Radiographic Reference Points Do Not Ensure Anatomic Femoral Fixation Sites in Medial Patellofemoral Ligament Reconstruction: A Quantified Anatomic Localization Method Based on the Saddle Sulcus

Abstract

Background: Medial patellofemoral ligament (MPFL) reconstruction is one of the main treatments for lateral patellar translation. Based on intraoperative true lateral radiographs, the accepted methods for femoral MPFL tunnel location are potentially inaccurate. Direct assessment of anatomic characteristics during surgery through palpation of the anatomic landmarks involving the saddle sulcus might help eliminate tunnel malposition. Hypothesis: The saddle sulcus is a reliable osseous landmark where the MPFL attaches for tunnel placement. Study Design: Descriptive laboratory study. Methods: A total of 9 fresh-frozen unpaired human cadaveric knees were dissected; MPFL insertion point and relative osseous structures were marked. Three-dimensional images and transformed true lateral radiographs were obtained for analysis; 3 previously reported radiographic reference points for MPFL femoral tunnel placement were determined on all images and compared with the anatomic insertion. Results: A saddle sulcus consistently existed where the MPFL was attached, located at 11.7 ± 5.9 mm from the apex of the adductor tubercle (AT) to the medial epicondyle (ME), 62.8% of the average distance between the apexes of the AT and ME, and 5.6 ± 2.8 mm perpendicular-posterior to the border connecting the AT and ME. The reported radiographic reference points were located at average distances of 6.2 ± 3.2 mm (Schöttle method), 5.9 ± 2.3 mm (Redfern method), and 7.3 ± 6.6 mm (Fujino method) from the saddle sulcus center on the true lateral radiographs. Conclusion: The saddle sulcus was a reliable landmark where the MPFL was anatomically attached, located approximately 12 mm from the AT to the ME (approximately 60% along a line from the AT to the ME) and 6 mm perpendicular-posterior to the border connecting the apexes of the AT and ME. Additionally, the saddle sulcus position presented variability on the femoral aspect of different knees. All of the average direct distances from the sulcus to the reference radiographic points exceeded 5 mm, and tunnel localizations on a true lateral radiograph were inaccurate. Clinical Relevance: This study demonstrates the potential precise position of the saddle sulcus, according to the ME and AT, as a reliable anatomic landmark for MPFL femoral tunnel location. Radiographic reference points were not accurate during MPFL reconstruction. Direct palpation of the landmarks might be effective for femoral MPFL tunnel placement.