Establishing 3D Printing at the Point of Care: Basic Principles and Tools for Success.

As the medical applications of three-dimensional (3D) printing increase, so does the number of health care organizations in which adoption or expansion of 3D printing facilities is under consideration. With recent advancements in 3D printing technology, medical practitioners have embraced this powerful tool to help them to deliver high-quality patient care, with a focus on sustainability. The use of 3D printing in the hospital or clinic at the point of care (POC) has profound potential, but its adoption is not without unanticipated challenges and considerations. The authors provide the basic principles and considerations for building the infrastructure to support 3D printing inside the hospital. This process includes building a business case; determining the requirements for facilities, space, and staff; designing a digital workflow; and considering how electronic health records may have a role in the future. The authors also discuss the supported applications and benefits of medical 3D printing and briefly highlight quality and regulatory considerations. The information presented is meant to be a practical guide to assist radiology departments in exploring the possibilities of POC 3D printing and expanding it from a niche application to a fixture of clinical care. An invited commentary by Ballard is available online. ©RSNA, 2022.

Time and Accuracy of the CEREC Omnicam Using Two Different Software Programs.

PURPOSE: The purpose of this in vitro study was to evaluate the effect of software on scan time, trueness, and precision of digital scans created using the CEREC Omnicam. MATERIAL AND METHODS: Sixty scans (20 scans/provider) of a standard reference cast were made by three different providers using the CEREC Omnicam with both CEREC Ortho 1.2.1 software (10 scans/provider) and CEREC SW 4.4.4 software (10 scans/provider). A digital full arch scan and the time to complete each scan were recorded. Trueness was calculated by overlaying the digital scans against a reference file created using the standard reference cast and a laboratory-based, white light, 3-dimensional scanner. Precision was calculated by overlaying each of digital scans against each other, using each scan as a reference. The non-parametric Mann-Whitney U-test was used to determine significant differences attributable to scanning software for each provider. RESULTS: The CEREC Ortho 1.2.1 software required a longer scan time than the CEREC SW 4.4.4 software for each provider (∼1 minute). No significant difference in trueness was observed within one provider. Two individual providers had higher precision when scanning with the CEREC Ortho 1.2.1 software than the CEREC SW 4.4.4 software. CONCLUSION: Software and scan strategy may affect the accuracy of complete-arch scans. The CEREC Ortho 1.2.1 software may demonstrate a speed-accuracy tradeoff, with generally longer scan times and possibly more precise scans.

Retentive Forces of Removable Partial Denture Clasp Assemblies Made from Polyaryletherketone and Cobalt-Chromium: A Comparative Study.

PURPOSE: To compare retentive forces of removable partial denture clasps traditionally fabricated with cobalt-chromium (CoCr) material and two computer-aided design and computer-aided manufactured (CAD/CAM) thermoplastic polymers. MATERIALS AND METHODS: Forty-eight clasp assemblies (16 CoCr, 16 polyetheretherketone (PEEK) and 16 polyetherketoneketone (PEKK) thermoplastic polymer) were fabricated for 48 mandibular tooth analogs. Individual clasps were inserted and removed on the tooth analogs utilizing a chewing simulator for 15,000 cycles to simulate 10 years of use. Retentive forces were measured utilizing a mechanical load tester at baseline and intervals of 1500 cycles. Data were analyzed with one-way Analysis of Variance, Tukey post-hoc, and paired T tests. RESULTS: Mean retentive forces between all groups were significantly different (p < 0.001). Retentive forces of CoCr clasps were significantly higher than both polymers (p < 0.001). The mean retentive forces for PEEK were not significantly different from PEKK (p = 0.23). A significant increase in retentive forces was observed for all three clasps after the first period of cycling, followed by continual decrease for the remaining cycles. At the endpoint of 15,000 cycles, no clasp assemblies showed lower retentive forces than at initial baseline. CONCLUSION: Thermoplastic polymer clasps demonstrated lower retentive forces compared to CoCr clasps. All three groups displayed a similar pattern of initial increase, followed by a gradual decrease, of retentive force. Despite this observation, the clasps maintained similar or higher retentive forces than measured at baseline. This resistance to fatigue and ability to fabricate with CAD/CAM technologies provides support for clinical use of these high-performance polymer (HPP) materials.

