Legg-Calve-Perthes Disease

Introduction

Osteonecrosis of the proximal femoral epiphysis in a growing child
Reported by Legg (USA, 1909), Calve (France, 1910) and Perthes (Germany, 1910)
Waldenstrom (1906) reported the features, but related them to TB
Phemister (1920) described pathology of necrotic bone

Epidemiology

Male : Female 4:1
Onset usually 2 – 12
- The majority are 5 – 8
- Mean 7 years
10 – 15% are bilateral

Anatomy

The ossific nucleus is covered by 3 layers of cartilage (in addition to the articular cartilage):

Superficial zone (lies just deep to the layer of articular cartilage)
Middle zone (zone of epiphyseal cartilage)
Deep zone

**The superficial and middle zones receive nutrition from the synovial fluid.

Etiology

Exact cause of Perthes disease is unknown
There is a 2-20% incidence of family history
some studies have shown it to be associated with:
- low birth weight
- lower socioeconomic groups
- urban communities
- children with ADHD
- delayed skeletal age/shorter stature
- Abnormal somatomedin levels (raised somatomedin A)
- incomplete anastomotic network at the proximal femur
- Abnormal Type II collagen has been demonstrated in familial, bilateral cases
- Thrombophilia – controversial
  - Potential abnormalities include:
    - Protein C and S deficiency
    - Factor V Leiden
    - Anticardiolipin antibodies
    - Antithrombin III deficiency

Vascular Embarrassment as a Possible Cause:

Alteration in blood supply to femoral head with fetal supply from metaphyseal vessels, lateral epiphyseal vessels running in the retinaculum up the neck and small supply from the ligamentum teres
Metaphyseal supply gradually decreases (by the age of 4)
Vessels in the ligamentum teres are not developed until about the age of 7
Between the age of 4 and 7, blood supply to the head may depend solely on lateral epiphyseal vessels, which are susceptible to external pressure
External pressure may occur from an effusion related to retinacular vessel occlusion, increased intra-capsular pressure, intra-epiphyseal thrombosis, vascular irregularities or increased vascularity
Kemp et al (1971) showed an effusion in the hip can decrease blood supply and cause ischaemia of the femoral head
Effusion may be enough to tip the balance in susceptible individuals
Repeated episodes are necessary to result in AVN of the bone and increased severity of disease may reflect increased number of ischemic events

Pathology

Pathological stages take 2 – 4 years to complete
Salter and Thompson description of events :
- Osteonecrosis of femoral head
- Temporary cessation of growth of epiphysis
- Revascularisation from periphery
- Resorption of avascular bone and production of woven bone
- Pathological fracture
- Resorption of underlying bone and replacement by biologically plastic (woven) bone
- Subluxation
- Deformity

Stages of Perthes Disease

Stage I: Initial (increased radiodensity)
- All or part of the bony femoral undergoes osteonecrosis
- X-Ray are normal
- The head stops enlarging, but the cartilage still nourished by diffusion continues to grow, showing increased apparent joint space
- Cessation of growth lasts 6 – 12 months
Stage II: Fragmentation
- Lasts ~ 1 year
- Crescent sign is seen early in fragmentation stage
  - Trabeculae in dead bone may fracture in subchondral region making tangential line
  - New bone laid down on dead trabeculae results in increased density on xray
- Hyperaemia and re-vascularization lead to bone resorption and head becomes rarefied / cystic
- Resorption usually complete by 12 – 17 months
Stage III: Reossification
- Lasts 3-5 years
- If repair / re-vascularization has been rapid, the head may maintain its shape
- The head may collapse with further flattening / fragmentation
- Abnormal stresses transmitted to the growth plate may cause distortion or growth arrest
- Lateral portion of head often becomes uncovered
- Normal bony architecture will return, but alteration in shape persists, leading to early degenerative changes
- Resolution usually takes 6 – 24 months, either heal or residual deformity
- As the physis is nourished by the epiphysis, AVN of the epiphysis also causes AVN of the physis to some extent and hence, growth arrest or retardation
- There is a direct correlation between severity of physeal involvement and deformity of the head
- Coxa magna secondary to premature physeal arrest and hypertrophy of epiphyseal cartilage
- The clinical picture varies depending on the age of the child, the stage of the disease and the amount of head involved
Stage IV: Healed
- residual deformity may be present

