Introduction
The angle produced between the quadriceps muscles and the patella tendon is known as the Q angle, commonly referred to as the quadriceps angle. Brattstrom described it for the first time in 1964.
The amplitude and direction of force produced by the quadriceps muscle have a significant impact on patellofemoral joint biomechanics.
The enormous cross-sectional area and force potential of vastus lateralis play a significant role in the quadriceps’ line of force extending laterally to the joint line. Assessing the overall lateral line of pull of the quadriceps relative to the patella is a significant clinical metric since there is a correlation between patellofemoral pathology and excessive lateral tracking of the patella.
Measurement
The Q angle is produced between:
- A line that connects a site near the ASIS to the midpoint of the patella to depict the quadriceps’ resulting line of force.
- The Q angle can be measured while lying or standing.
1. Since the natural weight-bearing forces are exerted on the knee joint during daily activities, standing is usually preferable. - The Q angle has traditionally been measured with the knee at or near full extension (but not hyperextension), subjects lying supine, and the quadriceps relaxed, as lateral stresses on the patella may be more of a concern in these conditions.
- With
2. The patella is positioned within the intercondylar notch when the knee is flexed, and even a considerable lateral force on the patella is unlikely to result in dislocation. Additionally, as the tibia rotates medially in proportion to the femur, the Q angle decreases. - This is considered the “traditional” or “conventional” approach.
- The Q angle has also been calculated when standing.
Comparative Values
- The Q angle in women should be less than 22 degrees with the knee extended and less than 9 degrees with the knee at 90 degrees of flexion.
- The Q angle in males should be less than 18 degrees when the knee is extended and less than 8 degrees when the knee is in 90 degrees of flexion.
- A normal Q angle for men is 12 degrees and 17 degrees for women.
‘Q’ Angle Measurement
- Position: The patient is supine, with one knee extended. The therapist is standing close to the patient.
- Implementation: When measuring, make sure the lower extremity is perpendicular to the line connecting each ASIS. The foot should be neutral in supination and pronation, and the hip should be neutral in medial and lateral rotation. Draw a line from ASIS to the patella’s center, and then from the patella’s midpoint to the tibial tubercle. The Q angle is the angle created by the intersection of these two lines.
- Positive indication: A typical Q angle score for females is between 13 and 18 degrees, with values more than or less than this considered abnormal and suggesting that the patient is at risk of developing chondromalacia patellae, patella alta, or patella mal-tracking.
Difficulties with Measuring the ‘Q’ Angle
- The line between the ASIS and the mid-patella is simply an approximation of the line of pull of the quadriceps and does not certainly represent the actual line of pull in the patient being evaluated, which is a problem with utilizing the Q angle as a measure of the lateral pull on the patella.
- If a patient’s vastus medialis and vastus lateralis muscles are significantly imbalanced, the Q angle may result in an inaccurate estimation of the lateral force on the patella since the actual pull of the quadriceps muscle is no longer along the estimated line.
- Besides that, a patella that sits in an inappropriate lateral position in the femoral sulcus due to unbalanced forces produces a reduced Q angle because the patella is better aligned with the ASIS and tibial tuberosity.
Factors that impact the ‘Q’ Angle
- An increase in Q angle is correlated to:
- The tibial tubercle deviated laterally.
- Femoral anteversion (inward rotation)
- Torsion of the tibia externally
- Genu valgum: increases the obliquity of the femur and, as a result, the obliquity of the quadriceps pull.
Clinical Relevance
Any examination of knee function must begin with an awareness of the typical anatomical and biomechanical aspects of the patellofemoral joint. Because of the lateral force, it exerts on the patella, the Q angle created by the vector for the combined pull of the quadriceps femoris muscle and the patellar tendon is significant.
Any alignment change that raises the Q angle is expected to increase lateral stress on the patella.
This can be dangerous because an increase in lateral force might compress the lateral patella on the lateral lip of the femoral sulcus.
When the quadriceps muscle is stimulated on an extended knee, the patella can perhaps actually sublux or dislocate over the femoral sulcus in the presence of a large sufficient lateral force.
An improper Q angle may also alter neuromuscular responses and quadriceps reflex reaction time, according to some research.
Uncommon Value (Pathology)
Genu varum and Genu Recuravatum
- The knee is closest packed and most stable in full extension with slight external rotation. The knee may be bent an additional 5 to 10 degrees from neutral, though this varies greatly from person to person. Standing with the knee fully extended typically places the body’s center of gravity slightly anterior to the knee’s medial-lateral axis of rotation.
- As a result, gravity causes a slight knee extension torque that may help naturally with knee locking while standing, allowing the quadriceps to occasionally relax. Normally, the stretched posterior capsule and the stretched flexor muscles of the knee, including the gastrocnemius, act as passive tension to resist this gravity-assisted extension torque.
- Genu recurvatum is the common name for hyperextension that extends beyond 10 degrees of neutral. When the posterior structures of the knee are lax overall, mild cases of recurvatum can develop in otherwise healthy people. An overpowering (net) knee extensor torque that develops over time and eventually overstretches the posterior structures of the knee is the main factor in more severe genu recurvatum. Poor postural control or a neuromuscular condition that paralyses the knee flexors and/or causes spasticity in the quadriceps muscles may be the cause of the excessive knee extension torque.
Excessive Genu Valgum
- When the legs are straightened, the knees angle in and touch one another, a condition known as Knock Knee. Individuals with severe valgus abnormalities are often unable to put their feet together while simultaneously straightening their legs.
- Excessive genu valgum, or knock knee, can be caused by a number of reasons. These include past injury, genetic susceptibility, a high BMI, and ligament laxity. Genu valgum can also be caused or aggravated by anomalous alignment or muscular weakness at either end of the lower limb.
- For example, coxa vara (a femoral neck-shaft angle less than 125 degrees) or weakening hip muscles (such as the gluteus medius) can increase the valgus strain on the knee.
- Excessive foot pronation may increase the valgus stress on the knee in some situations by permitting the distal end of the tibia to abduct farther away from the body’s midline. The tensional load produced on the MCL and surrounding capsule may damage the tissue over time.
- Excessive valgus of the knee may impair patellofemoral joint tracking and provide extra strain on the ACL. Standing with a valgus deformity that is 10 degrees larger than usual distributes the majority of the joint compression force to the lateral joint compartment. This increased regional stress may lead to lateral, mono-compartmental osteoarthritis. To repair a valgus deformity, knee replacement surgery may be necessary, especially if it is progressing, painful, or causes loss of function.
