Thore Zantop

Effects of Increasing Tibial Slope on the Biomechanics of the Knee

Purpose To determine the effects of increasing anterior-posterior (A-P) tibial slope on knee kinematics and in situ forces in the cruciate ligaments. Methods Ten cadaveric knees were studied using a robotic testing system using three loading conditions: (1) 200 N axial compression; (2) 134 N A-P tibial load; and (3) combined 200 N axial and 134 N A-P loads. Resulting knee kinematics were determined before and after a 5-mm anterior opening wedge osteotomy. Resulting in situ forces in each cruciate ligament were determined. Results Tibial slope was increased from 8.8 ± 1.8 ° to 13.2 ± 2.1 °, causing an anterior shift in the resting position of the tibia relative to the femur up to 3.6 ± 1.4 mm. Under axial compression, the osteotomy caused a significant anterior tibial translation up to 1.9 ± 2.5 mm (90 °). Under A-P and combined loads, no differences were detected in A-P translation or in situ forces in the cruciates (intact versus osteotomy). Conclusions Results suggest that small increases in tibial slope do not affect A-P translations or in situ forces in the cruciate ligaments. However, increasing slope causes an anterior shift in tibial resting position that is accentuated under axial loads. This suggests that increasing tibial slope may be beneficial in reducing tibial sag in a PCL-deficient knee, whereas decreasing slope may be protective in an ACL-deficient knee.

The role of the anteromedial and posterolateral bundles of the anterior cruciate ligament in anterior tibial translation and internal rotation

Background A rupture of the entire fibers of the anterior cruciate ligament leads to knee instability due to increased anterior tibial translation and increased internal tibial rotation. The influence of isolated deficiency of the anteromedial or posterolateral bundle of the anterior cruciate ligament on the resulting knee kinematics have not yet been reported. Hypothesis Transection of the anteromedial bundle will lead to increased anterior tibial translation at 90°. Transection of the posterolateral bundle will show an increased anterior tibial translation as well as a combined rotatory instability at 30°. Study Design Controlled laboratory study. Methods Kinematics of the intact knee were determined in response to a 134-N anterior tibial load and a combined rotatory load of 10 N·m valgus and 4 N·m internal tibial rotation using a robotic/universal force moment sensor testing system. Subsequently, the fibers of the anteromedial and posterolateral bundle were resected in an alternating order and the new translation in response to the same external loading conditions measured. Statistical analysis was performed using a 2-way ANOVA test. Results Transection of the anteromedial bundle increased anterior tibial translation at 60° and 90° of knee flexion significantly. Isolated transsection of the posterolateral bundle increased anterior tibial translation in response to 134-N anterior load at 30° of knee flexion significantly and resulted in a significant increase in combined rotation at 0° and 30° in response to a combined rotatory load compared with the intact knee and isolated resection of the anteromedial bundle. Conclusion The anteromedial and posterolateral bundles stabilize the knee joint in response to anterior tibial loads and combined rotatory loads in a synergistic way. Clinical Relevance The results of the current study suggest that, from a biomechanical point of view, it may be beneficial to reconstruct both bundles of the anterior cruciate ligament to better restore normal anterior tibial translation and combined rotation.

Tunnel Positioning of Anteromedial and Posterolateral Bundles in Anatomic Anterior Cruciate Ligament Reconstruction Anatomic and Radiographic Findings

Background The interest in double-bundle anterior cruciate ligament (ACL) reconstructions has recently reawakened. Hypothesis The center of the femoral posterolateral (PL) bundle and the center of the femoral anteromedial (AM) bundle are not within the same plane and change their orientation throughout passive knee flexion. Additionally, the tibial center of the AM bundle is aligned with the anterior horn of the lateral meniscus and the center of the PL bundle lies at the recommended tibial tunnel position for single-bundle ACL reconstruction reconstruction, 7 to 9 mm anterior to the posterior cruciate ligament. Study Design Descriptive laboratory study. Materials In 20 human cadaveric knees (age range, 45–87 years) the distances from the center of the AM and PL bundle to the articular cartilage were measured. Radiographic analyses were performed using the techniques of Bernard and Hertel at the femur as well as the method by Stäubli and Rauschning at the tibia. Results The center of the AM bundle was at a point 5.3 mm (± 0.7) from the roof of the notch and 5.7 mm (± 0.5) from the intercondylar line. The center of the PL bundle is located at 6.5 mm from the shallow cartilage margin and 5.8 mm from the inferior cartilage margin. On the tibia, the center of the AM bundle is aligned with the anterior horn of the lateral meniscus, while the center of the PL bundle was located 11.2 mm (± 1.2) posterior and 4.1 mm (± 0.6) medial to the anterior insertion of the lateral meniscus. Radiographically, the center of the PL bundle is anterior along Blumensaats line and lower in the femoral notch along the height of the condyles than the center of the AM bundle. At the tibia, the center of the AM bundle is at 30% and the PL bundle is located at 44% using the method of Stäubli and Rauschning. Conclusion The center of the femoral PL bundle is shallow and inferior to the AM bundle. On the tibia, the AM bundle lies anterior when compared with the typical single-bundle ACL tunnel that reflects the PL bundle. Clinical Relevance To imitate the anatomy of the intact ACL, it is mandatory to place the tunnels exactly within the femoral origin and tibial insertion of the ACL.

