Treatment of Anterior Cruciate Ligament Injuries
Regardless of whether surgical or nonsurgical treatment is ultimately pursued, patients should be advised to ice, compress, elevate, and limit the use of the injured knee immediately after the injury. If the injury to the ACL also affects the associated structures within the knee, including the menisci, PCL, medial collateral ligament, or lateral collateral ligament, surgical reconstruction is needed.
Nonsurgical (Conservative) Management of Anterior Cruciate Ligament Injuries
Some patients with ACL injuries may not be candidates for surgery because of serious comorbid medical conditions including serious cardiac, renal, or hepatic disease or because they no longer wish to participate in strenuous physical activities. For individuals who opt for conservative treatment, physical therapy with an experienced physical therapist or athletic trainer aimed at strengthening the muscles around the knee, especially the quadriceps femoris and hamstring muscles, is pursued. However, without surgical repair, the knee generally remains unstable and prone to further injury.
Long-term studies have shown that there is a significant increase in rates of damage to menisci and articular cartilage associated with delayed reconstruction. The rate of healing for meniscal tears is faster when done at the same time as ACL reconstruction as opposed to being performed alone. Generally, about one-third of patients who are selected as suitable for conservative treatment are able to complete the therapy regimen without the need for surgical intervention. However, patients with high level of sports activity show poor results after conservative treatment of ACL ruptures.
Surgical Management of Anterior Cruciate Ligament Injuries
Because of the frequent failure of nonsurgical approaches to ACL injuries, surgery remains the treatment of choice in almost all athletes who want to remain active. Unfortunately, surgery is not universally successful. Some problems that have resulted in failed ACL reconstruction are graft impingement on the intercondylar roof, graft tension, nonanatomic femoral and tibial tunnel placement (not reproducing the histological and biomechanical characteristics of the native ligament), and incomplete replication of an intact ACL, in particular omitting reconstruction of the PL bundle. Despite these efforts, 15% to 25% of patients who undergo ACL reconstruction continue to suffer pain and instability in their injured knee.
Often, when reconstruction is performed, there is a piece of the ruptured ACL remaining that can be either removed or left in the knee. If the ligament piece is left in place, it can impact visualization during surgery and possibly impact the quality of the reconstruction. In 1% to 9.8% of reconstructions, impingement or a Cyclop lesion (focal nodule[s] of fibrous tissue sitting in the intercondylar notch anterior to the reconstructed ACL) may occur when parts of the ACL are left.
When the ruptured ACL is left in place, mechanoreceptors may help with reinnervation. Sensory neurons involved in kinesthesia may also be preserved in the ruptured ACL. It has been suggested that the ACL functions as a sensory organ, not only providing proprioceptive feedback but also initiating protective and stabilizing muscular reflexes. In a study, patients who had undergone surgery 3 months to 3.5 years after the ACL injury had the remainder of the ruptured ACL "adapted to the posterior cruciate ligament … and sometimes with scar tissue connected to the femur," whereas the second group had "[free floating] … ACL remnants." In the first group, mechanoreceptors of Ruffini, paccinian, and, in 1 patient's specimen, Golgi-like organs were present (Figure 2). In the second group, no significant numbers of mechanoreceptors were found. If reinnervation of the ACL causes restoration of kinesthesia and if ACL remnants can be left without risking impingement in the postreconstruction knee biomechanics, it seems to be of benefit.
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Figure 2.
Mechanoreceptors, Ruffini (black arrow) and pacinian (white arrow), in a torn anterior cruciate ligament (ACL) specimen adapted to the PCL. Taken from Georgoulis et al with permission.
Graft Selection
The 2 most commonly used grafts in ACL reconstruction are the patellar tendon (PT) and the 4-strand hamstring (HS) tendon made of gracilis and semitendonosus tendons. Both PT and HS autografts result in a functionally stable knee in more than 95% of surgeries with a 3% absolute difference in graft failure: 1.9% with PT and 4.9% with HS tendon grafts. Benefits of PT grafts include that they are readily accessible, have good structural fixation properties, and have the potential for tendon-to-bone healing. Detriments include anterior knee pain, loss of sensation, patellar fracture, and inferior patellar contracture, although patellar knee pain has been associated with less aggressive rehabilitation methods and use of open kinetic chain extension exercises. The use of PT grafts has also been associated with postreconstruction extensor quadriceps weakness.
The HS tendon graft with all 4 strands equally tensioned can withstand much greater tension strains than a 10-mm PT graft. Some researchers have found that harvesting HS grafts can severely reduce HS strength and endurance up to 9 months after the surgery. Hamstring grafts can also be difficult to harvest because graft diameter and lengths are variable. A review of patients determined that HS graft diameter was related to height but not to body mass index. When height decreases below 147 cm and graft diameter decreases below 7 mm, there is an association between graft strength and its cross-sectional diameter.
In a meta-analysis, PT autografts were compared with HS tendon autografts. Using KT-1000 arthrometer testing, statistically significant differences between these graft types were found: the PT group had a 79% side-to-side difference of <3 mm compared with 73.8% for the HS group, leading the authors to conclude that PT autografts led to more stable reconstructed knees than HS tendon grafts. No significant differences between PT and HS grafts were found between the proportion of patients requiring postoperative meniscal surgery, and no statistically significant differences were seen between PT autografts and HS autografts infection rates.
