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), the Endobutton (Acufex Microsurgical, Mansfield, MA), and cross-pins. Complications related to graft fixation are often specific to the type of fixation used, although a number of recurring themes occur. 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 this complication separately.

Interference Screws

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

Intraoperative complications include intraarticular placement of the hardware, which ideally will be recognized during the procedure and adjusted accordingly (Fig. 76-1). During insertion of the screw, possible complications include laceration of the graft-passing suture,¹ advancement of the graft within the bone tunnel,¹ graft laceration¹ and even rupture,² fracture of the graft bone plug,³ and screw breakage.^4–6 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.¹ 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 intraarticular edge of the femoral tunnel, and a protective sheath or cannula can be used to protect the graft during screw placement.² Another helpful technique to protect the graft is to insert the femoral screw over a guidewire drilled through a cannulated screwdriver.

Fig. 76-1 A, Anteroposterior and, B, lateral X-rays and C,axial, D, coronal, and, E, sagittal computed tomography scans demonstrating a malplaced, intraarticular femoral screw.

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.^2,7 If the remaining graft length is insufficient, an 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.¹ Screw breakage during insertion has been reported with bioabsorbable screws in as many as 10% of cases.^4,5 Steps to minimize such a complication include use of a dilator device to create a pilot hole for screw insertion, maintenance of continuous pressure on the screwdriver to keep it fully seated, and use of a screw 1 mm smaller than the diameter of the tunnel.⁶

Postoperative complications include intraarticular 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^8–12 and delayed intraarticular migration of interference screws^13–16 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.^9,14,17 An arthroscopic approach is preferred,¹⁷ even if the screw is in the notch or popliteal fossa, although an arthrotomy may be required.¹⁵

Endobutton

The Endobutton is another widely used fixation device that has been associated with specific complications. The Endobutton may remain in the femoral tunnel rather than flipping outside of the tunnel to rest on the lateral femoral cortex¹⁸ (Fig. 76-2). Conversely, the Endobutton may be pulled too far off the femoral cortex into the overlying soft tissue¹⁹ (Fig. 76-3). To ensure that the Endobutton 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.¹⁸ Once the Endobutton 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 Endobutton 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 Endobutton, intraoperative fluoroscopy or x-rays should be used to confirm proper placement.¹⁹

Fig. 76-2 A, Lateral and, B, anteroposterior X-rays show the Endobutton is in the femur and is not extracortical, indicating it has not flipped outside of the bone and is not supporting the graft.

Fig. 76-3 The Endobutton is free in the soft tissues and is not providing support to the graft.

Postoperatively, Muneta et al²⁰ described late detachment and intraarticular 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 preferable not to affix the Endobutton in the joint, particularly near the patellofemoral joint.²⁰

Cross-Pin Fixation

Cross pin fixation is a relatively new method used for tendon–bone fixation with the hope of improving on the problems with interference screw and Endobutton fixation methods. As with all new surgical methods and devices, a learning curve exists, with the potential for new problems as the technology becomes more widely adapted. Intraoperative complications with cross-pin fixation include lack of pin convergence and pin breakage.

A number of postoperative complications associated with cross-pin fixation have recently 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 it may require reoperation for hardware removal²¹ (Fig. 76-4). The pin can break even after graft incorporation.²² The case of late breakage reported by Han et al²² using the Rigidfix system (Mitek Products, Norwood, MA) 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. Iliotibial band syndrome has also been described, either from direct irritation²³ or in association with breakage of the femoral bioabsorbable cross-pin, specifically BioTransfix (Arthrex, Naples, FL).²⁴

Fig. 76-4 Case 1: A, Coronal and, B, axial magnetic resonance imaging (MRI) demonstrates proud cross-pin laterally. Case 2: C, Axial MRI demonstrates proud cross-pin medially. In both cases the soft tissues were irritated, causing symptoms and requiring reoperation.

(Reprinted from Marx R, Spock CR. Complications following hamstring anterior cruciate ligament reconstruction with femoral cross-pin fixation. Arthroscopy 2005;21:762.)

Tibia Fixation

A number of options can be used for cortical fixation in the tibia, including interference screws and staples. Although early studies indicated a high incidence of hardware removal from the tibia due to pain when using interference screws,^23,25,26 low-profile interference screws are usually well tolerated.²⁷ Another option for tibial fixation when using hamstring grafts or Achilles allografts is a cortical screw with a spiked washer. Although one series using a higher-profile, round-headed screw reported a 70% incidence of hardware removal due to pain,²⁸ other studies reviewing lower-profile screws suggest a very low, almost negligible, rate of hardware removal with this type of fixation.^27,29 Staples are another method of fixation, used for supplementary fixation more often than primary fixation. The major concern with staples is their high profile and the resulting incidence (as high as 29%) of kneeling pain leading to hardware removal.³⁰

Skeletally Immature Patients

Graft fixation in skeletally immature patients has its own potential for complication regardless of the type of fixation device used. The primary concern is disruption of the growth plates, which can manifest itself in a number of different ways including limb length discrepancy,^31,32 tibial recurvatum,³³ and valgus deformity of the distal femur.^33,34 Specific recommendations with regard to fixation include avoidance of fixation hardware across the lateral distal femoral epiphysis and tibial tubercle apophysis.³³ Although this complication reflects the surgical approach and technique as much as the type of graft fixation, it is important to attempt to avoid or at least minimize disruption of the growth plate(s) whenever possible.

Conclusion

In summary, each method of graft fixation presents its own potential complications both at the time of surgery and in the short- and long-term postoperative period (Table 76-1). Surgeons should be aware of the potential complications with the methods of fixation they use, how to avoid them, and how to treat them if they occur. Special considerations should be made in skeletally immature patients to minimize disruption of the growth place, with graft harvest, tunnel placement and drilling, and graft fixation.