The Journal of Bone and Joint Surgery 81:1429-33 (1999)
© 1999 The Journal of Bone and Joint Surgery, Inc.
The Posterior Fat Pad Sign in Association with Occult Fracture of the Elbow in Children*
DAVID L. SKAGGS, M.D. and
RAFFY MIRZAYAN, M.D. , LOS ANGELES, CALIFORNIA
Investigation performed at the Division of Pediatric Orthopaedic Surgery, Children's Hospital of Los Angeles, and the University of Southern California School of Medicine, Los Angeles
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Abstract
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Background: An elevated posterior fat pad visible on a lateral radiograph of a child's elbow following trauma is generally considered to be suggestive of an intracapsular fracture about the elbow. However, in previous studies, the prevalence of fracture in elbows with an elevated posterior fat pad and no other radiographic evidence of fracture has ranged from only 6 percent (two of thirty-one) to 29 percent (nine of thirty-one). We are not aware of any prospective studies, limited to children, on the value of an elevated posterior fat pad as an indicator of an occult fracture about the elbow. While it is common practice to manage children who have radiographic evidence of an elevated posterior fat pad as if they have a fracture, scientific evidence for this approach is lacking.
Methods: Forty-five consecutive children who had an average age of four and a half years, a history of trauma to the elbow, and an elevated posterior fat pad without other radiographic evidence of a fracture were enrolled in the study. At an average of three weeks after the injury, anteroposterior, lateral, and two oblique radiographs were made and evaluated for evidence of fracture-healing. If there was evidence of new-bone formation on any of these four radiographs, it was considered to indicate a fracture of the elbow.
Results: Thirty-four (76 percent) of the forty-five patients had evidence of a fracture. Eighteen (53 percent) of the thirty-four had a supracondylar fracture of the humerus; nine (26 percent), a fracture of the proximal part of the ulna; four (12 percent), a fracture of the lateral condyle; and three (9 percent), a fracture of the radial neck.
Conclusions: This prospective study demonstrated that the posterior fat pad sign was predictive of an occult fracture of the elbow following trauma in thirty-four (76 percent) of forty-five children who had no other evidence of fracture on anteroposterior, lateral, and oblique radiographs after the injury. This finding is in contrast to those of previous studies, in which the highest prevalence of fracture in elbows with an elevated posterior fat pad and no other radiographic evidence of fracture was 29 percent (nine of thirty-one elbows). Our results support the practice of managing children who have a history of trauma to the elbow, an elevated posterior fat pad, and no other radiographic evidence of fracture as if they have a nondisplaced fracture about the elbow.
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Introduction
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The posterior fat pad sign was first described by Norell8 in 1954. The anatomical basis of his findings, as well as those of others1,5,10, was that the fat pads are intracapsular but extrasynovial. The anterior fat pad normally can be seen on a standard lateral radiograph of a flexed elbow, but the posterior fat pad cannot (Fig. 1-A)1-3,5,7,8. An effusion in the elbow joint elevates both the anterior and the posterior fat pad and makes them both visible on a lateral radiograph of the elbow (Fig. 1-B). An elevated posterior fat pad after an injury to the elbow suggests the possibility of an intracapsular fracture. In previous reports, lateral radiographs have demonstrated an elevated posterior fat pad in 41 to 100 percent of elbows with an obvious intracapsular fracture (thirty-two of seventy-eight elbows in one study3 and all of 118 in another8). The reported prevalence of fracture in patients who have a visible elevated posterior fat pad but no radiographically detectable fracture has ranged from 6 percent4 (two of thirty-one) to 29 percent6 (nine of thirty-one). The value of the posterior fat pad sign depends on its ability to predict an occult fracture in the absence of a radiographically visible fracture. As far as we know, all previous studies concerning the posterior fat pad either have been retrospective or have included combined data on adults and children. To the best of our knowledge, we are reporting the first prospective study of the value of the posterior fat pad sign in the detection of occult fracture about the elbow in children.
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Fig. 1-A Illustrations of normal anterior and posterior fat pads (Fig. 1-A) and anterior and posterior fat pads elevated from an effusion (Fig. 1-B), as seen on lateral radiographs.
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Fig. 1-B Illustrations of normal anterior and posterior fat pads (Fig. 1-A) and anterior and posterior fat pads elevated from an effusion (Fig. 1-B), as seen on lateral radiographs.
