Biomechanical Comparison of Posterior Fixation Combinations with an Allograft Spacer between the Lateral Mass and Pedicle Screws

Background: There are a few biomechanical studies that describe posterior fixation methods with pedicle screws (PS) and lateral mass screws (LMS); the combination of both screw types and their effect on an allograft spacer in a surgically treated cervical segment is unknown. Methods: Finite element model (FEM) analyses were used to investigate the effects of a hybrid technique using posterior PS and LMS. Stress distribution and subsidence risk from a combination of screws under hybrid motion control conditions, including flexion, extension, axial rotation, and lateral bending, were investigated to evaluate the biomechanical characteristics of different six-screw combinations. Findings: The load sharing on the allograft spacer in flexion mode was highest in the LMS model (74.6%) and lowest in the PS model (35.1%). The likelihood of subsidence of allograft spacer on C6 was highest in the screws from the distal LMS (type 5) model during flexion and extension (4.902 MPa, 30.1% and 2.189 MPa, 13.4%). In lateral bending, the left unilateral LMS (type 4) model screws on C5 (3.726 MPa, 22.9%) and C6 (2.994 MPa, 18.4%) yielded the greatest subsidence risks, because the lateral bending forces were supported by the LMS. In counterclockwise axial rotation, the left unilateral LMS (type 4) model screws on C5 (3.092 MPa, 19.0%) and C6 (3.076 MPa, 18.9%) demonstrated the highest subsidence risks. Conclusion: The asymmetrical ipsilateral use of LMS and posterior PS in lateral bending and axial rotation demonstrated the lowest stability and greatest subsidence risk. We recommend bilateral symmetrical insertion of LMS or posterior PS and posterior PS on distal vertebrae for increased stability and reduced risk of allograft spacer subsidenceope

Factors affecting accuracy and fusion rate in lumbosacral fusion surgery - a preclinical and clinical study

Lumbosacral fusion surgery is indicated in symptomatic degenerative lumbosacral disorder, when the origin of pain is demonstrated to lie within the restricted number of functional spinal units and when the pain is refractory to the conservative treatment, to eliminate painful motion of the spinal units. Inaccurate placement of pedicle screws may cause neurological symptoms, and result in early hardware failure and return of spinal instability symptoms. All spinal instrumentation eventually fails without solid bony fusion, and the presence of symptomatic bony non-union at least a year after fusion surgery is defined as pseudoarthrosis. Bioactive glasses (BAGs) are synthetic, biocompatible, osteoconductive and osteostimulative materials with angiogenic and antibacterial properties, able to bond to bone. In a study of 147 patients and 837 pedicle screws placed due to degenerative lumbosacral spine disorder, 14.3 % breached the pedicle. New neurological symptoms corresponding to the breach were observed in 25.9 % of patients with pedicle breach, and 89.2 % of the symptomatic breaches were either medially or inferiorly. A preclinical controlled study of novel BAG S53P4 putty showed good biocompatibility, slightly higher intramedullary ossification of putty group compared to the control group, and that the binder agent did not disturb formation of new bone in vivo. The interbody fusion rate was 95.8 % with BAG S53P4 putty as bone graft expander with autograft in clinical lumbosacral interbody fusion, indicating at least as good interbody fusion results as the presently used materials. One early operative subsidence remaining unchanged over the study period was observed with putty.Lannerangan luudutusleikkausten tarkkuuteen ja luutumiseen vaikuttavat tekijät Lannerangan luudutusleikkaus voidaan tehdä oireisessa lannerangan rappeumasairaudessa, kun kivun syyn on osoitettu sijaitsevan rajallisessa määrässä selkärangan toiminnallisia yksikköjä ja kun kipu ei vähene leikkauksettomilla hoidoilla. Leikkauksella voidaan poistaa kipua tuottava selkärangan toiminnallisten yksikköjen liike. Epätarkka pedikkeliruuvien asettaminen voi aiheuttaa neurologisia oireita ja johtaa nopeaan kiinnitysosien irtoamiseen ja rangan epätukevuusoireiden palaamiseen. Suuri osa selkärangan kiinnityslaitteista irtoaa lopulta, jollei luutumista kiinnitettyjen kohtien välillä tapahdu. Vuoden kuluttua luudutusleikkauksesta oireista luutumatonta kiinnityskohtaa nimitetään pseudoartroosiksi. Bioaktiiviset lasit ovat synteettisiä, bioyhteensopivia, osteokonduktiivisia ja osteostimulatiivisia materiaaleja, joilla on angiogeenisiä ja antibakteerisia ominaisuuksia, ja ne voivat sitoutua suoraan luuhun. 147 potilaalle lannerangan rappeumasairauden vuoksi asetetut 837 pedikkeliruuvia käsittävän tutkimuksen mukaan 14.3 % ruuveista rikkoi luisen pedikkelin seinämän. 25.9 %:lla potilaista, joilla ruuvi läpäisi pedikkelin seinämän, ilmeni uusia neurologisia oireita, ja 89.2 %:lla oireisista potilaista pedikkeliruuvi läpäisi pedikkelin seinämän mediaalisesti tai inferiorisesti. Prekliinisessä kontrolloidussa tutkimuksessa uudenlainen bioaktiivisesta lasista valmistettu S53P4 luunkorviketahna todettiin bioyhteensopivaksi, ja sen avulla saavutettiin hieman vertailuryhmää parempi luutuminen luuydinontelossa. Tahnan sidosaineen ei eläinkokeessa todettu häiritsevän luun muodostumista. Kliinisessä tutkimuksessa saavutettiin 95.8 %:n luutuminen käytettäessä S53P4 biolasitahnaa yhdessä oman luun kanssa lannerangan nikamasolmujen välisessä luudutuksessa. Siten yhdessä oman luun kanssa käytettäessä S53P4 biolasitahnalla saadaan aikaan vähintään yhtä hyvä nikamasolmujen välinen luutuminen kuin nykyisin käytettävillä synteettisillä luunkorvikkeilla. Tutkimuksessa todettiin yksi leikkauksen yhteydessä tapahtunut nikamasolmujen välisen implantin päätelevyyn painuminen, jonka suuruus ei muuttunut seurantakuvantamisissa

