Patella alta, or a high riding patella, describes a situation where the position of the patella is considered high. It may be idiopathic or may result secondary to a patellar tendon rupture.
Several conditions are known to be associated with patella alta, including:
- idiopathic retropatellar pain
- recurrent dislocation of the patella
- chondromalacia patellae
- knee joint effusion
Patella alta may also occur as a result of spastic cerebral palsy .
On sagittal images, it is usually considered when the Insall-Salvati ratio is greater than 1.3-1.5 .
On radiography, it is important that standard positioning is used, with the knee flexed at 30 degrees. An off-angle x-ray beam or non-standard positioning may result in a spuriously abnormal ratio.