Predicting Pedicle Screw Pullout and Fatigue Performance: Comparing Lateral Dual-Energy X-Ray Absorptiometry, Anterior to Posterior Dual-Energy X-Ray Absorptiometry, and Computed Tomography Hounsfield Units.

Background: As the prevalence and associated health care costs of osteoporosis continue to rise in our aging population, there is a growing need to continue to identify methods to predict spine construct integrity accurately and cost-effectively. Dual-energy x-ray absorptiometry (DEXA) in both anterior to posterior (AP) and lateral planes, as well as computed tomography (CT) Hounsfield units (HU), have all been investigated as potential preoperative predictive tools. The purpose of this study is to determine which of the 3 bone density analysis modalities has the highest potential for predicting pedicle screw biomechanics.

Novel microcomposite implant for the controlled delivery of antibiotics in the treatment of osteomyelitis following total joint replacement.

The objective of this study was to develop a novel microcomposite implant to be used in the treatment of osteomyelitis following total joint arthroplasty, with the dual purpose of releasing high local concentrations of antibiotic to eradicate the infection while providing adequate mechanical strength to maintain the dynamic or static spacer. Vancomycin-loaded microcomposite implants were fabricated by incorporating drug-loaded microparticles comprised of mesoporous silica into commonly employed polymethylmethacrylate (PMMA) bone cement, to yield a final drug loading of 10% w/w. In vitro release kinetics at 37°C were monitored by reverse-phase high-performance liquid chromatography, and compared to the release kinetics of current therapy implants consisting of drug alone incorporated at 10% w/w directly into PMMA bone cement.

K-wire Pull-Out Force After Multiple Redirection Attempts.

Purpose: To evaluate if redirecting a Kirschner wire (K-wire) through the same proximal hole will weaken the pull-out force and to test if multiple redirections will result in a continued stepwise decrease in pull-out force.

Methods: An Instron was used to test the pull-out force of K-wires using the peak initial failure load as a measure of failure of K-wire fixation. K-wires 0.

External fixator-augmented flexible intramedullary nailing of an unstable pediatric femoral shaft fracture model: a biomechanical study.

The objective of this study was to test the compressive strength and torsional stiffness provided by the addition of a two-pin external fixator to an unstable pediatric femoral shaft fracture model after being instrumented with flexible intramedullary nailing (FIMN), and to compare this to bridge plating and FIMN alone. A length-unstable oblique diaphyseal fracture was created in 15 pediatric sized small femur models. Fracture stabilization was achieved by three constructs: standard retrograde FIMN with two 3.

Sacral Endplate Penetrating Screw for Lumbosacral Fixation: A Cadaveric Biomechanical Study.

Background: Cortical bone trajectory is a relatively new alternative for instrumentation of the lumbar spine. When performing lumbosacral instrumentation, a novel S1 endplate penetrating screw (EPS) has been recently shown to have higher insertional torque than the traditional trajectory screw, but the biomechanical properties of this new trajectory are yet to be verified with the cadaveric studies.

Objective: To evaluate 2 screw trajectories in sacra using cyclic loading and pullout tests, and to determine whether bone quality had different effects on the 2 trajectories.

Degradation of Bioresorbable Mg-4Zn-1Sr Intramedullary Pins and Associated Biological Responses in Vitro and in Vivo.

This article reports the degradation and biological properties of as-drawn Mg-4Zn-1Sr (designated as ZSr41) and pure Mg (P-Mg) wires as bioresorbable intramedullary pins for bone repair. Specifically, their cytocompatibility with bone marrow derived mesenchymal stem cells (BMSCs) and degradation in vitro, and their biological effects on peri-implant tissues and in vivo degradation in rat tibiae were studied. The as-drawn ZSr41 pins showed a significantly faster degradation than P-Mg in vitro and in vivo.

Pedicle screws with modular head vs. preassembled head used in cortical bone trajectory: Can pars and pedicle fractures be prevented in osteoporotic bone?

