Aetiology & Classification

Definition

 

Idiopathic condition of the immature femoral capital epiphysis involving varying degrees of osteonecrosis

 

AKA

- Legg-Calve-Perthes disease

- coxa plana

 

Described in separate publications in 1912 by

- Legg (Boston)

- Calve (France)

- Perthes (Germany)

 

Epidemiology

 

M: F    4:1

 

1 in 740 males

 

Onset usually at age 4-8

- early as 2 to late as 12

 

Children small and thin & hyperactive with delayed bone age

 

Bilateral - between 8 - 24%

- will not be symmetric

- if symmetric think other causes

 

Risk Factors

 

Sex : M: F 4:1

Geographic Location - 1/1200 US; 1/12 000 UK ; More common in urban areas

Social Class - Higher incidence in lower socio-economic classes

Race - Caucasian > Asian > African (extremely rare)

Perinatal Factors - Maternal Smoking ; Breech ; Prematurity/ Low Birth Weight ; Older Parental Age

 

Aetiology

 

Uncertain

 

Multiple ischemic events causing AVN

- ? lateral epiphyseal blood vessel occlusion

- sole blood supply 4-8 years

 

Theories

 

1.  Microtrauma to retinacular vessels

 

2.  Increased synovial pressure 

- e.g. transient synovitis

 

3.  Venous HTN 2o to thrombotic occlusion

- hyperthrombotic state

- hypofibrinolysis 

 

Glueck 1996 JBJS

- 75% coagulation abnormality  

- decreased Protein C ± S / increased lipoprotein A

- this has never been a found association in any study since

 

Blood supply immature femoral head

 

Medial and lateral circumflex femoral 

- cruciate and trochanteric anastomoses

- extracapsular ring at base of neck

- retinacular vessels run in capsule

- intracapsular ring at base of head

- lateral epiphyseal artery most important

 

Ligamentum teres

- artery viable up to age 2

 

Associations

 

Short stature & delayed maturation 

 

Attention Deficit Hyperactivity Disorder / ADHD

 

Trauma

- parents often relate onset of symptoms to traumatic event 

- this association not clearly established

 

Irritable hip ~ 1%

 

Pathology

 

Head

 

Various areas of necrosis / revascularisation

- reossification from periphery

- typically anterior & lateral

 

Ossified epiphysis small

- stops growing

- cartilage keep growing with blood from synovium

- increased head to teardrop appearance but head does not subluxe

 

Head deformity secondary to collapse

- biological plasticity during creeping substitution

- head subjected to uneven & excess forces

- flattening or saddle deformity 

- anterolateral extrusion of cartilage

 

Coxa Magna 

- flattening of head with lateral extrusion of physis + periosteal new bone

 

Physis

 

Avascular

- growth arrest

- disordered cartilage columns in physis

 

Coxa Breva

- physeal arrest with short neck & long GT 

- LLD & Trendelenberg gait

 

Classification

 

Chronological

- Waldenstrom

 

Extent of femoral head involvement 

- Catteral

- Salter-Thompson

- Herring

 

End-result

- Mose 

- Stuhlberg

 

Waldenstrom Stages

 

History : Swedish Surgeon ; Described disease 1910 prior to being named by Legg-Calve-Perthe in 1912

 

1. Initial

 

Duration : 3- 6 months

 

Xray

- may be normal

- small, sclerotic epiphysis

- joint space widening

- increased density of ossific nucleus & cessation of growth

 

2. Resorption / fragmentation

 

Duration : 6/12

 

Pathologic Process

- necrotic bone irregularly resorbed / creeping substitution

- replaced with vascular fibrous tissue

- may be associated with collapse

 

XRay - Fragmentation of Physis

 

3.  Reossification

 

Duration : 1.5 - 3 years

 

Pathologic Process

- starts at margins & progresses centrally

- eventually new areas coalesce & epiphysis regains normal strength & density

 

XRay

- Better defined shape

- Return of bone density

 

4. Remodelling

 

Duration : Occurs until skeletal maturity

 

Xray - May have flattening of the head and neck

 

Herring Lateral Pillar

 

AP xray when disease in fragmentation / divide femoral head into 3 pillars

- lateral (25%)

- medial (25%)

- central (50%)

 

Group A

- no lateral pillar collapse or radiolucency

- all become Stuhlberg 1 & 2

 

Group B

- > 50% of lateral pillar height maintained

- outcome depends on age

- < age 9 almost all become Stuhlberg I and II

- > age 9 30% become Stuhlberg II / 70% become Stuhlberg III or IV

 

Group C

- pillar < 50% normal height

- majority do poorly

 

Catterall

 

Technique

- uses AP & lateral xray

- 4 groups

- significant inter & intra-observer error

 

Group I

- < 25% involved

- anterocentral head

 

Group II

- 25-50% head

- anterolateral region / lateral column intact

 

Group III

- 50-75% head involvement

- moderate collapse 

 

Group IV

- 100% of head sequestered

- severe collapse

 

Salter-Thompson

 

Group A

- Catterall 1 and 2

- < 1/2 of head involved

- viable lateral pillar 

- good prognosis

 

