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Adaptive Probabilistic Approach for Selecting Tumour Knee Prosthesis
Abstract
Tumour knee prostheses reconstruct bone gaps, left after resecting the tumour affected tissues, in limb salvage surgeries of bone cancer patients. They typically comprise of 6-12 different components chosen from a family of components that are manufactured in discrete variations (intended to cater to a wide range of patient conditions including gender, tumour position, leg (left/right), and resection length). These variations generate numerous combinations and selecting a correct set of components from a family of 100 or more total components has made the process difficult for a given patient. This article describes an adaptive probabilistic approach developed for selection of tumour knee prosthesis components, driven by geometric details. These details were extracted from the 3D virtual anatomical model, reconstructed from set of CT scan images of patients. The selection was performed in two steps. First, the grossly undersized and oversized components were eliminated. Then the geometric details of components were mapped, with the measured anatomical parameters of the patient, to form a fuzzy-logic based decision tree. This was based on pre-defined rules compiled from surgeons' experience. A set of measures (geometric difference, bone curvature, knee centre shift, and reconstruction length) were used to evaluate the selected prosthesis components. Evaluation was based on their suitability with respect to the patient's anatomy, and classified with a qualitative tag: "most suitable", "probably suitable", or "not suitable". A case study of distal femur replacement is presented to explain the proposed methodology. This approach eliminates the risk of over and under sizing of the prosthesis components and reduces the average inventory to be maintained for each patient.
... With these models it is possible to better perform pre-operative procedures, or to conduct intra-operative tasks with greater accuracy. Also, such models enable creation of customized bone implants and fixators using additive and/or other manufacturing technologies [3,4]. In order to create geometrical models which fulfill such requirements various methods are applied. ...
Information technology plays important role in the field of orthopedic surgery. The geometrical models created by the adequate software packages can be used in pre-operative simulations, intra-operative guidance, and post-operative treatment of the patient. In order to create such models various methods are used. In general these methods are based on scanned medical data acquired from CT scanners, X-ray, MRI, or other scanning devices. In order to create geometrical models it is possible to use volumetric rendering to visualise scanned medical data in adequate medical software, or to do some post-processing in CAD software. In this paper Method of Anatomical Features (MAF) is applied for the creation of the surface model of the human humerus. This method is based on the anatomical and morphometric properties of the human bone. With this method it is possible to create geometrically accurate and anatomically correct models of the human bones. Such models can be used for later implant and fixator creation, for the education of medical students and practitioners, for the Finite Element Analysis, etc. Results presented in this paper are quite satisfactory, and they demonstrate that MAF can be used for the creation of the surface model of the human humerus.
Personalization in medicine mainly refers to the treatments being adapted to a specific patient. The design and manufacturing of customized implants is a field that has been developed rapidly during recent years. This chapter presents an originally developed method for designing a 3D model of customized and anatomically adjusted implants for different fracture types. With this method, it is possible to design volumetric implants used to replace a part of the bone or a plate type for fixation of a fractured bone. In addition, it could be used as a guideline for modifying standard and/or creating personalized implant types. To provide flexibility for a specific patient’s case, each stage of the implant manufacturing process should be followed by adequate requirements, orthopedic surgeons’ recommendations and automation.
Aim:
Mega-prostheses required for reconstructing large gaps in bone after limb-saving surgeries for osteo-sarcoma patients have a long development cycle. This includes design of prosthesis components and surgical armamentarium, followed by pilot batch production, lab testing, human clinical trials and regulatory approvals. Most manufacturers stay away due to small market size coupled with the difficulties and high costs involved. Prostheses developed in the West are often unsuitable and unaffordable for the majority of Indian patients. There is a need for high-quality yet low-cost prostheses that are compatible with the anatomy and functionality of local population.
Method:
An inter-disciplinary group comprising orthopedic oncologists, mechanical engineers and materials scientists from three different organizations in India took up the above challenge. They developed a novel modular tumour knee prosthesis with rotating hinge, as well as surgical armamentarium with femoral and tibial cutting jigs and other instruments. Knee simulator and testing machines were developed to test the prosthesis. A dedicated pilot production facility along with inspection and quality management system was set up.
Result:
The new prosthesis provides flexion-extension up to 120 degrees and axial rotation of ±5 degrees. It successfully completed ten million cycles of fatigue and wear testing. The regulatory body of the government and institutional ethical committees of hospitals approved the human clinical trials, which are currently in progress.
