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- Discussion:
    - bone scan and MRI may help early involvement, but may not correlate with the extent of involvement;
           - bone scans are highly sensitive for Perthes disease;

- Radiographic Findings: (Waldenstrom):
    - initial findings:
           - ossific nucleus fails to grow and looks smaller;
           - surrounding bone may become osteopenic, causing nucleus to look more dense;
           - cartilage of femoral head continues to grow and therefore medial joint space looks widened;
           - crescent sign (Caffey's sign) may be seen;
                   - represents pathologic frx of resorbing femoral head and is best seen on a frog leg view of the pelvis;
    - avascular stage: ossific nucleus is small, dense, and uniform;
    - fragmentation stage:
           - epiphysis is seen to fragment;
           - the dense avascular bone is replaced by radiolucent granulation tissue;
    - re-ossification stage:
           - radiodense areas replace radiolucent areas;
           - normal bone density returns;

           Perthes in 6 yo female             later at 7 yrs                  later at 8 yrs            later at 9 yrs
                   

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- Radiographic Predictors:
    - radiographic findings associated with poor prognosis "head at risk"
           - lateral subluxation (most important)
           - calcification lateral to the epiphysis;
           - Gage's sign: V shaped defect laterally;
           - metaphyseal cysts
           - horizontal growth plate
    - Caterall & Salter Stages: (based on amount of femoral involvement)
           - Caterall   Salter/Thompson   Location                                  Prognosis
               I              A           Anterior (lat view)                                       Good
               II             A           Ant/partial lateral                                        Good
               III            B           Ant & lateral margin                                    Poor
               IV           B           Thruout Cap Fem Epiphysis Dome                Poor
          - references:
                 - Legg-Calve-Perthes disease. The prognostic significance of the
                        subchondral fracture and a two-group classification of the femoral head involvement.
    - Herring Classification:
          - most useful in the fragmentation stage;
          - compares the height of lateral epiphyseal pillar to the height of the contra-lateral epiphysis;
          - Group A there is no collapse of the lateral pillar;
          - Group B lateral pillar margins has more than 50% of original height;
          - Group C collapse of lateral pillar more than 50%;
          - references:
                 The treatment of Legg Calve Perthes Disease: A critical review.
                      JA Herring.  JBJS Vol 76-A. 1994. p448-458.
                 Legg Calve Perthes Disease.
                      DR Wenger et al. JBJS Vol 73-A. 1991. p 778-788.

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- Case Examples:

       Perthes in 5 yo male;
   

  Perthes in 6 yo male    later at 6 1/2 yrs     later at 7 yrs
           

  Perthes in 6 yo female       later at 7 yrs             later at 8 yrs            later at 9 yrs
           

   

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