Data-driven approaches to optical patterned defect detection.

Computer vision and classification methods have become increasingly wide-spread in recent years due to ever-increasing access to computation power. Advances in semiconductor devices are the basis for this growth, but few publications have probed the benefits of data-driven methods for improving a critical component of semiconductor manufacturing, the detection and inspection of defects for such devices. As defects become smaller, intensity threshold-based approaches eventually fail to adequately discern differences between faulty and non-faulty structures. To overcome these challenges we present machine learning methods including convolutional neural networks (CNN) applied to image-based defect detection. These images are formed from the simulated scattering of realistic geometries with and without key defects while also taking into account line edge roughness (LER). LER is a known and challenging problem in fabrication as it yields additional scattering that further complicates defect inspection. Simulating images of an intentional defect array, a CNN approach is applied to extend detectability and enhance classification to these defects, even those that are more than 20 times smaller than the inspection wavelength.

Design of angle-resolved illumination optics using nonimaging bi-telecentricity for 193 nm scatterfield microscopy.

Accurate optics-based dimensional measurements of features sized well-below the diffraction limit require a thorough understanding of the illumination within the optical column and of the three-dimensional scattered fields that contain the information required for quantitative metrology. Scatterfield microscopy can pair simulations with angle-resolved tool characterization to improve agreement between the experiment and calculated libraries, yielding sub-nanometer parametric uncertainties. Optimized angle-resolved illumination requires bi-telecentric optics in which a telecentric sample plane defined by a Köhler illumination configuration and a telecentric conjugate back focal plane (CBFP) of the objective lens; scanning an aperture or an aperture source at the CBFP allows control of the illumination beam angle at the sample plane with minimal distortion. A bi-telecentric illumination optics have been designed enabling angle-resolved illumination for both aperture and source scanning modes while yielding low distortion and chief ray parallelism. The optimized design features a maximum chief ray angle at the CBFP of 0.002° and maximum wavefront deviations of less than 0.06 λ for angle-resolved illumination beams at the sample plane, holding promise for high quality angle-resolved illumination for improved measurements of deep-subwavelength structures using deep-ultraviolet light.

Optimizing the nanoscale quantitative optical imaging of subfield scattering targets.

The full 3-D scattered field above finite sets of features has been shown to contain a continuum of spatial frequency information and, with novel optical microscopy techniques and electromagnetic modeling, deep-subwavelength geometrical parameters can be determined. Similarly, by using simulations, scattering geometries and experimental conditions can be established to tailor scattered fields that yield lower parametric uncertainties while decreasing the number of measurements and the area of such finite sets of features. Such optimized conditions are reported through quantitative optical imaging in 193 nm scatterfield microscopy using feature sets up to four times smaller in area than state-of-the-art critical dimension targets.

Deep-subwavelength Nanometric Image Reconstruction using Fourier Domain Optical Normalization.

Quantitative optical measurements of deep sub-wavelength, three-dimensional, nanometric structures with sensitivity to sub-nanometer details address an ubiquitous measurement challenge. A Fourier domain normalization approach is used in the Fourier optical imaging code to simulate the full three-dimensional scattered light field of nominally 15 nm sized structures, accurately replicating the light field as a function of the focus position. Using the full three-dimensional light field, nanometer scale details such as a 2 nm thin conformal oxide and nanometer topography are rigorously fitted for features less than 1/30th of the wavelength in size. The densely packed structures are positioned nearly an order of magnitude closer than the conventional Rayleigh resolution limit and can be measured with sub-nanometer parametric uncertainties. This approach enables a practical measurement sensitivity to size variations of only a few atoms in size using a high throughput optical configuration with broad application in measuring nanometric structures and nanoelectronic devices.

Optimizing Hybrid Metrology: Rigorous Implementation of Bayesian and Combined Regression.

Hybrid metrology, e.g., the combination of several measurement techniques to determine critical dimensions, is an increasingly important approach to meet the needs of the semiconductor industry. A proper use of hybrid metrology may yield not only more reliable estimates for the quantitative characterization of 3-D structures but also a more realistic estimation of the corresponding uncertainties. Recent developments at the National Institute of Standards and Technology (NIST) feature the combination of optical critical dimension (OCD) measurements and scanning electron microscope (SEM) results. The hybrid methodology offers the potential to make measurements of essential 3-D attributes that may not be otherwise feasible. However, combining techniques gives rise to essential challenges in error analysis and comparing results from different instrument models, especially the effect of systematic and highly correlated errors in the measurement on the χ2 function that is minimized. Both hypothetical examples and measurement data are used to illustrate solutions to these challenges.

