Contribution of the Medial Iliofemoral Ligament to Hip Stability After Total Hip Arthroplasty Through the Direct Anterior Approach.

BACKGROUND: Dislocation after total hip arthroplasty (THA) is a primary reason for THA revision. During THA through the direct anterior approach (DAA), the iliofemoral ligament, which provides the main resistance to external rotation (ER) of the hip, is commonly partially transected. We asked: (1) what is the contribution of the medial iliofemoral ligament to resisting ER after DAA THA? and (2) how much resistance to ER can be restored by repairing the ligament? METHODS: A fellowship-trained surgeon performed DAA THA on 9 cadaveric specimens. The specimens were computed tomography scanned before and after implantation. Prior to testing, the ER range of motion of each specimen to impingement in neutral and 10° of extension was computationally predicted. Each specimen was tested on a 6-degrees-of-freedom robotic manipulator. The pelvis was placed in neutral and 10° of extension. The femur was externally rotated until it reached the specimen's impingement target. Total ER torque was recorded with the medial iliofemoral ligament intact, after transecting the ligament, and after repair. Torque at extremes of motion was calculated for each condition. To isolate the contribution of the native ligament, the torque for the transected state was subtracted from both the native and repaired conditions. RESULTS: The medial iliofemoral ligament contributed an average of 68% (range, 34 to 87) of the total torque at the extreme of motion in neutral and 80% (58 to 97) in 10° of extension. The repaired ligament contributed 17% (1 to 54) of the total torque at the extreme of motion in neutral and 14% (5 to 38) in 10° of extension, restoring on average 18 to 25% of the native resistance against ER. CONCLUSIONS: The medial iliofemoral ligament was an important contributor to the hip torque at the extreme of motion during ER. Repairing the ligament restored a fraction of its ability to generate torque to resist ER.

Comparative Drug Solubility Studies Using Shake-Flask Versus a Laser-Based Robotic Method.

Drug solubility is of central importance to the pharmaceutical sciences, but reported values often show discrepancies. Various factors have been discussed in the literature to account for such differences, but the influence of manual testing in comparison to a robotic system has not been studied adequately before. In this study, four expert researchers were asked to measure the solubility of four drugs with various solubility behaviors (i.e., paracetamol, mesalazine, lamotrigine, and ketoconazole) in the same laboratory with the same instruments, method, and material sources and repeated their measurements after a time interval. In addition, the same solubility data were determined using an automated laser-based setup. The results suggest that manual testing leads to a handling influence on measured solubility values, and the results were discussed in more detail as compared to the automated laser-based system. Within the framework of unavoidable uncertainties of solubility testing, it is a possibility to combine minimal experimental testing that is preferably automated with mathematical modeling. That is a practical suggestion to support future pharmaceutical development in a more efficient way.

Acromioclavicular joint reconstruction implants have differing ability to restore horizontal and vertical plane stability.

PURPOSE: Persistent acromioclavicular joint (ACJ) instability following high grade injuries causes significant symptoms. The importance of horizontal plane stability is increasingly recognised. There is little evidence of the ability of current implant methods to restore native ACJ stability in the vertical and horizontal planes. The purpose of this work was to measure the ability of three implant reconstructions to restore native ACJ stability. METHODS: Three groups of nine fresh-frozen shoulders each were mounted into a robotic testing system. The scapula was stationary and the robot displaced the clavicle to measure native anterior, posterior, superior and inferior (A, P, S, I) stability at 50 N force. The ACJ capsule, conoid and trapezoid ligaments were transected and the ACJ was reconstructed using one of three commercially available systems. Two systems (tape loop + screw and tape loop + button) wrapped a tape around the clavicle and coracoid, the third system (sutures + buttons) passed directly through tunnels in the clavicle and coracoid. The stabilities were remeasured. The data for A, P, S, I stability and ranges of A-P and S-I stability were analyzed by ANOVA and repeated-measures Student t tests with Bonferroni correction, to contrast each reconstruction stability versus the native ACJ data for that set of nine specimens, and examined contrasts among the reconstructions. RESULTS: All three reconstructions restored the range of A-P stability to that of the native ACJ. However, the coracoid loop devices shifted the clavicle anteriorly. For S-I stability, only the sutures + buttons reconstruction did not differ significantly from native ligament restraint. CONCLUSIONS: Only the sutures + buttons reconstruction, that passed directly through tunnels in the clavicle and coracoid, restored all stability measures (A, P, S, I) to the native values, while the tape implants wrapped around the bones anteriorised the clavicle. These findings show differing abilities among reconstructions to restore native stability in horizontal and vertical planes. (300 words).

