Patella fracture

AO/OTA 34C1

Transverse, displaced

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The patella is the fulcrum of the extensor mechanism. In a transverse fracture the quadriceps pulls the proximal fragment upwards, so the patient cannot actively extend the knee if the retinacula are torn.

Transverse patella fracture, lateral knee. The quadriceps pulls the proximal fragment upwards. — Hellerhoff, CC BY-SA 3.0, via Wikimedia Commons.

Mechanism

Direct blow (dashboard, fall on the knee: comminuted) or sudden eccentric contraction of the quadriceps (transverse).

Clinical findings

Swollen knee with a palpable gap.
Straight-leg raise: if the patient cannot lift the extended leg, the extensor mechanism is disrupted.

Imaging

AP and lateral of the knee (the lateral shows the gap and the step).
Skyline (axial) view if possible: vertical fractures and the patellofemoral joint.
CT for comminuted patterns.

AP, lateral (best for displacement) and skyline views. Do not confuse with a bipartite patella (superolateral, rounded edges, often bilateral).

Classification

34A: Extra-articular (pole avulsion).
34B: Partial articular, vertical.
34C: Complete articular: C1 transverse, C2 transverse with a second fragment, C3 complex.

Types shown in 3D

34A: Extra-articular: avulsion of the inferior pole. Small pole fragments can be excised and the tendon reattached.
34B1: Partial articular, vertical (lateral facet). The extensor mechanism usually works: often non-operative.
34C1: Complete articular, transverse: the quadriceps pulls the proximal fragment up. Tension-band wiring.
34C3: Complete articular, multifragmentary (stellate). Plates, cerclage or partial patellectomy.

Treatment

Non-operative: Extensor mechanism intact and displacement < 2–3 mm step or gap: brace in extension, full weight bearing, progressive flexion.
Operative: Tension-band wiring (two K-wires or cannulated screws with a figure-of-eight wire) converts the pull of the quadriceps into compression on the articular side. Comminuted patterns: plates or partial patellectomy with reattachment of the tendon. Repair the retinacula.

Aftercare

Early range of motion in a hinged brace; avoid full active extension against resistance for 6 weeks.

Complications

Symptomatic hardware (very common)
Loss of reduction
Patellofemoral arthritis
Extension lag