French horse Male castrated 8 years of age presented with a history of chronic lameness 2/5 localised in the fetlock hind left radiographs of the hind left fetlock were taken. Radiographic examination Dorsoplantar (left), its close up (middle) and lateromedial (right) view of the hind left fetlock. Radiographic findings
- Soft tissues are normal.
- There is a subjective moderate thickening and sclerosis of the subchondral bone of P1 (arrows).
- There is a short and thin V shaped lucency in the subchondral bone of P1 at the level of the sagittal groove (arrowhead).
Close up of the dorsoplantar view of the hind left fetlock Radiographic diagnosis The radiographic diagnosis is: Sagittal chronic short articular fissure of P1 hind left. For a better evaluation of the region the horse underwent a CT examination before surgical approach. Close up of the multiplanar reconstruction (MPR) of the CT study, bone algorithm. Dorsopalmar view (left and middle image, the left in the dorsal part of the fetlock joint and the middle image more plantar) and sagittal view at the level of the sagittal groove. The lucent line visible on radiographs is more obvious (arrow). More plantar, a hypodense region within the subchondral bone is visible (empty arrow) with connection to the fissure line and the joint space. On the sagittal plane, the subchondral bone in this area is ill defined, mild flattened and hypodense compared to the most dorsal part (arrowheads). The radiographic diagnosis is sagittal chronic short fetlock fissure with subchondral cyst like lesion. Considering that the disease can be bilateral the contralateral limb was also previously radiographed and then scanned. Findings on the hind right fetlock were similar to the left and more severe. Front fetlocks were normal. Close up of the dorsoplantar view and MPR of the CT scan of the hind right fetlock joint. Similar and more severe findings than the contralateral are visible A surgical approach was elected. Post OP radiographs were taken. Post OP dorsoplantar and mediolateral view of the hind left fetlock. The right one was fixed in a similar way (not shown). Comments
- Subchondral bone cyst or defect can be induced by trauma to cartilage or can be a manifestation of osteochondrosis.
- Radiologically detectable osseous cyst-like lesions have been described in association with incomplete fractures of the proximal aspect of the proximal phalanx mainly in sport horses.
- It is possible that there is a continuum of injury, ranging from stress-related injury of the subchondral bone and/or full thickness cartilage defect extending into the subchondral bone to overt fracture.
- Most commonly, in cases with concomitant occurrence of an osseous cyst-like lesion and a fracture, the cyst-like lesion exists first representing site of decreased strength, subsequently leading to cavitation of the bone, eventually predisposing to further damage, e.g. a fracture (Scott et al. 1991).
- However, the opposite has also been reported (Yovich and Stashak 1989; Kuemmerle et al. 2008): an osseous cyst- like lesion may develop from a pre-existing intra-articular fracture, suggesting that synovial fluid, forced through articular cartilage defects, can produce a subchondral cyst.