Quadriceps tendon grafts used for ACL reconstruction have been associated with significantly less anterior knee pain and graft-site morbidity compared with PT grafts. These grafts are taken from the central third of the quadriceps tendon and are composed of the vastus medialus, vastus intermedius, and rectus femoris, yielding a bilaminar graft. The mean cross-sectional area for a 10-mm-wide quadriceps tendon graft is 64 mm, larger than 37 mm for the PT; hence, quadriceps tendon grafts produce a broader anatomic insertion of the reconstructed ACL to the tibia. This can decrease physiologic impingement on the intercondylar notch in full extension of the knee. Quadriceps muscle power is not compromised, despite sacrificing a part of the tendon. Overall, quadriceps tendon grafts have the advantage of ease of excision and are comparable with respect to graft size and strength with both PT and HS grafts.
The main advantage of allografts versus autografts is avoidance of donor-site morbidity. Other advantages include savings in operative time of graft harvest, availability of larger grafts, superior cosmesis, and the possibility for multiple ligament reconstructions. Potential disadvantages include delayed graft incorporation, disease transmission, potential immune reactions, altered mechanical properties caused by sterilization, and cost of the allograft. Of primary concern is whether allografts are less stable than autografts. A recent meta-analysis found that allografts failed 3 times more frequently than autografts. However, a recent study found that autografts and nonirradiated (vs radiated or chemically processed) allografts had similar side-to-side differences of <3 mm according to the KT-2000 arthrometer.
Single-bundle versus Double-bundle Reconstruction
Between 10% and 30% of patients reported persistent instability in their reconstructed knee after single-bundle surgery. This resulted in a return-to-sport rate of only 60% to 70% for single-bundle restorations. Single-bundle reconstruction can restore anterior-posterior knee stability but produces knees that are unable to resist combined rotatory loads and do not have normal rotational kinematics. Double-bundle restored knees are better at resisting extrinsic forces placed on the knee. Although the double-bundle technique is better at restoring normal knee kinematics, there are some disadvantages. It is more difficult to perform surgically and could be the cause of reconstruction failures due to the improper positioning of bone tunnels.
Graft Placement
Placement of grafts can have a major impact on the clinical outcome of ACL reconstruction. Failure to regain full flexion postoperatively can be caused by high graft tension during extension of the knee, which in turn may cause the graft to stretch. This may occur when the ACL graft is placed vertically at the apex of the notch, with the tibial tunnel being in a vertical orientation at an angle >70 degrees from the medial joint line of the tibia and the femoral tunnel and then drilled through that tibial tunnel. Prevention of PCL impingement can be achieved by 3 different techniques: widen the notch so that the space between the PCL and lateral femoral condyle exceeds the diameter of the graft by 1 mm, construct the tibial tunnel at an angle of 60 to 65 degrees with respect to the medial joint line of the tibia, which moves the femoral tunnel farther down the sidewall and decreases the risk of PCL impingement, and making certain that the lateral edge of the tibial tunnel is placed through the tip of the lateral tibial spine. There is no consensus on the amount of ligament tensioning or the optimal knee flexion angle. Some surgeons prefer to set the tension of the AM bundle in moderate flexion and the PL bundle near full extension. The preference for tensioning angles mirrors the position of the bundles to provide the greatest strength when at the most tension in intact knees.
Femoral Tunnel Drilling Techniques
There are different techniques for creating the femoral tunnel. The transtibial technique (drilling through the tibial tunnel) and the far anteromedial portal technique (drilling through the far anteromedial tunnel) are frequently used in ACL surgeries to create a femoral bone tunnel for the AM and PL graft in double-bundle reconstructions (Figure 3).
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Figure 3.
A, Extended lines of the virtual AM and PL graft to the femoral side at 90 degrees of knee flexion are acquired as a virtual femoral tunnel in the transtibial technique. B, The acquired position of the femoral attachment site of each bundle and that of the far anteromedial portal are connected and the virtual femoral tunnel are created along the connecting line to the femoral side at 110 degrees of knee flexion in the far anteromedial portal technique. Taken from Nishimoto et al with permission.
Although both are commonly used, the far anteromedial portal approach makes it easier to access the femoral footprint of the AM and PL bundles. This is because unlike in the transtibial technique, the placement of the femoral tunnel is not limited by the site or angulation of the tibial tunnel. For the far anteromedial portal procedure, the PL bundle tunnel should be drilled at a knee position of 110 degrees of extension to avoid damage to the subchondral bone, cartilage of the lateral femoral condyle, and peroneal nerve. For the transtibial technique, the knee should be flexed at 90 degrees for drilling of the femoral bone tunnel. For the transtibial technique, the graft bending angle of the AM and PL bundles are considerably larger than that of the far anteromedial portal technique at low flexion angles when the graft is fully stretched. Nishimoto et al believe that the far anteromedial portal technique can produce a more obtuse bending angle at the femoral tunnel in comparison to the transtibial technique and that the former approach might reduce the abrasive stress at this position in anatomic double-bundle ACL reconstructions.
Recently, investigators from Duke have emphasized the importance of placing the ACL graft within the ACL footprint on the femur to restore normal joint kinematics. In the tibial tunnel–independent technique, the graft is placed closer to the center of the native ACL attachment compared with the transtibial technique. Using MRI of 8 patients in each group, the transtibial technique placed the tunnel center an average of 9 mm from the center of the ACL attachment, compared with 3 mm for the tibial tunnel–independent technique. In another study, the same group used MRI and biplanar fluoroscopy to compare 12 patients where the graft was placed near the anteroproximal border of the ACL and 10 patients where the graft was placed near the center of the ACL. Grafts placed anteroproximally on the femur were longer and more vertical than the native ACL, whereas anatomically placed grafts more closely mimicked ACL motion and length in the contralateral knee.