Accuracy of an electromagnetic tracking device: a study of the optimal range and metal interference

The positional and rotational accuracy of a direct-current magnetic tracking device commonly used in biomechanical investigations was evaluated. The effect of different metals was also studied to determine the possibility of interference induced by experimental test fixtures or orthopaedic implants within the working field. Positional and rotational data were evaluated for accuracy and resolution by comparing the device output to known motions as derived from a calibrated grid board or materials testing machine. The effect of different metals was evaluated by placing cylindrical metal samples at set locations throughout the working field and comparing the device readings before and after introducing each metal sample. Positional testing revealed an optimal operational range with the transmitter and receiver separation between 22.5 and 64.0 cm. Within this range the mean positional error was found to be 1.8 percent of the step size, and resolution was determined to be 0.25 mm. The mean rotational error over a 1-20 degree range was found to be 1.6% of the rotational increment with a rotational resolution of 0.1 degrees. Of the metal alloys tested only mild steel produced significant interference, which was maximum when the sample was placed adjacent to the receiver. At this location the mild steel induced a positional difference of 5.26 cm and an angular difference of 9.75 degrees. The device was found to be insensitive to commonly used orthopaedic alloys. In this study, the electromagnetic tracking device was found to have positional and rotational errors of less than 2 percent, when utilized within its optimal operating range. This accuracy combined with its insensitivity to orthopaedic alloys should make it suitable for a variety of musculoskeletal research investigations.

Wear rate of highly cross-linked polyethylene in total hip arthroplasty. A randomized controlled trial

BACKGROUND

Highly cross-linked polyethylene was introduced for clinical use in total hip arthroplasty with the expectation that it would exhibit less wear when compared with conventional polyethylene. The purpose of this study was to report the clinical and radiographic results, after a minimum of five years of follow-up, of a randomized, blinded, controlled trial comparing a conventional polyethylene with a first-generation highly cross-linked polyethylene.

METHODS

One hundred patients were enrolled in a prospective, randomized controlled study comparing highly cross-linked and conventional polyethylene acetabular liners in total hip arthroplasty. Fifty patients were in each group. At the time of follow-up, clinical outcomes were assessed and steady-state femoral head penetration rates (after bedding-in) for each patient were calculated with use of a validated radiographic technique. In addition, a statistical comparison of polyethylene wear between groups was performed with use of generalized estimating equations.

RESULTS

At a mean of 6.8 years postoperatively, there were no differences between the two polyethylene groups with regard to the Harris hip score, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), or Short Form-12 (SF-12) score. The mean femoral head penetration rate in the first through fifth years was found to be significantly lower in the group treated with the highly cross-linked polyethylene (0.003 mm/yr [95% confidence interval, +/-0.027]) than it was in the group treated with conventional polyethylene (0.051 mm/yr [95% confidence interval, +/-0.022]) (p=0.006). Men treated with a conventional polyethylene liner had a significantly higher (p<or=0.012) femoral head penetration rate (0.081 mm/yr [95% confidence interval, +/-0.065]) than both men and women with a highly cross-linked liner (-0.013 mm/yr [95% confidence interval, +/-0.074] and 0.009 mm/yr [95% confidence interval, +/-0.028], respectively). The general estimating equations demonstrated that the group with a highly cross-linked polyethylene liner had a significantly lower femoral head penetration rate than the group with a conventional polyethylene liner (p=0.025), and a significantly higher femoral head penetration rate was demonstrated in men with a conventional polyethylene liner when compared with both men and women with a highly cross-linked liner (p=0.003).

CONCLUSIONS

At a minimum of five years postoperatively, the steady-state femoral head penetration rate associated with this first-generation highly cross-linked polyethylene liner was significantly lower than that associated with a conventional polyethylene liner. Long-term follow-up is required to demonstrate the clinical benefit of this new material.

Thigh pain after cementless hip arthroplasty. Annoyance or ill omen

A retrospective review of 148 consecutive porous-coated hip arthroplasties (PCA) showed an incidence of thigh pain of 13% one year after surgery, and 22% at two years. Positive correlations were made with femoral stem subsidence (greater than 2 mm) and with distal periosteal and endosteal bone formation. No positive correlations were made with parameters of bone quality or component fit. Resolution of pain occurred in one-third and an anti-inflammatory agent produced partial relief in two-thirds of the patients. We conclude that thigh pain is secondary to stem instability with distal stress transfer in the absence of stable proximal fixation.

