Patella fracture

Introduction



Patella is a sesmoid bone, with continuation from the quadriceps tendon, and patellar ligament.
It also receives insertion from vastus medialis and lateralis to it's medial and lateral edge.
The extensor snap is completed as the quadriceps muscles extends beyond the patella, and inserts into the proximal tibia (the medial and lateral retinacular fibres)

Mechanism of injury

Patella can be fractured by both direct and indirect forces.

Direct force : Usually caused by a fall on the knee cap, which results in undisplaced crack or comminuted fracture of the patella. In such cases, the extensor apparatus remains intact.

Indirect force : Usually resulted when the foot is stucked onto a solid obstacle, and as the patient tries not to fall, by sudden and vigorous contraction of the quadriceps muscles, it results in a transverse fracture of the patella, where the extensor apparatus is torn.

Clinical features

With the history of trauma, patient presents with typical symptoms of fracture.
If the fracture is undisplaced, tenderness is usually localised only over the patella.
If the fracture is displaced, then a gap may be able to felt in between the fragments.
If the fracture is comminuted, palpable crepitus may be felt.

Testing active knee extension is important to evaluate the function of the extensor apparatus of knee joint.
If it's too painful for the patient to do so, he/she can lie down on his/her side and try extending the knee joint.
If the patient is able to extent his/her knee joint actively, it means the extensor apparatus is intact.

Radiological features

AP, lateral and sometimes a skyline view of the knee joint is ordered.


Based on the radiological features, patella fractures can be classified as :

a) Longituidinal
b) Transverse
c) Comminuted

Which can be either displaced or non-displaced.
Significant displacement is indicated by the presence of a step on the articular surface of the patella, or in case of transverse fracture, the gap between the fractured fragments are > 3mm.

Management

a) Minimally displaced/non-displaced crack

Only conservative treatment is given.
Cylinder cast is applied over the knee joint and immobilisation is done for around 4-6 weeks, with early starting of quadriceps mobilisation exercises.

b) Comminuted/Stellate fracture

Since it is difficult to reduce such fracture, and the incongruity of the articular surface predisposes to secondary degenerative osteoarthritis of the knee joint.
Hence, patellectomy is usually done to prevent is complication.

c) Displaced transverse fracture

In this case, tension band wiring repair is done with repair of the extensor apparatus.

Category: Orthopedics Notes