Modern techniques in anterior cruciate ligament reconstruction (ACLR) continue to evolve as surgeons endeavor to restore the anatomy and kinematics of the native knee. Among the reported complications associated with ACLR, tunnel malposition has been recognized as the most commonly observed technical error. , , Although errors in the femoral tunnel position are the most frequently reported technical errors in ACLR, tibial tunnel malposition can occur as well. Tunnel malposition can have a number of deleterious consequences, including iatrogenic chondral and meniscal injury, restricted knee range of motion, and inadequate restoration of sagittal plane and/or rotatory stability, which may increase the likelihood of graft rupture. , , , , ,
The purposes of this chapter are to: (1) review the relevant anatomic relationships pertinent to anatomic ACLR, (2) offer strategies to mitigate the likelihood of femoral and tibial tunnel malposition, and (3) describe techniques that can be employed intraoperatively to deal with tibial and femoral tunnel malposition once recognized.
Visualization is Key: Three-Portal Knee Arthroscopy
The avoidance of tunnel malposition is contingent upon the surgeon obtaining adequate visualization of each patient’s unique anatomy and injury pattern. This process begins with correct placement of the arthroscopic portals. The anterolateral portal should be placed just lateral to the lateral border of the patella tendon and at the level of the inferior pole of the patella ( Fig. 7.1 ). Placing the anterolateral portal as proximal as possible provides the surgeon with a “bird’s eye” view of the tibial insertion of the anterior cruciate ligament (ACL). Additional portals are subsequently placed under spinal needle visualization. The medial portal is created so as to accommodate the proper angle of attack for instruments used for preparation of the medial wall of the lateral femoral condyle and drilling of the femoral tunnel, while avoiding iatrogenic damage to the articular surface of the medial femoral condyle. A more central, anterior portal is placed in line with the midpoint of the tibial remnant of the ACL. Once placed, the central portal can be used to more directly visualize the intercondylar notch, the femoral remnant of the ACL, and the back wall of the lateral femoral condyle ( Fig. 7.2 ). Viewing through this portal, guide pin insertion and femoral tunnel drilling are accomplished without obstruction from the lateral femoral condyle, in many cases obviating the necessity for an aggressive notchplasty and ensuring appropriate tunnel position on the wall. More broadly, this three-portal technique provides the surgeon with an enhanced perspective on all relevant intraarticular structures and allows for a precise understanding of the patient’s unique anatomy.
Respect the Patient’s Anatomy: Footprint Variation, Notch Morphology, and Individualized Surgical Techniques
In spite of efforts to generalize the sizes, shapes, and pertinent relationships of patients’ ACL anatomy, a considerable amount of variation exists. Anatomic ACLR is not “one size fits all” surgery. Surgeons ought not think of themselves as single-bundle or double-bundle surgeons. Rather, the surgical steps and overarching techniques are governed by each patient’s unique anatomy.
The cross-sectional area of the midsubstance of the ACL, as well as its insertions on both the femur and tibia, have been shown to vary greatly from person to person ( Figs. 7.3 and 7.4 ). , Among a sample of 137 patients undergoing ACLR, Kopf et al. observed that in approximately 33% of cases the length of the femoral ACL insertion was either less than 16 mm or greater than 18 mm. Moreover, the length of the tibial ACL insertion varied between 12 mm and 22 mm. Preoperative measurements of the femoral and tibial ACL insertion dimensions on magnetic resonance imaging can be helpful in planning for the appropriate surgical technique (single- vs. double-bundle ACLR) and counseling patients regarding the advisability of one graft type over another. , Intraoperative measurements can also be a useful adjunct in verifying the footprint measurements made preoperatively ( Fig. 7.5 ). Currently, we are reluctant to perform double-bundle ACLR in the setting of a femoral insertional length of less than 17 mm.