Pars and pedicle fractures as a result of CBT (cortical bone trajectory) during pedicle screw placement have been reported. The primary aim of the study is to compare the fracture rate between screws with modular heads to screws with standard pre-assembled tulip heads. The secondary aim of the study is to determine the potential variables that can be identified prior to instrumentation in order to predict risk of fractures.

A biomechanical comparison of the two- and four-hole side-plate dynamic hip screw in an osteoporotic composite femur model.

Objectives: The objectives of this study were (1) to compare the axial and torsional stiffness of a dynamic hip screw with a two- and four-hole side-plate in a synthetic model of a healed and stable intertrochanteric femur fracture and (2) to evaluate the load to failure, as well as propensity to peri-implant fracture.

Methods: Fourth-generation synthetic composite femur models, simulating osteoporotic bone, were implanted with 135° dynamic hip screws (DHS) with either a two- or four-hole side-plate with or without a stable intertrochanteric fracture. Specimens were cyclically loaded up to a nondestructive load to determine the axial and torsional stiffness.

Temperature Rise in Kirschner Wires Inserted Using Two Drilling Methods: Forward and Oscillation.

Background: Kirschner wires (K-wires) are commonly used in orthopedic surgery. However, the loosening of the pins can lead to delayed or improper healing or infection. Wire loosening can occur by thermal necrosis that occurs due to heat produced during wire insertion.

C1 Lateral Mass Displacement and Transverse Atlantal Ligament Failure in Jefferson's Fracture: A Biomechanical Study of the "Rule of Spence".

Background: Jefferson's fracture, first described in 1927, represents a bursting fracture of the C1 ring with lateral displacement of the lateral masses. It has been determined that if the total lateral mass displacement (LMD) exceeds 6.9 mm, there is high likelihood of transverse atlantal ligament (TAL) rupture, and if LMD is less than 5.

Does Barbed Suture Repair Negate the Benefit of Peripheral Repair in Porcine Flexor Tendon?

Advances in suture material and geometry have fueled interest in barbed suture tenorrhaphy. Theoretically, barbed suture allows better load distribution, smoother gliding under pulleys, and improved tendon blood flow. Minimal data exist on whether barbed tendon repair may benefit from supplementation by a peripheral stitch.

Comparison of Barbed Sutures in Porcine Flexor Tenorrhaphy.

Barbed suture use has become more popular as technology and materials have advanced. Minimal data exist regarding performance of the 2 commercially available products, V-LocTM and StratafixTM in tendon repairs. The purpose of this study was to compare gap resistance and ultimate tensile strength of both suture materials and nonbarbed suture in a porcine ex vivo model.

Preventing Instrumentation Failure in Three-Column Spinal Osteotomy: Biomechanical Analysis of Rod Configuration.

Study Design: Biomechanical analysis.

Objectives: To show the role of additional rods and long-term fatigue strength to prevent the instrumentation failure on three-column osteotomies.

Summary Of Background Data: Three-column osteotomy such as pedicle subtraction osteotomy (PSO) and vertebral column resections are surgical correction options for fixed spinal deformity.

Heat Generation During Bone Drilling: A Comparison Between Industrial and Orthopaedic Drill Bits.

Objectives: Cortical bone drilling for preparation of screw placement is common in multiple surgical fields. The heat generated while drilling may reach thresholds high enough to cause osteonecrosis. This can compromise implant stability.

A comparison of Staphylococcus aureus biofilm formation on cobalt-chrome and titanium-alloy spinal implants.

The use of cobalt chrome (CoCr) implants in spinal surgery has become increasingly popular. However, there have been no studies specifically comparing biofilm formation on CoCr with that of titanium-alloy spinal implants. The objective of this study was to compare the difference in propensity for biofilm formation between these two materials, as it specifically relates to spinal rods.

Effect of Plasma Sterilization on the Hemostatic Efficacy of a Chitosan Hemostatic Agent in a Rat Model.

Introduction: The United States military has had success with chitosan (CS)-based hemostatic agents to control trauma-induced hemorrhages. Despite the positive reviews, additional physical forms of CS may enhance its hemostatic efficacy. Additionally, standard sterilization techniques may negatively affect the hemostatic efficacy of CS.