Conclusion:
The design, manufacturing and testing of the prosthesis components and armamentarium took more than a decade and presented many challenges. These were overcome by several technological innovations by the engineering team and continuous feedback from the surgeons. The experience is expected to be useful to all others interested in this field.
Restoration of the position of the prosthetic joint line (JL) to the same level as the original JL is a challenging problem in primary adn revision knee arthroplasty, and there is no reliable method for achieving this objective. We hypothesized that there is a constant ratio between the interepicondylar distance (IED) and the perpendicular distance from this interepicondylar line to the JL and analyzed 100 computed tomography scans of the knee to study this relationship. The IED and the perpendicular distance from this interepicondylar line to the JL was measured using both the clinical epicondylar axis (CEA) and the surgical epicondylar axis (SEA). Results showed that the ration between the IED adn the perpendicular distance from the interepicondylar line to the JL was 3.0 using the CEA and 3.3 using the SEA. The ratio was found to be constant, irrespective of the patient's sex or height. We suggest using the CEA because of the ease in localizing epicondyle peaks and conclude that the position of the JL from the interepicondylar line is one-third the IED using the CEA. This will prove to be a valuable aid in restoring the JL position during knee arthroplasty.
Prosthesis refers to an artificial implant that can replace or substitute for a natural joint, and maintain the desired functionality, including cosmetic appearance. They are needed when joints are lost by injury (traumatic), missing from birth (congenital), or damaged by disease (such as cancer), and thereby save the remaining limbs. While a prosthesis can also be external (as in an artificial limb for amputees), the focus of this chapter is on internally placed artificial joints (or endo-prosthesis), especially those that fully replace a joint along with part of the bone (mega endo-prostheses), and provide the required functionality (see Fig. 10.1). They can be classified in different ways, depending on the articulation or site of joint, freedom of movement, material combination, extent of customization, indication for the replacement, and the fixation method. The development of such prostheses is highly challenging, requiring inter-disciplinary inputs from orthopedic surgeons, mechanical engineers, and material scientists, supported by information technology. The development of any new prosthesis begins with the study of the patient requirements. Bio-mechanical studies are needed to determine the loads, movements, and other functional requirements of the joint. The configuration and design have to be evolved depending on the functional requirements, but compatible with the selected implant materials and manufacturing processes. Bio-compatible materials with the desired properties need to be selected for various components of a prosthesis. Manufacturing processes must be planned to achieve the desired functionality, reliability and cost. Surgical instrumentation (called armamentarium) to implant the prosthesis must also be designed, considering efficiency and quality of surgical protocol. Software tools may be used to extract the geometry of customized prostheses from the medical images of the patient; carry out design, analysis, prototyping and manufacture of the (Figure presented) prosthesis; study prosthesis implantation protocols; train the surgeons; and educate the patients.
Modular endo-prostheses were introduced in 1980s with the intent of replacing custom made implants, which were criticized for lack of intra-operative flexibility, and high lead time and cost [1]. A typical modular prosthesis set may have as many as 200 components, making it difficult to select the right set of components in intra operative stage. An automated prosthesis selection methodology to limit the choice of prosthesis components with a qualitative tag such as: (1) ‘most suitable’, (2) ‘probably suitable’, and (3) ‘not suitable’, will greatly help the surgeons. This article describes a computer aided decision support system for selecting endo-prosthesis components driven by anatomical data of the patient. The methodology is explained with a case study of distal femur replacement.
Total hip arthroplasty (THA) has been targeted by the United States federal government for cost control because of its high cost and rising incidence in the aging population. The hospital cost for THA during the 1980s was controlled by utilization review and a reduction in the volume of services delivered for each THA. The single largest increase in the cost of THA during the 1980s was the cost of hip implants. The Lahey Clinic Hip Implant Standardization Program was developed to provide objective guidelines for hip implant selection. These guidelines are based on the demands a patient is expected to place on his or her hip prosthesis. Because not every patient requires an expensive high-demand hip prosthesis, the standardization program also has the potential to reduce the hospital cost for hip implants without compromising patient care. Patients are assigned to four demand categories based on five objective criteria: age, weight, expected activity, general health, and bone stock. Selection of the prosthesis in each of the four demand categories is intended to match the implant's capacity with expected patient demand. The standardization program was retrospectively applied to 103 THAs performed during 1991. Analysis of variance demonstrated that patient variables and demand categories were statistically significant groupings. The cost of hip implants would have been reduced by 25.7% with the Lahey Clinic Hip Implant Standardization Program. A prospective outcome study is required to determine the long-term validity of this standardization program.
