1. Vastus Medialis Obliquus Deficiency
VMO deficiency is best seen as the sitting patient actively maintains the unsupported foot and leg at 30° knee flexion. Normally, the VMO inserts into the upper half or third of the medial edge of the patella; a deficient VMO inserts higher into the medial edge of the quadriceps tendon, or it is absent and leaves a characteristic hollow at the medial edge of the patella (Figure 2).4
2. Medial Patellofemoral Ligament Laxity
MPFL laxity is assessed with the lateral glide test. Again, the patient sits, but with quadriceps relaxed and foot and leg supported at 30° knee flexion. With the clinician mentally dividing the patella into vertical quadrants and pushing the patella laterally, the normal patella moves about 1 quadrant or 1 fingerbreadth. Severe MPFL laxity often elicits a positive apprehension response during the test. (Tip: Many patients are unable to relax the quadriceps while sitting; therefore, examine them supine and lift the knee into 30° flexion.) Such laxity usually means the MPFL was torn in a previous dislocation and remains elongated, leaving the patella vulnerable to repeated dislocations. The clinician should be alert to the possibility of hyperelastosis (Ehlers-Danlos syndrome) and a hyper-mobile patella. The opposite limb should be evaluated for asymmetric laxity.
3. Lateral Retinaculum Tightness
LR tightness is assessed with the medial glide test, again with the quadriceps relaxed and the knee supported at 30° flexion. With a normal LR, the patella can be pushed medially about 1 quadrant or 1 fingerbreadth. Some clinicians prefer the lateral tilt-up test, in which the lateral edge of the patella is lifted up, but this method is more difficult to quantify, is affected by the cross-sectional shape of the patella, and lacks consistency.
4. Increased Quadriceps Angle
The Q angle is one of the most important factors in the normal functioning of the patellofemoral joint. For more than a century,8 multiple operations have been used successfully to move the tibial tubercle (TT) and patellar ligament from a lateral position to a medial position thereby decreasing the Q angle. It is only logical to measure this angle at every knee examination to check for an abnormal increase, and the degree. The term quadriceps angle, or Q angle, was first used in 1964 by Brattström,7 who defined it as the “supplemental angle” to the valgus angle formed by the “quadriceps’ resultant” (line of force or vector) “+ patella + ligamentum patellae”. This might be called the dynamic Q angle. With there being no clinical method of measuring the “quadriceps line of force”, or quadriceps vector, clinicians used a line from the anterior superior iliac spine to the center of the patella, yet still called it the Q angle. By convention, this anatomical Q angle has been accepted as the Q angle.
Because the Q angle is the only clinical measurement of TT lateralization at initial evaluation, its measurement should be standardized, accurate, and simple to perform. Placing the patient supine with the lower limb in neutral rotation (patella anterior) and the knee in full extension standardizes the position. In full extension, the tibia reaches its maximum external rotation owing to the terminal “screw home” mechanism. The clinician should center the patella to the trochlear groove (TG) while measuring the Q angle, as it is the relationship of the TT to the trochlea, not to the patella, that is important. If LR tightness prevents the patella from centering, that fact should be recorded during the medial glide test for LR tightness.
Despite the importance of measuring the Q angle, there has been no standard technique. Multiple authors have attempted to define the “normal” Q angle. In 1999, Post9 reviewed 7 articles on the topic and found no agreement. Mean normal Q angles varied widely, from 5° to 23° (SD range, 0.08°-5°). Grelsamer and colleagues,10 using a long-armed goniometer and standard technique, found a mean Q angle of 15.7° for women and 13.3° for men; the small, 2.4° difference between them disappeared when the measurements were corrected for height. Men and women of similar height have similar Q angles. These findings disproved the common misattribution of the differences to the wider female pelvis.
Given this confusion and the lack of accuracy in measuring the Q angle, many, if not most, surgeons turned to special CT and MRI scanning techniques to measure the distance of lateralization from TT to TG (TT-TG distance). This technique, by necessity, enforced a standardization not found in the earlier Q angles studies. Patients were positioned supine with the knee fully extended, and patellar position was ignored in favor of the TG. However, recent articles11-14have called into question the accuracy and usefulness of TT-TG distance as an assessment of TT lateralization. As such, standardized measurement of the Q angle remains a simple, inexpensive, and clinically relevant method of assessing TT lateralization.
The possible causes of an increased Q angle are valgus limb alignment, internal femoral torsion, external tibial torsion, combined internal femoral and external tibial torsion with foot pronation (the “miserable malalignment” of James and colleagues15), and a TT-lateralizing proximal tibial malformation.