Enabling High Precision Gradient Index Control in Subsurface Multiphoton Lithography.

Multiphoton lithography inside a mesoporous host can create optical components with continuously tunable refractive indices in three-dimensional (3D) space. However, the process is very sensitive at exposure doses near the photoresist threshold, leading previous work to reliably achieve only a fraction of the available refractive index range for a given material system. Here, we present a method for greatly enhancing the uniformity of the subsurface micro-optics, increasing the reliable index range from 0.12 (in prior work) to 0.37 and decreasing the standard deviation (SD) at threshold from 0.13 to 0.0021. Three modifications to the previous method enable higher uniformity in all three spatial dimensions: (1) calibrating the planar write field of mirror galvanometers using a spatially varying optical transmission function which corrects for large-scale optical aberrations; (2) periodically relocating the piezoelectrically driven stage, termed piezo-galvo dithering, to reduce small-scale errors in writing; and (3) enforcing a constant time between each lateral cross section to reduce variation across all writing depths. With this new method, accurate fabrication of optics of any index between n = 1.20 and 1.57 (SD < 0.012 across the full range) was achieved inside a volume of porous silica. We demonstrate the importance of this increased accuracy and precision by fabricating and characterizing calibrated two-dimensional (2D) line gratings and flat gradient index lenses with significantly better performance than the corresponding control devices. As a visual representation, the University of Illinois logo made with 2D line gratings shows significant improvement in its color uniformity across its width.

Hybrid achromatic microlenses with high numerical apertures and focusing efficiencies across the visible.

Compact visible wavelength achromats are essential for miniaturized and lightweight optics. However, fabrication of such achromats has proved to be exceptionally challenging. Here, using subsurface 3D printing inside mesoporous hosts we densely integrate aligned refractive and diffractive elements, forming thin high performance hybrid achromatic imaging micro-optics. Focusing efficiencies of 51-70% are achieved for 15µm thick, 90µm diameter, 0.3 numerical aperture microlenses. Chromatic focal length errors of less than 3% allow these microlenses to form high-quality images under broadband illumination (400-700 nm). Numerical apertures upwards of 0.47 are also achieved at the cost of some focusing efficiency, demonstrating the flexibility of this approach. Furthermore, larger area images are reconstructed from an array of hybrid achromatic microlenses, laying the groundwork for achromatic light-field imagers and displays. The presented approach precisely combines optical components within 3D space to achieve thin lens systems with high focusing efficiencies, high numerical apertures, and low chromatic focusing errors, providing a pathway towards achromatic micro-optical systems.

Carbene-Like Reactivity in an Iron Azametallacyclobutene Complex: Insights from Electronic Structure.

Herein we describe our investigation into the electronic structure of the first isolated monometallic iron azametallacyclobutene complex. Computational analysis through density functional theory calculations reveals electron delocalization throughout the four atoms of the ring system, in line with experimental observations and supporting the classification of this complex as a conjugated metallacycle. The results of this study also point to significant contribution from an imine-substituted iron carbene resonance structure to the overall bonding picture for the azametallacyclobutene. Accordingly, this complex participates in carbene-like reactivity in the presence of an isocyanide substrate to generate a ketenimine product. The related reaction with carbon monoxide leads to the isolation of a five-membered metallacycle that is analogous to the proposed intermediate in ketenimine formation, and confirms the α-carbon as the site of reactivity.

Direct laser writing of volumetric gradient index lenses and waveguides.

Direct laser writing (DLW) has been shown to render 3D polymeric optical components, including lenses, beam expanders, and mirrors, with submicrometer precision. However, these printed structures are limited to the refractive index and dispersive properties of the photopolymer. Here, we present the subsurface controllable refractive index via beam exposure (SCRIBE) method, a lithographic approach that enables the tuning of the refractive index over a range of greater than 0.3 by performing DLW inside photoresist-filled nanoporous silicon and silica scaffolds. Adjusting the laser exposure during printing enables 3D submicron control of the polymer infilling and thus the refractive index and chromatic dispersion. Combining SCRIBE's unprecedented index range and 3D writing accuracy has realized the world's smallest (15 µm diameter) spherical Luneburg lens operating at visible wavelengths. SCRIBE's ability to tune the chromatic dispersion alongside the refractive index was leveraged to render achromatic doublets in a single printing step, eliminating the need for multiple photoresins and writing sequences. SCRIBE also has the potential to form multicomponent optics by cascading optical elements within a scaffold. As a demonstration, stacked focusing structures that generate photonic nanojets were fabricated inside porous silicon. Finally, an all-pass ring resonator was coupled to a subsurface 3D waveguide. The measured quality factor of 4600 at 1550 nm suggests the possibility of compact photonic systems with optical interconnects that traverse multiple planes. SCRIBE is uniquely suited for constructing such photonic integrated circuits due to its ability to integrate multiple optical components, including lenses and waveguides, without additional printed supports.

