Patient-specific Reconstruction Research Articles

Accuracy of fibula reconstruction using patient-specific CAD/CAM reconstruction plates and dental implants: A new modality for functional reconstruction of mandibular defects

BackgroundThe purpose of this study was to analyze the accuracy of mandibular reconstruction using patient-specific computer-aided designed and computer-aided manufactured (CAD/CAM) reconstruction plates as a guide to place fibula grafts and dental implants in a one-stage procedure using pre-operative 3D virtual planning. MethodsSeven consecutive patients were analyzed retrospectively, the 3D accuracy of placement of the fibula grafts and dental implants was compared to the virtual plan. ResultsSix out of seven flaps survived for an average follow-up time of 9.4 months. The outcome was compared to the virtual plan, superimposed on the mandible. For the fibula segments, the mean deviation (SD) was 3.0 (1.8) mm and the mean angulation (SD) was 4.2° (3.2°). For the implants, the mean deviation (SD) was 3.3 (1.3) mm and the mean angulation (SD) was 13.0° (6.7°). The mean (SD) mandibular resection plane deviation was 1.8 (0.9) mm. ConclusionsA patient-specific reconstruction plate is a valuable tool in the reconstruction of mandibular defects with fibula grafts and dental implants. Implant angulation showed a greater deviation from the virtual plans in patients with a sharp ventral fibula rim, where the guide is removed after pilot drilling of the implants.

Patient-specific reconstruction plates are the missing link in computer-assisted mandibular reconstruction: A showcase for technical description

IntroductionPreoperative planning of mandibular reconstruction has moved from mechanical simulation by dental model casts or stereolithographic models into an almost completely virtual environment. CAD/CAM applications allow a high level of accuracy by providing a custom template-assisted contouring approach for bone flaps. However, the clinical accuracy of CAD reconstruction is limited by the use of prebent reconstruction plates, an analogue step in an otherwise digital workstream. Technical reportIn this paper the integration of computerized, numerically-controlled (CNC) milled, patient-specific mandibular plates (PSMP) within the virtual workflow of computer-assisted mandibular free fibula flap reconstruction is illustrated in a clinical case. Intraoperatively, the bone segments as well as the plate arms showed a very good fit. Postoperative CT imaging demonstrated close approximation of the PSMP and fibular segments, and good alignment of native mandible and fibular segments and intersegmentally. Over a follow-up period of 12 months, there was an uneventful course of healing with good bony consolidation. ConclusionThe virtual design and automated fabrication of patient-specific mandibular reconstruction plates provide the missing link in the virtual workflow of computer-assisted mandibular free fibula flap reconstruction.

Computer-Assisted Surgery for Mandibular Reconstruction Using a Patient-Specific Titanium Mesh Tray and Particulate Cancellous Bone and Marrow

Craniomaxillofacial surgery is difficult due to the complexity of the regional anatomy. Computer-assisted surgery is a promising tool aiming to improve the safety and precision of such surgery. A computer-assisted surgical navigation approach for reconstruction of mandibular defects using a patient-specific titanium mesh tray and particulate cancellous bone and marrow (PCBM) harvested from bilateral anterior ilia is proposed. This case report involves a large multicystic ameloblastoma affecting the right mandible of a 31-year-old male patient. Following detailed clinical examination, radiological interpretation, and histopathological diagnosis, computer-assisted surgical simulation with a virtual 3-dimensional (3-D) model was designed using surgical planning software based on the pre-operative computed tomography data. Long-span segmental resection of the mandible was planned, and the defect was analyzed for reconstruction using a patient-specific reconstruction titanium mesh tray mediated with computer-aided design and manufacturing (CAD/CAM) techniques. During the actual surgery, the ultrasonic bone cutting instrument in the surgeon’s hand was connected to the navigation system to touch an anatomical position on the patient. Therefore, osteotomies were performed finely and smoothly according to the navigation images of the cutting bone line by sequentially moving the instrument. Finally, a CAD/CAM-mediated titanium mesh tray condensed by PCBM was adapted to the remaining mandibular fragments. Six months postoperatively, the patient had a good mandibular configuration and facial contour. Integration of different technologies, such as software planning and 3-D surgical simulation, combined with intraoperative navigation and CAD/CAM techniques, provides safe and precise mandibular reconstruction surgery.

