Extra-articular, Intraepiphyseal Drilling for Osteochondritis Dissecans of the Knee: Characterization of a Safe and Reproducible Surgical Approach

BACKGROUND: Osteochondritis dissecans (OCD) is an idiopathic focal condition affecting the subchondral bone of joints, and it is increasingly prevalent among the active young adult population. For lesions that have failed nonoperative management, transarticular drilling and extra-articular drilling are surgical options. Although the extra-articular approach preserves the articular cartilage, it is technically challenging and could benefit from a study of surgical approach. PURPOSE: To use 3-dimensional modeling of magnetic resonance imaging (MRI) scans from skeletally immature individuals to characterize safe tunnel entry points, trajectories, and distances from the physeal and articular cartilage along the course of the distal femoral epiphysis to the OCD target in their most common location of the medial femoral condyle (MFC). STUDY DESIGN: Descriptive laboratory study. METHODS: A total of 17 MRI scans from skeletally immature patients were used to create 3-dimensional models of the knee joint. Virtual representations of an OCD lesion were placed in the lateral aspect of the MFC; cylinders simulating tunnel length, diameter, and trajectory were superimposed onto the models; and measurements were taken. RESULTS: Two safe tunnels were identified, 1 anterior and 1 posterior to the medial collateral ligament (MCL). The anterior tunnel had a diameter of 10.3 ± 1.4 mm, skin entry point of 16.9 ± 12.1 mm anterior and 7.1 ± 5.9 mm superior to the medial epicondyle, bony entry point of 12.1 ± 3.5 mm anterior and 2.4 ± 3.5 mm inferior to the medial epicondyle, and tunnel length of 31.8 ± 3.7 mm. The posterior tunnel had a diameter of 7.8 ± 1.8 mm, skin entry point of 9.4 ± 5.1 mm posterior and 26.0 ± 14.0 mm superior to the medial epicondyle, bony entry point of 8.6 ± 2.6 mm posterior and 5.1 ± 4.2 mm superior to the medial epicondyle, and tunnel length of 33.5 ± 4.5 mm. CONCLUSION: This anatomic characterization study identifies and defines 2 safe and reproducible tunnel approaches, 1 anterior and 1 posterior to the MCL, for drilling or creating tunnels to OCD lesions of the MFC in an extra-articular fashion. CLINICAL RELEVANCE: The study findings provide valuable anatomic references for surgeons performing extra-articular drilling or tunneling of OCD lesions.