Finite Element Analysis and Biomechanical Comparison of Short Posterior Spinal Instrumentation with Divergent Bridge Construct versus Parallel Tension Band Construct for Thoracolumbar Spine Fractures.

The ideal treatment for unstable thoracolumbar fractures remains controversial with posterior reduction and stabilization, anterior reduction and stabilization, combined posterior and anterior reduction and stabilization, and even nonoperative management advocated. Short segment posterior osteosynthesis of these fractures has less comorbidities compared with the other operative approaches but settles into kyphosis over time. Biomechanical comparison of the divergent bridge construct versus the parallel tension band construct was performed for anteriorly destabilized T11-L1 spine segments using three different models: (1) finite element analysis (FEA), (2) a synthetic model, and (3) a human cadaveric model. Outcomes measured were construct stiffness and ultimate failure load. Our objective was to determine if the divergent pedicle screw bridge construct would provide more resistance to kyphotic deforming forces. All three modalities showed greater stiffness with the divergent bridge construct. The FEA calculated a stiffness of 21.6 N/m for the tension band construct versus 34.1 N/m for the divergent bridge construct. The synthetic model resulted in a mean stiffness of 17.3 N/m for parallel tension band versus 20.6 N/m for the divergent bridge (p = 0.03), whereas the cadaveric model had an average stiffness of 15.2 N/m in the parallel tension band compared with 18.4 N/m for the divergent bridge (p = 0.02). Ultimate failure load with the cadaveric model was found to be 622 N for the divergent bridge construct versus 419 N (p = 0.15) for the parallel tension band construct. This study confirms our clinical experience that the short posterior divergent bridge construct provides greater stiffness for the management of unstable thoracolumbar fractures.

Risk of periprosthetic femur fracture after anterior cortical bone windowing: a mechanical analysis of short versus long cemented stems in pigs.

BACKGROUND AND PURPOSE: Removal of distal cement at femoral implant revision is technically challenging and is associated with complications such as cortical perforations. A technique that can reduce the risks and operating time is to make a small cortical window in the distal femur for enhanced access. We wanted to determine whether the use of long, bridging, cemented femoral stems is necessary to reduce the risk of postoperative periprosthetic fractures after using an anterior cortical bone window. METHODS: 66 fresh pig femurs underwent mechanical testing. Steel rods were implanted at 3 locations: (1) at the distal window edge, (2) 15 mm proximally to the cortical window edge, and (3) 15 mm distally. 54 femurs were tested using a 3-point bending setup and 12 femurs were tested using a torsional load setup. RESULTS: Load to fracture ratio and bending stiffness ratio were similar in the 3 groups, for either the 3-point bending test or the torsional load test. INTERPRETATION: Our findings suggest that bypass of cortical windows with a revision femoral component may not reduce the risk of periprosthetic fracture.

Revision total knee arthroplasty: clinical outcome comparison with and without the use of femoral head structural allograft.

The use of femoral head structural allograft (FHSA) for the management of massive bony defects during revision total knee arthroplasty (TKA) is well documented in the literature. The purpose of this study was to compare the clinical outcomes of patients undergoing revision (TKA) with FHSA to those without. All patients undergoing revision TKA between January 2000 and August 2005 were reviewed. Two cohorts were generated: a study cohort--revision TKA using FHSA (n = 24)--and control cohort--revision TKA without FHSA (n = 48). The 2 study cohorts groups were comparable. All patients completed validated outcome questionnaires. The FHSA cohort was found to have significantly better outcome scores. This study demonstrates improved clinical outcomes for patients undergoing revision TKA using a structural allograft compared with those without.

