Nitinol Memory Rods Versus Titanium Rods: A Biomechanical Comparison of Posterior Spinal Instrumentation in a Synthetic Corpectomy Model.

Study Design: Biomechanical investigation.

Objective: To compare the biomechanical performance of nitinol memory metal rods and titanium rods when used as posterior spinal instrumentation in a synthetic model.

Methods: Biomechanical testing was performed using ultra-high-molecular-weight polyethylene blocks.

Proximity of the Neurovascular Bundle During Posterior-Lateral Meniscal Repair: A Comparison of the Transpatellar, Anteromedial, and Anterolateral Portals.

Purpose: To compare the neurovascular proximity of the transpatellar portal with that of the medial and lateral portals and to determine the safe penetration depth for an all-inside device for use on the posterior horn lateral meniscus.

Methods: Dissection of the popliteal fossa was performed in 10 cadaveric knees to identify all structures. Arthroscopy was performed using penetration depths of 10, 12, 14, and 16 mm with the all-inside system through the anteromedial, anterolateral, and transpatellar portals.

Pediatric Supracondylar Fractures: Variation in Fracture Patterns and the Biomechanical Effects of Pin Configuration.

Background: Transverse pediatric supracondylar fractures through the midolecranon fossa are frequently encountered and modeled in biomechanical studies. Our objective is to investigate the optimal pin configurations for low, sagittal oblique, and high fracture varieties that have not been previously investigated.

Methods: A total of 100 synthetic composite pediatric humeri were tested.

Adjustment of suboptimally placed lumbar pedicle screws decreases pullout strength and alters biomechanics of the construct: a pilot cadaveric study.

Background: Lumbar pedicle screws are placed for internal fixation and help to enhance bony fusion. Optimal screws are medially directed, should be parallel or pointing to the superior endplate, and penetrate 50%-80% of the vertebral body. "Nonparallel" pedicle screws can be inadvertently placed within the confines of the pedicle and vertebral body but are sometimes replaced to obtain a more acceptable postoperative image.

Biomechanical performance of rigid compared to dynamic anterior cervical plating: analysis of adjacent upper and lower level compressive forces.

Dynamic anterior cervical plating is well established as a means of enhancing graft loading and subsequent arthrodesis. Current concerns center on the degree of adjacent-level stress induced by these systems. The aim of this study was to evaluate and compare the load transferred to adjacent levels for single-level anterior cervical discectomy and fusion utilizing rigid compared to dynamic anterior plating systems.

The use of bioabsorbable screws to fix Type II odontoid fractures: a biomechanical study.

Object: Anterior screw fixation of the Type II odontoid fracture stabilizes the odontoid without restricting the motion of the cervical spine. The metal screw may limit bone remodeling because of stress shielding (if not placed properly) and limit imaging of the fracture. The use of bioabsorbable screws can overcome such shortcomings of the metal screws.

A quantitative analysis of tension band plating of the femur diaphysis.

Objectives: To measure quantitatively the strains in the concave and convex sides of a femur to substantiate the Arbeitsgemeinschaft für Osteosynthesefragen (AO) tension band principle.

Methods: Eight cadaveric fresh-frozen femurs were cleaned of soft tissue and prepared for mounting the strain gages (Vishay, Raleigh, NC). The student strain gages were mounted at the anterior, lateral and medial surfaces of a femur.

Biomechanics of humerus fracture fixation by locking, cortical, and hybrid plating systems in a cadaver model.

The goal of this study was to discover how locking or cortical screws or a hybrid of both would perform in stabilizing a simulated humerus fracture. We simulated stripping of screw threads or poor bone quality by overdrilling the screw hole, and also studied a control group with no overdrilling. A total of 38 fresh frozen cadaver humeri were divided into 2 groups: 16 undergoing overdrilling with a drill bit 0.

Comparison of allograft bone and titanium cages for vertebral body replacement in the thoracolumbar spine: a biomechanical study.

Background: When an anterior approach to repair a burst fracture is indicated, several devices can be used to restore spinal stability (eg, bone graft, free-standing titanium cage, and expandable titanium cage).

Objective: We compare the biomechanical stability and prices of each of these systems.

Materials And Methods: Eight fresh human cadaver T11 through L3 vertebral specimens were harvested and cleaned of soft tissues.

Traumatic spondylolisthesis of the axis: a biomechanical comparison of clinically relevant anterior and posterior fusion techniques.

Object: Surgical management of unstable traumatic spondylolisthesis of the axis includes both posterior and anterior fusion methods. The authors performed a biomechanical study to evaluate the relative stability of anterior fixation at C2-3 and posterior fixation of C-1 through C-3 in hangman's fractures.

Methods: Fresh-frozen cadaveric spine specimens (occipital level to T-2) were subjected to stepwise destabilization of the C1-2 complex, replicating a Type II hangman's fracture.

Anterior subaxial cervical spine fixation using a plate with single screw per vertebral body: a simple and efficient construct - clinical series and a cadaver study.

Objective: To report our experience with a novel construct for traumatic and nontraumatic cervical spine lesions that was validated by biomechanical studies of cadaver cervical spine.

Study Design: Consecutive cases of anterior cervical spine fixation performed over six years reviewed for stability offered by a construct comprising of a plate fixed by a single screw to each vertebral body.