Total knee replacement is one of the most successful and commonly performed orthopedic procedures. However, when the implant fails, revision surgery is indicated. The prosthesis in-situ and the extent of ligamentous laxity and bone loss will dictate the appropriate revision implant required. Common options include posterior stabilized total knee replacement; constrained condylar knee with or without stem extensions; and a rotating-hinge prosthesis.
Thickness is a commonly used parameter in product design and manufacture. Its intuitive definition as the smallest dimension of a cross-section or the minimum distance between two opposite surfaces is ambiguous for intricate solids, and there is very little reported work in automatic computation of thickness. We present three generic definitions of thickness: interior thickness of points inside an object, exterior thickness for points on the object surface, and radiographic thickness along a view direction. Methods for computing and displaying the respective thickness values are also presented. The internal thickness distribution is obtained by peeling or successive skin removal, eventually revealing the object skeleton (similar to medial axis transformation). Another method involves radiographic scanning along viewing direction, with minimum, maximum and total thickness options, displayed on the surface of the object. The algorithms have been implemented using an efficient voxel based representation that can handle up to one billion voxels (1000 per axis), coupled with a near-real time display scheme that uses a look-up table based on voxel neighborhood configurations. Three different types of intricate objects: industrial (press cylinder casting), sculpture (Ganesha idol), and medical (pelvic bone) were used for successfully testing the algorithms. The results are found to be useful for early evaluation of manufacturability and other lifecycle considerations.
Ten cases of primary bone tumours in infants (1 osteosarcoma, 3 Ewing's sarcoma, 1 chondroblastoma and 5 angiomatosis) are
reported. All cases of angiomatosis showed characteristic radiographic findings. In all the other tumours the X-ray appearances
were different from those usually seen in older children and adolescents. In the authors' opinion the precise diagnosis of
malignant bone tumours in infancy is very difficult as no characteristic X-ray features are present in this age period.
Computer Assisted Orthopedic Surgery (CAOS) employing information and computer graphics technologies for preoperative planning, intraoperative navigation, and for guiding or performing surgical interventions, has received very little attention for bone tumor surgery applications. We have developed a CAOS system called OrthoSYS, driven by geometric reasoning algorithms to visualize tumor size, shape, and plan for resection according to the tumor's spread, starting from a 3D model reconstructed from CT images. Anatomical landmarks on bone are automatically identified and labeled, useful for registering patient model with virtual model during surgery and also as a reference for tumor resection and prosthesis positioning. The thickness of bone stock remaining after tumor resection is automatically analyzed to choose the best modular stem and fix the prosthesis. A method for prosthesis components selection using fuzzy logic has been developed to assist the surgeons. The medial axis of the long bones and anatomical landmarks are used for positioning the prosthesis in virtual planning and verification in the intraoperative stage. A set of anatomical metrics have been developed to measure the effectiveness of the prosthetic replacement of bone.
This paper describes a low-cost computer system that takes CT images of the knee, and with three-dimensional models of knee
prostheses allows a surgeon to position the prosthesis correctly pre-operatively in an interactive manner. Once in position
the computer can process bone and prosthesis geometry to derive a set of constraint boundaries that constitute a safe cutting
area for a force controlled robot (i.e. that avoids soft tissue such as ligaments), and provides the correct cutting planes
for good prosthesis/bone alignment. This boundary information is used to program the robot, allowing a surgeon to move the
robot within predefined regions to machine away bone accurately whilst preventing damage to soft tissue.
Accurate, simple, and quick measurement of anatomical deformities at preoperative stage is clinically important for decision making in surgery planning. The deformities include excessive torsional, angular, and curvature deformation. This paper presents computer-aided methods for automatically measuring anatomical deformities of long bones of the lower limb. A three-dimensional bone model reconstructed from CT scan data of the patient is used as input. Anatomical landmarks on femur and tibia bone models are automatically identified using geometric algorithms. Medial axes of femur and tibia bones, and anatomical landmarks are used to generate functional and reference axes. These methods have been implemented in a software program and tested on a set of CT scan data. Overall, the performance of the computerized methodology was better or similar to the manual method and its results were reproducible.