Two-stage total hip arthroplasty: how often does it control methicillin-resistant infection?

BACKGROUND: Methicillin-resistant hip infections are increasingly common. Reports of the surgical management of these patients using two-stage THA show variable control of infection, but all reports used static spacers. QUESTIONS/PURPOSES: We therefore determined (1) the rate of successful control of infection and (2) function in patients with methicillin-resistant infection treated with a two-stage THA using an articulated cement spacer during the first stage. METHODS: We retrospectively reviewed 50 patients who had a two-stage revision THA for methicillin-resistant Staphylococcus aureus or methicillin-resistant Staphylococcus epidermidis infection. Twelve patients died, leaving 38 for review. All eligible patients completed quality-of-life outcome questionnaires (WOMAC, SF-12, Oxford-12, UCLA activity score, hip and knee satisfaction score). Minimum followup was 24 months after the second stage (mean, 58 months; range, 24-123 months). RESULTS: Of the 38 patients, eight (21%) had recurrence of their infection requiring further revision surgery. Of the remaining 27 patients, the mean WOMAC was 62, mean Oxford-12 60, mean UCLA activity score 4.3, and mean hip and knee satisfaction score 66. CONCLUSIONS: We found a treatment failure rate of 21% for patients with methicillin-resistant S. aureus or methicillin-resistant S. epidermidis infection. This is a higher rate than reported for two-stage THA for studies including patients infected with both nonresistant and resistant organisms. The functional scores for patients were also lower than those reported in the literature. LEVEL OF EVIDENCE: Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Conversion of hip arthrodesis to total hip arthroplasty: survivorship and clinical outcome.

This study evaluated survivorship and clinical outcomes of patients undergoing conversion of a hip arthrodesis to a total hip arthroplasty (THA) and compared them to 2 patient cohorts: primary THA and first-time revision THA. Patients completed 5 standardized outcome questionnaires. The study cohort was compared to matched groups of primary THA and first-time revision THA patients. Twenty-six patients were identified, 2 deceased and 7 revised, leaving 17 patients available for review. A 10-year survivorship of 74.2% and complication rate of 54% were noted. All outcome scores were lower for the study cohort: clinically significant difference vs revision THA group and statistically significant difference vs primary THA group. Takedown arthrodesis patients experience poor clinical outcomes and high complication rates compared to primary and even revision THA.

Cement-in-cement femoral revision for the treatment of highly selected vancouver B2 periprosthetic fractures.

The use of the cement-in-cement technique for femoral component revisions has been well described. The application of this technique in the management of selected Vancouver B2 periprosthetic femur fractures, after careful preoperative and intraoperative evaluation, offers a novel alternative that is rapid and technically less demanding, with resulting decreased blood loss and decreased risk of iatrogenic fragmentation of bone during cement removal.

Use of a cement-loaded Kuntscher nail in first-stage revision hip arthroplasty for massive femoral bone loss secondary to infection: a report of four cases.

A 2-stage revision total hip replacement (THR) is the standard treatment for a chronically infected THR with severe metadiaphyseal bone loss. A long-stem cemented prosthesis as part of a temporary articular spacer is commonly used during the first-stage procedure. Nonetheless, this option is expensive and can pose difficulties for patients with a small medullary canal. A construct using an antibiotic cement-loaded Kuntscher nail cemented with a highly polished Exeter stem has been devised and used in 4 patients.

Femoral revision hip arthroplasty: a comparison of two stem designs.

