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Sixty-eight patients with Syme amputations resulting from industrial injuries were reviewed. The amount of end-weight-bearing was measured with a capacitance transducer. The majority of patients required fitting with a prosthesis designed to relieve end-weight-bearing. The old-fashioned prosthesis with a leather corset was the most effective in achieving reduction of end-weight-bearing.
OBJECTIVE: Transesophageal (TEE) and Transthoracic (TTE) comparative echocardiographic analysis of patients with mitral valve prosthesis. DESIGN: Prospective study. SETTING: In hospital and out patients with mitral prosthesis in a follow-up study by the Cardiology Department and referred to the echocardiographic laboratory of Gregorio Marañon General Hospital, Madrid. PATIENTS: We studied 90 consecutive patients with mitral prosthesis diagnosis. INTERVENTIONS: Comparative and prospective echocardiographic study of transthoracic and transesophageal techniques in mitral prosthesis pathology. RESULTS: TTE diagnosed 18% of dysfunctioning mitral prosthesis patients compared to 56% of cases identified by TEE. TTE observed 1% of mitral prosthesis vegetation compared to 8.8% by TEE. TEE diagnosed left atrial thrombosis in 2.2% and TEE in 10%. Left atrial spontaneous dynamic contrast was identified exclusively by TEE in 55% of all cases. Paravalvular mitral prosthesis leak was correctly identified exclusively by TEE in 20% of cases. CONCLUSIONS: TEE has a greater diagnostic capacity compared to TTE in mitral prosthesis patients. This technique can give a greater security in evaluating mitral prosthesis thrombi, vegetations and leak, establishing a more precise diagnosis of mitral prosthesis dysfunction. The authors concluded that TEE is the technique of choice in noninvasive evaluation of patients admitted with the suspicion of mitral prosthesis dysfunction.
OBJECTIVE: To determine the effect of the gelatin coating on the efficacy of Gelweave, a new gelatin-sealed woven polyester graft material, as an arterial prosthesis. DESIGN: In-vitro and in-vivo studies of the prosthesis. SETTING: A laboratory of experimental surgery in a university teaching institution. SUBJECTS: After in-vitro testing of the material, eight dogs were subjected to a series of in-vivo tests to evaluate the properties of Gelweave in comparison with its unsealed precursor and a commerically available collagen-coated woven polyester prosthesis. INTERVENTION: Implantation of the prosthesis as a thoracoabdominal bypass for prescheduled periods ranging from 4 hours to 6 months. MAIN OUTCOME MEASURES: Physical and chemical properties of the virgin prosthesis compared with the other two prostheses, effects of the gelatin-sealed prosthesis on healing, the hematologic characteristics of the dogs before operation and at sacrifice, microscopic studies, fibrin and platelet uptakes, prostaglandin secretion, and properties of the Gelweave grafts removed at varying periods after implantation. RESULTS: The gelatin sealant in the Gelweave prosthesis effectively reduced the water permeability of the new prototype to zero. Neither blood loss at implantation nor infection during the postimplantation period was observed. The gelatin impregnation did not cause any adverse response in the dogs and was completely lysed within 2 weeks, thus allowing encapsulation and graft healing to progress satisfactorily. After 2 weeks, the prostacyclin:thromboxane ratio was greater than 1.0, whereas the fibrin and platelet uptakes on the luminal surface of the Gelweave grafts remained low, regardless of the period of implantation. Analysis of the explanted grafts confirmed that this gelatin-sealed prototype prosthesis healed satisfactorily and no adverse biologic response occurred as a result of the gelatin coating. It maintained its biostability during 6 months in situ. CONCLUSION: The new Gelweave arterial prosthesis is ready for clinical use as a thoracic and abdominal vascular substitute.