A constrained-condylar fixed-bearing total knee arthroplasty is stabilised by the medial soft tissues.

PURPOSE: Revision constrained-condylar total knee arthroplasty (CCK-TKA) is often used to provide additional mechanical constraint after failure of a primary TKA. However, it is unknown how much this translates to a reliance on soft-tissue support. The aim of this study was therefore to compare the laxity of a native knee to the CCK-TKA implanted state and quantify how medial soft-tissues stabilise the knee following CCK-TKA. METHODS: Ten intact cadaveric knees were tested in a robotic system at 0°, 30°, 60° and 90° flexion with ± 90  N anterior-posterior force, ± 8 Nm varus-valgus and ± 5 Nm internal-external torques. A fixed-bearing CCK-TKA was implanted and the laxity tests were repeated with the soft tissues intact and after sequential cutting. The deep and superficial medial collateral ligaments (dMCL, sMCL) and posteromedial capsule (PMC) were sequentially transected and the percentage contributions of each structure to restraining the applied loads were calculated. RESULTS: Implanting a CCK-TKA did not alter anterior-posterior laxity from that of the original native knee, but it significantly decreased internal-external and varus-valgus rotational laxity (p < 0.05). Post CCK-TKA, the sMCL restrained 34% of the tibial displacing load in anterior drawer, 16% in internal rotation, 17% in external rotation and 53% in valgus, across the flexion angles tested. The dMCL restrained 11% of the valgus rotation moment. CONCLUSIONS: With a fully-competent sMCL in-vitro, a fixed-bearing CCK-TKA knee provided more rotational constraint than the native knee. The robotic test data showed that both the soft-tissues and the semi-constrained implant restrained rotational knee laxity. Therefore, in clinical practice, a fixed-bearing CCK-TKA knee could be indicated for use in a knee with lax, less-competent medial soft tissues. LEVEL OF EVIDENCE: Controlled laboratory study.

Robotic axial lower leg testing: repeatability and reproducibility.

PURPOSE: The purpose of this study was to determine the test-retest reliability and the repeatability over multiple days of a robotic testing device when used to measure laxity of the lower leg during a simulated dial test. METHODS: Ten healthy subjects were evaluated using an instrumented robotic lower leg testing system over 4 days. Three testing cycles were performed each day. Each leg was rotated into external and then internal rotation by servomotors until a torque threshold of 5.65 N m was reached. Load-deformation curves were generated from torque and rotation data. Both average-measure and single-measure intraclass correlation coefficients (ICC) were compared across the curves. ICC scores were also compared for features of the curves including: maximum external rotation at -5.65 N m of torque, maximum internal rotation at 5.65 N m of torque, rotation at torque 0, compliance (slope of load-deformation curve) at torque 0, endpoint compliance in external rotation, endpoint compliance in internal rotation, and play at torque 0. Play at torque 0 was defined as the width of the hysteresis curve at torque 0. RESULTS: Average-measure ICC scores and test-retest scores were >0.95 along the entire load-deformation curve except around zero torque. ICC scores at maximum internal and external rotation ranged from 0.87 to 0.99 across the left and right knees. ICC scores for the other features of the curves ranged from 0.61 to 0.98. The standard error of the mean ranged from 0.0497 to 1.1712. CONCLUSIONS: The robotic testing device in this study proved to be reliable for testing a subject multiple times both within the same day and over multiple days. These findings suggest that the device can provide a level of reliability in rotational testing that allows for clinical use of test results. Objective laxity data can improve consistency and accuracy in diagnosing knee injuries and may enable more effective treatment.