Fatigue Performance of Cortical Bone Trajectory Screw Compared With Standard Trajectory Pedicle Screw.

Study Design: Cadaveric biomechanical study.

Objective: To determine fatigue behavior of cortical bone trajectory (CBT) pedicle screws.

Summary Of Background Data: Cortical bone trajectory screws have been becoming popular in spine surgery; however, the long-term fatigue behavior of the new CBT screws remains understudied and limitations not well defined.

Cortical and Standard Trajectory Pedicle Screw Fixation Techniques in Stabilizing Multisegment Lumbar Spine with Low Grade Spondylolisthesis.

Background: Cortical screw (CS) fixation has been recently proposed as an alternative to the standard pedicle screw (PS) fixation technique. Biomechanical studies involving individual screw pullout and single level motion segment stabilization showed comparable performance of both techniques. However, whether this new fixation technique can be applied to the stabilization of multilevel lumbar segments with significant destabilization has been unclear.

Pars and pedicle fracture and screw loosening associated with cortical bone trajectory: a case series and proposed mechanism through a cadaveric study.

Background Context: Cortical bone trajectory (CBT) technique for pedicle screw placement in the lumbar spine has become more popular since its introduction in 2009. The distinct advantages of using the CBT technique involve increased screw purchase within the cortical bone and reduced surgical dissection. However, contrary to several favorable biomechanical results, there were anecdotal reports of clinical complications associated with CBT.

Unconstrained testing of spine with bi-axial universal testing machine.

Background: In-vitro biomechanical assessment of the spine reveals significant information on the mechanics of spinal disorders, treatment methods, and surgical implants. Specialized devices for the evaluation of spine biomechanics have thus become popular. However, these devices might not be affordable for all research groups.

Biomechanical comparison of Krackow locking stitch versus nonlocking loop stitch with varying number of throws.

Background: Common suture configuration techniques used for ligament and tendon grafts and repair are the Krackow locking stitch and a nonlocking loop stitch, such as a whipstitch. Clinically, the preferences of orthopaedic surgeons vary.

Hypothesis: The Krackow locking stitch and the nonlocking whipstitch, with varying suture loops, produce different biomechanical and physical effects on the tendon end.

Adaptive remodeling at the pedicle due to pars fracture: a finite element analysis study.

Object: Spondylolysis is a common condition among the general population and a major cause of back pain in young athletes. This condition can be difficult to detect with plain radiography and has been reported to lead to contralateral pars fracture or pedicle fracture in the terminal stages. Interestingly, some patients with late-stage spondylolysis are observed to have radiographic or CT evidence of a sclerotic pedicle on the side contralateral to the spondylolysis.

Load sharing in lumbar spinal segment as a function of location of center of rotation.

Object: The center (axis) of rotation (COR) in the lumbar spine has been studied well. However, there is limited information on the kinetic and kinematic consequences of imposed shift in the location of the COR, although this type of shift can be seen after surgeries using motion preservation or dynamic stabilization devices. The objective of this study was to assess the kinetic and kinematic changes in the lumbar spinal segment due to various imposed CORs.

Instantaneous center of rotation behavior of the lumbar spine with ligament failure.

Object: The goal of this study was to investigate the effect of ligament failure on the instantaneous center of rotation (ICR) in the lower lumbar spine.

Methods: A 3D finite element model of the L4-5 segment was obtained and validated. Ligament failure was simulated by reducing ligaments in a stepwise manner from posterior to anterior.

Multi-scale finite element modelling at the posterior lumbar vertebra: analysis of pedicle stresses due to pars fracture.

Multi-scale finite element (FE) model is a cost-effective way to analyse stress response of micro-level structures to the changes in loading at macro-level. This study deals with the development of a multi-scale model of a human vertebra and stress changes in the pedicle at high resolution after a gross fracture at the posterior neural arch. Spondylolysis (pars fracture) is a painful condition occurring in the vertebral neural arch and common especially among the athletic young population.