The biomechanical effect of artificial and human bone density on stopping and stripping torque during screw insertion.

Orthopedic surgeons apply torque to metal screws manually by "subjective feel" to obtain adequate fracture fixation, i.e. stopping torque, and attempt to avoid accidental over-tightening that leads to screw-bone interface failure, i.

The biomechanics of three different fracture fixation implants for distal femur repair in the presence of a tumor-like defect.

The femur is the most common long bone involved in metastatic disease. There is consensus about treating diaphyseal and epiphyseal metastatic lesions. However, the choice of device for optimal fixation for distal femur metaphyseal metastatic lesion remains unclear.

Biomechanical properties of an advanced new carbon/flax/epoxy composite material for bone plate applications.

This work is part of an ongoing program to develop a new carbon fiber/flax/epoxy (CF/flax/epoxy) hybrid composite material for use as an orthopaedic long bone fracture plate, instead of a metal plate. The purpose of this study was to evaluate the mechanical properties of this new novel composite material. The composite material had a "sandwich structure", in which two thin sheets of CF/epoxy were attached to each outer surface of the flax/epoxy core, which resulted in a unique structure compared to other composite plates for bone plate applications.

The biomechanical effect of notch size, notch location, and femur orientation on hip resurfacing failure.

For hip resurfacing, this is the first biomechanical study to assess anterior and posterior femoral neck notching and femur flexion and extension. Forty-seven artificial femurs were implanted with the Birmingham hip resurfacing (BHR) using a range of notch sizes (0, 2, and 5 mm), notch locations (superior, anterior, and posterior), and femur orientations (neutral stance, flexion, and extension). Implant preparation was done using imageless computer navigation, and mechanical tests measured stiffness and strength.

Biomechanical measurements of surgical drilling force and torque in human versus artificial femurs.

Few experimental studies have examined surgical drilling in human bone, and no studies have inquired into this aspect for a popular commercially-available artificial bone used in biomechanical studies. Sixteen fresh-frozen human femurs and five artificial femurs were obtained. Cortical specimens were mounted into a clamping system equipped with a thrust force and torque transducer.

The biomechanical effect of proximal tumor defect location on femur pathological fractures.

Objectives: The femur is the most common long bone affected by cancerous metastasis. Femoral tumor defects are known to induce pain and functional impairment in patients. Although prior studies exist evaluating the clinical and biomechanical effect of tumor defect size, no biomechanical studies have experimentally examined the risk of pathological fracture with respect to the anterior, posterior, medial, and lateral surfaces on which a proximal tumor defect is located on the femur.

Biomechanical properties of an intact, injured, repaired, and healed femur: an experimental and computational study.

There is no "gold standard" treatment for femoral mid-shaft fractures near the tip of a hip implant. Moreover, no study has quantified the changes in a femur's mechanical properties from injury through to healing. The present aim was to predict overall stiffness and peak bone stress in the same femur after injury, repair, and healing with respect to its intact condition.

Biomechanical measurements of cortical screw stripping torque in human versus artificial femurs.

Femur fracture plates are applied using cortical bone screws. Surgeons do this manually by subjective 'feel' without monitoring torque. Few studies have quantified stripping torque in human bone.

Prognostic factors for predicting outcomes after intramedullary nailing of the tibia.

Background: Prediction of negative postoperative outcomes after long-bone fracture treatment may help to optimize patient care. We recently completed the Study to Prospectively Evaluate Reamed Intramedullary Nails in Patients with Tibial Fractures (SPRINT), a large, multicenter trial of reamed and unreamed intramedullary nailing of tibial shaft fractures in 1226 patients. Using the SPRINT data, we conducted an investigation of baseline and surgical factors to determine any associations with an increased risk of adverse events within one year of intramedullary nailing.

A preliminary biomechanical study of cyclic preconditioning effects on canine cadaveric whole femurs.

