Abstract
We thank Dr Kose for the thoughtful letter regarding our recent publication 3 and for highlighting the work by Kose and others 2 evaluating fluoroscopic beam directionality in identifying the medial patellofemoral ligament (MPFL) femoral location. We appreciate the opportunity to clarify the intent of our study and to describe how this information fits into the broader context of the current literature and clinical practice.
The concept of a “perfect lateral” knee radiograph—defined by superimposition of the posterior femoral condyles—was originally described by Schottle et al 5 and was further supported by Kamath et al 4 to localize the MPFL femoral insertion site. These studies established a radiographic landmark where fluoroscopic techniques can approximate the anatomic MPFL insertion within a few millimeters. However, both investigations assume that a true lateral view can be reliably obtained and do not specifically address how this should be achieved in the presence of variable condylar morphology or differing fluoroscopic beam orientations.
Schottle et al 5 defined the landmarks on a lateral radiograph with the posterior condyles projected in the same plane but did not provide guidance regarding beam directionality or how to reconcile discrepancies in medial and lateral condyle size. Similarly, Kamath et al 4 emphasized the importance of posterior condyle overlap but demonstrated that even small deviations introduce measurable error. These findings underscore that the “perfect lateral” technique has not yet been standardized in clinical practice.
Our study was designed to address this knowledge gap. We evaluated how beam directionality and condylar alignment affect the perceived position of a fixed marker placed at the femoral MPFL insertion. We found that medial-to-lateral (ML) projection with posterior proximal condylar alignment minimized positional variability, suggesting that this configuration may provide a more reproducible localization image with intraoperative imaging when perfect condylar overlap is not achievable.
We agree with Dr Kose that a lateral-to-medial (LM) projection may improve the anatomic accuracy of a Schottle’s point localization of the MPFL anatomic footprint, particularly in patients with patellar instability who have more severe lateral condylar hypoplasia. In these patients, it may be technically easier to obtain a perfect lateral view with beam directionality in the LM direction (ie, lateral condyle farther away from the intensifier, thus slightly magnifying the lateral femoral condyle to minimize condylar mismatch). Their study emphasizes accuracy, whereas our study focuses on reproducibility.
Using both studies, the data support a stepwise approach to intraoperative fluoroscopy during MPFL reconstruction. First, surgeons should prioritize obtaining the perfect lateral radiograph, understanding that condylar asymmetry can affect the fluoroscopy appearance. Second, it is important to understand some of the limitations related to intraoperative fluoroscopy. Although our study focused on beam directionality and proximal versus distal condylar alignment, many other factors affect the fluoroscopic image related to distortion and magnification. 1 Although finding the femoral MPFL insertion using the perfect lateral view has greatly improved our ability to perform an MPFL reconstruction, the chosen point should still be meticulously critiqued for isometry given the potential inaccuracies and technical variations related to radiographic localization of the MPFL.
By addressing the limitations inherent in the “perfect lateral” paradigm, we believe our study contributes to improving the consistency and reliability of intraoperative fluoroscopic techniques. Future work is needed to integrate both reproducibility and accuracy of these techniques to standardize a consistent algorithm for surgical practice.
We thank Dr Kobe and AJSM for advancing this important discussion.
