Literature review of acquired patella baja

Abstract

Patella baja is one of the complications after total knee arthroplasty (TKA). It refers to an abnormal location of patella occurred secondary to shortening of the patellar tendon or distal positioning of the patella relative to the femoral trochlea. Clinically, it can be classified into congenital, acquired, and a combination of the above two types. Acquired patella baja is the most common type and usually occur as a result of trauma or surgery. Acquired patella baja is also caused by elevation of the joint line after TKA, which refers to pseudo-patella baja. Presently, its etiology is still uncertain. Some studies report the following causes of patella baja, including extending of quadriceps femoris, contracture of patella tendon or patellar fat pad, and fibrosis of joint. The diagnosis is mostly based on the lateral roentgenogram. The following parameters, including Insall-Salvati ratio, Modified Insall-Salvati ratio, Blackburne-Peel ratio, Caton-Deschamps ratio and Plateau-Patella angle, are used to assist diagnosis for patella baja. With the progress of imageology, some literatures describe several methods based on magnetic resonance imaging (MRI). However, the diagnostic methods of patella baja are not entirely precise. Patella baja can lead to decreased range of motion (ROM), a decreased lever arm, impingement of the patella against the tibial polyethylene or tibial plate, which may result in anterior knee pain, rupture of the patellar or quadriceps tendons. The treatment of patella baja depends on determining the cause and distinguishing between patella baja and pseudo-patella baja. Patients with severe symptom or failed for conservative treatment should receive surgery. The corrective measures for patella baja include lengthening of the patellar tendon and proximalize osteotomy of tibial tuberosity. In addition, the therapies for pseudo-patella baja include reestablishing the joint line by use of distal femoral augment, replacement of the patellar implant or polyethylene insert.