Accurate, simple, and quick measurement of anatomical deformities at preoperative stage is clinically important for decision making in surgery planning. The deformities include excessive torsional, angular, and curvature deformation. This paper presents computer-aided methods for automatically measuring anatomical deformities of long bones of the lower limb. A three-dimensional bone model reconstructed from CT scan data of the patient is used as input. Anatomical landmarks on femur and tibia bone models are automatically identified using geometric algorithms. Medial axes of femur and tibia bones, and anatomical landmarks are used to generate functional and reference axes. These methods have been implemented in a software program and tested on a set of CT scan data. Overall, the performance of the computerized methodology was better or similar to the manual method and its results were reproducible.
Identification of anatomical landmarks on skeletal tissue reconstructed from CT/MR images is indispensable in patient-specific preoperative planning (tumour referencing, deformity evaluation, resection planning, and implant alignment and anchoring) as well as intra-operative navigation (bone registration and instruments referencing). Interactive localisation of landmarks on patient-specific anatomical models is time-consuming and may lack in repeatability and accuracy. We present a computer graphics-based method for automatic localisation and identification (labelling) of anatomical landmarks on a 3D model of bone reconstructed from CT images of a patient. The model surface is segmented into different landmark regions (peak, ridge, pit and ravine) based on surface curvature. These regions are labelled automatically by an iterative process using a spatial adjacency relationship matrix between the landmarks. The methodology has been implemented in a software program and its results (automatically identified landmarks) are compared with those manually palpated by three experienced orthopaedic surgeons, on three 3D reconstructed bone models. The variability in location of landmarks was found to be in the range of 2.15-5.98 mm by manual method (inter surgeon) and 1.92-4.88 mm by our program. Both methods performed well in identifying sharp features. Overall, the performance of the automated methodology was better or similar to the manual method and its results were reproducible. It is expected to have a variety of applications in surgery planning and intra-operative navigation.
The possible association between pelvic obliquity and low-back pain is investigated in low-back pain patients and a control population. A precise method of erect posture radiography is used to carefully measure leg length inequality in these two groups. An age-related response of the postural scoliosis to shoe-raise is noted. The results of shoe-raise therapy with and without lumbosacral manipulation are compared, and preliminary results are reported.
Total hip arthroplasty (THA) has been targeted by the United States federal government for cost control because of its high cost and rising incidence in the aging population. The hospital cost for THA during the 1980s was controlled by utilization review and a reduction in the volume of services delivered for each THA. The single largest increase in the cost of THA during the 1980s was the cost of hip implants. The Lahey Clinic Hip Implant Standardization Program was developed to provide objective guidelines for hip implant selection. These guidelines are based on the demands a patients is expected to place on his or her hip prosthesis. Because not every patient requires an expensive high-demand hip prosthesis, the standardization program also has the potential to reduce the hospital cost for hip implants without compromising patient care. Patients are assigned to four demand categories based on five objective criteria: age, weight, expected activity, general health, and bone stock. Selection of the prosthesis in each of the four demand categories is intended to match the implant's capacity with expected patient demand. The standardization program was retrospectively applied to 103 THAs performed during 1991. Analysis of variance demonstrated that patient variables and demand categories were statistically significant groupings. The cost of hip implants would have been reduced by 25.7% with the Lahey Clinic Hip Implant Standardization Program. A prospective outcome study is required to determine the long-term validity of this standardization program.
An anthropometric computed tomography scan study was undertaken to design femoral components in 86 knees (47 osteoarthritic Indians-21 men, 26 women) who matched standards suggested by the Indian Council of Medical Research, 1990. Patients were classified into 3 random groups based on anteroposterior diameter (<55 mm, 55-59 mm, >59 mm). Most Indian men (86.8%) could have the femoral component satisfactorily replaced by available designs. A statistically significant number of women (60.4%, P < .001) had femoral anteroposterior diameters smaller than the smallest available (55 mm) femoral component. Splaying in mediolateral dimension (> 10 mm) in a given anteroposterior size was noted in all 3 groups. This pilot study representative of the Indian population can be used to manufacture prosthetic inventories suitable for most of the Asian-Pacific population having smaller anthropometric measurements than Western populations.
Accurate component placement in knee replacement surgery is important. The precision with which the implants are placed directly affects patient outcome as implant position and alignment influence stability, durability and patellar tracking. The ability to measure the accuracy of implantation of knee replacement components is valuable in assessing not only ones own technique but also in evaluating new instruments or implants and in teaching. The standard AP and lateral radiographs employed by most surgeons give inadequate information to assess alignment of each component accurately. We present a straightforward way of assessing femoral and tibial component alignment by using a series of three radiographs. This technique is reproducible and can be performed using standard equipment in any radiology department. This technique was applied to 160 total knee replacements performed using newly developed instrumentation. It was shown to be simple and the measurements were reproducible, with very little inter observer bias. We believe this technique has a role in audit, teaching, training and assessing new techniques and instruments.
