Cadaveric study on static medial patellar stabilizers: the dynamizing role of the vastus medialis obliquus on medial patellofemoral ligament.

Aim of this cadaveric biomechanical study was to describe the detailed anatomy of the static medial patellar stabilizers and further determine the role of each of them in preventing lateral patellar dislocation. Eight cadaver knees, after removing the skin and subcutaneous tissues, were used in the study. The medial patellofemoral ligament (MPFL), the medial retinaculum (MR) the medial patellomeniscal ligament (MPML), and the medial patellotibial ligament (MPTL) were dissected. Their origins, insertions, orientations and sizes were recorded. To the medial stabilizers, a tension of 10 pounds was applied, using a tensiometer held in a semicircular device while the knees were kept in 30 degrees of flexion. Then, the previously described ligaments were dissected and the resultant displacement recorded. The most anatomically distinct structure is the MPFL, whose length varies from 45-50 mm, and its width from 10-20 mm at its origin (medial femoral epicondyle) to 20-30 mm at its insertion to the patella. The "meshing" of the MPFL fibers to the fibers of the vastus medialis obliquus (VMO) close to its patellar insertion was the most interesting and very important finding. The contribution of MPFL to medial stability was more than 50%. Of the remaining ligaments, MPML contributes 24% and the MPTL and MR contribute only 13% respectively. The MPFL is the strongest medial static patellar stabilizer. Its contribution to patellar stability against lateral dislocation is far more than 50%, since its meshing with the VMO, shortens its fibers which thus pulls the patella to the medial part of the femoral groove and keeps it in the trochlea during the initial 20 degrees -30 degrees of flexion.