Three-dimensional deep sub-wavelength defect detection using λ = 193 nm optical microscopy.

Optical microscopy is sensitive both to arrays of nanoscale features and to their imperfections. Optimizing scattered electromagnetic field intensities from deep sub-wavelength nanometer scale structures represents an important element of optical metrology. Current, well-established optical methods used to identify defects in semiconductor patterning are in jeopardy by upcoming sub-20 nm device dimensions. A novel volumetric analysis for processing focus-resolved images of defects is presented using simulated and experimental examples. This new method allows defects as narrow as (16 ± 2) nm (k = 1) to be revealed using 193 nm light with focus and illumination conditions optimized for three-dimensional data analysis. Quantitative metrics to compare two-dimensional and three-dimensional imaging indicate possible fourfold improvements in sensitivity using these methods.

Fourier domain optical tool normalization for quantitative parametric image reconstruction.

There has been much recent work in developing advanced optical metrology methods that use imaging optics for critical dimension measurements and defect detection. Sensitivity to nanometer-scale changes has been observed when measuring critical dimensions of subwavelength 20 nm features or when imaging defects below 15 nm using angle-resolved and focus-resolved optical data. However, these methods inherently involve complex imaging optics and analysis of complicated three-dimensional electromagnetic fields. This paper develops a new approach to enable the rigorous analysis of three-dimensional, through-focus, or angle-resolved optical images. We use rigorous electromagnetic simulation with enhanced Fourier optical techniques, an approach to optical tool normalization, and statistical methods to evaluate sensitivities and uncertainties in the measurement of subwavelength three-dimensional structures.

Improving optical measurement uncertainty with combined multitool metrology using a Bayesian approach.

Recently, there has been significant research investigating new optical technologies for dimensional metrology of features 22 nm in critical dimension and smaller. When modeling optical measurements, a library of curves is assembled through the simulation of a multidimensional parameter space. A nonlinear regression routine described in this paper is then used to identify an optimum set of parameters that yields the closest experiment-to-theory agreement. However, parametric correlation, measurement noise, and model inaccuracy all lead to measurement uncertainty in the fitting process for optical critical dimension measurements. To improve the optical measurements, other techniques such as atomic force microscopy and scanning electronic microscopy can also be used to provide supplemental a priori information. In this paper, a Bayesian statistical approach is proposed to allow the combination of different measurement techniques that are based on different physical measurements. The effect of this hybrid metrology approach will be shown to reduce the uncertainties of the parameter estimators.

Scatterfield microscopy for extending the limits of image-based optical metrology.

We have developed a set of techniques, referred to as scatterfield microscopy, in which the illumination is engineered in combination with appropriately designed metrology targets to extend the limits of image-based optical metrology. Previously we reported results from samples with sub-50-nm-sized features having pitches larger than the conventional Rayleigh resolution criterion, which resulted in images having edge contrast and elements of conventional imaging. In this paper we extend these methods to targets composed of features much denser than the conventional Rayleigh resolution criterion. For these applications, a new approach is presented that uses a combination of zero-order optical response and edge-based imaging. The approach is, however, more general and a more comprehensive set of analyses using theoretical methods is presented. This analysis gives a direct measure of the ultimate size and density of features that can be measured with these optical techniques. We present both experimental results and optical simulations using different electromagnetic scattering packages to evaluate the ultimate sensitivity and extensibility of these techniques.

Lower dose of rhBMP-2 achieves spine fusion when combined with an osteoconductive bulking agent in non-human primates.

