Primary dynamic stabilizer of patella against the lateral pull of vastus lateralis is -

Ans. is 'b' i.e., Vastus medialis obliques Patella* Recurrent dislocation of the patella can follow a violent initial dislocation, but it occurs more often in knees with one or more underlying anatomical abnormalities that predispose the patella to dislocation or subluxation.* In these knees, minor trauma is needed for the initial dislocation to occur.* The underlying pathological condition causes an abnormal excursion of the extensor mechanism over the femoral condyles.* Several anatomical factors should be considered when evaluating a patient with recurrent dislocation of the patella. Anatomical studies have shown the contributions of the various portions of the quadriceps muscle to knee extension.* The vastus lateralis pulls laterally to the frontal plane of the femur at an angle of 7 to 10 degrees.* The vastus medialis is divided into two parts--the vastus medialis longus (with its muscle fibers pulling at 15 to 18 degrees medially) and the vastus medialis obliquus (with its muscle fibers pulling at a relatively horizontal 50 to 55 degrees medially).* The primary function of the vastus medialis obliquus muscle is to stabilize the patella against the lateral pull of the vastus lateralis, making the vastus medialis obliquus the dynamic stabilizer of the patella.* Static factors, the primary stabilizers of the patella, include the shape of the patella, the femoral sulcus, a patellar tendon of appropriate length, and a normally tensioned medial capsule reinforced by the patellofemoral and patellotibial ligaments.* The main factor that results in recurrent patellar dislocation is incompetence of the medial patellofemoral ligament (MPFL).* The MPFL is an extrasynovial ligament, as is the medial collateral ligament. Injury may result in minimal long-term damage with return of full function, mild-to-moderate laxity, or incompetence from avulsion or interligamentous failure with resultant instability.* MRI to evaluate the site and extent of injury is indicated for instability.