Arc Sign Special Test

What is it used for?

• Differentiating between Achilles Tendinosis (tendon degeneration) and Paratendonitis (inflammation of the sheath).

How to Perform

• Position: Patient lies prone.
• Action: Identify an area of localized swelling on the Achilles tendon.
• Movement: Ask the patient to actively dorsiflex and plantarflex the ankle.

Interpretation of Results

• Tendinosis (Positive Arc): The swelling moves up and down with the tendon movement.
• Paratendonitis: The swelling/thickening remains stationary while the tendon glides inside it.

Diagnostic Accuracy

• Sensitivity: 52%
• Specificity: 83%

References

• Magee, D. J. (2021). Orthopedic Physical Assessment (7th ed.). Elsevier.