In situ forces in the anterior cruciate ligament and its bundles in response to anterior tibial loads

The anterior cruciate ligament has a complex fiber anatomy and is not considered to be a uniform structure. Current anterior cruciate ligament reconstructions succeed in stabilizing the knee, but they neither fully restore normal knee kinematics nor reproduce normal ligament, function. To improve the outcome of the reconstruction, it may be necessary to reproduce the complex function of the intact anterior cruciate ligament in the replacement graft. We examined the in situ forces in nine human anterior cruciate ligaments as well as the force distribution between the anteromedial and posterolateral bundles of the ligament in response to applied anterioi tibial loads ranging from 22 to 110 N at knee flexion angles of 0–90°. The analysis was performed using a robotic manipulator in conjunction with a universal force-moment sensor. The in situ forces were determined with no device attached to the ligament, while the knee was permitted to move freely in response to the applied loads. We found that the in situ forces in the anterior cruciate ligament ranged from 12.8 ± 7.3 N under 22 N of anterior tibial load applied at 90° of knee flexion to 110.6 ± 14.8 N under 110 N of applied load at 15° of flexion. The magnitude of the in situ force in the posterolateral bundle was larger than that in the anteromedial bundle at knee flexion angles between 0 and 45°, reaching a maximum of 75.2 ± 18.3 N at 15° of knee flexion under an anterior tibial load of 110 N. The magnitude of the in situ force in the posterolateral bundle was significantly affected by knee flexion angle and anterior tibial load in a fashion remarkably similar to that seen in the anterior cruciate ligament. The magnitude of the in situ force in the anteromedial bundle, in contrast, remained relatively constant, not changing with flexion angle. Significant differences in the direction of the in situ force between the anteromedial bundle and the posterolateral bundle were found only at flexion angles of 0 and 60° and only under applied anterior tibial loads greater than 66 N. We have demonstrated the nonuniformity of the anterior cruciate ligament under unconstrained anterior tibial loads. Our data further suggest that in order for the anterior cruciate ligament replacement graft to reproduce the in situ forces of the normal anterior cruciate ligament, reconstruction techniques should take into account the role of the posterolateral bundle in addition to that of the anteromedial bundle.     

Implantatfreier Ersatz des vorderen Kreuzbandes in Double-bundle-Technik

Reconstruction of the anterior cruciate ligament using the double bundle technique provides better covering of the anatomic insertion site areas and fiber length change behavior. Biomechanical studies and intraoperative measurements with computer navigation systems document increased stability in particular due to rotational stability. To date the impact of the posterolateral bundle is questioned and clinical studies have reported divergent outcomes. In favor of enhanced rotational stability, some techniques leave the basic principles of aperture or central graft fixation, decreasing primary stability and running the risk of tunnel widening especially on the femoral site. Additional use of interference screws means increased implants and costs and bone void in cases of revision is challenging. A technique for anatomic double-bundle reconstruction without the use of implants is presented, which allows for femoral aperture fixation with high primary stability of both bundles. In terms of the knot/press-fit technique of Paessler in the U-shaped tendons, a knot is created at the free end, which serves as a rigid press-fit anchoring in bottleneck shaped femoral drill holes at the insertion site of the anteromedial and posterolateral bundles. The drill holes are prepared in flexion of 110–115° using common offset and target drill devices. Mersilen tapes are applied to introduce the grafts from femoral to tibial and to fix the tendons over a bony bridge on the tibial site after preconditioning. The gracilis tendon mimics the posterolateral bundle and is fixed in 20° of flexion, the semi- tendinosus tendon is used for the anteromedial bundle and is fixed in 40° of flexion. The advantages of the presented technique are the central, rigid femoral anchoring without hardware, the thin bone tunnels which show no tunnel widening and allow for an optimal bone tendon contact to enhance bony ingrowth. The technique is cost-efficient and provides anatomic double bundle reconstruction of the anterior cruciate ligament. The sacrifice of hardware ensures easy revisions. The disadvantages are the peripheral tibial fixation, the preparation of the tendons needs tendon length and the creation of tendon knots providing high stability requires practice. The two femoral bone tunnels have proved to be safe regarding the stability of the lateral femoral condyle.     

