An in-depth review of Patella Fractures.



The extensor mechanism of the knee is made up of the quadriceps muscles, quadriceps tendon, patella, patellar retinaculum, and patellar tendon.

Its function is important to assess in patellar fractures and can be assessed by an active straight leg raise.



< 40 y.o. -> Patellar tendon rupture (PTR)
> 40 y.o. -> Quadriceps tendon rupture (QTR)

The Insall-Salvati ratio can be used on lateral knee radiographs to assess patellar height.

Patients with QTR will present w/ patellar baja, while pts with PTR will present w/ patella alta.



When you suspect that a patient has a patellar fracture it is first important to rule out a bipartite patella (shown below) which occurs in 1-2% of the population.

The classification system for bipartite patella is the Saupe classification system (shown below).



Patellar fractures may occur by a direct injury or by indirect injury by forceful eccentric quadriceps contraction.

Common fracture types include transverse (seen on lateral radiograph), vertical (visualized on sunrise/ merchant views), and super/inferior pole fx.



Non-operative indications: ✯ Minimal Displacement (< 2 mm)
✯ Vertical fracture
✯ Must have intact extensor mechanism!

Initial non-op treatment includes immobilizing the knee in extension with WBAT.

Operative indications:
✯ Displacement > 2 mm
✯ Disruption of the extensor mechanism
✯ Open fracture

Surgical options depend on the fracture type and include ORIF with plate/screws, compression screws (left), and tension band construct (right).



A tension band construct is formed by the placement of two parallel k-wires or cannulated screws and utilizing wire or suture to form a figure-of-8 construct.

This construct causes the tension forces placed upon the patella to become compression forces.



Partial patellectomy with or without the need for tendon transfer is reserved for severely comminuted and unrepairable fragments since this decreases the strength of the extensor mechanism.

Complications:
✯ Symptomatic hardware
✯ Weakened extensor mechanism
✯ Patellofemoral arthritis
✯ Refracture and Non-union

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