eMedicine Specialties > Orthopedic Surgery > Neoplasms

Traumatic Heterotopic Ossification

Author: Chris McLean, MBBS, MRCS(Glasg), AFRCS(Ire), Specialist Registrar, Departments of Orthopedic and Trauma Surgery, Frimley Park Hospital, UK
Coauthor(s): Richard Hargrove, MBBS, FRCS(Ire), FRCS, Consulting Staff, Hip and Hip Revision Arthroplasty, Frimley Park Hospital; John B Wood, MBBS, FRCS(Edin), FRCS(Tr & Orth), FEBOT, Consulting Surgeon, Department of Trauma and Orthopedic Surgery, University Hospital Lewisham, London
Contributor Information and Disclosures

Updated: Nov 3, 2009

Introduction

Heterotopic ossification was originally described in 1692 by Guy Patin, the Doyen of the Faculté de Médecine de Paris. Patin described a condition he observed in children and called myositis ossificans progressiva. The next major development in the history of heterotopic ossification came in 1918 because of military injuries sustained during World War I. Dejerine and Ceillier described a condition they referred to as paraosteoarthropathy, which they observed in patients with paraplegia caused by gunshot wounds to the spinal cord.

The historical terms for heterotopic ossification have been superseded, but ectopic ossification and myositis ossificans are used interchangeably with the term heterotopic ossification. The condition may affect the bones or the joints. Three types of heterotopic ossification have been described: myositis ossificans progressiva (a rare pediatric metabolic disease whereby skeletal muscle ossifies), neurogenic heterotopic ossification (this occurs as a result of burns or neurologic injury), and traumatic heterotopic ossification (this follows injury to tissue surrounding the bones and joints). Traumatic heterotopic ossification is the focus of this article.

Alternatively, pathologic bone formation surrounding the bones and joints can be defined histologically. Heterotopic ossification is the formation of mature lamellar bone in nonosseous tissue, whereas myositis ossificans is a specific type of heterotopic ossification that occurs in inflammatory muscle. Both of these processes are examples of ectopic ossification, and they may coexist, although they are distinct from periarticular calcification, which is the deposition of pyrophosphates within the soft tissues surrounding the joints.

Recent studies

Pakos et al evaluated the efficacy of combined radiotherapy and indomethacin, as compared to indomethacin alone, for prevention of heterotopic ossification after hip arthroplasty in 96 patients, who received either a single dose of postoperative radiotherapy of 7.0 Gy and indomethacin for the first 15 postoperative days or indomethacin alone for the same period. A historical group of 50 patients who received indomethacin alone served as the control group. Four patients in the combined-therapy group developed heterotopic ossification, as compared with 13 patients in the indomethacin group and 13 patients in the control group. One patient in the combined-therapy group and one in the control group developed Brooker III heterotopic ossification. Duration of surgery and congenital hip disease were associated with heterotopic ossification development in the indomethacin groups; in the combined-therapy group, age and congenital hip disease were associated with heterotopic ossification.¹

Bal et al examined the incidence of heterotopic ossification in 121 patients who underwent total hip arthroplasties performed with a minimally invasive, 2-incision technique. Of the 121 patients, 32 (26.5%) developed heterotopic ossification, as follows: Brooker I, 16 patients; Brooker II, 9 patients; Brooker III, 6 patients; and Brooker IV, 1 patient.²

Frequency

Traumatic heterotopic ossification occurs in 10-20% of predisposed patients. Following total hip arthroplasty and acetabular fracture surgery, the incidence can be 2-63%. Heterotopic ossification does not seem to readily complicate nonoperative treatment of acetabular fractures, as case series only report this complication in surgically treated cases. Implant-related series have shown an incidence of 8-90% following cementless total hip arthroplasty, although many of the cases are asymptomatic. For distal humeral fractures and proximal humeral arthroplasty, the incidence can be 10-90%.

The incidence is the same in case series from the United States and Europe. Following total knee arthroplasty, the incidence of heterotopic ossification can be as high as 32%. In revision total knee arthroplasty, the incidence can be as high as 56%.

Some case series have suggested that heterotopic ossification that occurs as a complication of total hip arthroplasty tends to affect men more often than women (perhaps as much as a 3:1 male-to-female ratio), and it is more likely to occur if osteophytosis was a feature of the underlying degenerative joint disease. Other case series have shown that although men tend to be affected more often than women, women with heterotopic ossification experience more pronounced symptoms.

Etiology

The etiology is, to some extent, determined by the type of heterotopic ossification. The rare autosomal dominant condition myositis ossificans progressiva accounts for the inherited metabolic disease in children. Neurogenic heterotopic ossification may occur after head injury, spinal cord injury, infections of the central nervous system such as tetanus and polio, central nervous system tumors, multiple sclerosis, and cerebrovascular accidents. Traumatic heterotopic ossification, the main topic of this article, can be caused by trauma, iatrogenic or otherwise, to bones and joints.

