April 11, 2024

Osteochondroma as per WHO is ” a cartilage-capped bony projection arising in the external surface of bone containing a marrow cavity that is continuous with that of the surrounding bone.

It is also called Exostoses

Types:

  • Solitary and Multiple

Multiple exostoses are seen in diaphyseal aclasis / Hereditary Multiple Exostosis

Etiology

Osteochondroma is considered a developmental disorder.

It is a result of separating a fragment of epiphyseal growth plate cartilage and its subsequent herniation through the periosteal bone cuff that usually surrounds the growth plate.

Recently, Osteochondroma has been considered a mutation of the gene Exostosin-1(EXT 1). This gene supports, it is a true bone tumor.

It is the most common radiation-induced bone tumor

Incidence:

(10-15 %) of all bone tumor

(20-50 %) of benign bone tumor

Age:

Osteochondroma occurs during the growth period

Male: Female= 2:1

Site:

Metaphysis of a long bone

  • A distal femur (Most common)
  • Proximal tibia
  • Proximal Humerus

Clinical Features:

Asymptomatic/ Incidental finding

It is hard, immobile, non-tender swelling of long duration.

Pain is present in the following conditions:

  1. Bursitis
  2. Fracture
  3. Mechanical Irritation/ Pressure to muscle-tendon
  4. Neural Irritation/ Compressive neuropathy
  5. Ischemia necrosis of osseous components
  6. Malignant Change

Radiological Features:

There is an eccentric bone outgrowth from metaphysics, composed of the cortical and medullary portions which are continuous with the cortex and medulla of long bone

Osteochondroma is directed away from the growing end of the long bone.

The cartilaginous cap is not visible, Bursa is also not visible

Osteochondroma
Osteochondroma

There are 3 components:

  1. Bone
  2. Cartilaginous Cap
  3. Bursa

Metachrondomatosis: Osteochondroma with coexisting enchondromatous lesion.

MRI: It helps to characterize the lesion, especially the cartilage cap.

A Cartilage cap thickness (2 cm or more) is postulated to be a high risk of malignant change.

Pathology:

It is a shiny smooth cartilaginous cap

Beneath the cap, there is trabecular bone and fatty marrow

Microscopic :

There are three layers:

Outer: Fibrous connective tissue ( Periosteum)

Middle: Cartilage Cap

  • Superficial: Chondrocytes in the cluster
  • Deep: Chondrocytes in verticle column

Inner: Bone

  • Trabecular with intervening marrow spaces

Treatment

Osteochondroma which is small can be observed

Surgical Indications are:

  • Cosmesis
  • Limitation of joint function
  • Repeated painful bursitis
  • Fracture of lesion
  • Secondary impingement to tendon, nerve, and vessels
  • Suspicion of malignant change

Complete excision of tumor including perichondrium

Malignant transformation is 1 % in solitary lesions and up to 20 % in multiple osteochondromatosis

Multiple recurrences suggest malignant transformation

See: Chondrosarcoma

Hereditary Multiple Exostoses

Hereditary Multiple Exostoses are also called Multiple Osteochondroma or Diaphyseal Aclasia

It is a genetic disorder with Autosomal Dominant.

There is incomplete penetrance in females so male: female ratio is 2:1

There is a formation of multiple osteochondromas of bone arising from osteochondral ossification leading to skeletal deformity and short stature

Three Genes are involved:

  • EXT 1
  • EXT 2
  • EXT 3

Age of presentation: It is earlier than a solitary one

Short Stature +

  • Ulna shortening with forearm bowing
  • tibiofibular synostosis
  • valgus deformity at ankle
  • genu valgum
  • coxa valga
  • scoliosis

There are two forms:

  1. Mild
    • Females are common
    • EXT-2 mutations
  2. Severe
    • Male are common
    • Multiple sites (>20)
    • Functional Limitation
    • EXT-1 mutation

The greater portion of metaphysics and some diaphysis

Treatment

Excision of symptomatic exostosis and correction of deformity and limb length discrepancy

Multiple Procedures are there for complete treatment

Malignant transformation is seen more from the pelvis, scapula, and proximal part of the femur

OSTEOCHONDROMA VARIANTS

Subungual exostosis

Subungual exostosis is also called as Dupuytren’s exostosis.

It arises from the dorsal and dorsomedial aspects of the distal phalanx in relation to nail bed

It presents as a mass under/ adjacent to the nail bed.

Painful and shows secondary overlying skin ulceration

Toes (90 % Great toe) are the most common site of involvement

Histologically

  • Unlike osteochondroma
  • No continuity with the underlying cortex and medullary canal
  • Cartilage cap consists of fibro-cartilage: Not hyaline cartilage

Treatment:

Complete surgical excision with or without preservation of nail bed for cosmesis.

Dysplasia epiphysealis hemimelica

Dysplasia epiphysealis hemimelica also called Trevor’s disease is a rare entity.

There are 3 forms:

  • Localized form (monostotic involvement)
  • Classic form ( more than one site in a single extremity)
    • It is most common (Involves 2/3rd of an extremity)
  • The generalized or severe form
    • Disease involving an entire single extremity

Presentation:

  • It occurs in the first decade of life

Turret Exostosis

Development of osteochondroma from the epiphysis

Only one side of the single extremity is involved

Medial side > Lateral side (Affected twice)

The lower Extremity is commonly involved.

Turret Exostosis is osteocartilaginous proliferation.

There is a smooth dome-shaped, extra-cortical mass arising from the dorsum of the proximal and middle phalanx of the hand.

There is disruption of the periosteum, subperiosteal hematoma, hematoma ossified, and progressive reduction of finger flexion.

Bizarre parosteal osteochondromatous proliferation

Bizarre parosteal osteochondromatous proliferation is also called NORA’s lesion.

Osteochondroma-like lesions within considered to be reactive secondary to trauma.

More than 2/3rd affects meta-carpal and meta-tarsals joints.

Hand involvement > 50 %, then foot and long bones are involved.

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