Influence of tibial plateau levelling osteotomy on the tensile forces sustained by ligaments in cranial cruciate ligament-intact canine stifles: An ex vivo pilot study.

BACKGROUND: Tibial plateau levelling osteotomy (TPLO) changes the anatomical tibial conformation and might alter the positional relationship of the ligaments comprising the stifle joint. As a result, it is expected to affect the tensile force of the ligaments. However, studies analyzing the details of the effect of osteotomy are limited. OBJECTIVES: To evaluate the influence of TPLO on the tensile force on the stifle ligaments in the intact canine stifle using a six-degree-of-freedom (6-DOF) robotic testing system. METHODS: Eight stifles were categorised into the reference group and nine stifles into the TPLO group. The stifles were then analysed using a 6-DOF robotic joint biomechanical testing system. The stifles were applied 30 N at cranial, caudal, and compression loads and 1 Nm at the internal and external torque loads (the load applied to the tibia relative to the femur) on extension, at 135° and 120°, respectively. The tensile force placed on the cranial cruciate ligament (CrCL), the caudal cruciate ligament, the medial collateral ligament, lateral collateral ligament and the total tensile force placed on the four ligaments was calculated under each load. RESULTS: For the caudal load applied to the tibia relative to the femur, the CrCL tensile force in the TPLO group was lower than that in the reference group at 120° (p = 0.02). The CrCL tensile force in the TPLO group was lower than that in the reference group at 120° (p < 0.01) for the compression load. Regarding the cranial, internal, and external load, the CrCL tensile force remains unchanged between both groups at each angle. CONCLUSIONS: TPLO reduces CrCL tensile force during compression and caudal force application. TPLO may reduce tensile forces contributing to CrCL rupture.

Function of the crocodilian anterior cruciate ligaments.

The anterior cruciate ligament (ACL) is an important knee stabilizer that prevents the anterior subluxation of the tibia. Extant crocodiles have two ACLs, the ACL major and minor, yet their functional roles are unclear. We here examined in-situ forces within the ACL major and minor in saltwater crocodiles (Crocodylus porosus) with a 6-degree-of-freedom robotic testing system under the following loading conditions: (a) 30 N anterior tibial load at 150°, 120°, and 90° knee extension; (b) 1 Nm internal/external torque at 150° and 120° knee extension; (c) 30 N anterior tibial load +1 Nm internal/external torque at 150° and 120° knee extension. The In-situ force in the ACL minor was significantly higher than that of the ACL major in response to anterior tibial load at 90° knee extension, and anterior tibial load + external torque at both 150° and 120° knee extension. Meanwhile, the force in the ACL major was significantly higher than that of the ACL minor in response to internal torque at 120° knee extension, and anterior tibial load + internal torque at 150° knee extension. The present results showed that the ACL minor and major of saltwater crocodiles have different functions. In response to anterior tibial load + internal/external torques, either of two ACLs reacted to opposing directions of knee rotation. These suggest that two ACLs are essential for walking with long axis rotation of the knee in crocodiles.

Development of a novel in vitro cadaveric model for analysis of biomechanics and surgical treatment of Bertolotti syndrome.

