Updated: May 22, 2008
The term heterotopic ossification (HO) describes bone formation at an abnormal anatomical site, usually in soft tissue. HO can be classified into the following 3 types:
Despite many investigations, the etiology and pathogenesis of neurogenic heterotopic ossification remain unknown.3 An extensive review of the problem in 1973 by Rossier and colleagues attempted to address the question of pathogenesis by investigating the following parameters4 :
None of these observations explain the factors responsible for the development of HO. Although the etiology of HO remains unknown, clinical and experimental evidence supports the hypothesis that trauma is one of the most important initiating factors. In the studies in which HO was induced experimentally, 2 factors were found to be prerequisites for ectopic ossification: (1) traumatic ischemic degeneration of involved muscle and (2) tissue expression of bone morphogenic proteins (BMPs).
It also has been shown that expression of many genes, including BMP, is regulated by mechanical stress. The target cells in the muscle for BMP are mesenchymal stem cells, also called satellite cells. These cells are precursors capable of differentiating into many cell types, including osteoblasts. Thus, BMP may play a role as a paracrine factor in the differentiation of satellite cells into bone-forming cells.
Most likely, other factors also are involved in the etiology of HO. Studies have shown that AlkP may have an important role in ectopic calcification and ossification of soft tissues. The major role of AlkP in soft tissue is to remove inhibitors of mineralization. An increased expression of AlkP was found in vascular smooth muscle cells in the presence of macrophages and inflammatory cytokines. These observations may have clinical importance, because inflammation and trauma have long been suggested by many investigators as possible etiologic factors.
Clinically, muscle trauma has been reported as a cause of HO after SCI by numerous investigators, including Bodley and colleagues,5 as well as Snoecx and co-investigators.6 The types of muscle trauma proposed as initiating HO are muscle tears, ruptures, edema, and bleeding.
It has also been suggested that factors such as intensive rehabilitation, transfer activities, and repeated minor trauma during activities of daily living can cause superimposed mechanical stress and initiate HO. The hypothesis that trauma is an important factor in HO formation after SCI also has been documented by ultrasonographic and histologic studies. Various degrees of muscular damage with evidence of tissue bleeding have been found in the early stage of HO.
During the formation of HO, initially immature connective tissue, fibroblasts, ground substance, and collagen fibers are seen. Eventually, usually within 7-14 days, osteoblasts are noted, located irregularly in osteoid. New bone formation may start in multiple foci within osteoid. As mineralization progresses, amorphous calcium phosphate is gradually replaced by hydroxyapatite crystals. Commonly, after approximately 6 months, the appearance of true bone is noted. Rossier noted that after approximately 30 months, the pattern in HO approached that of normal young adult bone.4 Anatomically, HO is always extra-articular, but it may attach to the joint capsule without disrupting it. Occasionally, HO may attach to the cortex of adjacent bone, with or without cortical disruption.
The reported incidence of HO following SCI varies greatly from study to study. Incidence varies from a low of 3.4% to a high of 47% reported by Hassard, who found HO around the hips of 62 of 131 patients with SCI who were admitted to the Hot Springs Rehabilitation Center over a 2-year period.7 Most studies cite a range between these 2 extremes. Peak incidence is noted from 4-12 weeks postinjury and can occur up to 5 months following trauma. Later onset has been reported but is very rare.
In 1954, Irving and LeBrun first documented HO in patients with hemiplegia. Roberts reported 6 cases of HO following intracranial lesions (3 traumatic, 2 vascular, and 1 neoplastic) in 1968, and subsequent studies cited the incidence of clinically significant HO following severe closed head injury (CHI) as being 11-76%. Incidence of HO following other neurologic disorders has not been delineated yet, but it appears to be lower than the incidence following SCI or head injury.
The following reasons may be postulated for the large variability in incidence seen in different studies:
Approximately 10-35% of all patients with HO secondary to SCI have significant reduction of range of motion (ROM) at the affected joint or joints.3 Wharton and Morgan found that 3% of patients with SCI have an ankylosed joint caused by HO. Effects on activities of daily living (ADL) and functional mobility (eg, transfers) are not difficult to imagine. In addition, abnormal weight distribution may lead to increased frequency of decubitus ulceration, as Hassard noted in 1975.7
No known correlation exists between race and incidence of HO.
No known correlation exists between sex and incidence of HO.
