The retinaculum is the fibrous web-like network on the medial (inner) and lateral (outer) aspects of the kneecap. The lateral retinaculum is a powerful lateral stabiliser of the knee.
In the 1970’s two surgeons, Merchant and Mercer, published a paper called “Lateral Release of the Patella: A Preliminary Report”. This popularised surgery to cut or ‘release’ the lateral retinaculum and it soon became a panacea for any type of anterior knee pain. Because of the improper use of this procedure for the wrong indications, complication rates soared.
The operation was being used to treat patellar instability and all too often resulted in worsening of the situation to include weak vastus lateralis muscle (one of the quads muscle heads) and a switch from the kneecap being unstable to the outer side to it being unstable to the inner side (medial subluxation or even dislocation).
The cause of anterior knee pain is not always clear - the pain may come from nerve fibres supplying the bone beneath the cartilage covering under the patella, from nerves in the fat pad deep to the patella or to nerve fibres in the medial retinaculum.Physical examination for anterior knee pain should include examination of the knee in extension, with examination of the fat pads, the medial and lateral retinaculum (including the medial plica) and tests for hypermobility, in addition to standard tests for patellar tracking. In cases associated with instability the patellar apprehension test is often positive.
To determine the presence of patellar tilt, one may do a plain film x-ray “sunrise” view which allows the patella to be accurately and easily measured to evaluate the degree of tilt. The X-ray is taken at a special angle and the film shot as to appear as a “sunrise”. CT scan and MRI scan will also show this but they are more expensive.