Advancing Thoracic Spine Biomechanical Research

The long term objective of this research was to elucidate issues with current thoracic spine testing methods and develop more accurate ways to quantify the biomechanical impact of surgical procedures or medical devices. The ability to perform thoracic spine testing with a rib cage is limited by test machine variability and experimental design inconsistency, so surgeons are left with little reliable information on the biomechanical impacts of procedures and implants. This research sought to validate a novel spine test machine, provide biomechanical data to support the inclusion of an intact rib cage when testing the thoracic spine, and quantify the biomechanical impacts of sequential Ponte osteotomies. Specific Aim 1 validated the accuracy of the spine test machine for rigidity ranges that represent cadaveric specimen rigidities present in the spine. Cervical, thoracic, and lumbar spine specimens were modeled with synthetic rubber that represented the breadth of rigidities, and testing was conducted in bending and axial rotation. The maximum machine displacement error was less than 2° for lumbar and thoracic specimens, so it is suggested that researchers use an external motion-tracking system in conjunction with the test machine when high accuracy measurements are required. Specific Aim 2 quantified the biomechanical differences of testing full cadaveric thoracic spine specimens with and without an intact rib cage. While it was presumed that the rib cage provides structural stability to the thoracic spine, the extent to which the rib cage contributes to spinal motion had not been fully quantified. Testing quantified the motion and stiffness values of an intact thoracic spine specimen, and results showed that testing without a rib cage changes both motion and stiffness values. Specific Aim 3 quantified the biomechanical impact of sequential Ponte osteotomies in cadaveric thoracic spine specimens with intact rib cages. Overall and regional changes in motion due to Ponte osteotomies were analyzed, and results showed increased flexibility in the sagittal plane on both overall and regional levels. The results from this work could provide researchers and surgeons the tools they need to better understand and improve spine procedures and implants, which could ultimately improve the quality of life for patients

Stimulation of Piezo1 by mechanical signals promotes bone anabolism

Mechanical loading, such as caused by exercise, stimulates bone formation by osteoblasts and increases bone strength, but the mechanisms are poorly understood. Osteocytes reside in bone matrix, sense changes in mechanical load, and produce signals that alter bone formation by osteoblasts. We report that the ion channel Piezo1 is required for changes in gene expression induced by fluid shear stress in cultured osteocytes and stimulation of Piezo1 by a small molecule agonist is sufficient to replicate the effects of fluid flow on osteocytes. Conditional deletion o

Challenges in Kinetic-Kinematic Driven Musculoskeletal Subject-Specific Infant Modeling

Musculoskeletal computational models provide a non-invasive approach to investigate human movement biomechanics. These models could be particularly useful for pediatric applications where in vivo and in vitro biomechanical parameters are difficult or impossible to examine using physical experiments alone. The objective was to develop a novel musculoskeletal subject-specific infant model to investigate hip joint biomechanics during cyclic leg movements. Experimental motion-capture marker data of a supine-lying 2-month-old infant were placed on a generic GAIT 2392 OpenSim model. After scaling the model using body segment anthropometric measurements and joint center locations, inverse kinematics and dynamics were used to estimate hip ranges of motion and moments. For the left hip, a maximum moment of 0.975 Nm and a minimum joint moment of 0.031 Nm were estimated at 34.6° and 65.5° of flexion, respectively. For the right hip, a maximum moment of 0.906 Nm and a minimum joint moment of 0.265 Nm were estimated at 23.4° and 66.5° of flexion, respectively. Results showed agreement with reported values from the literature. Further model refinements and validations are needed to develop and establish a normative infant dataset, which will be particularly important when investigating the movement of infants with pathologies such as developmental dysplasia of the hip. This research represents the first step in the longitudinal development of a model that will critically contribute to our understanding of infant growth and development during the first year of life

Vertebral Body Tethering (VBT): Quantifying Tension in a VBT System for Scoliosis Treatment

The gold standard surgical treatment for children with adolescent idiopathic scoliosis is deformity correction with spinal instrumentation and fusion. However, there is associated significant, long-term morbidity in fusing multiple motion segments in a child. Pain, inflexibility, and degenerative arthritis are often sequelae of the surgery due to fusion sites being immobile [1], and longevity of the metal rods and screws is a long-term concern. However, an innovative approach, vertebral body tethering (VBT), was recently approved by the FDA and has since provided an alternate treatment option. VBT takes advantage of the natural growth of a child\u27s spine to modulate spinal growth and correct the deformity over time without spinal fusion. A flexible polyethylene tether is affixed to multiple spinal segments to apply compressive forces on the vertebral growth plates. Using a tensioner device, the amount of tension in the tether at each vertebral level is controlled, eventually correcting spinal curvature as the patient grows. Recent data shows 74% of patients treated with VBT achieve clinical success [2]. The tensioner device has tension settings of 0 to 5, though no data is available to correlate with the amount of tension generated in the tether at each setting. Furthermore, there are two different tensioner device designs that can be used in this medical device set (methods A and B), and it is unknown whether these different tensioners produce similar tension. Therefore, the purpose of this study was to quantify the forces generated with the two tensioner methods (A and B) at six categorical tension levels using current VBT instrumentation. References Hoernschemeyer DG et al. J Bone Joint Surg Am. 2020 Jul 1;102(13):1169-1176. Newton PO et al. Spine Deform. 2022 May;10(3):553-561

