Hardware Complications after Anterior Cruciate Ligament Reconstruction

Introduction

A variety of autograft and allograft tissues can be used for reconstruction of the anterior cruciate ligament (ACL), and a number of different tools and techniques can be used to achieve graft fixation, whether bone to bone or tendon to bone. Commonly used fixation devices include interference screws (metallic and bioabsorbable), suspensory fixation (the Endobutton [Acufex Microsurgical, Mansfield, Massachusetts], RetroButton [Arthrex, Naples, Florida], ACL TightRope [Arthrex, Naples, Florida]), and cross-pins. Complications related to graft fixation are often specific to the type of fixation used, although a number of themes recur. We will review each type of fixation and the related intraoperative and postoperative complications, as well as methods for managing both types of complication. Obviously the ideal management is avoidance of the complication in the first place. Skeletally immature patients are susceptible to a unique set of complications regardless of the method of fixation, and we will review these separately.

Interference Screws

Interference screws are a widely used method of fixation during ACL reconstruction, both for bone-to-bone fixation and soft tissue–to–bone fixation. A number of complications related to interference screws may be encountered, and they can occur intraoperatively or postoperatively.

Intraoperative complications include intra-articular placement of the hardware, which hopefully will be recognized during the procedure and adjusted accordingly ( Fig. 133.1 ). During insertion of the screw, possible complications include laceration of the graft passing suture, advancement of the graft within the bone tunnel, graft laceration and even rupture, fracture of the graft bone plug, and screw breakage. To minimize the risk of lacerating the passing suture, at least one suture can be passed through the tendon at the base of the bone plug. To minimize the risk of graft rupture, methylene blue can be used to mark the bone-tendon junction of the graft, the anterior portion of the bone tunnel can be notched to ease the initial engagement of the screw, the cancellous edge of the bone plug can be placed facing anterior flush with the intra-articular edge of the femoral tunnel, and a protective sheath or cannula can be used to protect the graft during screw placement. Another helpful technique to protect the graft is to insert the femoral screw over a guidewire drilled through a cannulated screwdriver.

If the graft ruptures during screw placement, a number of salvage options may be used. If a patellar tendon graft is cut at the bone-tendon junction, the graft can be reversed, placing the intact bone plug in the femoral tunnel and fixing the tendinous portion of the graft through the tibial tunnel with a post or button. If there is insufficient graft length remaining, alternative autograft or allograft should be used. To minimize the chance of graft advancement, it is important to maintain constant tension on the passing sutures during screw insertion. Screw breakage during insertion has been reported with bioabsorbable screws in up to 10% of cases. Steps to minimize such a complication include use of a dilator device to create a pilot hole for screw insertion, using a tap prior to screw insertion, maintaining continuous pressure on the screwdriver to keep it fully seated, and use of a screw 1 mm smaller than the diameter of the tunnel.

Postoperative complications include intra-articular placement of hardware, which may not be recognized at the time of surgery and can present clinically after the index procedure. A second procedure may be necessary to reposition or remove the misplaced hardware. Late screw breakage and delayed intra-articular migration of interference screws have also been described in the literature. Late migration of interference screws is rare but should be considered in the case of sudden pain in the late postoperative period after ACL reconstruction, and in the case of a metallic screw can easily be evaluated with plain films. If such a complication is encountered, removal is mandated to minimize mechanical problems and cartilage damage. An arthroscopic approach is preferred, even if the screw is in the notch or popliteal fossa, although an arthrotomy may be required.

Interference Screws

Interference screws are a widely used method of fixation during ACL reconstruction, both for bone-to-bone fixation and soft tissue–to–bone fixation. A number of complications related to interference screws may be encountered, and they can occur intraoperatively or postoperatively.

Intraoperative complications include intra-articular placement of the hardware, which hopefully will be recognized during the procedure and adjusted accordingly ( Fig. 133.1 ). During insertion of the screw, possible complications include laceration of the graft passing suture, advancement of the graft within the bone tunnel, graft laceration and even rupture, fracture of the graft bone plug, and screw breakage. To minimize the risk of lacerating the passing suture, at least one suture can be passed through the tendon at the base of the bone plug. To minimize the risk of graft rupture, methylene blue can be used to mark the bone-tendon junction of the graft, the anterior portion of the bone tunnel can be notched to ease the initial engagement of the screw, the cancellous edge of the bone plug can be placed facing anterior flush with the intra-articular edge of the femoral tunnel, and a protective sheath or cannula can be used to protect the graft during screw placement. Another helpful technique to protect the graft is to insert the femoral screw over a guidewire drilled through a cannulated screwdriver.