Memory metal in lumbar spinal fusion:biological, mechanical, clinical and radiological studies

Over the past 50 years, both surgical techniques and instrumentation for lumbar fusion have changed significantly. The goal of these changes is obviously to improve the success rates of lumbar fusion, and thus the clinical outcome measures. The specific goal of this dissertation aligns with this; to study various aspects of lumbar fusion, with the end goal of improving outcomes. What factors influence the occurrence of a successful fusion? Can we improve clinical and radiological outcomes with the introduction of new implants made of memory metal? Is there a tool that can help us better predict lumbar fusion? After describing the problem of chronic back pain, we started with basic laboratory research. We investigated whether leaving disc tissue behind while performing a lumbar fusion, theoretically, also affects the biological process of bone formation. The new implants made of memory metal are being investigated in 4 different studies. An in vitro biomechanical evaluation of the lumbar Memory Metal Spinal System (MMSS). Then, a prospective, non-comparative study of 27 patients to evaluate the safety and performance of the Memory Metal Spinal System. A biomechanical cadaver study to evaluate the primary stability and degree of acute subsidence when using two new Memory Metal Minimal Access Cage (MAC) designs. After demonstrating the MAC biomechanical behaviour, we proceeded to test them in an in vivo pilot study. This single-center, prospective, non-comparative study of 25 patients is being conducted to evaluate the safety and performance of the Memory Metal Minimal Access Cage (MAC) in Lumbar Interbody Fusion. The purpose of the last described study was to evaluate changes in bone mineral density (BMD) in the transverse fusion mass as a derivative for the process of bone remodelling after posterolateral spinal fusion

Variation in Prevertebral Soft Tissue Swelling after Staged Combined Multilevel Anterior-Posterior Complex Cervical Spine Surgery: Anterior Then Posterior (AP) versus Posterior Then Anterior-Posterior (PAP) Surgery

