Patellar fracture is one of the common knee injuries usually post direct trauma to the patella or sudden forceful contraction of the quadriceps muscles in the context of a sports injury.
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Epidemiology
Fractures of the patella represent ~1% of all fractures and are most common in those aged 20-50 years. Two-thirds of cases are in males 7.
Clinical presentation
Patients present with marked swelling and pain over the patella with point tenderness and marked reduction in extension strength. Usually, there is a large joint effusion or hemarthrosis.
Complications
- stiffness
- weak extensor mechanism
- degenerative disease of the patellofemoral joint
Pathology
Etiology
There are different causes of patella fracture:
- direct blow to the patella, e.g. dashboard injury (high energy) or fall onto the patella (low energy)
- severe forces by the extensor mechanism
- after anterior cruciate ligament reconstruction
- after total knee reconstruction
- pathological fracture
In practice, often both direct and indirect mechanisms are important, e.g. a direct trauma coupled with a forceful contraction of the quadriceps 7.
Morphology
- transverse fracture of mid patella (most common)
- comminuted fracture
- vertical fracture (least common)
- osteochondral defect usually from medial facet
- patellar sleeve fracture in children
Some fractures are more subtle and need to be differentiated from normal variants.
Treatment and prognosis
Treatment is determined by the amount of displacement of the fracture and whether the extensor mechanism of the knee is intact or disrupted.
For patients with a nondisplaced or minimally displaced fracture and an intact extensor mechanism, nonoperative treatment may be suitable. This usually involved a Zimmer knee splint for 4-6 weeks. The patient is usually allowed to weight bear in the splint during this period 6.
In the case of displaced fractures or disrupted extensor mechanism, surgical management is usually required 6. The surgical treatment of these fractures usually involves tension band wiring (K wire technique).
Differential diagnosis
The main differential is of multipartite patella, where there is a failure of fusion of secondary ossification centers. The unfused fragments are almost always in the superolateral quadrant of the patella. With a multipartite patella, the volume of the true patella plus that of the smaller ossification centers is greater than that expected of a normal patella. With a patellar fracture, the volume of the fractured components is equivalent to that of a normal patella.
Rarely a traumatic separation of a multipartite patella may occur 7.
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