A single-channel telemetric intramedullary nail for in vivo measurement of fracture healing.

Objective: The objective of this study was to develop a single-channel telemetric intramedullary nail that measures anterior-posterior bending strains and determine whether these forces decrease sigmoidally when normalized to the ground reaction force during fracture healing.

Methods: A transverse midshaft femoral osteotomy (1 mm) was stabilized using a customized TriGen intramedullary nail incorporating a strain gauge in the anterior-posterior plane. Fourteen skeletally mature sheep (2-3 years old) were treated in two pilot studies (n = 3/pilot) and a pivotal study (n = 8).

Evaluation of a synthetic vertebral body augmentation model for rapid and reliable cyclic compression life testing of materials for balloon kyphoplasty.

Screening of augmentation materials for use in balloon kyphoplasty (BKP) may be carried out using vertebral bodies (VBs) prepared from fresh cadaveric or animal model spines, but this approach has many drawbacks. Alternatively, a validated synthetic VB augmentation model may be used. In the present work, such a model-a cube (26 mm sides) of low-density polyurethane foam with a centrally located through-thickness cylindrical hole (diameter = 4 mm) completely filled with a bolus of augmentation material-was used to compare two BKP augmentation materials with very different chemistries (a high-viscosity acrylic bone cement (PMMA) and a calcium phosphate bone substitute (CP)) in cyclic compression life tests.

Preheating acrylic bone cement powder is not recommended for all brands.

One strategy that has been suggested for reducing the operating room time for cemented total joint arthroplasties-and, hence, for reducing the total cost of these procedures-is to accelerate the polymerization of the acrylic bone cement by preheating the powder to 65 degrees C. We quantified the effect of preheating the cement powders on the fracture toughness and fatigue life of 3 cement brands that are widely used in clinical practice. The results suggest judicious selection of cements whose powders are to be preheated for use in cemented arthroplasties.

Estimation of the optimum loading of an antibiotic powder in an acrylic bone cement: gentamicin sulfate in SmartSet HV.

Background: In some countries, commercially available antibiotic powder-loaded acrylic bone cement is routinely used in joint replacement, while, in others, "off-label" formulations are used in selected procedures (where the antibiotic powder is blended manually with the powder of a plain cement in the operating room/theater by either the surgeon or approved personnel). In the latter situation, an arbitrary rather than a rational approach is used for deciding on the amount of the antibiotic that is blended with the cement powder (herein referred to as "the antibiotic powder loading").

Methods And Results: The first objective of this study was to present two methods for estimating the optimum loading of gentamicin sulfate powder that may be blended manually with the powder of a commercially available acrylic bone cement, ABC (Wopt).

Alendronate in bone cement: fatigue life degraded by liquid, not by powder.

Bisphosphonates have the potential to reduce osteolysis, a phenomenon that has been postulated to play a key role in aseptic loosening of total joint replacements. Bisphosphonates may contribute to the in vivo longevity of total joint replacements. Some authors have suggested there are decreases in flexural strength and flexural modulus of the cured cement when a liquid form of disodium pamidronate is added to a commercially available acrylic bone cement (Palacos R).

Influence of the method of blending an antibiotic powder with an acrylic bone cement powder on physical, mechanical, and thermal properties of the cured cement.

Two variants of antibiotic powder-loaded acrylic bone cements (APLBCs) are widely used in primary total joint replacements. In the United States, the antibiotic is manually blended with the powder of the cement at the start of the procedure, while, in Europe, pre-packaged commercially-available APLBCs (in which the blending is carried out using an industrial mixer) are used. Our objective was to investigate the influence of the method of blending gentamicin sulphate with the powder of the Cemex XL formulation on a wide collection of properties of the cured cement.

The in vitro elution of gentamicin sulfate from a commercially available gentamicin-loaded acrylic bone cement, VersaBond AB.