Clinically

5 – 8 years of age
Many patients appear younger than their actual age
Insidious onset limp, often painless and intermittent
Pain usually in the groin or inner thigh, but may radiate to knee
Limitation of abduction, internal rotation
Thigh, calf, buttock atrophy secondary to disuse
- Possibly a positive Trendelenberg sign
Limb length discrepancy of 1 to 2.5cm

Investigations

Laboratory:

In light of evidence that coagulopathies may play a role in pathophysiology, some reccommend screening for:
- Protein C and S deficiency
- Factor V Leiden
- Anticardiolipin antibodies
- Antithrombin III deficiency

Imaging:

X-Rays : AP and lateral (Lauenstein)
- At-risk signs:
  - Gage sign: radiolucency in the lateral epiphysis and metaphysis and mineralization lateral to the epiphysis
    - poor prognositic indicator; sign of early ossification in enlarged epiphysis
  - Radiolucent lesions in the epiphysis
    - sign of potential disturbance of the physis
    - Subluxation
    - horizontal physis
  - Whole head involvement
- Residual deformities:
  - Relative overgrowth of greater trochanter
  - Coxa breva
  - Hanging rope sign is characteristic of old Perthes
MRI
- Very sensitive in detecting infarction
- Role yet to be determined
Arthrography
- Can be used to determine if the head and acetabulum are congruent when deciding upon surgical treatment

Classification

*Disease must reach the fragmentation stage before it can be classified and there is large inter-observer variation

Herring (Lateral Pillar)

Interobservor agreement is best with the Herring classification
Femoral head on the AP radiograph is divided into 3 parts with the lateral pillar occupying the lateral 15 – 30%, the central pillar ~ 50% and the medial pillar 20 – 35%
Stage determined at the end of the fragmentation phase
Group A
- No involvement of the lateral pillar
- There may be lucency and collapse in the central and medial pillars
Group B
- Greater than 50% of lateral pillar height maintained
Group C
- Less than 50% of lateral pillar height maintained

Catterall

Stage 1
- Antero-medial portion of head involved
- No collapse
- Metaphyseal changes do not occur
- Epiphyseal plate is not involved
- Heals without significant sequelae
Stage 2
- More head involved
- May have fragmentation of the involved segment
- The involved segment shows increased density
- Uninvolved pillars of normal bone prevent significant collapse
- Regenerates without much loss of height
- The end result is usually good
- Metaphyseal reaction is localised
Stage 3
- Collapse of the head seen, as uninvolved pillars not large enough to prevent collapse
- May show head within a head
- The metaphysis is usually diffusely involved, causing broad neck
- The epiphyseal plate is unprotected and usually involved
- Results are poor
Stage 4
- Whole head involvement
- Severe collapse occurs early
- Restoration of the femoral head usually less complete
- The metaphyseal changes may be extensive
- The epiphyseal plate is often involved, leading to abnormal growth (coxa magna, coxa breva, coxa vara and coxa valga)

Salter – Thompson

Stage A
- Lateral portion of femoral capital epiphysis present (Catterall 1 & 2)
- Less than 50% head involved
Stage B
- Lateral portion of femoral capital epiphysis absent (Catterall 3 & 4)
- More than 50% head involved
- Lateral margin of epiphysis protects epiphysis from stress

Ponseti

Those with less than 50% of head involvement
Those with more than 50% of head involvement

Differential Diagnosis

Multiple epiphyseal dysplasia
Other causes of Osteonecrosis
- Sickle cell disease
- Corticosteroid therapy
Gauchers disease
Traumatic AVN
Infection

Treatment

Observation:

Indicated for patients with a good prognosis, including:
- Patients younger than 6
- Pillar A
- Salte-Thompson A
- Catterall group 1
Conservative modalities may also be employed
- Includes range of motion exercises, night time abduction splinting, home traction
- Bracing is rarely used today
- Prolonged immobilization, bed rest, and protected weight bearing do not influence course of disease

Medical Treatment:

Promising results have been demonstrated with bisphosphonate therapy

Surgical containment:

Indications:
- Patients with poor prognosis in the initial stage or fragmentation stage
- Hips that are containable:
  - full range of motion
  - femoral head/acetabular congruity
Options:
- proximal femoral varus osteotomy
  - varus angle must be less than 110 degrees postoperatively
- innominate osteotmy
  - shelf
  - triple
- Combination femoral and acetabular osteotomy
  - combination osteotomies not typically performed

Salvage procedures

Indications
- Patients with significant residual deformity
Options:
- Valgus, extension osteotomy
- Cheilectomy
- Chiari osteotomy to cover the femoral head
- Lateral shelf arthroplsty
- Arthrodesis at skeletal maturity. Should be reserved for patients with severe functional impairment