STUDY DESIGN: A non-human primate lumbar intertransverse process arthrodesis model was used to evaluate the effectiveness of different formulations of recombinant human bone morphogenetic protein-2 (rhBMP-2) to induce consistent bone formation. OBJECTIVE: To determine if the combination of rhBMP-2/absorbable collagen sponge (ACS) wrapped around a bulking agent, consisting of a biphasic calcium phosphate/collagen composite, could achieve posterolateral spine fusion with a dose of rhBMP-2 (3.0 mg/side) that previously failed to induce posterolateral fusion in rhesus monkeys with other carriers. SUMMARY OF BACKGROUND DATA: Successful bone induction in both human and non-human primates has required higher concentrations of BMP than were required in lower order models. The Food and Drug Administration approved concentration of rhBMP-2 for interbody fusion (1.5 mg/mL) when delivered on the ACS alone without a bulking agent (doses 3-9 mg/side) has failed to induce clinically relevant amounts of bone formation in a posterolateral spine fusion model in rhesus monkeys. Previously, a higher concentration of 2.0 mg/mL of rhBMP-2 delivered on stacked sheets of a biphasic calcium phosphate ceramic/collagen compression resistant matrix (CRM) was required to achieve fusion in the rhesus monkey and was the basis for this study (doses of 6-12 mg/side). METHODS: Nine skeletally mature, rhesus macaque monkeys underwent single level posterolateral arthrodesis at L4-L5. Two different rhBMP-2 doses were evaluated in 3 delivery configurations. The first 3 monkeys received 10 mg/side (2.5 mL at 4.0 mg/mL) of rhBMP-2 loadeddirectly onto a CRM carrier (15% hydroxyapatite/85%beta-tricalcium phosphate ceramic/collagen matrix), resulting in a final concentration of 2.0 mg/mL. The second 3 monkeys received 3 mg/side (2.0 mL at 1.5 mg/mL) of rhBMP-2 loaded directly on the CRM carrier, resulting in a 0.6 mg/mL final concentration. Three additional monkeys also received the 3 mg/side (2.0 mL at 1.5 mg/mL) of rhBMP-2 delivered on an ACS, which was then wrapped around the dry CRM matrix used as a bulking agent, yielding a 1.5 mg/mL final concentration of rhBMP-2 on the sponge wrapped around the bulking agent. The monkeys were euthanized at 24 weeks after surgery. Manual palpation, plain radiographs, computerized tomography, and nondecalcified histology were used to evaluate fusion in a blinded fashion. RESULTS: The 3 monkeys with 10 mg rhBMP-2 placed directly on the CRM carrier (2.0 mg/mL final concentration) achieved solid fusion. The 3 monkeys that underwent fusion with 3 mg of rhBMP-2 placed directly on the CRM carrier (0.6 mg/mL final concentration) failed to achieve fusion. In contrast, the 3 monkeys that underwent fusion with the same 3 mg dose of rhBMP-2 dispensed only on an ACS that was wrapped around the CRM achieved solid bilateral fusion. CONCLUSIONS: This study shows the importance of carrier optimization and final implant protein concentration for the successful delivery of rhBMP-2. By combining the properties of the ACS with the CRM, the required dosage of rhBMP-2 was diminished by more than 3-fold in the non-human primate model. This finding suggests that the currently available concentration of rhBMP-2 (1.5 mg/mL) could be successful for achieving posterolateral spine fusion when combined with an osteoconductive bulking agent that can support the induced new bone formation.

Comparison of Healos/bone marrow to INFUSE(rhBMP-2/ACS) with a collagen-ceramic sponge bulking agent as graft substitutes for lumbar spine fusion.

