Anterior interval lesion
An anterior interval lesion is an area of localized arthrofibrosis of the anterior interval, which can occur after ACL reconstruction.
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Terminology
The anterior interval of the knee is found posterior to Hoffa’s fat pad, between the inferior and posterior patella and the anterosuperior tibial plateau 1. Arthrofibrosis can occur after ACL reconstruction, which can be localized in the form of cyclops lesions and/or anterior interval lesions. Different terminology is used in the literature when referring to anterior interval lesions, and these include intrapatellar fat pad fibrosis 2.
Clinical presentation
Post ACL reconstruction, patients can present with a lack of knee extension, new patella Baja 3, and/or a mechanical endpoint in knee movements.
Radiographic features
The ACL reconstruction should be assessed for possible areas of arthrofibrosis and MRI is the investigation of choice to assess for arthrofibrosis and intra-articular pathology of the knee.
Plain radiograph
Most often will not be identifiable. May show new patella baja.
CT
Best appreciated on soft tissue windows, nodular soft tissue density thickening of the anterior interval.
MRI
The anterior interval will be thickened and nodular.
T1: low signal intensity
T2: low signal intensity
Treatment
Arthroscopic release has been described 4, 5.
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