RadioGraphics Update: Medical 3D Printing for the Radiologist.

Editor's Note.-Articles in the RadioGraphics Update section provide current knowledge to supplement or update information found in full-length articles previously published in RadioGraphics. Authors of the previously published article provide a brief synopsis that emphasizes important new information such as technological advances, revised imaging protocols, new clinical guidelines involving imaging, or updated classification schemes. Articles in this section are published solely online and are linked to the original article.

CT-Based 3D Printing of the Glenoid Prior to Shoulder Arthroplasty: Bony Morphology and Model Evaluation.

To demonstrate the 3D printed appearance of glenoid morphologies relevant to shoulder replacement surgery and to evaluate the benefits of printed models of the glenoid with regard to surgical planning. A retrospective review of patients referred for shoulder CT was performed, leading to a cohort of nine patients without arthroplasty hardware and exhibiting glenoid changes relevant to shoulder arthroplasty planning. Thin slice CT images were used to create both humerus-subtracted volume renderings of the glenoid, as well as 3D surface models of the glenoid, and 11 printed models were created. Volume renderings, surface models, and printed models were reviewed by a musculoskeletal radiologist for accuracy. Four fellowship-trained orthopaedic surgeons specializing in shoulder surgery reviewed each case individually as follows: First, the source CT images were reviewed, and a score for the clarity of the bony morphologies relevant to shoulder arthroplasty surgery was given. The volume rendering was reviewed, and the clarity was again scored. Finally, the printed model was reviewed, and the clarity again scored. Each printed model was also scored for morphologic complexity, expected usefulness of the printed model, and physical properties of the model. Mann-Whitney-Wilcoxon signed rank tests of the clarity scores were calculated, and the Spearman's ρ correlation coefficient between complexity and usefulness scores was computed. Printed models demonstrated a range of glenoid bony changes including osteophytes, glenoid bone loss, retroversion, and biconcavity. Surgeons rated the glenoid morphology as more clear after review of humerus-subtracted volume rendering, compared with review of the source CT images (p = 0.00903). Clarity was also better with 3D printed models compared to CT (p = 0.00903) and better with 3D printed models compared to humerus-subtracted volume rendering (p = 0. 00879). The expected usefulness of printed models demonstrated a positive correlation with morphologic complexity, with Spearman's ρ 0.73 (p = 0.0108). 3D printing of the glenoid based on pre-operative CT provides a physical representation of patient anatomy. Printed models enabled shoulder surgeons to appreciate glenoid bony morphology more clearly compared to review of CT images or humerus-subtracted volume renderings. These models were more useful as glenoid complexity increased.

Complete-arch accuracy of intraoral scanners.

STATEMENT OF PROBLEM: Intraoral scanners have shown varied results in complete-arch applications. PURPOSE: The purpose of this in vitro study was to evaluate the complete-arch accuracy of 4 intraoral scanners based on trueness and precision measurements compared with a known reference (trueness) and with each other (precision). MATERIAL AND METHODS: Four intraoral scanners were evaluated: CEREC Bluecam, CEREC Omnicam, TRIOS Color, and Carestream CS 3500. A complete-arch reference cast was created and printed using a 3-dimensional dental cast printer with photopolymer resin. The reference cast was digitized using a laboratory-based white light 3-dimensional scanner. The printed reference cast was scanned 10 times with each intraoral scanner. The digital standard tessellation language (STL) files from each scanner were then registered to the reference file and compared with differences in trueness and precision using a 3-dimensional modeling software. Additionally, scanning time was recorded for each scan performed. The Wilcoxon signed rank, Kruskal-Wallis, and Dunn tests were used to detect differences for trueness, precision, and scanning time (α=.05). RESULTS: Carestream CS 3500 had the lowest overall trueness and precision compared with Bluecam and TRIOS Color. The fourth scanner, Omnicam, had intermediate trueness and precision. All of the scanners tended to underestimate the size of the reference file, with exception of the Carestream CS 3500, which was more variable. Based on visual inspection of the color rendering of signed differences, the greatest amount of error tended to be in the posterior aspects of the arch, with local errors exceeding 100 µm for all scans. The single capture scanner Carestream CS 3500 had the overall longest scan times and was significantly slower than the continuous capture scanners TRIOS Color and Omnicam. CONCLUSIONS: Significant differences in both trueness and precision were found among the scanners. Scan times of the continuous capture scanners were faster than the single capture scanners.