The influence of the sequence of surgery in the development of prevertebral soft tissue swelling (PSTS) in staged combined multilevel anterior-posterior complex spine surgery was examined. This study was conducted as a retrospective study of patients who underwent staged combined multilevel anterior-posterior complex cervical spine surgery from March 2014 to February 2021. Eighty-two patients were identified, of which fifty-seven were included in the final analysis after screening. PSTS was measured from routine serial monitoring lateral cervical radiographs prior to and after surgery for five consecutive days at each cervical level from C2 to C7 in patients who underwent anterior then posterior (AP) and posterior then anterior-posterior (PAP) surgery. The mean PSTS measurements significantly differed from the preoperative to postoperative monitoring days at all cervical levels (p = 0.0000) using repeated measures analysis of variance in both groups. PSTS was significantly greater in PAP than in AP at level C2 on postoperative day (POD) 1 (p = 0.0001). PSTS was more prominent at levels C2-4 during PODs 2-4 for both groups. In staged combined multilevel anterior-posterior complex spine surgery, PSTS is an inevitable complication. Therefore, surgeons should monitor PSTS after surgery when performing anterior-posterior complex cervical spine surgery, especially in the immediate postoperative period after PAP surgery.ope

'Clinical Triad' findings in Klippel-feil patients

E-Poster - Congenital Deformity: no. 530It has been propagated that Klippel-Feil Syndrome (KFS) is associated with the clinical triad findings (CTF) of short neck, low posterior hairline, and limited range of motion. This study noted that CTFs are not consistently noted in KFS patients. KFS patients with extensive congenitally fused cervical segments were more likely to exhibit one of the components of CTF.postprin

Selection of fusion levels in adolescent idiopathic scoliosis (AIS) using the fulcrum bending radiograph prediction: verification based on pedicle screw strategy

E-Poster - Adolescent Idiopathic Scoliosis: no. 297Utilizing the fulcrum bending radiographic technique to assess curve flexibility to aid in the selection of fusion levels, a prospective radiographic study was performed to assess the safety and effectiveness of pedicle screw fixation with alternate level screw strategy (ALSS) for thoracic AIS. This study suggests that ALSS obtains greater deformity correction than hook and hybrid systems, and improves balance without compromising fusion levels.postprin

The safety and efficacy of a remotely distractible, magnetic controlled growing rod (MCGR) for the treatment of scoliosis in children: a prospective case series with minimum two year follow-up

Concurrent Session 2B - Early Onset Scoliosis: paper no. 26SUMMARY: The growing rod has been the gold standard for the treatment of scoliosis in young children. However, such management requires multiple open surgeries under general anesthesia for rod distraction and is associated with numerous postoperative complications. To avoid such pitfalls, we utilized a magnetically-controlled growing rod (MCGR) implant. Our study found that the MCGR was safe and effective, allowing for distractions on a non-invasive out-patient basis at monthly intervals, eliminating the need for surgeries and their associated complications. Introduction: Traditionally, growing rods are the standard of treatment for young children with severe spinal deformities and significant residual growth potential. However, this requires repeated open distractions under general anesthesia and is associated with numerous post-operative complications. This report addresses the safety and efficacy of the MCGR implant for non-invasive out-patient distractions for scoliosis correction in young children. METHODS: This was a prospective, patient series of the MCGR procedure. From November 2009 to March 2011, five patients (n=3 female; n=2 male) were treated with the MCGR. In this study, we report the first three patients (2 females and 1 male) with minimum 2 years follow-up. All cases were non-invasively distracted using an external magnet on a monthly basis. Pre and post distraction radiographs were carried out to assess the Cobb’s angle, predicted versus achieved rod distraction length and spinal length. Clinical outcome assessment was performed with the pain score (Visual Analogue Scale) and the SRS-30 questionnaire. All procedural or rod related complications were recorded. RESULTS: The main correction of the Cobb’s angle was obtained in the initial surgery and was maintained. The mean monthly increase in T1-T12, T1-S1 and instrumented segment length was 1.6mm, 2.5mm and 1.2mm, respectively. Predicted versus actual length gain per distraction were similar. One case had a superficial wound infection and there was one event of loss of distraction. On last follow-up, no pain was noted and SRS-30 scores remained unchanged to baseline. CONCLUSION: The MCGR is a safe and effective procedure for the surgical treatment of scoliosis in children. The MCGR provides external distractions on an out-patient basis without the need for sedation or anesthesia, and that remote distraction allows more frequent lengthening of the rod that may more closely mimic physiologic growth.postprin

Next generation of growth-sparing techniques: preliminary clinical results of a magnetically controlled growing rod in 14 patients

