The "Lyon schuss" (LS) view is a fluoroscopically assisted radiographic technique of the knee in flexion. The quality of medial tibial plateau (MTP) alignment is a key element for accuracy and sensitivity to change of knee radiography. We collected data on the geometry of the osteoarthritic (OA) knee when positioned under fluoroscopy according to the LS protocol, then applied the results to develop an angulation standard for a nonfluoroscopically guided examination, and evaluated the performance of fluoroscopic and nonfluoroscopic alternatives for good alignment of the MTP.
1. For 50 patients with knee pain (100 knee radiographs): Standardized radiographic procedure under fluoroscopy (LS view and lateral weight-bearing radiograph of the 2 knees); measurement of the tibial plateau inclination with the horizontal (TPI-h); evaluation of the quality of MTP alignment; assessment of the mean x-ray beam angle to obtain satisfactory MTP alignment. 2. For 30 patients with knee OA: LS radiograph of the knee performed without fluoroscopy, using a fixed 11 degrees downward x-ray beam angle (mean value of the angle obtained in the first part of the study) and standardized procedure; then assessment of the quality of MTP alignment.
With the fluoroscopically assisted protocol, MTP alignment was satisfactory in 88% of cases. The mean x-ray beam angle was 11.2 degrees downward (SD 3.3 degrees, range 4-22 degrees ) and was unrelated to sex, height, weight, body mass index, and joint space width. The mean TPI-h was 19.6 degrees (SD 6.9 degrees, range 3-35 degrees ). Beam angle and TPI-h were correlated only in the satisfactorily aligned radiographs. In the 30 knees radiographed using a standardized procedure without fluoroscopy, the MTP alignment was satisfactory in 60% of cases.
Fluoroscopy is useful to obtain satisfactory MTP alignment in LS radiographs because of large interindividual variations in anatomy of the knee.