Compression Aperture Fixation of Soft-Tissue Anterior Cruciate Ligament Reconstructions

Introduction

Soft tissue anterior cruciate ligament (ACL) reconstruction using compression fixation at the aperture has been shown to achieve optimal biological and biomechanical properties. Numerous studies have proven the superior properties of compressive soft tissue–to-bone fixation at the aperture during ACL reconstruction. Bedi et al. studied direct tendon-to-bone healing in a dog model and showed a progressive increase in strength with compressive forces that correlated with improved soft tissue–to-bone healing via Sharpey-like fibers, mineralization, and maturation of healing tissue. Authors have identified graft-tunnel motion associated with suspensory fixation as a source of impaired early graft incorporation. Compression aperture fixation achieves a direct type of insertional anatomy with Sharpey-like fibers, whereas suspensory fixation results in fibrous tissue at the aperture. Suspensory fixation has been repeatedly associated with femoral tunnel widening and inferior soft tissue–to-bone healing at the aperture. Rodeo et al. studied graft-tunnel micromotion and tunnel diameter in a rabbit model with suspensory fixation. Graft-tunnel micromotion and tunnel diameter were greatest at the intra-articular aperture, and graft-tunnel micromotion was noted to correlate with impaired soft tissue–to-bone healing, with the slowest healing and widest tunnel diameters observed at the intra-articular aperture. Hoher et al. and Tsuda et al. reported that longer effective graft lengths (distance between points of fixation) associated with suspensory fixation correlated with increased longitudinal (bungee cord effect) and transverse (windshield wiper effect) motion. Numerous studies have shown a reduction in construct stiffness and secondary increases in graft-tunnel motion with increased distance between fixation points. Suspensory fixation has been proven to result in increased anterior tibial translation. Studies have also shown improved stability with tibial aperture fixation when compared with suspensory cortical fixation.

ACL reconstruction with hamstring autograft has been demonstrated to be an effective procedure for restoration of stability and function in the knee. The potential advantages of hamstring autograft over bone–patellar tendon–bone autograft include higher tensile load in biomechanical studies, less risk of osteoarthritis, and a decrease in harvest site morbidity.

Successful outcomes after soft tissue ACL reconstruction rely upon graft-to-host bone incorporation. Fixation techniques that compress graft to bone result in superior healing and outcomes. Surgeons have historically used soft tissue interference screws in achieving aperture fixation. However, disadvantages, including graft slippage, compromised graft integrity, and limited tendon-to-bone apposition, have been shown in numerous studies. Suspensory fixation was subsequently introduced as an alternative. Suspensory fixation has repeatedly been shown to lead to increases in longitudinal (bungee cord) and coronal (windshield wiper) translation. Increased effective graft length leads to increased graft motion and resultant femoral and tibial tunnel expansion. Some studies suggest that suspensory fixation and tunnel expansion lead to increased anterior translation on physical examination. Studies also suggest that suspensory devices undergo lengthening with cyclic loading.

More recent studies have questioned whether fixed and variable loop suspensory fixation devices undergo elongation with repetitive loading and cycling. Barrow et al. compared cyclic loading and load to failure in three suspensory devices currently on the market. His group found that all three had acceptable ultimate loads to failure, but all three had lengthening that surpassed the clinical failure threshold of 3 mm after 4500 cycles. Petre et al. also found loop lengthening with cyclic loading of selected suspensory devices. Femoral cross-pin fixation was introduced and initially showed favorable results. However, tunnel widening was noted on postoperative radiographs, complications related to soft tissue irritation were reported, and laxity associated with fracture of the cross-pins was observed.

The AperFix compression aperture ACL fixation system was introduced by Cayenne Medical (Scottsdale, AZ) in 2007. This system achieves aperture fixation at the anatomical footprint by using a unique circumferential compression implant to optimize soft tissue–to-bone healing ( Fig. 71.1 ). In addition to compression fixation at the aperture via engagement of two separate eyelets, the device also achieves compression fixation deeper within the femoral tunnel via separate deployment of wings at the terminal end of the implant. The AperFix device achieves superior pull-out strength and response to cyclic loading when compared to suspensory devices currently available. Compression aperture fixation reduces graft-tunnel motion, eliminating tunnel widening on the femoral side. It actively compresses the soft tissue to bone, encouraging a direct insertional anatomy at the soft tissue–to-bone interface. It also dramatically reduces the potential for synovial fluid influx between the soft tissue and bone at the aperture.