BACKGROUND CONTEXT: Bertolotti syndrome (BS) is caused by pseudoarticulation between an aberrant L5 transverse process and the sacral ala, termed a lumbosacral transitional vertebra (LSTV). BS is thought to cause low back pain and is treated with resection or fusion, both of which have shown success. Acquiring cadavers with BS is challenging. Thus, we combined 3D printing, based on BS patient CT scans, with normal cadaveric spines to create a BS model. We then performed biomechanical testing to determine altered kinematics from LSTV with surgical interventions. Force sensing within the pseudojoint modeled nociception for different trajectories of motion and surgical conditions. PURPOSE: This study examines alterations in spinal biomechanics with LSTVs and with various surgical treatments for BS in order to learn more about pain and degeneration in this condition, in order to help optimize surgical decision-making. In addition, this study evaluates BS histology in order to better understand the pathology and to help define pain generators-if, indeed, they actually exist. STUDY DESIGN/SETTING: Model Development: A retrospective patient review of 25 patients was performed to determine the imaging criteria that defines the classical BS patient. Surgical tissue was extracted from four BS patients for 3D-printing material selection. Biomechanical Analysis. This was a prospective cadaveric biomechanical study of seven spines evaluating spinal motions, and loads, over various surgical conditions (intact, LSTV, and LSTV with various fusions). Additionally, forces at the LSTV joint were measured for the LSTV and LSTV with fusion condition. Histological Analysis: Histologic analysis was performed prospectively on the four surgical specimens from patients undergoing pseudoarthrectomy for BS at our institution to learn more about potential pain generators. PATIENT SAMPLE: The cadaveric portion of the study involved seven cadaveric spines. Four patients were prospectively recruited to have their surgical specimens assessed histologically and biomechanically for this study. Patients under the age of 18 were excluded. OUTCOME MEASURES: Physiological measures recorded in this study were broken down into histologic analysis, tissue biomechanical analysis, and joint biomechanical analysis. Histologic analysis included pathologist interpretation of Hematoxylin and Eosin staining, as well as S-100 staining. Tissue biomechanical analysis included stiffness measurements. Joint biomechanical analysis included range of motion, resultant torques, relative axis angles, and LSTV joint forces. METHODS: This study received funding from the American Academy of Neurology Medical Student Research Scholarship. Three authors hold intellectual property rights in the simVITRO robotic testing system. No other authors had relevant conflicts of interest for this study. CT images were segmented for a representative BS patient and cadaver spines. Customized cutting and drilling guides for LSTV attachment were created for individual cadavers. 3D-printed bone and cartilage structural properties were based on surgical specimen stiffness, and specimens underwent histologic analysis via Hematoxylin and Eosin, as well as S-100 staining. Joint biomechanical testing was performed on the robotic testing system for seven specimens. Force sensors detected forces in the LSTV joint. Kruskal-Wallis tests and Dunnett's tests were used for statistical analysis with significance bounded to p<.05. RESULTS: LSTV significantly reduces motion at the L5-S1 level, particularly in lateral bending and axial rotation. Meanwhile, the LSTV increases adjacent segment motion significantly at the L2-L3 level, whereas other levels have nonsignificant trends toward increased motion with LSTV alone. Fusion involving L4-S1 (L4-L5 and L5-S1) to treat adjacent level degeneration associated with an LSTV is associated with a significant increase in adjacent segment motion at all levels other than L5-S1 compared to LSTV alone. Fusion of L5-S1 alone with LSTV significantly increases L3-L4 adjacent segment motion compared to LSTV alone. Last, ipsilateral lateral bending with or without ipsilateral axial rotation produces the greatest force on the LSTV, and these forces are significantly reduced with L5-S1 fusion. CONCLUSIONS: BS significantly decreases L5-S1 mobility, and increases some adjacent segment motion, potentially causing patient activity restriction and discomfort. Ipsilateral lateral bending with or without ipsilateral axial rotation may cause the greatest discomfort overall in these patients, and fusion of the L5-S1 or L4-S1 levels may reduce pain associated with these motions. However, due to increased adjacent segment motion with fusions compared to LSTV alone, resection of the joint may be the better treatment option if the superior levels are not unstable preoperatively. CLINICAL SIGNIFICANCE: This study's results indicate that patients with BS have significantly altered spinal biomechanics and may develop pain due to increased loading forces at the LSTV joint with ipsilateral lateral bending and axial rotation. In addition, increased motion at superior levels when an LSTV is present may lead to degeneration over time. Based upon results of LSTV joint force testing, these patients' pain may be effectively treated surgically with LSTV resection or fusion involving the LSTV level if conservative management fails. Further studies are being pursued to evaluate the relationship between in vivo motion of BS patients, spinal and LSTV positioning, and pain generation to gain a better understanding of the exact source of pain in these patients. The methodologies utilized in this study can be extrapolated to recreate other spinal conditions that are poorly understood, and for which few native cadaveric specimens exist.