Anatomical and nonanatomical double-bundle anterior cruciate ligament reconstruction: importance of femoral tunnel location on knee kinematics.

Background Studies have suggested that double-bundle anterior cruciate ligament reconstruction may restore intact knee kinematics better than single-bundle anterior cruciate ligament reconstruction. Although the tunnel position of the femoral anteromedial bundle is well established, the effects of different posterolateral bundle positions on knee kinematics are unknown. Hypothesis Double-bundle anterior cruciate ligament reconstruction with an anatomical (shallow) femoral posterolateral bundle tunnel placement will restore knee kinematics more closely than will a nonanatomical (deep) femoral posterolateral bundle tunnel position. Study Design Controlled laboratory study. Methods In 12 human cadaveric knees, the kinematics of the intact knee, anterior cruciate ligament-deficient knee, and double-bundle anterior cruciate ligament-reconstructed knees with nonanatomical femoral posterolateral tunnel placement and anatomical posterolateral bundle placement were determined in response to a 134-N anterior tibial load and a combined rotatory load of 10 Nm valgus and 4 Nm internal tibial rotation using a robotic/universal force moment sensor testing system. Statistical analyses were performed using a 2-way analysis of variance test. Results Double-bundle anterior cruciate ligament reconstruction with nonanatomical posterolateral bundle placement showed significantly higher anterior tibial translation under anterior tibial and combined rotatory load than did the intact knee at 0° and 30° of knee flexion (P < .05). Reconstruction with an anatomical posterolateral tunnel placement restored the intact knee kinematics and showed significantly lower anterior tibial translation under anterior tibial and combined rotatory load when compared with reconstruction with nonanatomical posterolateral placement (P < .05). Conclusion Double-bundle anterior cruciate ligament reconstruction using the anatomical posterolateral bundle tunnel position restores the intact knee kinematics. A nonanatomical posterolateral bundle position results in rotatory instability. Clinical Relevance Double-bundle anterior cruciate ligament reconstruction should be performed using anatomical tunnel placement of the anteromedial and posterolateral bundles. Nonanatomical double-bundle reconstruction may fail to show any clinical superiority to single-bundle reconstruction and should be avoided.

Anatomic, radiographic, biomechanical, and kinematic evaluation of the anterior cruciate ligament and its two functional bundles.

Outcomes following single-bundle anterior cruciate ligament reconstruction are generally good. However, a critical review of the literature shows that some patients have residual instability and pain following single-bundle anterior cruciate ligament reconstruction1-4. Recent clinical investigations have demonstrated that anteroposterior knee laxity, as measured with the KT-1000 and the Lachman test, is not associated with functional outcomes after anterior cruciate ligament reconstruction5. Conversely, there is a significant association between the pivot-shift test and functional outcomes after anterior cruciate ligament reconstruction (p = 0.03), which emphasizes the importance of rotational knee stability for functional recovery5. Biomechanical and kinematic studies have suggested that a more anatomical reconstruction of the anterior cruciate ligament may provide improved long-term outcomes. In this article, we describe the anatomy, radiographic characteristics, injury patterns, biomechanics, and kinematics of the anterior cruciate ligament. We also summarize the surgical technique and augmentation procedures used in an anatomic two-bundle approach to anterior cruciate ligament reconstruction. Fig. 1 The fetal knee demonstrates the two bundles of the anterior cruciate ligament: the anteromedial (AM) and the posterolateral (PL) bundle. LFC = lateral femoral condyle. Fetal, arthroscopic, and cadaver studies have shown that the anterior cruciate ligament consists of two functional bundles, the anteromedial bundle and the posterolateral bundle6-8 (Figs. 1, 2, and 3). The nomenclature of the two bundles corresponds to their tibial insertion sites. On the femoral side, the anteromedial bundle originates more proximally and the posterolateral bundle originates more distally. On the tibial side, the anteromedial bundle inserts anteromedially while the posterolateral bundle inserts posterolaterally. The relative position of the two bundles varies with the flexion angle of the knee. In extension, the two bundles are parallel. In flexion, the femoral insertion site of the posterolateral bundle moves anteriorly, and the …

