Investigation of genicular neurotomy of the knee: MRI characterization of anatomy and implications for intervention.

Background: Genicular nerve block and subsequent radiofrequency neurotomy (RFN) has emerged as a novel intervention and alternative for total knee arthroplasty in patients with refractory pain from knee osteoarthritis (OA). To our knowledge, there is no cited report correlating the accuracy of localizing the genicular nerves using bony landmarks on magnetic resonance imaging (MRI).

Objectives: To quantify the proximity of superomedial genicular nerve (SMGN), superolateral genicular nerve (SLGN), and inferomedial genicular nerve (IMGN) from a target point. The target point was an intersection marked by a line parallel to the diaphysis and a separate line parallel to the metaphyseal flare along the cortical surfaces of both the femur and tibia.

Design: Retrospective chart review.

Patients: A total of 25 de-identified knee MRIs were reviewed.

Methods: The coronal proton density fat suppressed sequence was used for identification and localization of the SLGN, SMGN, and IMGN. The neurovascular bundles were traced from posterior location along their origin as they wrap around the distal diaphysis. The nerve locations were determined by consensus measurements performed by two board-certified radiologists with certificates of added qualification in neuroradiology and interventional radiology. The proximity of each respective genicular nerves was measured by drawing a perpendicular line from each genicular nerve to the height of the target point. All measurements were taken on the mid-coronal view at the point of maximal epiphyseal flare.

Main Outcome Measurements: Positive values indicated the location of the neurovascular bundle to be superior to the target point. Negative values indicated the location of the neurovascular bundle to be inferior to the target point.

Results: The distance between our target point and the inferior border of SLGN ranged from -3 mm to 6 mm. Twenty-three out of 25 (92%) SLGN lied exactly at or above our target intersection. The distance between our target point and the inferior border of SMGN ranged from -1 mm to 2 mm with twenty-two out of 25 (88%) SMGN lied exactly at or above our target point. The distance between our target point and the superior border of IMGN ranged from 0 mm to 3 mm with all (100%) IMGN lying exactly at or above the target point.

Conclusion: The intersection of the femoral diaphyseal shaft to a line along the metaphyseal flare and the intersection of the tibial diaphyseal shaft to a line along the medial metaphyseal can be used as a target point to localize the genicular nerves with close proximity.