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We present two cases of Rotaflex hinged total knee arthroplasties in which the components forming the hinge mechanism have fractured. In one case this was the high density polyethelene sleeve bush of the tibial bearing, the other case being the titanium retaining peg of the tibial component. Component failure in this design of prosthesis is previously unreported.
Prosthetic voice restoration has considerably improved the results of vocal rehabilitation after total laryngectomy, and is presently the method of choice for many health-care providers treating laryngectomized patients. The Provox voice prosthesis, developed in the Netherlands Cancer Institute, is an indwelling device that has been applied in recent years with regular success. Its retrograde replacement method, using a disposable guide wire, assures reliable, atraumatic positioning of the prosthesis in the tracheoesophageal fistula. However, the method sometimes may be uncomfortable for the patient; therefore an adapted prosthesis and new replacement equipment were developed, which enable bidirectional insertion, i.e. not only in the traditional retrograde manner through the pharynx, but especially in an anterograde manner through the stoma. This second-generation voice prosthesis (Provox 2) was studied in a prospective clinical trial in 44 patients (33 experienced patients, seven first-time replacements and four primary insertions). The study demonstrated that the anterograde insertion with the Provox 2 system was applicable in all patients, making the voice prosthesis even easier to handle than with the traditional retrograde method. A stenosis of the pharyngoesophageal segment no longer interfered with the replacement. In addition, the patients judged the new method as being favourable, reporting significantly less discomfort during the replacement procedure (paired Student's t-test: p < 0.0001). Furthermore, the adapted voice prosthesis could be removed from the tracheoesophageal fistula without excessive force (mean 7.9 N, range 6.0-14.0 N), more easily than the original Provox (mean 20.9 N, range 5.5-25.0 N). It can be concluded that this second-generation indwelling voice prosthesis (Provox 2) seems to be a further improvement in the application of this voice rehabilitation system, not only simplifying the replacement procedure, but also diminishing the discomfort for the patient.
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PURPOSE: Patterns of von Mises stress values surrounding implants supporting fixed prostheses in the posterior edentulous maxilla were evaluated using 3-dimensional finite element analysis. MATERIALS AND METHODS: Implants were placed in maxillary bone in 2 different configurations. In the first configuration, implants were placed in the first premolar, second premolar, and second molar regions; in the second configuration, implants were placed in the second premolar and second molar regions, and a mesial cantilever was extended to the space of the first premolar tooth on the superstructure. On the implant placed in the socket of the second molar, 3 different inclinations were used (0, 15, and 30 degrees). Loading was applied in the vertical, oblique, and horizontal axes. RESULTS: Inclination of the implant in the molar region was found to result in increased stress. Significant increase in stress on the implant embedded in the premolar region was also seen in the design with the cantilever as compared to the conventional prosthesis design. DISCUSSION: The stress concentrations observed at the neck of the implant were similar to results reported in the literature. CONCLUSION: The highest stress value obtained in the study was 194.2 MPa with oblique loading. This value did not exceed the endurance limit of pure titanium, which is 259.9 MPa.
A better knowledge of the kinematics behavior of total knee replacement (TKR) during activity still remains a crucial issue to validate innovative prosthesis designs and different surgical strategies. Tools for more accurate measurement of in vivo kinematics of knee prosthesis components are therefore fundamental to improve the clinical outcome of knee replacement. In the present study, a novel model-based method for the estimation of the three-dimensional (3-D) position and orientation (pose) of both the femoral and tibial knee prosthesis components during activity is presented. The knowledge of the 3-D geometry of the components and a single plane projection view in a fluoroscopic image are sufficient to reconstruct the absolute and relative pose of the components in space. The technique is based on the best alignment of the component designs with the corresponding projection on the image plane. The image generation process is modeled and an iterative procedure localizes the spatial pose of the object by minimizing the Euclidean distance of the projection rays from the object surface. Computer simulation and static/dynamic in vitro tests using real knee prosthesis show that the accuracy with which relative orientation and position of the components can be estimated is better than 1.5 degrees and 1.5 mm, respectively. In vivo tests demonstrate that the method is well suited for kinematics analysis on TKR patients and that good quality images can be obtained with a carefully positioning of the fluoroscope and an appropriate dosage. With respect to previously adopted template matching techniques, the present method overcomes the complete segmentation of the components on the projected image and also features the simultaneous evaluation of all the six degrees of freedom (DOF) of the object. The expected small difference between successive poses in in vivo sequences strongly reduces the frequency of false poses and both the operator and computation time.
