A Novel and Inexpensive Technique for High-Tension Tendon Clamping With Expandable Mesh Sleeving for In Vitro Foot Biomechanics Testing.

In vitro biomechanical testing is common in the field of orthopedics when novel devices are investigated prior to human trials. It is typically necessary to apply loads through tendons to simulate normal activities, such as walking during a foot and ankle study. However, attachment of tendons to linear actuators has proven challenging because of the tendency of clamps to either slip off or rupture the tendon. Various techniques have been utilized. Freeze clamping is generally accepted as the gold standard for very high load testing in excess of 3000 N, but is expensive, time-consuming, and requires significant ancillary equipment. Purely mechanical solutions such as metal jaw clamps, wire meshes, and others have been explored, but these techniques are either costly, have low load capacities, or have not proven to be reproducible. We have developed a novel tendon clamping technique that utilizes a slip-resistant polyester mesh sleeving that encases the tendon and is fixated at the bottom of the tendon/sleeve interaction with a giftbox suture. The loose end of the sleeving can then be tied in to the linear actuator or load cell apparatus using a timber hitch knot. The sleeving technique allows for loads of 2000-2500 N on the Achilles tendon, and is inexpensive, reproducible, and can be modified to apply loads to smaller tendons as well, though a length of tendon/sleeve overlap of at least 16 cm is required to reach maximum loads. This technique should assist researchers in integrating muscle forces into future biomechanical study designs.

A generalized framework for determination of functional musculoskeletal joint coordinate systems.

Establishing anatomical coordinate systems (CS) from anatomical landmarks is sensitive to landmark selection. Vastly different results can be obtained amongst observers which can greatly affect the resulting joint kinematics. The aim of this study is to introduce an objective method for calculating functional CS definitions for bones in joints that observe three-cylindrical-joint kinematic chain decomposition methods and to apply the method on tibiofemoral joint specimens. This method is driven by low resistance joint motion during loading profiles and not from anatomical landmark selection. Two anatomical CS definitions were established from points collected by five observers, for twelve knees. The knees underwent passive flexion and internal/external rotation using the anatomical CSs. The kinematics from these profiles were used in linear least squares minimization of off-axis motions to redefine the tibia and femur origins, the femur flexion axis and the tibia internal rotation axis. Significant improvements in reproducibility of 7.4 mm (tibia origin, p < 0.001), 3.4 mm (femur origin, p < 0.001), and 2.9° (femur FE-axis, p < 0.001) between the two functional CSs compared to the two anatomical CSs were observed. Functional CSs led to significant decreases in off-axis motion during discrete passive flexion profiles. This new strategy for establishing functional CSs provides an objective approach that will reduce the effects of observer error in establishing CSs. Additionally, functional CSs allow for better interpretations of kinematic responses due to loading because effects of kinematic cross-talk is minimized.

Specimen specific imaging and joint mechanical testing data for next generation virtual knees.

Virtual knees, with specimen-specific anatomy and mechanics, require heterogeneous data collected on the same knee. Specimen-specific data such as the specimen geometry, physiological joint kinematics-kinetics and contact mechanics are necessary in the development of virtual knee specimens for clinical and scientific simulations. These data are also required to capture or evaluate the predictive capacity of the model to represent joint and tissue mechanical response. This document details the collection of magnetic resonance imaging data and, tibiofemoral joint and patellofemoral joint mechanical testing data. These data were acquired for a cohort of eight knee specimens representing different populations with varying gender, age and perceived health of the joint. These data were collected as part of the Open Knee(s) initiative. Imaging data when combined with joint mechanics data, may enable development and assessment of authentic specimen-specific finite element models of the knee. The data may also guide prospective studies for association of anatomical and biomechanical markers in a specimen-specific manner.

Reference tool kinematics-kinetics and tissue surface strain data during fundamental surgical acts.