Biomechanical Evaluation of Two Techniques for Double-Bundle Anterior Cruciate Ligament Reconstruction One Tibial Tunnel Versus Two Tibial Tunnels

Background This research was undertaken to determine whether there is a need for a second tibial tunnel in anatomic anterior cruciate ligament reconstruction. Hypothesis Anatomic two-bundle reconstruction with two tibial tunnels restores knee anterior tibial translation in response to 134 N and to 5-N·m internal tibial torque combined with 10-N·m valgus torque more closely to normal than does double-bundle reconstruction with one tibial tunnel. Study Design Controlled laboratory study. Methods Ten cadaveric knees were subjected to a 134-N anterior tibial load at 0°, 30°, 60°, and 90° and to 5-N·m internal tibial torque and 10-N·m valgus torque at 15° and 30°. Resulting knee kinematics and in situ force in the anterior cruciate ligament or replacement graft were determined by using a robotic/universal force-moment sensor testing system for (1) intact, (2) anterior cruciate ligament–deficient, (3) double-bundle/one tibial tunnel, and (4) double-bundle/two tibial tunnels. Results Anterior tibial translation for the reconstruction with two tibial tunnels was significantly closer to that of the intact knee than was the reconstruction with one tibial tunnel at 0° and 30° of flexion (0° = 3.82 vs 6.0 mm, P < .05; 30° = 7.99 vs 11 mm, P < .05). The in situ force normalized to the intact anterior cruciate ligament for the reconstruction with two tibial tunnels was significantly higher than the in situ force of the reconstruction with one tibial tunnel (30° = 89 vs 82 N, P < .05). With a combined rotatory load, the anterior tibial translation of specimens with a tibial two-tunnel technique was significantly lower than that of specimens with one tunnel (0° = 5.7 vs 8.4 mm, P < .05; 30° = 7.5 vs 9.5 mm, P < .05). Conclusions Anatomic reconstruction with two tibial tunnels may produce a better biomechanical outcome, especially close to extension. Clinical Relevance At the time of initial fixation, there appears to be a small biomechanical advantage to the second tibial tunnel in the setting of two-bundle anterior cruciate ligament reconstruction.

Importance of Tibial Slope for Stability of the Posterior Cruciate Ligament—Deficient Knee

Background Previous studies have shown that increasing tibial slope can shift the resting position of the tibia anteriorly. As a result, sagittal osteotomies that alter slope have recently been proposed for treatment of posterior cruciate ligament (PCL) injuries. Hypotheses Increasing tibial slope with an osteotomy shifts the resting position anteriorly in a PCL-deficient knee, thereby partially reducing the posterior tibial “sag” associated with PCL injury. This shift in resting position from the increased slope causes a decrease in posterior tibial translation compared with the PCL-deficient knee in response to posterior tibial and axial compressive loads. Study Design Controlled laboratory study. Methods Three knee conditions were tested with a robotic universal force-moment sensor testing system: intact, PCL-deficient, and PCL-deficient with increased tibial slope. Tibial slope was increased via a 5-mm anterior opening wedge osteotomy. Three external loading conditions were applied to each knee condition at 0°, 30°, 60°, 90°, and 120° of knee flexion: (1) 134-N anterior-posterior (A-P) tibial load, (2) 200-N axial compressive load, and (3) combined 134-N A-P and 200-N axial loads. For each loading condition, kinematics of the intact knee were recorded for the remaining 5 degrees of freedom (ie, A-P, medial-lateral, and proximal-distal translations, internal-external and varus-valgus rotations). Results Posterior cruciate ligament deficiency resulted in a posterior shift of the tibial resting position to 8.4 ± 2.6 mm at 90° compared with the intact knee. After osteotomy, tibial slope increased from 9.2° ± 1.0° in the intact knee to 13.8° ± 0.9°. This increase in slope reduced the posterior sag of the PCL-deficient knee, shifting the resting position anteriorly to 4.0 ± 2.0 mm at 90°. Under a 200-N axial compressive load with the osteotomy, an additional increase in anterior tibial translation to 2.7 ± 1.7 mm at 30° was observed. Under a 134-N A-P load, the osteotomy did not significantly affect total A-P translation when compared with the PCL-deficient knee. However, because of the anterior shift in resting position, there was a relative decrease in posterior tibial translation and increase in anterior tibial translation. Conclusion Increasing tibial slope in a PCL-deficient knee reduces tibial sag by shifting the resting position of the tibia anteriorly. This sag is even further reduced when the knee is subjected to axial compressive loads. Clinical Relevance These data suggest that increasing tibial slope may be beneficial for patients with PCL-deficient knees.