Effect of tibial slope or posterior cruciate ligament release on knee kinematics

An experimental study using fresh human cadaver knees was designed to evaluate the effect of partial posterior cruciate ligament release or posterior tibial slope on knee kinematics after total knee arthroplasty. Varus and valgus laxity, rotational laxity, anteroposterior laxity, femoral rollback, and maximum flexion angle were evaluated in a normal knee, an ideal total knee arthroplasty, and a total knee arthroplasty in which the ligaments were made to be too tight in flexion. The total knee arthroplasty specimens then were subjected to either partial posterior cruciate ligament release or increased posterior tibial slope, and the tests were repeated. Posterior tibial slope increased varus and valgus laxity, anteroposterior laxity, and rotational laxity in the knee that had flexion tightness. Posterior cruciate ligament release corrected only anteroposterior tightness, and had no effect on the abnormal collateral ligament tightness. Increased posterior tibial slope significantly improved varus and valgus laxity and rotational laxity in the knee that was tight in flexion more than with release of the posterior cruciate ligament. Therefore increasing posterior tibial slope is preferable for a knee that is tight in flexion during total knee arthroplasty.     

Effect of the angle of the femoral and tibial tunnels in the coronal plane and incremental excision of the posterior cruciate ligament on tension of an anterior cruciate ligament graft: an in vitro study

BACKGROUND: High tension in an anterior cruciate ligament graft adversely affects both the graft and the knee; however, it is unknown why high graft tension in flexion occurs in association with a posterior femoral tunnel. The purpose of the present study was to determine the effect of the angle of the femoral and tibial tunnels in the coronal plane and incremental excision of the posterior cruciate ligament on the tension of an anterior cruciate ligament graft during passive flexion. METHODS: Eight cadaveric knees were tested. The angle of the tibial tunnel was varied to 60 degrees, 70 degrees, and 80 degrees in the coronal plane with use of three interchangeable, low-friction bushings. The femoral tunnel, with a 1-mm-thick posterior wall, was drilled through the tibial tunnel bushing with use of the transtibial technique. After the graft had been tested in all three tibial bushings with one femoral tunnel, the femoral tunnel was filled with bone cement and the tunnel combinations were tested. Lastly, the graft was replaced in the 80 degrees femoral and tibial tunnels, and the tests were repeated with excision of the lateral edge of the posterior cruciate ligament in 2-mm increments. Graft tension, the flexion angle, and anteroposterior laxity were recorded in a six-degrees-of-freedom load-application system that passively moved the knee from 0 degrees to 120 degrees of flexion. RESULTS: The graft tension at 120 degrees of flexion was affected by the angle of the femoral tunnel and by incremental excision of the posterior cruciate ligament. The highest graft tension at 120 degrees of flexion was 169 +/- 9 N, which was detected with the graft in the 80 degrees femoral and 80 degrees tibial tunnels. The lowest graft tension at 120 degrees of flexion was 76 +/- 8 N, which was detected with the graft in the 60 degrees femoral and 60 degrees tibial tunnels. The graft tension of 76 N at 120 degrees of flexion with the graft in the 60 degrees femoral and 60 degrees tibial tunnels was closer to the tension in the intact anterior cruciate ligament. Excision of the lateral edge of the posterior cruciate ligament in 2 and 4-mm increments significantly lowered the graft tension at 120 degrees of flexion without changing the anteroposterior position of the tibia. CONCLUSIONS: Placing the femoral tunnel at 60 degrees in the coronal plane lowers graft tension in flexion. Our results suggest that high graft tension in flexion is caused by impingement of the graft against the posterior cruciate ligament, which results from placing the femoral tunnel medially at the apex of the notch in the coronal plane.     

