An increased Q-angle is often mentioned as a risk factor for injuries around the patella, in particular patella subluxation and patellofemoral pain syndrome (PFPS). But many questions exist over its relevance, the reproducibility of is measurement, and indeed its contribution to any injury around the patellofemoral joint. Let's take a look..
The Quadriceps or Q-angle was initially described by Brattstrom in 1964 . It is an index of the vector for the combined pull of the extensor mechanisms and the patellar tendon . It is measured by drawing a line from the anterosuperior iliac spine to the centre of the patella, and a second line from the centre of the tibial tubercle to the centre of the patella. The angle where these lines intersect is regarded as the Q-angle.
Traditionally, the Q-angle has been measured with subjects in supine, knee extended and with the quadriceps muscle relaxed. This is regarded as the ‘traditional’ or ‘conventional’ method of assessing Q-angle. The Q-angle has also been assessed standing.
Apart from the many other problems with the Q-angle, there is widespread disagreement on the actually criteria for normalcy. It is extremely difficult to find, let alone standardise, a "normal" measure for the Q angle anywhere in the literature, let alone quantify this for both male and female cohorts.
Despite this, the Q-angle measurement is widely used as an indicator of patellofemoral dysfunction, including patellofemoral pain syndrome (PFPS) and patella instability [1,2]. An increasing Q-angle represents a larger lateral vector and this is presumed to interfere with normal patella tracking within the trochlear groove of the femur, thereby increasing retropatella joint surface pressure. The resultant increased pressure between the lateral trochlear ridge and the patella causes pain, thus providing the source of PFPS, and ultimately, leads to degeneration of the articular cartilage . In addition, this increase in contact pressure may increase the likelihood of lateral patellar subluxation or dislocation .
It has also been suggested that an abnormal Q-angle may inﬂuence neuromuscular response and quadriceps reﬂex response time, an aetiological factor in PFPS .
Let's see what the science tells us about the Q-angle.
The popular belief regarding PFPS etiology is an increased Q-angle causes the quadriceps to exert a greater lateral force vector and predispose the patella to excessive lateral tracking as mentioned above. This theory is not supported by the research findings, and many works [15,16,17] have found no relationship between an increased Q-angle and PFPS. Reasons for these findings may reflect the poor reliability and validity associated with this measure .
Another reason may reflect the static nature of this measure. Many patients with PFPS may demonstrate a normal Q-angle when assessed in a static manner. However, many of these patients may exhibit faulty lower extremity kinematics duringdynamic activities like running, jumping, or singleleg landing that can increase the Q-angle .
To address limitations with this static measure, Powers [14,16] has described use of the dynamic Q-angle since it assesses changes during dynamic, weight bearing activities. He has theorized that increased femoral adduction (relative to the pelvis) and/or femoral internal rotation (relative to the pelvis) during weight bearing activities can impart a valgus knee force and stress lateral patellofemoral joint structures.
With the use of kinematic magnetic resonance imaging (MRI), preliminary evidence has shown that subjects with PFPS demonstrated increased femoral internal rotation under a relatively stable patella during a single-leg squat. These findings provided a rationale for incorporating exercises that target the hip for patients with PFPS.
Faulty foot mechanics also can affect the dynamic Q-angle. In a famous paper, Tiberio  theorized that excessive subtalar pronation can cause increased tibial internal rotation. Excessive tibial internal rotation would then require a greater amount of relative femoral internal rotation to extend the knee (i.e., the screw-home mechanism) during weight bearing activities. Lee and colleagues reported an association between increased lateral patellofemoral joint stress and excessive femoral internal rotation. Based on these findings, researchers have examined the use of hip strengthening and foot orthosis use for the treatment of PFPS.
In summary, the reliability of measurement for Q-angle is poor.
Reliability is deﬁned as the extent to which a measurement is consistent and free from error, and there has been much controversy over the reliabiliyt of the Q-angle for many years.
The ﬁndings of this review suggest that there is disagreement on the reliability and validity of the clinical Q angle measurement. This may be due to the variability in measurement procedure, gender and BMI amongst other parameters.
When assessing the clinical Q-angle, plain radiographs, magnetic resonance imagery and computed tomography images may be considered a gold standard.
