How Do You Evaluate Tunnel Position in the Revision Setting?
Given that tunnel malposition accounts for an estimated 70% to 80% of anterior cruciate ligament (ACL) graft failures, evaluation of tunnel position in the setting of revision reconstruction is perhaps the most important element of preoperative planning.1,2 Tunnel malposition can theoretically lead to graft failure through a variety of mechanisms, including impingement on the notch, posterior cruciate ligament (PCL), and lateral wall; development of abnormal tensile forces leading to graft elongation; and interference with normal knee motion via “capture.” The issue of appropriate tunnel position has become particularly complex with the introduction and increasing utilization of double-bundle reconstruction techniques, and although a detailed discussion of ideal tunnel position in the context of ACL reconstruction lies beyond the scope of this text, we hope to provide at least a basic framework for approaching this difficult question in the revision setting.
Appropriate evaluation of tunnel position requires not only adequate radiographic delineation of tunnel location in the femur and tibia but also accurate correlation between tunnel position and etiology of failure. We therefore consider patient history and physical exam to be important adjuncts to radiographic and arthroscopic evaluation of tunnel position and in answering the following questions:
1. Is apparent tunnel malposition the primary cause of graft failure?
2. What is the nature of tunnel malposition (ie, is the femoral tunnel too anterior? Is the tibial tunnel too posterior?)?
3. Can the malpositioned tunnel be repositioned in a single setting and, if so, can it be bypassed entirely or does it constitute a “near miss” that needs to be grafted?
In regard to patient history, if the failure has an apparent traumatic etiology, did the patient experience recurrent instability prior to the recounted traumatic event? Did the patient have significant motion loss postoperatively? Did the patient have recurrent discomfort or swelling postoperatively? Affirmative responses to any of these questions may suggest tunnel malposition as a causative element in failure of the index reconstruction.
We also find physical exam to be helpful in confirming apparent radiographic tunnel malposition as contributing to graft failure. For example, the finding of a pivot shift together with a grade I or II Lachman and a firm endpoint may suggest that a vertical-appearing femoral tunnel has controlled anterior-posterior translation but failed to correct rotatory instability and is therefore the principal etiology of failure.
Radiographic evaluation begins with a plain radiograph series consisting of a weight-bearing anteroposterior (AP), weight-bearing 45 degrees flexed posteroanterior (PA), and lateral. When a soft-tissue graft has been utilized for the index reconstruction, tunnel position is readily observable on plain radiographs (Figure 43-1). Use of grafts with bone blocks at one or both ends, however, may prevent accurate identification of bone tunnels. We are wary of accepting radiographic screw position as indicative of tunnel position, as—particularly on the femoral side—screw divergence may be present. In the coronal plane we look for the femoral tunnel to exit the lateral wall of the intercondylar notch at the 10:30 position on the left, and at the 1:30 position on the right.3 On the tibial side we look for the tunnel to exit the tibial plateau along the lower one-third of the medial tibial spine (relatively central) and to make an angle of approximately 70 degrees with the joint line, particularly when endoscopic technique has been utilized and the femoral tunnel has been drilled through the tibial tunnel.4,5 If a 2-incision technique has been used or the femoral tunnel has been drilled through an accessory portal, then the angle of the tibial tunnel in the coronal plane may be of less consequence.
Figure 43-1. Anteroposterior (AP) and lateral radiographs of a patient with recurrent instability following anterior cruciate ligament reconstruction. Screw divergence, (A) midline (near 12 o’clock) and (B) slightly anterior position, is noted with respect to the femoral tunnel. Tunnel widening is noted on the tibial side.
In the sagittal plane we look for the femoral tunnel to lie near the posterior cortex of the femur. On the tibial side we look for a line parallel to the path of the tibial tunnel to lie just posterior to Blumensaat’s line with the knee in full extension. At this time we also attempt to determine whether the malpositioned tunnel can be ignored at the time of revision reconstruction or whether it constitutes the problematic “near miss” that must be grafted because of its proximity to a more anatomically positioned tunnel.
We will typically obtain a non-arthrogram magnetic resonance imaging (MRI) scan as an adjunct for evaluating tunnel position as well as for identification of concomitant intra-articular pathology that may have contributed to failure of the index reconstruction. MRI permits evaluation of the intra-articular course of the graft and can be facilitated by capturing the plane parallel to the course of the graft.
Furthermore, we take care to evaluate not only the location of the femoral and tibial tunnels, but also to evaluate remaining bone stock and quality at each site—particularly when a soft-tissue graft has been used for the index reconstruction. We prefer computed tomography for qualitative and quantitative analysis of tunnel widening as radiographs.6 Significant tunnel widening in combination with tunnel malposition, for example, can preclude alternate tunnel placement with a single procedure. Staged debridement with bone grafting may be required in these situations.
At the time of revision reconstruction, arthroscopic evaluation affords the final opportunity to evaluate tunnel position (Figure 43-2). After debridement of the failed graft, we look for the tibial tunnel to exit the plateau such that the center point of the graft lies along a line tangent with the posterior edge of the anterior horn of the lateral meniscus and 7 mm to 8 mm anterior to the anterior margin of the posterior cruciate ligament.7 To evaluate the femoral tunnel we identify the over-the-top position and evaluate the proximity of the index tunnel to this point with respect to back-wall thickness and position along the lateral wall of the notch. Finally, we recommend the use of intraoperative fluoroscopy both during index reconstruction to prevent tunnel malposition and at the time of revision to ensure appropriate correction of tunnel malposition. Though some authors currently recommend the use of computer-assisted navigation techniques for more precise tunnel placement, we are unaware of any clinical data that would support the additional time and expense this technology demands.
Figure 43-2. Intraoperative arthroscopic images during revision anterior cruciate ligament reconstruction of the patient illustrated in Figure 43-1. Significant malposition permitted bypass of the index femoral tunnel via endoscopic technique. (A) A guide pin is positioned at the site of the revision femoral tunnel. (B) Successful revision reconstruction with bypass of the index femoral tunnel.
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2. Allen CR, Giffin JR, Harner CD. Revision anterior cruciate ligament reconstruction. Orthop Clin North Am. 2003;34(1):79-98.
3. Yamamoto Y, Hsu WH, Woo SL, et al. Knee stability and graft function after anterior cruciate ligament reconstruction: a comparison of a lateral and an anatomical femoral tunnel placement. Am J Sports Med. 2004; 32(8):1825-1832.
4. Howell SH, Gittins ME, Gottlieb JE, et al. The relationship between the angle of the tibial tunnel in the coronal plane and loss of flexion and anterior laxity after anterior cruciate ligament reconstruction. Am J Sports Med. 2001;29(5):567-574.
5. Harner CD, Baek GH, Vogrin TM, et al. Quantitative analysis of human cruciate ligament insertions. Arthroscopy. 1999;15(7):741-749.
6. Webster KE, Feller JA, Elliott J, et al. A comparison of bone tunnel measurements made using computed tomography and digital plain radiography after anterior cruciate ligament reconstruction. Arthroscopy. 2004; 20(9):946-950.
7. Morgan CD, Kalman VR, Grawl DM. Definitive landmarks for reproducible tibial tunnel placement in anterior cruciate ligament reconstruction. Arthroscopy. 1995;11(3):275-288.