In Vitro Biomechanical Testing and Computational: Modeling in Spine

Two separate in vitro biomechanical studies were conducted on human cadaveric spines (Lumbar) to evaluate the stability following the implantation of two different spinal fixation devices interspinous fixation device (ISD) and Hybrid dynamic stabilizers. ISD was evaluated as a stand-alone and in combination with unilateral pedicle rod system. The results were compared against the gold standard, spinal fusion (bilateral pedicle rod system). The second study involving the hybrid dynamic system, evaluated the effect on adjacent levels using a hybrid testing protocol. A robotic spine testing system was used to conduct the biomechanical tests. This system has the ability to apply continuous unconstrained pure moments while dynamically optimizing the motion path to minimize off-axis loads during testing. Thus enabling precise control over the loading and boundary conditions of the test. This ensures test reliability and reproducibility. We found that in flexion-extension, the ISD can provide lumbar stability comparable to spinal fusion. However, it provides minimal rigidity in lateral bending and axial rotation when used as a stand-alone. The ISD with a unilateral pedicle rod system when compared to the spinal fusion construct were shown to provide similar levels of stability in all directions, though the spinal fusion construct showed a trend toward improved stiffness overall. The results for the dynamic stabilization system showed stability characteristics similar to a solid all metal construct. Its addition to the supra adjacent level (L3- L4) to the fusion (L4- L5) indeed protected the adjacent level from excessive motion. However, it essentially transformed a 1 level into a 2 level lumbar fusion with exponential transfer of motion to the fewer remaining discs (excessive adjacent level motion). The computational aspect of the study involved the development of a spine model (single segment). The kinematic data from these biomechanical studies (ISD study) was then used to validate a finite element model

The safety and efficacy of mesenchymal stem cells for prevention or regeneration of intervertebral disc degeneration: a systematic review

General Posters: abstract no. GP86INTRODUCTION: Mesenchymal stem cells (MSCs) have been used to halt the progression or regenerate the disc with hopes to prevent or treat discogenic back pain. However, the safety and efficacy of the use of MSCs for such treatment in animal and human models at short and long term assessment (i.e. greater than 48 weeks) have not been systematically addressed. This study addressed a systematic review of comparative controlled studies addressing the use of MSCs to that of no treatment/saline for the treatment of disc degeneration. METHODS: Online databases were extensively searched. Controlled trials in animal models and humans were eligible for inclusion. Trial design, MSC characteristics, injection method, disc assessment, outcome intervals, and complication events were assessed. Validity of each study was assessed addressing trial design. Two individuals independently addressed the aforementioned. RESULTS: Twenty-two animal studies were included. No human comparative controlled trials were reported. All three types of MSCs (i.e. derived from bone marrow, synovial and adipose tissue) showed successful inhibition of disc degeneration progression. From three included studies, bone marrow derived MSC showed superior quality of disc repair when compared to other treatments, including TGF-β1, NP bilaminar co-culture and axial distraction regimen. However, osteophyte development was reported in two studies as potential complication of MSC transplantation. CONCLUSIONS: Based on animal models, the current evidence suggests that in the short-term MSC transplantation is safe and effective in halting disc degeneration; however, additional and larger studies are needed to assess the long-term regenerative effects and potential complications. Inconsistency in methodological design and outcome parameters prevent any robust conclusions. In addition, randomized controlled trials in humans are needed to assess the safety and efficacy of such therapy.published_or_final_versio

Biomechanical strategies to reduce subsidence in Posterior Lumbar Interbody Fusion procedures

Posterior approaches remain among the most used to perform lumbar interbody fusion (LIF) surgery. It happens because of the advantage of providing direct access to the neural elements in the lumbar spine and the surgeons\u27 preference for the approach. But the interbody fusion devices (IFD) inserted using posterior approaches are of limited size, and implant subsidence remains the most common complication after LIF surgery. It can be catastrophic for the patient resulting in worse outcomes or even requiring revision surgery. Since increasing the cage\u27s size is not possible in PLIF surgeries, this thesis will explore biomechanical strategies to increase the load distribution across the IFD and reduce the risk of subsidence. It will be done using patient-specific devices, matching the bony endplate anatomy, manufactured through rapid prototyping and exploring the role of the bone graft housed inside the cage to increase load sharing