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Materials and Methods
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Between October 1996 and January 1999, all children who were seen with a history of trauma to the elbow and an elevated posterior fat pad but no other radiographic evidence of a fracture were included in the study, which was approved by our institutional review board. The initial anteroposterior, lateral, and two oblique radiographs were examined by an attending pediatric radiologist and an attending physician specializing in pediatric emergency medicine who were blinded to the study as well as by an orthopaedic resident. We chose not to have an attending orthopaedic surgeon evaluate the initial radiographs, as we wished to simulate the usual situation in the emergency room. Moreover, as the attending orthopaedic staff followed these patients, we believed that allowing them to evaluate the radiographs might have introduced bias into the study. Patients were excluded from the study if any one of the three examiners noted a fracture on the radiographs.
An above-the-elbow cast was applied in the emergency room with the elbow flexed. At three weeks, anteroposterior, lateral, and oblique radiographs were made with the limb out of the plaster cast and were evaluated for signs of fracture-healing, such as callus formation or periosteal elevation, or both.
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Results
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Forty-five children (thirty-one boys and fourteen girls) were enrolled in the study. The average age was four and a half years (range, one year and four months to seven years and nine months). The average time between the injury and the visit to the emergency room was 0.4 day (range, zero to two days). Follow-up radiographs were made at an average of twenty days (range, eight to thirty-seven days) after the injury, and they revealed evidence of a fracture in thirty-four (76 percent) of the forty-five patients. Eighteen (53 percent) of the thirty-four children had a supracondylar fracture of the humerus (Figs. 2-A, 2-B, 2-C and 2-D); nine (26 percent), a fracture of the proximal part of the ulna; four (12 percent), a fracture of the lateral condyle; and three (9 percent), a fracture of the radial neck (Figs. 3-A, 3-B, 3-C and 3-D). The patients who did not have a fracture had the radiographic examination at an average of twenty-one and a half days (range, eighteen to thirty-five days) after the injury, and the patients who were found to have a fracture had the examination at an average of twenty days (range, eight to thirty-seven days) after the injury. No fracture was displaced at the time of follow-up.
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Figs. 2-A through 2-D: Radiographs of a boy who sustained an injury of the elbow at the age of two years and five months.
Figs. 2-A and 2-B: Anteroposterior and lateral radiographs made at the time of the injury. An elevated posterior fat pad (arrows) is seen on the lateral radiograph.
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Figs. 2-A and 2-B: Anteroposterior and lateral radiographs made at the time of the injury. An elevated posterior fat pad (arrows) is seen on the lateral radiograph.
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Fig. 2-C Anteroposterior and lateral radiographs made twenty-eight days after the injury, demonstrating periosteal callus formation (arrows) in the supracondylar aspect of the humerus.
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Fig. 2-D Anteroposterior and lateral radiographs made twenty-eight days after the injury, demonstrating periosteal callus formation (arrows) in the supracondylar aspect of the humerus.
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Figs. 3-A through 3-D: Radiographs of a girl who sustained an injury of the elbow at the age of four years and four months.
Figs. 3-A and 3-B: Anteroposterior and lateral radiographs made at the time of the injury. An elevated posterior fat pad (arrows) is seen on the lateral radiograph.
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Figs. 3-A and 3-B: Anteroposterior and lateral radiographs made at the time of the injury. An elevated posterior fat pad (arrows) is seen on the lateral radiograph.
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Figs. 3-C and 3-D: Lateral and oblique radiographs made twenty-one days after the injury, demonstrating periosteal callus formation (arrows) in the radial neck.
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Figs. 3-C and 3-D: Lateral and oblique radiographs made twenty-one days after the injury, demonstrating periosteal callus formation (arrows) in the radial neck.
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Discussion
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The posterior fat pad sign is radiographic evidence of intracapsular effusion in the elbow and is a well recognized finding in association with intracapsular fractures1,5,8. Norell8 first described the posterior fat pad sign in 1954. In his study, twelve (8 percent) of 156 intracapsular fractures about the elbow could not be identified on anteroposterior and lateral radiographs but were associated with an elevated posterior fat pad. Of these twelve fractures, ten were identified on additional radiographs made with different projections. Norell recommended that additional oblique radiographs be made when a patient has an elevated posterior fat pad without an obvious fracture. Kohn5 found the posterior fat pad sign to be visible on the radiographs of 100 (66 percent) of 151 elbows that had radiographic evidence of a fracture. Corbett3 reported a visible fat pad in thirty-two (41 percent) of seventy-eight elbows with a radiographically evident fracture.
