Preoperative imaging of cervical pedicles: comparison of accuracy of oblique radiographs versus axial CT scans.

In spite of concerns about safety during their insertion, cervical spine pedicle screws have demonstrated biomechanical superiority over lateral mass screws in several biomechanical studies. One of the concerns for placement of cervical pedicle screws is their small size. Preoperative planning with computed tomography to assess pedicle width has been shown to be extremely accurate and is recommended by several authors.

A biomechanical study of distal interphalangeal joint subluxation after mallet fracture injury.

Purpose: There is no consensus in the literature regarding the size of a mallet fracture fragment that may lead to subluxation of the distal interphalangeal (DIP) joint. The purpose of this study was to determine the relationship between the size of the dorsal articular fragment and DIP joint subluxation in a cadaveric mallet fracture model.

Methods: Twenty-nine fresh-frozen fingers without evidence of DIP joint osteophytes were dissected to the metacarpal base.

Mechanical evaluation of fracture fixation augmented with tricalcium phosphate bone cement in a porous osteoporotic cancellous bone model.

Objective: The purpose of this study was to examine the effects of resorbable bone cement on screw and plate-screw fracture fixation in a porous osteoporotic bone model.

Methods: Experiment 1: Screw pullout strength was assessed for 4 sets of 4.5-mm cortical screws inserted into a synthetic osteoporotic cancellous bone model, including screws inserted without cement augmentation (control), screws augmented with tricalcium phosphate (TCP) bone cement (Norian SRS; Synthes USA, Paoli, PA), and screws augmented with polymethylmethacrylate.

Cervical pedicle screws vs. lateral mass screws: uniplanar fatigue analysis and residual pullout strengths.

Background Context: Although successful clinical use of cervical pedicle screws has been reported, anatomical studies have shown the possibility for serious iatrogenic injury. However, there are only a limited number of reports on the biomechanical properties of these screws which evaluate the potential benefits of their application.

Purpose: To investigate if the pull-out strengths after cyclic uniplanar loading of cervical pedicle screws are superior to lateral mass screws.

Effects of surgical errors on small fragment screw fixation.

Objectives: The purpose of this study is to determine the effects of technical errors that occur during the application of small fragment screw fixation and to assess which screw holes can be salvaged.

Intervention: Testing of screw pullout from a bone substitute model on a universal testing instrument (Instron Corp., Canton, MA).

The effect of angled osteochondral grafting on contact pressure: a biomechanical study.

Background: Flush osteochondral plugs can reduce contact pressure compared with an empty defect in the articular cartilage. However, incongruities such as graft angulation have an unknown effect.

Hypothesis: Incongruity of the articular cartilage after osteochondral transplantation affects articular surface contact pressure.

Plantar forefoot pressure changes after second metatarsal neck osteotomy.

Background: The aim of this study was to evaluate plantar pressure changes after second metatarsal neck osteotomy using the Weil technique.

Methods: Six below-knee cadaver specimens were used. Each specimen was held in a custom-built apparatus and loaded to 500 N for a period of 3 seconds.

The effect of graft height mismatch on contact pressure following osteochondral grafting: a biomechanical study.

Hypothesis: Incongruity of the articular cartilage following osteochondral transplantation affects surface contact pressure.

Study Design: An 80 N load was applied for 120 seconds to the femoral condyles of 10 swine knees. Contact pressures were measured using Fuji prescale film.

Effects of sterilization on the Tekscan digital pressure sensor.

Investigations into the effects of sterilization on a new biomechanical pressure sensor are necessary before contemplating in vivo use. Ten, designated Experimental, "K-Scan" digital pressure sensor arrays were sterilized with ethylene oxide gas (EtO), and their ability to accurately and reproducibly measure an applied load of 2225 N (500 lb) was assessed. Simultaneously, 10 un-sterilized sensor arrays, designated Control, were assessed.

Biomechanical and viscoelastic properties of skin, SMAS, and composite flaps as they pertain to rhytidectomy.

Previous studies have focused on biomechanical and viscoelastic properties of the superficial musculoaponeurotic system (SMAS) flap and the skin flap lifted in traditional rhytidectomy procedures. The authors compared these two layers with the composite rhytidectomy flap to explain their clinical observations that the composite dissection allows greater tension and lateral pull to be placed on the facial and cervical flaps, with less long-term stress-relaxation and tissue creep. Eight fresh cadavers were dissected by elevating flaps on one side of the face and neck as skin and SMAS flaps and on the other side as a standard composite rhytidectomy flap.

Changes in prosthetic screw stability because of misfit of implant-supported prostheses.

Purpose: The effect of two levels of prosthesis misfit on prosthetic screw stability was evaluated.

Materials And Methods: Two levels of vertical discrepancies--100 and 175 microns--were introduced between an implant-supported complete denture and the terminal abutment. An implant-supported complete denture without vertical discrepancy served as a control.

The effect of processing conditions on the properties of poly(methyl methacrylate) fibers.

Brittle failure of bone cement remains a problem for the long-term stability of hip prostheses. Fibers have been developed from poly(methyl methacrylate) (PMMA) that retain the chemistry of bone cement, but improve the mechanical properties greatly. To fabricate the fibers, a polymer melt is extruded out of a small die (spinneret) and pulled onto a take-up wheel.

Effect of initiation chemistry on the fracture toughness, fatigue strength, and residual monomer content of a novel high-viscosity, two-solution acrylic bone cement.

Porous-free, two-solution bone cements have been developed in our laboratory as an alternative to commercial powder/liquid formulations. Each pair of solutions consist of poly(methyl methacrylate) (PMMA) powder dissolved in methyl methacrylate (MMA) monomer, with benzoyl peroxide (BPO) added to one solution as the initiator and N,N-dimethyl-p-toluidine (DMPT) added to the other as the activator. When mixed, the solutions polymerize via a free radical reaction, which is governed by the concentrations of initiator and activator and their molar stoichiometry.