The Hip: Preservation, Replacement and Revision Tracking Pixel
Duke Orthopaedics
presents
Wheeless' Textbook of Orthopaedics

Merchant Technique



- 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 (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. A prospective, randomized outcome study.

- 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;
             - Agliettis, et al noted that angle of congruence might be more accurately
                    defined with an upper limit of normal of 4 degrees;
    - Aglietti, et al. (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 through patella at a 60 deg angle from vertical or 30 deg angle from horizontal;

- Aglietti, et al. (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.

Patellofemoral Joint: 30 degrees Axial Radiograph with Lateral Rotation of the Leg.

Roentgenographic Analysis of Patellofemoral Congruence.

The Abnormal Lateral Patellofemoral Angle. A Diagnostic Roentgenographic Sign of Recurrent Patellar Subluxation.



Original Text by Clifford R. Wheeless, III, MD.

Last updated by Data Trace Staff on Friday, August 31, 2012 1:45 pm