Die Zwei-Bündel-Technik – eine anatomische Rekonstruktion des vorderen Kreuzbandes

OBJECTIVE: To improve the rotational stability of the knee by anatomic reconstruction of the anterior cruciate ligament by socalled double-bundle technique using anteromedial and posterolateral grafts from native semitendinosus and gracilis. The grafts are fixed with bioabsorbable screws utilizing aperture fixation. INDICATIONS: Complete tear of the anterior cruciate ligament with positive Lachman sign and pivot shift. CONTRAINDICATIONS: Open growth plate. Osteoarthritis > grade 1 according to J?ger & Wirth. Age > or = 50 years with low sports activity (relative contraindication). SURGICAL TECHNIQUE: Graft harvest of the semitendinosus and gracilis tendons via a 3-cm horizontal skin incision parallel to pes anserinus and preparation of the tendons as double-looped grafts. Arthroscopy, resection of the stump of the anterior cruciate ligament, and clearance of its origin and insertion. Tunnel placement by means of aiming devices in the following order: tibial posterolateral, tibial anteromedial, femoral anteromedial (transtibial or via the anteromedial portal in 120 degrees flexion), and femoral posterolateral (via additional medial arthroscopic portal). The anteromedial (semitendinosus tendon) and posterolateral (gracilis tendon) bundles are passed through the tunnels and fixed on the femoral side. Tibial fixation of the graft by bioresorbable interference screw with knee flexion of 45 degrees (anteromedial) and 10 degrees (posterolateral). POSTOPERATIVE MANAGEMENT: Depending on the degree of swelling, rehabilitation with partial weight bearing for 14 days and full range of motion. Return to sports after 6 months, no contact sports until 9 months. RESULTS: From May 2004 to June 2005, anatomic double-bundle reconstruction was performed in 19 patients (13 male, six female, average age 31 years [18-48 years]) with isolated anterior cruciate ligament rupture without concomitant lesions. Clinical follow-up examination on average at 21.3 months (16-30 months) postoperatively. The Lysholm Score improved from an average of 65.2 to 94.5 points (75-100 points). The IKDC (International Knee Documentation Committee) Score yielded nine very good and ten good results in the relevant subgroups of motion, effusion and ligament stability. Measurement of anteroposterior translation with the KT-1000 instrument at 134 N showed increased translation of 1.8 mm (-2 to 5 mm) compared to the contralateral knee.     

Review article: anatomic double bundle anterior cruciate ligament reconstruction

The anterior cruciate ligament (ACL) consists of 2 bundles: a slightly larger anteromedial bundle and a posterolateral bundle, named according to their relative tibial insertion sites. Both bundles are crucial to knee stability. Although it is more technically demanding, a double bundle ACL reconstruction restores the knee biomechanics better and provides more rotational stability than a single bundle ACL reconstruction. Intermediate and long-term clinical investigation including the measurement of rotational laxity and the evaluation of osteoarthritic change is needed to confirm biomechanical and short-term clinical outcomes.     

Aperture Fixation in Arthroscopic Anterior Cruciate Ligament Double-Bundle Reconstruction