Short arm plaster cast for distal pediatric forearm fractures

Ten years' clinical experience with below-elbow plaster cast treatment of distal one third pediatric forearm fractures was subjected to an independent retrospective radiographic review. In the study population of 761 fractures, no significant displacement occurred while the forearm remained in plaster. The average angulation change was 4.5 degrees (SD +/- 2.2 degrees). In each angulation change > 5 degrees, poor cast molding was evident, as reflected by a high "cast index" (p < 0.01). Although this technique is technically demanding, excellent results are obtained in all distal pediatric forearm fractures if proper cast molding is used.

Effect of screw placement on fixation in the humeral head

The objectives of this study were (1) to determine the most advantageous screw locations within the humeral head when plate and screw fixation is to be used and (2) to determine the effect of positioning the screw tip abutting the subchondral bone. Ten paired humeral heads were harvested with a monoplanar cut through the anatomic neck. Through use of a standardized template, 7 holes were drilled and tapped in each specimen for insertion of 6.5-mm fully threaded cancellous screws perpendicular to the plane of the cut. Paired specimens were randomized into 2 groups, one with the screw purchase in central cancellous bone and the other with the screw purchase up to the subchondral bone. Each screw was pulled out axially at a displacement rate of 10 mm/min through use of a servohydraulic testing machine. The length of thread purchase, position within the head, and screw pullout load to failure were recorded. The normalized pullout force to failure was calculated by dividing absolute pullout force to failure by length of screw purchase. Data were analyzed by means of a 2-way repeated measures analysis of variance and post hoc Student-Newman-Keuls test. The central position had a significantly higher absolute pullout force to failure than all other sites (P < .05). By virtue of the humeral head shape, the central position also had a significantly greater length of screw purchase than all other positions (P < .05). The central position had a significantly higher relative pullout force to failure than all other positions (P < .05). Subchondral bone abutment positioning improved both the absolute and the relative pullout forces to failure (P < .05). When screws and plates are used in open reduction and internal fixation of a proximal humerus fracture, a major mode of failure is loss of fixation within the humeral head. On the basis of this study, optimal screw purchase with respect to bone fixation can be achieved by including screws located in the center of the humeral head in the subchondral abutment position. To minimize screw fixation failure, the anterosuperior position should be avoided. The pattern of distribution of the relative pullout force as measured in this study is consistent with previous observational studies of patterns of trabecular density within the humeral head.

Regulation of oxidative phosphorylation complex activity: effects of tissue-specific metabolic stress within an allometric series and acute changes in workload

The concentration of mitochondrial oxidative phosphorylation complexes (MOPCs) is tuned to the maximum energy conversion requirements of a given tissue; however, whether the activity of MOPCs is altered in response to acute changes in energy conversion demand is unclear. We hypothesized that MOPCs activity is modulated by tissue metabolic stress to maintain the energy-metabolism homeostasis. Metabolic stress was defined as the observed energy conversion rate/maximum energy conversion rate. The maximum energy conversion rate was assumed to be proportional to the concentration of MOPCs, as determined with optical spectroscopy, gel electrophoresis, and mass spectrometry. The resting metabolic stress of the heart and liver across the range of resting metabolic rates within an allometric series (mouse, rabbit, and pig) was determined from MPOCs content and literature respiratory values. The metabolic stress of the liver was high and nearly constant across the allometric series due to the proportional increase in MOPCs content with resting metabolic rate. In contrast, the MOPCs content of the heart was essentially constant in the allometric series, resulting in an increasing metabolic stress with decreasing animal size. The MOPCs activity was determined in native gels, with an emphasis on Complex V. Extracted MOPCs enzyme activity was proportional to resting metabolic stress across tissues and species. Complex V activity was also shown to be acutely modulated by changes in metabolic stress in the heart, in vivo and in vitro. The modulation of extracted MOPCs activity suggests that persistent posttranslational modifications (PTMs) alter MOPCs activity both chronically and acutely, specifically in the heart. Protein phosphorylation of Complex V was correlated with activity inhibition under several conditions, suggesting that protein phosphorylation may contribute to activity modulation with energy metabolic stress. These data are consistent with the notion that metabolic stress modulates MOPCs activity in the heart.