Biomechanical preconditioning of biological specimens by cyclic loading is routinely done presumably to stabilize properties prior to the main phase of a study. However, no prior studies have actually measured these effects for whole bone of any kind. The aim of this study, therefore, was to quantify these effects for whole bones.

Predictors of femoral neck fracture following hip resurfacing: a cadaveric study.

We aimed to establish if radiological parameters, dual energy x-ray absorptiometry (DEXA) and quantitative CT (qCT) could predict the risk of sustaining a femoral neck fracture following hip resurfacing. Twenty-one unilateral fresh frozen femurs were used. Each femur had a plain digital anteroposterior radiograph, DEXA scan and qCT scan.

Biomechanical measurements of axial crush injury to the distal condyles of human and synthetic femurs.

Few studies have evaluated the 'bulk' mechanical properties of human longbones and even fewer have compared human tissue to the synthetic longbones increasingly being used by researchers. Distal femur fractures, for example, comprise about 6% of all femur fractures, but the mechanical properties of the distal condyles of intact human and synthetic femurs have not been well quantified in the literature. To this end, the distal portions of a series of 16 human fresh-frozen femurs and six synthetic femurs were prepared identically for mechanical testing.

Changes in femoral cortical porosity after reaming and intramedullary canal preparation in a canine model.

This study examined changes in femoral cortical porosity resulting from femoral canal preparation during cemented total hip arthroplasty (THA). Twenty-four canines were randomly assigned to 3 groups: (1) reaming only, (2) cementing without pressurization, and (3) cementing with pressurization. Femoral cortical porosity was measured from histologic samples of the femurs at 7 positions.

The biomechanical effect of torsion on humeral shaft repair techniques for completed pathological fractures.

In the presence of a tumor defect, completed humeral shaft fractures continue to be a major surgical challenge since there is no "gold standard" treatment. This is due, in part, to the fact that only one prior biomechanical study exists on the matter, but which only compared 2 repair methods. The current authors measured the humeral torsional performance of 5 fixation constructs for completed pathological fractures.

A preliminary study of platelet activation after embolization of marrow contents.

Objectives: Intravasation of bone marrow contents into venous circulation and pulmonary embolization after intramedullary nailing may be coupled with the activation of coagulation and fibrinolytic cascades. The objective of this study was to assess hemostatic response to pulmonary extravasated marrow contents. We hypothesize that activation of platelet activity and the coagulation cascade may occur after embolization of marrow contents in an experimental animal model of intramedullary nailing.

A biomechanical comparison of static versus dynamic lag screw modes for cephalomedullary nails used to fix unstable peritrochanteric fractures.

Background: The gamma nail has an option to statically lock its lag screw (static mode) or to allow its lag screw to move within the nail to compress the intertrochanteric fracture (dynamic mode). The purpose of this study was to compare the biomechanical stiffness of static and dynamic lag screw modes for a cephalomedullary nail used to fix an unstable peritrochanteric fracture.

Methods: Unstable four-part peritrochanteric fractures were created in 30 synthetic femurs and fixed with Long Gamma 3 Nails.

Biomechanical stress maps of an artificial femur obtained using a new infrared thermography technique validated by strain gages.

Femurs are the heaviest, longest, and strongest long bones in the human body and are routinely subjected to cyclic forces. Strain gages are commonly employed to experimentally validate finite element models of the femur in order to generate 3D stresses, yet there is little information on a relatively new infrared (IR) thermography technique now available for biomechanics applications. In this study, IR thermography validated with strain gages was used to measure the principal stresses in the artificial femur model from Sawbones (Vashon, WA, USA) increasingly being used for biomechanical research.

The physiologic and pathologic effects of the reamer irrigator aspirator on fat embolism outcome: an animal study.

Objectives: Intramedullary reaming of long bones before nail insertion has been known to cause an increase in fat emboli introduction into the bloodstream, which is a potentially fatal phenomenon. The goal of this study was to assess whether the reamer irrigator aspirator (RIA) reamer can reduce fat embolic load compared with the standard AO reamer.

