Define Fracture of the Patella. Describe its clinical features, classification and management.
Definition & Mechanism
The patella is the largest sesamoid bone and part of the extensor mechanism of the knee. A fracture results either from a direct blow (dashboard injury, fall onto the knee — often comminuted/stellate) or from an indirect violent quadriceps contraction against resistance (a transverse fracture with distraction of the fragments).
Clinical Features
Pain, swelling and a tense haemarthrosis of the knee. A palpable gap between the fragments and, most importantly, an inability to perform a straight-leg raise / extend the knee against gravity indicates disruption of the extensor mechanism.
Classification
Fractures are described as undisplaced, transverse (displaced), comminuted/stellate, or vertical, and as osteochondral. The key questions are whether the fragments are separated (>2–3 mm) and whether the extensor mechanism is intact.
Tension-band principle: parallel K-wires with an anterior figure-of-eight wire convert the distracting quadriceps pull into compression across the fracture during flexion.
Management
- Undisplaced fractures with an intact extensor mechanism are treated conservatively in a cylinder cast / knee brace in extension for a few weeks with early quadriceps exercises.
- Displaced fractures (gap > 3 mm, articular step, or loss of active extension) require open reduction and internal fixation, classically tension-band wiring over two K-wires (which converts tensile quadriceps force into compression at the fracture). A severely comminuted lower pole may need partial patellectomy with reattachment of the patellar tendon
- total patellectomy is a last resort as it weakens extension.
CLINICAL PEARL
The two aims of treatment are to restore the extensor mechanism and to reconstruct the articular surface; tension-band wiring achieves both and permits early movement.
DANGER / REMEMBER
A patient who cannot straight-leg-raise has a disrupted extensor mechanism until proven otherwise — even with an apparently minor fracture, this mandates surgical repair.
| Type | Feature | Management |
|---|---|---|
| Undisplaced | Extensor mechanism intact | Cylinder cast |
| Transverse displaced | Extensor lag present | Tension band wiring |
| Comminuted | Multiple fragments | Partial / total patellectomy |
| Vertical | Usually undisplaced | Conservative |
KEY POINT
Key points TO remember
- Direct blow → comminuted; indirect quads pull → transverse with a gap.
- Inability to extend the knee / do a straight-leg raise = extensor mechanism disruption.
- Undisplaced + intact extensor mechanism → cast in extension.
- Displaced → ORIF with tension-band wiring; comminuted pole → partial patellectomy.
EXAM TIP
Sources: Maheshwari's Essential Orthopaedics; Apley & Solomon's System of Orthopaedics and Trauma; AO Principles of Fracture Management.
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