If the graft ruptures during screw placement, a number of salvage options may be used. If a patellar tendon graft is cut at the bone-tendon junction, the graft can be reversed, placing the intact bone plug in the femoral tunnel and fixing the tendinous portion of the graft through the tibial tunnel with a post or button. If there is insufficient graft length remaining, alternative autograft or allograft should be used. To minimize the chance of graft advancement, it is important to maintain constant tension on the passing sutures during screw insertion. Screw breakage during insertion has been reported with bioabsorbable screws in up to 10% of cases. Steps to minimize such a complication include use of a dilator device to create a pilot hole for screw insertion, using a tap prior to screw insertion, maintaining continuous pressure on the screwdriver to keep it fully seated, and use of a screw 1 mm smaller than the diameter of the tunnel.

Postoperative complications include intra-articular placement of hardware, which may not be recognized at the time of surgery and can present clinically after the index procedure. A second procedure may be necessary to reposition or remove the misplaced hardware. Late screw breakage and delayed intra-articular migration of interference screws have also been described in the literature. Late migration of interference screws is rare but should be considered in the case of sudden pain in the late postoperative period after ACL reconstruction, and in the case of a metallic screw can easily be evaluated with plain films. If such a complication is encountered, removal is mandated to minimize mechanical problems and cartilage damage. An arthroscopic approach is preferred, even if the screw is in the notch or popliteal fossa, although an arthrotomy may be required.

Button Fixation

Suspensory fixation with a button is another widely used technique that can be associated with specific complications. The button may remain in the femoral tunnel rather than flipping outside of the tunnel to rest on the lateral femoral cortex ( Fig. 133.2 ). Conversely, the button may be pulled too far off the femoral cortex into the overlying soft tissue ( Fig. 133.3 ). To ensure that the button has flipped and is in the correct position, the femoral tunnel length should be overdrilled by 6 mm and the graft should be marked at a location 6 mm distal to the desired insertion level. Once the button has flipped, the surgeon should feel for the button flipped on the lateral side of the femur against the cortex by pulling on the sutures. The surgeon can then pull back on the graft from below and pull both button sutures to make sure the button is not flipping with tension on the graft from the tibial side. If there is any doubt as to the position of the button, intraoperative fluoroscopy or x-ray should be used to confirm proper placement. If the button is pulled through the lateral cortex, an oversized Xtendobutton (Smith & Nephew, Andover, Massachusetts) can fit over the button after a lateral incision is made. In this way, the graft does not have to be repassed, and it can be pulled back to seat the Xtendobutton on the lateral femoral cortex.

Postoperatively, Muneta et al. described late detachment and intra-articular migration of an Endobutton that had been fixed in the suprapatellar pouch, most likely due to impingement between the patella and femoral groove. To avoid this impingement and possible inflammatory reaction, it is obviously preferable not to affix the Endobutton in the joint, particularly near the patellofemoral joint.

Cross-Pin Fixation

Cross-pin fixation is another method used for tendon-to-bone fixation or bone-to-bone fixation, designed to improve upon the problems with interference screw and Endobutton fixation methods. Most studies that have compared cross-pin femoral fixation with other fixation techniques, however, have found no clinically significant differences in outcomes of the fixation techniques. Furthermore in recent years cross-pin fixation has been associated with a number of intraoperative and postoperative complications; combined with the technically challenging nature of this fixation, the use of the cross-pin fixation technique may be declining.

Intraoperative complications with cross-pin fixation include a lack of pin convergence and pin breakage. A number of postoperative complications associated with cross-pin fixation have also been described in the literature. Incorrect placement, including leaving the pin proud on the lateral side of the femur as well as advancing the pin too far to penetrate the medial cortex of the femur, should be avoided, as this may require reoperation for hardware removal ( Fig. 133.4 ). The pin can break even after graft incorporation. The case of late breakage reported by Han et al. using the RigidFix system (Mitek Products, Norwood, Massachusetts) was attributed to an improper femoral tunnel with posterior wall blowout and posterior direction of the cross-pins, potentially leading to abnormally high stress on the pins. Posterior misplacement can also lead to graft failure and the need for revision ( Fig. 133.5 ). Iliotibial band syndrome has also been described, either from direct irritation or in association with breakage of the femoral bioabsorbable cross-pin, specifically BioTransfix (Arthrex, Naples, Florida).