Biomechanical contribution of the alar ligaments to upper cervical stability.

Acute and chronic whiplash-associated disorders pose a significant healthcare burden due to chronic pain, which is associated with upper cervical instability resulting from ligamentous injury. No standard measure exists for diagnosing alar ligament injury and imaging findings vary widely. Multiple physical examination maneuvers are used to diagnose alar ligament injury including the C2 Spinous Kick, Flexion-Rotation, and Bending-Rotation tests. The objective of the current study was to determine the mechanical contribution of the alar ligaments to upper cervical stability and quantify the biomechanical changes seen during simulated clinical examinations after alar ligament injury. Eight cadaveric C0-C3 specimens were evaluated using a robotic testing system. Range of motion and moment at the end of intact specimen replay were the primary outcomes. Clinical examinations were simulated by rotation through two axes as performed during physical examination. Intact, unilateral and bilateral alar ligament injury states were tested. Unilateral alar ligament injury led to significant increases in lateral bending (12.0 ± 7.2%, p < 0.05), axial rotation (4.1 ± 2.4%, p < 0.05), and flexion-extension (5.3 ± 4.3%, p < 0.05) compared with intact specimens. The alar ligaments also contributed to resistance to intact motion in extension (13.4 ± 6.6%, p < 0.05), flexion (4.4 ± 2.2%, p < 0.05), axial rotation (19.3 ± 2.7%, p < 0.05), and lateral bending (16.0 ± 2.8%, p < 0.05). The C2 Spinous Kick Test showed the largest percentage change (-23.0 ± 14.8%), and the Bending-Rotation Test towards the side of injury significantly increased axial rotation by the largest absolute magnitude (5.5° ± 5.1°). Overall, quantifiable changes to motion measured during simulated physical examinations were found, but the ability of a clinician to feel these changes remains unknown.

In situ force in the anterior cruciate ligament, the lateral collateral ligament, and the anterolateral capsule complex during a simulated pivot shift test.

The role of the anterolateral capsule complex in knee rotatory stability remains controversial. Therefore, the objective of this study was to determine the in situ forces in the anterior cruciate ligament (ACL), the anterolateral capsule, the lateral collateral ligament (LCL), and the forces transmitted between each region of the anterolateral capsule in response to a simulated pivot shift test. A robotic testing system applied a simulated pivot shift test continuously from full extension to 90° of flexion to intact cadaveric knees (n = 7). To determine the magnitude of the in situ forces, kinematics of the intact knee were replayed in position control mode after the following procedures were performed: (i) ACL transection; (ii) capsule separation; (iii) anterolateral capsule transection; and (iii) LCL transection. A repeated measures ANOVA was performed to compare in situ forces between each knee state (*p < 0.05). The in situ force in the ACL was significantly greater than the forces transmitted between each region of the anterolateral capsule at 5° and 15° of flexion but significantly lower at 60°, 75°, and 90° of flexion. This study demonstrated that the ACL is the primary rotatory stabilizer at low flexion angles during a simulated pivot shift test in the intact knee, but the anterolateral capsule plays an important secondary role at flexion angles greater than 60°. Furthermore, the contribution of the "anterolateral ligament" to rotatory knee stability in this study was negligible during a simulated pivot shift test. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:847-853, 2018.

Magnesium ring device to restore function of a transected anterior cruciate ligament in the goat stifle joint.

