Comparison of mechanical loads produced by current intramedullary reamer systems.

OBJECTIVE: This study evaluated the mechanical loading experienced by four clinically used intramedullary reamer cutter designs to evaluate the effects of variations in speed and feed rate on reamer system performance. DESIGN: Biomechanical laboratory study. SETTING: Research laboratory. MAIN OUTCOME MEASURE: Four clinically used reamer systems with detachable cutters were tested using a computer-controlled machining system at representative reaming and drilling speeds of 250 and 750 revolutions per minute (RPM), respectively. Hard oak blocks with mechanical properties similar to cortical bone were reamed using cutter heads with diameters from nine to fourteen millimeters (in 0.5-millimeter increments) at feed rates of 1.0 and 7.6 centimeters per second. Reactive axial loads and torques were recorded and analyzed. RESULTS: All systems demonstrated reduced maximal loads/torques for small reamer sizes (9 to 10.5 millimeters) at drilling speeds rather than reaming speeds. Individual systems demonstrated measurable differences in sensitivity to alterations in operating speed, indicating that some designs are not amenable to operation at increased speeds. In tests where reamer head cutting characteristics were isolated by using identical solid drive shafts, the deeply fluted design with a long lead taper and a rounded, burrlike body consistently produced significantly lower mechanical loading at all speeds and feed rates. In addition, two of the four systems tested use a larger flex shaft diameter for reamer head sizes of thirteen millimeters or greater. There was no indication of a need to use larger flex shafts for the larger reamers, based on mechanical load/torque data for those systems. CONCLUSIONS: The tests performed demonstrate that appropriate control of reaming speeds (RPM) can be used to minimize mechanical loading for all systems. Caution should be exercised, however, so that any operational changes that reduce resistive loads and torques do not lead the surgeon to increased feed rates. Additional study is required to investigate the variable effects of increasing the operating speed of each system on localized thermal changes.

Comparison of growth and metabolism of avian osteoblasts on polished disks versus thin films of titanium alloy.

The purpose of this study was to evaluate the efficacy of using high vacuum, thermal evaporation to deposit thin films of Ti-6Al-4V onto plates for subsequent cell culture investigations. Osteoblastic response to thin-film coated plates was compared to that of cells grown on Ti alloy disk inserts and uncoated culture plates. The Ti alloy disks were polished, cleaned, and passivated following a commercial protocol for orthopedic implants. Mean surface roughness was 262 nm for the Ti alloy disks and 4.756 nm for the coated culture plates. Osteoblasts isolated from 16-day chick embryo calvariae were cultured on polystyrene, thin films, and disks. At confluence, the cells were cultured an additional 48 h and were evaluated for cell number (DNA content), rate of glycolysis (lactate production), alkaline phosphatase activity (ALPase), and collagenous (3H-proline hydroxylation) and noncollagenous protein synthesis. Cell morphology was similar for the controls, disks, and thin-film groups. DNA, lactate, cell layer ALPase, 3H-hydroxyproline, and noncollagenous protein were not different (p > 0.05) among the control, thin-film, and disk groups. Medium ALPase was lower (p < 0.05) in the thin-film group compared to the control group. Although aluminum and vanadium percentages varied from nominal in the thin-film groups (11Al-2V as opposed to 6Al-4V), avian osteoblasts responded similarly to the Ti alloy thin films, disks, and uncoated culture plates for the smooth surfaces tested. The thin-film cell culture system used for elemental material studies appears to offer a promising method for the investigation of cellular response to alloyed biomaterials as well. Proper adjustments in alloy percentages before deposition, however, need to be made if thermal evaporation is utilized.

Measurement of thumb abduction strength: normative data and a comparison with grip and pinch strength.

Abduction strength of the thumb was measured in normal men (n = 101; age range, 21-94 years) and women (n = 208; age range, 20-97 years). Abduction-strength measurements were conducted concurrently with grip and pinch strength measurements made by well-established clinical methods. Normal values were established and stratified by age and sex. Thumb abduction strength generally correlated with grip and pinch strength. All strength variables at all ages were greater in men than in women. The magnitude of all strength variables was maintained from 20 to 59 years of age, then decreased with increasing age in both men and women. Measurement of thumb abduction strength may prove to be a useful adjunct to the various tests currently used by hand surgeons to assess hand function.

Comparative biomechanical analysis of supracondylar femur fracture fixation: locked intramedullary nail versus 95-degree angled plate.

