- Along the dorsomedial margin of the proximal diaphysis of the metatarsus, a medium-sized well-defined, irregular marginated and amorphous osseous fragment is identified. This osseous fragment is mildly more mineral opaque than the adjacent cortical bone. Along the cortical margins, a small amount of smoothly marginated periosteal proliferation is also identified. Additionally, this osseous fragment is surrounded by a well-defined lucent region with peripheral sclerosis. The overlying soft tissues are moderately thickened with associated bulging the cutaneous margins.
Conclusions:
- Right proximal diaphyseal metatarsal sequestrum formation with moderate regional cellulitis secondary to the reported open wound/laceration.
Follow-up:
- The sequestrum was surgically removed.
- The wound subsequently healed as expected.
A little bit more…
- Sequestrum formation in horses is a common complication following trauma or injury to the metacarpal (MC) or metatarsal (MT) bones. These bones are particularly vulnerable due to their minimal soft tissue coverage, which offers little protection against external forces (Butler et al., Moens et al.).
- Pathophysiology
- When the outer surface of the bone is damaged—often due to blunt trauma or penetrating wounds—the periosteal blood supply can be disrupted. This loss of vascular support leads to necrosis of the outer third of the cortical bone, resulting in the formation of a sequestrum, which is a segment of dead bone that becomes separated from healthy tissue (Butler et al., Moens et al.).
- Radiographic Timeline and Features
- Initial signs of bone inflammation (osteitis) are typically not visible on radiographs until 7–10 days post-injury.
- A sequestrum becomes radiographically apparent as a distinct, dense (sclerotic) bone fragment usually within 3–4 weeks.
- Surrounding the sequestrum is a radiolucent zone, which represents granulation tissue or purulent material.
- The involucrum is the thickened, sclerotic bone that forms around the sequestrum as the body attempts to wall off the infection.
- A cloaca may develop, which is a draining tract that allows pus or necrotic material to escape to the surface.
- The appearance of a sequestrum on radiographs can vary significantly depending on the angle of the x-ray beam. Therefore, using multiple oblique views is often necessary to accurately identify and assess the extent of the lesion (Butler et al.).
- Sequestrectomy: This is the surgical removal of the sequestrum. It is the most effective and commonly recommended treatment once the dead bone is clearly demarcated (Clem et al.).
- The procedure may be done under general anesthesia or in a standing, sedated horse, depending on the location and size of the lesion.
- Debridement of the surrounding infected or necrotic tissue is also performed to promote healing
References:
- Moens Y, Verschooten F, Moor D, Wouters L. Bone sequestration as a consequence of limb wounds in the horse. Veterinary Radiology. 1980 Jan;21(1):40-4.
- Clem MF, DeBowes RM, Yovich JV, Douglass JP, Bennett SM. Osseous sequestration in the horse a review of 68 cases. Veterinary Surgery. 1988 Jan;17(1):2-5.
- Butler JA, Colles CM, Dyson SJ, Kold SE, Poulos PW. Clinical radiology of the horse. John Wiley & Sons; 2017 Mar 13.