OBJECTIVE: To determine the influence of femoral hip prosthesis design and composition on regional periprosthetic bone remodelling as a function of time in asymptomatic patients. MATERIALS AND METHODS: Bone mineral density (BMD) changes surrounding two differently designed porous-coated femoral prostheses (S-ROM, n=111; and Multilocki, n=62) were determined serially over a 24 month interval. There was a subset of patients with Multilock implants that were coated with a 50 micron film of hydroxy-apatite (n=23) over the porous surface. Seven Gruen zones defined the periprosthetic bone regions (LUNAR ORTHO software). Inclusion criteria were primary implants, Harris hip scores >or=95 and no radiographic evidence of loosening. RESULTS: For the S-ROM femoral component, at 6 months all zones showed a significant decrease in BMD relative to the immediate postoperative baseline measurements; mean loss varied from 4.3% to 17.4%. At 24 months mineral change varied from -10.8% to +1% for Gruen zones 1 to 6. Gruen zone 7, the calcar, differed in that it was the site of greatest mineral loss, attaining a mean of 17% at 24 months, and it was also significantly greater than the losses registered in the other zones at that time point. For the Multilock, maximal mineral losses were registered at zones 1 and 7. There were significant differences in mineral losses between the S-ROM and Multilock implants in zones 1, 2 and 3 at 24 months; S-ROM losses of 7.3%, 10.8% and 3.5% respectively, compared to Multilock losses of 23.8%, 15.9% and 6.9% respectively. Comparison of hydroxyapatite coated and uncoated Multilock implants demonstrated significantly less loss in the coated implants in zones 1 (greater trochanter) and 7 at 24 months. Coated losses were -16.9% and 11.3% for zones 1 and 7, respectively, whereas uncoated losses were 23.8% and 20.5% respectively.
Time to revision is an important criterion describing the quality of implants in total joint surgery. Estimates of failure probabilities are required to inform a patient about the risk of suffering a reoperation. Also, regression models are used for comparing different prosthesis designs. Typically, patients dying before a revision are considered as censored for time to prosthesis failure. We argue that this technique is inadequate for estimation of failure probabilities and insufficient for comparison of different designs. We propose a new approach based on a competing risk model to account for concurrent mortality. We describe differences in the estimation of failure probabilities and in the interpretation of regression models for implant failure. Additionally, we introduce a random effects term in the regression model to account for potential dependencies in the failure times of bilaterally treated patients. The new approach is illustrated with fictitious data and data from an observational study conducted at a specialized hospital in Switzerland.
OBJECTIVE: To compare the cognitive demand of walking when using a conventional prosthesis with that using a microprocessor-controlled prosthesis. DESIGN: Ten unilateral transfemoral amputees wearing conventional pneumatic swing phase control (conventional prosthesis) prostheses walked on a treadmill which enforced a pattern of constantly varying speeds. The subjects simultaneously performed a simple or a complex distracting task. Following a period of accustomization, the subjects performed the same test wearing a prosthesis with microprocessor control of swing phase damping (the Intelligent Prosthesis). OUTCOME MEASURES: The three-dimensional trajectory (sway) of a retroreflective marker attached to the forehead was measured by a video-based motion analysis system, and used as a measure of gait quality. The ratio of the sway for the complex task over the simple task (the 'automation index') was used as a measure of the degree of automation of gait. RESULTS: No significant differences were found in the automation index between the two devices. However, the total sway for the conventional prosthesis was significantly higher. Sway during the complex distracting task was significantly higher than during the simple task. CONCLUSIONS: The microprocessor-controlled prosthesis was not found to be less cognitively demanding than a conventional prosthesis.
Amputees who wear prosthetic limbs often experience discomfort from blisters and sores due to mechanical insult; these skin conditions are exacerbated by elevated skin temperatures and excessive perspiration within the prosthetic socket. The goal of this study was to create a tool for developing new prostheses that accommodate varying thermal loads arising from everyday activities. A three-dimensional thermal model of a transtibial residual limb and prosthesis was constructed using the finite element (FE) method. Transverse computerized tomography (CT) scans were used to specify the geometry of the residual limb and socket. Thermal properties from the literature were assigned to both biological tissue and prosthetic socket elements. The purpose of this work was to create a model that would aid in testing the effect of new prosthesis designs on skin temperature. To validate its output, the model was used to predict the skin temperature distribution in a common prosthetic socket system (silicone liner, wool sock, and carbon fiber socket) at rest with no mechanical loading. Skin temperatures were generally elevated near muscle and decreased anteriorly and at the distal end. Experimental temperature measurements taken at the skin-prosthesis interface of five human subjects were used to validate the model. Data extracted from the thermal model at anterior, posterior, lateral, and medial locations were typically within one standard deviation of experimental results; the mean temperatures were within 0.3 degree C for each section and were within 0.1 degree C overall.