A Craniomaxillofacial Surgical Assistance Workstation for Enhanced Single-Stage Reconstruction Using Patient-Specific Implants.

BACKGROUND: Craniomaxillofacial reconstruction with patient-specific, customized craniofacial implants (CCIs) is ideal for skeletal defects involving areas of aesthetic concern-the non-weight-bearing facial skeleton, temporal skull, and/or frontal-forehead region. Results to date are superior to a variety of "off-the-shelf" materials, but require a protocol computed tomography scan and preexisting defect for computer-assisted design/computer-assisted manufacturing of the CCI. The authors developed a craniomaxillofacial surgical assistance workstation to address these challenges and intraoperatively guide CCI modification for an unknown defect size/shape. METHODS: First, the surgeon designed an oversized CCI based on his/her surgical plan. Intraoperatively, the surgeon resected the bone and digitized the resection using a navigation pointer. Next, a projector displayed the limits of the craniofacial bone defect onto the prefabricated, oversized CCI for the size modification process; the surgeon followed the projected trace to modify the implant. A cadaveric study compared the standard technique (n = 1) to the experimental technique (n = 5) using surgical time and implant fit. RESULTS: The technology reduced the time and effort needed to resize the oversized CCI by an order of magnitude as compared with the standard manual resizing process. Implant fit was consistently better for the computer-assisted case compared with the control by at least 30%, requiring only 5.17 minutes in the computer-assisted cases compared with 35 minutes for the control. CONCLUSION: This approach demonstrated improvement in surgical time and accuracy of CCI-based craniomaxillofacial reconstruction compared with previously reported methods. The craniomaxillofacial surgical assistance workstation will provide craniofacial surgeons a computer-assisted technology for effective and efficient single-stage reconstruction when exact craniofacial bone defect sizes are unknown.

Cranioplasty in the deployed environment: experience for host-country nationals.

OBJECTIVE: Decompressive craniectomy (DC) is the definitive neurosurgical treatment for managing refractory malignant cerebral edema and intracranial hypertension due to combat-related severe traumatic brain injury (TBI). To date, the long-term outcomes and sequelae of this procedure on host-country national (HCN) populations during Operation Iraqi Freedom (Iraq, 2003-2011), Operation Enduring Freedom (Afghanistan, 2001-2014), and Operation Freedom's Sentinel (Afghanistan, 2015-2021) have not been described, specifically the process and results of delayed custom synthetic cranioplasty. The Joint Trauma System's Clinical Practice Guidelines (JTS-CPG) for severe head injury counsels surgeons to discard the cranial osseous explant when treating coalition service members. Ongoing political and healthcare system instabilities often preclude opportunities for delayed cranioplasty by host-country assets. Various surgical options (such as hinge craniectomy) are inadequate in the setting of complicated cranial comminution from blast or missile injuries, severe cerebral edema, grossly contaminated wounds, complex polytrauma, and tissue devitalization. Delayed cranioplasty with a custom synthetic implant is a viable but logistically challenging alternative. In this retrospective review, the authors present the first patient series describing delayed custom synthetic cranioplasty in an HCN population performed during active military conflict. METHODS: Patients were identified through the Joint Trauma System/Theater Medical Data Store, and subgroup analyses were performed to include mechanisms of injury, surgical complications, and clinical outcomes. RESULTS: Twenty-five patients underwent DC between 2012 and 2020 to treat penetrating, blast, and high-energy closed head injuries per JTS-CPG criteria. The average time from injury to surgery was 1.4 days, although 6 patients received delayed care (3-6 days) due to protracted evacuation from local hospitals. Delayed care correlated with an increased rate of intracranial abscess and empyema. The average time to cranioplasty was 134 days due to a lack of robust mechanisms for patient follow-up, tracking, and access to NATO hospitals. HCN patients who recovered from DC demonstrated overall benefit from custom synthetic cranioplasty, although formal statistical analysis was impeded by a lack of long-term follow-up. CONCLUSIONS: This review demonstrates that cranioplasty with a custom synthetic implant is a safe and feasible treatment for vulnerable HCN patients who survive their index DC surgery. This unique paradigm of care highlights the capabilities of deployed neurosurgical healthcare teams working in partnership with the prosthetics laboratory at Walter Reed National Military Medical Center.

