An anterior interval release is a surgical procedure to remove scar tissue in the 'anterior interval' - a region behind the patellar tendon.
Surgery for such scarring (arthrofibrosis) is specialist domain, and this procedure should only be carried out by a surgeon experienced in this problem.
Intraarticular arthrofibrosis of the knee alters patellofemoral contact biomechanics. Mikula JD, Slette EL, Dahl KD, Montgomery SR, Dornan GJ, O’Brien L, Turnbull TL and Hackett TR. J Exp Orthop. 2017 Dec; 4: 40.