Computer-Assisted Mandibular Reconstruction using a Patient-Specific Reconstruction Plate Fabricated with Computer-Aided Design and Manufacturing Techniques.

We investigated the workflow of computer-assisted mandibular reconstruction that was performed with a patient-specific mandibular reconstruction plate fabricated with computer-aided design and computer-aided manufacturing (CAD/CAM) techniques and a fibula flap. We assessed the feasibility of this technique from virtual planning to the completion of surgery. Computed tomography (CT) scans of a cadaveric skull and fibula were obtained for the virtual simulation of mandibular resection and reconstruction using ProPlan CMF software (Materialise(®)/DePuy Synthes(®)). The virtual model of the reconstructed mandible provided the basis for the computer-aided design of a patient-specific reconstruction plate that was milled from titanium using a five-axis milling machine and CAM techniques. CAD/CAM techniques were used for producing resection guides for mandibular resection and cutting guides for harvesting a fibula flap. Mandibular reconstruction was simulated in a cadaveric wet laboratory. No problems were encountered during the procedure. The plate was fixed accurately to the residual bone without difficulty. The fibula segments were attached to the plate rapidly and reliably. The fusion of preoperative and postoperative CT datasets demonstrated high reconstruction precision. Computer-assisted mandibular reconstruction with CAD/CAM-fabricated patient-specific reconstruction plates appears to be a promising approach for mandibular reconstruction. Clinical trials are required to determine whether these promising results can be translated into successful practice and what further developments are needed.

Haemodynamic conditions of patient-specific carotid bifurcation based on ultrasound imaging

The purpose of this paper is to complement the characterisation of patient-specific carotid artery bifurcation haemodynamics based on image data obtained by Doppler ultrasound imaging. A methodology for patient-specific 3D luminal surface reconstruction followed by structured hexahedral meshing of the volume and blood flow simulation is presented. Quantitative descriptors of the flow based on wall shear stress (WSS) are used to compare healthy and stenosed carotid bifurcation haemodynamic disturbances. Independently on the presence of stenosis, the internal carotid artery has been identified as a region of abnormal high values of oscillating shear index and relative residence time and low values of time averaged WSS. For the healthy carotid bifurcation, WSS descriptors manage to capture flow disturbances at the external carotid artery. This work addresses the lack of quantitative analysis on anatomically realistic stenosed carotid bifurcations.

Patient Specific Haemodynamic Modeling after Occlusion Treatment in Leg

In this work we propose a method for analysis of postsurgical haemodynamics after femoral artery treatment of occlusive vascular disease. Patient specific reconstruction algorithm of 1D core network based on MRI data is proposed as a tool for such analysis. Along with presurgical ultrasound data fitting it provides effective personalizing predictive method that is validated with clinical observations.

Finite element analysis of customized reconstruction plates for mandibular continuity defect therapy

Large mandibular continuity defects pose a significant challenge in oral maxillofacial surgery. One solution to this problem is to use computer-guided surgical planning and additive manufacturing technology to produce patient-specific reconstruction plates. However, when designing customized plates, it is important to assess potential biomechanical responses that may vary substantially depending on the size and geometry of the defect.The aim of this study was to assess the design of two customized plates using finite element method (FEM). These plates were designed for the reconstruction of the lower left mandibles of two ameloblastoma cases (patient 1/plate 1 and patient 2/plate 2) with large bone resections differing in both geometry and size. Simulations revealed maximum von Mises stresses of 63MPa and 108MPa in plates 1 and 2, and 65MPa and 190MPa in the fixation screws of patients 1 and 2. The equivalent strain induced in the bone at the screw-bone interface reached maximum values of 2739 micro-strain for patient 1 and 19,575 micro-strain for patient 2. The results demonstrate the influence of design on the stresses induced in the plate and screw bodies. Of particular note, however, are the differences in the induced strains. Unphysiologically high strains in bone adjacent to screws can cause micro-damage leading to bone resorption. This can adversely affect the anchoring capabilities of the screws. Thus, while custom plates offer optimal anatomical fit, attention should be paid to the expected physiological forces on the plates and the induced stresses and strains in the plate–screw–bone assembly.

