الفهرس 
ANATOMY OF PATELLOFEMORAL JOINTOnly 14 pages are availabe for public view
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Abstract
Patellofemoral instability generally is defined as acute or chronic. Acute instability refers to a primary, traumatic episode in which the patella dislocates laterally, while chronic instability denotes recurrent dislocations. Medial dislocations are rare and are typically iatrogenic. Understanding this complex topic requires a sound knowledge of the anatomy and biomechanics of the patellofemoral joint, an ability to elicit a good history, and the skill to perform a thorough physical examination, as well as an understanding of the principles of both nonsurgical and surgical treatments.
Despite the complexity of the patellofemoral joint, the anatomical and biomechanical features can be considered from the following 4 components: lower extremity alignment, articular geometry, and muscular, and ligamentous stabilizers. The understanding of each component allows for patient specific assessment and management plans.
The reasons for chronic patellar instability are now well characterized: the most common etiology is osseous, notably trochlear dysplasia, patella alta, and problems with the alignment or twisting of the lower limbs; next are muscular problems with failure of the vastus medialis obliquus (VMO); and finally, destabilization of the medial patella due to failure of the medial ligaments; namely the medial patellofemoral ligament (MPFL), the medial patellomeniscal ligament (MPML), the medial patellotibial ligament (MPTL), and the medial superficial retinaculum. Biomechanically, it has been shown that the MPFL provides 50–60% of the medial patella-stabilizing force.
The diagnosis of patellar instability is not always straightforward. Patients often do not report a frank patellar dislocation and frequently do not require an emergency room visit for reduction. Instead, they describe giving way episodes when going into a flexed knee position while changing direction.
A systematic and thorough physical examination, with the patient walking, standing, sitting, supine, and prone must be performed and include assessment of limb alignment, range of motion, strength testing, and neurovascular status. Ligamentous stability of the knee should be evaluated to rule out concomitant cruciate or collateral ligament tears. The findings should be compared with the uninjured knee. Failure to perform provocative examination maneuvers can contribute to delays or failure to diagnose instability.
In addition to a thorough history and physical examination, radiographic imaging assists the orthopedic surgeon in the diagnosis and treatment of patellofemoral instability. X-ray, CT scan, and MRIs can have quantitative measurements (e.g. Insall-Salvati index, Sulcus angle, TT-TG measurement, etc. )
Initial acute patellofemoral dislocations should be treated with immobilization and rehabilitation, as a majority of patients will do well without surgery. In the chronic setting, it is imperative to understand each patient’s reason for repeated instability, with a tailored individual surgical strategy being developed, based on correction of any underlying anatomical abnormalities. The surgical introduction of any new anatomical abnormality should be avoided. Several operative techniques based on patellofemoral biomechanics may be used for the treatment of patellar instability. Osteotomy procedures can correct malalignment. Trochlear dysplasia can be treated with trochleoplasty. The commonly injured VMO is often addressed surgically with repair. Finally, MPFL injury, the essential lesion in patellar instability, can be precisely reconstructed based on its anatomical and biomechanical features.