Graft Length in the Tunnel in Anterior Cruciate Ligament Reconstruction

Introduction

The nature of anterior cruciate ligament (ACL) reconstruction is to create new graft-bone connections. Although in native ACL the ligament fibers attach to the bone surface of the femur and tibia, in ACL reconstruction, no one has been reported trying to attach the graft directly to the bone surface. It is hard to believe that a strong tendon-bone connection can be realized through tendon-bone surface attachment, although it is a common pattern of repair in rotator cuff tear. Traditional ACL reconstruction includes four steps: preparation of the graft, creation of bone tunnels in the tibia and the femur, placement of the graft inside the bone tunnels to bridge the tibia and the femur, and graft fixation. For a graft tissue to be functional, a strong graft-bone connection should be realized. The purpose of putting the graft in the tunnels is first for a strong graft-bone anchorage in the early stage and then for a satisfactory graft-bone healing in the long term.

Various grafts have been used in ACL reconstruction. These grafts can be categorized into four types: synthetic or artificial graft, graft with bony tissue one both ends (such as bone–patellar tendon–bone graft), graft with bony tissue on one end (such as quadriceps tendon and Achilles tendon graft), and pure soft tissue graft (such as hamstring tendons graft).

For an artificial graft, graft-bone healing cannot be expected. The bone tunnels are used to accommodate the graft and the interference screws and to realize long-standing mechanical fixation. On this condition, the artificial structure should be so long as to extrude the outer orifice of the bone tunnels. For the graft with bony end, the healing between graft tissue and host bone is not of concern, due to the nature of graft-to-bone healing is bone-to-bone healing, and there is no need to form a new tendon-bone connection. For this kind of graft end, when an interference screw is used for graft-end fixation, the bone fragment in the tunnel should be long enough to enable secure graft purchasing by the screw. In clinical practice, a 25-mm long bone end is usually fashioned and put into the tunnel. In recent years, suspension fixations are used for the graft end with bony tissue. However, it still needs to be explored whether the bony graft end in the tunnel can be shortened and to what extent it can be shortened without the compromise of graft-host bone healing.

For the soft tissue graft end, the graft length in the tunnel is more critical to initial graft fixation and final tendon-bone healing. The first kind of related graft is the graft with one soft tissue end, which mainly includes the autogenous quadriceps tendon and allogenous Achilles tendon, and is not routinely used for ACL reconstruction. There is really no study reported regarding the optimal length of its soft tissue end in the tunnel. The second kind of graft related is the graft with two soft tissue ends. This kind of graft is usually fashioned with autogenous hamstring tendons or peroneus longus tendons, as well as allogenous tendons without bony tissue. In this chapter, we will discuss the necessary or optimal graft length in the tunnel regarding the soft tissue graft end in ACL reconstruction, mainly regarding the kind of graft with two soft tissue ends, with the hamstring tendon as a representative.