Patient specific mandible reconstruction—virtual pre-operative planning for ideal oral rehabilitation

Background: Oral dental rehabilitation after ablative surgery in head and neck cancer is demanding. Besides soft tissue deficiencies due to resection and scarring, bony reconstruction has an important impact on functional and aesthetic result. Limited bone graft dimensions restrict adequate oral rehabilitation with dental implants. Disproportions between soft and hard tissue result often in later periimplantitis and early implant loss. Pre-operative virtual planning in mandible reconstruction could ease predictable oral rehabilitation.

Imaging, Virtual Planning, Design, and Production of Patient-Specific Implants and Clinical Validation in Craniomaxillofacial Surgery

The purpose of this article was to describe the workflow from imaging, via virtual design, to manufacturing of patient-specific titanium reconstruction plates, cutting guide and mesh, and its utility in connection with surgical treatment of acquired bone defects in the mandible using additive manufacturing by electron beam melting (EBM). Based on computed tomography scans, polygon skulls were created. Following that virtual treatment plans entailing free microvascular transfer of fibula flaps using patient-specific reconstruction plates, mesh, and cutting guides were designed. The design was based on the specification of a Compact UniLOCK 2.4 Large (Synthes(®), Switzerland). The obtained polygon plates were bent virtually round the reconstructed mandibles. Next, the resections of the mandibles were planned virtually. A cutting guide was outlined to facilitate resection, as well as plates and titanium mesh for insertion of bone or bone substitutes. Polygon plates and meshes were converted to stereolithography format and used in the software Magics for preparation of input files for the successive step, additive manufacturing. EBM was used to manufacture the customized implants in a biocompatible titanium grade, Ti6Al4V ELI. The implants and the cutting guide were cleaned and sterilized, then transferred to the operating theater, and applied during surgery. Commercially available software programs are sufficient in order to virtually plan for production of patient-specific implants. Furthermore, EBM-produced implants are fully usable under clinical conditions in reconstruction of acquired defects in the mandible. A good compliance between the treatment plan and the fit was demonstrated during operation. Within the constraints of this article, the authors describe a workflow for production of patient-specific implants, using EBM manufacturing. Titanium cutting guides, reconstruction plates for fixation of microvascular transfer of osteomyocutaneous bone grafts, and mesh to replace resected bone that can function as a carrier for bone or bone substitutes were designed and tested during reconstructive maxillofacial surgery. A clinically fit, well within the requirements for what is needed and obtained using traditional free hand bending of commercially available devices, or even higher precision, was demonstrated in ablative surgery in four patients.

Augmented reality patient-specific reconstruction plate design for pelvic and acetabular fracture surgery

The objective of this work is to develop a preoperative reconstruction plate design system for unilateral pelvic and acetabular fracture reduction and internal fixation surgery, using computer graphics and augmented reality (AR) techniques, in order to respect the patient-specific morphology and to reduce surgical invasiveness, as well as to simplify the surgical procedure. Our AR-aided implant design and contouring system is composed of two subsystems: a semi-automatic 3D virtual fracture reduction system to establish the patient-specific anatomical model and a preoperative templating system to create the virtual and real surgical implants. Preoperative 3D CT data are taken as input. The virtual fracture reduction system exploits the symmetric nature of the skeletal system to build a "repaired" pelvis model, on which reconstruction plates are planned interactively. A lightweight AR environment is set up to allow surgeons to match the actual implants to the digital ones intuitively. The effectiveness of this system is qualitatively demonstrated with 6 clinical cases. Its reliability was assessed based on the inter-observer reproducibility of the resulting virtual implants. The implants designed with the proposed system were successfully applied to all cases through minimally invasive surgeries. After the treatments, no further complications were reported. The inter-observer variability of the virtual implant geometry is 0.63mm on average with a standard deviation of 0.49mm. The time required for implant creation with our system is 10min on average. It is feasible to apply the proposed AR-aided design system for noninvasive implant contouring for unilateral fracture reduction and internal fixation surgery. It also enables a patient-specific surgical planning procedure with potentially improved efficiency.

