Preoperative planning of medial opening wedge high tibial osteotomy using 3D computer-aided design weight-bearing simulated guidance: Technique and preliminary result

BACKGROUND

High tibial osteotomy (HTO) is an established treatment for uni-compartmental osteoarthritis with varus deformity in relatively active young patients with good knee mobility. The most important factor for success and low complications of HTO is the precise correction of osteotomy. The objective of this study was to evaluate the accuracy of pre-operative planning of open-wedge HTO using t3D computer-aided design (CAD) weight-bearing simulated guidance technique for the succession of surgery.

MATERIALS AND METHODS

Nineteen patients who met the inclusion criteria were recruited between July 2013 and June 2014. 3D CAD weight-bearing simulated guidance technique was obtained from standard anterior-posterior, lateral of hip-to-ankle full leg standing radiographs, and computed tomography (CT) scan provided the weight-bearing corrective axis of preoperative planning and predictive corrective mechanical axis value. Post-operative mechanical axis value was obtained after surgery.

RESULTS

This comparative study between the predictive corrective, using 3D CAD weight-bearing simulated guidance technique, and post-operative mechanical axis value, analysed with t-test statistical analysis, showed the insignificant difference ( p > 0.05).

CONCLUSION

We conclude that the 3D CAD weight-bearing simulated guidance technique has good accuracy as preoperative planning of open-wedge HTO for succession surgery.

Three-Dimensional Prediction of the Nose for Facial Approximation in a Thai Population

Most of the previous studies about nose prediction were concentrated only some landmarks of the nose. This study aimed to generate prediction equations for ten landmarks of the nose in the midline and alar regions for forensic facial approximation. The six midline landmarks were the sellion, nasion-pronasale posterior, nasion-pronasale anterior, pronasale, nasal drop, and subnasale. The four landmarks of the alar region were the alare, superior alar groove, posterior alar groove, and inferior alar groove. We used the skull landmarks in the nasal, zygomatic, and maxillary bone to predict the landmarks of the nose. Cone-beam computed tomography scans of 108 Thai subjects with normal BMI and age ranging from 21.0 to 50.9 years were obtained in a sitting position. The data were converted into three-dimensional (3-D) images of the skull and face. The Cartesian coordinates of the landmarks of the skull and nose were used to formulate the multiple regression equations. The formulated equations were tested in 24 new subjects. The mean differences in the predicted midline landmarks varied between -0.4 mm and 0.5 mm, whereas those for bilateral landmarks varied between -1.0 mm and 1.4 mm. In conclusion, the prediction equations formulated here will be beneficial for facial approximation of the nose in a Thai population.

Stress relieving behaviour of flowable composite liners: A finite element analysis

The purpose of this study was to investigate the consequences of using flowable composite as a liner beneath class I resin composite restorations on polymerization shrinkage stress and occlusal force. Models of class I resin composite restorations were generated. A control model received no flowable composite liner. Thirteen test models received different flowable composite liners with varying elastic modulus. Finite element analysis was used. The polymerization shrinkage of the resin composite and an occlusal force were simulated in the models. The stress and strain energy density in each model were investigated. The results demonstrated that all flowable composite linings were able to reduce polymerization shrinkage stress and occlusal force in enamel, dentin, the hybrid layer, and the adhesive layer to various degrees in tooth-restoration systems. Therefore, additional techniques may be applied to reduce the remaining stress and to ensure the long-term success of restorations.

3D CAD/reverse engineering technique for assessment of Thai morphology: Proximal femur and acetabulum

PURPOSE

To assess morphological parameters of proximal femur and acetabulum in Thai population with three-dimensional measurement technique, and to analysis of collateral side symmetric, gender difference, and correlation between morphometric parameters.

METHODS

Investigation was performed in 240 femurs. All three-dimensional femur models were acquitted from 64-slice spiral CT scanner. Morphometric parameters under consideration included acetabular diameter, femoral head diameter, shaft isthmus location, intramedullary canal diameter, diaphyseal diameter, femoral head height, femoral neck isthmus, femoral neck length, neck shaft angle, bow angle, and anteversion angle. All parameters were measured based on functions and least-square regression function in CAD software. Obtained measured data were then used for analysis of collateral side symmetric, gender difference, correlation between morphometric parameters, and compared with other populations.

RESULTS

Female had a smaller dimension compared with male in most of the parameters. No significant difference was observed between left and right femurs. High correlation pairs of morphometric parameters included femoral head diameter-acetabular diameter, femoral head diameter-neck isthmus diameter, femoral head diameter-diaphyseal diameter at shaft isthmus level, acetabular diameter-neck isthmus diameter, neck isthmus diameter-diaphyseal diameter at shaft isthmus level, and acetabular diameter-diaphyseal diameter at shaft isthmus level. Some morphometric parameters of Thai are smaller than other Caucasian, and some Asian nation, i.e. femoral head diameter, femoral neck length, and femoral head height.

