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:
- Bursitis
- Fracture
- Mechanical Irritation/ Pressure to muscle-tendon
- Neural Irritation/ Compressive neuropathy
- Ischemia necrosis of osseous components
- 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
There are 3 components:
- Bone
- Cartilaginous Cap
- 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:
- Mild
- Females are common
- EXT-2 mutations
- 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
- Dysplasia epiphysealis hemimelica
- Turret exostosis
- Bizarre parosteal osteochondromatous proliferation
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.