Metal-on-metal versus polyethylene in hip arthroplasty: a randomized clinical trial

A prospective, randomized, blinded clinical trial was done to evaluate polyethylene versus metal bearing surfaces in total hip replacement. Forty-one patients were randomized to receive either a metal (23 patients) or a polyethylene (18 patients) insert. The femoral and acetabular components were identical with the acetabular insert the only variable. Patients were assessed preoperatively and postoperatively using radiographs, multiple outcome measures (Western Ontario MacMaster University Score, Harris hip score, Short Form-12), erythrocyte metal ion analysis (cobalt, chromium, titanium), and urine metal ion analysis (cobalt, chromium, titanium). Patients were followed up for a minimum of 2 years (mean 3.2 years; range, 2.2-3.9 years). There were no differences in radiographic outcomes or outcome measurement tools between patients. Patients receiving a metal-on-metal articulation had significantly elevated erythrocyte and urine metal ions compared with patients receiving a polyethylene insert. Patients who had metal-on-metal inserts had on average a 7.9-fold increase in erythrocyte cobalt, a 2.3-fold increase in erythrocyte chromium, a 1.7-fold increase in erythrocyte titanium, a 35.1-fold increase in urine cobalt, a 17.4-fold increase in urine chromium, and a 2.6-fold increase in urine titanium at 2 years followup. Patients receiving a polyethylene insert had no change in erythrocyte titanium, urine cobalt, or urine chromium and a 1.5-fold increase in erythrocyte cobalt, a 2.2-fold increase in erythrocyte chromium, and a 4.2-fold increase in urine titanium. Forty-one percent of patients receiving metal-on-metal articulations had increasing metal ion levels at the latest followup.

Patellar position after total knee arthroplasty: influence of femoral component malposition

Patellar shift, tilt, and rotation were analyzed in 7 cadaveric knee specimens during simulated quadriceps loading, in the intact knee, and after implant reconstruction. Femoral component medialization, lateralization, and external rotation were also investigated. Relative motion of the patella with respect to the femur was measured using an electromagnetic tracking system. The spatial position of the patella did not change with standardized total knee arthroplasty (P <.05). After malpositioning of the femoral component, patellar rotation also did not change (P >.05); however, patellar tilt was altered by femoral component external rotation malposition (P <.05), and patellar shift was affected by all femoral component malpositions (P <.05). The spatial position of the patella relative to the femoral shaft was changed with any femoral component malposition, suggesting that the soft tissues were abnormally tensioned. This could result in subsequent wear on the patellar component and, therefore, early failure.

Effect of the posterior cruciate ligament in knee-joint proprioception in total knee arthroplasty

The primary purpose of the study was to examine the role of the posterior cruciate ligament (PCL) in knee-joint proprioception after total knee arthroplasty (TKA). Knee-joint proprioception was measured in 10 patients with nonsacrificed PCL TKAs and 10 with sacrificed PCL TKAs. Knee-joint proprioception was evaluated through reproduction of static knee angles using a Penny and Giles electrogoniometer. The primary variable was absolute angular error (AAE). AAE was defined as the absolute value of the difference between the test angle and the patient's perceived version of the test angle. Proprioception deficit was compared to the WOMAC questionnaire which evaluates pain, stiffness, and physical function of the lower extremity. No significant difference was found between the nonsacrificed PCL TKA (4.33 degrees +/- 1.52 degrees) and sacrificed PCL TKA (4.38 degrees +/- 1.39 degrees) AAE values (P > .4). Furthermore, no significant differences were observed in the WOMAC questionnaire scores for all three parameters between the two types of knee prosthesis (P > .35). The current findings suggest that the preservation of the PCL in TKA may not improve knee-joint proprioception and subsequently may not improve TKA functional performance.

Autocrine effect of vascular endothelial growth factor-A is essential for mitochondrial function in brown adipocytes

OBJECTIVE

The obesity epidemic in the United States, as well as the accompanying condition of type 2 diabetes, puts a majority of the population at an increased risk of developing cardiovascular diseases including coronary artery disease, stroke, and myocardial infarction. In contrast to white adipose tissue (WAT), brown adipose tissue (BAT) is well vascularized, rich in mitochondria, and highly oxidative. While it is known that the angiogenic factor VEGF-A is required for brown adipocyte development, the functional consequences and exact mechanism remain to be elucidated. Here, we show that VEGF-A plays an essential autocrine role in the function of BAT.

