What is the mortise width on an ankle gravity stress view that indicates the need for surgical intervention?

Mortise Width on Ankle Gravity Stress View for Surgical Intervention

A medial clear space (MCS) of ≥5 mm on an ankle gravity stress view indicates the need for surgical intervention, as this represents an unstable ankle mortise. 1, 2

Understanding Ankle Stability Assessment

Gravity stress views are crucial for evaluating ankle stability in the setting of ankle trauma, particularly in supination-external rotation (SER) type injuries with isolated fibular fractures. These views help determine the integrity of the deltoid ligament and overall mortise stability.

Normal vs. Abnormal Measurements

• Normal medial clear space on gravity stress view ranges from 3.1-3.6 mm in healthy individuals 3, 4
• MCS widening to ≥5 mm on gravity stress view indicates deltoid ligament disruption and ankle instability requiring surgical intervention 1, 2
• A difference of >2 mm between the standard mortise view and gravity stress view also suggests instability 3, 4

Advantages of Gravity Stress Views

• More reliable and easier to perform than manual stress views for evaluating supination-external rotation injuries 5
• Higher discriminative ability for diagnosing complete deltoid ligament tears compared to regular ankle mortise views 1
• Patient muscle activation during the test does not significantly affect results, supporting the validity of the gravity stress view 2

Decision Algorithm for Surgical Intervention

1. Obtain standard radiographs: AP, lateral, and mortise views 5
2. Perform gravity stress view if isolated lateral malleolus fracture is present without obvious mortise widening on standard views 5
3. Measure the medial clear space on both standard mortise and gravity stress views 1, 3
4. Surgical intervention indicated if:
   • MCS ≥5 mm on gravity stress view 1, 2, 4
   • Increase in MCS >2 mm between standard and stress views 3
   • Visible talar tilt on gravity stress view 4

Clinical Correlation

The gravity stress test results should be interpreted in conjunction with clinical findings:

• When gravity stress test results align with clinical findings (medial tenderness, swelling, ecchymosis), they accurately predict ankle mortise stability 6
• Medial tenderness, particularly when combined with swelling and/or ecchymosis, correlates with potential instability even when radiographs appear normal 6
• Weight-bearing radiographs, if possible, provide additional information about fracture stability 5

Common Pitfalls and Caveats

• False negative results may occur when clinical examination suggests medial-side injury but gravity stress test appears normal 6
• A medial clear space of <4 mm on standard views does not always confirm stability; gravity stress views are still necessary 5, 1
• Increased incidence of instability is associated with medial tenderness, bruising, swelling, fibular fracture above the syndesmosis, bi/trimalleolar fractures, open fracture, or high-energy injury 5
• Gravity stress views with MCS ≥6 mm have 100% sensitivity and 91.7% specificity for complete deltoid ligament rupture 1