Intercondylar notch morphology has also recently been recognized as an important anatomic consideration when contemplating the most appropriate ACLR technique. Similar to preoperative measurements of the ACL insertional footprints, the dimensions of the intercondylar notch can be appreciated, although more variability between measurements techniques has been observed, , which underscores the utility of intraoperative measurements. More general descriptions of the intercondylar notch morphology have been used (A-, U-, and W-shaped notches), with the A-shaped notch recognized in particular as a patient-specific characteristic that may obviate the surgeon’s ability to perform double-bundle ACLR. The relatively narrow width of the A-shaped notch creates a tighter space in which to access the medial wall of the lateral femoral condyle for guide pin placement. Even with selective notchplasty, seldom is it feasible to drill two femoral tunnels in this setting. For this reason, in our experience, an intercondylar notch width of 12 mm or less precludes double-bundle ACLR. Moreover, even if single-bundle ACLR is performed, great care must be taken to avoid iatrogenic chondral injury to the medial femoral condyle as the reamer is advanced into the intercondylar notch in preparation for femoral tunnel drilling.
Femoral Tunnel Drilling
Errors in the placement of the femoral tunnel on the medial wall of the lateral femoral condyle may increase the likelihood of suboptimal outcomes that are likely to be more apparent postoperatively (anterior tunnel: terminal knee extension deficit; vertical tunnel: persistent rotatory knee instability). However, a tunnel positioned too posteriorly risks posterior wall blowout, which can immediately compromise interference screw fixation, thus necessitating an alternate surgical tactic.
Prevention of tunnel malposition again begins with appropriate visualization of the medial wall of the lateral femoral condyle and the “over-the-top” position, which represents the intersection between the posterior femoral cortex and the metaphyseal flare. Care should be taken to judiciously clear soft tissues using a combination of electrocautery, arthroscopic shaver, and rasps to ensure that key anatomic landmarks can be identified, while at the same time taking care to preserve any residual ACL footprint tissue that may guide the position of tunnel placement. If an offset guide is used to introduce a guide pin into the medial wall of the lateral femoral condyle, residual soft tissues on the posterior aspect of the condyle can prevent proper seating of the guide, resulting in an inappropriate anterior starting position for guide pin insertion. Thus meticulous care must be taken to ensure that all soft tissues are removed and the offset guide is seated directly on bone.
When drilling the femoral tunnel using an inside-out technique, the knee should be flexed to at least 90 degrees, as the likelihood of posterior wall blowout increases when tunnel drilling is accomplished in lesser degrees of knee flexion. Additionally, regardless of whether or not guide pin insertion is accomplished with a “freehand” technique or with any one of a number of offset “over-the-top” guides, the surgeon should proceed such that at least a 2-mm rim of posterior cortical bone remains intact. Several authors have recommended “scoring” the footprint of the anticipated tunnel on the medial wall of the lateral femoral condyle with the reamer before drilling the tunnel as the knee is maintained in 90 degrees of flexion. Once this is done, the viewing through the central/anterior and the medial portals can accommodate a close inspection of the posterior margin of the tunnel and the posterior cortex.
In the event of posterior wall blowout, suspensory fixation of the graft on the lateral femoral cortex is commonly used to address the situation, and a number of different techniques for obtaining stable fixation have been described. Should the medial and lateral cortices remain intact and the blowout remain confined to the posterior cortex, suspensory fixation with a cortical button can be used to fix the graft. If the integrity of either the medial or lateral cortices is compromised, suspensory fixation can be accomplished with a screw and washer post. Briefly, a longitudinal incision is made over the lateral aspect of the distal thigh, where dissection is carried down through the iliotibial band (ITB) to the lateral femoral cortex, and the previously drilled femoral tunnel is visualized. A 4.5-mm partially threaded, cancellous screw with washer is placed 1 cm anterior and distal to the existing femoral tunnel and partially advanced, whereupon the sutures from the graft can be secured and the screw and washer tightened until flush with the lateral femoral cortex. Care should also be taken to ensure that the screw and washer are placed posterior to the intermuscular septum so as to avoid irritation of the overlying ITB ( Fig. 7.6 ).