MATERIALS AND METHODS

Mouse models were generated with an adipose-specific and macrophage-specific ablation of VEGF-A. Adipose tissue characteristics and thermogenic response were analyzed in vivo, and mitochondrial morphology and oxidative respiration were analyzed in vitro to assess effects of endogenous VEGF-A ablation.

RESULTS

VEGF-A expression levels are highest in adipocyte precursors compared to immune or endothelial cell populations within both WAT and BAT. Loss of VEGF-A in adipocytes, but not macrophages, results in decreased adipose tissue vascularization, with remarkably diminished thermogenic capacity in vivo. Complete ablation of endogenous VEGF-A decreases oxidative capacity of mitochondria in brown adipocytes. Further, acute ablation of VEGF-A in brown adipocytes in vitro impairs mitochondrial respiration, despite similar mitochondrial mass compared to controls.

CONCLUSION

These data demonstrate that VEGF-A serves to orchestrate the acquisition of thermogenic capacity of brown adipocytes through mitochondrial function in conjunction with the recruitment of blood vessels.

An evaluation of three loading configurations for the in vitro testing of femoral strains in total hip arthroplasty

Despite recent advances in total hip arthroplasty, proximal femoral resorption and osteopenia remain problems. To analyze the proximal strain effects of three different loading conditions, strains produced in intact and postarthroplasty femora have been compared. Ten adult cadaveric femora of similar size, shape, and rigidity were tested. Ten strain-gauge rosettes were positioned on each femur. To simulate the "single leg support" phase of gait, fixtures were developed to load the femora under three different configuration: the VS (vertical shaft) configuration, with a vertically orientated femur having rotational freedom proximally and distally; the ITB (iliotibial band) configuration of a femur with rotational freedom positioned 11 degrees from the vertical, with a strain-gauge adjustable metallic simulation of the lateral muscles of the thigh; and the ABD (abductor) configuration of a femur with rotational freedom positioned 11 degrees from the vertical, with a strain-gauge adjustable metallic simulation of the abductor muscles. Each femur was loaded less than or equal to 600 N through the medial point, located at one sixth of the transcondylar distance. Strain patterns and magnitudes produced by the three loading configurations were quite different in both the intact and postarthroplasty femora. Both the ITB and the ABD configurations resulted in greater proximal medial compression and lateral tension than did the VS configuration. The magnitudes of the proximal strains were significantly greater in the ABD configuration (p less than 0.05). Postarthroplasty femora showed similar proximal results. It is proposed that meaningful strain data for the physiologically loaded femur can be obtained only with simulations that include the forces produced by the iliotibial band. To overcome the indeterminate nature and biological variation in these forces, the studies have to consider a range of forces.

Computer-assisted gap equalization in total knee arthroplasty

This in vitro biomechanical study compared a conventional balancing technique in knee arthroplasty to a technique using computer assistance. The experimental technique used a soft tissue tensioner instrumented with computer-monitored load cells to quantify soft tissue tension. To assess outcome, a tibial load transducer measured medial and lateral compartment forces and tibial rotation. An electromagnetic tracking system quantified knee position under simulated muscle loading. The computer-assisted technique improved knee balance before insertion of components. However, once components were implanted, there was no difference in knee load balance between the 2 techniques. No correlation was shown between compartmental load balance and tibial rotation or mechanical axis misalignment. Although computer-assisted surgery may improve technical accuracy, further work is necessary to achieve an optimal final knee load balance.

Quadriceps neuromuscular function and self-reported functional ability in knee osteoarthritis

The purposes of this study were to determine 1) the relationships of self-reported function scores in patients with knee osteoarthritis (OA) to both maximal isometric torque and to isotonic power at a variety of loads, and 2) the degree to which muscle volume (MV) or voluntary activation (VA) are associated with torque and power measures in this population. Isometric maximal voluntary contraction (MVC) torque and isotonic power [performed at loads corresponding to 10, 20, 30, 40, and 50% MVC, and a minimal load ("Zero Load")] were measured in 40 participants with knee OA. Functional ability was measured with the Western Ontario and McMaster Osteoarthritis Index (WOMAC) function subscale. MV was determined with magnetic resonance imaging, and VA was measured with the interpolated twitch technique. In general, power measured at lower loads (Zero Load and 10-30% MVC, r(2) = 0.21-0.28, P < 0.05) predicted a greater proportion of the variance in function than MVC torque (r(2) = 0.18, P < 0.05), with power measured at Zero Load showing the strongest association (r(2) = 0. 28, P < 0.05). MV was the strongest predictor of MVC torque and power measures in multiple regression models (r(2) = 0.42-0.72). VA explained only 6% of the variance in MVC torque and was not significantly associated with power at any load (P > 0.05). Quadriceps MVC torque and power are associated with self-reported function in knee OA, but muscle power at lower loads is more predictive of function than MVC torque. The variance in MVC torque and power between participants is due predominantly to differences in MV and has little to do with deficits in VA.