We reviewed 139 consecutive femoral or tibial revision knee arthroplasties to determine if the outcome of revision knee arthroplasty using revision implant systems was superior to revisions using primary implant systems. Group 1 (n = 42) consisted of revisions performed with implants designed for primary total knee arthroplasty. Group 2 (n = 42) consisted of revisions performed with modified primary components. Group 3 (n = 55) consisted of revisions performed with components specifically designed for revision arthroplasty. The implant status was known in 123 of 139 knees at a mean follow-up of 7 years (range, 5-12 years). The implant-related failure rate, defined as reoperation requiring component revision or removal, was 26% for group 1, 14% for group 2, and 6% for group 3 (P<.05). Revision implants exhibited superior performance and durability despite their use in more difficult reconstructions. The improved longevity of revision implants justifies the evolution of modular revision components.
The anteroposterior (AP) and medial-lateral (ML) dimensions of 200 consecutive osteoarthritic knees (100 males and 100 females) undergoing unilateral primary total knee arthroplasty were compared. For all patients, the mean AP dimension was 57.3 mm (range: 49-66 mm) and the dimension was 10.5% taller in height in men than women. The mean ML dimension was 71.6 mm (range: 56-85 mm), and the dimension was 13.7% wider in men than women. The mean AP/ML ratio was 0.8 for all patients, 0.82 (range: 0.73-0.93) for females and 0.79 (range: 0.70-0.89) for males (P<.001). The data suggest that for any given AP femoral dimension, women tend to have a narrower ML dimension than men, independent of AP height, and an AP/ML ratio of 0.80 most closely approximates a standard-sized distal femur across gender. This report documents important gender differences that may serve as a reference for femoral implant designers and knee surgeons.
Patellar complications following endoprosthetic reconstruction can occur as a result of anatomic, physiologic, and surgical reasons. Patellar impingement on tibial polyethylene is a complication of distal femoral replacement, and it is frequently related to inaccurate restoration of the joint line and to soft-tissue contracture. The purpose of our study was to determine the prevalence and type of patellar complications following distal femoral replacements after excisions of bone tumors.
The results of reconstruction with use of a rotating-hinge endoprosthesis following excision of a distal femoral tumor in forty-three patients were retrospectively reviewed. Patients were followed clinically and radiographically for a minimum of forty-eight months or until death. Pain status, functional scores, and the range of motion were determined from a prospectively maintained database. The ratio of the patellar tendon length to the height of the patellar tendon insertion, as described by Insall and Salvati, was calculated. In addition, we attempted to determine whether the position of the patella was associated with anterior knee pain or with the functional scores derived with use of the International Society of Limb Salvage (ISOLS) scoring system.
Thirty-five patellar complications, including eleven cases of impingement, occurred in twenty-seven patients (63%). We found no difference, on the basis of our sample size, with regard to the presence of patellar pain, the range of motion, or the Insall-Salvati ratio between the patients with and those without impingement. The ratio of the patellar tendon length to the height of the patellar tendon insertion averaged 0.9 in the group with impingement and 1.4 in the group without impingement (p = 0.07). The ISOLS score averaged 21.2 points in the group with impingement compared with 24.2 points in the group without impingement (p = 0.01). Patella baja occurred in nine patients. The average ISOLS score (and standard deviation) was 20.1 +/- 4.4 points for the patients with patella baja compared with 24.8 +/- 3.9 points in the group with a normal patellar position (p = 0.004). Patellar fracture occurred in two patients, and osteonecrosis occurred in two patients. These patients were treated nonoperatively.
Patellar complications are common after distal femoral resection and endoprosthetic reconstruction. Patellar impingement on the polyethylene tibial bearing surface is a more common and important complication of distal femoral replacement than has been reported to date. Patella baja is also a relatively common complication, which has a negative impact on knee function.
It is quite rare but some primary sarcomas of the bone can be misdiagnosed as benign and be treated using intralesional procedures. An unplanned surgical excision occurs when tumors are removed without the appropriate preoperative evaluation and consideration for the need to obtain tumor-free margins. Residual tumor tissue as a result of unplanned excision of soft tissue sarcoma is a risk factor for local recurrence.
