Patellar Fractures

Question 1

Clinically relevant anatomy

Answer 1

The patella is a triangular bone situated on the anterior surface of the knee at the distal end of the femur. It is the largest sesamoïd bone in the body and makes part of the knee joint. Vastus medialis and lateralis, as part of the quadriceps group, control movement at the patella.

The extensor mechanism as a whole plays a major role in patella fractures. This consists of the quadriceps, quadriceps tendon, retinaculum, patella tendon, tibial tubercle and patellofemoral and patellotibial ligaments

Question 2

Types of fractures

Answer 2

Patella fractures are classified as either displaced or non-displaced. Displaced fractures are unstable and can be further classified as:

Comminuted: As a result of direct trauma (mostly due to blows or falls on flexed knee)
Can cause damage to the articular cartilage of patella and femoral condyles.

Tansverse/stellate: As a result of muscle contraction/extensive stress on the extensor mechanism, e.g. explosive quadriceps contraction after jumping from height.
Most common type
Proximal blood supply may be compromised
Usually as a result of hyper-flexion of the knee

Marginal: As a result of a fall on the knee
Vertical/longitudinal
Lower/upper pole
Osteochondral
Sleeve (only in paediatric patients)

Question 3

Physical examination

Answer 3

Observation:
Whole extremity
Swollen, bruised knee
Deformity around knee
Possible wounds (open fracture)
Palpation (often done after local anesthetics to eliminate pain):
Tenderness around patella
Palpable gap (for displaced fractures)
Rule out concomitant injuries:
e.g. fractures of the acetabulum, femur and tibia
Haemarthrosis

Range of motion:
Acute:
Limited knee and painful knee flexion and extension
Often unable to do straight leg raise
Chronic:
Full knee flexion with extension lag
Distal pulses
Assess compartment of the leg
Neurological assessment