UNLABELLED: For various reasons the tapered, fluted, modular titanium (TFMT) stem has become our component of choice over cylindrical, nonmodular cobalt chrome (CNCC) components for THA revision. We therefore asked whether the TFMT femoral components better achieved three important goals of revision arthroplasty than CNCC stems: (1) improving quality of life; (2) avoiding complications; and (3) preserving or restoring femoral bone stock. We compared patients undergoing femoral component revision hip arthroplasty with either a CNCC (N = 105) component or a TFMT (N = 95) component to determine if the increased use of TFMT components is justified. We retrospectively reviewed all patients undergoing revision total hip arthroplasty between January 2000 and March 2006. All eligible patients completed outcome questionnaires (WOMAC, SF-12, Oxford-12, UCLA Activity Score, and Satisfaction Scores). Radiographs were evaluated for loosening and preservation or restoration of the proximal femur host bone. The TFMT and CNCC cohorts were comparable with respect to age, gender, diagnosis, and comorbidities. The TFMT cohort had worse preoperative bone defects (65% Paprosky 3B and 4). The TFMT cohort had higher outcome scores (WOMAC pain, WOMAC stiffness, Oxford-12, and Satisfaction), fewer intraoperative fractures, and better restoration of the proximal femur host bone. Our data suggest the TFMT stem provided improved clinical outcomes (improved quality of life, decreased complications, and preservation of bone stock) than the CNCC stem. LEVEL OF EVIDENCE: Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Severe femoral bone loss in infected total hip arthroplasty: surgical management.

The management of severe bone loss in a patient with a chronically infected total hip arthroplasty is a complex surgical challenge. The surgical alternatives are numerous and include the use of allografts, both structural and morcellized; cemented and cementless femoral components; and segmental replacement megaprostheses.

Vancouver type B3 periprosthetic fractures: evaluation and treatment.

Periprosthetic fracture with preexisting severe loss of bone stock is a challenging condition to treat. Available surgical options can be divided into three categories: complex reconstruction of the deficient proximal femur with secure distal fixation; segmental substitution of the proximal femur with a megaprosthesis or allograft/stem composite; and distally fixed replacement with a modular stem, which acts as a scaffold around which the remaining deficient proximal bone can be assembled, to unite and possibly reconstitute.

Distally fixed scaffold technique for the management of Vancouver B3 periprosthetic fractures.

Periprosthetic femoral fractures with associated severe bone loss are challenging problems to treat. High failure rates are reported throughout the literature for the various surgical options. The novel distally fixed scaffold technique is a rapid procedure with reduced blood loss and high versatility that allows early mobilization. Early results have been promising, but further long-term data are required.

Risk of periprosthetic femoral neck fracture after hip resurfacing arthroplasty: valgus compared with anatomic alignment. A biomechanical and clinical analysis.

BACKGROUND: Early clinical results of hip resurfacing arthroplasty have led to the recommendation to achieve a neck-shaft angle of 140 degrees when inserting the femoral component. In addition, the idea of adhering to an absolute angle when inserting instrumentation in hips with excessive anatomic varus or valgus neck-shaft angles has raised concern. A biomechanical analysis was completed in order to determine if the achieved valgus orientation of the femoral component reduced the risk of periprosthetic fracture. METHODS: Twenty fresh-frozen cadaveric femora were blindly assigned to be implanted with a neutral or valgus-oriented hip-resurfacing femoral component. Bone mineral density scans were acquired for all femora. All specimens were loaded axially to failure at a rate of 0.21 mm per second. Radiographs of the specimens were measured in order to determine the relative valgus orientation of the femoral components and the change in offset. RESULTS: There was a significant increase in the ultimate failure load for the valgus-oriented components. While the bone density scans revealed that the bone mineral densities measured in the neutral and valgus-oriented femoral components were almost identical, the ultimate failure load was found to be significantly increased for the valgus-oriented components (6955 N) compared with the neutral-oriented components (5254 N). For the valgus-oriented femoral components, two had failure at the subcapital level, seven had vertical shear fractures, and one had an anterior shear fracture. For the neutral-oriented components, five subcapital fractures and five vertical shear failures were observed. CONCLUSIONS: The study suggests that a valgus orientation decreases the risk of periprosthetic femoral neck fracture following hip resurfacing. It also brings into question the use of an absolute angle for all patients. Obtaining the maximum possible valgus angle, while avoiding notching, may in fact provide the optimum protection from periprosthetic femoral neck fractures.

Surgical nuances to minimize muscle damage during the anterolateral intermuscular approach in minimally invasive hip replacement.

Muscle damage that can occur during minimally invasive total hip replacement is an important concern. Minimizing this iatrogenic injury can help achieve the goals of the minimally invasive approach: decreased postoperative pain, decreased blood loss, and faster rehabilitation. Knowledge of particular aspects of minimally invasive anterolateral total hip arthroplasty is important, with focus on the nuances that aid in reducing muscle injury.