Setting: A university hospital and a biomechanical lab.

Comparison of pressure effects on adjacent disk levels after 2-level lumbar constructs: fusion, hybrid, and total disk replacement.

Background: With increasing advocacy for the use of TDR procedure as a surgical alternative to fusion in the management of lumbar DDD, intradiskal pressures at the adjacent levels of spine have generated considerable interest. The common belief is that adjacent-level disk pressures will be lower after a TDR as opposed to conventional fusion. The aim of this study is to present the effect of different constructs on adjacent-level disk pressures in lumbar spine.

Changes in load distribution in the knee after opening-wedge or closing-wedge high tibial osteotomy.

The treatment of unicompartmental osteoarthritis of the knee by high tibial osteotomy has been carried out by closing-wedge osteotomy. The advantages for opening-wedge osteotomy are ease of procedure and improved correction with comparable short-term to midterm results. It is not known how the opening-wedge high tibial osteotomy procedure alters the load distribution between the medial and lateral compartments of the knee.

A biomechanical study of simulated femoral neck fracture fixation by cannulated screws: effects of placement angle and number of screws.

The angle of placement of hip screws to fix femoral neck fractures is still a controversial subject, and it must be addressed. In the study reported here, we compared the relative stiffness of fixation of simulated Pauwels type III femoral neck fractures fixed with either 2 or 3 cannulated screws implanted at 135 degrees, 145 degrees, and 150 degrees. Each femur was fixed with 2 or 3 cannulated screws and tested under axial loading and anteroposterior (AP) bending.

A biomechanical study of bankart lesion fixation - biodegradable ArthroRivet tack vs. suture repair.

Bioabsorbable fixation is commonly used in soft tissue procedures performed in the shoulder. ArthroRivettrade mark tacks (referred to as rivets here), made from a copolymer of 82% poly-L-lactic acid and 18% polyglycolic acid, were developed for the Bankart procedure. Although a previous in vivo study demonstrated favorable comparison of the fixation strength and absorption characteristics of this device with that of polyglyconate bioabsorbable tacks, there have been no published biomechanical studies of this rivet in the shoulder.

Accuracy of pedicle screw placement for lumbar fusion using anatomic landmarks versus open laminectomy: a comparison of two surgical techniques in cadaveric specimens.

Objective: We determined whether the accuracy of lumbar pedicle screw placement is optimized by performing a laminectomy before screw placement with screw entry point and trajectory being guided by pedicle visualization and palpation (Technique 1). This technique was compared with a technique using anatomic landmarks for pedicle screw placement (Technique 2). The biomechanical stability of the instrumented constructs, in the absence and presence of a laminectomy, was also compared.

A biomechanical study of posterior spinal instrumentation using pedicle screws with and without cross-links.

Objective: It is not clear from the studies reported in the literature whether the addition of cross-links to bilateral pedicle screws increases the stiffness of the construct significantly to fix multilevel vertebral bodies. The current study addresses the question of how cross-links change the rotational stiffness of constructs with 6, 12, and 20 pedicle screws.

Methods: Seven thoracolumbar 10-level spine segments (T4-L1), from individuals of average age 72 years (range 46-83 years), were instrumented with pedicle screws (6, 12, and 20) and tested in torsion with and without cross-links.

Distal tibiofibular syndesmosis fixation: a cadaveric, simulated fracture stabilization study comparing bioabsorbable and metallic single screw fixation.

Metal screws that are used for ruptured tibiofibular syndesmosis repair are often removed within 3 months of placement, suggesting the utility of bioabsorbable screws. A biomechanical study was performed to compare fixation of a simulated syndesmosis separation with a 5-mm oriented copolymer bioabsorbable (82:18 poly-L-lactic acid/poly-glycolic acid) versus a stainless steel screw. Eight pairs of cadaveric lower-leg specimens were cleaned and a pronation external rotation-type injury was created in each.

A biomechanical study of unilateral posterior atlantoaxial transarticular screw fixation.

The purpose of this study was to investigate the fixation of C1-C2 instability with the use of a unilateral screw. Transarticular screw placement across C1-C2 may be contra-indicated in up to 20% of specimens on at least one side because of anatomic variations or other pathological processes. Hence the current study looks into unilateral screw fixation of C1- C2 instability.

Bioabsorbable screw fixation in coracoclavicular ligament reconstruction.

The purpose of this study is to evaluate the biomechanical properties of stainless steel and bioabsorbable screw fixation of the clavicle to the base of the coracoid. Seven matched pairs of fresh frozen shoulders were prepared by removing all soft tissue except the acromioclavicular and coracoclavicular ligament complexes. The shoulders were randomly selected and fixed with 4.

A biomechanical study of femoral neck fracture fixation with the VHS Vari-Angle Hip Fixation System.

Femoral neck fracture fixation with a new device, the VHS Vari-Angle Hip Fixation System (Biomet Orthopaedics Inc, Warsaw, IN), was studied in 14 fresh-frozen cadaver femurs. A Pauwels class III fracture was simulated in these femurs. Seven femurs were fixed by placing the screw at a high (150 degrees) angle to the femoral axis; the other 7 femurs were fixed by placing the screw at a low (135 degrees) angle to the femoral axis.