Fractured Patella in a Horse

A teenage gelding presented for sudden non-weight bearing lameness in the right hind limb. There was a history of a "kick" from another horse but the exact location of the kick was not witnessed. On presentation, there was a basketball-size swelling centered on the stifle and the horse was very painful. He was not willing to walk on the limb. The initial radiographs were not conclusive due to the severe swelling and a follow-up exam was performed 10 days later. On presentation, the gelding was walking on the limb but was very resistant to have the limb flexed at the stifle/hock. There was minimal swelling compared to previous exam.
Figure 1 is a lateral radiograph of the patella. The yellow lines corresponds to bone fragments that are noted along the edges of the patella.

Figure 1

In order to better assess the patella, a special "sky line" projection is required and was especially difficult in this horse because he was resistant to having the stifle flexed! However, it proved to be the most important radiographic view. In  Figure 2, the patella is imaged and a distinct line can be noted traveling through the body of the patella. In Figure 3, the "line" is highlighted in red and is consistent with a complete or near-complete fracture of the patella. In Figure 4, a normal patella is imaged for comparison to the fractured patella.

Figure 2

Figure 3

The degree of fracture appears complete or near-complete which significantly worsens the prognosis. There are cases of patella fracture in horses that are described in the literature that have healed after several months of stall rest. However, there is minimal discussion regarding the future of these horses with regards to as equine athletes. The prognosis for this horse to return to work is poor and his outcome is yet to be determined.