AIR is an abbreviation for 'anterior interval release'.

Cleaning out scar tissue in the anterior interval.
Technique of AIR
AIR is a surgical procedure to free adhesions under the patellar tendon in the 'anterior interval', usually via an incision on the side of the patellar tendon.
Synonyms:
Anterior interval release
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CLINICAL PUBLICATIONS
Arthroscopic Lysis of Adhesions and Anterior Interval Release With Manipulation Under Anesthesia for Severe Post-traumatic Knee Stiffness: A Simple and Reproducible Step-by-Step Guide. Kukreja M, Kang J, Curry EJ and Li X. Arthrosc Tech. 2019 May; 8(5): e429–e435.