Adductor tubercle appears more posterior on radiographs of knees with trochlear dysplasia.

Purpose: The purpose of this study was to compare the radiographic positions of commonly utilized landmarks between symptomatic and normal knees and to assess the influence of morphologic risk factors.

Methods: 3D models were created from knees of patients with patellar instability and compared to control knees. On the 3D models, the adductor tubercle, medial epicondyle and gastrocnemius tubercle were marked. A 2D view was created from these models to simulate radiographs, and the radiographic location of each landmark was described with respect to the anteroposterior relation to the posterior cortical line, and proximal-distal relationship to the posterior condylar line. The position of each landmark was compared between symptomatic and control groups and assessed for variations in position with severity of anatomic risk factors.

Results: 40 patients were included in this study. On the 2D views, the medial epicondyle was found to be more posterior and more distal than in the control group. Association between severity of trochlear dysplasia and posterior position of the adductor tubercle trended toward significance (R=0.43, R2=0.18, p=0.058). In symptomatic knees with trochlear dysplasia, the radiographic landmark for the medial epicondyle was posterior by 3.3mm (p=0.052), adductor tubercle by 2.7mm (p=0.009), and gastrocnemius tubercle by 3.9mm (p=0.010) when compared to symptomatic knees without dysplasia.

Conclusion: This study demonstrates that commonly utilized anatomic landmarks are more posterior and distal on radiographs in knees with patellar instability when compared to normal knees. Trochlear dysplasia is associated with the radiographic landmarks of the adductor and gastrocnemius tubercles appearing 3mm posterior to those without dysplasia, and its severity is associated with posterior radiographic appearance of the adductor tubercle.

Level of evidence: III, Retrospective Case Control.