Comparisons of physical exposure between workers harvesting apples on mobile orchard platforms and ladders, part 1: Back and upper arm postures.

This study compared farmworkers' exposure to non-neutral postures using a new mobile platform apple harvesting method and the traditional method using ladders. Twenty-four workers were recruited and assigned into three groups: ladder workers (n = 8) picking apples from full trees using a ladder, mobile platform workers (n = 8) picking apples from upper part of the trees while standing on a moving platform, and ground-based mobile platform workers (n = 8) picking apples from lower part of the trees which the mobile platform workers left out. Upper arm and back inclinations were continuously monitored during harvesting using tri-axial accelerometers over full work shifts (~8 h).

Comparisons of physical exposure between workers harvesting apples on mobile orchard platforms and ladders, part 2: Repetitive upper arm motions.

Farmworkers are exposed to physical risk factors including repetitive motions. Existing ergonomic assessment methods are primarily laboratory-based and, thus, inappropriate for use in the field. This study presents an approach to characterize the repetitive motions of the upper arms based on direct measurement using accelerometers.

Accuracy and Precision of a Surgical Navigation System: Effect of Camera and Patient Tracker Position and Number of Active Markers.

Introduction: Surgical navigation systems are increasingly used to aid resection and reconstruction of osseous malignancies. In the process of implementing image-based surgical navigation systems, there are numerous opportunities for error that may impact surgical outcome. This study aimed to examine modifiable sources of error in an idealized scenario, when using a bidirectional infrared surgical navigation system.

Performance of Alpine Touring Boots When Used in Alpine Ski Bindings.

Alpine touring (AT) equipment is designed for ascending mountains and snow skiing down backcountry terrain. Skiers have been observed using AT boots in alpine (not made for Alpine Touring) ski bindings. We tested the effect on the retention-release characteristics of AT boots used in alpine bindings.

Head Impact Exposure During a Weekend Youth Soccer Tournament.

Concussion is a known risk in youth soccer, but little is known about subconcussive head impacts. The authors provided a prospective cohort study measuring frequency and magnitude of subconcussive head impacts using accelerometry in a middle school-age soccer tournament, and association between head impacts and changes in (1) symptoms, (2) cognitive testing, and (3) advanced neuroimaging. A total of 17 youth completed the study (41% female, mean 12.

Articular congruency of the Salto Talaris total ankle prosthesis.

Background: The Salto-Talaris polyethylene articulating surface was designed to allow, but limit accessory motion. This investigation examines surface characteristics between the polyethylene bearing and anatomic talar component in various positions of function.

Methods: A Salto Talaris talar prosthesis and matching polyethylene bearing were scanned to create digital solid body models and manipulated to assess surface contact during simulated gait.

Effect of simulated early weight bearing on micromotion and pullout strength of uncemented distal femoral stems.

The effect of simulated early weight bearing on both micromotion and pullout strength of uncemented distal femoral stems was evaluated in this study. The effect of stem endosteal contact and bone quality on implant pullout strength was also analyzed. A randomized matched-pair study was performed using 8 bilateral pairs of fresh human cadaveric femoral specimens.

Biomechanical evaluation of metacarpal fracture fixation: application of a 90° internal fixation model.

Purpose: Complications in metacarpal fracture treatment increase in proportion to the severity of the initial injury and the invasiveness of the surgical fixation technique. This manuscript evaluates the feasibility of minimizing internal fixation construct size and soft tissue dissection, while preserving the advantages of stable internal fixation in a biomechanical model. We hypothesized that comparable construct stability could be achieved with mini-plates in an orthogonal (90/90) configuration compared with a standard dorsal plating technique.

Whole-body Vibration Exposure Intervention among Professional Bus and Truck Drivers: A Laboratory Evaluation of Seat-suspension Designs.

Long-term exposure to seated whole-body vibration (WBV) is one of the leading risk factors for the development of low back disorders. Professional bus and truck drivers are regularly exposed to continuous WBV, since they spend the majority of their working hours driving heavy vehicles. This study measured WBV exposures among professional bus and truck drivers and evaluated the effects of seat-suspension designs using simulated field-collected data on a vibration table.

Assessment of registration accuracy during computer-aided oncologic limb-salvage surgery.

Purpose: Computer-aided surgery is used in musculoskeletal tumor procedures to improve the surgeon's orientation to local anatomy during tumor resection. For the navigation system to function correctly, preoperative imaging (e.g.

The effect of hardhats on head and neck response to vertical impacts from large construction objects.

We evaluated the effectiveness of hardhats in attenuating head acceleration and neck force in vertical impacts from large construction objects. Two weight-matched objects (lead shot bag and concrete block) weighing 9.1 kg were dropped from three heights (0.

Burst fractures of the lumbar spine in frontal crashes.

Background: In the United States, major compression and burst type fractures (>20% height loss) of the lumbar spine occur as a result of motor vehicle crashes, despite the improvements in restraint technologies. Lumbar burst fractures typically require an axial compressive load and have been known to occur during a non-horizontal crash event that involve high vertical components of loading. Recently these fracture patterns have also been observed in pure horizontal frontal crashes.