The native anterior cruciate ligament (ACL) consists of 2 bundles, which have distinct biomechanical yet synergistic functions with respect to anterior tibial translation and combined rotatory loads. Traditionally, most ACL reconstruction techniques have primarily addressed the restoration of the anteromedial bundle, and less consideration was given to the posterolateral bundle. Recently, various ACL double-bundle reconstruction techniques have been described. With most of these techniques, however, an indirect extra-anatomic fixation far from the articular surface was performed. Because extra-anatomic fixation techniques, rather than aperture fixation techniques, are associated with graft tunnel motion, windshield wiper action, and suture stretch-out, concerns may arise regarding delayed biological incorporation, tunnel enlargement, and secondary rotational and anterior instability. We, therefore, present a novel arthroscopic technique that reapproximates the footprints of native ACL with the use of double-strand semitendinosus and gracilis autografts for reconstruction of the anteromedial and posterolateral bundles, respectively. A separate femoral and tibial tunnel is drilled for each double-strand autograft. The femoral tunnel for the anteromedial bundle is drilled primarily through a transtibial technique, and the femoral tunnel for the posterolateral bundle is drilled via an accessory anteromedial portal with the use of a 4-mm offset drill guide in the anteroinferior aspect of the femoral tunnel for the anteromedial bundle. Bioabsorbable interference screws are used in aperture fixation for anatomic fixation of each bundle. This technique attempts to reproduce closely the native ligament and its biomechanical function.     

Isolierter Bündelersatz bei Partialruptur des vorderen Kreuzbandes

Objective

Partial augmentation of isolated tears of the anteromedial and posterolateral bundle of the anterior cruciate ligament (ACL) with autologous hamstring tendons. The intact fibers of the ACL are preserved.

Indications

Symptomatic isolated tear of the anteromedial or posteromedial bundle of the ACL or rotational instability after ACL reconstruction with malplaced tunnels (e.g., high femoral position)

Contraindications

In revision cases: loss of motion due to malplaced ACL and excessive tunnel widening of the present tunnels with the risk of tunnel confluence.

Surgical technique

Examination of anterior–posterior translation and rotational instability under anesthesia. Diagnostic arthroscopy, repetition of the clinical examination under direct visualization of the ACL, meticulous probing of the functional bundles. Resection of ligament remnants, preparation/preservation of the femoral and tibial footprint. Harvesting one of the hamstring tendons, graft preparation. Positioning of a 2.4 mm K-wire in the anatomic center of the femoral anteromedial/posterolateral bundle insertion, cannulated drilling according to the graft diameter. Positioning of a 2.4 mm K-wire balanced according to the femoral tunnel at the tibia, cannulated drilling. Insertion of the graft and fixation.

Postoperative management

Analogous to that for ACL reconstruction.     

Anatomic Double Bundle: A New Concept in Anterior Cruciate Ligament Reconstruction Using the Quadriceps Tendon

Surgical procedures for double-bundle anterior cruciate ligament reconstruction, which currently use hamstring graft, have been described, but some concerns remain regarding graft fixation and the ability to obtain adequate bundle size. We report an original double-bundle anterior cruciate ligament reconstruction technique using a quadriceps tendon graft and a simplified outside-in femoral tunnel–drilling process. The graft consists of a patellar bone block with its attached tendon split into superior and inferior portions, which yields 2 bundles. The anteromedial tunnel is drilled from the outside through a small lateral incision by use of a guide. The posterolateral tunnel is made through the same incision with a specific guide engaged in the anteromedial tunnel. A single tibial tunnel is created. The graft is routed from the tibia to the femur with the bone block in the tibial tunnel and the 2 bundles in their respective femoral tunnels. After fixation of the bone block in the tibia, the 2 bundles are tensioned and secured separately in their femoral tunnels.     

关节镜下半腱肌腱和股薄肌腱双隧道重建前十字韧带

目的探讨关节镜下联合应用半腱肌腱和股薄肌腱重建前十字韧带(anteriorcruciateligament,ACL)的方法及疗效。方法回顾自1998年4月～2000年5月在关节镜下联合应用半腱肌腱和股薄肌腱重建ACL的患者12例。于ACL前内侧束和后外侧束的附着部分别钻直径4.5mm的隧道,用半腱肌腱重建前内侧束,股薄肌腱重建后外侧束,保留半腱肌腱和股薄肌腱的附着点,在股骨隧道外口将半腱肌腱和股薄肌腱打结固定,不行内固定。所有患者术前及术后18个月行膝关节屈曲30°、60°、90°前抽屉试验,Lysholm评分方法评定膝关节功能。结果术后随访18～43个月,平均26个月。术前所有患者前抽屉试验均为阳性,术后9例阴性,2例屈膝30°位阳性,1例屈膝30°、60°位阳性。术前Lysholm评分为40～58分,平均50.5分,手术后18个月为62～92分,平均85分,总优良率为91.7%。结论应用半腱肌腱和股薄肌腱联合重建ACL,术后膝关节动态稳定性好,疗效满意。     

