From the Guidelines
Assessing syndesmosis stability is not effectively done with a 3-phase bone scan due to its low specificity in distinguishing between infection and aseptic loosening, as evidenced by a study published in the Journal of the American College of Radiology in 2023 1. When evaluating syndesmosis stability, it is crucial to prioritize methods that offer high sensitivity and specificity for diagnosing instability and distinguishing between potential causes such as infection or aseptic loosening.
- The external rotation stress test, squeeze test, and fibular translation test are valuable clinical tools for assessing pain and excessive movement at the distal tibiofibular joint.
- Radiographic assessment, including standard ankle views (AP, lateral, mortise) and weight-bearing radiographs, is essential for evaluating diastasis and widening of the tibiofibular clear space, with a width of more than 6mm considered abnormal.
- For a more detailed evaluation, CT scans can precisely measure the tibiofibular relationship, while MRI directly visualizes the syndesmotic ligaments to assess for tears, providing critical information for treatment decisions.
- Dynamic fluoroscopy during external rotation stress can reveal subtle instability not apparent on static images, further aiding in the diagnosis of syndesmotic instability. The use of a 3-phase bone scan, as discussed in the context of total knee arthroplasty 1, may not be the most appropriate initial choice for assessing syndesmosis stability due to its limitations in distinguishing between infection and aseptic loosening, highlighting the need for a comprehensive assessment approach that incorporates multiple diagnostic modalities.
From the Research
Assessing Syndemosis Stability
- The diagnostic accuracy of clinical tests for assessing ligamentous injury of the ankle syndesmosis has been evaluated in several studies 2, 3, 4.
- A systematic review with meta-analysis found that no individual test was associated with both high sensitivity and high specificity, but tests with high sensitivity included palpation and dorsiflexion lunge, while tests with high specificity included the squeeze test and external rotation 2.
- Another study found that the squeeze test had the highest specificity, while syndesmosis ligament tenderness and the dorsiflexion-external rotation stress test had the highest sensitivity values 3.
- The external rotation test had the fewest false-positive results and the smallest inter-observer variance in a study evaluating the feasibility of clinical tests in diagnosing syndesmotic injury of the ankle 4.
- Imaging modalities such as weight-bearing CT and ultrasonography can provide a physiologic and dynamic assessment of the syndesmosis, allowing for the identification and treatment of syndesmotic instability 5.
- The hook test is a widely used intraoperative method for assessing syndesmosis stability, but its reliability is unclear and it may not be able to detect relevant syndesmosis injury even in a standardized manner 6.
Clinical Tests for Syndemosis Stability
- Palpation: high sensitivity (92%) 2
- Dorsiflexion lunge: high sensitivity (75%) 2
- Squeeze test: high specificity (85%) 2, (88%) 3
- External rotation: high specificity (78%) 2, fewest false-positive results and smallest inter-observer variance 4
- Dorsiflexion-external rotation stress test: high sensitivity (71%) 3
- Syndesmosis ligament tenderness: high sensitivity (92%) 3