The effects of graft rotation on attachment site separation distances in anterior cruciate ligament reconstruction

We created a model to see if twisting the graft in an anterior cruciate ligament reconstruction affected the distance separating the femoral and tibial attachments of the perimeter fibers of a patellar tendon graft. Graft bone plugs were simulated by two 12.5-mm diameter Delrin cylinders. Holes, 1 mm in diameter, were placed at the four corners of a centralized rectangle measuring 5 by 10 mm. Graft ligament fibers were represented by color-coded sutures passed through the holes in the modeled bone plugs. This graft model was fixed in tunnels reamed under arthroscopic guidance at the anterior cruciate ligament attachment sites of the femur and tibia in six fresh-frozen knee specimens. Spring gauges were used to measure indirectly the changes in distance of separation during knee flexion between the femoral and tibial attachments relative to a zero defined at 90 degrees of knee flexion. The tibial cylinder was rotated at 45 degrees increments from 90 degrees external to 180 degrees internal rotation relative to the femoral cylinder and measurements were repeated after each incremental rotation. External rotation resulted in a statistically significant higher mean separation distance (4.5 mm) for peripheral graft attachments than internal rotation (2.8 mm) (P = 0.05).