Patellar Hypermobility Diagnosis and Management

Definition and Clinical Significance

Patellar hypermobility is characterized by excessive lateral movement of the patella when manual pressure is applied during physical examination, and is associated with patellofemoral instability, which has an incidence of 1% to 12% after total knee arthroplasty, according to the American College of Radiology 1, 2, 3
Imbalance in the extensor mechanism, which may be caused by excessive tightness of the lateral retinaculum, component malrotation, or valgus alignment of the extensor retinaculum, is often linked to patellar hypermobility 1, 2

Axial radiographs can demonstrate the degree of patellar tilt or subluxation, and weight-bearing axial radiographs are recommended to better assess patellofemoral kinematics, as suggested by the American College of Radiology 1, 3
CT is the modality most commonly used for measuring axial malrotation of a knee prosthesis when evaluating component rotation that may affect patellar alignment 2, 4

Transverse patellar fractures are associated with patellar maltracking, which can result from hypermobility, and patellar complications after total knee arthroplasty occur in approximately 3.6% of cases, according to the American College of Radiology 1, 3
Radiographs are usually satisfactory for assessment of patellar complications and can guide treatment, and CT with metal artifact reduction techniques may be useful for detecting patellar complications in patients with prostheses 1, 3