Twenty-five patients, undergone unplanned intralesional procedures of lower extremities, were enrolled in this study. There were 22 (88%) cases of osteosarcomas, 2 (8%) MFH of bone and 1 (4%) adamantinoma. Twenty-two (88%) cases had a limb salvage and among them, 4 (18%) cases had local recurrences. Three cases (12%) had amputation without any local event.
Lung metastasis developed in 6 (24%) cases. The CDF 5 year survival for 22 osteosarcoma cases was 65%(confidence interval: 52-82%).
Despite the high recurrence rate, the CDF survival of osteosarcoma cases was comparable to the primary one. Limb salvage procedures are worthwhile in cases whose initial radiographic findings simulate benign lesions, showing favorable response to neoadjuvant chemotherapy. The relative contraindication to the limb salvage is cases with a history of a pathologic fracture and extensive operative fixation.
Limb-salvage surgery, including endoprosthetic reconstruction after tumour resection, has become the standard management for local control of tumours around the knee. As the nature of surgery is technically complex and demanding, there is potential for significant morbidity arising from complications. This study describes our experience with complications following endoprosthetic reconstruction around the knee.
Retrospective analysis of consecutive resections and endoprosthetic reconstructions for tumours around the knee between 1996 and September 2005 performed at St Vincent's Hospital, Melbourne.
Fifty consecutive cases were reviewed, with a median follow-up of 24.5 (range, 2-124) months. Median age was 41 (range, 13-79) years. Tumour types included 38 primary musculoskeletal malignancies, 8 metastatic tumours, 2 bony lymphomas and 2 benign lesions. There were eight deaths, nine cases of subsequent metastatic spread and no local recurrences. There were six cases of deep infection, two each of non-resolving nerve palsy, fracture and mechanical wear, and one each of symptomatic patellofemoral impingement, aseptic loosening and intraoperative popliteal artery trauma. Five patients required endoprosthetic revision, and three subsequent amputations were described. Excellent functional outcome and emotional acceptance was observed amongst patients that underwent revision.
Resection and endoprosthetic reconstruction of tumours around the knee is both technically challenging and resource-intensive. It is imperative that morbidity from complications is limited through the minimisation of their incidence and the provision of optimal management. This series demonstrates that good patient outcomes can be achieved in specialist centres with experienced surgeons and adoption of a multidisciplinary approach.
Total knee replacement (TKR) operation is one of the most effective procedures, both clinically and in terms of cost. Because of increased volume and cost for this procedure during the past 3 decades, TKRs are often targeted for cost reduction. The purpose of this study was to evaluate the efficacy of two cost reducing methodologies, establishment of critical clinical pathways, and standardization of implant costs.
Ninety patients (90 knees) were randomly selected from a population undergoing primary TKR during a 2-year period at a tertiary teaching hospital. Patients were assigned to three groups that corresponded to different strategies implemented during the evolution of the joint-replacement program. Medical records were reviewed for type of anesthesia, operative time, length of stay, and any perioperative complications. Financial information for each patient was compared among the three groups.
Data analysis demonstrated that the institution of a critical pathway significantly shortened length of hospital stay and was effective in reducing the hospital costs by 18% (p < 0.05). In addition, standardization of surgical techniques under the care of a single surgeon substantially reduced the operative time. Selection of implants from a single vendor did not have any substantial effect in additionally reducing the costs.
Standardized postoperative management protocols and critical clinical pathways can reduce costs and operative time. Future efforts must focus on lowering the costs of the prostheses, particularly with competitive bidding or capitation of prostheses costs. Although a single-vendor approach was not effective in this study, it is possible that a cost reduction could have been realized if more TKRs were performed, because the pricing contract was based on projected volume of TKRs to be done by the hospital.
The ubiquitous availability of high power' computers has opened up the possibility of handling large (high resolution) volumetric data to accurately represent medical models, and performing geometric reasoning for various applications. In this paper, we present an efficient protocol to reconstruct accurate medical models from CT/MR images having equal or unequal values of slice thickness, inter slice distance, and pixel size. It involves modifying the slice thickness while leaving the in-slice resolution intact; issues such as slice overlap and inter-slice gap are handled using slice based interpolation. Noise reduction and better delineation of object boundaries and segmentation are performed in voxel space. Geometric analysis of reconstructed volumetric data is performed to generate internal thickness mapping, useful for pre-operative planning and custom implant design. A test case of pelvic model reconstruction from CT slices is described to illustrate the algorithms.
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