PainScience.com • Good advice for aches, pains & injuries

Functional implications of the Q-angle in the patellofemoral joint

updated

Tags: patellar pain, etiology, biomechanics, arthritis, aging, pain problems, knee, leg, limbs, overuse injury, injury, running, exercise, self-treatment, treatment, pro

One article on PainSci cites Freedman 2014: The Complete Guide to Patellofemoral Pain Syndrome

PainSci notes on Freedman 2014:

Does the Q-angle actually provide a measure of how the quadriceps is pulling on the kneecap? And can adding different angles or levels of quadriceps contraction improve the tests reliability?

No, and No. Not according to this study, which compared several measures of Q-angle with magnetic resonance imaging and their relationship with kneecap movement (patellofemoral kinematics).

Their findings? “Q-angle did not represent the line of action of the quadriceps.” There were up to 8° differences in angle between measurement techniques, which varied even more across subjects: -25.8° to 3.9°! That's quite the range considering a "painful knee" apparently has a 3° difference from a non-painful knee.

What's more, adding quadriceps contraction or changing the knee flexion angle didn't improve the reliability — so the whole “you're doing it wrong” argument doesn't work here.

Interestingly, there was a correlation between Q-angle and medial kneecap position in people with knee pain. Still, the authors conclude with: “Clinicians are cautioned against using the Q-angle to infer patellofemoral kinematics.”

original abstract Abstracts here may not perfectly match originals, for a variety of technical and practical reasons. Some abstacts are truncated for my purposes here, if they are particularly long-winded and unhelpful. I occasionally add clarifying notes. And I make some minor corrections.

BACKGROUND: The Q-angle is widely used clinically to evaluate individuals with anterior knee pain. Recent studies have questioned the utility of this measure and have suggested that a large Q-angle may not be associated with lateral patellofemoral translation, as often assumed. The objective of this study was to determine: 1) how accurately the Q-angle represents the line-of-action of the quadriceps and 2) if adding active quadriceps contraction or a bent knee position to the measurement of the Q-angle improves its reliability, accuracy, and association with patellofemoral kinematics.

METHODS: The study included individuals diagnosed with chronic idiopathic patellofemoral pain and control subjects (n=43 and n=30 knees). Three measures of the clinical Q-angle (straight- and bent-knee with relaxed quadriceps and straight-knee with maximum isometric quadriceps contraction) were obtained with a goniometer and compared to a fourth MR-based measure of Q-angle. Patellofemoral kinematics were derived from dynamic cine-phase contrast images, acquired while subjects extended/flexed their knee from approximately 0° and 45°.

FINDINGS: The Q-angle did not represent the line-of-action of the quadriceps. The average difference between each clinical and the MR-based Q-angle ranged from 5° to 8°. These differences varied greatly across subjects (range: -28.5° to 3.9°). Adding an active quadriceps contraction or a bent knee position, did not improve the reliability of the Q-angle. An increased Q-angle correlated to medial patellar displacement and tilt (r=0.38-0.54, P<0.001) in the cohort with anterior knee pain.

INTERPRETATION: Clinicians are cautioned against using the Q-angle to infer patellofemoral kinematics.

This page is part of the PainScience BIBLIOGRAPHY, which contains plain language summaries of thousands of scientific papers & others sources. It’s like a highly specialized blog. A few highlights: