History of Synthetic Grafts for Anterior Cruciate Ligament Reconstruction

Although unsuccessful, Alwyn-Smith first attempted synthetic anterior cruciate ligament (ACL) reconstruction in 1918 with silk sutures. Synthetic grafts were not commercially introduced until the 1970s, and their use in ACL augmentation and/or reconstruction had a significant surge in popularity in the late 20th century. At the time, routine surgery entailed open patellar tendon autograft ACL reconstruction and 6 weeks of strict postoperative immobilization. A sterile, off-the-shelf synthetic ligament offers immediate availability while obviating donor site morbidity due to autograft harvest and the requirement for significant range of motion restrictions. Similarly, synthetic grafts reduce the risk of disease transmission associated with allograft use. However, early clinical data revealed relatively higher rate of failure with first-generation synthetic grafts compared with autogenous tissue, as well as an increased risk of late infection, considerable bone tunnel enlargement, and pronounced sterile effusions or diffuse synovitis. In response, West and Harner stated that there was no current indication for synthetic ligaments in cruciate ligament reconstruction.

Types of Synthetic Grafts

During the 1980s, numerous synthetic grafts were developed and released commercially for ligament augmentation or a complete prosthetic replacement, including those with carbon fiber and polyester composite designs. One of the original, first-generation grafts, the Kennedy ligament augmentation device (LAD; 3M, St. Paul, Minnesota), was sutured to the autogenous graft and affixed to the bone at both terminal ends. However, clinical failure resulted due to stressed shielding of the autogenous graft and attritional compromise of synthetic implant. Gore-Tex (Gore and Associates, Flagstaff, Arizona) was also an early prosthetic implant that was placed in a nonanatomical position over the top of the femur in order to avoid the bending forces previously seen at the tunnel aperture. Given this nonanatomical position, graft failure eventually occurred at the proximal tunnel (a second tunnel was drilled in the femur several inches above the joint capsule). Similarly, the Dacron graft (Stryker, Kalamazoo, Michigan) was also a complete replacement graft placed through anatomical tunnels, but evidence of clinical failure was seen in almost a third of all patients. More recently, the Ligastic graft evolved to the ligament augmentation and reconstruction system (LARS; Surgical Implants and Devices, Arc-sur-Tille, France) graft, a second-generation polyester device placed through bony tunnels for either augmentation or prosthetic replacement. The Trevira ligament (Telos, Marburg, Germany) was another analogous polyester design similar to the LAD and placed in a nonanatomical position. The Leeds-Keio graft (Xiros [formerly Neoligaments], Leeds, England), a co-venture between Leeds University in England and Keio University in Japan, was another polyester mesh graft released in 2003 as an augment for autogenous graft tissue.

Causes of Failure of Synthetic Grafts

The most common cause of failure of synthetic grafts was the fiber abrasion due to bending forces over the edge of the bony tunnels, typically at the intra-articular, femoral aperture ( Fig. 18.1 ). In order to circumvent this problem, some surgeons preferentially adopted an over-the-top position on the femur with proximal extra-articular tunnel fixation of synthetic grafts (e.g., Gore-Tex). However, as with other nonanatomic techniques common to early ACL reconstruction, anterior or inappropriate femoral tunnel placement was one of the most commonly cited technical errors associated with graft failure. The literature is replete with series describing the unacceptably high failure rate after synthetic ACL reconstruction. Kumar and Maffuli reported on the significant stress shielding seen with early augmentation devices, whereas Riel reported numerous complications following the use of the LAD, eventually abandoning its use. Similarly, Muren et al. published results that showed no advantage to augmenting the patellar tendon graft with the LAD device. Guidoin et al. reviewed 69 failed synthetic fiber ligament grafts and found that they all failed by fiber abrasion of the textile fiber around the bony tunnel edge. Kock et al. stated that the Trevira ligament also failed due to fiber abrasion and nonanatomical position of the graft. Using the Dacron graft, Wredmark and Engstrom revealed an 80% failure rate, and Andersen et al. and Barrett et al. (47%) also reported unsatisfactory outcomes in their series. Engstrom et al. performed a comparison of autogenous patellar tendon graft with or without the Leeds-Keio augmentation, and found the failure rate of the synthetic to be unacceptable. Bowyer and Matthews reported an unacceptable failure rate with the Gore-Tex ligament graft. Indelicato et al. reported on the sterile effusions that were foreign body reactions to the synthetic graft. Woods et al. published the deteriorating results of the Gore-Tex graft with longer follow-up from 2 to 3 years. Paulos et al. reported 13% fair and 42% poor results with the Gore-Tex graft. Looseness and failure of the graft occurred in 30% of the cases, with this graft placed in the nonanatomic over-the-top position, and the 2.7% infection rate was higher than that reported with autogenous grafts.

The Gore-Tex ligament failure at the tunnel entrance.

Despite abysmal results historically reported with first-generation implants, some authors have expressed optimism for newer iterations of synthetic polyester grafts, most notably the LARS implant. A recent systematic review evaluating objective endpoints after ACL reconstruction using synthetic devices, the LARS implant demonstrated the lowest cumulative failure rate (2.6%) and rates of noninfectious synovitis or effusion (0.4%) among 13 studies, followed by the second-generation Leeds-Keio (failure, 7.7%). However, these limited results must be interpreted with caution, as these series reflect more short-term outcomes, inconsistent reporting of outcome measures, and limited diagnostic sensitivity for identifying implant failure or poor biologic incorporation.