Sex differences in quadriceps strength in OA

The purposes of this study were to determine 1) whether sex differences in quadriceps torque and isotonic power persist when controlling for muscle volume (i. e., torque/muscle volume and power/muscle volume) in participants with knee osteoarthritis (OA) and 2) the factors responsible for potential sex differences. Isometric torque, isotonic power (the product of torque and velocity, measured at 10, 20, 30, 40 and 50% maximal voluntary contraction; MVC) and maximal unloaded velocity were assessed in men (n=16, mean age=62.1 ± 7.2) and women (n=17, mean age=60.4 ± 4.3) with knee OA. Torque and power were normalized to muscle volume. The interpolated twitch technique was used to measure voluntary activation (VA) and evoked twitch and torque-frequency characteristics were measured to obtain information about muscle fibre distribution. Torque and power at all loads were significantly lower in women (p<0.05). Sex differences in power were reduced by 50% when controlling for muscle volume but were still significant at 10-40% MVC (p<0.05). No differences in VA, torque-frequency properties or time-to-peak tension of the evoked twitch were observed (p>0.05). These results suggest that only minor sex differences in torque and power persist when controlling for muscle volume. As VA and contractile property differences were not observed, other factors seem to be responsible.

Glenoid vault endosteal dimensions: an anthropometric study with special interest in implant design

An understanding of the morphology of the glenoid is important from the viewpoint of implant design and selection. This study describes the endosteal dimensions and shape of the glenoid and correlates these results with age, gender, and the presence of osteoarthritis. This study used 72 scapulae. Data were obtained from computed tomography scans of both cadaveric and in vivo glenoids. The glenoid is relatively straight-sided in the coronal plane and more highly fluted in the transverse plane. The endosteal dimensions were larger for male specimens, but there was no difference in endosteal shape with respect to gender. These findings were not influenced by age or the presence of osteoarthritis. This study suggests that traditional glenoid component designs may not be optimal. To maximize fixation, a rectangular keel may be most effective in the coronal plane and a triangular keel may be most effective in the transverse plane.

Does keel size, the use of screws, and the use of bone cement affect fixation of a metal glenoid implant?

The objective of this study was to determine the effect of screws and keel size on the fixation of an all-metal glenoid component. A prototype stainless-steel glenoid component was designed and implanted in 10 cadaveric scapulae. A testing apparatus capable of producing a loading vector at various angles, magnitudes, and directions was used. The independent variables included six directions and three angles of joint load, and five fixation modalities-three different-sized cross-keels (small, medium, and large), screws, and bone cement. Implant micromotion relative to bone was measured by four displacement transducers at the superior, inferior, anterior, and posterior sites. The components displayed a consistent response to loading of ipsilateral compression and contralateral distraction. Use of progressively larger keels did not significantly improve implant stability. Stability decreased as the angle of load application increased (P <.05). Screw and cement fixation resulted in the most stable fixation (P <.05).

Intrafocal (Kapandji) pinning of unstable distal radius fractures: a preliminary report

