Andre Weimann

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 Femoral Tunnel Placement in Double-Bundle Posterior Cruciate Ligament Reconstruction Biomechanical Analysis Using a Robotic/Universal Force-Moment Sensor Testing System

Background Previous studies have identified the femoral attachment of the posterior cruciate ligament fibers as one of the primary determinants of fiber tension behavior. In addition, a double-bundle posterior cruciate ligament reconstruction has been shown to restore the intact knee kinematics more closely than does a single-bundle reconstruction. Hypothesis An anterior tunnel position in double-bundle posterior cruciate ligament reconstruction restores the biomechanics of the normal knee more closely than does a posterior tunnel position. Study Design Controlled laboratory study. Methods Kinematics and in situ forces of human knees after double-bundle posterior cruciate ligament reconstruction with 2 different femoral tunnel positions (anterior vs posterior) were evaluated using a robotic/universal force-moment sensor testing system. Within the same specimen, the resulting knee kinematics and in situ forces were compared. For statistical analysis, 2-way analysis of variance repeated measures were performed. Results The femoral tunnel position of the double-bundle hamstring graft had significant effect on the resulting posterior tibial displacement and in situ forces of the hamstring grafts. The anterior femoral tunnel position provided significantly less posterior tibial translation than did the posterior tunnel position. There was a tendency toward higher in situ forces of grafts fixed in the anterior tunnel when compared to the posterior position, but this difference was statistically not significant. Conclusion An anterior position of the bone tunnels in double-bundle posterior cruciate ligament reconstruction restores the normal knee kinematics more closely than does a posterior position of the tunnels. Clinical Relevance In double-bundle posterior cruciate ligament reconstruction, posterior placement of the tunnel should be avoided.

Initial Fixation Strength of Two Bioabsorbable Pins for the Fixation of Hamstring Grafts Compared to Interference Screw Fixation Single Cycle and Cyclic Loading

Background During the early postoperative period, the fixation of a hamstring graft to the bone tunnel is the primary factor in limiting rehabilitation. Hypothesis The initial fixation strength of a double cross pin fixation technique is comparable with the biodegradable interference screw fixation technique. Study Design Experimental laboratory study. Methods The authors examined the initial fixation strength of two 3.3-mm bioabsorbable pins compared to interference screws for hamstring grafts in bovine knees. Results Analysis of yield load, maximum load, and stiffness in the single-cycle loading test showed no statistically significant differences for cross pin and interference fixation (P< .05). For cross pins and interference screws, the mean displacement under 1000 cycles to 250 N was 5.07 (±1.9) mm and 4.81 (±2.5) mm, stiffness 252 (±78) N/mm and 289 (±148) N/mm. Only grafts fixed with cross pins survived 1000 cycles to 450 N. Conclusion The initial fixation strength of the double cross pin technique is comparable to that of interference screw fixation with a stiffness comparable to that of the native ACL. Clinical Relevance Hamstring graft fixation using two cross pins provides an alternative to bioabsorbable interference screw fixation.

Cyclic Testing of Flexible All-Inside Meniscus Suture Anchors Biomechanical Analysis

Background Flexible meniscus repair devices are designed to combine the benefits of rigid all-inside meniscus anchors with the biomechanical properties of sutures. Hypothesis Stiffness and pull-out strength of flexible all-inside suture anchors and conventional sutures under cyclic loading conditions will be comparable. Study Design Controlled laboratory study Methods In 50 fresh frozen bovine menisci, artificial meniscus lesions were repaired with different meniscus fixation techniques: horizontal and vertical FasT-Fix, RapidLoc, and horizontal and vertical 2-0 Ethibond sutures. The specimens were cycled 1000 times between 5 and 20 N and then loaded to failure. Results All devices survived the cyclic loading protocol. There was no significant difference in the displacement between all repair techniques tested (horizontal FasT-Fix, 6.23 mm; vertical FasT-Fix, 5.34 mm; RapidLoc, 6.84 mm; horizontal 2-0 Ethibond, 6.03 mm; vertical 2-0 Ethibond, 5.61 mm (P >. 05). Vertical and horizontal FasT-Fix suture anchors had a significantly higher stiffness and pull-out strength (94.1 N and 80.8 N, respectively) than did horizontal sutures (50.2 N) and RapidLoc devices (30.3 N) (P >. 05). Conclusions In this study, flexible all-inside meniscus anchors (FasT-Fix) had higher pull-out strength than did conventional vertical suture techniques. Biomechanical characteristics of the flexible RapidLoc are comparable to those of horizontal sutures. Clinical Relevance Flexible all-inside meniscus repair devices are an alternative to conventional suture techniques.