Prediction and measurement of residuum shape change inside the prosthesis under various loading conditions is important for prosthesis design and evaluation. Residual limb surface measurements with the prosthesis in situ were used for construction of a finite element model (FEM). These surface measurements were obtained from volumetric computed tomography. A new experimental method for modeling the shape of the in situ lower residual limb was developed based on spiral X-ray computed tomography (SXCT) imaging. The p-version of the finite element method was used for estimating the material properties from known load and displacement data. A homogeneous, isotropic, linear constitutive model with accommodation of the constitutive soft and hard tissues of the residuum was evaluated with static axial loading applied to the in situ prosthesis and compared with experimental results obtained in a human volunteer. Two FEMs were created for similar coronal cross sections of the below knee residuum under two loading conditions. Agreement between observed (from SXCT) and predicted (from FEA) residual limb shape changes inside the prosthesis were maximized with a single modulus of elasticity for the residuum soft tissue of 0.06 MPa, consistent with previously published results. This methodology provides a framework to predict and objectively evaluate FEMs and determine residuum material properties by inverse methods.
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AIM: Does the pressfit anchorage of cementless acetabular cups depend on the roughness of the pole? To answer this question the primary pressfit of two cementless acetabular cups which differ only with regard to the roughness of their poles were compared by means of finite elements analysis. MATERIALS AND METHODS: It was assumed that the material properties of bone are homogeneous, isotropic and linearly elastic. Material-specific values of cancellous bone with three different bone densities were used. Assumption of isotropy represents an approximation. RESULTS: Comparison of the two prosthesis designs revealed that both designs/shapes cause similar patterns of bone deformation and tension. CONCLUSIONS: It can therefore be concluded that with regard to pressfit anchorage the prosthesis with milled polar surface is according to FEA mechanically equivalent to the prosthesis with non-milled polar surface.
UNLABELLED: In patients with deficient bone in the proximal end of the tibia, the mechanical support of a conventional total knee replacement may be inadequate. We have developed a custom design for use in situations in which there is extensive deficiency of tibial cancellous bone. To do this, we examined conventional and custom prosthetic tibial components using finite-element analysis. Several loading configurations were tested, and the worst loading conditions were found to be those in which eccentric loads were placed on the margin of the tibial component. The results showed that the stresses on the cancellous bone beneath a conventional-design prosthesis may be lowered if a metal tray and metal peg are employed. A salvage-design concept for revision in the presence of deficient cancellous bone was tested analytically and used successfully. This concept requires that some portion of the applied load be transferred directly to the tibial cortical shell. Stresses in the remaining cancellous bone were lowered by the combination of a thickened metal tray and a metal support buttress. CLINICAL RELEVANCE: This study demonstrates the advantage of metal trays for the tibial plateau and suggests that they should be used whenever the supporting tibial bone is insufficient. In knees in which there are large defects in the bone, direct transfer of the load to the cortical shell through the prosthesis, made possible by a custom design, appears to be necessary.
OBJECTIVE: Current prosthetic heart valves necessitate permanent anticoagulation or have limited durability and impaired hemodynamic performance compared to natural valves. Recently a polymeric valve prostheses with special design for mitral position demonstrated excellent in vitro and in vivo results with improved durability and no need for permanent anticoagulation. In this study, a respective flexible polymeric aortic valve is presented and in vitro and in vivo results are reported. METHODS: The aortic prosthesis (ADIAM lifescience AG, Erkelenz, Germany) is entirely made of polycarbonaturethane. The tri-leaflet flexible prosthesis mimicks the natural aortic valve and has a diminished pressure loss and reduced stress and strain peaks at the commissures. The valve underwent long-term in vitro testing and in vivo-testing in a growing calve animal model (20 weeks, 7 aortic valves) and was compared to two different commercial bioprostheses. RESULTS: The polymeric aortic heart valve substitute demonstrated excellent in vitro and in vivo hemodynamics. Five/seven animals with aortic PCU-prostheses had an excellent clinical long-term course. The explanted valves showed a variable degree of calcification. Two of the seven animals died at 27 and 77 days due to pannus overgrowth causing severe LVOTO without degeneration of the valve itself. Both animals with commercial bioprostheses had to be sacrificed because of congestive heart failure related to structural degeneration of the bioprosthesis after 10 and 30 days of implantation. There was no increased thrombogenity of the PCU valves compared to bioprostheses. CONCLUSION: The new flexible polymeric aortic valve prosthesis is superior to current bioprostheses in animal testing.