CONCLUSIONS

This study provides essential morphometric data for various orthopedic implant designs relating to proximal femur region.

Porous 45S5 Bioglass®-based scaffolds using stereolithography: Effect of partial pre-sintering on structural and mechanical properties of scaffolds

Scaffolds made from 45S5 Bioglass® ceramic (BG) show clinical potential in bone regeneration due to their excellent bioactivity and ability to bond to natural bone tissue. However, porous BG scaffolds are limited by their mechanical integrity and by the substantial volume contractions occurring upon sintering. This study examines stereolithographic (SLA) methods to fabricate mechanically robust and porous Bioglass®-based ceramic scaffolds, with regular and interconnected pore networks and using various computer-aided design architectures. It was found that a diamond-like (DM) architecture gave scaffolds the most controllable results without any observable closed porosity in the fired scaffolds. When the pore dimensions of the DM scaffolds of the same porosity (~60vol%) were decreased from 700 to 400μm, the compressive strength values increased from 3.5 to 6.7MPa. In addition, smaller dimensional shrinkage could be obtained by employing partially pre-sintered bioglass, compared to standard 45S5 Bioglass®. Scaffolds derived from pre-sintered bioglass also showed marginally improved compressive strength.

Biocompatibility of hydroxyapatite scaffolds processed by lithography-based additive manufacturing

The fabrication of hydroxyapatite scaffolds for bone tissue engineering applications by using lithography-based additive manufacturing techniques has been introduced due to the abilities to control porous structures with suitable resolutions. In this research, the use of hydroxyapatite cellular structures, which are processed by lithography-based additive manufacturing machine, as a bone tissue engineering scaffold was investigated. The utilization of digital light processing system for additive manufacturing machine in laboratory scale was performed in order to fabricate the hydroxyapatite scaffold, of which biocompatibilities were eventually evaluated by direct contact and cell-culturing tests. In addition, the density and compressive strength of the scaffolds were also characterized. The results show that the hydroxyapatite scaffold at 77% of porosity with 91% of theoretical density and 0.36 MPa of the compressive strength are able to be processed. In comparison with a conventionally sintered hydroxyapatite, the scaffold did not present any cytotoxic signs while the viability of cells at 95.1% was reported. After 14 days of cell-culturing tests, the scaffold was able to be attached by pre-osteoblasts (MC3T3-E1) leading to cell proliferation and differentiation. The hydroxyapatite scaffold for bone tissue engineering was able to be processed by the lithography-based additive manufacturing machine while the biocompatibilities were also confirmed.

Prevention of excessive medialisation of trochanteric fracture by a buttress screw: a novel method and finite element analysis

This paper proposes a novel method of using an antero-posterior buttress screw at the distal fragment just below the fracture site in conjunction with the sliding hip screw (SHS) to resist excessive femoral medialisation. A virtual assessment of the effectiveness of this new method was performed using the finite element analysis. The results indicate that the use ofa sliding hip screw (SHS) combined with a buttress screw can help resistfemoral medialisation better than using an SHS with no buttress screw. The von Mises equivalent stress (EQ ) was found to be in a safe range, which indicates increased integrity of the lateral wall with the addition of the buttress screw.

Optional entry point for retrograde femoral nailing: an anatomical study using the reverse engineering method

OBJECTIVE

To investigate the optimal entry point for retrograde femoral nailing using medical imaging and reverse engineering technologies.

MATERIAL AND METHOD

One hundred and eight adult cadaveric femurs were scanned using a computed tomography (CT) scanner. To obtain three-dimensional models, medical imaging and reverse engineering technologies were used. The insertion assessment was performed using computer aided design (CAD) software. The curve representing the mid-line in the intramedullary canal in the mid-shaft region was approximated using regression analysis. The curve was extended tangentially toward the femoral condyle, where the intersection between the curve and the condylar surface is the insertion site. The location of the insertion site was determined using the center of the anterior most of the intercodylar notch as a reference point. The measured distances were presented in medial-lateral and anterior-posterior perspectives from the reference point.

RESULTS

Average insertion site for Thai population was 0.56 mm lateral to and 12.67 mm medial to the anterior most of the intercondylar notch. The distance measured from intercondylar notch to the insertion site in the anterior-posterior direction was not significantly different between males and females; however a significant difference in the insertion site was found in medial-lateral directions.