Biomechanical Evaluation of Minimally Invasive Repairs for Complete Acromioclavicular Joint Dislocation

Background The conventional coracoclavicular ligament augmentation with a single polydioxanone loop has been shown to have some pivotal disadvantages. Hypothesis A minimally invasive flip button/polydioxanone repair provides similar biomechanical properties to the conventional polydioxanone cerclage around the coracoid. However, the authors expected a difference in linear stiffness, ultimate load, and permanent elongation between suture anchor repairs and polydioxanone repairs. Study Design Controlled laboratory study. Methods The tensile fixation strength of 4 different minimally invasive repairs was tested in a porcine metatarsal model: (1) 1.3-mm single polydioxanone cerclage with a subcoracoidal flip button fixation, (2) 1.3-mm single polydioxanone cerclage, (3) Twinfix Ti 3.5-mm/Ultrabraid 2-suture anchor, and (4) Twinfix Ti 5.0-mm/Ultrabraid 2-suture anchor. The testing protocol included cyclic superoinferior loading and a subsequent load to failure trial. Results The flip button repair (646 N) and the conventional polydioxanone banding (663 N) revealed significant higher ultimate loads than did the suture anchor repairs (295 and 331 N, respectively; P < .001), whereas no significant differences were found for the elongation behavior under cyclic loading. Conclusion There was no significant difference between the 2 polydioxanone repairs. The ultimate load of the flip button procedure reaches the level of the native coracoclavicular ligament complex as it has been quantified in the literature. Clinical Relevance Although the biomechanical results comparing a minimally invasive flip button procedure versus a conventional polydioxanone cerclage are similar, the authors recommend the flip button procedure because of its minimally invasive approach and the secure subcoracoidal fixation technique with a minimized risk of anterior loop dislocation and neurovascular damage.

Biomechanical Evaluation of Different Fixation Methods for Tibial Eminence Fractures

Background Tibial eminence fractures have become more common, but the best method of fixing these fractures arthroscopically has not been elucidated. Objective The objective of this study is to assess the stability of different fixation methods for tibial eminence fractures. Study Design Controlled laboratory study. Methods The authors evaluated the initial fixation strength of 4 different fixation techniques for tibial eminence fractures (2 screws, 1 screw, suture fixation with 1 mm Ethibond, and suture fixation with No. 5 FiberWire) using single cycle and cyclic loading tests. The tests were performed by loading the knee with an anterior tibial shear force. Results Suture cerclage with the FiberWire showed significantly higher maximum load (599.6 N) and stiffness (36.99 N/mm) than all other fixation methods tested. The lowest maximum load in the single cycle loading test was observed in the group with 2 screws (1 screw, 371.2 N; 2 screws, 249.8 N). The lowest stiffness was found in the Ethibond group (14.5 N/mm). After 1000 cycles of loading, the maximum load of the FiberWire fixation was significantly higher than the maximum load of the Ethibond fixation (399.4 N), the fixation with 1 screw (354.2 N), and the fixation with 2 screws (301.5 N). Conclusion These biomechanical data suggest that under cyclic loading conditions, suture fixation of tibial eminence fractures provides more fixation strength than screw fixation. Clinical Relevance A second screw has no positive effect on the biomechanical characteristics of screw fixation.

Initial Fixation Strength of Flexible All-Inside Meniscus Suture Anchors in Comparison to Conventional Suture Technique and Rigid Anchors: Biomechanical Evaluation of New Meniscus Refixation Systems

Background The newest generation of meniscus repair devices is designed to combine the benefits of the all-inside technique with the biomechanical properties of sutures. Hypothesis New flexible all-inside suture anchors have better fixation strength than rigid anchors, but there is no difference when compared to conventional horizontal and vertical mattress sutures. Study Design Controlled laboratory study. Methods In fresh-frozen bovine menisci, initial fixation strength, stiffness, and failure mode of different meniscus fixation techniques (FastT-Fix, RapidLoc, Meniscus Arrow, horizontal and vertical 2.0 Ethibond sutures) were evaluated in a computer-based materials testing machine at a rate of 12.5 mm/sec. Results The vertical and horizontal FastT-Fix suture anchors were the strongest devices with regard to pullout strength, with no significant difference compared to the vertical 2-0 Ethibond sutures. Horizontal sutures, Meniscus Arrow, and RapidLoc had significantly lower pullout strength. Vertical and horizontal FastT-Fix suture anchors showed significantly higher stiffness than the other devices. Conclusions Biomechanical properties of flexible all-inside meniscus anchors (FastT-Fix) are comparable to conventional vertical suture techniques. Characteristics of the flexible RapidLoc are comparable to rigid anchors (Meniscus Arrow). Clinical Relevance From the biomechanical point of view, flexible all-inside meniscus refixation devices are an alternative to conventional suture techniques and rigid meniscus anchors.

