Multiple Cartilaginous Exostoses (Hereditary Exostosis)

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- Discussion:
    - an osteochondroma that results from a dysplasia of peripheral growth plate;
           - as its name implies, multiple hereditary exostosis is an inherited condition which produces multiple exostoses;
    - occurs in 1 out of 50,000 people;
    - typically inherited as an autosomal dominant trait, w/ 96% penentrance;
           - 10% may have no family history;
           - EXT1 on 8q24.1 and EXT2 on 11p13 are the two genes most strongly associated with MHE  
           - ref: EXT1 regulates chondrocyte proliferation and differentiation during endochondral bone development.  
    - average age of diagnosis is 3 yrs;
    - cartilaginous exostoses arise from metaphyses, point away from epiphysis, and appear to extend down diaphysis during growth;
    - they increase in size & number w/ growth, but may become latent at maturity;
    - osteochondromas are seen in several sites;
    - in over 90% of cases distal tibia, proximal tibia, proximal femur, and proximal humerus are involved.
           - will also involve iliac crests, scapulae, and ribs;
    - sarcomatous degeneration:
           - chondrosarcoma may develop in 1-2% of patients > 21 yrs of age;
           - lesions at risk are those occurring near pelvis, scapula, proximal humerus, proximal femur, & spine have increased risk of malignant transformation;
           - change in size of the exostosis or onset of pain in an affected adult is cause for concern and investigation.
           - monitoring pts via annual bone scans has been recommended, but its efficacy remains unproven.

- Radiographic Distribution of Lesions:
    - scapula: 40%
    - proximal humerus: 50%
    - ribs: 40%
    - distal radius: 30%
    - distal ulna: 30%
    - hands: 20-30%
    - ilium: 15%
    - mid femur 30%
    - distal femur: 70%
    - proximal tibia 70%
    - proximal fibula 30%
    - distal tibal and fibula: 20-25%
    - feet: 10-15%

- Clinical Presentation:
    - despite the high frequency of radiographic findings, a much smaller percentage of patients will demonstrate clinical lesions;
          - 75% of patients will have at least one clinically evident lesion;
          - 50% will demonstrate a forearm deformity;
          - 45% will demonstrate an ankle deformity;
          - 20% will demonstrate knee deformity;
    - clinical problems include:
          - fracture;
          - pressure of exostosis on surrounding soft tissues;
          - neurovascular compromise;
          - stature:
                 - 40% will demonstrate short stature;
                 - individuals may be small, but are not considered dwarfs;
          - leg length inequality may be severe enough to require equalization procedures in half of the individuals;

- Ulna in MED:
    - shortening is the major problem.
          - distal ulna contributes more to total bone length than does distal radius and therefore is more prone to shortening from a distal exostosis;
          - over 50% of patients will be affected;
    - diff dx: multiple enchondromatosis:
    - effects of ulnar shortening include;
          - radial bowing and angulatory deformity;
          - ulnar deviation of the wrist;
          - ulnar translation;
          - radial head dislocations
                - more common w/ severe ulnar shortening;
                - may lead to loss of pronation and increased ulnar variance;
                - ulnar varience is measured as the difference between the radial and  ulnar physis;

    - treatment:
          - probably most patients with forearm involvement do not require treatment despite severe deformity;
                 - references:
                         - Evaluation of the Forearm in Untreated Adult Subjects with Multiple Hereditary Osteochondromatosis
                         - Forearm Deformities in Hereditary Multiple Exostosis: Clinical and Functional Results at Maturity
          - excision of a distal osteochondroma gives unpredictable results;
          - radial head should never by excised in a growing patient;
          - stapling of radial hemiepiphysis may improve wrist alignment as well as improving supination and pronation;
          - ulnar lengthening:


- Knee Joint in MED:
       - leg length inequality may require equalization procedures in 50%;
       - fibular involvement by osteochondroma may cause: genu valgum;

- Ankle in MED:

    - valgus ankle deformity;
    - diastasis of the ankle; 
    - surgical indications:
          - pain from trauma or from prominent masses;
          - ankle pain assoc w/ deformity
          - w/ tibiotalar valgus > 15 deg, hemiepiphyseal stapling is indicated;
    - surgical treatment:
          - fibular lengthening + hemiepiphyseal stapling when valgus coexists w/ leg length discrepancy

Multiple hereditary osteochondromata.

Management of deformities of the forearm in multiple hereditary osteochondromas.

Synovial osteochondromatosis: a histopathological study of thirty cases.

Deformities of the forearm in patients who have multiple cartilaginous exostosis.

The natural history of hereditary multiple exostoses.

Knee deformities in multiple hereditary exostoses. A longitudinal radiographic study.

Hereditary Multiple Exostoses: One Center’s Experience and Review of Etiology.  

Severity of disease and risk of malignant change in hereditary multiple exostoses. A genotype-phenotype study.

Involvement of the Spine in Patients with Multiple Hereditary Exostoses

Original Text by Clifford R. Wheeless, III, MD.

Last updated by Data Trace Staff on Wednesday, January 2, 2013 3:08 pm