Definition: Self limited idiopathic affection of the femoral head characterised by avascular necrosis of the whole or a part of the head, produced by interrupted blood supply followed by sub-chondral fracture, re-vascularisation and repair of dead bone.

A part of group of disorder known as osteochondroses characterised by avascular necrosis of primary and secondary centres.

Commonly involved primary centre –

Tarsal navicular bone (Kohler’s),

Lunale (Keinbocks)

Vertebral body (Calve’s).

Commonly involved secondary centre -

Apophysis and epiphysis of capitellum (Panner’s),

Metatorsal head (Freibergs) and capital femoral

Epiphysis of femoral head (Perthe’s).

Scaphoid (Preisier’s)

Incidence: M:F::5:1

Onset 2 – 12 yrs. usually 4 - 8 yr with mean at 7yr of age. 10 -20% are bilateral & familial in 10%.

Predisposed child - delayed bone age, low birth weight & low socio-economic status.

Pathogenesis:

Blood supply to the head is through three main vessels

1. Metaphyseal vessels

2. Lateral epiphyseal vessel

3. Small supply from ligamentum teres.

The metaphyseal supply gradually decreases by the age of four years and vessels in the ligamentum teres are not well developed till seven yrs of age. Thus betweeen 4 - 8 yrs, the epiphysis is solely dependent on ascending retinacular artery for the supply which are suspectable to the external pressure form the effusion probability related to retinacular vessel occlusion, raised intra-capsular pressure, intra-epiphyseal thrombosis, vascular irregularities or increased vascular Idiopathic capital femoral ischemia (Initial information)

Temporary cessation of growth of epiphysis

Epiphyseal revascularisation from the periphery.

Resortption of avascular bone and production of woven bone

Potential form of Perthe’s disease

Revascularisation leads ot increased resorption compared to the worven bone depostion and if the critical point of stress is reached, results in path. fracture

Re-resorption of underlying bone and replacement by biologically plastic (woven) bone

— Bio-plasticity and re-modelling

— Subluxation

— Deformation

Pathological Stages :-

A. Ischemia / Necrosis - All or a part of the head dies at which time the x-rays remain normal. The head stops enlarging but the cartilage still nourished by diffusion from synovial fluid continues to grow with increased apparent joint space and apparent mild subluxation known as the Waldenstorm’s sign.

cessation of the growth of head lasts 6-12mths.

B. Fragmentation / Resorption :

• The trabeculae in the dead bone giving rise to increased density on x-ray.

• Hyperemia and re-vascularisation causes bone resorption and the head becomes rarefied / cystic.

• Lysis of the bone occuring at the supero-lateral portion of the head forms a lytic ‘V’ or Gage sign.

C. Reossification / Resolution.

• The stage of resorption and reossification run hand in hand with new bone being laid down on the dead trabeculae.

D. Remodelling :

• If repair / revascularisation is rapid, the head may maintan its shape – the biological plasticity.

• The head may collapse further – resulting in flattening / fragmentation.

• Abnormal stresses transmitted to the growth plate may cause distortion to growth arrest.

• Coxa magna secondary to premature physeal arrest and hypertrophy of the epiphyseal cartilage.

• Lateral portion of the head becomes uncovered.

• If alternation of shape persists – early degenerative changes.

Clinical Features :

1. Limp

2. Pain – dull aching, sometimes refered to knee and may even be absent.

3. Limitation of abduction and internal rotaion; Catterral sign of obligatory external

rotation may be present i.e on flexion of hip the limb goes into external rotation.

4. Trendlenburg’s test is positive.

5. Muscle wasting is present.

Investigations

1. Radiographs : The x rays will show typical changes in the head depending on the stage & things that help in determining the prognosis are :

a) Salter extrusion angle : it less than 50° suggest poor prognosis.

b) Salter extrusion index >20% suggest poor prognosis.

2. MRI : Helps in early diagnosis

• Since complete head cannot be seen on the x rays, it helps in identifying area of epiphyseal infractions and the contours of the femoral head, both of which are prognostically important.

3. Arthrogram : It is a dynamic investigation. So determines the best portion to splint the position of containment and appropriate planning of the osteotomy.

Catterral’s ‘head at risk signs’ : Suggestive of a poor prognosis are :

I) Radiological

1. Lateral subluxation of the head (head partially uncovered)

2. Involvement of the whole head.

3. Metaphyseal cysts.

4. Calcification lateral to the epiphysis.

5. Horizontal physis.

6. Gage sign – ‘V’ shaped metaphyseal indentation laterally.

II) Clinical

Obligatory external rotation on flexion – Catterral’s sign
Poor range of movements
Flexion deformity
Internal rotation deformity

Overall indicators for poor prognosis

1. Female sex

2. Bone age more than 10yr

3. Uncovering of the femoral head.

4. More than 50% head involved

5. Loss of the hip range of movement

6. Premature physeal closure.

Anatomic and prognostic classification – depending on the state and involvement of

— Epiphysis

— The epiphyseal plate

— Metaphyseal changes

—

A. Catterral’s Classification

Has large inter and intra observer variation

Stage I

• Antero-medial portion of the head and no collapse.

