Isometric osteopathic manipulation influences on cervical ranges of motion and correlation with osteopathic palpatory diagnosis: A randomized trial.

INTRODUCTION: Isometric manipulation is a current practice in osteopathy and treatment benefits have been reported in the literature. Such benefits could be assessed using experimental non-invasive cervical mobility measurements. The main objective was to quantitatively measure the effects of isometric manipulation on principal and compensatory cervical motions. METHODS: 101 healthy volunteers were included in this study. 51 healthy volunteers selected randomly underwent the experimental protocol before and after isometric treatment and were compared to 50 healthy volunteers who underwent a placebo treatment. Osteopathic diagnosis was performed on each healthy volunteer before and after the treatment. The experimental protocol included measurements by a motion capture system focusing on principal range of motion and compensatory motions. RESULTS: In both the isometric and the placebo sample, respectively including 51 (age: 29.2 ± 8.1, BMI: 22.2 ± 3.5) and 50 healthy volunteers (age: 27.4 ± 6.8, BMI: 22.9 ± 2.8), a pre-treatment diagnosis revealed a light cervical dysfunction in all subjects, mainly in levels C3 and C4. Altered ranges of motion thresholds (C3/C4 alterations) were identified: 113.2° for flexion, 130.0° for rotation and 90.2° for lateral flexion. After manipulations, the volunteers who underwent the isometric treatment presented a slight increase in amplitude for lateral flexion (p < 0.04), which was not found in the volunteers who underwent the placebo treatment. Compensatory motions showed differences pre and post isometric treatment without reaching significant values. CONCLUSION: Principal ranges of motion were found significantly higher after osteopathic treatment when compared to the placebo treatment. Osteopathic palpatory diagnosis showed significant correlation with range of motions before treatment.

Biomechanical comparison of sacral and transarticular sacroiliac screw fixation.

STUDY DESIGN: A detailed finite element analysis of screw fixation in the sacrum and pelvis. OBJECTIVE: To biomechanically assess and compare the fixation performance of sacral and transarticular sacroiliac screws. Instrumentation constructs are used to achieve fixation and stabilization for the treatment of spinopelvic pathologies. The optimal screw trajectory and type of bone engagement to caudally anchor long fusion constructs are not yet known. METHODS: A detailed finite element model of the sacroiliac articulation with two different bone densities was developed. Two sacral and one transarticular sacroiliac screw trajectories were modeled with different diameters (5.5 and 6.5 mm) and lengths (uni-cortical, bi-cortical and quad-cortical purchase). Axial pullout and flexion/extension toggle forces were applied on the screws representing intra and post-operative loads. The force-displacement results and von Mises stresses were used to characterize the failure pattern. RESULTS: Overall, sacroiliac screws provided forces to failure 2.75 times higher than sacral fixation screws. On the contrary, the initial stiffness was approximately half as much for sacroiliac screws. High stresses were located at screw tips for the sacral trajectories and near the cortical bone screw entry points for the sacroiliac trajectory. Overall, the diameter and length of the screws had significant effects on the screw fixation (33% increase in force to failure; 5% increase in initial stiffness). A 20% drop in bone mineral density (lower bone quality) decreased the initial stiffness by 25% and the force to failure by 5-10%. High stresses and failure occurred at the screw tip for uni- and tri-cortical screws and were close to trabecular-cortical bone interface for bi-cortical and quad-cortical screws. CONCLUSIONS: Sacroiliac fixation provided better anchorage than sacral fixation. The transarticular purchase of the sacroiliac trajectory resulted in differences in failure pattern and fixation performance.

Biomechanical analysis of two insertion sites for the fixation of the sacroiliac joint via an oblique lateral approach.

BACKGROUND: The sacroiliac joint is an important source of low back pain. In severe cases, sacroiliac joint fusion is used to reduce pain, but revision rates can reach 30%. The lack of initial mechanical stability may lead to pseudarthrosis, thus not alleviating the patient's symptoms. This could be due to the damage induced to the interosseous ligament during implant insertion. Decoupling instrumentation steps (drilling-tapping and implant insertion) would allow verifying this hypothesis. Moreover, no biomechanical studies have been published on sacroiliac joint fixation with an oblique lateral approach, while it has important clinical advantages over the direct lateral approach. METHODS: Eight cadaveric human pelves with both ischia embedded were tested in three sequential states: intact, drilled-tapped and instrumented with one cylindrical threaded implant with an oblique lateral trajectory. Specimens were assigned one of two insertion sites (distal point; near the posterior superior iliac spine, and proximal point; anterosuperior to the distal point) and tested in compression and flexion-extension. Vertical and angular displacements of the sacroiliac joint were measured locally using digital image correlation methods. FINDINGS: In compression, instrumentation significantly reduced vertical displacements (17% (SD 22%), P = 0.04) but no difference was found for angular displacements or flexion-extension loads (P > 0.05). Drilling-tapping did not change the stability of the sacroiliac joint (P > 0.05); there was no statistical difference between the insertion sites (P > 0.05). INTERPRETATIONS: Insertion of one implant through either the distal or proximal insertion site with an oblique lateral approach significantly reduced vertical displacements of the sacroiliac joint in compression, a predominant load of this joint. RESEARCH ETHICS COMMITTEE: Polytechnique Montreal: CÉR-1617-30.