Seventeen consecutive patients (17 wrists) who underwent intrafocal pinning of unstable distal radius fractures, as described by Kapandji, were retrospectively reviewed at a mean of 42 weeks after surgery (range, 13-88 weeks). The patients were immobilized for 6 weeks postoperatively. All patients were assessed by a single physician and were asked a set of questions regarding subjective and functional status. All patients underwent physical examination of their upper extremities, and bilateral wrist PA and lateral x-rays were taken. There were 13 females and four males; the average age was 49 years. Ten dominant and seven nondominant extremities were involved. Average volar tilt on follow-up lateral wrist radiography was 7 degrees. This compares with -20 degrees at initial presentation, -12 degrees preoperatively, 6 degrees immediately postoperatively, and 10 degrees in the normal wrists. Radial shortening (average) was -2 mm at initial presentation, -1mm preoperatively, 1 mm postoperatively, 0 mm at follow-up, and 1 mm in the normal wrists. Radial inclination was 17 degrees initially, 20 degrees preoperatively, 23 degrees immediately postoperatively, 23 degrees on follow-up, and 24 degrees in the normal wrists. There was a trend for patients with osteopenic bone to lose their postoperative reduction. However, this was not statistically significant. Patients older than 65 years of age had significantly inferior radiologic results. Loss of pronation and supination averaged 2 degrees (range 0-10 degrees) compared with the uninjured wrist. Loss of dorsiflexion averaged 6.5 degrees, and palmar flexion averaged 7.6 degrees. The patients' subjective complaints were minimal. Average pain on visual analog scale (VAS) was 0.44/10. Function measured 8.64/10 (VAS). Sixteen of the patients were happy with the surgery and the outcome of their wrists. Complications included extensor tendon rupture (one patient), pin migration requiring premature removal (one patient), and initial loss of reduction requiring reoperation (one patient). Intrafocal pinning of unstable distal radius fractures provides an effective means to stabilize these complex injuries. Early follow-up suggests that the patients have a satisfactory functional outcome. The complications in this series were preventable. Intrafocal pinning should be added to the surgical armamentarium in treating distal radius fractures.

Pharmacy utilization and the Medicare Modernization Act

To control expenditures and use medications appropriately, the Medicare drug coverage program has established pharmacy utilization management (PUM) measures. This article assesses the effects of these strategies on the care of seniors. The literature suggests that although caps on drug benefits lower pharmaceutical costs, they may also increase the use of other health care services and hurt health outcomes. Our review raises concerns regarding the potential unintended effects of the Medicare drug program's PUM policies for beneficiaries. Therefore, the economic and clinical impact of PUM measures on seniors should be studied further to help policymakers design better drug benefit plans.

Optimizing multiphoton fluorescence microscopy light collection from living tissue by noncontact total emission detection (epiTED)

A benefit of multiphoton fluorescence microscopy is the inherent optical sectioning that occurs during excitation at the diffraction-limited spot. The scanned collection of fluorescence emission is incoherent; that is, no real image needs to be formed on the detector plane. The nearly isotropic emission of fluorescence excited at the focal spot allows for new detection schemes that efficiently funnel all attainable photons to detector(s). We previously showed [Combs, C.A., et al. (2007) Optimization of multiphoton excitation microscopy by total emission detection using a parabolic light reflector. J. Microsc. 228, 330-337] that parabolic mirrors and condensers could be combined to collect the totality of solid angle around the excitation spot for tissue blocks, leading to ∼8-fold signal gain. Using a similar approach, we have developed an in vivo total emission detection (epiTED) instrument modified to make noncontact images from outside of living tissue. Simulations suggest that a ∼4-fold enhancement may be possible (much larger with lower NA objectives than the 0.95 NA used here) with this approach, depending on objective characteristics, imaging depth and the characteristics of the sample being imaged. In our initial prototype, 2-fold improvements were demonstrated in the mouse brain and skeletal muscle as well as the rat kidney, using a variety of fluorophores and no compromise of spatial resolution. These results show this epiTED prototype effectively doubles emission signal in vivo; thus, it will maintain the image signal-to-noise ratio at two times the scan rate or enable full scan rate at approximately 30% reduced laser power (to minimize photo-damage).

Load relaxation and forces with activity in Hoffman external fixators: a clinical study in patients with Colles' fractures

A small-frame Hoffman external fixation bar instrumented with strain gauges to quantify bending and torsional forces was applied to 4 patients with a displaced metaphyseal fracture of the distal radius. Measurements were taken during surgery as well as at 1, 3, and 6 weeks after surgery during activities of daily living and hand therapy mobilization. Radiographs also were taken before and after reduction and at each subsequent visit. Force decay occurred after reduction of the fracture, averaging only 26% of the initial distraction forces by 5 minutes. These forces plateaued and did not significantly change over the subsequent 40-minute observation period. There was no correlation between carpal height index and the forces measured in the external fixator. Significant changes in external fixator forces were measured during activities of daily living and hand therapy mobilization, but these returned to baseline after the activities were performed. The most provocative activities studied were twisting a doorknob and lifting heavy objects. These activities should be performed with caution by patients with unstable distal radial fractures.