A variety of problems faces the prosthodontist attempting reconstruction of maxillary defects. This article reviews developments in materials and techniques of obturator prosthesis design for patients experiencing maxillectomy. The size of the maxillectomy defect is one of the main factors governing the prognosis for treatment. Many patients require special prosthodontic techniques. However, routine attention to extension of the prosthesis and balanced occlusion is essential. Obtaining satisfactory retention and stability in the definitive obturator prosthesis can be elusive. Resilient denture base materials are extremely useful in retaining the prosthesis, which obturates small defects. However, the flexibility of these materials makes them unsuitable in large maxillectomy cavities because of the deformation that occurs during mastication. Alternative forms of retention, eg., osseointegrated implants and sectional prostheses retained by magnets, are discussed.
BACKGROUND: Introduced in 1993, the Carbomedics Top Hat (Sulzer, Carbomedics, Austin, TX) valve is a bileaflet mechanical aortic prosthesis designed to be placed in a supraannular position. Five institutions pooled their clinical experiences to evaluate early outcome in patients with this prosthesis. METHODS: From 1994 to 2000, 639 patients underwent aortic valve replacement with Top Hat (Sulzer Carbomedics) valves at 5 institutions. Mean age was 60 +/- 13 years. In this heterogeneous population, 28% of patients had previous cardiac operations and 64% had concomitant procedures, including procedures involving more than 1 heart valve in 32%. Implanted prostheses sizes included the 19 mm (15%), 21 mm (37%), 23 mm (33%), 25 mm (13%), and 27 mm (2%). Mean follow-up was 2.0 +/- 1.5 years, and there were 1,206 patient-years of follow-up available for analysis. RESULTS: Thirty-day mortality was 5.3%. Five-year survival was 74%. Risk factors for death included older age (p = 0.01), decreased ejection fraction (p = 0.007), and increased New York Heart Association functional class (p = 0.003). Five-year freedoms from thromboembolism and hemorrhage were 90% and 85%, respectively. Five-year freedoms from explant and endocarditis were both 99%. There were no structural valve failures. CONCLUSIONS: The Top Hat valve outcomes have been similar to those of the standard Carbomedics intraannular prostheses. The unique design of the Top Hat valve, with all its components in the aortic sinuses, has particular advantages in the small aortic root, in settings where leaflet entrapment may occur, and in multiple valve replacement.
The implant tooth-supported fixed partial denture presents a biomechanical design problem, because the implant is rigidly fixed within the alveolus, and the tooth is surrounded by a periodontal ligament that allows movement. Nonrigid fixed partial denture designs are advocated by some dentists as a method of compensating for this differential movement. Rigid fixed partial denture designs, however, are advocated by many clinicians. Studies have failed to show the advantage of one design over the other. This study developed an in vitro method for testing such prosthesis designs and measured movement of a natural tooth abutment during simulated function. The movement of the natural tooth abutment was not found to change substantially with the fixed partial denture designs tested.
We have designed a new polycentric knee adopting a hydraulic unit and an intelligent mechanism. The biomechanical parameters of this prototype, such as the stance duration, peak knee flexion angle in stance and swing, peak hip flexion angle, and peak hip extension moments were analyzed at three different cadences (88, 96, 104 steps/min) in three amputees, and then compared to those of polycentric hydraulic knees currently in use. The same parameters were also measured for 10 healthy volunteers and subsequently analyzed. In the prototype, almost all the values of the parameters showed no significant variety in individuals at the different cadences. The situation was the same with the healthy volunteers. However, the values of the parameter for the conventional knee varied significantly with the individual at the different cadences. The prototype may be of practical use, contributing to a stable walk even at different cadences.
