Q Angle
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Background[edit | edit source]
Measurement
[edit | edit source]
The Q angle is acute angle formed between:
- A line representing the resultant line of force of the quadriceps, made by connecting a point near the ASIS to the mid-point of the patella
- A line representing a long axis of the patellar tendon, made by connecting a point on the tibial tuberosity with the mid-point of the patella.
Traditionally, Q-angle has been measured with the knee at or near full extension (but not hyperextension)with subjects in supine and quadriceps relaxed because lateral forces on the patella may be more of a problem in these circumstances. With the knee flexed, the patella is set within the intercondylar notch, and even a very large lateral force on the patella is unlikely to result in dislocation. Furthermore, the Q-angle will reduce with knee flexion as the tibia rotates medially in relation to the femur.[1] This is regarded as the 'traditional' or 'conventional' method. The Q angle has also been assessed on standing.
Normative Values [edit | edit source]
- 13.5±4.5 degrees is considered as normal Q angle for healthy subjects between the ages of 18 and 35 years.[2]
- The Qangle for women is 4.6 degrees higher than that for men.[2]
- Women have a slightly greater Q-angle than do men because of the presence of a wider pelvis, increased femoral anteversion, and a relative knee valgus angle.
Problems with Measuring 'Q' Angle[edit | edit source]
- Problem with using the Q-angle as a measure of the lateral pull on the patella is that the line between the ASIS and the midpatella is only an estimate of the line of pull of the quadriceps and does not necessarily reflect the actual line of pull in the patient being examined.
- If a substantial imbalance exists between the vastus medialis and vastus lateralis muscles in a patient, the Q-angle may lead to an incorrect estimate of the lateral force on the patella because the actual pull of the quadriceps muscle is no longer along the estimated line.
- Furthermore, a patella that sits in an abnormal lateral position in the femoral sulcus because of imbalanced forces will yield a smaller Q-angle because the patella lies more in line with the ASIS and tibial tuberosity.
Factors affecting 'Q' Angle[edit | edit source]
Increases in q-angle are associated with [3]:
- Femoral anteversion
- External tibial torsion
- Laterally displaced tibial tubercle
- Genu valgum : increases the obliquity of the femur and, concomitantly, the obliquity of the pull of the quadriceps.
Clinical Importance[edit | edit source]
References[edit | edit source]
- ↑ 1.0 1.1 Levangie, P.K. and Norkin, C.C. (2005). Joint structure and function: A comprehensive analysis (4th ed.). Philadelphia: The F.A. Davis Company.
- ↑ 2.0 2.1 2.2 Horton MG, Hall TL. Quadriceps Femoris Muscle Angle:Normal Values and Relationships with Gender and Selected Skeletal Measures. Phy Ther 1989; 69: 17-21
- ↑ http://moon.ouhsc.edu/dthompso/namics/qangle.htm