Experimentally induced incomplete burst fractures - a novel technique for calf and human specimens.

BACKGROUND: Fracture morphology is crucial for the clinical decision-making process preceding spinal fracture treatment. The presented experimental approach was designed in order to ensure reproducibility of induced fracture morphology. RESULTS: The presented method resulted in fracture morphology, found in clinical classification systems like the Magerl classification. In the calf spine samples, 70% displayed incomplete burst fractures corresponding to type A3.1 and A3.2 fractures. In all human samples, superior incomplete burst fractures (Magerl A3.1) were identified by an independent radiologist and spine surgeon. CONCLUSIONS: The presented set up enables the first experimental means to reliably model and study distinct incomplete burst fracture patterns in an in vitro setting. Thus, we envisage this protocol to facilitate further studies on spine fracture treatment of incomplete burst fractures.

Double-bundle reconstruction cannot restore intact knee kinematics in the ACL/LCL-deficient knee.

INTRODUCTION: The aim of this study was to evaluate the effect of single-bundle (SB) and anatomic double-bundle (DB) anterior cruciate ligament (ACL) reconstruction on the resulting knee kinematics in a simulated clinical setting with ACL rupture and associated extra-articular damage to the lateral structures. It was hypothesized that anatomic DB ACL reconstruction restores the intact knee kinematics in ACL/LCL-deficient knees, whereas SB ACL reconstruction fails to restore the intact knee kinematics. MATERIALS AND METHODS: Ten fresh-frozen human cadaver knees were subjected to anterior tibial load of 134 N (simulated KT 1000) and combined rotatory load of 10-Nm valgus and 4-Nm internal tibial torque (simulated pivot shift) using a robotic/UFS testing system. The resulting knee kinematics was determined for intact, ACL/LCL-deficient, SB ACL-reconstructed/LCL-deficient, and DB ACL-reconstructed/LCL-deficient knee. Statistical analysis was performed using a two-way ANOVA test with the level of significance set at P < 0.05. RESULTS: Under a simulated KT 1000 test, anterior tibial translation (ATT) following SB ACL reconstruction was statistically significant at 0 degrees , 30 degrees and 60 degrees of knee flexion when compared to the intact knee. ATT after DB ACL reconstruction showed no statistically significant difference from the intact knee; however, there was a significant difference in SB reconstruction at 0 degrees and 30 degrees of knee flexion. Under a simulated pivot shift test, both SB and DB ACL reconstruction failed to restore the intact knee kinematics. CONCLUSION: The results of the study did not support our initial hypothesis. Though DB reconstructions were significantly superior to SB reconstruction under simulated KT 1000 test, SB as well as DB reconstruction failed to restore the intact kinematics under simulated pivot shift loads. The clinical relevance of this study is that caution and precise preoperative diagnostics are needed to avoid failure of intra-articular ACL reconstruction if the extra-articular stabilizers are torn.

Coracoclavicular ligament reconstruction: biomechanical comparison of tendon graft repairs to a synthetic double bundle augmentation.

For currently presented anatomical coracoclavicular ligament repairs issues such as autologous tendon graft versus synthetic suture augmentation and the optimum fixation strategies for both types of reconstruction are not solved. The purpose of the study was to compare the biomechanical properties of different tendon graft repairs to the characteristics of a synthetic polyester augmentation. Four anatomical coracoclavicular ligament repairs were biomechanically tested: 5 mm coracoclavicular tendon loop with suture fixation, tendon loop with flip button fixation, tendon loop with interference screw fixation versus a double 1.0-mm polyester repair with flip button fixation. The biomechanical testing included cyclic superio-inferior loading and a subsequent load to failure protocol. The ultimate failure loads were significantly higher for the double polyester/flip button repair (927 N) compared to all tendon repair techniques (maximum 640 N). In contrast the stiffness level was higher for the tendon repairs compared to the polyester/flip button repair (68.7 N/mm) but strongly dependent on the fixation technique (interference screw 97.2 N/mm, flip button 84.9 N/mm, side to side suture 60.9 N/mm). A synthetic coracoclavicular augmentation using a polyester suture provides adequate structural properties compared to a tendon repair. Therefore the decision for a tendon graft should be made by the necessity of a biologic substrate rather than by the assumption of a biomechanical advantage.

Rotational instability of the knee: internal tibial rotation under a simulated pivot shift test.

INTRODUCTION: Recently, several publications investigated the rotational instability of the human knee joint under pivot shift examinations and reported the internal tibial rotation as measurement for instrumented knee laxity measurements. We hypothesize that ACL deficiency leads to increased internal tibial rotation under a simulated pivot shift test. Furthermore, it was hypothesized that anatomic single bundle ACL reconstruction significantly reduces the internal tibial rotation under a simulated pivot shift test when compared to the ACL-deficient knee. METHODS: In seven human cadaveric knees, the kinematics of the intact knee, ACL-deficient knee, and anatomic single bundle ACL reconstructed 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/UFS testing system. Statistical analyses were performed using a two-way ANOVA test. RESULTS: Single bundle ACL reconstruction reduced the anterior tibial translation under a simulated KT-1000 test significantly compared to the ACL-deficient knee (P < 0.05). After reconstruction, there was a statistical significant difference to the intact knee at 30 degrees of knee flexion. Under a simulated pivot shift test, anatomic single bundle ACL reconstruction could restore the intact knee kinematics. Internal tibial rotation under a simulated pivot shift showed no significant difference in the ACL-intact, ACL-deficient and ACL-reconstructed knee. CONCLUSION: In conclusion, ACL deficiency does not increase the internal tibial rotation under a simulated pivot shift test. For objective measurements of the rotational instability of the knee using instrumented knee laxity devices under pivot shift mechanisms, the anterior tibial translation should be rather evaluated than the internal tibial rotation.