Blunt pelvic and perineal trauma has been previously reported to result in site-specific veno-occlusive dysfunction and/or site-specific cavernosal artery insufficiency. We herein describe a case of erectile dysfunction in a young previously potent amputee. We postulate that the erectile dysfunction is associated with a newly described form of blunt trauma, that is, site-specific compression from a perineal weight-bearing lower extremity above-knee prosthetic device. It is hypothesized that when the force exerted by the above-knee prosthesis is directed medially towards the ischiopubic ramus, the penile crura and common penile arterial blood supply become susceptible to crush-like injury, since they are in fixed anatomic locations in the perineum sandwiched between the compressive force and the bone. Clinical evaluation of the erectile dysfunction in this patient revealed site-specific corporal veno-occlusive dysfunction and site-specific common penile arterial occlusive pathology in the precise region of the contact of the above-knee prosthesis with the perineum. Further research is needed in above-knee prosthesis design to prevent erectile dysfunction.
PURPOSE: The aim of the present article was to describe the treatment planning for an implant-supported maxillary fixed prosthesis and the clinical procedure involved, including the laboratory fabrication sequence. MATERIALS AND METHODS: If patients request a fixed prosthesis to restore the edentulous maxilla, it is essential to decide as soon as possible whether this prosthesis design can satisfy the requirements of esthetics, phonetics, comfort, and function. Thus, the crucial clinical factors need to be checked during examination. Furthermore, the relationships between ideal implant angulation, available bone, and intended crown should be assessed using reformatted computed tomography. RESULTS: In patients with minimal bone resorption and limited intermaxillary space, implants can usually be placed in the prosthetically driven implant position for a fixed prosthesis. To evaluate and optimize esthetics, biology, and function, a fixed provisional restoration should be inserted for a 6-month diagnostic period. The ideal provisional then serves as a guide for the final restoration. CONCLUSION: If clinical and radiologic diagnostics indicate that an implant-supported fixed complete denture is feasible, meticulous presurgical planning, precise execution of implant positioning, and a progressive prosthetic treatment sequence are required. The ceramometal fixed implant-supported restoration can then be established in an ideally prepared and matured oral environment.
The common modes of failure of total wrist arthroplasty have been fracturing, loosening, pain on pronation and supination, and muscle soft-tissue imbalance. To overcome some of these problems a total modular wrist prosthesis has been designed for use both as a primary prosthesis and for revision surgery. An uncemented and cemented radial component, secure fixation in three metacarpal bones, and an unconstrained and constrained version account for the modularity, including optional treatment of the distal radioulnar joint. We present the design of the prosthesis including the preliminary clinical and radiographic results after a mean follow-up of 20 months in 32 patients of whom four have had earlier implants revised.
STUDY DESIGN: An in vitro biomechanical study of C4-C5 intervertebral disc replacement using a cadaveric model. OBJECTIVES: To investigate the degree of motion afforded by a ball-and-socket cervical intervertebral disc prosthesis design. SUMMARY OF BACKGROUND DATA: Intervertebral disc prostheses designs attempt to restore or maintain cervical disc motion after anterior cervical discectomy and reduce the likelihood of accelerated degeneration in adjacent discs by maintaining normal motion at the affected disc level. Surprisingly, the actual kinetic and biomechanical effects that cervical disc arthroplasty imparts on the spine have not been widely reported. Accordingly, we investigated what effect implanting a cervical disc prosthesis has on the range of motion at the affected level as well as how it changes the coupled motion patterns at the level of implantation. METHODS: Six fresh-frozen human cadaveric cervical spines (C2-C7) were used in this study. We evaluated two different spinal conditions: intact and after disc replacement at C4-C5. Compression (using the follower load concept) and pure moment loading were applied to the specimen. Range of motion was measured using an optical tracking system. Statistical differences between the intact and replaced condition range of motion was determined using analysis of variance with post hoc comparisons (alpha = 0.05). RESULTS: The data indicate that the intervertebral disc prosthesis approximated the intact motion in all three rotation planes at the affected level. Finally, changes in cervical coupled rotations, specifically lateral bending during axial rotation loading and axial rotation during lateral bending loading, were not statistically significant between the two tested conditions. CONCLUSIONS: Our data demonstrate that a ball-and-socket design can replicate physiologic motion at the affected and adjacent levels. More importantly, the data indicate that motion coupling, which is most dramatic in the cervical spine and plays an important biomechanical role, is maintained.