Vastus medialis motor unit properties in knee osteoarthritis

BACKGROUND

Maximal isometric quadriceps strength deficits have been widely reported in studies of knee osteoarthritis (OA), however little is known about the effect of osteoarthritis knee pain on submaximal quadriceps neuromuscular function. The purpose of this study was to measure vastus medialis motor unit (MU) properties in participants with knee OA, during submaximal isometric contractions.

METHODS

Vastus medialis motor unit potential (MUP) parameters were assessed in 8 patients with knee OA and 8 healthy, sex and age-matched controls during submaximal isometric contractions (20% of maximum isometric torque). Unpaired t-tests were used to compare groups for demographic and muscle parameters.

RESULTS

Maximum knee extension torque was ~22% lower in the OA group, a difference that was not statistically significantly (p = 0.11). During submaximal contractions, size related parameters of the needle MUPs (e.g. negative peak duration and amplitude-to-area ratio) were greater in the OA group (p < 0.05), with a rightward shift in the frequency distribution of surface MUP negative peak amplitude. MUP firing rates were significantly lower in the OA group (p < 0.05).

CONCLUSIONS

Changes in MU recruitment and rate coding strategies in OA may reflect a chronic reinnervation process or a compensatory strategy in the presence of chronic knee pain associated with OA.

Three-dimensional motion tracking for high-resolution optical microscopy, in vivo

When conducting optical imaging experiments, in vivo, the signal to noise ratio and effective spatial and temporal resolution is fundamentally limited by physiological motion of the tissue. A three-dimensional (3D) motion tracking scheme, using a multiphoton excitation microscope with a resonant galvanometer, (512 × 512 pixels at 33 frames s(-1)) is described to overcome physiological motion, in vivo. The use of commercially available graphical processing units permitted the rapid 3D cross-correlation of sequential volumes to detect displacements and adjust tissue position to track motions in near real-time. Motion phantom tests maintained micron resolution with displacement velocities of up to 200 μm min(-1), well within the drift observed in many biological tissues under physiologically relevant conditions. In vivo experiments on mouse skeletal muscle using the capillary vasculature with luminal dye as a displacement reference revealed an effective and robust method of tracking tissue motion to enable (1) signal averaging over time without compromising resolution, and (2) tracking of cellular regions during a physiological perturbation.

A biomechanical analysis of intrascaphoid compression using the 3.00 mm Synthes cannulated screw and threaded washer: an in vitro cadaveric study

This study evaluated the compressive capabilities of the 3.0 mm Synthes cannulated screw and threaded washer. A transverse osteotomy was performed at the waist of eight cadaveric scaphoids and a custom-designed load cell was inserted before internal fixion with a 3.0 mm cannulated screw and threaded washer. The mean intrascaphoid compression achieved was 108 (SD, 60) N. This compressive force is comparable to that produced by standard cortical screws.

Effect of polyethylene component thickness on range of motion and stability in primary total knee arthroplasty

Total knee arthroplasty (TKA) is a common procedure with good survivorship and functional results. Optimal results are dependent on proper osseous cuts and soft tissue balancing. Soft tissue tensioning via the polyethylene spacer thickness is an important component of soft tissue balancing. Increased thickness increases soft tissue tension and, therefore, has the potential to increase stability but decrease range of motion (ROM). Decreased polyethylene thickness may decrease soft tissue tension and has the potential to increase ROM but decrease stability. Using computer-based navigation, the intraoperative effect of increasing and decreasing polyethylene thickness in 1-mm increments on ROM and coronal stability throughout the ROM of 35 patients was examined. It was found that increasing the polyethylene thickness by 1-mm increments had a statistically significant impact on the ability to achieve full extension but had no impact on flexion. Increased polyethylene thickness decreased coronal plane motion. Coronal plane laxity increased with increased flexion irrespective of polyethylene thickness. In this patient cohort, lateral laxity became >1° when the knee was flexed. However, medial structures prevented valgus angulation of >1° in all scenarios except when the polyethylene was diminished by 2 mm. Changes in polyethylene thickness had an impact on the ability to gain full extension and coronal plane motion.