Biomechanical evaluation of an augmented coracoacromial ligament transfer for acromioclavicular joint instability.

PURPOSE: The purpose of this study was to establish and biomechanically evaluate an augmented coracoacromial ligament (CAL) transfer technique that eliminates the biomechanical drawbacks of the conventional Weaver-Dunn procedure and restores the intact joint kinematics. METHODS: The acromioclavicular joints of 12 human shoulder specimens were tested for anterior, posterior, and superior translation during cyclic loading as well as for stiffness and ultimate tensile strength in a subsequent load-to-failure protocol. After luxation, the specimens were randomly assigned to 2 treatment groups: CAL transfer and polyester-augmented CAL transfer. For the coracoclavicular augmentation, a strong 1-mm polyester loop was intertwined between 2 flip buttons for coracoid and clavicle fixation. Only the medial half of the CAL was transferred and fixed in a medialized position at the clavicle. RESULTS: Translational testing showed significantly higher anterior (12.1 mm), posterior (9 mm), and superior (13.4 mm) translation for the CAL transfer technique as compared with the native joint (5.4 mm, 3.3 mm, and 3.4 mm, respectively) and the modified augmented CAL transfer procedure (6.2 mm, 4.2 mm, and 3.6 mm, respectively) (P < .05). No significant differences were found between the intact acromioclavicular joint and the augmented CAL transfer regarding anterior and superior translation. Posterior translation was significantly higher for the augmented CAL transfer compared with the native joints (P = .033), but the quantitative difference was small (0.8 mm). CONCLUSIONS: The augmented CAL transfer using the medial half of the CAL and supplementing it with a strong 1-mm polyester loop intertwined between 2 flip buttons for coracoid and clavicle fixation has been shown to restore anterior and superior translation of the native acromioclavicular joint. CLINICAL RELEVANCE: The promising biomechanical in vitro results must be interpreted in the context of clinical investigations regarding the risk of bony erosion resulting from the use of permanent suture material.

Effect of coracoacromial ligament resection on glenohumeral stability under active muscle loading in an in vitro model.

PURPOSE: The purpose of this study was to determine whether or not the coracoacromial ligament (CAL) has a relevant effect in stabilizing the humeral head under active rotator cuff and deltoid loading compared to passive loading conditions without muscular stabilization. METHODS: Nine human cadaver shoulders were tested in a dynamic shoulder simulator. Forces of the rotator cuff muscles and the middle deltoid muscle were applied using servohydraulic cylinders, while glenohumeral motion was imposed in closed-loop force-control by a sensor-guided robot. Translational movement was measured with the CAL intact and resected under two different testing conditions: (1) simulated physiologic muscle force loading and (2) the passive drawer test, with loads applied in anterior, anterio-inferior, and anterio-superior directions in different glenohumeral positions. RESULTS: The resection of the CAL caused a significant increase in anterior and superior translation during translational testing and muscle force loading. However, the passive testing mode revealed differences in translation from 2.4 to 4.4 mm. The differences were quantitatively minor under muscle loading conditions, ranging from 0.5 to 1.0 mm. CONCLUSIONS: CAL resection induces an increased glenohumeral translation under passive loading conditions without muscular stabilization, whereas the effect under rotator cuff and deltoid loading was defined to be quantitatively small. CLINICAL RELEVANCE: A resection of the CAL should be critically discussed in shoulders with massive rotator cuff tears. In contrast, in muscularly intact shoulders, the release of the CAL evokes a light increase of translation, the clinical relevance of which is questionable.

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 N x m valgus and 4 N x m 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 degrees and 30 degrees 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.

The role of the posterior oblique ligament in controlling posterior tibial translation in the posterior cruciate ligament-deficient knee.