CONCLUSION

The insertion site can be clinically approximated lying on the anterior-posterior axis, since the distance from the anterior-posterior axis to the insertion site is relatively small. The insertion site for the Thai population was found to be 12 mm anterior to the center of the anterior most of the intercondylar notch.

Bone tissue engineering scaffolding: computer-aided scaffolding techniques

Tissue engineering is essentially a technique for imitating nature. Natural tissues consist of three components: cells, signalling systems (e.g. growth factors) and extracellular matrix (ECM). The ECM forms a scaffold for its cells. Hence, the engineered tissue construct is an artificial scaffold populated with living cells and signalling molecules. A huge effort has been invested in bone tissue engineering, in which a highly porous scaffold plays a critical role in guiding bone and vascular tissue growth and regeneration in three dimensions. In the last two decades, numerous scaffolding techniques have been developed to fabricate highly interconnective, porous scaffolds for bone tissue engineering applications. This review provides an update on the progress of foaming technology of biomaterials, with a special attention being focused on computer-aided manufacturing (Andrade et al. 2002) techniques. This article starts with a brief introduction of tissue engineering (Bone tissue engineering and scaffolds) and scaffolding materials (Biomaterials used in bone tissue engineering). After a brief reviews on conventional scaffolding techniques (Conventional scaffolding techniques), a number of CAM techniques are reviewed in great detail. For each technique, the structure and mechanical integrity of fabricated scaffolds are discussed in detail. Finally, the advantaged and disadvantage of these techniques are compared (Comparison of scaffolding techniques) and summarised (Summary).

Rapid-prototype endoprosthesis for palliative reconstruction of an upper extremity after resection of bone metastasis

PURPOSE

To present a rapid-prototype (RP) endoprosthesis replacement after tumor resection in patients with bone metastasis of the upper extremity. The short-term complications and functional outcomes were evaluated as well as the survival of patients and endoprosthesis.

METHODS

Bone metastasis patients who required bone resection and endoprosthesis replacement were enrolled and consented before operation. Custom-made endoprosthesis was fabricated from polymethyl methacrylate assisted by RP technology. After surgery was performed, patients were followed up daily until discharge and monthly until 6 months postoperatively for immediate post-operative complications and for signs of endoprosthesis failure. The functional outcome was evaluated 6 months postoperatively by the Musculoskeletal Tumor Society score (MTSS) and the Mankin score. Thereafter, patients' survival and arm condition were monitored every 3 months.

RESULTS

Sixteen cases participated on this study. There were nine proximal-, four total- and two distal humerus, and one proximal ulna replacement. The median follow-up period was 486 days. The mean MTSS was 55 % and the Mankin score was good in 64 % and fair in 36 % of the patients. Glenohumeral subluxation was observed in 23 % of the patients; however, a stable shoulder was achieved in all cases. There were no prosthesis failure or systemic breakage.

CONCLUSIONS

An RP endoprosthesis may have significant advantages when the entire humerus needs to be replaced, or periarticular sites are involved. This technique offers custom-made endoprosthesis with enough durability, and in a relatively short production time at reasonable costs which are suitable for palliative reconstruction.

Biomechanical evaluation of a novel porous-structure implant: finite element study

PURPOSE

The biomechanical performance of a novel engineered porous-structure implant (EPSI) with various porosities and a conventional solid-structure implant (CSSI) was investigated and compared.

MATERIALS AND METHODS

The three-dimensional finite element method was applied to titanium dental implant models placed in a block of bone that included both cortical and medullary bone. Five different pore sizes and porosities of the EPSI (58% porosity [PSI-58], 62% porosity [PSI-62], 71% porosity [PSI-71], 75% porosity [PSI-75], and 79% porosity [PSI-79]), were compared with the CSSI. Equivalent von Mises (EQV) stress, strain energy density, and displacement were examined for each implant design.

RESULTS

The maximum EQV stresses exhibited in cortical bone of the EPSI models were lower than those of the CSSI model. Higher EPSI porosity tended to increase the EQV stress. The EPSI appeared to share the load with the cortical bone, as evidenced by lower strain energy density in the cortical bone of EPSI models. High values for displacement were observed at the coronal part of the implant in all models. Slight differences in maximum displacement values were seen between EPSI and CSSI models.

CONCLUSION

The EPSI effectively reduced the maximum EQV stress in the cortical bone and enhanced the load-sharing capacity. A significant amount of energy was absorbed by the implant instead of being transferred to the surrounding cortical bone. Varying the porosity of an implant had less effect on implant displacement.

