Heterotopic+Bone+(Benign)

-Risk factors for heterotopic ossification (HO) include the presence of other bone-forming disorders, such as diffuse idiopathic skeletal hyperostosis, ankylosing spondylitis and Paget disease. A personal history of previous HO also increases the risk of future occurrences. 3 || -Following trauma, HO often begins as a painful, palpable mass that gradually becomes nontender and smaller, as well as firmer to palpation. -The clinical impact of HO depends on the clinical setting and extent of the disease. A single lesion caused by trauma usuallly stabilizes and may regress; resulting symptoms depend on the location and size of the lesion. HO related to spinal cord injury or traumatic brain injury tends not to regress and may cause pain and decreased range of motion in affected joints; in such cases, the condition occasionally results in complete ankylosis and severe disability. Among patients with neurologic deficits, 8-10% have severe functional limitations resulting directly from HO. The involvement is correlated positively with poorer outcome in rehabilitation patients recovering from traumatic brain injury. 3 || -Bone scanning is the method of choice for earliest detection and, once the diagnosis is established, for assessing the maturity of a known lesion. -Ultrasonography may have a role as a screening tool in the hip region after spinal cord injury. 3 || Grade 2: Bone spurs; seperated by > 1cm Grade 3: Bone spurs; separated by < 1cm Grade 4: Apparent bony ankylosis 5 || Planning photo of a heterotopic hip. 7 
 * Epidemiology: || "Heterotopic ossification (HO) occurs in 30% of patients undergoing hip arthroplasty. The incidence is greater than 80% in patients who have a history of ipsilateral or contralateral heterotopic ossification, and more than 60% in patients with other high-risk factors such as hypertrophic osteoarthritis, ankylosing spondylitis, and diffuse idiopathic skeletal hyperostosis." 1 ||
 * Etiology: || ​-High-risk factors for heterotopic bone formation include trauma, osteoarthritis, active rheumatoid spondylitis and previous ectopic bone formation. 2 ​
 * Signs & Symptoms: || -Heterotopic ossification (HO) is the abnormal formation of bone within extraskeletal soft tissues. Posttraumatic HO can be found at any site. The most common postsurgical site is the hip following total hip arthroplasty. The hip is also the most common site in patients with traumatic brain injury or spinal cord injury. The next most common sites of involvement in patients with traumatic brain injury are the shoulders and elbows, with the knees being rarely being affected. The knees are frequently involved in patients with spinal cord injury.
 * Diagnostic Procedures: || -Radiography is the preferred method of initial assessment for virtually all musculoskeletal conditions, including HO. Given their relatively low expense, radiographs should be obtained first (even if other imaging modalities are planned) in order to assess the extend of known HO.
 * Histology: || Pluripotent mesenchymal cells are induced to differentiate into osteogenic progenitor cells. These cells subsequently develop osteoblastic tissue, resulting in the production of heterotopic bone. 6 ||
 * Lymph Node Drainage: || Because heterotopic bone does not spread to other sites, lymphatic drainage does not play a significant role. ||
 * Metastatic Spread: || This diagnosis does not metastasize to distant sites, but in extremely rare cases malignant degeneration to osteosarcoma can occur. 3 ||
 * Grading: || <span style="color: #ff0000; font-family: Arial,Helvetica,sans-serif; font-size: 10pt;">Grade 1: Isolated bone islands
 * Staging: || <span style="color: #ff0000; font-family: Arial,Helvetica,sans-serif; font-size: 10pt;">Indicated after a total hip replacement. <span style="color: #ff0000; font-family: Arial,Helvetica,sans-serif; font-size: 80%; vertical-align: super;">5 ||
 * Radiation Side Effects: || Radiation treatments for HO increases the risk of bony nonunion. Studies have shown that nonunion occurs in 20-30% of cases prophylactically treated with RT and only in 2-15% of cases not treated with RT. 8 ||
 * Prognosis: || Ultimately the prognosis of these patients is excellent as this is a benign condition. A study found that only 5% of patients who received prophylactic irradiation developed HO compared to 60% of patients who did not receive irradiation. 8 ||
 * Treatments: || Radiation Therapy Postoperative period, with doses ranging from a single fraction of 7Gy or 8 to 10y in 4 to 5 fractions. 1 ||
 * TD5/5: || The TD5/5 for bone and cartilage is >30Gy for single dose and >70Gy for fractionated dose. 1 ||
 * Planning Photos || <span style="color: #ff0000; font-family: Arial,Helvetica,sans-serif;">Planning photo of a heterotopic TMJ. <span style="color: #ff0000; font-family: Arial,Helvetica,sans-serif; font-size: 80%; vertical-align: super;">6 <span style="color: #ff0000; font-family: Arial,Helvetica,sans-serif;">

<span style="color: #008000; font-family: Arial,Helvetica,sans-serif;">The following shows the isodose distribution and AP DRR of a heterotopic bone radiation treatment to the knee. <span style="color: #008000; font-family: Arial,Helvetica,sans-serif; font-size: 80%; vertical-align: super;">4 <span style="font-family: Arial,Helvetica,sans-serif; font-size: 80%; vertical-align: super;">

|| <span style="font-family: Arial,Helvetica,sans-serif;">**References** 1. Chao KS, Perez CA, Brady LW. //<span style="font-family: Arial,Helvetica,sans-serif;">Radiation Oncology - Management Decisions. // <span style="font-family: Arial,Helvetica,sans-serif;"> 2nd ed. Philadelphia: Lippincott, Williams & Wilkins, 2002: 677-688. 2. Meyer JL (ed): The Radiation Therapy of Benign Diseases. Current Indications and Techniques. Front Radiat Ther Oncol. Basel, Karger, 2001, vol 35, pp 120-134. 3. eMedicine. Heterotopic Ossifiicaton. []. Accessed February 16, 2010. 4. Digitally Reconstructed Radiographs courtesy of Bridget Keehan, RT(T). The Cancer Team at Bellin Health. 5. Gunderson and Tepper. Clinical Radiation Oncology. 2nd Edition. Philadelphia, PA: Churchill Livingstone. 2007. 6. Durr E., et al. Radiation Treatment of Heterotopic Bone Formation in the Temporomandibular Joint Articulation. //Int. J. Radiation Oncol.// 1993; 27(4): 863-869. 7. Konski A., et al. Randomized Trial Comparing Single Dose Versus Fractionated Irradiation for Prevention of Heterotopic Bone: A Preliminary Report. //Int. J. Radiation Oncol.// 1990; 18(5): 1139-1142. 8. Baird E, Kang Q. Prophylaxis of heterotopic ossification - an updated review. //Journal of Orthopaedic Surgery & Research// [serial online]. January 2009;4:1-8. Available from: Academic Search Complete, Ipswich, MA. Accessed February 20, 2010.