STUDY DESIGN: A rabbit lumbar intertransverse process arthrodesis model was used to evaluate the efficacy of two different bone substitute materials: 1) collagen-hydroxyapatite sponge (Healos bone void filler) combined with heparinized bone marrow; and 2) recombinant human bone morphogenetic protein-2 delivered in a collagen sponge (INFUSE Bone Graft) wrapped around an additional collagen-ceramic sponge (Mastergraft Matrix) as a "bulking agent." OBJECTIVES: To compare the relative efficacy of two different bone graft substitutes to achieve posterolateral lumbar spine fusion in rabbits. SUMMARY OF BACKGROUND DATA: Autogenous bone graft is considered the gold standard graft material for spine fusion. Complications with its use, however, may occur in as many as 30% of patients. A variety of bone substitutes have been used for spine fusion, but there are few direct comparison experiments to determine the relative efficacy of any two alternatives. METHODS: Adult New Zealand white rabbits (n = 24) were divided into two groups and underwent bilateral posterolateral intertransverse process spine arthrodesis at L5-L6. The fusions were augmented by different bone substitute materials as follows: Group 1 (n = 12) received 3 mL of collagen-hydroxyapatite sponge (Healos bone void filler) (10 x 30 x 5 mm, two per side) with 3.0 mL of heparinized bone marrow on each side of the spine. (ratio 1:1); Group 2 (n = 12) received 1.5 mL of rhBMP-2 (0.43 mg/mL solution) on a Type 1 collagen sponge (INFUSE Bone Graft) wrapped around an additional 1.5 mL collagen-ceramic (15%HA/85%TCP) sponge (Mastergraft Matrix) as a bulking agent to provide 3 mL of graft on each side of the spine. Bone marrow was aspirated from posterior iliac crest, and 1 mL of bone marrow was sent to count number of nucleated cells. The rabbits were killed after 8 weeks; the spines were evaluated by manual palpation, radiographs (plain radiograph and CT scan), tensile mechanical testing, and nondecalcified histology. RESULTS: The bone marrow had average of total nucleated cell count 9 x 10 cells. All rabbits (100%) in Group 2 (INFUSE/Mastergraft Matrix) achieved solid spinal fusions by manual palpation and radiographs, whereas solid spinal fusion was not achieved by manual palpation and radiographs in any of the rabbits treated with Healos combined with heparinized bone marrow (Group 1). The plain radiograph and CT scans of Group 1 showed some minimal new bone formation near the transverse processes, but none of these rabbits formed a continuous fusion mass. In contrast, all of plain radiographs and CT scans in Group 2 showed continuous fusion mass and complete graft incorporation between transverse processes bilaterally. Biomechanically, the relative strength and relative stiffness values of L5-L6 (fusion segment) in Group 2 were statistically significant greater than L5-L6 in Group 1 (P < 0.001). Histologic sections confirmed the palpation and radiographic results. CONCLUSION: From the manual palpation, radiographic and biomechanical assessment of fusion, the results in this study showed that INFUSE (rhBMP-2/collagen sponge) consistently produced spine fusion when wrapped around a collagen-ceramic sponge bulking agent (Mastergraft Matrix). Meanwhile, Healos was ineffective as a bone graft material when combined with heparinized autogenous bone marrow.

Postoperative Level 1 anticoagulation therapy and spinal surgery: practical guidelines for management.

OBJECT: The authors conducted a review of the literature to establish reasonable practical guidelines for the management of complications in patients who have undergone recent spinal surgery and who require Level 1 anticoagulation therapy. METHODS: A MEDLINE (PubMed) literature search was performed using the key words "postoperative anticoagulation," "spinal surgery," and "postoperative epidural hematoma," for articles published between 1990 and 2004. The search yielded 148 articles, which were then further screened for relevance and classified according to level-of-evidence guidelines established by the American Association of Neurological Surgeons/Congress of Neurological Surgeons joint committee for spinal cord injury. A total of 12 relevant articles were reviewed. There were no relevant articles meeting Class 1 standards of evidence, two met Class 2 evidence standards (one was a nonrandomized cohort study, the other was case-controlled), and the remaining 10 articles contained Class 3 evidence. CONCLUSIONS: There are insufficient data to establish evidence-based guidelines for the use of Level 1 heparin or an equivalent anticoagulation protocol in patients who have recently undergone spinal surgery. Nevertheless, a search of the limited peer-reviewed literature on the subject indicates that there is an anecdotally high risk of complications in patients who have undergone spinal surgery and in whom a Level 1 or equivalent heparin protocol is administered. It therefore seems most prudent to arrange for placement of a vena cava filter in patients who have undergone spinal surgery and in whom a pulmonary embolus is found postoperatively. In patients who undergo spinal surgery and who require heparinization therapy for myocardial ischemia or infarction, the use of frequent neurological examinations in conjunction with anticoagulation therapy seems to be the only reasonable option.

Cervical osteomyelitis: a brief review.

OBJECT: The authors conducted a literature-based review of the etiology, diagnosis, and treatment of cervical vertebral osteomyelitis (CVO). METHODS: A Medline (PubMed) search using the key words "cervical vertebral osteomyelitis" yielded 256 articles. These were further screened for relevance, yielding 15 articles. Each publication was reviewed, and several others not identified in the PubMed search were screened and included in the review according to relevance. Each article was identified as involving either the epidemiology/etiology, diagnosis, or treatment of CVO. Separate categories were created for case reports and general reviews. CONCLUSIONS: Cervical vertebral osteomyelitis has a spectrum of origins, which include spontaneous, postoperative, traumatic, and hematogenously spread causes. The majority of patients have medical risk factors and comorbidities that include diabetes, trauma, drug abuse, and infectious processes in extraspinal areas. The diagnosis of CVO can be accomplished in most cases by using plain x-ray films and computerized tomography scans. Nevertheless, preferential use of magnetic resonance imaging in cases in which there is a neurological deficit is helpful in identifying epidural compressive processes. Treatment for CVO can be successfully initiated with intravenous antibiotic therapy. Nevertheless, in cases in which there is a neurological deficit, spinal deformity and/or progressive lysis, or intractable pain, the earliest feasible surgical intervention with debridement and fusion is warranted.