Pre-operative planning for mandibular reconstruction - A full digital planning workflow resulting in a patient specific reconstruction

ObjectivesReconstruction of large mandiblular defects following ablative oncologic surgery could be done by using vascularized bone transfer or, more often, primarily with simultaneous or delayed bone grafting, using load bearing reconstruction plates. Bending of these reconstruction plates is typically directed along the outer contour of the original mandible. Simultaneously or in a second operation vascularized or non-vascularized bone is fixed to the reconstruction plate. However, the prosthodontic-driven backward planning to ease bony reconstruction of the mandible in terms of dental rehabilitation using implant-retained overdentures might be an eligible solution. The purpose of this work was to develop, establish and clinically evaluate a novel 3D planning procedure for mandibular reconstruction.Materials and methodsThree patients with tumors involving the mandible, which included squamous cell carcinoma in the floor of the mouth and keratocystic odontogenic tumor, were treated surgically by hemimandibulectomy.ResultsIn primary alloplastic mandible reconstruction, shape and size of the reconstruction plate could be predefined and prebent prior to surgery.Clinical relevanceThis study provides modern treatment strategies for mandibular reconstruction.

Technique of temporomandibular joint replacement using a patient-specific reconstruction system in the edentulous patient

The dental occlusion sets the intermaxillary relation during planning, construction of a prosthesis, and surgery for total replacement of the temporomandibular joint (TMJ), and enables accurate placement of the prosthesis. However, in edentulous patients this no longer exists. We describe techniques to overcome the problems encountered in such patients having TMJ replacement using the patient-specific TMJ Concepts ® system (Ventura, California, USA).

Individuelles und funktionsabhängiges Therapiekonzept nach vorderer Kreuzbandruptur

The knee joint is a ligament guided and muscular stabilized joint. Therefore the rupture of the anterior cruciate ligament (ACL) causes a functional deficit with change of the knee kinematics and the dynamic muscle stabilization. The muscular dysfunction can be the result of inadequate muscle strength, a neuro-muscular control defizit, a propriozeptive dysfunction or often the combination of these causes. Due to the complex anatomy of the ACL an exact, patient specific operative anatomical reconstruction is not possible. Therefore we suggest primarily a conservative therapeutic approach. If this approach fails the reconstruction will be performed after the first rehabilitation phase. Independently from the conservative or surgical approach, the rehabilitation program consists of four function-based phases and the overall therapy goal is to achieve the same or even higher activity level than before the lesion.

Patient-specific computational fluid dynamics: structured mesh generation from coronary angiography

Patient-specific simulations are widely used to investigate the local hemodynamics within realistic morphologies. However, pre-processing and mesh generation are time consuming, operator dependent, and the quality of the resulting mesh is often suboptimal. Therefore, a semi-automatic methodology for patient-specific reconstruction and structured meshing of a left coronary tree from biplane angiography is presented. Seven hexahedral grids have been generated with the new method (50,000-3,200,000 cells) and compared to nine unstructured tetrahedral grids with prismatic boundary layer (150,000-3,100,000 cells). Steady-state blood flow simulation using Computational Fluid Dynamics (CFD) has been used to calculate the Wall Shear Stress (WSS). Our results (99 percentile, area-weighted and local WSS values along a line) demonstrate that hexahedral meshes with respect to tetrahedral/prismatic meshes converge better, and for the same accuracy of the result, six times less cells and 14 times less computational time are required. Hexahedral meshes are superior to tetrahedral/prismatic meshes and should be preferred for the calculation of the WSS.