Session 3A - Early Onset Scoliosis: Paper no. 33SUMMARY: Growth-sparing techniques are commonly used for the treatment of progressive EOS. The standard growing rod (GR) technique requires multiple surgeries for lengthening. The preliminary results of MCGR has shown the comparable outcomes to standard GR without the need for repeated surgery which can be expected to reduce the overall complication rate in GR surgery. INTRODUCTION: The growing rod (GR) technique for management of progressive Early-Onset Scoliosis (EOS) is a viable alternative but with a high complication rate attributed to frequent surgical lengthenings. The safety and efficacy of a non-invasive Magnetically Controlled Growing Rod (MCGR) has been previously reported in a porcine model. We are reporting the preliminary results of this technique in EOS. METHODS: Retrospective review of prospectively collected multi-center data. Only patients who underwent MCGR surgery and at least 3 subsequent spinal distractions were included in this preliminary review. Distractions were performed in clinic without anesthesia or analgesics. T1-T12 and T1-S1 height and the distraction distance inside the actuator were analyzed in addition to conventional clinical and radiographic data. RESULTS: Patients (N=14; 7 F and 7 M) had a mean age of 8y+10m (3y+6m to 12y+7m) and underwent a total of 14 index surgeries (SR: index single rod in 5 and DR: dual rod in 9) and 91 distractions. There were 5 idiopathic, 4 neuromuscular, 2 congenital, 2 syndromic and one NF. Mean follow-up (FU) was 10 months (5.8-18.2). Mean Cobb changed from 57° pre-op to 35° post-op and correction was maintained (35°) at latest FU. T1-T12 increased by 4 mm for SR and 10 mm for DR with mean monthly gain of 0.5 and 1.39, respectively. T1-S1 gain was 4 mm for SR and 17 mm for DR with mean monthly gain of 0.5 mm for SR and 2.35 mm for DR. The mean interval between index surgery and the first distraction was 66 days and thereafter was 43 days. Complications included one superficial infection in (SR), one prominent implant (DR) and minimal loss of initial distraction in three after index MCGR (all SR). Overall, partial loss of distraction was observed following 14 of the 91 distractions (one DR and 13 SR). This loss was regained in subsequent distractions. There was no neurologic deficit or implant failure. CONCLUSION: MCGR appears to be safe and provided adequate distraction similar to the standard GR technique without the need for repeated surgeries. DR patients had better initial curve correction and greater spinal height. No major complications were observed during the short follow-up period. The FDA has not cleared the drug and/or medical device for the use described in this presentation (i.e., the drug or medical device is being discussed for an ‘off label’ use).postprin

Keeping a Chin Up in the Face of Adjacent Segment Pathology: A Biomechanical Analysis of Prophylactic Treatments for Proximal Junctional Kyphosis in Adult Spinal Fusions

The use of prophylactic tethers for treatment of proximal junctional kyphosis has been gaining clinical interest in recent years. There is currently no clinical consensus on appropriate technique and little biomechanical data to provide initial guidance. The intent of this work is to provide an improved understanding of the basic techniques relevant to spinal reconstructive surgery and to provide initial biomechanical characterization of basic tethering techniques. Three primary goals are proposed: 1) complete a review of spinal tethering techniques to determine the current state of the art of spinal tethering, 2) conduct a series of mechanical characterizations of basic tethering parameters in order to demonstrate their effects on spine biomechanics, and 3) provide concise engineering commentary and perspectives that help tie study findings to relevant clinical concepts and concerns. A review of the literature on spinal tethering resulted in six common techniques, twelve devices, and only six publications to date focusing on tethering for prophylactic treatments in adult spinal deformity. The review indicated a severe lack in current understanding of biomechanical effects. The characterizations of basic technique parameters was done in a series of four biomechanical cadaveric studies which investigated the effects of tether tension, looping technique, and anchoring methods on segment range of motion, intervertebral disc pressures, spinous process loads, and failure modes. The primary results indicate that tether tension plays a significant role in the effectiveness/effect of a tethering technique and that increased spinous process loads are most critical at the uppermost tethered level. Additional findings indicate that the combination of varying multiple technique parameters allows for great flexibility in treatment strategies. While basic in nature, the results found in this work stand are the first of their kind and provide a basis upon which further investigations may better elucidate the relationship of tethering techniques to clinical outcomes