Intracerebral hemorrhage secondary to vascular lesions.

The article reviews intracerebral hemorrhage caused by vascular malformations. The article also reviews incidence, prevalence, and distribution of parenchymal hemorrhage caused by aneurysms, arteriovenous malformations, and cavernous malformations are defined, and less common vascular lesions. There is a discussion of the role of cerebral vascular malformations in producing cerebral hemorrhage in young adults abusing illicit drugs.

Allograft implants for posterior lumbar interbody fusion: results comparing cylindrical dowels and impacted wedges.

OBJECTIVE: With the proliferation of implant types available for use in posterior lumbar interbody fusion (PLIF) procedures, the choices for surgeons have become increasingly complex. The goal of this study was to retrospectively review a series of 49 patients who underwent PLIF with the use of allograft cylindrical threaded cortical bone dowels (TCBDs) and allograft impacted wedges. Nerve root injury rates, fusion rates, and clinical outcomes of the allograft impacted wedge group are compared with those in the allograft cylindrical TCBD group. METHODS: We performed a retrospective chart and radiographic review of 49 patients. Twenty-seven patients underwent PLIF with impacted allograft wedges, and 22 patients underwent PLIF with allograft cylindrical TCBD. Permanent nerve root injury rates, fusion rates, and clinical outcomes were assessed on the basis of a minimum of 1 year of follow-up data in this nonconsecutive series. RESULTS: Permanent nerve root injuries in the impacted wedge and TCBD groups were documented with physical examinations conducted pre- and postoperatively. The cylindrical TCBD group showed a 13.6% rate of permanent nerve root injury, and the impacted wedge group demonstrated a 0% rate, and these rates were statistically significant (analysis of variance, P = 0.049). The fusion rate at a mean of 13.9 months of follow-up was 95.4% in patients in whom the cylindrical TCBD was implanted and 88.9% after a mean of 17.4 months of follow-up in patients in whom impacted wedges were used. The fusion rate difference between the TCBD and impacted wedge groups was not significant. The satisfactory outcome rate was 72.7% for the TCBD group and 85.1% for the impacted wedge group, and the impacted wedge group was found to have a significantly higher rate of satisfactory outcomes (P = 0.016, analysis of variance). Analysis of the patient outcomes in the TCBD and impacted wedge groups according to sex, mean length of follow-up, workman's compensation claim rate, and smoking habit yielded no significant difference. CONCLUSION: With a minimum of 1 year of follow-up in this nonconsecutive series of 49 patients, a comparison of the use of allograft TCBD versus allograft impacted wedges in PLIF procedures reveals a statistically significant increase in permanent nerve root injury rates with the use of cylindrical TCBD implants as compared with impacted allograft wedges. There is no difference between the two groups in terms of fusion rates, and clinical outcomes with the use of impacted wedges were significantly better.

Anterior cervical plating enhances arthrodesis after discectomy and fusion with cortical allograft.

