“RESIDENTS RIDGE”: DOES IT EXIST? : AN ANATOMICAL STUDY

Background: The term ‘resident9s ridge’ originated from trans-tibial ACL reconstruction where a bony ridge on the medial surface of the lateral femoral condyle was mistakenly thought to represent the posterior articular margin of the condyle. This was then mistakenly used to position the ‘over the top’ guide resulting in graft malposition. With anatomical anteromedial ACL reconstruction some surgeons use the same ridge to define the anterior margin of the ACL femoral insertion in order to guide graft placement. However there is debate about whether this ridge is a consistent and reliable anatomical structure. There are no anatomical studies that define the features of the ‘resident9s ridge’. Therefore, our aim was to identify whether the ‘resident9s ridge’ is a consistent anatomical structure in non-operated human cadaveric femoral specimens. Methods: Using a digital microscribe, we mapped the medial surface of the lateral femoral condyle in cadaveric human femora denuded of soft tissue. This technique creates an exact 3D model of surfaces and from this we evaluated whether there was an identifiable bony ‘residents ridge’. 23 cadaveric specimens were used. Results: All 23 specimens had a defined identifiable ridge on the medial surface of the lateral femoral condyle. When viewed anatomically, the proximal extent of the ridge lies at the superior junction of the articular margin and the femoral shaft. From this point, the ridge forms an oblique line travelling proximal-to-distal and anterior-to-posterior to a point approximately 30–40% anterior to the posterior articular margin. The ridge therefore divides the medial surface into anterior 2/3 rd and posterior 1/3 rd when viewed anatomically. Conclusion: This study shows that the “resident9s ridge” is a consistent anatomical structure that defines the anterior margin of the ACL insertion. This therefore supports its use as a landmark for femoral tunnel placement in ACL reconstruction surgery.