Technical Note

For coronary computed tomography (CT) angiography, the reconstruction phase finally used has to be iteratively adapted to the patient-specific heart motion to provide optimal image quality and therewith to improve the diagnostic value. The purpose was to provide an automatically raw data-based identification of the patient-specific optimal reconstruction phase for cardiac computed tomography imaging. We validated our method by a visual assessment of 65 patient data sets. In 52% of all cases, the highest correlation of the computed and the visually identified optimal reconstruction phase was ensured. In 30% of the cases, our method provided a higher image quality compared with the results obtained in routine clinical work. Our identification of the optimal reconstruction phase is a reliable method and can improve the medical workflow by providing optimal image quality with the initial image reconstruction, making multiple time-consuming image reconstructions obsolete.

Real-time determination of the optimal reconstruction phase to control ECG pulsing in spiral cardiac CT

The reconstruction phase providing optimal image quality in coronary CT angiography is dependent on the heart rate but additionally displays substantial patient-dependent variation. The purpose of this study was to provide online identification of the patient-specific optimal reconstruction phase during CT coronary angiography data acquisition and to allow adaptation of tube current modulation for the individual patient. A raw data-based cardiac motion signal (kymogram) was used for the detection of the optimal reconstruction phase. The individual motion curve of each patient was correlated with dedicated template curves to reduce signal noise. Data sets of 90 consecutive patients were used for validation purposes. The reliability of our approach increased with scan time and provided highest correlation with the visually identified optimal reconstruction phase already after half of the total scan time indicated by a difference value of 13.2% and 8.2%, respectively. A high correlation of the computed and the visually identified optimal reconstruction phase was assured in most cases providing a dose reduction of 36% compared to conventional TCM application for a confidence interval of 80%. Our method is a fully automatic computer-assisted approach identifying the optimal reconstruction phase with high reliability while online capability can be ensured. We conclude that our method can identify cardiac phases providing highest image quality already during CT scanning. Reduction of the tube current by a patient-specific optimization providing a minimal dose level is the major benefit for the patients.

Volumic patient-specific reconstruction of muscular system based on a reduced dataset of medical images

Three-dimensional mechanical modelling of muscles is essential for various biomechanical applications and clinical evaluation, but it requires a tedious manual processing of numerous images. A muscle reconstruction method is presented based on a reduced set of images to generate an approximate parametric object from basic dimensions of muscle contours. A regular volumic mesh is constructed based on this parametric object. The approximate object and the corresponding mesh are deformed to fit the exact muscles contours yielding patient-specific geometry. Evaluation was performed by comparison of geometry to that obtained by contouring all computed tomography (CT) slices, and by quantification of the mesh quality criteria. Muscle fatty infiltration was estimated using a threshold between fat and muscle. Volumic fat index (VFI) of a muscle was computed using first all the complete CT scan slices containing the muscle (VFIref) and a second time only the slices used for reconstruction (VFIrecons). Mean volume error estimation was 2.6% and hexahedron meshes fulfilled quality criteria. VFIrecons respect the individual variation of fat content.

Assessment of derived 12-lead electrocardiograms using general and patient-specific reconstruction strategies at rest and during transient myocardial ischemia