OBJECTIVE: Anterior plate fixation has gained widespread acceptance for the treatment of cervical spondylosis, theoretically enhancing the rate of arthrodesis. There are few studies comparing fusion rates after anterior cervical discectomy and fusion (ACDF) with and without a plate. The purpose of this study was to evaluate the efficacy of anterior cervical plating for fusion enhancement after one- and two-level ACDF with cortical allograft. METHODS: A retrospective review was performed with 251 patients who underwent one- or two-level ACDF with cortical allograft and plate stabilization between 1993 and 1999. An independent surgeon reviewer determined fusion status and complications. A successful fusion was defined by the absence of lucency around the graft, evidence of bridging bone between the endplate and the graft, and the absence of movement on dynamic imaging scans. Follow-up data, ranging from 9 months to 3.6 years, were available for 233 patients. A control group of 289 patients who underwent ACDF without plating was described in a previously published report by the senior author (RWH). Therefore, a total of 540 patients were evaluated for determination of the efficacy of anterior cervical plating with cortical allograft bone. Statistical significance was determined by chi(2) test. RESULTS: The fusion rates for one- and two-level ACDF with anterior fixation were 96 and 91%, respectively, compared with 90 and 72% for one- and two-level ACDF without anterior fixation. The observed increases in fusion rates for both one- and two-level procedures proved to be statistically significant (P < 0.05). There were no recorded infectious, neurological, or graft-related complications among the cohort treated with anterior cervical plating. Compared with the results for the cohort treated without anterior cervical plates, there was a statistically significant decrease in the graft-related complication rate with the application of plates (P < 0.001). Two patients who received plates were noted to have adjacent-segment degenerative changes that required surgical intervention. No hardware fractures were noted; however, one patient was noted to have a single displaced screw, without clinical consequences. CONCLUSION: The use of anterior cervical plating after one- and two-level ACDF with allograft cortical bone significantly enhanced arthrodesis. The improved fusion rate and negligible complication rate associated with anterior cervical plating are compelling factors justifying its use in the treatment of cervical spondylosis.

Early results using the Atlantis anterior cervical plate system.

OBJECT: The authors present a retrospective review of 77 patients in whom they performed anterior cervical discectomy and fusion (ACDF) in the treatment of radiculopathy and/or myelopathy. In all cases anterior interbody fusion was performed using the Atlantis locking plate system to treat the degenerative disease. METHODS: There were 41 men and 36 women (mean age 53.8 years), and 24 active cigarette smokers (31%) in the group. All patients presented with signs and symptoms of cervical radiculopathy and/or myelopathy, and magnetic resonance imaging or computerized tomography myelography demonstrated evidence of radicular and/or spinal cord compression at one or more cervical levels. Thirty-one patients underwent single-level ACDF, 20 patients underwent multilevel ACDF without posterior instrumentation, in eight patients one- to four-level corpectomies were supplemented with posterior fixation, 12 patients underwent single-level corpectomy, and six patients underwent multilevel corpectomy with no posterior instrumentation. The mean follow-up period was 15.33 months; overall good-to-excellent outcome was seen in 75% of patients; osseous fusion was demonstrated in 93.5%. In all patients except three, fibular allograft was used as graft material. The degree of overall cervical lordosis was measured at the last follow up and was compared with normal values obtained in age-matched individuals. In addition, the degree of cervical lordosis at fusion levels was compared with overall cervical lordosis. In patients in all five of the aforementioned categories significantly less lordosis was demonstrated than in age-matched controls. In patients who underwent single-level ACDF, single-level corpectomy, and multilevel ACDF significantly less lordosis was observed at the fusion segment than that in the overall cervical spine. Complications included one episode of chronic anterior wound drainage treated with intravenous antibiotic medication and one postoperative posterior wound infection, which required reoperation and intravenous antibiotic medication. Two cases (2.6%) of anterior screw backout and/or breakage were identified. One patient died of unrelated causes within 3 months of operation. CONCLUSIONS: These initial results indicate that use of the Atlantis plate system for anterior cervical arthrodesis produces fusion rates and clinical outcomes that are comparable with those obtained using other locking plating systems. It has the unique advantage, however, of providing the surgeon with the choice of fixed, variable, or hybrid screw constructs as a way of tailoring screw angles to individual anatomical/biomechanical needs.

The Cervical Spine Study Group anterior cervical plate nomenclature.

The authors review historical and biomechanical aspects of anterior cervical plate (ACP) systems. They propose a novel classification system for ACPs based on the biomechanical and graft-loading properties of these systems. A retrospective review of the literature comprising both clinical and laboratory investigations regarding the ACP system was undertaken. Comparison of each system is considered in the context of the biomechanical attributes and graft-loading properties of each type of plate. Salient characteristics reviewed include restriction of screw backout, screw-angle variability, and mobility at the screw-plate interface. A new classification system for ACPs is proposed that primarily considers the ability of the construct to restrict screw backout, as well as the properties of the plate-screw interface--that is, the capacity for rotational or translational movement. A new classification system is presented that provides unified, biomechanically descriptive nomenclature. Using this nomenclature, the ACP devices currently available and those developed in the future can be uniformly categorized.