Authors of section

Executive editor

Michael Baumgaertner


Michael Huo, Michael Leslie, Iain McFadyen

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Disrupted extensor mechanism

General considerations

This is a rare injury. It is clinically important if the extensor mechanism is disrupted. Assessment of the extensor mechanism is important to decide if operative treatment is required.

A gap of 2 mm or less can be managed nonoperatively.

These fractures are classified by UCPF as V.34-A.

Disrupted extensor

Greater fracture displacement is associated with retinacular disruption. Patella alta or patella baja might be present. This can be evaluated clinically and with imaging studies.

Patella alta, patella baja


Avulsion fracture of the quadriceps or patella tendon insertion.

Clinical and radiological signs

  • Loss of straight leg raise
  • Patella alta or patella baja
Patella alta, patella baja


Plain X-rays remain the first line of investigation.

CT Scan can be used to assess the size and position of the fragment.

Comparison with previous X-rays is useful.

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