The present study was designed to yield results that would be used to contribute to the ongoing debate about the mechanism of the in vitro elution of an antibiotic from an antibiotic-loaded acrylic bone cement. To this end, the elution rates (R) of gentamicin sulfate (expressed as a weight percentage of the initial mass of the antibiotic in the specimen, normalized with respect to the duration of the test) from statically loaded (STATIC) and dynamically loaded (+/-10 MPa; 2 Hz; until fracture; DYNAMIC) specimens fabricated from a commercially available acrylic bone cement (VersaBond AB), in phosphate-buffered saline solution at 37 degrees C, were obtained with the use of a spectrophotometric method. There was evidence of microcracking in the fracture surfaces of DYNAMIC specimens, but no such evidence in the case of STATIC specimens.

The influence of the viscosity classification of an acrylic bone cement on its in vitro fatigue performance.

The goal of the present work was to investigate the influence of the viscosity classification of an acrylic bone cement on its in vitro fatigue performance, as determined in fully-reversed tension-compression (+/-15 MPa) fatigue tests. The test matrix comprised six commercially available bone cements [Orthoset1, (OS1), Orthoset(R)3 (OS3), CemexRX (CRX), Cemex XL (CXL), Palacos R (PR) and Osteopal (OP)], two methods of mixing the cement constituents (hand-mixing and vacuum-mixing), two methods of fabricating the test specimens (direct molding and molding followed by machining), two specimen cross-sectional shapes (rectangular or "flat" and circular or "round"), and four test frequencies (1, 2, 5, and 10 Hz). In total, 185 specimens, distributed among 20 sets, were tested.

Effect of fabrication pressure on the fatigue performance of Cemex XL acrylic bone cement.

During a cemented arthroplasty, the prepared polymerizing dough of acrylic bone cement is subjected to pressurization in a number of ways; first, during delivery into the freshly prepared bone bed, second, during packing in that bed (either digitally or with the aid of a mechanical device), and, third, during the insertion of the prosthesis. Only a few studies have reported on the influence of the level of pressurization experienced during these events (which, depending on the cementing technique used, has been put at between 8 and 273 kPa) on various properties of the cement. That was the focus of the present study, in which the fully reversed tension-compression (+/-15 MPa; 5 Hz) fatigue lives (expressed as number of cycles to fracture, N(f)) of rectangular cross-sectioned "dog-bone" specimens (Type V, per ASTM D 638) fabricated from Cemex XL cement, at pressure applied continuously to the cement dough during curing in the specimen mold, p=75,150, and 300 kPa, were determined.

Effect of test specimen cross-sectional shape on the in vitro fatigue life of acrylic bone cement.

Constant-amplitude uniaxial tension-compression fatigue tests were conducted on specimens fabricated from 12 sets of acrylic bone cements, covering cement formulations with three different viscosities (so-called "high-", "medium-" and "low-viscosity" varieties), two different methods of mixing the cement constituents (so-called "hand-" and "vacuum-mixed" methods) and two test specimen shapes (rectangular-cross-sectioned or "flat" and circular-cross-sectioned or "round"). The test results-namely, the number of fatigue stress cycles, N(f)-were analyzed using the linearized transformation of the three-parameter Weibull relationship, allowing the values of the Weibull mean, N(WM), to be determined for each set. Values ranged from 14,300 to 1,284,331 for the round specimen sets and from 2898 to 72,960 for the flat specimen sets.

Effect of test frequency on the in vitro fatigue life of acrylic bone cement.

The goal of the present work was to test the hypothesis that test frequency, f, does not have a statistically significant effect on the in vitro fatigue life of an acrylic bone cement. Uniaxial constant-amplitude tension-compression fatigue tests were conducted on 12 sets of cements, covering three formulations with three very different viscosities, two different methods of mixing the cement constituents, and two values of f (1 and 10 Hz). The test results (number of fatigue stress cycles, N(f)) were analyzed using the linearized form of the three-parameter Weibull equation, allowing the values of the Weibull mean (N(WM)) to be determined for each set.