Other Treatment Algorithms:

Treatment by Catterall stage: (Apley)

Stage I : No treatment needed
Stage II & III
- No treatment needed if less than 7 years of age, unless head at risk signs present
- Aged more than 7 years or head at risk signs, proceed to containment therapy for about 6 – 14 months or until signs of recalcification of head
- Full range of movement should exist before using abduction device
Stage IV
- At any age : containment unless undue force required
- Choice between operative and non-operative treatment may not alter natural history of disease
- Pelvic or femoral osteotomies have similar results

Treatment recommended by Herring (JBJS 76A 448-458, 1994)

Patient less than 6 years old
- No evidence that any form of treatment alters the growth potential of the physis or the outcome
- Principle is symptom relief
Patient 6 – 8 years old
- All group A and those group B patients with bone age of less than 7
  - No alteration of outcome by treatment
  - Symptomatic relief only
- Those group B with bone age 7 or over
  - Better outcome with containment
  - No difference between method of containment
- Those in group C
  - Effect of treatment not known
  - Currently advocates containment
Patient 9 years old or older
- Difficult to manage
- Tend to get more severe disease
- Do not tolerate bracing well, thus more likely to have surgery over bracing
- Group A : Symptomatic only
- Group B+C : Advocates containment by whatever means

Treatment of the child with significant femoral head deformity

Defined significantly involved if :
- Femoral head is at least 4 mm out of round
- Overly symptomatic
Salvage procedures
- Cheilectomy or chiari osteotomy to cover the femoral head
- Valgus osteotomy to increase abduction and bring more normal medial femoral head into the weight bearing area
- Arthrodesis at about skeletal maturity. Should be reserved for patients with severe functional impairment
If planning for containment therapy :
- Perform arthrogram
  - Determine if containment can be achieved
  - Determine optimal position
- Brace / POP
- Operate if :
  - Failure of bracing
  - Intolerant of brace

Prognosis

70-90% of patients are free of pain 20-40 years after the onset of symptoms despite abnormal radiographs.

Clinical determinants

Increased age at onset harbors worse prognosis (age less than 6-8 do well)
Total head involvement has poor prognosis
Prolonged disease duration
Females have poorer prognosis (possibly due to earlier skeletal maturity and less remodeling potential)
The most important factor for long-term outcomes after the patient has reached the healed stage is degree of deformity of the femoral head and congruency between the femoral head and acetabulum

Mose (Acta Orthop Scand, supp 169, 1977)

Rings of increasing diameter (2 mm)
- If head conforms to a single ring in both X-Ray planes, has good prognosis
- If head varies from perfect circle by no more than 2 mm, has fair results
- If head varies by more than 2 mm in any plane, has poor results

Stulberg’s Classification of Residual Deformity: (JBJS 63A: 1095-1108, 1981)

Class 1: Normal hip joint
Class 2: Spherical femoral head, with one or more of the following:
- Coxa magna
- Coxa breva
- Increased acetabular index
Class 3: Aspherical, but not flat femoral head (Ovoid or mushroom-shaped) and:
- Coxa magna
- Coxa breva
- Increased acetabular index
Class 4: Flat femoral head and abnormal head, neck and acetabulum
Class 5: Flat femoral head and a normal neck and acetabulum

Stulberg’s results

Spherical congruency (class 1+2) : No risk of OA
Aspherical congruency (class 3+4) : Mild-moderate OA in late adulthood
Aspherical incongruency (class 5) : Severe OA before age 50

Conclusion

These results showed that lack of sphericity alone was not the only predictor of a poor outcome (Mose)
As many as 50% do well without treatment
Most of the remaining 50% do well into the 5th decade, despite CE angles less than 20 and Mose sphericity more than 2 mm out of round
No follow up study of sufficient length exists to show containment has altered the natural history of the condition

Radiological determinants

Extent of head involved, i.e. grade of disease
At risk factors
Herring group :
- Group A : 100% are Stulberg 1 or 2
- Group B
  - Less than 9 years old at onset
    - 92% are Stulberg 1+2
    - 8% Stulberg 3
  - More than 9 years old at onset
    - 30% are Stulberg 2
    - 50% Stulberg 3
    - 20% Stulberg 4
- Group C
  - 29% are Stulberg 2
  - 52% Stulberg 3
  - 19% Stulberg 4