Poster 246: Radiographic Landmarks for Femoral Tunnel Positioning During MPFC Reconstruction Vary With Trochlear Dysplasia
Authors: Tanaka Miho , Hammerle Maria Virginia Velasquez , Howard Patrick T. , Crasta Nikitha , Liu Fang 
Published: October 2024

Objectives: Accurate femoral tunnel positioning during medial patellofemoral complex (MPFC) reconstruction has been shown to be critical in optimizing outcomes and avoiding complications. Multiple anatomic and radiographic studies have described methods to accurately identify the appropriate femoral attachment of the MPFC, commonly referencing the adductor tubercle and medial epicondyle as landmarks. However, these studies have been performed in normal knees, and the relevance to knees with patellar instability and anatomic risk factors has not been described. Therefore, the purpose of this study was to compare the radiographic positions of commonly utilized landmarks between symptomatic and normal knees. Methods: Three-dimensional (3D) models were created from computed tomography scans of knees with patellar instability and compared to age- and sex-matched control knees. On the 3D models, the locations of the adductor tubercle (AT), medial epicondyle (ME) and gastrocnemius tubercle (GT) were marked. A 2-dimensional perfect lateral view was then created from these models to simulate radiographs, and the radiographic location of each landmark was described with respect to the following: 1) anteroposterior relation to the posterior cortical line and 2) proximal-distal relationship to the posterior condylar line. The position of each landmark was compared between symptomatic and control groups, and linear regression analysis was performed to assess variations in position with severity of anatomic risk factors including trochlear dysplasia, tuberosity lateralization and patella alta. Results: Forty knees were included in this study, including 20 symptomatic and 20 control knees (8 men and 12 women in each group, age 21.5+/-6.9 years old vs 21.3+/-7.0 years old). On the 2D (radiographic) views, the ME landmarks in the symptomatic group were found to be significantly more posterior (6.9+/-3.7mm vs 9.5+/-4.2 mm, p = 0.031) and significantly more distal (9.2+/-4.4 vs 12.1+/-5.6, p = 0.047) than in the control group. For the AT, no significant differences were noted in the anteroposterior (0.7+/-2.4 vs 1.3+/-2.6 mm anterior to the posterior cortex, p = 0.238) or proximal-distal (4.9+/-2.8 vs 5.4+/-2.3mm proximal to the posterior condylar line, p = 0.259) positions. Similarly, no differences for the GT were found (4.4+/-3.4 vs 2.8+/-3.7 mm posterior to the posterior cortex, p = 0.100; and 5.1+/-4.6 vs 4.0+/-3.2 mm distal to the posterior condylar line, p = 0.175). An association between severity of trochlear dysplasia and posterior position of the AT was identified (R = 0.43, R2 = 0.18, p = 0.058). Conclusions: Although intraoperative fluoroscopy is commonly utilized to identify femoral tunnel positioning during MPFC reconstruction, this study demonstrates that commonly utilized anatomic reference points such as the medial epicondyle in symptomatic knees are more posterior and more distal on perfect lateral radiographs when compared to normal knees. Furthermore, the severity of trochlear dysplasia appears to influence radiographic AT position. These findings should be taken into consideration when utilizing fluoroscopy during MPFC reconstruction. Further studies are needed to identify optimal femoral tunnel positioning for knees with anatomic risk factors when performing surgical treatment for patellar instability.