This work is aimed at developing an innovative simulation environment supporting and improving the design of standard joint implants (JPD integrated design environment (JIDE)). The conceptual workflow starts from the design of a new implant, by using conventional CAD programmes and completes with the generation of a report that summarises the goodness for a new implant against a database of human bone anatomies. For each dataset in the database, the JPD application calculates a set of quantitative indicators that will support the designer in the evaluation of its design on a statistical basis. The resulting system is thus directed to prostheses manufacturers and addresses a market segment that appears to have a steady growth in the future.
BACKGROUND: Understanding muscle architecture of the foot may assist in the design of surgical procedures such as tendon transfer, biomechanical modeling of the foot, prosthesis design, and analysis of foot function. There is limited published information regarding foot intrinsic muscle architecture. METHODS: Eleven fresh-frozen cadaveric feet were studied from eight males and three females. Twenty-eight intrinsic muscles were dissected in each foot, and measurements of fiber length, muscle length, and muscle volume obtained using calipers and water displacement technique. The physiologic cross-sectional area, fiber/muscle length ratio, muscle mass fraction, and tension fraction were then calculated. RESULTS: Intrinsic muscle length was related to foot size. The mean fiber length ranged from 13.6 mm (first plantar interosseous) to 28.0 mm (second extensor digitorum brevis). The mean muscle length ranged from 24.8 mm (adductor hallucis transverse) to 115.8 mm (abductor hallucis). The mean muscle volume ranged from 0.4 cc (fifth lumbrical) to 15.2 cc (abductor hallucis). The physiologic cross-sectional area ranged from 0.28 cm2 (second and third lumbrical) to 6.68 cm2 (abductor hallucis). The fiber/ muscle ratio ranged from 0.20 (abductor hallucis) to 0.82 (adductor hallucis transverse). The mass fraction ranged from 0.33% (fifth lumbrical) to 16.59% (abductor hallucis). The tension fraction ranged from 0.34% (fifth lumbrical) to 15.37% (abductor hallucis). CONCLUSIONS: The abductor hallucis and adductor hallucis oblique had much greater physiologic cross-sectional areas compared to those of the other intrinsic muscles. The lumbrical muscles had relatively low physiologic cross-sectional areas. These observations illustrate the underlying structural basis for the functional capacities of the intrinsic muscles of the foot.
The results of the follow-up study of 271 bypass operations in aortoiliofemoral position are analyzed. The interventions are done using monotype double-velour dacron prosthesis, standard operative technique and tactics. At 5.4 percent operative lethality, the postoperative complications include infection (2%) and rethrombosis (4%), necessitating reoperation which is successful in 64 per cent. Secondary cumulative patency of the prostheses implanted, amounting to 90 percent at three years, 80 percent at 5 years, and 66 percent at ten years postoperatively, is recorded, with aortobifemoral bypasses yielding superior results. Serious late complications are registered, such as prosthesis infection, abnormal dilatation of the implant, periprosthetic seromas and aneurysms by anastomosis. The underlying causes of complications and the indications for reoperation are discussed. The role played by late reoperations, leading to a successful outcome in 63 percent of cases is underscored. Attention is called to a number of characteristic features of the prosthesis employed, including the need of precise preclotting, restrained post-implantation increase in its diameter up to 20 percent necessitating implantation of prostheses isodiametric to the recipient artery, high incidence of postoperative complications making mandatory, periodic check-ups of operated patients and the like. In conclusion, it is estimated that over the 10-year observation period, the prosthesis suggested yields satisfactory results upon implantation in the aortoiliofemoral segment, and these results may be accepted as a basis for comparison with new vascular prosthesis designs.
