Complications With Fixation Devices in Anterior Cruciate Ligament Surgery

Introduction

Stable graft fixation is critical for a successful outcome after anterior cruciate ligament reconstruction (ACLR). The advantages of early joint motion and weight bearing after ACLR have been well documented. Anterior cruciate ligament (ACL) graft fixation must provide sufficient strength for rehabilitation and activities of daily living until biologic fixation takes place. The ultimate strength of all commonly used grafts in ACL reconstruction exceeds the strength of all current ACL fixation devices. Therefore the fixation device represents the weakest link in the early postoperative period. Fixation of the graft is especially important in the first 6 to 8 weeks to provide this initial stability while biologic healing begins. If the graft slips or loosens before biologic healing, the graft may heal in an elongated fashion, resulting in persistent knee instability. Animal studies have shown that fixation devices are the point of failure for ACL reconstructions for 6 weeks after bone-patellar tendon-bone (BPTB) autografts and 12 weeks after hamstring tendon (HT) grafts. ^, The ideal fixation device would facilitate but not interfere with healing of the ACL graft within the bone tunnel, be easily removed if necessary, and avoid an inflammatory response, irritation to the surrounding structures, and distortion on postoperative imaging.

The two most commonly used grafts in ACLR are BPTB and hamstring tendon (HT) grafts. BPTB and hamstring tendon (HT) grafts heal differently, which impacts selection fixation techniques. BPTB grafts require bone to bone healing, whereas hamstring and other soft tissue grafts require soft tissue to bone healing. As a result, the common fixation method for BPTB grafts and hamstring tendon (HT) grafts differs.

The bone quality of both the proximal tibia and distal femur has a substantial effect on ACL graft fixation. The bone mineral density of the proximal tibia is less than that of the distal femur, resulting in increased concern regarding fixation strength in the tibial tunnel. Decreased bone mineral density results in decreased strength of interference screw fixation. In addition, the force on the graft and the fixation device within the proximal tibia is oriented in line with the tunnel, resulting in greater forces being exerted on the tibial fixation device. For these reasons, tibial graft fixation is considered the weakest point in ACLR and requires special consideration.

Many different devices have been created in an attempt to accomplish stable ACL graft fixation. Broadly, ACL graft fixation devices can be categorized as intratunnel or suspensory fixation devices. Fixation devices exist as both absorbable and nonabsorbable devices and include different forms such as screws, staples, pins, and buttons. The majority of research has focused on the biomechanical properties of these devices, although fixation devices also have significant effects on graft healing within the tunnel, biologic reaction, appearance on postoperative imaging, and consequences for revision surgery. Although these implants often allow for successful ACLR, their use can be associated with numerous complications.