Examination for patellar instability

1. The anteroposterior radiograph of the knee joint is of little value in determining whether the patellofemoral joint alignment is normal. The lateral radiograph is the best radiograph to evaluate the vertical position of the patella and is used to determine the high position of the patella. The axial patella radiograph is considered to be the best radiograph to evaluate the effectiveness of the patellofemoral joint alignment. The most cost-effective examination method can observe the tilt and subluxation of the patella. Using the patella external displacement indexing method on the axial patellar radiograph can not only reflect the external displacement of the patella, but also accurately determine the degree of external displacement. It can also be used as the basis for the diagnosis and treatment of patellar external displacement.

2. Arthroscopy

The positional relationship and movement trajectory of the patella and femur, as well as the scope, degree and location of articular cartilage damage between the patella and femur can be directly observed under the microscope. Release of the lateral retinaculum of the patella will also help to choose an appropriate surgical method. More importantly, it is necessary to determine whether there are other intra-articular disorders, such as synovitis, chondritis dissecans, loose bodies, etc. After the disease is clearly identified, At the same time, corresponding processing can also be done. Jackson divided it into 3 types based on the degree of articular cartilage changes under arthroscopy:

(1) Type I: There are localized softening lesions on the patellar cartilage surface.

(2) Type II: The cartilage surface of the patella has cracks and invasion, while the articular surface of the femoral condyle is normal.

(3) Type III In addition to type II changes, the articular cartilage surface of the femoral condyle also has destructive changes.

3. CT or MRI examination

Use CT or MRI technology to relax the quadriceps muscles in the extended position of the knee joint and examine the middle part of the patellar joint. Cross-sectional scanning has clear images, good repeatability, and is easy to measure and calculate. It is a powerful diagnostic method for patellar instability.

4. Ultrasound examination

Ultrasound examination can measure the cartilaginous femoral groove angle on the patellar surface of the femoral condyle. In pathological conditions, the angle is 154° to 195°, exceeding the normal 135° to 153°. This is a morphological basis that causes the patella to easily dislocate laterally. Measuring this angle can clearly determine whether patellar instability is present.