Many unsolved problems in dental implant research concern the interfacial stress distributions between the implant components, as well as between the implant surface and contacting bone. To obtain a mechanical understanding of how vertical and horizontal occlusal forces are distributed in this context, it is crucial to develop in vitro testing systems to measure the force transmission between dental implants and attached prostheses. A new approach to such testing, involving a robotic system, is described in this investigation. The system has been designed to produce simulated mandibular movements and occlusal contact forces so that various implant designs and procedures can be thoroughly tested and evaluated before animal testing or human clinical trials. Two commonly used fixed prosthesis designs used to connect an implant and a tooth, a rigid connection and a nonrigid connection, were fabricated and used for experimental verification. The displacement and force distributions generated during simulated chewing activities were measured in vitro. Force levels, potentially harmful to human bone surrounding the connected dental implant and tooth, were analyzed. These results are useful in the design of prostheses and connecting components that will reduce failures and limit stress transfer to the implant/bone interface.
When treating a septic hip-joint prosthesis with bone loss of the proximal femur secondary to osteomyelitis, we implanted a specially designed prosthesis to act as a local antibiotic and spacer between the acetabulum and femur until the infection abated. Arthroplasty could then be carried out with no trouble and there was no recurrence of infection.
OBJECTIVES: The purpose of this study was to measure the stress relaxation behavior at elevated temperatures of three experimental opaque porcelains and three experimental body porcelains. METHODS: Feldspathic porcelain formulations covering a range of thermal contraction coefficients were supplied by a dental ceramics manufacturer. Six specimens, 11 mm in diameter by 22 mm long, were fabricated for each porcelain. The specimens were tested in compression at five temperatures controlled to +/- 1 degree C in a hot stage furnace attached to a screw-type uni-axial testing machine. RESULTS: Mean values of relaxation time, tau u, and the b function were determined by a regression fit to the relation: psi (t) = exp [-(t/tau u)b]. Values of b ranged from 0.23 to 0.53 for opaque porcelain and 0.47 to 0.64 for body porcelain. Relaxation times ranged from 2.6 s to 4 x 10(4) s for the opaque porcelains and 1.5 s to 5.5 x 10(2) s for the body porcelains. A statistically significant variation of b with temperature for three of the experimental porcelains is an indication that these porcelains do not satisfy the theoretical requirements for the porcelains to be classified as thermorheologically simple. SIGNIFICANCE: A knowledge of the relaxation behavior of dental porcelains is necessary so that dental researchers can identify metal/porcelain combinations that will result in low stress values and, therefore, reduce the potential for failure from thermally induced stresses. These properties can be used in the optimization of prosthesis design to reduce the destruction of healthy tissue to accommodate the placement of the dental prosthesis.
OBJECTIVES: Despite the diversity of wheelchair cushions currently in clinical use, pressure on bony prominences continues to be a major problem for wheelchair-bound patients, and the incidence of pressure ulcers remains high. No static surface has been reported to reduce resting pressure under the ischial tuberosities to below that of capillary pressure, which may well be the threshold for inducing tissue damage. An entirely new form of seating was designed to decrease absolute pressure using a prosthetic fitting technique analogous to a below-the-knee prosthesis. DESIGN: A repeated measures randomized design was used to test differences between the experimental (TCS) and three other standard cushions. SETTING: A Veterans Medical Center outpatient service. PATIENTS: Wheelchair-bound volunteer subjects, n = 47, were selected who weighed more than 60kg. MAIN OUTCOME MEASURES: Pressures were measured by a standard air pressure pad and also by a computer-linked array of pressure transducers. The grid was standardized and used to generate topographic maps for each site over time. These data were used to measure the seating interface pressures. RESULTS: There was a significant main effect of cushion over site, F = 131 for left ischial tuberosity. Pressure were lowest while patients sat on the experimental seat and differences were significant at all time points. Using 1psi as presumed capillary pressure, frequency of success at achieving this pressure threshold was greatest for the experimental seat, p < .001. This difference persisted throughout the 30 minutes of testing. CONCLUSIONS: A computerized pressure grid was developed that allowed evaluation of anatomically localized pressures. The prosthetically designed TCS displays lower seating pressures than any other cushion tested. Consistent and sustained pressures were below the postulated threshold for tissue damage.
