Anterior interval release

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Anterior interval release

Anterior interval release (AIR) is a type of arthroscopic knee surgery performed to alleviate pain and associated symptoms caused by scar tissue (or fibrosis) accumulation in the anterior region of the knee, behind and under the knee cap (or patella), in a condition called arthrofibrosis. In normal, asymptomatic knees, this anterior compartment of the knee comprises mobile, scar-free tissues such as the infrapatellar (Hoffa's) fat pad. With progression, scar tissue (or fibrosis) leads to closure of the anterior interval, tethering the patella tendon and causing pain, loss of range of motion, damage to knee cartilage, and/or pain, among other symptoms.[1]

Diagnosis of arthrofibrosis or scar tissue in the anterior interval can consist of clinical signs such as a positive Hoffa test, loss in knee flexion, and/or diminished superoinferior patella mobility, with supplementation by magnetic resonance imaging (or MRI)[1]

Post-surgical rehabilitation should be conservative in nature, focusing on maintaining joint mobility via early motion to avoid reformation of scar tissue. Early motion may be promoted by specific mobility exercises and use of continuous passive motion. Restoration of joint range of motion may be augmented by specialized bracing devices. Weight bearing is delayed appropriately post-surgically to promote control of swelling, pain, and joint irritation. Strengthening is delayed to a minimum of 6 weeks, often several months, post-operatively.[1][2]

The origins leading to arthrofibrosis are unclear. They frequently have involved previous knee injury or trauma, such as anterior cruciate ligament reconstruction surgery.[3][4] More subtle origins of fibrotic contracture in the anterior interval have also been attributed to plica (or naturally occurring folds in the knee joint lining) that become stiff and restrictive.[5]


  1. ^ a b c Steadman JR, Dragoo JL, Hines SL, Briggs KK (September 2008). "Arthroscopic release for symptomatic scarring of the anterior interval of the knee". Am J Sports Med. 36 (9): 1763–9. doi:10.1177/0363546508320480. PMID 18753680. S2CID 44492674.
  2. ^ Millett PJ, Johnson B, Carlson J, Krishnan S, Steadman JR (November 2003). "Rehabilitation of the arthrofibrotic knee". Am. J. Orthop. 32 (11): 531–8. PMID 14653482.
  3. ^ Paulos LE, Wnorowski DC, Greenwald AE (1994). "Infrapatellar contracture syndrome. Diagnosis, treatment, and long-term followup". Am J Sports Med. 22 (4): 440–9. doi:10.1177/036354659402200402. PMID 7943507. S2CID 26107064.
  4. ^ Fisher SE, Shelbourne KD (1993). "Arthroscopic treatment of symptomatic extension block complicating anterior cruciate ligament reconstruction". Am J Sports Med. 21 (4): 558–64. doi:10.1177/036354659302100413. PMID 8368417. S2CID 838712.
  5. ^ Steadman JR (2009). "Arthroscopic treatment of arthrofibrosis of the knee". In Gill TJ (ed.). Arthroscpic Techniques of the Knee: A Visual Guide (Visual Arthroscopy). Slack. ISBN 978-1-55642-858-6.