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INTRODUCTION
Significant advances in surgical reconstruction of the anterior cruciate ligament (ACL) have been made since Jones' described open reconstruction with the central one-third patellar tendon in 1963.29 Advancements in technology, arthroscopic instrumentation, and surgical skills have decreased surgical morbidity while improving functional outcome.5, 23 Continued technological and surgical improvements in the 1990's eventually enabled surgeons to perform ACL reconstructions endoscopically.3, 4, 19, 23, 24, 37

During the evolution of ACL reconstruction surgery, numerous graft sources have been described. Currently, the most commonly utilized tissues for ACL reconstruction are autologous semitendinous/gracilis tendons (ST-G), central one-third patellar tendon (B-PT-B), and allograft patellar tendon.13, 14, 21, 22, 31, 32, 46, 49, 50 Each of these grafts has been touted to reliably restore knee stability, thereby enabling many patients to return to pre-injury activity levels. Despite these reports, complications have been noted with all three types of tendons, the most frequent being anterior knee pain.1, 6, 7, 9, 10, 12, 17, 18

Based upon its proven efficacy, the central 1/3 autologous patellar tendon is considered by a large number of orthopaedic surgeons to be the graft of choice in the symptomatic ACL-deficient patient. However, the incidence of anterior knee pain with the use of this graft has been reported from 13% to 47%, which diminishes the functional outcome in a large percentage of individuals.1, 35, 43-45, 51 Moreover, due to technical factors such as tunnel angle and graft length, many B-PT-B grafts cannot be secured at the joint level, resulting in non-anatomic graft fixation. In an effort to eliminate these problems, other graft sources have been explored. The ideal ACL graft should result in minimal or no damage to the patient's tissues after harvest. It should enable immediate rigid fixation and reproduce the normal anatomy of the native ACL. It should also restore normal proprioception and kinematics to the knee. Although numerous graft sources have been reported, currently, no graft material, autograft or allograft, can meet all these requirements.

In an effort to minimize post-surgical anterior knee pain after ACL reconstruction, the use of semitendinosus/gracilis tendons has been reported. Advocates of ST-G (hamstrings) point out that post-operative patellar pain is diminished by virtue of the patellar mechanism not being violated during graft harvest. Various authors have reported the incidence of anterior pain to vary from 3% to 21% following hamstrings ACL reconstruction.2, 11, 15, 26, 30, 33, 42 However, in the author's experience, the use of hamstrings for ACL reconstruction does not eliminate anterior knee pain in many patients. In addition, some authors have reported increased tibial translation in females after ST-G ACL reconstruction.16

Allograft B-PT-B has been advocated as an alternative graft source due to the lack of harvest morbidity and decreased operative time required.25, 32, 36, 41, 46 However, despite the diminished risk of disease transmission, opponents of allografts cite reports of prolonged graft-tunnel healing and intraarticular reactions to some allografts.28, 40

As a result of the continued controversy regarding the correct ACL graft source, an alternative graft has emerged, the central quadriceps tendon (CQT). The central quadriceps tendon was reported as a graft source as early as 1979 by Marshall et al, however, it did not gain popularity among surgeons until the 1980's and 1990's. 8, 21, 34, 47 Proponents of the CQT cite it's greater cross-sectional area, lower strain at failure, and lower modulus of elasticity when compared to patellar tendon.48 Advocates have also cited the lower incidence of patellofemoral symptoms after CQT graft usage.20, 31 Our experience at the University of South Alabama Medical Center is similar, with less then 5% of patients demonstrating postoperative anterior knee pain symptoms after CQT ACL reconstruction.

The CQT consists of a central portion of the quadriceps tendon approximately 10-11mm wide. The graft depth extends 7mm with an average length of approximately 80-90mm. When the graft is harvested as the initial portion of the surgical procedure, the central portion is obtained without violation of the suprapatellar pouch or transection of the quadriceps tendon. This eliminates the need to repair the pouch or tendon before proceeding with the arthroscopic portion of the procedure.

Initial descriptions of the use of the CQT described harvest of the tendon without a bone block from the patella.31 Prior to the development of bioabsorable screws for soft tissue fixation, such a graft would have required the tendon ends had to be secured by sutures tied over a post, such a staple, button, or screw. Several biomechanical studies have demonstrated that such fixation does not reconstitute the normal isometricity of the ACL, with increased instability noted as the tibial side is fixed further away from the articular surface.27, 38 Consequently, many authors now advocate graft fixation near the articular surface insertions of the native ACL.39 When the CQT is being contemplated as a graft source, articular fixation can be accomplished by harvesting a patellar bone block and fixing both ends of the graft with bioabsorbable screws near the surface of the tibia and femur.