Haptic based surgical simulations are popular training aids in medicine. Previously, surgical tool loads and motion were measured during cutting and needle insertion on non-human tissue and several haptic based simulations were developed to enhance surgical training. However, there was a lack of realistic foundational data regarding the mechanical responses of human tissue and tools during fundamental acts of surgery, i.e., cutting, suturing, retracting, pinching and indenting. This study used four recently developed surgical tools in a variety of procedures on a diverse set of cadaver leg specimens from human donors. The kinematics and kinetics of surgical tools were recorded along with topical three-dimensional strain during commonly performed surgical procedures. Full motion and load signatures of foundational surgical acts can also be used beyond the development of authentic visual and haptic simulations of surgery, i.e., they provide mechanical specifications for the development of autonomous surgical systems.

Reference data on in vitro anatomy and indentation response of tissue layers of musculoskeletal extremities.

The skin, fat, and muscle of the musculoskeletal system provide essential support and protection to the human body. The interaction between individual layers and their composite structure dictate the body's response during mechanical loading of extremity surfaces. Quantifying such interactions may improve surgical outcomes by enhancing surgical simulations with lifelike tissue characteristics. Recently, a comprehensive tissue thickness and anthropometric database of in vivo extremities was acquired using a load sensing instrumented ultrasound to enhance the fidelity of advancing surgical simulations. However detailed anatomy of tissue layers of musculoskeletal extremities was not captured. This study aims to supplement that database with an enhanced dataset of in vitro specimens that includes ultrasound imaging supported by motion tracking of the ultrasound probe and two additional full field imaging modalities (magnetic resonance and computed tomography). The additional imaging datasets can be used in conjunction with the ultrasound/force data for more comprehensive modeling of soft tissue mechanics. Researchers can also use the image modalities in isolation if anatomy of legs and arms is needed.

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.

Robotically Simulated Pivot Shift That Represents the Clinical Exam.

A thorough understanding of anterior cruciate ligament (ACL) function and the effects of surgical interventions on knee biomechanics requires robust technologies and simulation paradigms that align with clinical insight. In vitro orthopedic biomechanical testing for the elucidation of ACL integrity doesn't have an established testing paradigm to simulate the clinical pivot shift exam on cadaveric specimens. The study aim was to develop a robotically simulated pivot shift that represents the clinical exam. An orthopedic surgeon performed a pivot shift on an instrumented ACL-deficient cadaver leg to capture 6 degree-of-freedom motion/loads. The same knee was mounted to the robot and the sensitivity of the motion/loading profiles quantified. Three loading profile candidates that generated positive pivot shifts on the instrumented knee were selected and applied to 7 ACL-intact/deficient specimens and resulted in the identification of a profile that was able to induce a positive pivot shift in all ACL-deficient specimens ( p < 0.001). The simulated shifts began at 22 ± 8° and ended at 33 ± 6° of flexion with the average magnitude of the shifts being 12.8 ± 3.2 mm in anterior tibial translation and 17.6 ± 4.3° in external tibial rotation. The establishment and replication of a robotically simulated clinical pivot shift across multiple specimens show the robustness of the loading profile to accommodate anatomical and experimental variability. Further evaluation and refinement should be undertaken to create a useful tool in evaluating ACL function and reconstruction techniques. Statement of clinical significance: Creation and successful demonstration of the simulated clinical pivot shift validates a profile for robotic musculoskeletal simulators to analyze ACL related clinical questions. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2601-2608, 2019.

Reference data on thickness and mechanics of tissue layers and anthropometry of musculoskeletal extremities.

Musculoskeletal extremities exhibit a multi-layer tissue structure that is composed of skin, fat, and muscle. Body composition and anthropometric measurements have been used to assess health status and build anatomically accurate biomechanical models of the limbs. However, comprehensive datasets inclusive of regional tissue anatomy and response under mechanical manipulation are missing. The goal of this study was to acquire and disseminate anatomical and mechanical data collected on extremities of the general population. An ultrasound system, instrumented with a load transducer, was used for in vivo characterization of skin, fat, and muscle thicknesses in the extremities of 100 subjects at unloaded (minimal force) and loaded (through indentation) states. For each subject, the unloaded and loaded state provided anatomic tissue layer measures and tissue indentation response for 48 and 8 regions, respectively. A publicly available web-based system has been used for data management and dissemination. This comprehensive database will provide the foundation for comparative studies in regional musculoskeletal composition and improve visual and haptic realism for computational models of the limbs.