Introduction

• Cause: direct trauma - kick, hitting fence while jumping.
• Signs: acute moderate → severe hindlimb lameness Musculoskeletal: gait evaluation, stifle effusion, crepitus, soft tissue injury and swelling.
• Diagnosis: radiography Hindlimb: radiography, intrasynovial anesthesia Hindlimb: joint anesthesia, arthroscopy Joint: arthroscopy - overview, ultrasonography Ultrasonography: musculoskeletal.
• Treatment: conservative, surgery - partial patellectomy or reduction and screw fixation.
• Prognosis: good for conservative management of non-displaced fractures or surgical management; poor if conservative management of displaced fractures or where concurrent degenerative joint disease Musculoskeletal: osteoarthritis (joint disease).

Pathogenesis

Etiology

• Usually, the consequence of direct trauma including kicks or impact from hitting a hard object during jumping.

Predisposing factors

General

• Eventing.
• Hunting.

Specific

• Direct trauma to cranial stifle region.

Pathophysiology

• Jumping fence → stifle fully flexed, patella held against femoral trochlea → direct trauma, eg stifle strikes fence → fracture of patella Musculoskeletal: fracture.
• Most common fracture after this incident is a parasagittal fracture of the medial part of the patella. Possibly related to the more prominent medial trochlear ridge of the distal femur cleaving off the medial side of the patella. The fracture line may occur anywhere from the midline medially, but smaller more medial fragments are the most common.
• Transverse fractures are much less common and arise from direct trauma plus increased tension through the quadriceps apparatus at the time of impact – stifle partially flexed. They are usually horizontal and in the middle of the patella. These fractures are more likely to distract.
• Chip fractures are also uncommon but are usually due to direct trauma. They can be medial, lateral, or proximal.
• Distal osteochondral patellar fragmentation may be a degenerative disorder rather than a direct fracture and has been most regularly recognized as a consequence of medial patellar desmotomy Medial patellar ligament: desmotomy.
• All fractures can trigger off osteoarthritis of the femoropatellar joint if inadequately treated Musculoskeletal: osteoarthritis (joint disease).

Timecourse

• Acute - for direct trauma.
• Chronic - for degenerative joint disease post-undiagnosed or untreated fracture.

Diagnosis

Treatment

Outcomes