Biomechanical Comparison of Traditional Laminectomy and Minimally‑Invasive Facetectomies

The facet joints of the lumbar spine are one of the sources of low‑back pain that affects a great portion of the population. Minimally‑invasive (MI) procedures have been becoming more popular in the surgical decompression of the spine because they offer shorter recovery time and involve removal of smaller amounts of important structures. With these features, it is believed that MI procedures lead to less clinical instability, and the functionality of the segment is maintained. Another important factor is how the facet angle in the lumbar segments affects the biomechanical instability. In spite of all this interest in MI procedures, there is little biomechanical research to back these claims. Therefore, in this study two MI procedures were compared with the laminectomy, the gold‑standard for lumbar decompression. Eight lumbar cadaveric motion segment units were procured, mounted, and tested intact, and then following MI unilateral facetectomy (UF), MI bilateral facetectomy (BF), and a traditional laminectomy (TL) using three different loading scenarios. The three different loading scenarios utilized in this study were the pure moment (PM), combined loading and moment (CLM), and the coupled‑eccentric loading (CEL) protocols. The PM testing protocol is the standard form of biomechanical testing of the spine. The CLM testing protocol introduced compressive and shear forces to increase translation in the sagittal plane. The CEL protocol was used because it combined a sagittal bend with a forced axial rotation. Rotational values were analyzed at the end limit of 8 Nm for flexion and extension and at 6 Nm for left and right lateral bending. Translations under PM and CLM were calculated utilizing a simulation software Visual Nastran. The criterion for instability was used to see if UF, BF, and TL met this criterion as compared to what would be clinically seen radiographically. In addition to these biomechanical data, CT images were analyzed to determine the change in the facet angle, contact area of the facet, and length of the joint removed after the BF. Increased motion was seen in the BF and TL compared to the harvested spine condition in all protocols. A decrease in rotation was seen in the UF condition in all protocols, with the exceptions being in right lateral for PM. None of the PM and CLM data met the criteria for instability. A decrease in facet angle, contact area, and length of the facet after the BF was observed. The TL had the most number of significant biomechanical increases when compared to the harvested condition, making it a less favorable surgical procedure when compared to each of the MI procedures. No studies have used the multiple loading scenarios, have quantified the amount of instability, or have taken account the amount of resection and change in facet angle due to MI procedures. Further investigation of the biomechanical effects of the MI procedures is still needed to gain more insight on how MI procedures affect spine biomechanics

Outcome after surgery for isthmic spondylolisthesis and degenerative disc disease

Individuals with isthmic spondylolisthesis and lumbar degenerative disc disease may have low back and leg pain. Those with persistent symptoms non-responsive to conservative treatment are sometimes treated surgically. Various surgical methods have been introduced, but long-term outcome comparisons are scarce. The Swedish Spine register (Swespine) was used to study long term outcome after fusion surgery for isthmic spondylolisthesis and lumbar degenerative disc disease. In addition, we determined the effect of loss to follow-up on patient reported outcome interpretation, as well as the diagnostic accuracy of surgical information in Swespine. Another cohort was used to determine the long-term risk of radiologically verified adjacent segment degeneration after interbody fusion and posterolateral fusion. We found that the Swedish Spine register gives fairly reliable information about the surgical event. Loss to follow-up is of minor importance in the outcome interpretation after lumbar spine surgery. At long term, patient reported outcome was similar when comparing interbody fusion and posterolateral fusion in isthmic spondylolisthesis and degenerative disc disease. The long-term risk of radiologically verified adjacent segment degeneration was similar after interbody fusion and posterolateral fusion. The risk of additional lumbar spine surgery for any reason was significantly higher in those individuals that had undergone interbody fusion compared to those that had undergone posterolateral fusion. Even though patient reported outcome was improved after surgery for isthmic spondylolisthesis, the quality of life did not reach the levels of the normative population

Clinical and Radiographic Assessment of Lumbar Spine Total Disc Replacement in Athletes with Two Year Follow Up