The posterior fat pad sign is most commonly used as an indication of a possible occult fracture. In a retrospective review that included patients of all ages, Quinton et al.9 reported that only six (12 percent) of fifty-one patients who had an elevated posterior fat pad without radiographic evidence of fracture had evidence of fracture at the time of follow-up. In another retrospective study, Morewood6 showed that nine (29 percent) of thirty-one patients who initially had an isolated posterior fat pad sign actually had a fracture at the time of follow-up. The age range in that study was nine to seventy-three years, and only nine patients were less than sixteen years old. De Beaux et al.4, in a retrospective study of thirty-one elbows that initially had an effusion without an obvious fracture, reported that two (6 percent) were found to have a fracture at the time of follow-up; it was their belief that routine follow-up radiography is unnecessary.
In contrast to previous reports, we found that thirty-four (76 percent) of forty-five patients who initially had an isolated posterior fat pad sign were found to have a fracture at the time of follow-up. In most of the previous studies that we mentioned, the follow-up radiographic examinations were performed at fourteen days or earlier; this may have resulted in false-negative findings because there was not enough time for signs of fracture-healing to appear. In addition, those studies all were either retrospective or included combined data on adults and children.
No fracture in the present study showed evidence of displacement. We do not know whether less restrictive treatment, such as use of a sling or splint, or a shorter period of immobilization would have yielded equivalent results. No radiographs made at three weeks after the injury led us to alter the care of any patient, as treatment with the cast was discontinued for every child at that time. While it could be argued that follow-up radiographs at three weeks are therefore not indicated, we do not believe that the number of patients or the duration of follow-up in our study is sufficient for us to draw that conclusion.
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Footnotes
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*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.
 This paper was read in part at the American Orthopaedic Association Residents' Conference, Sacramento, California, Feb. 22, 1998, and at the Annual Meetings of the Orthopaedic Trauma Association, Vancouver, British Columbia, Oct. 7, 1998; the American Academy of Pediatrics, Orthopaedic Section, San Francisco, California, Oct. 17, 1998; the American Academy of Orthopaedic Surgeons, Anaheim, California, Feb. 5, 1999; and the Western Orthopaedic Association, San Diego, California, July 31, 1999.
Division of Pediatric Orthopaedic Surgery, Children's Hospital of Los Angeles, 4650 West Sunset Boulevard, Mailstop 69, Los Angeles, California 90027.
University of Southern California School of Medicine, 2025 Zonal Avenue, GNH 3900, Los Angeles, California 90033.
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References
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Bledsoe, R. C., and Izenstark, J. L.: Displacement of fat pads in disease and injury of the elbow. A new radiographic sign. Radiology, 73: 717-724, 1959.
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Bohrer, S. P.: The fat pad sign following elbow trauma. Its usefulness and reliability in suspecting "invisible" fractures. Clin. Radiol., 21: 90-94, 1970.[Medline]
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Corbett, R. H.: Displaced fat pads in trauma to the elbow. Injury, 9: 297-298, 1978.[Medline]
-
de Beaux, A. C.; Beattie, T.; and Gilbert, F.: Elbow fat pad sign: implications for clinical management. J. Royal Coll. Surgeons Edinburgh, 37: 205-206, 1992.[Medline]
-
Kohn, A. M.: Soft tissue alterations in elbow trauma. Am. J. Roentgenol., 82: 867-874, 1959.
-
Morewood, D. J.: Incidence of unsuspected fractures in traumatic effusions of the elbow joint. British Med. J. (Clin. Res. Ed.), 295: 109-110, 1987.
-
Murphy, W. A., and Siegel, M. J.: Elbow fat pads with new signs and extended differential diagnosis. Radiology, 124: 659-665, 1977.[Abstract]
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Norell, H.-G.: Roentgenologic visualization of the extracapsular fat. Its importance in the diagnosis of traumatic injuries to the elbow. Acta Radiol., 42: 205-210, 1954.
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Quinton, D. N.; Finlay, D.; and Butterworth, R.: The elbow fat pad sign: brief report. J. Bone and Joint Surg., 69-B(5): 844-845, 1987.
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Smith, D. N., and Lee, J. R.: The radiological diagnosis of posttraumatic effusion of the elbow joint and its clinical significance: the displaced fat pad sign. Injury, 10: 115-119, 1978.[Medline]
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Abstract
Introduction