Experimental assessment of cervical ranges of motion and compensatory strategies.

Background: Literature is still limited regarding reports of non-invasive assessment of the cervical range of motion in normal subjects. Investigations into compensatory motions, defined as the contribution of an additional direction to the required motion, are also limited.The objectives of this work were to develop and assess a reliable method for measuring the cervical range of motion in order to investigate motion and compensatory strategies. Methods and data collection: Ninety-seven no neck-related pain subjects (no severe cervical pathology, 57 women, age: 28.3 ± 7.5y. old, BMI: 22.5 ± 3.2 kg/m2) underwent a non-invasive cervical range of motion assessment protocol. In-vivo head's motion relative to the thorax was assessed through the measurement of the main angular amplitudes in the 3 directions (flexion/extension, axial rotations and lateral inclinations) and associated compensatory motions using an opto-electronic acquisition system. Results: The principal motion reproducibility resulted in intra-class correlation coefficients ranging from 0.81 to 0.86. The following maximum ranges of motion were found: 127.4 ± 15.1° of flexion/extension, 89.3 ± 12° of lateral inclinations and 146.4 ± 13° of axial rotations after 6 outlier exclusions. Compensatory motions highly depend on the associated principal motion: for flexion/extension: (3.5 ± 7.6;-2.1 ± 7.8°), for rotation: (25.7 ± 17.9°;0.4 ± 4.7)°, for inclination: (22.9 ± 34.7°;-0.04 ± 8.7°). Age, BMI and weight significantly correlated with flexions (p < 0.032). Motion patterns were identified through clustering. Conclusions: This kinematic analysis has been proven to be a reliable diagnostic tool for the cervical range of motion. The non-unicity and variability of motion patterns through the clustering of motion strategy identification have been shown. Compensatory motions contributed to such motion pattern definition despite presenting significant intra-individual variability.

Thoracic pedicle screw fixation under axial and perpendicular loadings: A comprehensive numerical analysis.

BACKGROUND: Many studies have assessed the pullout fixation strength of pedicle screws, but only a few investigated the fixation strength under non-axial forces such as the ones applied with modern instrumentation techniques. The purpose is to biomechanically compare the fixation strength of different pedicle screw dimensions, bone engagement, entry point preparation and vertebra dimensions under axial pull-out and perpendicular loadings. METHODS: A finite element model of two thoracic vertebrae (T3, T8) with three different cortical bone thickness configurations (5th, 50th and 95th percentile) was used. Two bone engagements, two screw diameters and three entry point enlargement scenarios were numerically tested under an axial and four perpendicular forces (cranial, caudal, medial and lateral) until failure for a total of 180 simulations. Force-displacement responses were analyzed using ANOVA and Pareto charts to determine the individual effects of each parameter. FINDINGS: The screw diameter was the predominant parameter affecting the screw anchorage in all loading directions. The larger screw diameter increased by 35% the initial stiffness and force to failure. Cortical bone removal around the entry point reduced the axial and perpendicular initial stiffness (27% and 17% respectively) and force to failure (20% and 13%). Better screw anchorage was obtained with bicortical bone engagement. INTERPRETATION: The screw diameter and amount of cortical bone left around the entry point are essential for pedicle screw fixation in all loading scenarios. The proximity of the screw threads to the cortical bone (pedicle fill) has a major role in pedicle screw fixation.

Minimizing Pedicle Screw Pullout Risks: A Detailed Biomechanical Analysis of Screw Design and Placement.

STUDY DESIGN: Detailed biomechanical analysis of the anchorage performance provided by different pedicle screw designs and placement strategies under pullout loading. OBJECTIVE: To biomechanically characterize the specific effects of surgeon-specific pedicle screw design parameters on anchorage performance using a finite element model. SUMMARY OF BACKGROUND DATA: Pedicle screw fixation is commonly used in the treatment of spinal pathologies. However, there is little consensus on the selection of an optimal screw type, size, and insertion trajectory depending on vertebra dimension and shape. METHODS: Different screw diameters and lengths, threads, and insertion trajectories were computationally tested using a design of experiment approach. A detailed finite element model of an L3 vertebra was created including elastoplastic bone properties and contact interactions with the screws. Loads and boundary conditions were applied to the screws to simulate axial pullout tests. Force-displacement responses and internal stresses were analyzed to determine the specific effects of each parameter. RESULTS: The design of experiment analysis revealed significant effects (P<0.01) for all tested principal parameters along with the interactions between diameter and trajectory. Screw diameter had the greatest impact on anchorage performance. The best insertion trajectory to resist pullout involved placing the screw threads closer to the pedicle walls using the straightforward insertion technique, which showed the importance of the cortical layer grip. The simulated cylindrical single-lead thread screws presented better biomechanical anchorage than the conical dual-lead thread screws in axial loading conditions. CONCLUSIONS: The model made it possible to quantitatively measure the effects of both screw design characteristics and surgical choices, enabling to recommend strategies to improve single pedicle screw performance under axial loading.