The purpose of the study was to evaluate the consequences of athletic activity on the clinical and radiographic outcomes of lumbar spine total disc replacement (TDR) patients. The data for this study is drawn secondarily from a prospective randomized study evaluating the Prodisc prosthesis at Yale New Haven Hospital. Athletic activities prior to the onset of spinal injury, after the onset of spinal injury, and post lumbar spine total disc replacement (TDR) surgery were assessed. Athletic activity was classified into three groups. These were contact/vigorous, moderate, and light, based on effect on the involved spinal segments. Outcomes were assessed both clinically and radiographically. Out of 195 patients enrolled in the Prodisc study at Yale, 82 qualified for inclusion and fulfilled all follow-up criteria. In these 82 patients 120 disc replacements were performed. The average reduction from pre-operative visual analog pain scale was 44 (std dev 30.1) at a minimum of 2 years follow up. The average reduction in Oswestry disability index was 38% (std dev 23). 74/82 patients returned to athletic activity following TDR. 19 (23%) patients returned to pre-injury athletic activity levels, 47 (57%) returned to athletic activity but not to pre-injury levels, 14 (17%) patients reported activity levels that were unchanged since surgery, and 2 (3%) had activity levels become more impaired since surgery. Of those that returned to athletic activity, 4/74 complained of radiculopathy symptoms during athletic participation. Overall, 14 of 82 patients reported persistent back pain and 8 of these patients reported radiculopathy symptoms. Segmental flexion and extension at the levels of the implant, and the levels adjacent, revealed that the goal of physiologic motion was not reached at either the level of the implant, nor at the superior or inferior adjacent segments. Three L5/S1 subluxations occurred in heavy weight lifters and were the only radiographic complications. Athletic activities of varying degrees appear to be well-tolerated following lumbar TDR surgery in single and multi-level cases. Contact-vigorous athletic activities do not appear to result in high levels of clinical or radiographic complications in the lumbar TDR patients except for heavy weight lifting activities in patients who have undergone L5/S1 Prodisc surgery in which we experienced 3 implant subluxations. Further biomechanical and clinical studies are necessary before general recommendations can be made

Human lumbar spine biomechanics: study of pathologies and new surgical procedures

This thesis aims to shed light on the process that undergoes the lumbar spine as a result of intervertebral disc degeneration and different lumbar surgeries, paying special attention on the main risk factors and how to overcome them. Low back pain is the leading musculoskeletal disorder in all developed countries generating high medical related costs. Intervertebral disc degeneration is one of the most common causes of low back pain. When conservative treatments fail to relieve this pain, lumbar surgery is needed and, in this regard, lumbar fusion is the \textquotedblleft gold standard\textquotedblright technique to provide stability and neural decompression.Degenerative disc disease has been studied through two different approaches. An in-vivo animal model was reproduced and followed-up with MRI and mechanical testing to see how the water content decreased while the stiffness of the tissue increased. Then, degeneration was induced in a single disc of the human lumbar spine and the effects on the adjacent disc were investigated by the use of the finite element models. Further on, different procedures for segmental fusion were computationally simulated. A comparison among different intersomatic cage designs, supplemented with posterior screw fixation or placed in a stand-alone fashion, showed how the supplementary fixation drastically decreased the motion in the affected segment increasing the risk of adjacent segment disease more than a single placed cage. However, one of the main concerns regarding the use of cages without additional fixation is the subsidence of the device into the vertebral bone. A parametric study of the cage features and placement pointed to the width, curvature, and position as the most influential parameters for stability and subsidence.Finally, two different algorithms for tissue healing were implemented and applied for the first time to predict lumbar fusion in 3D models. The self-repairing ability of the bone was tested after simple nucleotomy and after instrumentation with internal fixation, anterior plate or stand-alone intersomatic cage predicting, in agreement with previous animal and clinical studies, that instrumentation may be not necessary to promote segmental fusion. In particular, the intervertebral disc height was seen to play an important role in the bone bridge or osteophyte formation.To summarize, this thesis has focused in the main controversial issues of intervertebral disc degeneration and lumbar fusion, such as degenerative process, adjacent segment disease, segment stability, cage subsidence or bone bridging. All the models described in this thesis could serve as a powerful tool for the pre-clinical evaluation of patient-specific surgical outcomes supporting clinician decisions. This thesis aims to shed light on the process that undergoes the lumbar spine as a result of intervertebral disc degeneration and different lumbar surgeries, paying special attention on the main risk factors and how to overcome them. Low back pain is the leading musculoskeletal disorder in all developed countries generating high medical related costs. Intervertebral disc degeneration is one of the most common causes of low back pain. When conservative treatments fail to relieve this pain, lumbar surgery is needed and, in this regard, lumbar fusion is the \textquotedblleft gold standard\textquotedblright technique to provide stability and neural decompression. Degenerative disc disease has been studied through two different approaches. An in-vivo animal model was reproduced and followed-up with MRI and mechanical testing to see how the water content decreased while the stiffness of the tissue increased. Then, degeneration was induced in a single disc of the human lumbar spine and the effects on the adjacent disc were investigated by the use of the finite element models. Further on, different procedures for segmental fusion were computationally simulated. A comparison among different intersomatic cage designs, supplemented with posterior screw fixation or placed in a stand-alone fashion, showed how the supplementary fixation drastically decreased the motion in the affected segment increasing the risk of adjacent segment disease more than a single placed cage. However, one of the main concerns regarding the use of cages without additional fixation is the subsidence of the device into the vertebral bone. A parametric study of the cage features and placement pointed to the width, curvature, and position as the most influential parameters for stability and subsidence. Finally, two different algorithms for tissue healing were implemented and applied for the first time to predict lumbar fusion in 3D models. The self-repairing ability of the bone was tested after simple nucleotomy and after instrumentation with internal fixation, anterior plate or stand-alone intersomatic cage predicting, in agreement with previous animal and clinical studies, that instrumentation may be not necessary to promote segmental fusion. In particular, the intervertebral disc height was seen to play an important role in the bone bridge or osteophyte formation. To summarize, this thesis has focused in the main controversial issues of intervertebral disc degeneration and lumbar fusion, such as degenerative process, adjacent segment disease, segment stability, cage subsidence or bone bridging. All the models described in this thesis could serve as a powerful tool for the pre-clinical evaluation of patient-specific surgical outcomes supporting clinician decisions. <br /