Group B

- Catterall 3 and 4

- > 1/2 head involved, loss of lateral pillar

- poorer prognosis

 

Mose

 

Quantifies degree of sphericity

- graded according to variance from perfect circle in either AP or lat

- many authors do not agree that Mose sphericity is accurate predictor of long term outcome

- good or fair Mose rating = good result

- poor Mose rating not necessarily = poor result

 

Good - no deviation on the 2 views 

Fair - up to 2 mm variance 

Poor - 3 mm or more variance 

 

Stuhlberg

 

Based on congruency & sphericity

 

Class 1 

- normal 

- 0 % OA

 

Class II:  Spherical & Congruent

- femoral head spherical (mose circles overlaid on AP / lateral of femoral head show <2mm variation)

- At least 2 other abnormal features including Coxa Magna , Coxa Breva or Abnormally Steep Acetabulum

- 15% OA

 

Class III:  Aspherical Congruity

- head ovoid (mushroom or umbrella shaped) and aspherical i.e Mose circles show > 2mm variation  

- 60% OA in middle age

 

Class IV: Aspherical Congruous Incongruity

- head flat, steep acetabulum

- 75% OA usually in middle age

 

Perthes Stuhlberg Class IVPerthes Stuhlberg Class IV lateral

 

Class V:  Aspherical Incongruous Incongruity

- head flat, normal acetabulum

- 80% OA at young age before 50

 

Natural History

 

Osteoarthritis 10x more prevalent than general population

 

Only 40% have normal radiographs

 

20-40 years after onset of symptoms

- 80% active & pain-free

- only 10% have THR

 

At 50 years after onset of symptoms

- 50% have disabling pain

- 40% have THR

 

Weinstein

- probably best you can say is function deteriorates with time

- 50% THR at 50 years

 

Prognostic Factors

 

1. Age of onset

- most important

- < 6 good Stulberg I-II

- 6-9 variable Stulberg I-IV

- > 9  Stulberg III & IV

- related to amount skeletal growth & thus remodeling available

 

2. Sex

- F worse than M

- ? early maturation, less time to remodel

 

3. Extent head involvement

- quantified by Caterall / Salter-Thompson / Herring classification

 

4. Containment of head

- extrusion and asymmetric growth leads to worse prognosis

 

5. ROM

- hip irritability causes adductor tightness

- loss of abduction ROM prevents remodeling head by acetabulum

 

7. Lateral Pillar Collapse

 

Catterall "Head at Risk" Signs

 

Only lateral subluxation shown to be prognostic 

 

5 Xray

 

1. Lateral subluxation head

2. Lateral epiphyseal calcification

3. Gage Sign - V shaped defect in lateral physis

4. Horizontal physis angle

5. Metaphyseal cysts

 

4 Clinical

 

1. Progressive loss ROM

2. Adduction contracture

3. Flexion with abduction

4. Obesity

 

Gage's sign

- lateral bulge of metaphysis

- extruded cartilage may calcify lateral to acetabulum 

- gives appearance of head extrusion

- coxa breva

 

Symptoms

 

Most present early 

- 75% during necrotic / fragmentation stages

- insidious painless limp commonest

- ache groin / anterior thigh or knee

- exacerbated by activity

 

Examination

 

Short stature 

- usually short with delayed bone age

 

Antalgic / Trendelenberg gait

 

Decreased ROM

 

Early

- synovitis with tight adductor and/or psoas

- loss abduction in extension and flexion

- loss IR / flex into ER

 

Late

- bony impingement

- "hinge subluxation" 

- lateral extrusion, flattening & enlargement of head prevent normal motion

 

LLD usually small

- apparent LLD from adduction contracture

 

Occasionally thigh / gluteal wasting in advanced cases

 

Xray

 

Grade stage of Perthes

Lateral Pillar classification

 

US

 

Nonspecific findings of synovitis usually found

- thickening synovial membrane vs. synovitis

- synovial effusion

 

CT

 

Perthes CT

 

MRI

 

Advantage

- can assess amount of cartilaginous head outside of acetabulum

- very good way of assessing containment of cartilage head

 

DDx

 

AVN

MED / SED

Hypothyroidism

 

MED

- bilateral and symmetrical

- acetabular involvement

- no metaphyseal cysts

- other physeal involvement therefore consider skeletal survey in those with bilateral "perthes"

 

MED

 

Complications of Perthes

 

1. LLD 25% 

 

Causes

- subchondral fracture & collapse 

- arrest proximal femoral epiphysis

- adductor contracture

- varising osteotomy

 

2. Trendelenburg gait

 

Proximal greater trochanter

- collapse of epiphysis / coxa breva

- varus osteotomy

 

Management

- growth arrest of greater trochanter at 10 years or distal transfer

- femoral neck lengthening osteotomy

 

3. Hinge abduction

 

Extrusion of epiphysis laterally

 

Management

- treat with cheilectomy once physis closed

- has poor reputation 

- may worsen arthrosis by exposing fresh bone

- if done prior to physeal closure may cause SUFE or growth arrest

 

4. Labral tears 

 

Rare

- abnormal stress by head on lateral acetabulum

 

5. Secondary OA