Methods: Fifteen pigs were prepared using an intravenous catheter inserted into the marginal ear vein for fluid balance and drug administration.

Femoral head lag screw position for cephalomedullary nails: a biomechanical analysis.

Objectives: The purpose of this study was to determine if lag screw position affects the biomechanical properties of a cephalomedullary nail used to fix an unstable peritrochanteric fracture.

Methods: Unstable peritrochanteric fractures were created in 30 synthetic femurs and repaired with Long Gamma 3 Nails using one of 5 lag screw positions: superior, inferior, anterior, posterior, or central. Radiographic measurements including tip-apex distance and a calcar referenced tip-apex distance were calculated from anteroposterior and lateral radiographs.

Computer navigation in the reduction and fixation of femoral shaft fractures: a randomized control study.

Objectives: We investigated the accuracy of reduction of intramedullary nailed femoral shaft fractures in human cadavers, comparing conventional and computer navigation techniques.

Methods: Twenty femoral shaft fractures were created in human cadavers, with segmental defects ranging from 9 to 53 mm in length (Winquist 3-4, AO 32C2). All fractures were fixed with antegrade 9 mm diameter femoral nails on a radiolucent operating table.

Ideal tibial intramedullary nail insertion point varies with tibial rotation.

Objectives: The aim of the study was to investigate how superior entry point varies with tibial rotation and to identify landmarks that can be used to identify suitable radiographs for successful intramedullary nail insertion.

Methods: The proximal tibia and knee were imaged for 12 cadaveric limbs undergoing 5° increments of internal and external rotation. Medial and lateral arthrotomies were performed, the ideal superior entry point was identified, and a 2-mm Kirschner wire inserted.

A preliminary biomechanical assessment of a polymer composite hip implant using an infrared thermography technique validated by strain gage measurements.

With the resurgence of composite materials in orthopaedic applications, a rigorous assessment of stress is needed to predict any failure of bone-implant systems. For current biomechanics research, strain gage measurements are employed to experimentally validate finite element models, which then characterize stress in the bone and implant. Our preliminary study experimentally validates a relatively new nondestructive testing technique for orthopaedic implants.

Pathophysiology of fat embolism: a rabbit model.

Objectives: The objective of this study was to assess the effects of fat embolism on rabbit physiology.

Methods: After anesthetic administration, both femoral condyles of the right knee only of 23 New Zealand white rabbits were exposed through a medial parapatellar approach to the knee. In the pulmonary fat embolism group (n = 15), the femoral canal was drilled in a retrograde fashion and then reamed and pressurized with a 1- to 1.

Function plateaus by one year in patients with surgically treated displaced midshaft clavicle fractures.

Background: Based on short-term (1 year or less) followup, primary fixation of displaced midshaft clavicle fractures reportedly results in better function compared with that reported for nonoperative methods. Whether better function persists beyond 1 year is unclear.

Questions/purposes: For displaced midshaft clavicle fractures, do the better mean Disabilities of the Arm, Shoulder and Hand (DASH) and Constant-Murley Shoulder (CSS) scores for operative versus nonoperative treatment at 1 year change between 1- and 2-year followup?

Patients And Methods: We previously reported 132 patients in a randomized prospective trial at 1 year, and here we report a further followup of 95 of the 132 patients (72%) at 2 years after injury.

A biomechanical comparison of epiphyseal versus metaphyseal fixed bone-conserving hip arthroplasty.

Background: The Birmingham Mid-Head Resection (BMHR) is a bone-conserving, short-stem alternative to hip resurfacing for patients with abnormal femoral head anatomy.

Methods: The current study examines whether a bone-preserving femoral component that is fixed into the femoral neck metaphysis provides a mechanical advantage in terms of resisting femoral neck fracture in comparison with a conventional hip resurfacing implant in a human cadaveric femoral model.

Results: Femora with a BMHR femoral component failed at an average of 23% less load than those prepared with a conventional hip resurfacing component (mean and standard deviation, 5434 ± 2297 compared with 7012 ± 2619 N; p < 0.