The many faces of sequestra/ involucrum formation

Puncture wounds are common with horses running together in a common pasture with the possibility of puncture wounds and secondary sequestrum formation. This presentation shows the variation in radiographic appearance of these lesions.

The sequestrum is small with minimal involucrum formation. Probably an early lesion, perhaps 10-14 days duration since the trauma

The sequestrum (black arrow) is rather long and easily identified as it maintains opacity. The involucrum (white arrow) is not as mature in appearance as suggested by the lack of opacity and creates a rather large cavity.

An older, more mature lesion has a persistent sequestrum with a well formed involucrum. The sequestrum is relatively small suggesting removal of bone tissue at the time of maturation of the involucrum. The two images on the right are post operative. The lesion is certainly more than 14 days duration.

Another example of a more chronic lesion the distal metacarpal bone with a dense involucrum with a sharply identified cavity. The sequestrum is not identified in this yearling. A lesion of this appearance must be long standing although the mature appearance of the lesion may be influenced by the young age of the patient.

A different appearance to the sequestrum because of the larger size and only early development of the involucrum. The persistent opacity in the sequestrum is easily noted. The separation of the sequestrum from the underlying bone does not appear as a traumatic fracture.

Summary

Factors that influence the radiographic appearance of the sequestrum/involucrum with time.

• Age of patient
  • Presence of overlying soft tissue
  • Nature of periosteum around bone
• The bone affected
• The cortical bone comprising the sequestrum sharp margination retains opacity and
• Size of the original injury
  • The comparison of the size of the sequestrum with the size ofthe involucrum certainly suggests removal of bone tissue from the sequestrum following re-establishment of a blood supply tothe previously avascular bone fragment. The manner of this repair probably greatly influences thepathophysiology of repair of the lesion.
  • The manner of this repair probably greatly influences thepathophysiology of repair of the lesion.

Comments

• The comments on age of the lesions are based primarilyon my observations of the behavior of injured bonetissue from different etiologies and are nothing morethan assumptions. Their value is probably just toappreciate a different radiographic appearance under different circumstances one being the age of the lesion.
• The immature patient probably loses its periostealattachment and suffers infarction within the cortical bone earlier than the older patient and shows a morerapid change in appearance.
• The behavior of the sequestrum and thus itsradiographic appearance resulting from separation of afragment of fractured bone is assumed to be influencedby a number of different factors.
• Unfortunately, these patients rarely have a history of thetime of the injury and are usually not followed clinicallybecause of successful surgical treatment.