OBJECTIVE: To monitor the hematological and clinical sequelae of a single tilting disc cardiac valve prosthesis. DESIGN: Prospective nonrandomized trial. SETTING: University teaching hospital. PARTICIPANTS: All patients receiving a single mechanical cardiac valve prosthesis were offered the Sorin Monostrut valve if they met the criteria for valve use. Seventy-five per cent of the patients entered were in New York Heart Association (NYHA) functional class III or IV. One hundred and forty-seven patients were subsequently followed at three months and then yearly after valve implantation for seven years. MAIN OUTCOME MEASURES: At one year, preoperative indexes of hemolysis were compared with three-month and one-year postoperative values. Actuarial curves for survival, freedom from cerebrovascular events and explantation were constructed for the seven-year follow-up period. RESULTS: Hemolysis, as measured by lactate dehydrogenase values, commonly occurs preoperatively, remaining significantly elevated three months and one year following valve implantation. Serum haptoglobin was normal preoperatively but was significantly low at one year. Anemia was uncommon and most patients had normal reticulocyte counts at one year. At three years, 81% of patients were in NYHA functional class I. CONCLUSIONS: Midterm results show that this valve is structurally reliable and meets all current requirements for a safe mechanical valve.
The Zenith endovascular graft is the culmination of a worldwide collaboration of experts whose experience and developments were compiled, resulting in an endovascular prosthesis designed to treat infrarenal abdominal aortic aneurysms. The device is made of stainless steel, self-expanding Z-stents and polyester fabric. It has an uncovered stent with barbs (for fixation) that extend into the suprarenal aorta and is modular in design and allows for disparity in the length and diameter of the iliac arteries that are incorporated into the repair. A prospective study contrasting endovascular and open surgical patients was completed in 2002 and resulted in US Food and Drug Administration approval of the device for commercial sale within the USA. Although long-term data from the trial are still being evaluated, the worldwide experience with this device and its predicate devices has allowed for certain conclusions to be made with respect to performance expectations and aneurysm sac behavior. The periprocedural mortality in healthy patients with anatomy meeting the device instructions for use should be under 2%. The expected risk of endoleak (mostly Type II) was 7.4% at 12 months and 5.4% at 24 months. Migration (based on the reporting standards for endovascular aneurysm repair recommended by the vascular surgical societies, published in the Journal of Vascular Surgery in 2001) was not seen in any patients over 12 months. The majority of the aneurysms shrink at 1 and 2 years, and any patient exhibiting aneurysm growth had a detectable cause and required treatment. Coupled with European and Australian data, including several device explants, the device integrity issues are limited to barb separation (which has about a 2% incidence and appears incidental in the US trial) and suprarenal stent detachment (six cases detected worldwide). In order to address the latter problem, a design alteration was implemented with a double suture attachment, significantly increasing the tensile strength of the device. No separations have been noted since the change instituted at the conclusion of the US trial.
Anterior, partially edentulous residual ridges often have hard-tissue and soft-tissue defects that create esthetic and functional problems when conventional fixed prostheses are used to replace the missing teeth. However, tissue-tinted porcelain can be used in conjunction with fixed prostheses to solve many of these problems. Proper prosthesis design and shade matching are important considerations in the fabrication of fixed prostheses that incorporate tissue-tinted porcelain to restore hard-tissue and soft-tissue defects.
In this report we describe the use of an indwelling stent for end-to-end anastomosis of an arterial prosthesis. Designed as an alternative to conventional suturing in patients with heavily calcified arteries harvested from human cadavers. After the prosthesis is introduced into the artery, an angioplasty balloon catheter is inflated to expand the Palmaz stent and press the prosthesis against the calcified wall of the popliteal artery. From January 1993 to February 1994 we used this technique for end-to-end anastomosis of a polytetrafluoroethylene graft on the popliteal artery in six patients with extensive circumferential calcification of the popliteal artery. In all patients surgery was indicated to avoid amputation and no other method was suitable (no available vein graft, poor runoff). Stent anastomosis was successful in all six patients with no postoperative complications. Intraoperative controls using arteriography and angioscopy and postoperative Doppler ultrasound studies were normal in all patients. During follow-up, graft occlusion occurred in two patients at 10 and 14 months, respectively. Three patients died after control studies at 2, 6, and 8 months had shown the grafts to be patent. No false aneurysms were detected by clinical examination or ultrasound imaging. Although our data do not allow assessment of long-term outcome, this study demonstrates the feasibility of stent anastomosis in patients with extensive, circumferential calcification of the popliteal artery.