The etiology of traumatic heterotopic ossification remains uncertain. During the past 50 years, a number of theories have been developed. Migrated bone marrow cells have been suggested as a potential cause of osteogenesis in connective tissue. Alternatively, muscle lesions or interstitial hemorrhagic foci have been suggested as a potential cause of muscle degeneration, perivascular connective tissue proliferation, and subsequent bone metaplasia. A further theory has considered that periosteal damage could induce a differentiation of periarticular osteogenic cells. However, various models exist, and it is thought that 3 conditions must be met for heterotopic ossification to develop:

• Osteogenic precursor cells must be present.
• An inductive stimulus should exist.
• The local tissue environment should be favorable. The osteogenic precursor cells are thought to be pluripotential mesenchymal cells that are stimulated to differentiate into osteoblasts.

Pathophysiology

Because the etiology is not entirely understood, it is not surprising that the pathophysiology is also not completely understood. Once the osteogenic cells are stimulated, they begin to form osteoid, which in turn develops into mature heterotopic ossification. The underlying process is thought to be an inflammatory process in response to local tissue trauma. Bone morphogenic protein is believed to be important in regulating the development of heterotopic ossification. The heterotopic bone is known to be metabolically very active and contains more osteoblasts than ordinary bone. In addition, the tissue does not follow anatomic tissue planes and is generally more diffuse in nature than normal bone. The presence of the heterotopic ossification surrounding the bones and joints may affect the function of the normal soft tissues around them. Cases of heterotopic ossification causing ankylosis have been reported.

Presentation

Following arthroplasty, heterotopic ossification can be noted in 1 of 2 ways: the condition can be a cause of physical symptoms, notably pain and stiffness, or it may be entirely asymptomatic and detected radiologically on follow-up films.

If a person has symptomatic heterotopic ossification, he or she may present with a loss in the range of movement in the affected joint. This may coexist with pain and soft-tissue swelling. As such, differential diagnoses of this clinical picture would include the following:

• Trauma to the soft tissue or fracture
• Infective or inflammatory processes, such as cellulitis, erysipelas, thrombophlebitis, septic arthritis, and osteomyelitis
• Allergy to implanted material
• Neoplasia of local soft tissue or bone
• Vascular or blood-related conditions such as wound hematoma or deep vein thrombosis

Indications

Heterotopic ossification is seldom excised, because pain relief is often inadequate and improvement in range of motion may not last. In established cases of heterotopic ossification following total hip arthroplasty, excision may be performed. The results of this procedure are varied. Patients may find that their range of movement improves, but pain relief is likely to be limited.

Following trauma to the elbow, surgical excision may be indicated based on pain, nerve entrapment, and stiffness. In such procedures, the surgery may be beneficial as associated contractures are released, and their release can be as important as removal of the heterotopic ossification. The timing of surgery is controversial. Heterotopic ossification is often thought to take approximately 12 months to mature; however, surgery on posttraumatic heterotopic ossification at the elbow has been performed effectively at 3 and 6 months post trauma.

The pearls for surgery are the following:

• Handle tissue carefully.
• Avoid excess bleeding.
• Achieve good hemostasis.
• Beware of lesions that span internervous tissue planes.

Relevant Anatomy

Operating on heterotopic ossification is difficult and thus seldom performed, because pain relief is poor and improvements in the range of movement may not be sustained. The removal of heterotopic bone is technically difficult because the abnormal bone does not confine itself to the normal tissue planes. Furthermore, normal anatomic landmarks may be obscured. Consequently, to visualize the heterotopic ossification to excise it, an extensile surgical exposure is required. The heterotopic ossification itself is typically fragile and friable and not readily removed from the soft tissues; it is embedded and blended into the soft tissues. Surgical removal may involve substantial blood loss and incomplete excision, and the risks of recurrence are high. Surgeons attempting the procedure need to be familiar with the relevant surgical approaches to the affected region and how to safely enlarge and extend the wounds.

Contraindications

As heterotopic ossification is seldom excised, a definitive list of surgical contraindications has not been established. However, excision should not be performed before the heterotopic ossification has matured, because incomplete and inadequate excision may result. Surgery on a joint that has wound sepsis or deep sepsis is contraindicated because the outcome is likely to be suboptimal. Because the outcome of surgery is unpredictable, the indications need to be considered carefully. Pain relief cannot be predicted reliably following excision of heterotopic ossification as a complication of total hip arthroplasty, whereas better results for improved range-of-movement arcs are more likely.

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