Analysis of modified double-bundle anterior cruciate ligament reconstruction with implantless fixation on tibial side

Purpose: To avoid potential problems of double-bundle anterior cruciate ligament reconstruction (ACLR), various modifications have been reported. This study analyzed a novel technique of modified doublebundle (MDB) ACLR without implant on tibial side in comparison to single-bundle (SB) ACLR. Methods: Eighty cases of isolated anterior cruciate ligament tear (40 each in SB group or MDB group) were included. SB ACLR was performed by outside in technique with quadrupled hamstring graft fixed with interference screws. In MDB group, ACLR harvested tendons were looped over each other at the center and free ends whipstitched. Femoral tunnel was created by outside in technique. Anteromedial tibial tunnel was created with tibial guide at 55. The anatomic posterolateral aiming guide (SmithNephew) was used to create posterolateral tunnel. With the help of shuttle sutures, the free end of gracillis was passed through posterolateral tunnel to femoral tunnel followed by semitendinosus graft through anteromedial tunnel to femoral tunnel. On tibial side the graft was looped over bone-bridge between external apertures of anteromedial and posterolateral tunnel. Graft was fixed with interference screw on femoral side in 10 knee flexion. International Knee Documentation Committee (IKDC), Tegner score, Pivot shift and knee laxity test (KLT, Karl-Storz) were recorded pre- and post-surgery. At one year magnetic resonance imaging (MRI) was done. Statistical analysis was done by SPSS software. Results: Mean preoperative KLT reading of (10.00 ± 1.17) mm in MDB group improved to (4.10 ± 0.56) mm and in SB group it improved from (10.00 ± 0.91) mm to (4.80 ± 0.46) mm. The mean preoperative IKDC score in MDB group improved from (49.49 ± 8.00) to (92.5 ± 1.5) at one year and that in SB group improved from (52.5 ± 6.9) to (88.4 ± 2.6). At one-year 92.5% cases in MDB group achieved their preinjury Tegner activity level as compared to 60% in SB group. The improvement in IKDC, KLT and Tegner scale of MDB group was superior to SB group. MRI confirmed graft integrity at one year and clinically at 2 years. Conclusion: MDB ACLR has shown better outcome than SB ACLR. It is a simple technique that does not require fixation on tibial side and resultant graft is close to native ACL.     

Anatomically Oriented Anterior Cruciate Ligament Reconstruction with a Bone–Patellar Tendon–Bone Graft via Rectangular Socket and Tunnel: A Snug-fit and Impingement-Free Grafting Technique

An anterior cruciate ligament (ACL) reconstruction technique is described to place bone–patellar tendon–bone (BPTB) graft in an anatomically oriented fashion to mimic the 2 bundles of the normal ACL, based on the concept of twin tunnel ACL reconstruction, to maximize the graft-tunnel interface. In this technique, the attached bone plug is introduced into a rectangular femoral socket via a halfway rectangular tibial tunnel for the anterior portion of the graft to function as the anteromedial bundle and for its posterior portion to behave as the posterolateral bundle. A snug fitting of the graft is achieved not only at the femoral socket, but also in the tibial tunnel.     

