OSTEOCHONDROMA

Osteochondromas are the second most common benign bone tumors and are primarily found in children and adolescents.⁴ They account for 10-15% of all bone tumors and 20-50% of benign bone tumors.  Osteochondromas can occur as either an isolated osteochondroma or in association with the condition hereditary multiple osteochondromas (HMO). While isolated osteochondromas typically develop in longer bones and rarely affect the hand, hand involvement is much more likely in HMO, with a particularly high incidence in younger populations. In these cases, osteochondromas can grow on the phalanges, metacarpals, or carpals, and while typically asymptomatic, can lead to pain and/or functional impairments in some patients. Although somewhat controversial, treatment recommendations generally call for careful observation alone unless symptoms are present, in which case surgical options such as resection and corrective osteotomies may be considered.^1-4

Pathophysiology

• An isolated osteochondroma is a hamartomatous proliferation of bone and cartilage that can arise due to a Salter-Harris fracture, surgery, radiation therapy or without an identifiable cause. The origin of these tumors is believed to be secondary to a defect within the periosteum of the carpals or other bones of the hand.
  • Osteochondromas are inherited in an autosomal-dominant fashion and are believed to result from a mutation in the EXT gene, which affects prehypertrophic chondrocytes of growth plates.
  • In children, osteochondromas are located adjacent to growth plates and move away from the growth plate over time. Because they are essentially isolated growth plates, these osteochondromas are affected by and respond to various growth factors, and they grow until skeletal maturity is complete and the growth plates fuse.³
  • HMO, also known as multiple hereditary exostoses, multiple cartilaginous exostoses, multiple osteochondromata, diaphyseal aclasis, osteogenic disease, and dyschondroplasia, is an autosomal-dominant skeletal dysplasia formed by enchondral ossification.⁵
    • HMO is caused by a defect in the EXT1, EXT2, or EXT3 genes. These are tumor-suppressing genes that play a role in regulating chondrocyte maturation and differentiation, and can affect normal endochondral ossification.²
    • Individuals with the EXT1 mutation have a more severe presentation than patients with the EXT2 mutation.²
    • Clinical evidence of the exostoses usually occurs in the first decade of life, and the characteristic osteochondromas are usually located on the metaphysis of long bones. The most common upper limb sites are the proximal humerus, distal radius, distal ulna, and hand.⁵
    • Secondary chrondrosarcoma can develop from a malignant transformation of an isolated osteochondroma or in HMO.
      • Older patients are far more likely to develop this malignancy, and it is extremely rare in the pediatric population.
      • The risk for malignant transformation is <1% in isolated osteochondromas and ~5-10% in HMO. Proximal lesions are also more likely to undergo malignant transformation than distal lesions.⁶

Related Anatomy

• Phalanges
• Metacarpals
• Carpals
• Radius
• Ulna
• Metaphysis
• Epiphyseal growth plate
• Diaphysis
• Epiphysis
  • Pathological analysis of osteochondromas shows the presence of a cartilage cap with benign-appearing cartilage that resembles the normal epiphysis.³
  • One study classified osteochondromas affecting the pediatric digits into the following 3 types based on their locations:
    • Type A: tumors located at the nonepiphyseal metaphysis
    • Type B: tumors in the metaphysis on the epiphyseal plate side
    • Type C: tumors that extend toward the diaphysis⁴

Incidence and Related Conditions

• Osteochondromas are believed to account for 10-15% of all bone tumors and 20-50% of benign bone tumors, but their true incidence is unknown because many cases are asymptomatic and remain undiagnosed.⁷
• Osteochondromas can occur in any bone that undergoes enchondral bone formation, but usually occur in long bones, with about 40% developing around the knee joint.¹
  • Only about 4% of isolated osteochondromas involve the hand and wrist, but involvement is much more likely in HMO. When osteochondromas develop in the hand, there are varying reports regarding which bones are most commonly affected, with some finding it to be the proximal phalanx¹ and others identifying the metacarpals, particularly the index and little metacarpals.²
  • Reports also vary on the percentage of patients with HMO who have osteochondromas of the hand, with incidences ranging from 30-79%.²
  • Another study found that the forearm was involved in 30-60% of patients with HMO.⁵
  • Between 75-80% of all osteochondromas are diagnosed before the age of 20, and males are more frequently affected than females at a ratio of about 3:1.⁷
  • Secondary chondrosarcoma
  • Parosteal osteosarcoma
  • Bizarre parosteal osteochondromatous proliferation (BPOP)

Differential Diagnosis

• BPOP
• Florid reactive periostitis
• Turret exostosis (distal phalanx osteochondroma)
• Dysplasia Epiphysealis Hemimelica (DEH)

A typical patient is a 12-year-old, right-handed boy. After sustaining a little metacarpal fracture in his right hand at age 10, the boy had an X-ray that revealed a mass in that bone. Over time, more masses were identified during follow-up X-rays, particularly in the index and little metacarpals. While the tumors did not result in any pain, they did cause minor functional impairments when performing fine-motor skills, and their appearance was alarming to the boy and his parents. The boy’s pediatrician subsequently diagnosed him with HMO, but did not recommend any immediate treatment beyond observation.