Biomechanics of Disc Degeneration

Disc degeneration and associated disorders are among the most debated topics in the orthopedic literature over the past few decades. These may be attributed to interrelated mechanical, biochemical, and environmental factors. The treatment options vary from conservative approaches to surgery, depending on the severity of degeneration and response to conservative therapies. Spinal fusion is considered to be the “gold standard” in surgical methods till date. However, the association of adjacent level degeneration has led to the evolution of motion preservation technologies like spinal arthroplasty and posterior dynamic stabilization systems. These new technologies are aimed to address pain and preserve motion while maintaining a proper load sharing among various spinal elements. This paper provides an elaborative biomechanical review of the technologies aimed to address the disc degeneration and reiterates the point that biomechanical efficacy followed by long-term clinical success will allow these nonfusion technologies as alternatives to fusion, at least in certain patient population

Development and application of methods for the biomechanical characterization of spine ligaments and intervertebral discs

The spine is one of the major organs subject to trauma or genetic problems. Today 30% of people suffer from back pain and every day a large number of surgical interventions on the spine are performed to treat those patients with severe spinal deformities (i.e. scoliosis or kyphosis). From a statistical analysis, the percentage of failures for this type of interventions is around 25-30%. The aim of my PhD thesis was the improvement of the knowledge of the strain distribution on biological tissues, in particular on ligaments and intervertebral discs of the human spine. The first part of this thesis aimed at improvement of the methodologies used to measure the strain distribution, simultaneously on hard (vertebrae) and soft tissues (ligaments and intervertebral discs), using Digital Image Correlation. The second part of my research studied the biomechanical behaviour of the intervertebral discs and of the different ligaments. The disc acts as a shock absorber for the spine, reducing shocks and impacts. The anterior longitudinal ligament (ALL), supraspinous and interspinous ligaments were studied analysing how they were deformed under different loading conditions. These ligaments limit the movement of the spine during flexion reducing the overload on the intervertebral disc. The ALL does not offer great mechanical strength during lateral bending and axial torsion. Summarizing, the study underlines the necessity of having a full-field strain analysis tool to enhance the knowledge of the biomechanics of the spine and the interaction between different types of tissue. Furthermore, the results reported in this thesis could be useful also to build better multibody spine models and to include more realistic properties in finite element models. These results could be a starting point for future works in which the effect of different surgical procedures and the use of new surgical devices could be investigated