OBJECTIVES: To compare the initial stability of the genucephalic (GSH) intramedullary nail and the 95-degree condylar compression screw and side plate (DCS) for distal femur fractures. DESIGN: Human cadaveric biomechanical study. PARTICIPANTS: Twelve matched pairs of fresh frozen human cadaveric femurs. INTERVENTION: Genucephalic intramedullary nail device (Smith and Nephew Richards, Memphis, TN, U.S.A.) and the 95-degree DCS device (Synthes USA, Paoli, PA, U.S.A.) were compared. Grouped or dispersed screw constructs were tested for each fracture fixation system with progressively more severe simulated fracture patterns. MAIN OUTCOME MEASUREMENT: Axial and torsional stiffness values. RESULTS: The DCS plate with the dispersed screw configuration had the greatest torsional stiffness (p < 0.0011). The GSH nail with the grouped screw configuration absorbed more energy (work) during axial loading compared with the plate constructs (p < 0.0007). There were no significant differences in axial or torsional stiffness within treatment groups for fracture patterns of increasing severity. CONCLUSIONS: Based on the authors' results, the selection of a GSH nail or a DCS plate should not be determined by the severity of the fracture. If a DCS plate construct is selected, the authors recommend a dispersed screw configuration, including the most proximal hole in the plate, to provide superior stiffness in torsional loading and equal stiffness in axial loading when compared with the GSH nail constructs. If a GSH nail is selected, the authors recommend a grouped screw configuration, which absorbed more energy during axial loading compared with the DCS plate constructs and the nail with the dispersed screw configuration.

Modular tibial augmentations in total knee arthroplasty.

Proximal tibial bony deficiencies are not uncommon in primary and revision total knee arthroplasty. Modular tibial augmentations were introduced to address these deficiencies. Alterations in strain distribution as a result of medial wedge and block augmentations were evaluated for a modular total knee arthroplasty system in 6 fresh frozen anatomic specimen tibias. Full-field strain patterns were examined using photoelastic coating methods, and high strain regions were evaluated using strain gage rosette techniques. The total knee arthroplasty installations were tested in static physiologic axial and torsional load configurations. The relative effects of sequential wedge and block augmentations compared with the nonaugmented case were statistically analyzed. There were no overall statistical differences in the 3 treatments in terms of maximal (principal) strains. A secondary analysis that evaluated specific location and load pattern combinations established several minor statistical differences along with insights into the manner in which each construct loads the proximal tibia. Although metal wedge augmentation commonly is used, block augmentation seems to be an appropriate alternative from a strain distribution standpoint in cases in which the block geometry better approximates the bony defect.

On the biomechanics of human shoulder complex--I. Kinematics for determination of the shoulder complex sinus.

Effectiveness of the multi-segmented total-human-body models to predict realistically live human response depends heavily on the proper biomechanical description and simulation of the major articulating joints of the body. In these models, the most difficult and the least successful modelling of a joint has been the shoulder complex because of the lack of appropriate biomechanical data as well as the anatomical complexity of the region. This paper in Part I presents various aspects of a research program to collect three-dimensional kinematic data for the shoulder complex. A sonic digitizing technique which utilizes an overdeterminate number of sonic emitters on the moving body segment was used for the kinematics analysis. The numerical results are presented for three male subjects for their voluntary shoulder complex sinuses. The results are given in a locally-defined joint axis system as well as in the torso-fixed coordinate system in the form of globographic representation.

On the biomechanics of human shoulder complex--II. Passive resistive properties beyond the shoulder complex sinus.

In multi-segmented total-human-body models the most difficult and the least successful modeling of a major articulating joint has been the shoulder complex because of the lack of appropriate biomechanical data as well as the anatomical complexity of the region. In this paper, quantitative results on the three-dimensional passive resistive properties beyond the voluntary shoulder complex sinus are presented by applying the methodology developed in part I. Constant-restoring-force(moment) contours are established for the shoulder complex and the numerical results are presented for the three subjects tested. In addition, functional expansions are presented for the voluntary and restoring force(moment) contours using spherical coordinates.

Kinematic and force data collection in biomechanics by means of sonic emitters--I: Kinematic data collection methodology.

In this paper, first, the principles of sonic digitizing are presented. Next, a description of quantitative determination of the relative motion between two body segments by utilization of sonic emitters is provided. A new kinematic data collection methodology and data analysis is proposed to check continuously the accuracy of the data collected by means of the sonic emitters. The first part of the paper is terminated by establishment of an accuracy criteria and selection of the most accurate data set and associated error analysis. Quantitative results based upon the kinematic data collection methodology of Part I were obtained for the forced kinematic motion of the human shoulder complex and are presented in Part II.

Kinematic and force data collection in biomechanics by means of sonic emitters--II: Force data collection and application to the human shoulder complex.

In multisegmented mathematical models of the human body the most difficult and the least successful modeling of a major articulating joint has been the shoulder complex because of the lack of appropriate biomechanical data as well as the anatomical complexity of the region. In this paper, quantitative results on the variability of the stiffness of the shoulder complex dependent upon orientation of the upper arm are presented by applying the principles and theory developed in Part I. The paper starts with a description of a multiple-axis force and moment transducer and its utilization with sonic emitters in determining direction as well as location of the general force and moment vectors applied on a body segment. The numerical results which are presented for three subjects are in the form of plots showing the passive resistance of the shoulder complex as functions of drawer displacements of the upper arm along its long bone axis. Exponential and power curve fitting of the numerical results are also provided to establish intra-subject variations and similarities of the behavioral patterns of the axial stiffness characteristics of the human shoulder complex.