HARD knocks

Bone bruises present in different ways, and can require lengthy healing time with variable prognoses. Thijs de Bont MRCVS explains

- Thijs de Bont

BONE bruising, also referred to as bone oedema or bone contusion, is a descriptive term used for a traumatic type of bone injury.

It is diagnosed primarily by magnetic resonance imaging (MRI). The finding is characterised by a high fluid (bright) signal on a specific sequence of images taken during the scan – short tau inversion recovery (STIR) sequence. This sequence suppresses the bright fat signal normally found within the bone marrow and allows the signal from the bone bruise to be identified.

Bone bruising indicates microscopic damage to the bone, and although not as dramatic as a fracture, it can be a precursor to fracture and can be identified together with a stress fracture. For simplicity, bruising is characterised by localised bleeding and a build-up of fluid within the external framework of the bone, causing pain.

In horses it is most often found as a source of lower-limb lameness, primarily associated with the fetlock, distal phalanges (long pastern, short pastern and coffin bone) and the navicular bone. This can be attributed to the small surface area and increased loading forces that occur through the lower limb during exercise.

The region primarily affected is a layer of important bone adjacent to the cartilage surface of a joint, known as subchondral bone.

Bone bruising can be caused either by repetitive trauma following consistent strenuous exercise or following a single isolated traumatic impact. It is less associated with a kick or an external trauma, but rather an internal bone overload such as landing awkwardly after a jump.