Joint kinematics and in situ forces after single bundle PCL reconstruction: a graft placed at the center of the femoral attachment does not restore normal posterior laxity

Introduction: Femoral tunnel placement has a great influence on the clinical outcome after PCL reconstruction. Materials and methods: Using a robotic/universal force moment sensor (UFS) testing system, we examined joint kinematics and in situ forces of human knees following soft-tissue single bundle PCL reconstruction fixed at the center of the femoral attachment. Results: Posterior tibial translation significantly increased at all flexion angles after transsection of the posterior cruciate ligament (p<0.05). PCL reconstruction resulted in significantly less posterior tibial translation at all flexion angles when compared to the PCL deficient knee (p<0.05). The differences in the in situ force between the intact ligament and the reconstructed graft were statistical significant (p<0.05). Conclusion: Single bundle PCL reconstruction with a soft-tissue graft fixed at the center of the femoral attachment is able to reduce the posterior tibial translation significantly. However, it cannot restore kinematics of the intact knee and in situ forces of the intact PCL.

Reconstruction of the Posterior Oblique Ligament and the Posterior Cruciate Ligament in Knees With Posteromedial Instability

PURPOSE Posterior cruciate ligament (PCL) injuries are often associated with injuries of the posteromedial structures of the knee. The motivation for this study was the attempt to test different reconstruction techniques for the structures of the posteromedial corner in a biomechanical experiment. METHODS Kinematic studies were carried out on 10 cadaveric knees exposed to a 134-N posterior tibial load, 10-Nm valgus torque, and 5-Nm internal torque at 0°, 30°, 60°, and 90° of flexion. The resulting posterior tibial translation (PTT) was determined using a robotic/universal force-moment sensor testing system for (1) intact knees, (2) PCL-deficient knees, (3) knees with deficiency of the PCL and the posteromedial structures, (4) knees with only the PCL reconstructed, (5) knees with the PCL and posterior oblique ligament (POL) reconstructed, and (6) knees with the PCL, medial collateral ligament (MCL), and POL reconstructed. Kinematic data were analyzed by a 2-factor repeated analysis of variance. RESULTS When both the PCL and the posteromedial structures were cut, PTT increased significantly at all flexion grades under a posterior tibial load (P < .05). Reconstruction of only the PCL could not restore PTT at 0°, 30°, 60°, and 90° of flexion under loading conditions in a knee with combined injury of the PCL and the posteromedial structures (P > .05). Additional reconstruction of the POL improved PTT at all flexion angles in comparison with only the PCL-reconstructed knee. Reconstruction of the MCL had no significant effect on PTT. CONCLUSIONS This study shows that reconstruction of the POL contributes significantly to the normalization of coupled PTT in knees with combined injury of the PCL and the posteromedial structures under valgus or internal rotational moment. The supplementary reconstruction of the MCL did not provide significant improvement in knee kinematics. CLINICAL RELEVANCE The POL should be addressed in the patient with combined injuries of the PCL and the posteromedial structures.

Elongation and Structural Properties of Meniscal Repair Using Suture Techniques in Distraction and Shear Force Scenarios Biomechanical Evaluation Using a Cyclic Loading Protocol

Background Most biomechanical studies on meniscal repairs have focused on testing distraction scenarios to evaluate structural properties of the repaired meniscus. An application of shear forces might replicate the in vivo situation more closely. Hypothesis In the shear force scenario, meniscal repair using a vertical suture technique will result in significantly less elongation when subjected to a cyclic loading protocol than that resulting from a horizontal suture technique. Study Design Controlled laboratory study. Methods In fresh-frozen porcine menisci (n = 10 in each group), horizontal and vertical 2.0 Ethibond suturing techniques were tested in distraction and shear force scenarios. Elongation after 1000 cycles between 5 and 20 N and the structural properties such as stiffness, yield load, maximum load to failure, and failure mode were evaluated using a testing machine at a rate of 12.5 mm/s. Results In the distraction force scenario, no statistically significant difference in elongation after cyclic loading was found between specimens repaired with vertical or horizontal suture techniques. After 1000 cycles of cyclic loading in the shear force scenario, the horizontal suturing revealed significantly less elongation (2.8 ± 1.1 mm) than did the vertical suture technique (4.6 ± 2.0 mm). No statistically significant difference in yield and maximum load was found (P > .05). Conclusion The results of the present study do not support the authors’ hypothesis. In the shear force test, horizontal sutures were superior to vertical suture techniques. Clinical Relevance Meniscal repair with horizontal suture techniques can withstand elongation due to shear forces more effectively than can vertical mattress sutures.