Finite Element Analysis of Sacroiliac Joint Fixation under Compression Loads.

BACKGROUND: Sacroiliac joint (SIJ) is a known chronic pain-generator. The last resort of treatment is the arthrodesis. Different implants allow fixation of the joint, but to date there is no tool to analyze their influence on the SIJ biomechanics under physiological loads. The objective was to develop a computational model to biomechanically analyze different parameters of the stable SIJ fixation instrumentation. METHODS: A comprehensive finite element model (FEM) of the pelvis was built with detailed SIJ representation. Bone and sacroiliac joint ligament material properties were calibrated against experimentally acquired load-displacement data of the SIJ. Model evaluation was performed with experimental load-displacement measurements of instrumented cadaveric SIJ. Then six fixation scenarios with one or two implants on one side with two different trajectories (proximal, distal) were simulated and assessed with the FEM under vertical compression loads. RESULTS: The simulated S1 endplate displacement reduction achieved with the fixation devices was within 3% of the experimentally measured data. Under compression loads, the uninstrumented sacrum exhibited mainly a rotation motion (nutation) of 1.38° and 2.80° respectively at 600 N and 1000 N, with a combined relative translation (0.3 mm). The instrumentation with one screw reduced the local displacement within the SIJ by up to 62.5% for the proximal trajectory vs. 15.6% for the distal trajectory. Adding a second implant had no significant additional effect. CONCLUSION: A comprehensive finite element model was developed to assess the biomechanics of SIJ fixation. SIJ devices enable to reduce the motion, mainly rotational, between the sacrum and ilium. Positioning the implant farther from the SIJ instantaneous rotation center was an important factor to reduce the intra-articular displacement. CLINICAL RELEVANCE: Knowledge provided by this biomechanical study enables improvement of SIJ fixation through optimal implant trajectory.

Pedicle Screw Fixation Under Nonaxial Loads: A Cadaveric Study.

STUDY DESIGN: An experimental study of pedicle screw fixation in human cadaveric vertebrae. OBJECTIVE: The aim of this study was to experimentally characterize pedicle screw fixation under nonaxial loading and to analyze the effect of the surgeons' screw and placement choices on the fixation risk of failure. SUMMARY OF BACKGROUND DATA: Pedicle screw fixation performance is traditionally characterized with axial pullout tests, which do not fully represent the various tridimensional loads sustained by the screws during correction maneuvers of severe spinal deformities. Previous studies have analyzed the biomechanics of nonaxial loads on pedicle screws, but their effects on the screw loosening mechanisms are still not well understood. METHODS: A design of experiment (DOE) approach was used to evaluate 2 screw thread designs (single-lead and dual-lead threads), 2 insertion trajectories in the transverse and sagittal planes, and 2 loading directions (lateral and cranial). Pedicle screws were inserted in both pedicles of 12 cadaveric lumbar vertebrae for a total of 24 tests. Four sinewave loading cycles (0-400 N) were applied, orthogonally to the screw axis, at the screw head. The resulting forces, displacements, and rotations of the screws were recorded. RESULTS: In comparison to the other cycles, the first loading cycle revealed important permanent deformation of the bone (mean permanent displacement of the screw head of 0.79 mm), which gradually accumulated over the following cycles to 1.75 mm on average (plowing effect). The cranial loading direction caused significantly lower (P < 0.05) bone deformation than lateral loading. The dual-lead screw had a significantly higher (P < 0.05) initial stiffness than the single-lead thread screw. CONCLUSIONS: Nonaxial loads induce screw plowing that lead to bone compacting and subsequent screw loosening or even bone failure, thus reducing the pedicle screw fixation strength. Lateral loads induce greater bone deformation and risks of failure than cranial loads. LEVEL OF EVIDENCE: N/A.

Optimizing porous lattice structures for orthopaedic implants.

Porous lattice structures are increasingly used for tissue and implant device design, and require precise structural characteristics such as stiffness, porosity, volume fraction and surface area. A non-uniform distribution of these properties may be required to suit design requirements or to match in-vivo conditions. Thus, porous lattice design is complex due to competing objectives from the distributed structural properties. A lattice structural design and optimization methods is presented using global objective functions for effective stiffness, porosity, volume fraction and surface area.