Femoral tunnel placement in anterior cruciate ligament reconstruction: rationale of the two incision technique

Endoscopic anterior cruciate ligament (ACL) reconstruction can be performed through one-incision or two-incision technique. The current one-incision endoscopic ACL single bundle reconstruction techniques attempt to perform an isometric repair placing the graft along the roof of the intercondylar notch, anterior and superior to the native ACL insertion. However the ACL isometry is a theoretical condition, and has not stood up to detailed testing and investigation. Moreover this type of reconstruction results in a vertically oriented non-anatomic graft, which is able to control anterior tibial translation but not the rotational component of the instability. Femoral tunnel obliquity has a great effect on rotational stability. To improve the obliquity of graft, an anatomical ACL reconstruction should be attempt. Anatomical insertion of ACL on the femur lies very low in the notch, spreading between 11 and 9–8 o'clock position and the center lies lower than at 11 o'clock position. Femoral aiming devices through the tibial tunnel aim at an isometric placement, and they do not aim at an anatomic position of the graft. Also, a placement of tunnel in a position of 11 o'clock is unable to restore rotational stability. The two-incision technique, with the possibility to position femoral tunnel independently by tibial tunnel, allows us to place femoral tunnel entrance in a position of 10 'clock that can most accurately reproduce the anatomic behaviour of the ACL and can potentially improve the response of the graft to rotatory loads. This positioning results in a more oblique graft placement, avoiding problem related to PCL impingement during knee flexion. Further studies are required to understand if this kind of reconstruction can ameliorate proprioception as well as clinical outcome at a long-term follow-up.     

Oblique femoral tunnel or oblique graft? A modified anteromedial portal technique to obtain vertical femoral tunnel and oblique graft in anatomic anterior cruciate ligament reconstruction

In anterior cruciate ligament (ACL) reconstruction, transtibial drilling of the femoral tunnel has been criticized for its vertical and less anatomical tunnel, which accompanied rotational instability of knee. Many authors recommend anteromedial (AM) portal drilling technique, which creates more oblique and anatomic femoral tunnel. However, recent researches show that oblique tunnel is related to risks of too short femoral tunnel, blowout of back wall, and posterolateral structures injury. Is oblique femoral tunnel really essential for anatomic reconstruction? We introduce a modified AM technique, which abandons the oblique tunnel and provides vertical femoral tunnel and oblique graft with anatomic starting point. The fundamental of the new technique is that oblique graft but not oblique tunnel is essential for rotational stability of knee. Thus, it avoids the risks and preserves anatomic reproduction of ACL.     

Effects of femoral tunnel placement on knee laxity and forces in an anterior cruciate ligament graft.

The purpose of this study was to measure the effects of variation in placement of the femoral tunnel upon knee laxity, graft pretension required to restore normal anterior-posterior (AP) laxity and graft forces following anterior cruciate ligament (ACL) reconstruction. Two variants in tunnel position were studied: (1) AP position along the medial border of the lateral femoral condyle (at a standard 11 o'clock notch orientation) and (2) orientation along the arc of the femoral notch (o'clock position) at a fixed distance of 6-7 mm anterior to the posterior wall. AP laxity and forces in the native ACL were measured in fresh frozen cadaveric knee specimens during passive knee flexion-extension under the following modes of tibial loading: no external tibial force, anterior tibial force, varus-valgus moment, and internal-external tibial torque. One group (15 specimens) was used to determine effects of AP tunnel placement, while a second group (14 specimens) was used to study variations in o'clock position of the femoral tunnel within the femoral notch. A bone-patellar tendon-bone graft was placed into a femoral tunnel centered at a point 6-7 mm anterior to the posterior wall at the 11 o'clock position in the femoral notch. A graft pretension was determined such that AP laxity of the knee at 30 deg of flexion was restored to within 1 mm of normal; this was termed the laxity match pretension. All tests were repeated with a graft in the standard 11 o'clock tunnel, and then with a graft in tunnels placed at other selected positions. Varying placement of the femoral tunnel 1 h clockwise or counterclockwise from the 11 o'clock position did not significantly affect any biomechanical parameter measured in this study, nor did placing the graft 2.5 mm posteriorly within the standard 11 o'clock femoral tunnel. Placing the graft in a tunnel 5.0 mm anterior to the standard 11 o'clock tunnel increased the mean laxity match pretension by 16.8 N (62%) and produced a knee which was on average 1.7 mm more lax than normal at 10 deg of flexion and 4.2 mm less lax at 90 deg. During passive knee flexion-extension testing, mean graft forces with the 5.0 mm anterior tunnel were significantly higher than corresponding means with the standard 11 o'clock tunnel between 40 and 90 deg of flexion for all modes of constant tibial loading. These results indicate that AP positioning of the femoral tunnel at the 11 o'clock position is more critical than o'clock positioning in terms of restoring normal levels of graft force and knee laxity profiles at the time of ACL reconstruction.     