Age has no significant correlation with HO formation, although the condition is somewhat less frequent in pediatric and geriatric patients with SCI.
See Pathophysiology.
Cellulitis
Osteomyelitis
Thrombophlebitis
Joint sepsis
Fracture
Hematoma
Early pressure sore (before skin breakdown is evident)
Local trauma
The use of physical therapy (PT) in HO has long been controversial. Rossier and co-investigators noted occasional transverse microfractures on sections of HO that they thought might be caused by spasticity or by overly aggressive PROM.4 Since then, the debate between resting the joint and aggressive PROM has continued. In the literature, however, the developing consensus appears to be that aggressive PROM and continued mobilization, once acute inflammatory signs have subsided, are indicated, because they help to maintain ROM and (in more extensive HO) they may lead to the formation of a pseudarthrosis. Resting the joint appears more likely to lead to decreased ROM or to ankylosis.
During the acute inflammatory stage, the patient should rest the involved joint in a functional position, and the physical therapist should initiate gentle PROM as soon as possible. The role of continuous PROM machines has not been studied in this situation. For patients with incomplete SCI or head injuries, maintaining ROM may be difficult because of pain from ROM exercises. The use of joint manipulation has been reported in patients with HO who, because of limited joint ROM, have functional limitations. However, such manipulation is controversial owing to the risk of the formation of new hematoma and because of the chance that long-bone fracture will occur in patients with secondary osteoporosis.
Nonarticular complications of HO are rare, but they have been reported. These complications include ulnar nerve compression with HO at the elbow, vascular (predominantly venous) compression with or without associated deep venous thrombosis (DVT), and lymphatic obstruction leading to lymphedema.16,17
The usual surgical technique used on HO occurring anteriorly at the hip is anterior wedge resection. Postoperatively, position the joint properly with foam wedges so that the surgical correction can be maintained and any strain on the incision or pressure sores can be prevented. Start gentle PROM about 72 hours postoperation, and increase therapy intensity gradually to incorporate retraining in functional activities. Patient selection and careful identification of functional goals are critical for successful surgical intervention.
Consultation with an orthopedist is necessary for any consideration of surgical management of HO.
Today, the medical treatment of HO is directed at early HO. In the later stages of the development of mature bone, medical treatment is ineffective. Etidronate (Didronel) is the only available medication for the treatment of HO after SCI.14,22 Treatment with NSAIDs may be required initially, until the resolution of inflammation and the normalization of CRP levels.3
Presumed to have direct and indirect effects on the formation of HO. Direct effect refers to the inhibition of the differentiation of mesenchymal cells into osteogenic cells, and indirect effect refers to the inhibition of posttraumatic bone remodeling by suppression of the prostaglandin-mediated inflammatory response.
Known to inhibit synthesis of prostaglandins.
25 mg PO tid for 3-6 wk from time of surgery for excision of HO
<14 years: Not recommended
>14 years: Administer as in adults
Coadministration with aspirin increases risk of serious NSAID-related adverse effects; probenecid may increase concentrations and possibly toxicity of NSAIDs; may decrease effect of hydralazine, captopril, and beta blockers; may decrease diuretic effects of furosemide and thiazides; monitor PT closely (instruct patients to watch for signs of bleeding); may increase risk of methotrexate toxicity; phenytoin levels may be increased when administered concurrently
Documented hypersensitivity
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
D - Fetal risk shown in humans; use only if benefits outweigh risk to fetus
Acute renal insufficiency, hyperkalemia, hyponatremia, interstitial nephritis, and renal papillary necrosis may occur; increases risk of acute renal failure in patients with preexisting renal disease or compromised renal perfusion; reversible leukopenia may occur, (discontinue if persistent leukopenia, granulocytopenia, or thrombocytopenia presents)
The bisphosphonate group of compounds has properties similar to naturally occurring pyrophosphate, which may be a regulator of calcification.2 Etidronate disodium is the most extensively studied of this class of drugs for the treatment of HO. Etidronate acts by (1) inhibiting precipitation of calcium phosphate from unsaturated solutions, (2) delaying aggregation of apatite crystals into layers, and (3) blocking conversion of calcium phosphate into hydroxyapatite. Apparently, predisposition to the inflammatory process and mineralization decreases with time, although it is not understood why. This phenomenon may be why there is no massive rebound bone formation after cessation of etidronate. Thus, the effectiveness of etidronate depends entirely on when and how long it is given, and the drug does not affect HO that has already formed.
