Simulated graft recession in endoscopic ACL reconstruction: influence on graft strain.

Eight fresh cadaveric knee specimens underwent arthroscopic-assisted ACL reconstruction to examine the influence of femoral graft recession on graft strain pattern. Length changes between tibial origin and femoral insertion (simulating graft strain or isometry pattern) were measured throughout knee motion (0 degrees-90 degrees) with a simulated ACL construct. Measurements were taken at the "endo" position (replicating the normal endoscopic position) and in progressive 1.5-mm increments proximally within the femoral tunnel (mimicking femoral graft recession). After recession up to a maximum of 15 mm, a block was placed anterior to the "recessed" graft construct (simulating placement of bone graft anterior to the recessed graft) and strain patterns were remeasured. Graft strain patterns were altered with as little as 1.5 mm recession in two of eight specimens. Compared to the "endo" position, all specimens showed a statistically significant decrease in strain by 3 mm of graft recession (P<.001 for 7 of 8, and P=.0138 for 1 of 8). A direct relationship exists between graft placement and ACL strain patterns, with more proximal graft "recession" adversely influencing normal graft strain. Bone graft placement anterior to the recessed graft restores strain patterns to those seen at the normal "endoscopic" position.