Enhancing pedicle screw fixation in the lumbar spine using allograft bone plug interference fixation.

Study Design: A within-subjects controlled laboratory study.

Objective: To examine a biological alternative to cement augmentation for pedicle screw fixation comparing bilateral axial pullout tests of augmented and nonaugmented (controls) pedicle screws.

Summary Of Background Data: Fixation in the osteoporotic spine remains a difficult challenge with failure by loosening or backout.

Developmental biomechanics of the human cervical spine.

Head and neck injuries, the leading cause of death for children in the U.S., are difficult to diagnose, treat, and prevent because of a critical void in our understanding of the biomechanical response of the immature cervical spine.

Coupling between the spinal cord and cervical vertebral column under tensile loading.

Current neck injury criteria are based on structural failure of the spinal (vertebral) column without consideration of injury to the spinal cord. Since one of the primary functions of the vertebral column is to protect the cord, it stands to reason that a more refined measure of neck injury threshold would be the onset of spinal cord injury (SCI). This study investigated the relationship between axial strains in the cervical vertebral column and the spinal cord using an in vitro primate model (n=10) under continuous tensile loading.

Developmental biomechanics of neck musculature.

Neck mechanics is central to head injury prevention since it is the musculoskeletal neck, which dictates the position and movement of the head. In the US, traumatic injury is the leading cause of death for children; however prevention is hampered by the lack of data concerning the mechanics of the immature head-and-neck. Thus, the objective of this study was to quantify neck muscle strength and endurance across the maturation spectrum and correlate these with head-and-neck anthropometry.

A comparison of the shock-absorbing properties of cervical disc prosthesis bearing materials.

Background Data: Cervical arthroplasty offers theoretical advantages over traditional spinal fusion, including elimination of adjacent segment disease and elimination of the risk of pseudoarthrosis formation. Initial studies of cervical arthroplasty have shown promising results, however, the ideal design characteristics for disc replacement constructs have not been determined. The current study seeks to quantify the differences in the shock absorption characteristics of three commonly used materials in cervical disc arthroplasty.

The effect of bilateral laminotomy versus laminectomy on the motion and stiffness of the human lumbar spine: a biomechanical comparison.

Study Design: A cadaveric simulation model of the lumbar spine was used to study the intervertebral motion characteristics of the lumbar spine after bilateral laminotomy and facet-sparing laminectomy.

Objective: To assess differences in motion patterns and lumbar spine stiffness after bilateral laminotomy versus laminectomy.

Summary Of Background Data: Spondylolisthesis after facet-sparing laminectomy has been reported with a frequency of 8% to 31%.

The efficacy of using vibrometry to detect osteointegration of the Agility total ankle.

Arthritis is a chronic, debilitating disease affecting one in six people in the United States annually. One of the most promising surgical treatments is total joint replacement. After decades of development, some joint replacement (arthroplasty) systems such as the hip and knee enjoy high success rates while others, particularly newer ones for the ankle, have disappointing survival rates.

Helmet and shoulder pad removal in football players with unstable cervical spine injuries.

Football, one of the country's most popular team sports, is associated with the largest overall number of sports-related, catastrophic, cervical spine injuries in the United States (Mueller, 2007). Patient handling can be hindered by the protective sports equipment worn by the athlete. Improper stabilization of these patients can exacerbate neurologic injury.

Dynamic tensile failure mechanics of the musculoskeletal neck using a cadaver model.

Although the catapult phase of pilot ejections has been well characterized in terms of human response to compressive forces, the effect of the forces on the human body during the ensuing ejection phases (including windblast and parachute opening shock) has not been thoroughly investigated. Both windblast and parachute opening shock have been shown to induce dynamic tensile forces in the human cervical spine. However, the human tolerance to such loading is not well known.

Intervertebral disc degeneration in a naturally occurring primate model: radiographic and biomechanical evidence.

Classic degenerative disc disease is a serious health problem worldwide, whose etiological basis-mechanical stimulus, biochemical changes, or natural aging-is poorly understood. Animal models are critical to the study of degenerative disc disease initiation and progression and for attempts to regulate, ameliorate, or eliminate it. The macaque represents a primate model with natural disc degeneration that might serve to advance the field; we aimed to provide radiographic (morphologic) and biomechanical evidence of natural disc degeneration in this model.

Translational constraint influences dynamic spinal canal occlusion of the thoracic spine: an in vitro experimental study.

Mechanical constraints to spine motion can arise in a variety of real-world situations such as when shoulder belts prevent anterior translation of the thorax during automotive collisions. The effect of such constraint on spinal column-spinal cord interaction during injury remains unknown. The purpose of the present study was to compare maximal dynamic spinal canal occlusion, measured via a specialized transducer, in cadaveric upper thoracic spine specimens under a variety of anterior-posterior constraint conditions.

Neural space and biomechanical integrity of the developing cervical spine in compression.

Study Design: A factorial study design was used to examine the biomechanical and neuroprotective integrity of the cervical spine throughout maturation using a postmortem baboon model.

Objective: To investigate changes with spinal development that affect the neuroprotective ability of the cervical spine in compressive loading.

Summary Of Background Data: Child spinal cord injuries claim and debilitate thousands of children in the United States each year.