Resident's ridge: assessing the cortical thickness of the lateral wall and roof of the intercondylar notch.

PURPOSE: The purpose of this study was to better delineate the anatomy of "resident's ridge," a term coined by William Clancy Jr., M.D., to describe the raised bony landmark commonly visualized just anterior to the femoral attachment of the anterior cruciate ligament (ACL). This landmark can mislead the novice surgeon into misplacing the femoral tunnel of ACL reconstructions.

TYPE OF STUDY: Cadaveric anatomic study.

METHODS: Ten human distal femurs harvested from embalmed specimens were fixed, sectioned, and analyzed for the presence and descriptive characteristics of resident's ridge. A single, blinded examiner evaluated slope, cortical thickness at 4 sites, and the presence or absence of a distinct ridge relative to the attachment of the ACL.

RESULTS: A defined resident's ridge was present in 9 of 10 specimens. This was directly associated with a change in slope of the intracondylar roof in the same 9 of 10 patients. The mean cortical thickness at the ACL attachment site was 1.6 mm. This was thicker than at resident's ridge (mean, 0.90 mm), the cartilage-intercondylar notch junction (mean, 0.96 mm), and a point midway between the ACL attachment and the cartilage-intercondylar notch junction (mean, 0.90 mm).

CONCLUSIONS: The phenomenon of "resident's ridge" is accounted for by a distinctive change in slope of the femoral notch roof that occurs just anterior to the femoral attachment of the ACL. The density change apparent at the time of notchplasty is probably caused by the transition between normal cortical thickness just anterior to the ACL and the cortical thickness of the ACL attachment. No distinctive increased cortical thickness can be identified as "resident's ridge."