BACKGROUND: Posterior cruciate ligament injuries are often associated with injuries to other structures. The role of the posteromedial structures of the knee in these injuries has received little attention. HYPOTHESIS: The posterior oblique ligament is an important restraint to posterior tibial translation in the posterior cruciate ligament-deficient knee. STUDY DESIGN: Controlled laboratory study. METHODS: Kinematic studies were performed on 10 cadaveric knees to test 3 external loading conditions at 0 degrees , 30 degrees , 60 degrees , and 90 degrees of flexion (134 N posterior tibial load, 10 N x m valgus rotation, and 5 N x m internal rotation). Resulting posterior tibial translation was determined by using a robotic/universal force-moment sensor testing system for (1) intact, (2) posterior cruciate ligament-deficient, (3) posterior cruciate ligament/superficial medial collateral ligament-deficient, (4) posterior cruciate ligament/superficial medial collateral ligament/deep medial collateral ligament/posterior oblique ligament-deficient, and (5) posterior cruciate ligament/superficial medial collateral ligament/deep medial collateral ligament/posterior oblique ligament/posteromedial capsule-deficient knee. RESULTS: When both the superficial medial collateral ligament and deep medial collateral ligament were cut in the posterior cruciate ligament-deficient knee, posterior tibial translation did not increase significantly at any flexion grade under all external loading conditions (P > .05). Additional cutting of the posterior oblique ligament increased posterior tibial translation significantly at 0 degrees , 30 degrees , 60 degrees , and 90 degrees of flexion under posterior tibial load and at all flexion angles tested under valgus or internal tibial load (P < .05). Additional cutting of the posteromedial capsule increased posterior tibial translation only at 0 degrees and 30 degrees in response to a valgus and internal tibial load (P < .05). CONCLUSION: The posterior oblique ligament and posteromedial capsule have a significant role in the prevention of additional posterior tibial translation in the knee with posterior cruciate ligament injury. CLINICAL RELEVANCE: The posterior oblique ligament should be addressed in the patient with combined injuries to the posterior cruciate ligament and the posteromedial structures.

Arthroscopic techniques for the fixation of a three-dimensional scaffold for autologous chondrocyte transplantation: structural properties in an in vitro model.

PURPOSE: The aim of the present study was to evaluate the structural properties of matrix-associated autologous chondrocyte implantation with multiple fixation techniques implanted in fresh porcine knees after they had undergone load to failure. METHODS: We evaluated the ultimate failure load, yield load, and stiffness of 3 different techniques for the fixation of a 2-mm thick polymer fleece: (1) fixation with biodegradable polylevolactide pins, (2) a transosseous anchoring technique, and (3) conventional suture fixation. Techniques 1 (pin) and 2 (transosseous anchoring) can be used arthroscopically. RESULTS: Maximum load and yield load were significantly higher in the group 1 (pin fixation) and group 2 (transosseous anchoring) compared to group 3 (conventional suture). Stiffness was significantly higher in group 1 than in groups 2 or 3. CONCLUSIONS: Our biomechanical data show that two fixation techniques (pin fixation and transosseous anchoring) have a higher ultimate load, yield load, and stiffness than the conventional suture technique at time point zero. However, these data can be interpreted only with the Bioceed-C matrix (BioTissue Technologies GmbH, Freiburg, Germany). CLINICAL RELEVANCE: Our biomechanical data show outstanding fixation strength with arthroscopic techniques that use Bioceed-C matrix scaffolds during autologous chondrocyte transplantation. Thus, arthroscopic fixation done with this biomaterial should benefit patients, which, in turn, should lead to further research on these arthroscopic techniques and this biomaterial.

Anterolateral rotational knee instability: role of posterolateral structures. Winner of the AGA-DonJoy Award 2006.

INTRODUCTION: The aim of this study was to determine the anterolateral rotational instability (ALRI) of the human knee after rupture of the anterior cruciate ligament (ACL) and after additional injury of the different components of the posterolateral structures (PLS). It was hypothesized that a transsection of the ACL will significantly increase the ALRI of the knee and furthermore that sectioning the PLS [lateral collateral ligament (LCL), popliteus complex (PC)] will additionally significantly increase the ALRI. MATERIALS AND METHODS: Five human cadaveric knees were used for dissection to study the appearance and behaviour of the structures of the posterolateral corner under anterior tibial load. Ten fresh-frozen human cadaver knees were subjected to anterior tibial load of 134 N and combined rotatory load of 10 Nm valgus and 4 Nm internal tibial torque using a robotic/universal force moment sensor (UFS) testing system and the resulting knee kinematics were determined for intact, ACL-, LCL- and PC-deficient (popliteus tendon and popliteofibular ligament) knee. Statistical analyses were performed using a two-way ANOVA test with the level of significance set at P < 0.05. RESULTS: Sectioning the ACL significantly increased the anterior tibial translation (ATT) and internal tibial rotation under a combined rotatory load at 0 and 30 degrees flexion (P < 0.05). Sectioning the LCL further increased the ALRI significantly at 0 degrees , 30 degrees and 60 degrees of flexion (P < 0.05). Subsequent cutting of the PC increased the ATT under anterior tibial load (P < 0.05), but did not increase the ALRI (P > 0.05). CONCLUSION: The results of the current study confirm the concept that the rupture of the ACL is associated with ALRI. Current reconstruction techniques should focus on restoring the anterolateral rotational knee instability to the intact knee. Additional injury to the LCL further increases the anterior rotational instability significantly, while the PC is less important. Cautions should be taken when examining a patient with ACL rupture to diagnose injuries to the primary restraints of tibial rotation such as the LCL. If an additional extraarticular stabilisation technique is needed for severe ALRI, the technique should be able to restore the function of the LCL and not the PC.