Heterotopic Ossification in Unidentified Skeletal Remains

DiMaio, Vincent J. M. M.D.; Francis, Jeffrey R. M.A.

American Journal of Forensic Medicine & Pathology: June 2001 - Volume 22 - Issue 2 - pp 160-164

Heterotopic ossification is a benign, ectopic bone growth that develops in muscle and other soft tissue. The exact cause is poorly understood, but it is a rarely serious complication of soft tissue trauma. Its most common form, myositis ossifications traumatica, occurs as a secondary complication of direct muscle injury. However, other forms are less common and can result from specific pathologic conditions, such as spinal cord trauma and metabolic disorders. In patients who have had spinal cord injury and subsequent paraplegia, heterotopic ossification often results in ankylosis of the hip and a loss in range of motion. Ectopic ossification occurs below the injury site, and, although the specific muscle groups can vary, it usually involves those for which the origin and insertion involve the anterior pelvis and proximal femur. In dried bone, heterotopic ossification can appear as a smooth, irregularly shaped benign tumor of mature bone, extending from the surface but not invading the cortical bone. These tumors range in size from a few millimeters to several centimeters. Because heterotopic ossification is often associated with specific types of injuries, it has a unique anthropological use in forensic cases.

From the Bexar County Forensic Science Center, San Antonio, Texas, U.S.A.

Manuscript received August 4, 2000; accepted August 22, 2000.

Address correspondence and reprint requests to Jeffrey R. Francis, M.A., 7337 Louis Pasteur, San Antonio, TX 78229, U.S.A.; email: jfrancis@co.bexar.tx.us.

Article Outline

The presence of pathologic conditions in unidentified skeletal remains greatly enhances the standard biologic profile developed by the medical examiner or forensic anthropologist. Evidence of fractures or disease tends to individualize the characteristics of an unidentified victim and can increase the chances of obtaining a positive identification. Pathologic conditions, such as heterotopic ossification, can provide clues to how people lived and events in their life history and ultimately can lead to their identification. Heterotopic ossification can occur as a metabolic disorder secondary either to direct soft tissue injury or to spinal cord injury. In paraplegics who have had spinal cord trauma, heterotopic ossification and ankylosis of the hip is a common complication. Generally speaking, the location of the ectopic bone can provide information as to the nature of the insult. This case study describes an individual with extensive heterotopic ossification of the pelvis and femora, which, in the absence of other pathologic conditions, contributed significant information to his biologic profile.

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Human skeletal remains were found partially buried in a shallow grave in a rural county in southwest Texas. Examination suggested they were that of a white male about 5′5″ to 6′ tall and 50 to 60 years of age with several pathologic conditions, including lower thoracic spinal reconstructive surgery, which suggested a history of trauma with subsequent paraplegia. In addition, there were several malformations of the skeletal tissue, including a 10- × 6- × 6.5-cm area of exostosis of the medial aspect of the proximal left femur, extending below the neck from the base of the greater trochanter and involving the entire lesser trochanter. The ossified tissue extended from the surface of the cortical bone without involvement. The right femur showed essentially the same pattern of bony exostosis, approximately 12- × 6- × 8-cm in size.

The right half of the pelvis showed some fenestration, with bony exostosis in the area of the anterior superior iliac spine that extended to the cavity of the body of the ilium. This area measured 9 × 6 × 6 cm. There was a healing 6-× 2-cm surgical defect of the iliac crest. The left half of the pelvis showed a 9- × 4- × 4-cm area of bony exostosis in the same general area as described for the right pelvis. The 10th, 11th, and 12th thoracic vertebrae and the 1st and 2nd lumbar vertebrae were held together by two steel rods on the posterior surface of the vertebral arch. There was ankylosis of the posterior and lateral aspects of the 10th thoracic vertebrae through the 2nd lumbar vertebra. The 12th thoracic vertebra was surgically resected anteriorly and on its side. The rest of the vertebrae, including the sacrum and coccyx, were unremarkable. There was a proliferation of bone on the posterior aspect of the medial end of the left clavicle. There was a complete fracture of the distal left tibia, with evidence of healing and fusion of the site to the fibula. The cause of death was undetermined; the manner of death was homicide.

A description of the decedent was provided to police investigators, and missing persons bulletin was issued to law enforcement agencies in Texas. In addition, medical examiner investigators began a search of the manufacture’s stamp and serial numbers on the prosthetic device in an effort to locate and contact the manufacturer. The stamp consisted of a lower case d inside an oval, which is the trademark of the Cotrel-Dubousset/CD Instrumentation Co. A local representative of the company was given the lot and serial numbers from the device and requested to furnish a list of the hospitals that had received these items in the past 5 years.

