The relationship between anterior cruciate ligament reconstruction tibial tunnel location and the anterior aspect of the posterior cruciate ligament insertion.

A retrospective study of arthroscopic anterior cruciate ligament reconstruction in 20 patients was conducted. These patients underwent computed tomography (CT) scans on the involved knee postoperatively to determine sagittal placement of the proximal end of the tibial tunnel (TTp) based on a distance from a specific anatomic reference known as the over-the-back (OTB) ridge. The distance from the posterior aspect of the TTp to the OTB ridge, defined as the backset, was measured from the CT scans. The mean backset was 6.2 mm. The anterior to posterior (AP) tibial plateau diameter was measured from the CT and by plain view radiograph. The mean AP diameter by CT scan was 55.1 mm and the mean AP diameter by radiograph was 55.4 mm. A Pearson correlation coefficient of r = .633 comparing backset versus AP diameter suggests a moderately significant positive relationship. For the AP diameter comparing measurement method, CT versus radiograph, r = .985, representing a highly significant positive relationship, confirming AP diameter sizing accuracy by inexpensive radiography versus CT scan. A proposed backset model based on these data uses three fixed distances, derived by ratio, within a 2-mm range. This model is defined by 5-, 6-, and 7-mm backset intervals for < 50 mm, 50 to 60 mm, and > 60 mm AP diameters respectively, and is currently under prospective clinical investigation.