Anatomic double-bundle anterior cruciate ligament reconstruction with hamstrings

This article describes a double-bundle gracilis and semitendinosus technique that guarantees a more anatomic anterior cruciate ligament (ACL) reconstruction and allows the surgeon to avoid the use of hardware for graft fixation. The tendons are harvested maintaining their tibial insertion. Sutures are tightened at the free proximal tendon ends to obtain a sufficient strength to traction. The tibial tunnel is located in the medioposterior part of the ACL tibial insertion. For the femoral tunnel, the knee is flexed around 130° and the guide pin is advanced until it passes the femoral cortex. The exit point in the lateral aspect of the femur should be immediately above the end of the lateral femoral condyle. After the lateral incision, the tendons are passed over the top. The correct placement is found by palpating the posterior tubercle of the lateral femoral condyle with a finger. The stitches on the free end of the tendons are tied onto the passing suture that is pulled through the knee joint into the over-the-top position. A suture loop is introduced into the joint through the anteromedial portal using a suture passer and then pulled into the femoral tunnel under the arthroscopic view. The stitches on the free end of the tendons are looped again onto the passing suture, which is pulled through the femoral tunnel, knee joint, and tibial tunnel to retrieve the graft from the tibial incision. The combined gracilis and semitendinosus tendons are then tensioned and secured with a transosseus suture knot. This technique attempts to reproduce the kinematic effect of both anteromedial and posterolateral bundle of the ACL with a 4-bundle reconstruction with a better performance from the anatomic and functional point of view.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 19, No 5 (May-June), 2003: pp 540–546     

In vivo anterior cruciate ligament length pattern assessment secondary to differences in the femoral attachment under loading condition using image-matching techniques

Background

The anterior cruciate ligament is composed of two functional bundles and is crucial for knee function. There is limited understanding of the role of each individual bundle and the influence on length pattern due to difference in bone tunnel position under loading conditions throughout the range of motion. We measured point to point length between the femoral and tibial footprints of the ligament throughout the range of motion in normal knees, under normal loading conditions, and investigated length pattern changes secondary to differences in the femoral footprint. We hypothesized that anteromedial and posterolateral bundles have complementary roles, and the ligament length pattern is influenced by the footprint position.

No Tunnel 2-Socket Technique: All-Inside Anterior Cruciate Ligament Double-Bundle Retroconstruction

This report describes an all-inside, double-bundle anterior cruciate ligament retroconstruction (all-inside ×2 technique), which is a less invasive technique because of the use of sockets (2 femoral and 2 tibial) instead of complete bone tunnels. When performed with allograft, this may be termed a “no-incision” technique. The femoral sockets are reamed via the anteromedial arthroscopic portal. The tibial sockets are created with the all-inside RetroDrill (Arthrex, Naples, FL) from within the joint. The posterolateral bundle graft is passed first and shuttled through the anteromedial portal and fixed on the femur with a RetroButton (Arthrex), interference screw, or both. It is then fixed on the tibia with a bioabsorbable RetroScrew (Arthrex) near full extension. The anteromedial bundle graft is passed through next, and the process is repeated with tibial fixation performed at 45° of flexion. Posterolateral and anteromedial tibial fixation may be backed up by tying over a cortical button.     