Within several days (after release of the missing persons bulletin) investigators were contacted by the police department at a local veterans’ hospital. The hospital investigator was following up on a missing persons report that involved an orthopedics patient discharged from the hospital in July 1994. The patient was scheduled for a follow-up appointment several weeks later but never returned; since then he had been missing from his family. The missing patient was a paraplegic with a history of vertebral reconstructive surgery. This information was relayed to the medical examiner along with antemortem medical records and radiograph films. A positive identification was made comparing antemortem and postmortem radiographs of the vertebral trauma and prosthesis. A review of the patient’s medical history showed that he had been involved in a motor vehicle accident and had sustained several serious injuries, including fractured lower thoracic vertebrae. Several entries in the medical records indicated that he had not complied with his physical therapy regimen. A progressive series of radiology reports, extending for several years since the onset of injury, showed the development of heterotopic bone in the areas described above.

After making a positive identification, the investigation revealed that the decedent and a fellow patient had left the hospital together and were to travel out of the state. About 6 weeks after their discharge, the decedent’s traveling companion was found dead within the city limits. The manner of death was homicide; the cause of death was undetermined. Nearly 1½ years later, the skeletal remains of the second victim were discovered in a shallow grave almost 130 miles away from the hospital from which he was discharged.

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Specific forms of heterotopic ossification, such as myositis ossificans, can provide additional information to the biologic and behavioral characteristics of an unidentified victim. Clinically, it is a benign osseous formation that involves muscles, tendons, and occasionally subcutaneous fat. According to Enzinger and Weiss (4), cases involving subcutaneous fat (panniculitis ossificans) occur more frequently in the hands and fingers of women, although these authors provide no cause for this prevalence among females. Heterotopic bone is usually well defined and can be located anywhere within the muscle; however, it is most often contiguous to bone and appears at the site of muscle insertion or origin. Although an associated periosteal reaction also may occur, heterotopic ossification rarely, if ever, invades the cortical bone. Ectopic bone can range in size from a few millimeters to several centimeters in diameter and is considered self-limiting, a diagnostic characteristic that differentiates it from a malignant tumor. In dried bone, it has a smooth thin outer cortex with an interior of well-developed trabecular bone. Often, the tumor has an odd shape, somewhat depicting its soft tissue origin. There are three subsets of myositis ossificans, each having a different cause and generally defined as either traumatic or nontraumatic in origin. These three subsets are defined as follows.

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Myositis Ossificans Progressiva

This is a rare, congenital, metabolic disorder that results in the heterotopic ossification of the major muscle groups. It develops in early childhood and usually results in the premature death of the individual (11).

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Myositis Ossificans Traumatica

This is nonneoplastic heterotopic bone that forms from a hemorrhagic site, following a single or multiple episodes of localized trauma. It also may be associated with spinal trauma, burns, neuromuscular damage, or chronic neuromuscular disease.

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Myositis Ossificans (Without History of Trauma)

This is the spontaneous formation of heterotopic bone in otherwise healthy individuals.

Although other forms of heterotopic ossification can occur without a behavioral correlate, these are typically rare. Most cases develop as myositis ossificans traumatica and involve either athletes involved in contact sports or individuals involved in an activity in which there is a potential risk of soft tissue injury (1,2,7,9,10,14,17). Heterotopic ossification also occurs frequently in individuals who have had spinal cord trauma and subsequent paraplegia (5,6,9,12–16). This case study focuses on the anthropologic use of heterotopic ossification, specifically myositis ossificans traumatica, as an identifying characteristic in unidentified skeletal remains.

Myositis ossificans traumatica is commonly associated with soft tissue injuries resulting from a single major soft tissue injury or repeated minor injuries (7). After injury, the site becomes organized by granulation and fibrous tissue with fibroblastic cells from the endomysium (10). Although no osseous tissue is formed in the early phase of growth, mature bone can form in as fast as 1 or 2 weeks but usually not before about 3 weeks after the initial insult (3,4). Osseus tissue forms through endochondral ossification and, within 3 to 8 weeks, becomes mature bone with a thin cortex and trabecular region. Myositis ossificans tends to form in muscle tissue in close proximity to bone but can be found anywhere in the muscle or other tissue (2). The most common sites for myositis ossificans are the anterior thigh (quadriceps femoris), buttocks, elbow, and anterior upper arm (brachialis muscle). Other sites include the masseter muscle, lower leg, ankle, and foot (10). Although myositis ossificans traumatica is more commonly found among individuals who lead an active lifestyle, it also can be found in paraplegics who have had spinal cord trauma.

