:

• Hip flexion approximately 90° to 100°
• Controlled spontaneous abduction

Avoid forced extreme abduction.

The child should retain active movement.

Ultrasound is used to confirm reduction.

Follow up should occur early, commonly around:

• 3 to 4 weeks
• 6 to 8 weeks

If the hip remains dislocated after several weeks of correct harness treatment, stop persisting with an ineffective harness because prolonged treatment of an unreduced hip increases femoral head and acetabular injury.

Pavlik complications

Femoral nerve palsy

Usually caused by excessive hip flexion.

Reduce flexion or stop treatment temporarily.

Osteonecrosis

Risk increases with forced excessive abduction.

Inferior dislocation

Can occur with excessive flexion and inadequate abduction.

The harness must be monitored rather than simply applied and left unchecked.

Approximately 6 to 18 months

If harness treatment fails or the child presents after harness age:

Closed reduction under general anaesthesia plus hip spica cast is usually the next treatment.

Perform an arthrogram to confirm:

• Concentric reduction
• Labral relationship
• Stable zone of reduction

An adductor tenotomy may be required when tight adductors prevent safe reduction.

Do not force the hip into extreme abduction.

A stable reduction should remain within a safe zone without excessive pressure on the femoral head.

Spica immobilisation is commonly maintained for approximately 12 weeks, often with cast change according to protocol.

Failed closed reduction

Proceed to open reduction when:

• Concentric reduction cannot be achieved
• Hip immediately redislocates
• Soft tissue obstacles prevent reduction

Important obstacles include:

• Tight iliopsoas tendon
• Tight adductors
• Hypertrophied ligamentum teres
• Pulvinar tissue
• Transverse acetabular ligament
• Inverted labrum

Open reduction

Approaches include:

Medial approach

Advantages:

• Direct approach
• Limited dissection

Useful particularly in younger infants.

Disadvantages:

• Limited exposure
• Difficult capsulorrhaphy
• Risk to medial circumflex femoral vessels

Anterior approach

Provides broad exposure and permits:

• Removal of obstacles
• Iliopsoas release
• Capsulorrhaphy
• Simultaneous pelvic reconstruction when required

Child older than approximately 18 months

Late presentation increasingly requires open reduction with correction of bony deformity because acetabular remodelling potential decreases with age.

Options include:

• Femoral shortening
• Femoral derotation
• Varus osteotomy
• Pelvic osteotomy

Femoral shortening

When the femoral head cannot be reduced without substantial force, femoral shortening reduces tension across:

• Femoral head blood supply
• Capsule
• Soft tissues

This is preferable to forcing the hip into the acetabulum.

Pelvic osteotomy

Indicated when acetabular dysplasia will not remodel sufficiently.

Options include:

Salter innominate osteotomy

Redirects the acetabulum as one unit.

Useful in younger children with a flexible triradiate cartilage.

Pemberton osteotomy

Incomplete pericapsular osteotomy that reshapes the acetabulum and increases anterolateral coverage.

Dega osteotomy

Reshaping acetabuloplasty providing customised coverage.

In older adolescents with symptomatic residual dysplasia and closed triradiate cartilage, a periacetabular osteotomy can reorient the native acetabulum while preserving the hip joint.

Residual dysplasia

A successfully reduced hip still requires long term radiographic surveillance.

Residual acetabular dysplasia may persist despite early successful treatment.

Follow through skeletal development when clinically indicated rather than assuming that reduction alone guarantees normal acetabular maturation.

Osteonecrosis

This is the most feared treatment related complication.

Risk increases with:

• Excessive abduction
• Forceful reduction
• High dislocation
• Repeated failed reductions
• Surgical vascular injury

Late consequences include:

• Coxa vara
• Coxa breva
• Trochanteric overgrowth
• Femoral head deformity
• Early osteoarthritis

Other complications include:

• Redislocation
• Residual acetabular dysplasia
• Limb length discrepancy
• Stiffness
• Early secondary osteoarthritis