Craniometric study of Thai skull based on three-dimensional computed tomography (CT) data

The present study revealed an advanced method using data obtained from three-dimensional computed tomography (3D CT) to evaluate the craniometric data of the Thai population. Ninty-one Thai cadaveric dry skulls from the Faculty of Medicine, Khon Kaen University were investigated in the present study. It enabled the authors to assess the three-dimensional anatomical landmarks in digital format without physical measurements. The results have revealed that the craniometric data of Thai males were larger than Thai females with a statistical significant difference, especially, the maximum cranial length, basion-bregma height, nasion-basion length, nasion-bregma length and bizygomatic breadth parameters (p << 0.001). In addition, the craniometric data based on Thai skulls of the people in the northeast region was different from the people in the central region. Furthermore, the linear regression equations obtained from the pairwise parameter, it is useful to predict the craniometric parameters in forensic medicine.

A finite element study of stress distributions in normal and osteoarthritic knee joints

OBJECTIVE

To study the stress distributions in normal and osteoarthritic knee joints using the finite element method (FEM).

MATERIAL AND METHOD

Three normal and three varus knee joints are included in the study. Computed tomography (CT) images of the lower extremities are used to create 3D geometric models consisting of bones, articular cartilages, menisci, and knee ligaments. Each of the lower extremities includes the femur, tibia, fibula, and talus. Each 3D geometric model is adjusted to the normal standing configuration with the help of its corresponding 2D radiographic image. After that, 3D finite element (FE) models are created from the adjusted 3D geometric models. FEM is then used to obtain stress distributions on the articular cartilages. In the analysis, the displacements on the posterior calcaneal articular surface of the talus are fully fixed. A vertical concentrated force equal to the body weight is applied at the femoral head.

RESULTS

In the normal knee joints, the maximum normal stresses on the articular cartilages in the lateral compartments are always higher than those in the medial compartments. In the varus knee joints, the opposite results are observed. However, in each normal knee joint, the stress distribution on the whole articular cartilage is moderately uniform. On the contrary, in each varus knee joint, comparatively high magnitudes of the normal stress are found on a large area of the articular cartilage in the medial compartment.

CONCLUSION

Varus knee joints have higher stresses in the medial compartments while normal knee joints have higher stresses in the lateral compartments. This pilot study shows that FE studies are comparable to cadaveric studies. FEM can be used as an alternative method for studying and examining knee joints of patients.

Three-dimensional morphometric study of the Thai proximal humerus: cadaveric study

Seventy-six cadaveric humeri were investigated to study the three-dimensional morphometric data based on CT data. The present study was an advanced method to determine the 3D proximal humeral parameters for both intra and extra geometries through the utilization of medical imaging and reverse engineering techniques. The following parameters were calculated for each humerus and then compared with the 3D Caucasian data such as diameter of humeral head, articular surface thickness, inclination angle, retroversion angle, medial offset, posterior offset, curve length, radius of curvature, and mediolateral angle. It was found that the Thai humeral parameters were smaller than Caucasian except the retroversion angle and posterior offset. This data could be further used to develop a proper design of shoulder arthroplasty for Thai patients.

3D geometrical assessment of femoral curvature: a reverse engineering technique

OBJECTIVE

Investigate the 2D/3D geometry of femoral curvature and femoral length using the advanced technique of computerized tomography combined with reverse engineering techniques.

MATERIAL AND METHOD

The present study was performed using reverse engineering technique based on CT data of 99 cadaveric femora. The femur was divided into three segments, proximal, mid-shaft, and distal regions by defining 35% and 65% of the femoral total length as a boundary of each region. The intramedullary canal in the mid-shaft region was mainly extracted to determine the set of circular center, which could consequence to approximate the 3D femoral radius of curvature using the 3D least square best fit. The 3D femoral curvature was then projected into A-P and M-L directions to investigate the correlation of 2D/3D femoral curvature as normal radiographic images.

RESULTS

It was found that the average 3D Thai femoral curvature was 895.46-mm (SD = 238.06) and the average femoral total length is 421.96-mm (SD = 27.61). In addition, the 2D femoral curvature derived from sagittal radiographic image can be used to determine the 3D femoral curvature with this equation: R3D = RSagittal + 3.67 with r = 0.987.

CONCLUSION

This described technique is a non-destructive method that can effectively assess the internal/ external 3D geometric data of the femur The obtained data is useful to develop a proper design of prosthesis that required inserting into the intramedullary canal. From the present study, it can be concluded that the 2DSagittal femoral curvature derived from standard radiographic image can be represented for the 3D femoral curvature.

