Introduction
With approximately 200,000 anterior cruciate ligament (ACL) tears per year, primary anterior cruciate ligament reconstruction (ACLR) is one of the most common orthopedic procedures performed, and accounts for $1 billion to $2 billion dollars in healthcare per year. ACL tears frequently result from sports-related injuries, especially those activities with noncontact pivoting or cutting motions, and many of the patients are younger and expect a full return to their previous level of activity. Success with primary ACLR ranges from 75% to 97%, and although outcomes are generally satisfactory, failures do occur in sizeable numbers given the high volume of procedures performed. Unfortunately, revision ACLR (RACLR) is not associated with the same level of success as primary ACLR. The success rate for RACLR is reported to be only 65% to 75%, with return to previous levels of activities seen in a mere 54% of patients. Despite the humbling literature, there is some evidence to support similar results in RACLR when compared with primary ACLR. Failures may stem from a variety of sources throughout the preoperative, intraoperative, and postoperative periods causing graft rupture and persistent instability. Ultimately, surgery is considered a failure when the graft fails to effectively reestablish a restraint to anterior tibial translation and rotational stability. Rehabilitation becomes prolonged with RACLR, and patient expectations must be tempered. Given the inferior results with RACLR, it becomes crucial for the orthopedic surgeon to minimize the risks of perioperative complications. Successful navigation of RACLR requires scrutinizing the previous surgery and the reason for primary failure as to prevent repetition of previous results. Broadly speaking, reasons for failure of the primary reconstruction may include technical error in tunnel placement, inappropriate graft material, insufficient graft incorporation, the presence of coexisting cartilage or ligamentous injuries, recurrent trauma, limb malalignment, problems with rehabilitation, and limited patient compliance. Oftentimes the exact etiology of graft failure is difficult to determine or may be a combination of factors. However, failures may be characterized as early (occurring within 6 months of surgery) or late (occurring approximately 1 year after surgery). Early failures are thought to be associated with surgical errors, overaggressive rehabilitation, failure of the graft to incorporate, or return to sports too early after the reconstruction. Injuries later than 1 year may result from recurrent trauma to the knee.
As with any revision surgery, initial workup of the patient should include a thorough history and clinical examination. Ligamentous laxity should be compared with the contralateral knee. Anterior-posterior and lateral radiographs are helpful in determining the bony anatomy of the knee joint as well as tibial slope. Standing radiographs may reveal limb malalignment. If a corrective osteotomy is necessitated, one should consider factors that may impair bony healing, another source of complications in revision surgery. Advanced imaging such as computed tomography (CT) or magnetic resonance imaging (MRI) are invaluable in determining the position of previous hardware, tunnel position and size, evidence of osteolysis, and degenerative changes to the joint. MRI provides information about the overall quality of the graft and important information regarding concomitant injury to other soft tissue structures including the other ligaments, menisci, and cartilage. Whether or not to stage procedures in RACLR must be considered, and the decision is heavily based on graft availability and selection, position of bony tunnels, size of the bony tunnels with or without osteolysis, ability to fixate the graft, and the healing milieu. Surgeons may construct a timeline to stratify complications into those that occur preoperatively, intraoperatively, and postoperatively to be prepared to navigate these possible complications and maximize patient outcomes with RACLR.
Preoperative Complications in Revision Anterior Cruciate Ligament Reconstruction
Inherent to the nature of revision surgery, preoperative complications to RACLR are largely the same as the postoperative complications from an ACLR. As previously mentioned, a plan for RACLR requires meticulous critique of the index procedure and why the graft failed. In determining these causes, Wright et al. support that 24% of graft failures stem from technical errors, with repeat trauma and biological failure comprising 32% and 7%, respectively. The remainder (32%) result from a combination of factors.