Additive Manufacturing for Fabrication of Point-of-Care Therapies in Austere Environments.

INTRODUCTION: Known as the "golden hour," survival of most critically injured patients is highly dependent on providing the required treatment within the first hour of injury. Recent technological advances in additive manufacturing (also known as three-dimensional [3D] printing) allow for austere deployment and point-of-care rapid fabrication of a variety of medical supplies, including human tissues and bioactive bandages, in prolonged field care scenarios. In this pilot project, our aim was to investigate the ability to 3D print a range of potential biomedical supplies and solutions in an austere field environment. MATERIALS AND METHODS: We specifically designed and fabricated novel surgical tools, bioactive bandages, objects (screw and anatomic models), and human meniscal tissue in an austere African desert environment. A total of seven packages were sent using a commercial carrier directly to the end destination. A multi-tool ruggedized 3D printer was used as the manufacturing platform for all objects fabricated downrange. Human mesenchymal stem cells were shipped for 3D bioprinting of human menisci and bioactive bandages. Design and fabrication for all 3D-printed products utilized computer-aided design (CAD) tools. RESULTS: Initial shipment from a single U.S. site to the sub-Saharan Africa location was relatively prompt, taking an average of 4.7 days to deliver three test packages. However, the actual delivery of the seven packages from Orlando, FL, to the same sub-Saharan Africa site took an average of 16 days (range 7-23 days). The ruggedized printer successfully fabricated relevant medical supplies using biocompatible filament, bioink hydrogels, and stem cell-loaded bioinks. This prototype did not, however, have the capacity to provide a sterile environment. A multi-material complete bandage was 3D printed using polyamide polyolefin and cellulose, live cells, neomycin salve, and adhesive. The bandage, wound covering backing, and adhesive backing print took under 2 min to 3D print. Surgical instrument CAD files were based on commercially available medical-grade stainless-steel instruments. The screw CAD file was downloaded from the NIH 3D Print Exchange website. The prints of the two surgical tools and screw using thermoplastic material were successful. Menisci, relatively complex forms of the cartilage, were 3D bioprinted with a gel that held their form well after printing and were then solidified slightly using a cross-linking solution. After 2 min of solidification, it was possible to remove and handle the menisci. CONCLUSION: The current and future challenges of prolonged field care need to be addressed with new techniques, training, and technology. Ruggedized, deployable 3D printers allow for the direct fabrication of medical tools, supplies, and biological solutions for austere use. Delivery of packages can vary, and attention to routes and location is key, especially for transit of time-sensitive perishable supplies such as live cells. The significance of this study provides the real possibility to 3D print "just-in-time" medical solutions tailored to the need of an individual service member in any environment. This is a potentially exciting opportunity to bring critical products to the war front.

Volumetric changes in edentulous alveolar ridge sites utilizing guided bone regeneration and a custom titanium ridge augmentation matrix (CTRAM): a case series study.