• Infection
• Bony deformity secondary to growth disturbance
• Mechanical joint problems
• Vascular/tendon compression
• Arterial/venous thrombosis
• Aneurysm/pseudoaneurysm
• Ischemia
• Phlebitis
• Bursitis
• Hemothorax
• Fracture
• Paresthesia
• Paraplegia
• Peroneal neuropathy
• Upper limb neuropathy
• Bursa formation
• Chondrosarcoma
• Recurrence

• In one study that compared patients with types A, B, and C osteochondromas treated surgically, overall outcomes were good in types B and C, but surgery was less successful for type A lesions. Thus, researchers recommend that when type A tumors increase in size and cause the deviation of fingers, corrective osteotomy is indicated to correct deformities.⁴

• How osteochondromas change in number and size over time is not clearly understood because long-term follow-ups on patients with HMO affecting the hand are lacking.²
• Unfortunately, many of the treatment recommendations for osteochondromas are based on retrospective studies and case reports involving small series, or on experience with similar lesions elsewhere in the body that may not be fully applicable to the hand and upper extremity.³

Cited

1. Rajappa S, Kumar MM, Shanmugapriya S. Recurrent solitary osteochondroma of the metacarpal: a case report. J Orthop Surg (Hong Kong) 2013;21(1):129-31. PMID: 23630007
2. Woodside JC, Ganey T, Gaston RG. Multiple osteochondroma of the hand: initial and long-term follow-up study. Hand (N Y) 2015;10(4):616-20. PMID: 26568714
3. Payne WT, Merrell G. Benign bony and soft tissue tumors of the hand. J Hand Surg Am 2010;35(11):1901-10. PMID: 20961700
4. Ohnishi T, Horii E, Shukuki K, Hattori T. Surgical treatment for osteochondromas in pediatric digits. J Hand Surg Am 2011;36(3):432-8. PMID: 21333463
5. Gottschalk HP, Kanauchi Y, Bednar MS, Light TR. Effect of osteochondroma location on forearm deformity in patients with multiple hereditary osteochondromatosis. J Hand Surg Am 2012;37(11):2286-93. PMID: 23040641
6. Bovée JV, Sakkers RJ, Geirnaerdt MJ, et al. Intermediate grade osteosarcoma and chondrosarcoma arising in an osteochondroma. A case report of a patient with hereditary multiple exostoses. J Clin Pathol 2002;55(3):226-9. PMID: 11896078
7. Murphey MD, Choi JJ, Kransdorf MJ, et al. Imaging of osteochondroma: variants and complications with radiologic-pathologic correlation. Radiographics 2000;20(5):1407-34. PMID: 10992031
8. Ting BL, Jupiter JB. Recurrent bizarre parosteal osteochondromatous proliferation of the ulna with erosion of the adjacent radius: case report. J Hand Surg Am 2013;38(12):2381-6. PMID: 24183508

New Articles

1. Woodside JC, Ganey T, Gaston RG. Multiple osteochondroma of the hand: initial and long-term follow-up study. Hand (N Y) 2015;10(4):616-20. PMID: 26568714

Reviews

1. Kitsoulis P, Galani V, Stefanaki K, et al. Osteochondromas: review of the clinical, radiological and pathological features. In Vivo 2008;22(5):633-46. PMID: 18853760
2. Hakim DN, Pelly T, Kulendran M, Caris JA. Benign tumours of the bone: A review. J Bone Oncol 2015;4(2):37-41. PMID: 26579486

Classics

1. Ganzhorn RW, Bahri G, Horowitz M. Osteochondroma of the distal phalanx. J Hand Surg Am 1981;6(6):625-6. PMID: 7310094
2. Wood VE, Sauser D, Mudge D. The treatment of hereditary multiple exostosis of the upper extremity. J Hand Surg Am 1985;10(4):505-13. PMID: 3874896