Anterior interval release - the rationale behind this surgical procedure

The anterior interval of the knee is the area between the anterior portion of the tibia (or the front portion of the tibia) and the fat pad (which lies in this area) and area posterior to (or just behind) the patellar tendon.

This area is sometimes called the 'pre-tibial recess' or the 'anterior interval of the knee'.

There are several important structures in this region, including the infrapatellar fat pad, the ligamentum mucosum (sometimes called the infrapatellar plica), the intermeniscal ligament and then the patellar tendon -which is the anterior border - and the tibia - which is the posterior border.

Quite frequently we see scarring in this area after knee surgery – most commonly after ACL surgery where the fat pad has been violated or damaged - and scarring and contractures in this region lead to loss of the normal excursion of the knee if placed through flexion and extension.

The patellar tendon changes its angle of takeoff from the tibia as the knee is placed through flexion and extension, and when this area becomes scarred that normal excursion and change in angle does not occur - and that leads to abnormal loading in the patello-femoral joint and can lead to premature arthritis in that area.

When it is treated surgically, it is important for the surgeon to recognise that this is a common area of scarring because the portal location for surgery needs to be positioned so that you can visualise in that area, as it can sometimes be difficult to visualise that area if your portals are not placed appropriately. And then the scar tissue in that area needs to be appropriately resected or released so that the patellar tendon can move in its normal way. It is very important to preserve and not damage the intermeniscal ligament - which is a ligament that runs between the medial and lateral menisci - and it is important not to damage the ACL or to excessively damage or create additional trauma to the fat pad because the fat pad then can become scarred. 

So it is a very important area that we look at in patients with arthrofibrosisis. Sometimes the examination findings are very subtle – such as decreased patellar tendon mobility, or pain in the front of the knee. And MRIs can be very helpful to help diagnose it too – to look for thick bands of scarring in this region, or at the time of surgery one can look and see whether the meniscus moves normally if the knee is placed through flexion and extension - because if it doesn’t it is likely that it is entrapped with scar in this anterior interval of the knee which prevents normal patellar tendon mobility and normal meniscal mobility.