Reduces bone formation and does not alter renal tubular reabsorption of calcium. The effects of etidronate increase as the dose increases. Agent does not appear to affect fracture healing.
20 mg/kg PO q24h for 2 wk followed by 10 mg/kg for 10 wk
If GI upset occurs, give in divided doses
To maximize absorption, food, vitamins, and antacids should be avoided within 2 h of dosing
Not indicated; may result in rachitis
Coadministration with calcium-containing products and other multivalent cations decreases absorption
Documented hypersensitivity; hypocalcemia, renal impairment, osteomalacia
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Monitor hypercalcemia-related parameters (eg, serum levels of calcium, phosphate, magnesium and potassium); maintain adequate intake of calcium and vitamin D to prevent severe hypocalcemia; caution if active upper GI problems; do not administer with alendronate for osteoporosis in postmenopausal women
Kaplan FS, Xu M, Glaser DL, et al. Early diagnosis of fibrodysplasia ossificans progressiva. Pediatrics. May 2008;121(5):e1295-300. [Medline].
Shafer DM, Bay C, Caruso DM, et al. The use of eidronate disodium in the prevention of heterotopic ossification in burn patients. Burns. May 2008;34(3):355-60. [Medline].
Subbarao JV, Garrison SJ. Heterotopic ossification: diagnosis and management, current concepts and controversies. J Spinal Cord Med. Winter 1999;22(4):273-83. [Medline].
Rossier AB, Bussat P, Infante F, et al. Current facts of para-osteo-arthropathy (POA). Paraplegia. May 1973;11(1):38-78. [Medline].
Bodley R, Jamous A, Short D. Ultrasound in the early diagnosis of heterotopic ossification in patients with spinal injuries. Paraplegia. Aug 1993;31(8):500-6. [Medline].
Snoecx M, De Muynck M, Van Laere M. Association between muscle trauma and heterotopic ossification in spinal cord injured patients: reflections on their causal relationship and the diagnostic value of ultrasonography. Paraplegia. Aug 1995;33(8):464-8. [Medline].
Hassard GH. Heterotopic bone formation about the hip and unilateral decubitus ulcers in spinal cord injury. Arch Phys Med Rehabil. Aug 1975;56(8):355-8. [Medline].
Downing MR, Knox D, Gibson P, et al. Impact of trochanteric heterotopic ossification on measurement of femoral bone density following cemented total hip replacement. J Orthop Res. Apr 10 2008;[Medline].
Macfarlane RJ, Ng BH, Gamie Z, et al. Pharmacological treatment of heterotopic ossification following hip and acetabular surgery. Expert Opin Pharmacother. Apr 2008;9(5):767-86. [Medline].
Garland DE, Blum CE, Waters RL. Periarticular heterotopic ossification in head-injured adults. Incidence and location. J Bone Joint Surg Am. Oct 1980;62(7):1143-6. [Medline].
Singh RS, Craig MC, Katholi CR, et al. The predictive value of creatine phosphokinase and alkaline phosphatase in identification of heterotopic ossification in patients after spinal cord injury. Arch Phys Med Rehabil. Nov 2003;84(11):1584-8. [Medline].
Sherman AL, Williams J, Patrick L, et al. The value of serum creatine kinase in early diagnosis of heterotopic ossification. J Spinal Cord Med. 2003;26(3):227-30. [Medline].
Estrores IM, Harrington A, Banovac K. C-reactive protein and erythrocyte sedimentation rate in patients with heterotopic ossification after spinal cord injury. J Spinal Cord Med. 2004;27(5):434-7. [Medline].
Banovac K. The effect of etidronate on late development of heterotopic ossification after spinal cord injury. J Spinal Cord Med. Spring 2000;23(1):40-4. [Medline].
Freed JH, Hahn H, Menter R, et al. The use of the three-phase bone scan in the early diagnosis of heterotopic ossification (HO) and in the evaluation of Didronel therapy. Paraplegia. Aug 1982;20(4):208-16. [Medline].
Bradleigh LH, Perkash A, Linder SH, et al. Deep venous thrombosis associated with heterotopic ossification. Arch Phys Med Rehabil. Mar 1992;73(3):293-4. [Medline].