BACKGROUND: The purpose of this study was to evaluate the volumetric changes in partially edentulous alveolar ridges augmented with customized titanium ridge augmentation matrices (CTRAM), freeze-dried bone allograft, and a resorbable collagen membrane. METHODS: A pre-surgical cone beam computed tomography (CBCT) scan was obtained for CTRAM design/fabrication and to evaluate pre-surgical ridge dimensions. Ridge augmentation surgery using CTRAM, freeze-dried bone allograft, and a resorbable collagen membrane was performed at each deficient site. Clinical measurements of the area of augmentation were made at the time of CTRAM placement and re-entry, and a 2nd CBCT scan 7 months after graft placement was used for volumetric analysis. Locations of each CTRAM in situ were also compared to their planned positions. Re-entry surgery and implant placement was performed 8 months after CTRAM placement. RESULTS: Nine subjects were treated with CTRAM and freeze-dried bone allograft. Four out of the nine patients enrolled (44.4%) experienced premature CTRAM exposure during healing, and in two of these cases, CTRAM were removed early. Early exposure did not result in total graft failure in any case. Mean volumetric bone gain was 85.5 ± 30.9% of planned augmentation volume (61.3 ± 33.6% in subjects with premature CTRAM exposure vs. 104.9% for subjects without premature exposure, p = 0.03). Mean horizontal augmentation (measured clinically) was 3.02 mm, and vertical augmentation 2.86 mm. Mean surgical positional deviation of CTRAM from the planned location was 1.09 mm. CONCLUSION: The use of CTRAM in conjunction with bone graft and a collagen membrane resulted in vertical and horizontal bone gain suitable for implant placement.

Creating patient-specific anatomical models for 3D printing and AR/VR: a supplement for the 2018 Radiological Society of North America (RSNA) hands-on course.

Advanced visualization of medical image data in the form of three-dimensional (3D) printing continues to expand in clinical settings and many hospitals have started to adapt 3D technologies to aid in patient care. It is imperative that radiologists and other medical professionals understand the multi-step process of converting medical imaging data to digital files. To educate health care professionals about the steps required to prepare DICOM data for 3D printing anatomical models, hands-on courses have been delivered at the Radiological Society of North America (RSNA) annual meeting since 2014. In this paper, a supplement to the RSNA 2018 hands-on 3D printing course, we review methods to create cranio-maxillofacial (CMF), orthopedic, and renal cancer models which can be 3D printed or visualized in augmented reality (AR) or virtual reality (VR).

Using 3D models in orthopedic oncology: presenting personalized advantages in surgical planning and intraoperative outcomes.

BACKGROUND: Three Dimensional (3D) printed models can aid in effective pre-operative planning by defining the geometry of tumor mass, bone loss, and nearby vessels to help determine the most accurate osteotomy site and the most appropriate prosthesis, especially in the case of complex acetabular deficiency, resulting in decreased operative time and decreased blood loss. METHODS: Four complicated cases were selected, reconstructed and printed. These 4 cases were divided in 3 groups of 3D printed models. Group 1 consisted of anatomical models with major vascular considerations during surgery. Group 2 consisted of an anatomical model showing a bone defect, which was intended to be used for substantial instrumentation, pre-operatively. Group 3 consisted of an extra-compartmental bone tumor which displayed a deteriorated cortical outline; thus, using CT and MRI fused images to reconstruct the model accurately. An orthopedic surgeon created the 3D models of groups 1 and 2 using standard segmentation techniques. Because group 3 required complex techniques, an engineer assisted during digital model construction. RESULTS: These models helped to guide the orthopedic surgeon in creating a personalized pre-operative plan and a physical simulation. The models proved to be beneficial and assisted with all 4 cases, by decreasing blood loss, operative time and surgical incision length, and helped to select the appropriate acetabular supporting ring in complex acetabular deficiency, pre-operatively. CONCLUSION: Qualitatively, using 3D printing in tumor cases, provides personalized advantages regarding the various characteristics of each skeletal tumor.

Using computed tomography and 3D printing to construct custom prosthetics attachments and devices.

