Jenni Buckley

How placement affects force and contact pressure between a volar plate of the distal radius and the flexor pollicus longus tendon: a biomechanical investigation

Open reduction and internal fixation of a distal radius fracture can leave a volar plate in close proximity or touching the tendons of the wrist. This cadaveric study examines the how volar plate position changes contact pressure and force against the flexor pollicis longus (FPL) tendon in multiple wrist extension positions. This study suggests that moving the plate from an ideal position (distal edge at the watershed line) to a malposition (5 mm distal to the watershed line) significantly increased the force by 72.7% and contact pressure by 33.5% on the FPL. Multiple clinical case reports have described rupture of the flexor tendons associated with distally positioned plates or protruding screw heads, creating prominent or sharp edges. This study illustrates that in order to minimize contact pressure on the flexor tendons, plating distal to the watershed line should be avoided when possible.

Biomechanical Evaluation of an Interfacet Joint Decompression and Stabilization System

A majority of the middle-aged population exhibit cervical spondylosis that may require decompression and fusion of the affected level. Minimally invasive cervical fusion is an attractive option for decreasing operative time, morbidity, and mortality rates. A novel interfacet joint spacer (DTRAX facet screw system, Providence Medical) promises minimally invasive deployment resulting in decompression of the neuroforamen and interfacet fusion. The present study investigates the effectiveness of the device in minimizing intervertebral motion to promote fusion, decompression of the nerve root during bending activity, and performance of the implant to adhere to anatomy during repeated bending loads. We observed flexion, extension, lateral bending, and axial rotation resonant overshoot mode (ROM) in cadaver models of c-spine treated with the interfacet joint spacer (FJ spacer) as stand-alone and supplementing anterior plating. The FJ spacer was deployed bilaterally at single levels. Specimens were placed at the limit of ROM in flexion, extension, axial bending, and lateral bending. 3D images of the foramen were taken and postprocessed to quantify changes in foraminal area. Stand-alone spacer specimens were subjected to 30,000 cycles at 2 Hz of nonsimultaneous flexion-extension and lateral bending under compressive load and X-ray imaged at regular cycle intervals for quantitative measurements of device loosening. The stand-alone FJ spacer increased specimen stiffness in all directions except extension. 86% of all deployments resulted in some level of foraminal distraction. The rate of effective distraction was maintained in flexed, extended, and axially rotated postures. Two specimens demonstrated no detectable implant loosening (<0.25 mm). Three showed unilateral subclinical loosening (0.4 mm maximum), and one had subclinical loosening bilaterally (0.5 mm maximum). Results of our study are comparable to previous investigations into the stiffness of other stand-alone minimally invasive technologies. The FJ spacer system effectively increased stiffness of the affected level comparable to predicate systems. Results of this study indicate the FJ spacer increases foraminal area in the cervical spine, and decompression is maintained during bending activities. Clinical studies will be necessary to determine whether the magnitude of decompression observed in this cadaveric study will effectively treat cervical radiculopathy; however, results of this study, taken in context of successful decompression treatments in the lumbar spine, are promising for the continued development of this product. Results of this biomechanical study are encouraging for the continued investigation of this device in animal and clinical trials, as they suggest the device is well fixated and mechanically competent.

Method to Quantify Cadence Variability of Individuals with Lower-Limb Amputation

Introduction The ability to walk with different cadences (cadence variability) is considered an important factor for determining the functional ability of individuals with lower-limb amputation and making prosthetic recommendations. However, a method to quantify cadence variability of these individuals has never been presented before, so there are no standardized methodologies or values to guide prosthesis prescription. The purpose of this study was to develop and demonstrate feasibility of a method to quantify real-world cadence variability. Materials and Methods The method utilizes step-count data collected by an accelerometer-based activity monitor. Cadence at each minute is calculated. Then, the spread of the cadence data distribution during a 7-day observation period is measured to quantify cadence variability. To demonstrate feasibility, this method was applied to a set of step-count data for individuals with unilateral lower-limb amputation classified by their health care provider as a K2 or K3 ambulator. Results Results showed that this method was able to differentiate the cadence characteristics of individuals classified as K2 versus K3. On average, individuals classified as K2 walked with significantly less cadence variability than those classified as K3. Conclusions This study provides a novel method for objectively determining cadence variability and provides a foundation for ultimately developing normative cadence characteristic values for K2 and K3 levels.

Modular Steering and Braking System for Assistive Bicycling

There are a variety of commercially available cycling systems for users with physical disabilities. These include arm-driven recumbent bicycle and tricycle frames for individuals with limited leg function and tandem system for visually or mobility-impaired individuals. More complex adaptive cycling systems, such as the BerkelBike, have also been developed, which have integrated arm and leg driving mechanisms as well as on-board motor assistance and, in some cases, Functional Electrical Stimulation (FES). These units cost upwards of US

Research-Focused Undergraduate Laboratory Exercises in Biomechanics

8,000 and are beyond the price range of many individuals and community centers. All current assistive cycling systems also require some degree of fine motor control, either in the torso or the arms, to control steering and braking mechanisms. That would make these systems inaccessible for individuals with severe motor control disabilities, such as Parkinsons or advanced MS.Copyright

Development of a Biomechanical Model Producing Proximal Pedicle Pullout of Long Fusion Spinal Constructs

Undergraduate laboratory exercises in core engineering courses do not always subscribe to the Problem Based Learning approaches advocated by the educational community [1–3]. Common shortcomings include “cookie cutter” labs where students are not engaged in experimental design as well as a general detachment from the “real world” application of the laboratory exercise. Soft skills like proper documentation during experiments as well as scientific writing may also be overlooked in lab curricula. This is unfortunate, as the undergraduate laboratory experience is a perfect opportunity to develop essential research skills as well as inspire and excite students about their chosen field.Copyright

Development of a Biomechanical Model for Sacroiliac Range of Motion

Proximal pedicle screw pullout is a common clinical occurrence for long fusion constructs. Recently, novel spinal hardware and surgical techniques have been in development to alleviate this complication [1]. However, there is currently no biomechanical model to simulate this mode of failure in vitro to adequately evaluate these strategies in a rigorous laboratory setting. Standard pure moment loading and range of motion testing are not equipped to reproduce this failure modality [2] and a vast majority of such outcomes have merely been observed clinically [3]. It is hypothesized that a combination of anterior-posterior (AP) shear and compressive force is required to induce screw pullout with clinically similar fatigue patterns. The goal of this preliminary study is the development of such a biomechanical model to simulate clinically observed proximal pedicle screw failure.Copyright

Effect of varus and valgus alignment on implant loading after proximal femur fracture fixation

In the last seven years, increasing interest has been shown in the sacroiliac (SI) joint. Recent evidence has shown that more than 22% of lower back pain cases are caused by SI joint instability. Sacroiliac joint problems mimic discogenic and/or radicular low back pain, leading to many misdiagnoses (Weksler 2007). Over the last decade, SI fusion devices have been developed and have achieved clinical success (Wise 2008). However, there is no standard biomechanical testing procedure for SI fusion devices, although such a protocol would benefit further product development and comparison testing. The goal of our study is to develop a biomechanical model of sacroiliac range of motion. This study puts forth two methods of producing SI ROM: one model simulating a single leg stance and the second model simulating double leg stance. Our hypothesis was that the single leg stance model would produce ROM similar to what has been observed in vivo; the double leg stance model would produce ROM significantly lower. We aimed to test this hypothesis through comparison of ROM for both models and in vivo results obtained from the literature.Copyright