Twelve-lead ST-segment monitoring is a widely used tool for capturing focal ischemia and transient intermittent episodes. However, continuous registration of all 10 electrodes is impractical in clinical settings. This study investigated the accuracy of 2 derived 12-lead strategies that required 6 electrodes, including all limb leads, and 2 precordial leads by using population-based (generalized) and individualized (patient-specific) reconstruction coefficients to derive the additional 4 chest leads. A total of 26,880 simultaneous digital conventional 12-lead generalized and patient-specific electrocardiograms were monitored over 112 hours in 39 patients during percutaneous coronary intervention, including 159 balloon occlusions in 63 arteries, to test accuracy at rest and during ischemia. Occlusion duration was 78 seconds (range 42 to 96) in the left main coronary in 2 patients, the left anterior descending artery in 15, the right coronary artery in 10, the circumflex artery in 2, and graft segments in 5 patients. Average summated 12-lead ST deviation over the study population at baseline was 377 microV (range 104 to 1,718), which increased at peak ischemia to an average of 1,086 microV (range 282 to 4,099). Median absolute differences at peak ischemic ST deviation were 25 microV in lead V(1), 0 microV in lead V(2), 35 microV in lead V(3), 34 microV in lead V(4), 0 microV in lead V(5), 11 microV in lead V(6), and 114 microV for summated 12-lead ST deviation with the generalized method and 7 microV in lead V(1), 4 microV in lead V(2), 1 muV in lead V(3), 5 microV in lead V(4), 4 microV in lead V(5), 9 microV in lead V(6), and 83 microV for the summated 12-lead ST deviation with the patient-specific method. Limb leads (I, II, III, aVR, aVL, and aVF) were identical in all patients. Thus, generalized and patient-specific methods derived from 12-lead electrocardiography using actual limb and 2 precordial electrodes accurately derived the additional chest leads at rest and during ischemia. These approaches appear to be more practical than conventional 10-electrode monitoring but preserve high accuracy.

Reconstruction of the 12-lead electrocardiogram from reduced lead sets

In clinical practice, continuous recording of all leads of the 12-lead electrocardiogram (ECG) is often not possible. We wanted to assess how well absent, noisy, or defective leads can be reconstructed from different lead subsets and how well lead reconstruction performs over time. A data set of 234 24-hour ECG recordings was divided into an equally sized training and test set. Precordial leads were systematically removed, and for all lead subsets including both limb leads and at least one precordial lead, the absent leads were reconstructed using general and patient-specific reconstruction templates. Reconstruction performance was measured by correlation between the original and reconstructed leads over the QRS and T waves, by average and maximum absolute ST differences, and by agreement when a clinical decision rule was applied. Reconstruction performance over time was evaluated at baseline, at 20 minutes, and 1, 6, 12 and 24 hours after the start of each recording. Reconstruction accuracy was high (correlation ≥0.932, average ST difference ≤30 μV, agreement ≥94.9%) with general reconstruction for lead sets with 1 or 2 precordial leads removed but was less satisfactory when more leads were missing. Patient-specific reconstruction performed well when up to 4 precordial leads were removed (correlation ≥0.967, average ST difference ≤26 μV, agreement ≥95.7%). Patient-specific reconstruction performance initially slightly decreased and then stabilized over time but remained much better than general reconstruction after 24 hours. Accurate reconstruction of the 12-lead ECG from lead subsets is possible over time. General reconstruction allows reconstruction of 1 or 2 precordial leads, whereas up to 4 leads can be reconstructed well using patient-specific reconstruction.

Minimal lead sets for reconstruction of 12-lead electrocardiograms

It may not always be possible to record all precordial leads of the standard 12-lead electrocardiogram (ECG). Especially in monitoring situations, a minimal lead set from which the 12-lead ECG can be reconstructed, would be valuable. This article assesses how well missing precordial leads could be synthesized from the remaining leads of the 12-lead ECG. A total of 2,372 diagnostic 12-lead ECG recordings were obtained from subjects with chest pain suggestive for acute myocardial infarction. Representative average beats were computed from the digital 12-lead ECG recordings with our Modular ECG Analysis System. The recordings were divided into a learning set and a test set. We considered all lead sets with one or more precordial leads removed, but always including limb leads I and II. By using the learning set, general reconstruction coefficients were computed to synthesize the missing precordial leads to each lead set. Performance of the synthesis was assessed by cross correlation between the original and the reconstructed leads. Also, patient-specific reconstruction coefficients were derived for each ECG in the test set and correlations were determined. High correlation coefficients were found with both reconstruction techniques. For different sizes of lead sets, the best patient-specific reconstructions had higher correlation values than the general reconstructions. For example, when 2 precordial leads were excluded, the best patient-specific median correlation was 0.994 compared to 0.963 for the best general reconstruction correlation. General reconstruction allows synthesis of 2 or 3 excluded precordial leads in good approximation. When patient-specific reconstruction can be applied, a minimal lead set including the limb leads and only 2 precordial leads suffices.