- Discussion:
- for evaluation of both the patella and trochlea surfaces of femur;
- disadvantages:
- this view does not necessarily predict which patients will show functional improvements
w/ surgical realignment;
- as pointed out by O'Neil (JBJS 1997) some patients with functional improvement from lateral retinacular
release will show lateralization on the postoperative Merchant view whereas other patients will not
show clinical improvement despite showing medialization of the patella on postoperative radiographs;
- reference:
Open lateral retinacular lengthening compared with arthroscopic release.
DB O'Neil MD.
JBJS Vol 79-A. No 12. Dec 1997. p 1759.
- Congruence Angle:
- angle of congruence is an
index of Subluxation but does not assess tilt;
- measured using the Merchant technique:
- congruence angle defines relationship of apex of patella to bisected
femoral trochlea;
- technique for measurement:
-
sulcus angle: establishes a zero reference line
-
2nd line is projected from the apex of sulcus angle to lowest point of
articular ridge of the patella;
- interpretation:
- if congruence angle is is
lateral to congruence line, then angle is positive;
"
"
"
medial to congruence line, then anlge is negative;
- normal angle is defined as <
- 16 deg;
- Aglietti et al noted that angle of congruence might be more accurately
defined with an upper limit of normal of 4 degrees;
- Agliettis et. al. Clin. Ortho 1983
- 75 norm males:
sulcus < was 137 deg &
cong. angle = neg
6 deg
- 75 norm females:
sulcus < was 137 deg &
cong. angle = neg10 deg
- w/
Chondromalacia: congruence angle > neg 2 deg;
- patellar tilt:
- patellar subluxation:
- Technique:
- patient is supine with the knee flexed 45 deg at the tables edge;
- cassette is held perpendicular to the tibia;
- central beam directed caudally thru patella at a 60 deg angle from vertical
or 30 deg angle from horizontal;
- Agliettis et. al. Clin. Ortho 1983
- normal and abnormal values:
- 75 normal males:
-
Q angle = 14 deg (+/- 3)
- using
Merchant technique
- sulcus < was 137 deg, Cong. angle = -6 deg
- 75 normal females:
-
Q angle = 17 deg (+/- 3)
- using
Merchant technique
- sulcus < was 137 deg, Cong. angle = -10
- both sexes:
-
LT/LP ratio: 1.04 (0.8 to 1.38)
- AB ratio = .95 w/ range of 0.65 to 1.38;
-
Merchant technique
- sulcus < was 137 deg
- 53 patients w/
Chondromalacia:
-
Q angle was 20 deg (versus 15 deg;)
-
LT/LP differed only in the males = 1.08 versus 1.01
- AB shows No difference (males and fem) versus control;
-
congruence angle = - 2 deg (sig diff. for males and fem)
- 37 patients w/ recurrent patellar
Subluxation
-
Q angle = 15 deg (no sig change)
-
LT/LP = 1.23 (increase)
- AB ratio (1.08) (sig diff w/ females)
- sulcus angle = 147 & C. < = 16 deg (sig for both sexes)
Radiographic analysis of patellar tilt.
Subluxation of the patella. Computed tomography analysis of patellofemoral congruence.
Use of a modified Elmslie-Trillat procedure to improve abnormal patellar congruence angle.
Patellar Pain and Incongruence. I: Measurements of Incongruence.
Aglietti, Paolo; Insall, J. N.; and Cerulli, G.:
Clin. Orthop., 176: 217-224, 1983.
Patellofemoral Joint: 30 degrees Axial Radiograph with Lateral Rotation of the Leg.
Malghem, Jacques, and Maldague, Baudouin:
Radiology, 170: 566-657, 1989.
Roentgenographic Analysis of Patellofemoral Congruence.
Merchant, A. C.; Mercer, R. L.; Jacobsen, R. H.; and Cool, C. R.:
J. Bone and Joint Surg., 56-A: 1391-1396, Oct. 1974.
The Abnormal Lateral Patellofemoral Angle. A Diagnostic Roentgenographic Sign of Recurrent Patellar Subluxation.
Laurin, C. A.; Levesque, H. P.; Dussault, R.; Labelle, H.; and Peides, J. P.:
J. Bone and Joint Surg., 60-A: 55-60, Jan. 1978.