• Epiphyseal plate not involved.

• No metaphyseal change

• Heals without significant sequelae.

Stage II: Lateral pillar intact

• More head involved and fragmentation of the involved segment.

• The involved segment show increased density, but the uninvolved pillar of the normal

bone prevent its significant collapse.

• The metaphyseal reaction is localised.

• Regeneration occurs without much loss of the height and the result is usually good.

Stage III: Involvement of the lateral margin

• More of the head involvement, collapse occures as the un-involved pillars are not large

enough to prevent collapse.

• May show head-with-in head appearance (Crescent sign).

• Metapghyseal involvement is usually widespread

• Result is poorer.

Stage IV: Whole head involvement

• Severe collapse

• Extensive metaphyseal changes

• Epihyseal plate often involved – abnormal growth occurs - coxa magna, coxa vara

or coxa valga may occur.

B. Salter Thompson Classification

Stage A = Lateral portiono of the capital epiphysis is present i.e catterral’s 1 & 2 or roughly speaking less than 50% head involved.

Stage B = Lateral portion of capitla epiphysis is absent i.e catterral’s 3 & 4 or more than 50% involvement of the head.

C. Herring’s Classification

A.- No collapse of lateral pillar

B.- Lateral pillar margin - more than 50% of original height is maintained

C.- Laterall pillar - collapse of more than 50%.

Deformities at Maturity:

1. Coxa Magna

2. Hanging rope sign. - indicative of severe epiphyseal disturbance, seen on x-ray as line present in neck droping down distally.

3. Coxa Brevis: Short neck with overgrowth of the trochanter as a result of premature

physeal arrest.

4. Coxa irregularis : collapse and lateral extrusion of the femoral head, forming a groove

under the lateral edge of the acetabulum.

5. Osteochondritis dessicans.

D. Stulberg’s classification of healed Perthe’s

1. Spherical congriuty (< 2mm head deformation measured by moss’ circles)

2. Aspherical congruity

3. Aspherical in-congruity.

Management

Aims:

1. Elimination of hip irritability

2. Restoration and maintance of the range of movement

3. Prevent epiphyseal extrusion and subluxation.

4. Attainment of spherical head on healing.

Concept of containement: It is believed that during avascular phase the head is soft, so by re-distributing the compressive forces healing and re-modelling can be facilitated. (The concept of biological plasticity).

This can be done by

1) Making the child non weight bearing for 18 - 24 months till head ossifies but this is not a practical measure

2) Containment procedures.

• Surgical

• Non-surgical.

Current concept of management

1) Observation

2) Intermittent symptomatic treatment.

3) Early definitive treatment.

4) Surgical treatment of the exisiting deformity.

A. Observation

1) Appropriate for all children under 6 yr of age, regardless of any stage except when

there is/are head at risk sign(s).

2) More than 6 years, catterral’s grade 1 & 2 without any head at risk sign. However in Indian patients, it is believed that any child above 7 yrs specially females with any stage more than catterral’s grade I, even without head at risk sign should be offered containment surgery.

B. Intermittent symptomatic treatment

Periodic treatment with complete bed rest and abduction stretching exercises in these cases associated with hyper-irritability and a temporary decrease in ROM commonly in phase of subchordral fracture

Definitive surgical management in early stages

Containement procedures - Indications

1. Age > 6 years.

2. Class III and IV catterral’s or Grade II Salter-Thompson’s

3. Head at risk signs.

Prerequisite -- Full range of motion with no residual irritability.

Non surgical methods - Abducation casts eg: Petrie’s brace, Toronto brace, Synder sling, Tachdjian’s brace, Atlanta scottish rite brace, Newington abduction brace.

Surgical method - Advantages

1) Period of restriction less than 2 month

2) Permanent containment

3) Better containment & hence better femoral remodelling.

Procedures - MRI preferably done before surgery

a) Varus derotation osteotomy (VDRO)

Disadvantage

i) Shortening

ii) Coxa vara (prevented by adding the procedure of trochanteric arrest)

iii) Trendlenburg’s gait.

Advantage - can be used when significant femoral antetorsion is present.

b) Innominate osteotomy

Advantage

(1) Better anterior & lateral coverage

(2) No shortening

(3) No coxa breva.

Late surgical procedures:

1) Hinge abduction - with normal abduction rotation of the femoral head occurs about a

locus in the centre of the femoral head. With the hinge abduction, the centre of rotation is shifted to the lateral edge of acetabulum, while the infero-medial corner continues to move laterally, the superior portion of the head is prevented from moving medially.

2) Malformed head -cheilectomy

3) Coxa Magna - shelf osteotomy

4) large malformed head subluxation – Chiari’s ostertomy

5) Capital femoral physeal arrest – Trendlendburg’s gait - Trochanteric advancement procedure of Wagner may be required.