Effects of Weight-Bearing on Tibiofemoral, Patellofemoral, and Patellar Tendon Kinematics in Older Adults

Quantification of natural knee kinematics is essential for the assessment of joint function in the diagnosis of pathologies. Combined measurements of tibiofemoral and patellofemoral joint kinematics are necessary because knee pathologies, such as progression of osteoarthritis and patellar instability, are a frequent concern in both articulations. Combined measurement of tibiofemoral and patellofemoral kinematics also enables calculation of important quantities, specifically patellar tendon angle, which partly determines the loading vector at the tibiofemoral joint and patellar tendon moment arm. The goals of this research were to measure the differences in tibiofemoral and patellofemoral kinematics, patellar tendon angle (PTA), and patellar tendon moment arm (PTMA) that occur during non-weight-bearing and weight-bearing activities in older adults. Methods: High-speed stereo radiography was used to measure the kinematics of the tibiofemoral and patellofemoral joints in subjects as they performed seated, non-weight-bearing knee extension and two weight-bearing activities: lunge and chair rise. PTA and PTMA were extracted from the subject’s patellofemoral and tibiofemoral kinematics. Kinematics and the root mean square difference (RMSD) between non-weight-bearing and weight-bearing activities were compared across subjects and activities. Results: Internal rotation increased with weight-bearing (mean RMSD from knee extension was 4.2 ± 2.4° for lunge and 3.6 ± 1.8° for chair rise), and anterior translation was also greater (mean RMSD from knee extension was 2.2 ± 1.2 mm for lunge and 2.3 ± 1.4 mm for chair rise). Patellar tilt and medial–lateral translation changed from non-weight-bearing to weight-bearing. Changes of the patellar tendon from non-weight-bearing to weight-bearing were significant only for PTMA. Conclusions: While weight-bearing elicited changes in knee kinematics, in most degrees of freedoms, these differences were exceeded by intersubject differences. These results provide comparative kinematics for the evaluation of knee pathology and treatment in older adults

DOES HAND SPEED RELATE TO CLUB HEAD SPEED OR BALL SPEED DURING A GOLF SWING?

Many golf swing analyses use club or ball speed to indicate performance, although these are difficult to obtain using motion capture. This study examined the relationship between hand speed and club head and ball speeds to examine if hand can indicate performance and if different capturing frequencies affect these relationships. A 10-camera Vicon system recorded golfers performing eight golf swings (500 Hz n=11, 100 Hz n=15). A TrackMan system recorded club head and ball speed. The resultant hand speed was calculated at peak velocity, the lowest position of the hands, and at ball impact. Hand speed at ball impact and club head speed had the strongest relationship (r=0.501, p\u3c0.001), though most correlations were r\u3c0.400. Higher capturing frequency had better relationships with the performance outcomes, and the ball impact was the best time point for analysis

Effect of follower load on motion and stiffness of the human thoracic spine with intact rib cage

Researchers have reported on the importance of the rib cage in maintaining mechanical stability in the thoracic spine and on the validity of a compressive follower preload. However, dynamic mechanical testing using both the rib cage and follower load has never been studied. An in vitro biomechanical study of human cadaveric thoracic specimens with rib cage intact in lateral bending, flexion/extension, and axial rotation under varying compressive follower preloads was performed. The objective was to characterize the motion and stiffness of the thoracic spine with intact rib cage and follower preload. The hypotheses tested for all modes of bending were (i) range of motion, elastic zone, and neutral zone will be reduced with a follower load, and (ii) neutral and elastic zone stiffness will be increased with a follower load. Eight human cadaveric thoracic spine specimen (T1–T12) with intact rib cage were subjected to 5 Nm pure moments in lateral bending, flexion/extension, and axial rotation under follower loads of 0–400 N. Range of motion, elastic and neutral zones, and elastic and neutral zone stiffness values were calculated for functional spinal units and segments within the entire thoracic section. Combined segmental range of motion decreased by an average of 34% with follower load for every mode. Application of a follower load with intact rib cage impacts the motion and stiffness of the human cadaveric thoracic spine. Researchers should consider including both aspects to better represent the physiologic implications of human motion and improve clinically relevant biomechanical thoracic spine testing