BACKGROUND: The prosthetic devices the military uses to restore function and mobility to our wounded warriors are highly advanced, and in many instances not publically available. There is considerable research aimed at this population of young patients who are extremely active and desire to take part in numerous complex activities. While prosthetists design and manufacture numerous devices with standard materials and limb assemblies, patients often require individualized prosthetic design and/or modifications to enable them to participate fully in complex activities. METHODS: Prosthetists and engineers perform research and implement digitally designs in collaboration to generate equipment for their patient's rehabilitation needs. 3D printing allows for these devices to be manufactured from an array of materials ranging from plastic to titanium alloy. Many designs require form fitting to a prosthetic socket or a complex surface geometry. Specialty items can be scanned using computed tomography and digitally reconstructed to produce a virtual 3D model the engineer can use to design the necessary features of the desired prosthetic, device, or attachment. Completed devices are tested for fit and function. RESULTS: Numerous custom prostheses and attachments have been successfully translated from the research domain to clinical reality, in particular, those that feature the use of computed tomography (CT) reconstructions. The purpose of this project is to describe the research pathways to implementation for the following clinical designs: sets of bilateral hockey skates; custom weightlifting prosthetic hands; and a wine glass holder. CONCLUSION: This article will demonstrate how to incorporate CT imaging and 3D printing in the design and manufacturing process of custom attachments and assistive technology devices. Even though some of these prosthesis attachments may be relatively simple in design to an engineer, they have an enormous impact on the lives of our wounded warriors.

Custom Titanium Ridge Augmentation Matrix (CTRAM): A Case Report.

This is a case report of a custom titanium ridge augmentation matrix (CTRAM). Using cone beam computed tomography (CBCT), a custom titanium space-maintaining device was developed. Alveolar ridges were virtually augmented, a matrix was virtually designed, and the CTRAM was additively manufactured with titanium (Ti6Al4V). Two cases are presented that resulted in sufficient increased horizontal bone volume with successful dental implant placement. The CTRAM design allows for preoperative planning for increasing alveolar ridge dimensions to support dental implants, reduces surgical time, and prevents the need for a second surgical site to gain sufficient alveolar ridge bone volume for dental implant therapy.

Custom Anatomical 3D Spacer for Temporomandibular Joint Resection and Reconstruction.

Two cases are presented using a two-stage approach and a custom antibiotic spacer placement. Temporomandibular reconstruction can be very demanding and accomplished with a variety of methods in preparation of a total joint and ramus reconstruction with total joint prostheses (TMJ Concepts, Ventura, CA). Three-dimensional reconstructions from diagnostic computed tomography were used to establish a virtually planned resection which included the entire condyle-ramus complex. From these data, digital designs were used to manufacture molds to facilitate intraoperative fabrication of precise custom anatomic spacers from rapidly setting antibiotic-impregnated polymethyl methacrylate. Molds were manufactured using vat polymerization (stereolithography) with a photopolymer in the first case and powder bed fusion (electron beam melting) with Ti6AL4V for the second. Surgical methodology and the use of molds for intraoperative spacer fabrication for each case are discussed.

Computer-assisted single-stage cranioplasty.

Cranioplasty treats and repairs cranial defects with a custom craniofacial implant (CCI). Typically, surgeons know the defect size prior to surgery. Recent efforts consider single-stage cranioplasty-performing the bony resection and fixating the CCI in a single operation. This paper develops a computer-assisted technique to perform single-stage cranioplasty. Intraoperatively, the surgeon traces the bony resection. The outline of the bony cuts is projected on a preoperatively-designed CCI to guide the surgeon during the resizing. A cadaveric case study showed good fit with minimal gaps between the implant and remaining skull. Moreover, the procedure reduced the time to resize the implant by an order of magnitude compared to manual resizing without the use of the computer-assisted technique. This approach represents the next step in quickly, effectively, and robustly performing single-stage CCI to treat craniofacial defects.

Effects of medializing calcaneal osteotomy on Achilles tendon lengthening and plantar foot pressures.

