Unimpinged and impinged anterior cruciate ligament grafts: MR signal intensity measurements.

Regionalized magnetic resonance (MR) signal intensities were quantitatively measured in impinged and unimpinged anterior cruciate ligament (ACL) grafts. Images were obtained with a 1.5-T imager, and signal intensity was measured in the proximal, middle, and distal thirds of the graft. In 15 unimpinged ACL grafts, the signal intensity remained low and did not vary during the 1st year of graft implantation (45 images). In contrast, 17 impinged ACL grafts showed an increase in signal intensity in the distal two-thirds of the graft that persisted 1-3 years after implantation (P less than .001). Unimpinged grafts were placed in tibial tunnels posterior and parallel to the slope of the intercondylar roof. Reconstructions with anterior tibial tunnels resulted in graft impingement that caused increases in graft signal intensity. This increase demonstrates a clear association between surgical technique and the subsequent MR appearance of the graft.