Copyright 2009
Author John Udall MD
Definition
The medial patellar retinaculum is the soft tissue restraint on the medial side of the patella. It is a fibrous expansion of the tendon of the vastus medialis which attaches to the medial margin of the patella, the ligamentum patellae and the tibial condyle.
Its unique structural features include a deep and superficial layer, with the most important medial restraint, the Medial Patellofemoral Ligament (MPFL), residing in the deeper layer of the retinaculum. It runs just deep to the distal VMO to attach to the superior two-thirds of the medial patellar margin and originates from the adductor tubercle.
It is supplied by the geniculate arteries which can be damaged in medial approaches to the knee
The nerve supply is the medial retinacular nerve.
The function or action of the medial retinaculum and the MPFL is to prevent lateral translation of the patella, preventing lateral dislocations (the most common type). It functions in conjunction with the bony trochlear groove which keeps the patella centered between the condyles of the femur.
Common problems include tears of the medial retinaculum and the MPFL. Tears of these structures can occur with patella fractures as well as dislocations of the patella. Sometimes these tears are solely soft tissue tears, while other times it includes an osteochondral fragment avulsed from the medial aspect of the patella.
Commonly used diagnostic procedures include physical exam and MRI. On physical exam, a patient will have apprehension (positive apprehension sign) when the examiner laterally translates the patella, causing it to dislocate out of the trochlear groove. There will also be a soft endpoint on translation with attenuation of the MPFL. MRI can visualize the retinaculum and MPFL and help determine if there is a tear or an accompanying osteochondral fragment.
It is usually treated with rest and physical therapy. If the patella continues to dislocate multiple times, reconstruction of the MPFL is performed with allograft, or a medial plication can be performed. Often times, these procedures are performed in conjunction with release of the lateral retinaculum.
References
http://www.medcyclopaedia.com/library/topics/volume_ii/m/medial_patellar_retinaculum.aspx
http://www.ejbjs.org/cgi/content/abstract/85/10/1909