In paraplegics, myositis ossificans traumatica can develop in isolation either as the result of an unrealized focal injury to the soft tissue or as a secondary complication of spinal cord or neuromuscular injury (1,5,6,12–16). The latter is more properly termed heterotopic ossification because its cause is somewhat different than ossification resulting from direct traumatic insult. Heterotopic ossification of the hip is a well-known complication of spinal cord injuries, with an incidence of from 10% to 25%(13). Ossification occurs below the level of the injury and develops radiographically in 3% to 5% of patients, 1 to 18 months after the injury (13,14). The principal sites are the anterior pelvis and the adductor muscles of the thigh (6). About one third of these result in a reduced range of motion for the patient (15,16). Wharton (15,16) describes the position of wheelchair-bound patients with extensive heterotopic ossification and a loss in range of motion as a reclining sitting position. Often, ankylosis and fracture, without evidence of healing callus, can occur in the ectopic bone (8). The location and extent of ossification appear to be the diagnostic features of this condition among paraplegics versus cases involving direct focal trauma. However, not all cases of heterotopic ossification secondary to spinal cord trauma result in bilateral tumors (5).

Heterotopic ossification and myositis ossificans traumatica can be used either to provide additional information to the biologic and behavioral characteristics of an unidentified individual or as an identifying characteristic to tentatively identified skeletal remains. Because soft tissue tumors rarely go unnoticed in patients in a clinical setting, it is likely that a record of medical treatment will exist, the size and location of the tumor being the primary factor in whether the victim sought medical attention. Most clinical literature reports that patients felt localized pain or noticed a loss in range of motion before they sought medical attention.

If heterotopic ossification is present in an unidentified victim, the location of the affected muscle group may suggest the kind of stress or behavior that would have resulted in the formation of the tumor. For example, professional or avocational horse riders have developed local ossification in the adductors of the thigh, a condition sometimes known as rider’s bone(7). Ossification in the deltoid or pectoralis minor is common among hunters or people who frequently shoot high-powered rifles (7). In cases involving the femur, Young et al. (17) suggest dividing the thigh into anatomic compartments to assist in both differential diagnosis and determination of the pathomechanics that led to the injury. Extensive heterotopic ossification of the anterior pelvis and proximal femora would tend to suggest a history of spinal cord injury and paraplegia. Although this would be a potential and likely diagnosis even in the absence of spinal trauma, its presence should not be used strictly as an exclusionary criterion. Other evidence, such as cortical bone atrophy and lack or loss of muscular development, should also be taken into consideration. The unique shape or site of the tumor will also allow for a positive identification based on radiographic comparison in the absence of other more traditional criteria.

The unidentified victim in this case had bilateral heterotopic ossification involving the iliacus muscle, which originates from the upper two thirds of the iliac fossa and inserts with the psoas muscle inferior and anterior to the lesser trochanter (Figs. 1 and 2). Although the specific muscle groups may vary, the musculature of the anterior pelvis and proximal femur are the typical sites for heterotopic ossification in paraplegics. When the skeletal remains arrived at the medical examiner’s office, the femora and pelvis were separate, but there was clear evidence that ankylosis had been present and that perimortem fractures in the ectopic bone had caused the pelvis and femora to separate (Fig. 3). The fractured ends fit together by rotating the femur anteriorly by 90° to the pelvis. Ankylosis in the ectopic bone between the pelvis and femur would have caused the bones to be fixed in a flexed sitting position.

Although evidence of obvious vertebral trauma was present at examination, this is not always the case. Thorough recovery of skeletal remains is often the exception rather then the rule. In the absence of surgically or pathologically altered vertebrae, the presence and location of the heterotopic ossification would have provided significant information about the victim’s physical condition and could have been used as criteria to a positive identification.

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An unidentified individual with heterotopic ossification in the musculature of the pelvis and femora was discovered in a shallow grave. Although vertebrae recovered from the scene suggested a history of paraplegia, the presence and location of the heterotopic ossification, in the absence of other evidence, could have been used to provide significant information about the decedent’s medical history. Heterotopic ossification is a benign, ectopic bone growth that results from either neuromuscular damage or direct trauma. It has a high frequency in paraplegics with spinal cord damage and tends to occur at specific sites in the femora and anterior musculature of the pelvis. The location of this ectopic ossification can be used as a diagnostic feature in the absence of obvious vertebral trauma. In addition, heterotopic ossification can provide additional descriptive information about an unidentified victim, add support to a tentative identification, or be used to make a positive identification in the absence of more traditional criteria.

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Forensic anthropology; Heterotopic ossification; Myositis ossificans; Paraplegia

© 2001 Lippincott Williams & Wilkins, Inc.