By far the most common source for technical error is aberrant tunnel placement which alters how the graft functions and the stresses on the reconstruction. Historically, the femoral tunnel is positioned incorrectly more often than the tibial tunnel. Drilling a tunnel too posteriorly may result in blowout, whereas an inferior tunnel increases the risk of fracture ( Fig. 11.1 ). Femoral tunnels that are too vertical and anterior cause the graft to be rotationally unstable, which can result in a positive pivot shift ( Fig. 11.2 ). Anterior malposition of the tibial tunnel may lead to a loss of extension because of notch impingement ( Fig. 11.3 ), whereas posterior malposition may cause posterior cruciate ligament impingement ( Fig. 11.4 ). The posterior border of the anterior horn of the lateral meniscus is commonly used a landmark for tibial tunnel placement in the anterior–posterior axis. However, recent literature has highlighted variability in tunnel placement using the anterior horn of the lateral meniscus a landmark. Using intraoperative fluoroscopy to obtain true laterals, this study stratified tibial tunnels as anterior or posterior to 40% of the total tibial plateau length. At 2.5 years postoperatively, the side-to-side difference of anterior translation using a KT-1000 machine between the operative and nonoperative leg was much lower in the tunnels anterior to 40% of the tibial plateau length as opposed to those posterior. In the coronal plane, drilling the tunnel too far medially or laterally increases the occurrence of medial tibial plateau fractures or wall impingement, respectively ( Fig. 11.5 ).
Osteolysis of both the tibial and femoral tunnels, another potential postoperative complication of ACLR, has long frustrated orthopedic surgeons. The exact mechanism is currently unknown, but a complex interplay of mechanical and biological factors likely plays a role in the development of osteolysis. One proposed mechanism relates to the windshield-wiper motion (oscillation of the graft as the knee flexes and extends) or the bungee cord-type motion (compression and elongation of the graft as it is stretched about its longitudinal axis) ( Fig. 11.6 ). Not only do these movements cause mechanical wear on the tunnels, they are also thought to create a pressure differential that preferentially pushes synovial fluid into the tunnel, promoting expansion and osteolysis. Drawing parallels from studies on rheumatoid arthritis, it is thought that synovial fluid carries proinflammatory cytokines and macrophages that stimulate osteoclastic activity through the RANKL and interleukin pathways. Gravity is also thought to play a role in this, and has been proposed to be one of the reasons that tibial tunnel osteolysis occurs more frequently than femoral tunnel osteolysis. Ultimately, the repetitive motion leads to bony resorption and tunnel widening. Recently, a study by Flanigan et al. has implicated the presence of subclinical indolent infections with biofilm-forming bacteria, which may result in a chronic cycle of inflammation leading to tunnel osteolysis and graft failure. The literature suggests that, if the location of the tunnels does not compromise the planned revision tunnels and the tunnel enlargement is less than 14 mm in diameter as measured on CT scans, a single-stage revision may be considered ( Fig. 11.7 ). However, if greater than 14 mm of tunnel widening ( Fig. 11.8 ) or convergent revision tunnels are observed ( Fig. 11.9 ), or if the patient exhibits risk factors associated with poor healing, such as increased age, tobacco use, diabetes, or other comorbidities, then a two-stage revision procedure is preferred. Options for primary tunnel revision in the form of impaction grating include autologous iliac crest graft or other local bone grafts, femoral head allografts, or allograft bone dowels. It is recommended to wait at least 4 months to give the allograft sufficient time to incorporate before placing new tunnels. This is typically confirmed by a repeat CT scan which can appropriately quantify the percentage of incorporation ( Fig. 11.10 ). Uchida et al. detailed the algorithm for calculating the amount of bony dowel incorporation based upon measurements taken from axial cuts of a CT image ( Fig. 11.11 ). The process involves calculating the occupying ratio, measured as the ratio of the cross-sectional area of the bone graft to that of the tibial tunnel, the union ratio, the total amount of united margin between the bone graft and the tunnel, and the bone mass density of the bone graft compared with the contralateral tibia. Their results suggested that adequate incorporation of the osseous dowel allografts required at least 24 weeks (occupying ratio of 94% and union ratio of 89% on average) before reimplantation of a revision graft. The operative technique for staged ACLR with bony dowels includes removing the indwelling fixation hardware and graft and placing a centering pin within the primary tunnel. The tunnel then may be enlarged by sequential reaming, and an appropriately sized bony dowel placed ( Fig. 11.12 ). Once successful incorporation has occurred, a new tunnel may be placed in the second stage of the revision reconstruction ( Fig. 11.13 ).