Several studies have shown excellent biomechanical and clinical results with the AperFix system. Gadikota et al. showed improved knee kinematics with the AperFix system when compared with conventional single-bundle ACL reconstruction. Uribe et al. performed a retrospective review of 185 knees using the AperFix system for both the femur and tibia and found no failures or device migration with good subjective patient scores. Eajazi et al. performed a small randomized trial comparing the AperFix with two other systems (one suspensory and one cross-pin). Results revealed improved Lysholm outcomes scores and improved stability testing with the AperFix when compared with the suspensory and cross-pin systems. Similarly, Uzumcugil et al. prospectively compared the AperFix and a cross-pin system in a series of 38 patients and found improved Lysholm scores in the AperFix group.

Technique

ACL reconstruction with the Cayenne AperFix system achieves compression aperture fixation while simplifying standard reconstruction techniques. Biomechanical and biological advantages include near circumferential compression fixation at the aperture, minimizing femoral tunnel widening by avoidance of graft-tunnel motion (elimination of the bungee and windshield wiper effects), minimizing influx of synovial fluid around the soft tissue graft in the femoral tunnel, improved graft stiffness via rigid aperture fixation, creation of two distinct graft bundles at the aperture, and minimization of attritional graft damage during deployment of fixation.

The Cayenne AperFix reconstruction technique has multiple advantages when compared to other types of femoral fixation. The technique is both simpler and safer as a result of eliminating the need to pass a pin through the femur during graft passage into the femoral tunnel. Studies have shown potential risk to the peroneal nerve, lateral collateral ligament, and femoral articular cartilage when using the anteromedial portal for femoral tunnel drilling and passage of a transfemoral pin in advancement of the graft. The AperFix technique is further simplified by achieving graft-to-femoral tunnel fixation without the need to flip/engage a suspensory device, eliminating the need to pass the graft multiple times and/or the need for fluoroscopy to confirm proper engagement. The AperFix system offers both 24- and 29-mm femoral implants to accommodate variation in femoral tunnel lengths. Dual eyelets at the aperture separate a four-strand soft tissue graft into two distinct limbs with drilling only one femoral tunnel. In addition, the two limbs of the graft can be easily oriented in the femoral and tibial tunnels to anatomically re-create the anteromedial and posterolateral bundles ( Fig. 71.2 ). The result is a more anatomic ACL reconstruction that utilizes known advantages of compression fixation at the aperture while simplifying the surgical procedure and limiting the risk of complications. Preparation of soft tissue autograft or allograft is done in the standard fashion. Two graft limbs are prepared with removal of muscle and devitalized soft tissue. For patients less than 6 feet tall, the graft limbs are cut at 22 cm; for patients taller than 6 feet, the graft limbs are cut at 24 cm. The diameter of the quadruple-stranded graft is determined. The graft is placed under 10 lb of tension for 10 minutes. The femoral and tibial tunnels are sized 1–1.5 mm larger than the graft diameter to allow deployment of the femoral and tibial compression fixation within the tunnel. Reconstruction can be performed via either a transtibial or anteromedial portal technique. The authors favor an anteromedial portal technique, with the portal placed as far medial as possible while still avoiding direct contact with the medial femoral condyle. This directs the guidepin more anteriorly in the lateral femoral condyle and optimizes the length of the femoral tunnel achieved before reaching the lateral cortex. Low-profile hemi-fluted reamers are used in drilling the femoral tunnel to minimize risk of injury to the medial femoral condyle, posterior cruciate ligament, and posterior root attachment of the lateral meniscus.

