Knee Dislocation
All knee dislocations require vascular imaging of the popliteal artery due to injury risk. Popliteal artery injury occurs in up to 40% of knee dislocations, and a delay in diagnosis carries a significant risk of amputation.
Direction of dislocation: Anterior (most common), posterior, medial, lateral, or rotatory.
Key actions:
- Obtain popliteal CTA for any suspected knee dislocation, including spontaneously reduced dislocations
- Ankle-brachial index (ABI) less than 0.9 warrants CTA even if a distal pulse is present
Patellar Fractures
Surgical indications:
- Articular incongruity >2 mm
- Fragment separation >3 mm
- Extensor mechanism disruption
Bipartite patella: A normal developmental variant occurring at the superolateral pole with smooth corticated margins. Do not confuse with an acute fracture — the key distinguishing features are the superolateral location, smooth margins, and absence of cortical disruption.
Tibial Spine Avulsion
Tibial spine avulsion fractures are associated with ACL, MCL, and medial meniscus injuries. When identified on radiograph or CT, recommend MRI for ligamentous assessment.
Deep notch sign: Depression of the lateral femoral condyle cortex on lateral radiograph or sagittal CT — an indicator of ACL injury.
Proximal Tibiofibular Joint (PTFJ) Dislocation — Ogden Classification
| Type | Description |
|---|---|
| I | Subluxation |
| II | Anterolateral (most common) |
| III | Posteromedial — peroneal nerve injury risk |
| IV | Superior |
Fibular Fractures
Fibular head fracture: Associated with peroneal nerve injury (foot drop) and posterolateral corner injury.
Fibular shaft fracture: Image the ipsilateral ankle to exclude a Maisonneuve fracture.
Mid Tibia and Fibula Fractures
Key descriptive terms for reporting:
- Butterfly fragment: Triangular cortical wedge fragment that does not involve the full bone circumference
- Ring butterfly: Wedge fragment involving the full circumference
- Bayonet apposition: Overriding of fracture fragments with loss of length
- Segmental fracture: Intercalated fragment creating two separate fracture levels — associated with impaired vascularity
Reporting Checklist — Mid Tibia/Fibula
- Fracture morphology: simple, wedge, or complex
- Shortening or distraction at the fracture site
- Intercalated fragment (segmental fracture)
- Soft tissue or vascular compromise