Effect of Tunnel-Graft Length on the Biomechanics of Anterior Cruciate Ligament–Reconstructed Knees Intra-articular Study in a Goat Model

Background In anterior cruciate ligament (ACL) reconstruction using hamstring grafts, the graft can be looped, resulting in an increased graft diameter but reducing graft length within the tunnels. Hypothesis After 6 and 12 weeks, structural properties and knee kinematics after soft tissue ACL reconstruction with 15 mm within the femoral tunnel will be significantly inferior when compared with the properties of ACL reconstruction with 25 mm in the tunnel. Study Design Controlled laboratory study. Methods In an intra-articular goat model, 36 ACL reconstructions using an Achilles tendon split graft were performed with 15-mm (18 knees) and 25-mm (18 knees) graft length in the femoral tunnel. Animals were sacrificed 6 weeks and 12 weeks after surgery and knee kinematics was tested. In situ forces as well as the structural properties were determined and compared with those in an intact control group. Histologic analyses were performed in 2 animals in each group 6 and 12 weeks postoperatively. Statistical analysis was performed using a 2-factor analysis of variance test. Results Anterior cruciate ligament reconstructions with 15 mm resulted in significantly less anterior tibial translation after 6 weeks (P < .05) but not after 12 weeks. Kinematics after 12 weeks and in situ forces of the replacement grafts at both time points showed no statistically significant differences. Stiffness, ultimate failure load, and ultimate stress revealed no statistically significant differences between the 15-mm group and the 25-mm group. Conclusion The results suggest that there is no negative correlation between short graft length (15 mm) in the femoral tunnel and the resulting knee kinematics and structural properties. Clinical Relevance Various clinical scenarios exist in which the length of available graft that could be pulled into the bone tunnel (femoral or tibial) could be in question. To address this concern, this study showed that reducing the tendon graft length in the femoral bone tunnel from 25 mm to 15 mm did not have adverse affects in a goat model.

Intraarticular rupture pattern of the ACL.

To date, the intraarticular rupture pattern of the anterior cruciate ligament (ACL) has not been reported. The ACL is a complex structure consisting of two functionally synergistic structures: the anteromedial (AM) and posterolateral (PL) bundle. The purpose of our study was to evaluate the intraarticular rupture pattern of the ACL with regard to its two functional bundles. We examined ACL rupture patterns with regard to the integrity of AM and PL bundle in 121 consecutive patients undergoing anterior cruciate ligament reconstruction surgery within 120 days after injury. The intraarticular pattern was observed by one experienced surgeon. In 25% of the patients a partial rupture of the ACL was found, whereas in the remaining 75% a complete rupture of AM and PL bundles was seen. A partial rupture could only be detected by careful dissection of the ligament. In 44% of all patients the AM and PL bundles did not rupture at the same location. In 12% of the patients the PL bundle showed no signs of rupture. When performing ACL reconstruction, care should be taken when dissecting down the ACL remnants to evaluate intact fiber bundles of the ACL.Level of Evidence: Level IV, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.

Open Shoulder Repair of Osseous Glenoid Defects Biomechanical Effectiveness of the Latarjet Procedure Versus a Contoured Structural Bone Graft

Background To address glenoid bone deficiency, 2 competing surgical approaches are currently recommended: transplantation of a structural bone graft or the coracoid transfer according to Latarjet. Nonetheless, no clear advantages for either procedure are evident. Hypothesis The Latarjet procedure will provide an equivalent beneficial effect on glenohumeral stability as the placement of an intra-articular bone graft. Study Design Controlled laboratory study. Methods Stability testing of 8 cadaveric shoulders was performed in a dynamic shoulder simulator under 4 different conditions: (1) anteroinferior capsulotomy, (2) anteroinferior glenoid defect, (3) transplantation of a contoured bone graft, and (4) Latarjet procedure. Translational movement of the humeral head in response to a load of 25 N was evaluated in the anterior and anteroinferior directions. Results The Latarjet procedure significantly reduced translation by 354% relative to the glenoid defect condition at 30° of abduction and by 374% at 60° of abduction. In comparison, the bone graft significantly reduced translation by 179% at 30° of abduction and by 159% at 60° of abduction. The effect of the bone graft was lowest in external rotation at 60° of abduction where a decrease of translation of 133% was observed. Comparing both reconstruction techniques, the Latarjet procedure resulted in significantly less anterior and anteroinferior translation at 60° of abduction. Conclusion Biomechanically, the Latarjet procedure outperforms the bone graft in reducing translation in anteroinferior glenoid bone defects. The advantage of the Latarjet procedure is particularly evident at 60° of glenohumeral abduction. Clinical Relevance On the basis of the results of this biomechanical study, the authors recommend the Latarjet procedure for restoring stability in shoulders with a significant glenoid bone defect.