What Is the “Perfect” Lateral Radiograph? Effects of Beam Directionality and Condylar Alignment on the Perceived Location of the Medial Patellofemoral Ligament: Letter to the Editor

Dear Editor:

I read with great interest the cadaveric study by Johnson et al, ² who quantified the influence of fluoroscopic beam directionality and posterior condylar alignment on the perceived location of the medial patellofemoral ligament (MPFL) insertion on lateral knee radiographs. Their data indicate that among the tested configurations, a medial-to-lateral (ML) projection with posterior proximal condylar alignment results in the smallest variation in marker position and therefore provides a consistent framework for standardizing intraoperative lateral fluoroscopy.

I would like to place these findings in the context of a recently published cadaveric study, “Lateral to Medial Fluoroscopic View Improves the Accuracy of Identifying the MPFL Femoral Footprint Using Schottle’s Technique,” ¹ by myself and colleagues. In our work on 44 dry femora, the center of the anatomic MPFL femoral footprint was identified using established bony landmarks and marked with a radiopaque thumbtack. Two true lateral fluoroscopic images, one in the ML and one in the lateral-to-medial (LM) direction, were then obtained for each specimen, both with perfect posterior condylar overlap. On each image, Schottle’s radiographic point was constructed, and the distance between this point and the anatomic footprint was measured. In line with previous work, we considered femoral tunnel positions within 5 mm and 7 mm of the anatomic footprint as acceptable error margins.^3,4 We found that the LM view yielded a significantly smaller mean deviation from the anatomic footprint than the ML view (3.2 ± 1.5 vs 4.5 ± 2.1 mm, respectively; P < .001) and that the LM view achieved “within 5-mm” tunnel positions more often than the ML view (90.9% vs 65.9%).

Although both studies investigate similar fluoroscopic variables, they address different primary questions. Johnson et al ² examined how changes in beam direction and condylar alignment shift the apparent position of a fixed radiopaque marker, aiming to minimize variability across imaging configurations. Their endpoint, the magnitude of displacement between marker positions across settings, captures image reproducibility but does not directly assess how closely any given setting reproduces Schottle’s point behavior relative to that footprint. In contrast, our study focused on a strictly defined “perfect” lateral view (exact posterior condylar overlap) and compared ML versus LM beam direction specifically in terms of the absolute distance between Schottle’s point and the anatomic MPFL footprint.

Taken together, these cadaveric data can be interpreted as complementary. Johnson et al ² provide practical guidance for obtaining a reproducible lateral fluoroscopic image by favoring ML imaging with posterior proximal condylar alignment when beam direction and alignment may vary intraoperatively. Our findings suggest that once a high-quality true lateral view has been achieved and Schottle’s technique is used, an LM projection may bring Schottle’s point closer to the anatomic MPFL femoral footprint than does an ML projection. In clinical terms, surgeons might therefore consider 2 sequential aims during MPFL reconstruction: first, to obtain a consistent true lateral view with reliable posterior condylar overlap, and second, when relying on Schottle’s landmarks, to preferentially use an LM projection, recognizing that even small deviations in condylar alignment or beam direction can introduce additional millimetric shifts.

Johnson and colleagues are to be congratulated for rigorously quantifying the effects of beam directionality and condylar alignment on lateral knee fluoroscopy, and I hope that juxtaposing these 2 cadaveric studies will help refine both the standardization and the anatomic precision of intraoperative imaging during MPFL reconstruction.