Posterior tibial tendon insufficiency, or adult acquired flatfoot deformity, involves collapse of the longitudinal arch of the foot with ensuing changes in the bony architecture of the foot as well. While it is generally accepted that a medializing calcaneal osteotomy (MCO) is a very useful treatment for restoring the fallen arch, questions regarding the effects of this procedure upon plantar foot pressures and Achilles tendon length changes need to be answered. This study focuses on changes in plantar foot pressures and Achilles tendon length as the result of performing a MCO. Fourteen fresh-frozen cadaver legs were used to test the effects of MCO on Achilles tendon length changes 2 cm proximal to the Achilles tendon insertion on the calcaneus. Differential variable reluctance transducers were anchored in ventromedial, dorsomedial, dorsolateral, and ventrolateral positions of the Achilles tendon at the aforementioned level. The effects of the MCO on plantar foot pressures were assessed simultaneously using the Tekscan HR Mat. Axial loading (100 lbs) of each specimen was performed in neutral and dorsiflexion (15 degrees). Data were gathered for Achilles tendon length changes and plantar foot pressures for three trials in both the neutral and dorsiflexed positions. A medializing calcaneal osteotomy (1 cm medial translation) was then performed and testing was repeated in the fashion outlined heretofore. Analysis of the data revealed that there was no significant increase in Achilles tendon length as a result of the MCO. The data also showed that average pressure over the first and second metatarsal regions of the forefoot decreased significantly after MCO. At the same time there was a significant increase in average pressure over the medial and lateral aspect of the heel. These findings suggest that the Achilles tendon aids in inversion of the forefoot without undergoing a significant increase in length change of Achilles tendon fibers in any of the regions tested.

Computational modeling to predict mechanical function of joints: application to the lower leg with simulation of two cadaver studies.

Computational models of musculoskeletal joints and limbs can provide useful information about joint mechanics. Validated models can be used as predictive devices for understanding joint function and serve as clinical tools for predicting the outcome of surgical procedures. A new computational modeling approach was developed for simulating joint kinematics that are dictated by bone/joint anatomy, ligamentous constraints, and applied loading. Three-dimensional computational models of the lower leg were created to illustrate the application of this new approach. Model development began with generating three-dimensional surfaces of each bone from CT images and then importing into the three-dimensional solid modeling software SOLIDWORKS and motion simulation package COSMOSMOTION. Through SOLIDWORKS and COSMOSMOTION, each bone surface file was filled to create a solid object and positioned necessary components added, and simulations executed. Three-dimensional contacts were added to inhibit intersection of the bones during motion. Ligaments were represented as linear springs. Model predictions were then validated by comparison to two different cadaver studies, syndesmotic injury and repair and ankle inversion following ligament transection. The syndesmotic injury model was able to predict tibial rotation, fibular rotation, and anterior/posterior displacement. In the inversion simulation, calcaneofibular ligament extension and angles of inversion compared well. Some experimental data proved harder to simulate accurately, due to certain software limitations and lack of complete experimental data. Other parameters that could not be easily obtained experimentally can be predicted and analyzed by the computational simulations. In the syndesmotic injury study, the force generated in the tibionavicular and calcaneofibular ligaments reduced with the insertion of the staple, indicating how this repair technique changes joint function. After transection of the calcaneofibular ligament in the inversion stability study, a major increase in force was seen in several of the ligaments on the lateral aspect of the foot and ankle, indicating the recruitment of other structures to permit function after injury. Overall, the computational models were able to predict joint kinematics of the lower leg with particular focus on the ankle complex. This same approach can be taken to create models of other limb segments such as the elbow and wrist. Additional parameters can be calculated in the models that are not easily obtained experimentally such as ligament forces, force transmission across joints, and three-dimensional movement of all bones. Muscle activation can be incorporated in the model through the action of applied forces within the software for future studies.

Effect of pigmentation on the mechanical and polymerization characteristics of bone cement.

The impact on performance of additives to bone cement must be assessed before clinical use of the modified product. This study performed several standard acrylic bone cement tests on 3 commercially available products: Endurance, Surgical Simplex P, and Pigmented Endurance. The polymerization characteristics, consisting of doughing time, setting time, and maximum exothermic temperature, were found to be acceptable by the standards of the American Society for Testing and Materials/International Organization for Standards. For the mechanical characterization, analysis revealed statistical equivalence among all cement types, with the exception of compressive strength where Pigmented Endurance was stronger than Surgical Simplex P (P < .02). In mechanical fatigue, there were no significant differences in the log cycles to failure among the cements; however, Weibull analysis predicted Surgical Simplex P to have a higher characteristic life than the other cements. In conclusion, differences do exist among cement types, but the addition of pigment to Endurance did not alter its performance.