Finite element study of the proximal femur with retained trochanteric gamma nail and after removal of nail

This study aims to evaluate the stress and strain distributions in the healed proximal femur after fixation with a trochanteric gamma nail (TGN) and after TGN removal, using the finite element method. The stress distributions in the proximal femur with retained TGN and after TGN removal were very similar. The strain and the strain energy density in the femoral neck region with retained TGN were much higher than in the lag screw hole at the subtrochanter and the distal locking screw hole at the proximal femur, and even higher after TGN removal. Stair climbing resulted in higher strain and higher strain energy density at the femoral neck than normal walking. The conclusion can be drawn that removal of the TGN may result in high risk of femoral neck fracture.

Morphology of the radial head: A reverse engineering based evaluation using three-dimensional anatomical data of radial bone

The proximal part of the radius has a complex shape and dimension that cannot be precisely determined by standard roentgenogram for real three-dimensional anatomical shape which is important for prosthesis design. This study presents a method by which computer tomography (CT) images are combined with the reverse engineering technique to obtain and analyse the three-dimensional inner and outer geometry of the proximal radius. The three-dimensional models were reconstructed from CT images obtained from 40 radial bones and approximated with two- and three-dimensional fitting algorithms based on reverse engineering methods. The mean total length of the radius was 240.0mm [standard deviation (SD) = 17.3]. The radial head in this study is more likely to be circular with an average diameter of 20.5 mm (SD = 1.9). The outer diameter of the radial neck averages 14.7 mm (SD = 1.0). The thickness of the radial head averages 12.9 mm (SD = 1.4). The intramedullary canal diameter of the radial neck averages 7.4 mm (SD = 1.4). The depth of the fossa at the articular surface averages 1.5 mm (SD = 0.4).

Fit-and-fill analysis of trochanteric gamma nail for the Thai proximal femur: a virtual simulation study

The present study present a three-dimensional virtual simulation method to evaluate the fit-and-fill effect of the insertion of a trochanteric gamma nail (TGN) in 98 Thai dadaveric proximal femora. The circular best fit of the 2-dimensional cross-section of the femoral canal and the nail at 4 levels [d100, d120, d140 and d160] which were located at 100, 120, 140 and 160 mm distal to the tip of the greater trochanter were calculated. The evaluation of each level included, 1) the diameters of the medullary canal, 2) the percentage of area filled by the nail in the unreamed medullary canal, 3) the minimal reamer diameter that required enlargement of the canal to accommodate TGN insertion, 4) the minimal inner cortical reaming thickness that needed to be removed, 5) the percentage of cortical bone area that needed to be removed prior to nail insertion and 6) the deviation of the nail center from the center of the medullary canal. The results showed that at 4 studied locations the diameter of unreamed medullary canal averaged 10.3 to 11.8 mm. The nail cross-section that could fill the medullary canal averaged 86.9-95.1%. The minimal reaming diameter for the medullary canal to accommodate the TGN insertion averaged 11.3 to 12.3 mm. The inner cortical thickness that should be removed averaged 0.6 to 0.8 mm. The cortical bone that needed to be removed averaged 13.6 to 19.3% of the total cortical area. The deviation of the nail center from the canal center averaged 0.3 to 0.8 mm. The present study showed some mismatching of the TGN to that of the Thai proximal femur. Appropriate reaming to prepare the medullary canal should be considered prior to TGN insertion to prevent technical problem. Future re-design of the implant may be considered for Thai patients.

Finite element study of trochanteric gamma nail for trochanteric fracture

A three-dimensional finite element study of trochanteric fracture fixation by a trochanteric gamma nail (TGN) was investigated in this study. The analyses were performed under one-legged stance load boundary conditions to study the stress distribution and displacements. The influence of material properties (E-modulus) of the implant, the bone and contact condition in the fracture zone was determined. The results show that the stresses in the implant were lower in case of titanium alloy implant material but at the same time higher displacements occurred. The results also indicate that the stresses in the TGN gradually reduced throughout the healing process of the bone in the fracture zone.

Morphological study of the proximal femur: a new method of geometrical assessment using 3-dimensional reverse engineering

This study presents a new method of using computerized tomography images combined with the reverse engineering technique to obtain and analyse the three-dimensional inner and outer geometry of the proximal cadaveric femur. Three-dimensional models were reconstructed from the computerized tomography images and approximated with 2D and 3D fitting algorithms based on reverse engineering methods. The following parameters were calculated for each femur: femoral head diameter, femoral neck axis, femoral shaft axis, anteversion angle and neck-shaft angle. These data represent the geometry of the studied proximal femur, and can be used for the design of proper size and shape of femoral prostheses and trochanteric nail systems.