Effects of follower load and rib cage on intervertebral disc pressure and sagittal plane curvature in static tests of cadaveric thoracic spines

The clinical relevance of mechanical testing studies of cadaveric human thoracic spines could be enhanced by using follower preload techniques, by including the intact rib cage, and by measuring thoracic intervertebral disc pressures, but studies to date have not incorporated all of these components simultaneously. Thus, this study aimed to implement a follower preload in the thoracic spine with intact rib cage, and examine the effects of follower load, rib cage stiffening and rib cage removal on intervertebral disc pressures and sagittal plane curvatures in unconstrained static conditions. Intervertebral disc pressures increased linearly with follower load magnitude. The effect of the rib cage on disc pressures in static conditions remains unclear because testing order likely confounded the results. Disc pressures compared well with previous reports in vitro, and comparison with in vivo values suggests the use of a follower load of about 400 N to approximate loading in upright standing. Follower load had no effect on sagittal plane spine curvature overall, suggesting successful application of the technique, although increased flexion in the upper spine and reduced flexion in the lower spine suggest that the follower load path was not optimized. Rib cage stiffening and removal both increased overall spine flexion slightly, although with differing effects at specific spinal locations. Overall, the approaches demonstrated here will support the use of follower preloads, intact rib cage, and disc pressure measurements to enhance the clinical relevance of future studies of the thoracic spine

Hip Mechanics of Infants: Understanding Hip Angles of an Infant in Different Baby Carrier Styles

Infant position in baby carriers can affect their hip development and health. The Pavlik Harness is a device used to treat Developmental Dysplasia of the Hip (DDH) and is the standard for the healthy hip position of 90° flexion and 80° abduction angles. Standardized baby carrier styles that promote healthy hip position have not yet been established. The purpose of this study was to develop testing methods to accurately measure infant hip angles in various baby carriers. Three baby carriers under four conditions were placed on an adult manikin. One manikin representing a newborn which weighed approximately 2.83 kilograms was placed under the four conditions. The hip flexion and abduction angles were measured using a goniometer. The flexion angles were calculated through a MATLAB photo analysis function. The maximum force, peak pressure, and mean pressure that the carrier exerted onto the infant were measured during the first trial using two Novel pressure sensors. The sensors were placed around one thigh and the back and gluteus maximus. The Novel data was inconsistent and unreliable to measure forces exerted on the infant. Carrier B’s data resulted in the most similar hip position to the Pavlik Harness positioning. Carrier C’s data proved that it does not support the infant’s hips for healthy positioning. 75% of the photo analysis method resulted in smaller flexion angles compared to the measured angles using the goniometer. Labeling the anatomical landmarks for the photo analysis method was accessible and consistent. It was difficult to measure angles with the goniometer due to its shape and the positioning of the infant in the baby carrier. This preliminary data collection will lead to more advanced and detailed research with human subjects. A possible method for measuring hip flexion and abduction more accurately is to imbed a digital goniometer into the infant manikin or use a marker-based motion capture system like VICON. A standard for new baby carrier designs will be created when the optimal baby carrier style for hip position is identified

Comparing Infant Hip Joint Center Estimations Between Manual and Digital Measures

Comparing Infant Hip Joint Center Estimations Between Manual and Digital MeasuresDespite the high prevalence of developmental hip disorders in infants, there has been little research on understanding infant hip anatomy. The hip joint center (HJC) is the center of rotation of the hip joint, usually assumed to be the center of the femoral head, and it is the critical location for calculating moments and forces about the hip joint. The HJC cannot be externally identified, and thus localization requires diagnostic imaging or approximation when using motion capture systems. Approximations are calculated from regression equations dependent on anthropometric data and anatomical landmarks. None of the current regression equations are based on infant anatomy. The purpose of this study was to determine whether the HJC estimation equations recommended by the International Society of Biomechanics yield comparable results when tested on a 3-dimensional (3D) digital model and a 3D physical model of the infant hip. Anatomical positions needed for the computation of the HJC were identified in the digital and physical models. Ten measures were collected on each model and the HJC was estimated using the four Bell methods. An independent samples T-test was performed for each dataset. No significant differences in HJC estimations were found between the manual and digital measures for each method. This indicates that anatomical landmarks utilized in a digital model are comparable to a physical model and supports that the use of manual measurements may be viable for estimating the infant HJC in clinical settings where diagnostic imaging is unavailable. The lack of significant findings may partially be due to the fact that only one model was tested, thus we were unable to compare between subjects. Additionally, the current models were bone-only and lacked representation of soft-tissue, which may have altered our results. Further testing with more robust models and methods are needed to confirm the results. This study serves as preliminary research in the development of HJC estimation standards for infants