Varghese G, Williams K, Desmet A, et al. Nonarticular complication of heterotopic ossification: a clinical review. Arch Phys Med Rehabil. Nov 1991;72(12):1009-13. [Medline].
Banovac K, Williams JM, Patrick LD, et al. Prevention of heterotopic ossification after spinal cord injury with indomethacin. Spinal Cord. Jul 2001;39(7):370-4. [Medline].
Banovac K, Williams JM, Patrick LD, et al. Prevention of heterotopic ossification after spinal cord injury with COX-2 selective inhibitor (rofecoxib). Spinal Cord. Dec 2004;42(12):707-10. [Medline].
Strauss JB, Chen SS, Shah AP, et al. Cost of radiotherapy versus NSAID administration for prevention of heterotopic ossification after total hip arthroplasty. Int J Radiat Oncol Biol Phys. Jan 28 2008;[Epub ahead of print]. [Medline].
Sautter-Bihl ML, Liebermeister E, Nanassy A. Radiotherapy as a local treatment option for heterotopic ossifications in patients with spinal cord injury. Spinal Cord. Jan 2000;38(1):33-6.
Banovac K, Gonzalez F, Renfree KJ. Treatment of heterotopic ossification after spinal cord injury. J Spinal Cord Med. Jan 1997;20(1):60-5. [Medline].
paraosteoarthropathy, periarticular bone formation, neurogenic ossifying fibromyopathy, osteosis neurotica (ie, para-articularis), myositis ossificans circumscripta neurotica, myositis ossificans progressiva, fibrodysplasia ossificans progressiva, traumatic myositis ossificans, neurogenic heterotopic ossification
Kresimir Banovac, MD, PhD, Professor, Departments of Rehabilitation Medicine and Medicine, Associate Vice Chairman, Department of Rehabilitation Science, University of Miami Miller School of Medicine; Medical Director, Spinal Cord Injury Rehabilitation Unit, Jackson Memorial Medical Center
Kresimir Banovac, MD, PhD is a member of the following medical societies: American Spinal Injury Association
Disclosure: Nothing to disclose.
John Speed, MBBS, Interim Chairman, Associate Professor, Division of Physical Medicine and Rehabilitation, University of Utah School of Medicine
John Speed, MBBS is a member of the following medical societies: American Academy of Pain Medicine, American Academy of Physical Medicine and Rehabilitation, American Association of Neuromuscular and Electrodiagnostic Medicine, American Pain Society, Association of Academic Physiatrists, International Association for the Study of Pain, International Society of Physical and Rehabilitation Medicine, and Utah Medical Association
Disclosure: Nothing to disclose.
Robert L Sheridan, MD, Assistant Chief of Staff, Chief of Burn Surgery, Shriners Burns Hospital; Associate Professor of Surgery, Department of Surgery, Division of Trauma and Burns, Massachusetts General Hospital and Harvard Medical School
Robert L Sheridan, MD is a member of the following medical societies: American Academy of Pediatrics, American Association for the Surgery of Trauma, American Burn Association, and American College of Surgeons
Disclosure: Nothing to disclose.
Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: Nothing to disclose.
Patrick M Foye, MD, FAAPMR, FAAEM, Associate Professor of Physical Medicine and Rehabilitation, Co-Director of Musculoskeletal Fellowship, Co-Director of Back Pain Clinic, Director of Coccyx Pain (Tailbone Pain, Coccydynia) Service, University of Medicine and Dentistry of New Jersey, New Jersey Medical School
Patrick M Foye, MD, FAAPMR, FAAEM is a member of the following medical societies: American Academy of Physical Medicine and Rehabilitation, American Association of Neuromuscular and Electrodiagnostic Medicine, Association of Academic Physiatrists, and International Spine Intervention Society
Disclosure: Nothing to disclose.
Kelly L Allen, MD, Consulting Staff, Department of Physical Medicine and Rehabilitation, Lourdes Regional Rehabilitation Center, Our Lady of Lourdes Medical Center
Disclosure: Nothing to disclose.
Consuelo T Lorenzo, MD, Consulting Staff, Department of Physical Medicine and Rehabilitation, Alegent Health Care, Immanuel Rehabilitation Center
Consuelo T Lorenzo, MD is a member of the following medical societies: American Academy of Physical Medicine and Rehabilitation
Disclosure: Nothing to disclose.
© 1994-
by Medscape.
All Rights Reserved
(http://www.medscape.com/public/copyright)