Biomechanical comparison of tibial inlay and tibial tunnel techniques for reconstruction of the posterior cruciate ligament. Analysis of graft forces

BACKGROUND: The tibial inlay technique of reconstruction of the posterior cruciate ligament offers potential advantages over the conventional transtibial tunnel technique, particularly with regard to the graft force levels that develop over a functional range of knee flexion. Abnormally high graft forces generated during rehabilitation activities could lead to stretch-out of the graft during the critical early healing period. The purpose of this study was to compare graft forces between these two techniques and with forces in the native posterior cruciate ligament. METHODS: A load cell was installed at the femoral origin of the posterior cruciate ligament in twelve fresh-frozen cadaveric knees to measure resultant forces in the ligament during a series of knee loading tests. The posterior cruciate ligament was then excised, and the femoral ends of 10-mm-wide bone-patellar tendon-bone grafts were attached to the load cell to measure resultant forces in the grafts. For the tunnel reconstruction, the distal bone block of the graft was placed into a tibial tunnel and thin stainless-steel cables interwoven into the bone block were gripped in a split clamp attached to the anterior tibial cortex. With the inlay technique, the distal bone block was fixed in a tibial trough with use of a cortical bone screw with a washer and nut. The proximal ends of all grafts were pretensioned to a level of force that restored intact knee laxity at 90 degrees of flexion, and loading tests were repeated. RESULTS: There were no significant differences in mean graft forces between the two techniques under tibial loads consisting of 100 N of posterior tibial force, 5 N-m of varus and valgus moment, and 5 N-m of internal and external tibial torque. Mean graft forces with the tibial tunnel technique were approximately 10 to 20 N higher than those with the inlay technique with passive knee flexion beyond 95 degrees. Mean graft forces with both reconstruction techniques were significantly higher than forces in the native posterior cruciate ligament with the knee flexed beyond approximately 90 degrees for all but one mode of loading. CONCLUSIONS: In this cadaveric testing model, neither technique for reconstruction of the posterior cruciate ligament had a substantial advantage over the other with respect to generation of graft forces.     

In vitro comparison of elongation of the anterior cruciate ligament and single- and dual-tunnel anterior cruciate ligament reconstructions.

This study evaluated strain in the normal anterior cruciate ligament (ACL) and compared it to four different double-strand hamstring tendon reconstructive techniques. Seventeen fresh-frozen knees from 11 cadavers were tested. The strain in the anteromedial and posterolateral bands of the native ACL and their equivalents in four autograft techniques were measured using differential variable reluctance transducers. The anteromedial band of the intact ACL shortened from 0 degree -30 degrees of flexion, then lengthened to 120 degrees; the posterolateral band of the intact ACL shortened from 0 degree - 120 degrees of flexion. Following ACL excision, these knees underwent reconstruction with double-strand hamstring tendons with either single tibial and femoral tunnels, single tibial and dual femoral tunnels, dual tibial and single femoral tunnels, or dual tibial and dual femoral tunnels. With the exception of the dual-band, dual-tunnel technique, all of the procedures placed greater strain on the reconstructive tissues than was observed on the native ACL, after approximately 30 degrees of flexion. These results indicate that dual-band hamstring tendon reconstructions placed with single tibial and femoral tunnels do not address the complexity of the entire ACL. Rather, these procedures appear to only duplicate the effect of the anteromedial band, while perhaps overconstraining the joint as a result of its inability to reproduce the function of the posterolateral band. During rehabilitation following ACL reconstruction, therefore, only from 0 degree - 30 degrees of the graft tissues are not significantly strained. Dual tibial and femoral tunnel techniques should be evaluated further to more closely recreate knee kinematics following ACL reconstruction.