The following technique outlines reconstruction performed through the anteromedial portal. After débridement of the femoral and tibial tunnel ACL footprint, the knee is placed in hyperflexion and a femoral guidepin is passed into the lateral femoral cortex via either a freehand technique or via use of an over-the-top guide. The flexion angle must remain constant during reaming and graft passage to ensure parallel tunnel alignment. Preservation of a 1-mm backwall is imperative in use of any form of compression fixation at the aperture. The femoral guidepin is calibrated, providing the surgeon an estimate of femoral tunnel length before reaming. The smooth surface of a hemifluted low-profile reamer is advanced past the medial femoral condyle, with careful attention to avoid damage to the articular cartilage, PCL, and posterior root of the lateral meniscus. An entry point along the lateral bifurcate ridge, separating the anteromedial and posterolateral bundles of the ACL, is marked. The low-profile reamer is advanced 5–10 mm into the femur to mark the footprint for reconstruction. Viewing the femoral tunnel via the anteromedial portal enhances visualization and verification of tunnel position. If the footprint and posterior wall are acceptable, the low-profile reamer is advanced to the desired length to accommodate a 24- or 29-mm implant or until the lateral cortex is engaged. In general, the tunnel length is typically longer anteriorly than posteriorly as a result of the intercondylar notch anatomy. To ensure containment of the femoral AperFix within the femoral tunnel, the shortest tunnel distance should be 25 mm for the 24-mm implant and 30 mm for the 29-mm implant. Use of a calibrated tunnel dilator can be helpful in confirming anterior and posterior tunnel lengths. A femoral tunnel dilator is passed and loose bone is removed from the femoral tunnel via an oscillating shaver.

The knee is then positioned at 90 degrees of flexion for tibial tunnel preparation. The tibial guidewire is placed within the central footprint of the native ACL, in line with the posterior reflection of the insertion of the anterior horn of the lateral meniscus. The tibial tunnel is then reamed over the guidewire with a full-radius reamer. Careful attention is made to place the guidepin at the lateral base of the medial tibial spine, to limit the risk of damaging the medial tibial plateau articular cartilage while reaming the tibial tunnel. Bone debris is removed and a tunnel dilator is passed to ensure adequate tunnel diameter.

Preparation of the graft is completed. The end of each graft is whipstitched to a length of 15 mm with the same-colored #2 nonabsorbable suture. The ends of the second graft limb are sutured with different same-colored suture to differentiate it from the first limb during tibial fixation. The smallest end of each graft is passed through an eyelet in the femoral AperFix, the graft lengths are made equal, and the sutures are secured to the insertion handle ( Fig. 71.3 ). The graft is circumferentially marked with indelible ink at the level of the tip of the eyelets, at the terminal end of the implant. This facilitates verification of fully seating the AperFix implant in the femoral tunnel before deployment. To enable passage of the free distal ends of the grafts through the tibial tunnel, a free suture loop from the reconstruction kit is then passed from inferior through one of the eyelets. The knee is placed back into the same angle of flexion used in drilling the femoral tunnel.

The implant and attached soft tissue graft are then advanced through the anteromedial portal, with the release pin oriented proximally and the grafts oriented in the native position of the anteromedial and posterolateral bundles. The implant is advanced into the intercondylar notch and the free loop is retrieved from the eyelet via the tibial tunnel to facilitate later passage of the free limbs through the tibial tunnel ( Figs. 71.4 and 71.5 ). The femoral AperFix is then fully seated in the femoral tunnel, with the graft limbs anatomically oriented.

The indelible ink mark on the graft is verified to be advanced just past the aperture of the femoral tunnel ( Figs. 71.6 and 71.7 ). The release pin is removed, and the implant is deployed by turning the insertion handle clockwise until fully seated. The suture limbs are released from the insertion handle, and the femoral implant is disengaged from the insertion handle by releasing the terminal end of the insertion handle. If the insertion handle does not easily fully disengage, a mallet can be used to release the handle by lightly tapping away from the implant. The knee is then returned to 90 degrees flexion (the position of tibial tunnel preparation). The free limbs of the suture are passed through the free loop. The end of the free loop previously retrieved through the tibial tunnel is then advanced out of the tibial tunnel, delivering the free ends of the graft through the tibial tunnel. The knee is then cycled to ensure near-isometric graft length and proper tunnel placement