Q-angle undervalued? The relationship between Q-angle and medio-lateral position of the patella
PainSci summary of Herrington 2004
In 2004, this Manchester research group showed that abnormal patellar position tends to throw off Q-angle measurements. Specifically, if a Q-angle measurement is taken based on a patella that is displaced laterally, the result will not be as large as the real Q-angle.
BACKGROUND: For an accurate quadriceps angle measurement, the patella must be centralised in the femoral trochlear groove, numerous authors have described lateral displacement of the patella in patellofemoral pain patients, this leads to the intriguing possibility that the Q-angle might be undervalued within patellofemoral pain patients who have laterally displaced patella.
METHOD: 109 asymptomatic subjects (51 male, 58 female) were assessed. Medio-lateral patella position was measured using a previous validated method and Q-angle was measured in standing with the quadriceps relaxed. FINDINGS: Mean Q-angle was 11.6 degrees (SD 5.2) left knee, 11.3 degrees (SD 4.9) right knee in the male subjects and 14.4 degrees (SD 5.2) left knee, 13.3 degrees (SD 5.5) right knee for female subjects. 40 females and 28 males had laterally displaced patellae. 13 subjects had centrally placed patellae (7 females, 6 males) with 28 subjects having medially displaced patellae (11 females, 17 males). Recalculation of Q-angle for the laterally displaced group brought about a statistically significant increase in angle. In the medial displaced group failed to produce a statistically significant decrease.
INTERPRETATION: The adjusted Q-angle values for medially and neutral placed patellae brought the values very much into the centre of the reported ranges for Q-angles. After adjustment for lateral patella displacement, Q-angle values were towards the under end of values reported as normal, especially female values which were close to the previously reported pathological cut off point. Because of the inverse relationship between quadriceps strength and the magnitude of Q-angle and quadriceps crucial role in the aetiology of patellofemoral pain, any method which improves the reliability and applicability of Q-angle measurement could prove useful in investigations into the aetiology of and outcome from treatment of patellofemoral pain syndrome.
These two articles on PainScience.com cite Herrington 2004 as a source:
- PS Save Yourself from Patellofemoral Pain Syndrome! — Patellofemoral pain syndrome (aka runner’s knee) explained and discussed in great detail, including every imaginable self-treatment option and all the available scientific evidence
- PS Patellofemoral Tracking Syndrome — The beating heart of the conventional wisdom about patellofemoral pain is mostly nonsense