A bioresorbable, mono-crystalline magnesium (Mg) ring device and suture implantation technique were designed to connect the ends of a transected anterior cruciate ligament (ACL) to restabilize the knee and load the ACL to prevent disuse atrophy of its insertion sites and facilitate its healing. To test its application, cadaveric goat stifle joints were evaluated using a robotic/universal force-moment sensor testing system in three states: Intact, ACL-deficient, and after Mg ring repair, at 30°, 60°, and 90° of joint flexion. Under a 67-N anterior tibial load simulating that used in clinical examinations, the corresponding anterior tibial translation (ATT) and in-situ forces in the ACL and medial meniscus for 0 and 100 N of axial compression were obtained and compared with a control group treated with suture repair. In all cases, Mg ring repair reduced the ATT by over 50% compared to the ACL-deficient joint, and in-situ forces in the ACL and medial meniscus were restored to near normal levels, showing significant improvement over suture repair. These findings suggest that Mg ring repair could successfully stabilize the joint and load the ACL immediately after surgery, laying the framework for future in vivo studies to assess its utility for ACL healing. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:2001-2008, 2016.

Effect of Device Rigidity and Physiological Loading on Spinal Kinematics after Dynamic Stabilization : An In-Vitro Biomechanical Study.

OBJECTIVE: To investigate the effects of posterior implant rigidity on spinal kinematics at adjacent levels by utilizing a cadaveric spine model with simulated physiological loading. METHODS: Five human lumbar spinal specimens (L3 to S1) were obtained and checked for abnormalities. The fresh specimens were stripped of muscle tissue, with care taken to preserve the spinal ligaments and facet joints. Pedicle screws were implanted in the L4 and L5 vertebrae of each specimen. Specimens were tested under 0 N and 400 N axial loading. Five different posterior rods of various elastic moduli (intact, rubber, low-density polyethylene, aluminum, and titanium) were tested. Segmental range of motion (ROM), center of rotation (COR) and intervertebral disc pressure were investigated. RESULTS: As the rigidity of the posterior rods increased, both the segmental ROM and disc pressure at L4-5 decreased, while those values increased at adjacent levels. Implant stiffness saturation was evident, as the ROM and disc pressure were only marginally increased beyond an implant stiffness of aluminum. Since the disc pressures of adjacent levels were increased by the axial loading, it was shown that the rigidity of the implants influenced the load sharing between the implant and the spinal column. The segmental CORs at the adjacent disc levels translated anteriorly and inferiorly as rigidity of the device increased. CONCLUSION: These biomechanical findings indicate that the rigidity of the dynamic stabilization implant and physiological loading play significant roles on spinal kinematics at adjacent disc levels, and will aid in further device development.

Kinematic Analysis of Five Different Anterior Cruciate Ligament Reconstruction Techniques.

Several anatomical anterior cruciate ligament (ACL) reconstruction techniques have been proposed to restore normal joint kinematics. However, the relative superiorities of these techniques with one another and traditional single-bundle reconstructions are unclear. Kinematic responses of five previously reported reconstruction techniques (single-bundle reconstruction using a bone-patellar tendon-bone graft [SBR-BPTB], single-bundle reconstruction using a hamstring tendon graft [SBR-HST], single-tunnel double-bundle reconstruction using a hamstring tendon graft [STDBR-HST], anatomical single-tunnel reconstruction using a hamstring tendon graft [ASTR-HST], and a double-tunnel double-bundle reconstruction using a hamstring tendon graft [DBR-HST]) were systematically analyzed. The knee kinematics were determined under anterior tibial load (134 N) and simulated quadriceps load (400 N) at 0°, 15°, 30°, 60°, and 90° of flexion using a robotic testing system. Anterior joint stability under anterior tibial load was qualified as normal for ASTR-HST and DBR-HST and nearly normal for SBR-BPTB, SBR-HST, and STDBR-HST as per the International Knee Documentation Committee knee examination form categorization. The analysis of this study also demonstrated that SBR-BPTB, STDBR-HST, ASTR-HST, and DBR-HST restored the anterior joint stability to normal condition while the SBR-HST resulted in a nearly normal anterior joint stability under the action of simulated quadriceps load. The medial-lateral translations were restored to normal level by all the reconstructions. The internal tibial rotations under the simulated muscle load were over-constrained by all the reconstruction techniques, and more so by the DBR-HST. All five ACL reconstruction techniques could provide either normal or nearly normal anterior joint stability; however, the techniques over-constrained internal tibial rotation under the simulated quadriceps load.