What is the relation between Q angle and Patellofemoral dysfunction? What are the results of increase and decreased Q angle, and dysfunction related?

The Q (Quadriceps) angle is the angle formed by the intersection of two lines that cross at the center of the patella. One line goes from the anterior superior iliac spine (ASIS) to the center of the patella and the other from the anterior tuberosity of the tibia to the center of the patella.

The Q -angle is widely used for evaluating patients with knee problems, especially patellofemoral pain syndrome (PFPS). Normal Q angles are < 10 degrees in boys, men and prepubescent girls and <15 degrees in women. The larger the q-angle is, the greater the lateralization force on the patella, which increases the retropatellar pressure between the lateral facet of the patella and the lateral femoral condyle. The continuous compressive forces between these structures may give rise to PFPS and, over the long term, cause degeneration of the joint cartilage of the patella. A study by Huberti and Hayes (1984) reported that a 10% increase in the q-angle increased the stress on the patellofemoral joint by 45%. Ref 1.

If the Q angle is greater than 15 degrees, it is considered consistent with, but not diagnostic of PFPS. PFPS is a very common knee problem. The patient has pain in the anterior knee, especially when the knee is flexed for a long time (e.g. after a long movie, hence the term ‘movie-goers’ knee). Other symptoms include pain when walking down stairs or walking or running downhill.

Normally, the patella migrates laterally with flexion and medially with extension. If the patella is inappropriately lateral in extension, the underlying femoral condyle jams into the overlying patella causing pain. The most common reason for the inappropriate excursion of the patella with extension is quadriceps atrophy (especially of the large medial head of the vastus medialis). This commonly occurs after knee injuries if no quadriceps rehabilitation or maintenance was initiated.

Ref 2; Berg D. Worzala K. Atlas of Adult Physical Diagnosis. 2006. Lippincott Williams & Wilkins Publishers. Chapter 8. Knee Examination: Practice and Teaching. Patellofemoral pain syndrome. Pg 208.