SURGICAL TECHNIQUE
After previous studies (radiographs, MRI) and clinical examination confirm that the ACL is disrupted and causing symptomatic instability, the patient is brought to the operating room for reconstruction. The CQT is harvested through a short 2-3 inch incision obliquely along the lines of the quadriceps mechanism. After delineation of the quadriceps tendon, a 10mm x 7mm x 85mm graft is harvested, being careful to not violate the suprapatellar pouch. At the distal end of the quadriceps tendon a 10mm x 25mm x 8mm bone plug is harvested from the proximal end of the patella. The patellar defect can be later filled with cancelleous bone from the tibial reamings or with allograft chips. The CQT is sized on a back table to fit through the smallest tunnel that the tendon (not the bone) will glide through easily; the bone plug is trimmed to fit accordingly. This usually represents 9-10mm. Two #2 Ethibond sutures are placed in the patellar bone plug, while two #1 Ethibond sutures are whipped stitched in the tendon end.

After the stitches are in place and CQT has been sized, appropriate markings are made to aid the surgeon during arthroscopic reconstruction. In our use of the CQT, we place the tendon side in the femoral tunnel, with the patellar bone block in the tibia. First, a pen mark is made at the bone-tendon junction. Next, a distance of 35mm is measured from the CQT-bone junction. This marked area represents the approximate intraarticular distance of the native ACL. This distance is approximately 30mm in most individuals, however, we allocate an additional 5mm in case the graft slides more proximally in the femoral tunnel. The distance of the remaining tendon represents the portion of the tendon that will be pulled into the femoral tunnel (~25mm). The following calculation is what we use in preparing the CQT graft for implantation:
85mm {total graft} - 60mm {bone plug + intraarticular tendon} = 25mm {femoral tunnel}
The graft is set in a moist sponge until later implantation.

After harvest of the CQT, a routine knee arthroscopy is performed. We routinely perform a 5-7mm lateral notchplasty, along with debridement or repair of any meniscal lesions. Using a standard tibial guide set at an angle of 55o, we drill a 9mm tibial tunnel centered 5mm anterior to the PCL within the footprint of the native ACL. After the posterior portion of the tibial tunnel has been debrided of all soft tissue and rasped posteriorly, a 7mm offset endoscopic guide is placed through the tibial tunnel at the "10:30" or "1:30" positions on the posterior femoral notch. A 9-10mm femoral tunnel is reamed to the depth of the previous calculations (~ 25mm).

After reaming, an eyed Beath pin (Arthrex, Naples, FL) is placed in the femoral tunnel. Sequential impaction dilatation of the tibial and femoral bone tunnels is performed to increase the bone density of the tunnels for bioabsorable screw placement. After the tunnels are dilated to the size of the graft (9-10mm), the tendon side of the CQT is brought into the femoral tunnel. Through the anteromedial or an accessory anterior portal, a bioabsorable screw of the same diameter as the femoral tunnel is placed anterior to the graft. Fixation of the graft is assessed by pulling upon the tibial sutures,while the knee is put through a range of motion. Tensioning the graft through several motion cycles diminishes creep within the graft prior to tibial fixation. After the graft is assessed in extension for signs of impingement, the knee is placed in 10o-20o of flexion with 5kg of tension place upon the tibial sutures. The graft is fixed adjacent to the tibial articular surface with a 10mm bioabsorable interference screw. The knee is assessed for anterior tibial translation and the wounds closed with absorbable sutures. Prior to waking the patient, an intraarticular pain pump is placed within the knee.

CLINICAL EXPERIENCE
At the University of South Alabama Medical Center, our experience with CQT spans over 2 years, with nearly 20 cases. To date we are gathering 2 year follow-up data. 1 patient ruptured his graft during athletics (collegiate athlete) at 9 months postoperatively. No patient has reported significant patellofemoral pain and there have been no ruptures of the quadriceps tendon. All patients have been happy with their results, indicating that they believe the procedure improved their quality of life.

Other authors have reported good results with the CQT. Fulkerson reported excellent results with the use of the CQT with either endobutton or bioabsorbable screw fixation.20, 31 Leitman et al reported on 65 CQT graft cases with a KT-1000 side to side differences of 2.1mm at 1-2 year follow-up. The authors noted that no patient had patellofemoral pain and all subjects had returned to their previous level of activity with no instances of quadriceps tendon rupture.31

CONCLUSIONS
Individuals with a disrupted anterior cruciate ligament and symptomatic knee instability often require surgical reconstruction of the ACL. Over the last several decades, tremendous technological advances have enabled surgeons to reconstruct the ACL with a more anatomic and durable graft, while minimizing postoperative morbidity. As the evolution of ACL graft material continues, numerous graft choices are available. The central quadriceps tendon (CQT) is an alternative graft source with biomechanical properties comparable to or better than a bone-patellar tendon-bone or double-looped hamstrings graft. In early follow-up studies, patients undergoing CQT ACL reconstruction have demonstrated minimal patellofemoral symptoms and excellent clinical function. The CQT provides another weapon in the orthopaedic surgeon's repertoire of surgical graft alternatives to reconstruct the symptomatic ACL-deficient knee.

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Address correspondence to:
Albert W. Pearsall, IV, MD
Department of Orthopaedic Surgery
University of South Alabama Medical Center
2451 Fillingim Street
Mobile, Alabama 36617
Email: apearsal@usamail.usouthal.edu