Insall et al.’s method of Q-angle measurement remains in widespread use, however there has been confusion and disagreement on its reliability. This has resulted in the accuracy of the Q-angle measurement being questioned repeatedly. Establishing the evidence-base to examine the reliability and validity of the Q-angle has considerable clinical importance, given that surgeons, physiotherapists, podiatrist and other clinicians have reported the use of the Q-angle as a mean of assessing treatment success in patellofemoral joint dysfunction.
My recommendation is that the Q-angle be noted, but not used as a primary measure for management of PFPS. Of far more importance, is an assessment of hip muscle strength, especially the hip abductors, since there is now a large and fairly compelling body of evidence suggeting hip muscle weakness, leading to increased hip adduction, is a a primary determinant in PFPS.
In the past much emphasis has been placed on the assessment of the quadriceps mechanism, with a particular focus on VMO. It now seems increasingly likely, that structures more proximal (hip) and distal (foot), play a far more important role in the establishment and develpoment of PFPS.
1. Fredericson M, Yoon K. Physical examination and patellofemoral pain syndrome. Am J Phys Med Rehabil 2006; 85:234-43.
2. Powers CM. The influence of altered lower-extremity kinematics on patellofemoral joint dysfunction: a theoretical perspective. J Orthop Sports Phys Ther 2003;33:639-46.
3. Park SK, Stefanyshyn DJ. Greater Q angle may not be a risk factor of patellofemoral pain syndrome. Clin Biomech 2011;26:392-6.
4. Tomsich DA, Nitz AJ, Threlkeld AJ, Shapiro R. Patellofemoral alignment: reliability. J Orthop Sports PhysTher 1996;23:200-8.
5. Thomeé R, Augustsson J, Karlsson J. Patellofemoral pain syndrome: a review of current issues. Sports Med 1999;28: 245-62.
6. Lun V, Meeuwisse WH, Stergiou P, Stefanyshyn D. Relation between running injury and static lower limb alignment in recreational runners. Br J Sports Med 2004;38:576-80.
7. Witvrouw E, Lysens R, Bellemans J, Cambier D, Vanderstraeten G. Intrinsic risk factors for the development of anterior knee pain in an athletic population. A two-year prospective study. Am J Sports Med 2000;28:480-9.
8. Nguyen AD, Shultz SJ. Identifying relationships among lower extremity alignment characteristics. J Athl Train 2009;44:511-8.
9. Duffey MJ, Martin DF, Cannon DW, Craven T, Messier SP. Etiologic factors associated with anterior knee pain in distance runners. Med Sci Sports Exerc 2000;32:1825-32.
10. Messier SP, Davis SE, Curl WW, Lowery RB, Pack RJ. Etiologic factors associated with patellofemoral pain in runners. Med Sci Sports Exerc 1991;23:1008-15.
11. Tiberio D. The effect of excessive subtalar joint pronation on patellofemoral mechanics: a theoretical model. J Orthop Sports Phys Ther 1987;9:160-5.
12. Buchbinder MR, Napora NJ, Biggs EW. The relationship of abnormal pronation to chondromalacia of the patella in distance runners. J Am Podiatr Med Assoc 1979;69:159-62.
13. Buchbinder MR, Napora NJ, Biggs EW. Gait analysis in patients with anterior knee pain. Clin Biomech 1994;9:79-84.
14. Powers CM, Maffucci R, Hampton S. Rearfoot posture in subjects with patellofemoral pain. J Orthop Sports Phys Ther 1995;22:155-60.
15. Herrington L, Nester C. Q-angle undervalued? The relationship between Q-angle and medio-lateral position of the patella. Clin Biomech. 2004;19:1070-1073.
16. Powers CM. The influence of altered lower-extremity kinematics on patellofemoral joint dysfunction: A theoretical perspective. J Orthop Sports Phys Ther. 2003;33(11):639-646.
17. Boling MC, Padua DA, Marshall SW, Guskiewicz K, Pyne S, Beutler A. A prospective investigation of biomechanical risk factors for patellofemoral pain syndrome: the Joint Undertaking to Monitor and Prevent ACL Injury (JUMP-ACL) cohort. Am J Sports Med. 2009;37(11):2108-2116.
18. Smith TO, Hunt NJ, Donell ST. The reliability and validity of the Q-angle: a systematic review. Knee Surg Sports Traumatol Arthrosc. 2008;16:1068–1079.
19. Tiberio D. The effect of excessive subtalar joint pronation on patellofemoral mechanics: A theoretical model. J Orthop Sports Phys Ther. 1987;9(4):160-165.