Determination of optimal graft lengths for posterior cruciate ligament reconstruction--a theoretical analysis.

Various graft materials have been used in posterior cruciate ligament (PCL) reconstruction. However, it is unclear if these grafts can reproduce the structural behavior of the PCL. This paper analyzed the effect of graft length on the structural behavior of the graft using a minimal deformation energy method. An analytical solution was obtained to determine the optimal effective graft length that can best reproduce the structural behavior of the PCL. This optimal graft length was determined as a function of the axial rigidity of the graft. Two typical grafts, bone-patella tendon-bone (BPTB) and Achilles tendon, were analyzed. The data demonstrated that in order to reproduce the PCL behavior, the effective length of a BPTB graft (10 mm width) should be 34 mm, while the Achilles tendon graft (with a cross sectional area of 55 mn2) needs to be 48 mm in length. Longer grafts result in less resistance and shorter graft increased the graft resistance. An initial graft tension cannot help recreate the overall structural behavior of the PCL. These results suggest that graft length is an important surgical variable in PCL reconstruction. An optimal reconstruction of the PCL should reproduce the structural properties of the PCL by using a graft with an optimal length.