Material related aspects of surface structured endoprostheses

In this article technical problems of surface-structured endoprostheses for cementless implantation are discussed. On the basis of four prostheses (two hip and two knee endoprostheses) various different porous coating technologies are compared. One sintered sphere layer, a cast sphere layer, a cast layer with "spongy-bone" structure and a plasma sprayed coating were compared. The quality of the bonding between the prosthesis and the porous surface layer was examined metallographically using polished specimens, with additional investigation of fraction surfaces of special tension test specimens. Additional information is given on the notch effect of the different coatings, in terms of a reduction in fatigue strength. The notch sensitivity differs for each material, and the reduction in fatigue strength is discussed for different implant alloys and different technologies for surface structuring. The investigation shows that the present quality of surface-structured endoprostheses is not satisfactory. We would like to thank the Dr. Johannes Heidenhain Foundation for financial support of this research.     

Computed tomography analysis of radiostereometric data to determine flexion axes after total joint replacement: Application to the elbow joint

Kinematic analysis for in vivo assessment of elbow endoprostheses requires knowledge of the exact positions of motion axes relative to bony landmarks or the prosthesis. A prosthesis-based reference system is required for comparison between individuals and studies. The primary aim of this study was to further develop an earlier described algorithm for fusion of radiostereometric analysis (RSA) data and data obtained in 3D computed tomography (CT) for application to the elbow after total joint replacement. The secondary aim was to propose a method for marking of prostheses in 3D CT, enabling definition of a prosthesis-based reference system. Six patients with elbow endoprostheses were investigated.The fusion of data made it possible to visualize the motion axes in relation to the prostheses in the 3D CT volume. The differences between two repeated positioning repetitions of the longitudinal prosthesis axis were less than 0.6° in the frontal and sagittal planes. Corresponding values for the transverse axis were less than 0.6° in the frontal and less than 1.4° (in four out of six less than 0.6°) in the horizontal plane.This study shows that by fusion of CT and RSA data it is possible to determine the accurate position of the flexion axes of the elbow joint after total joint replacement in vivo. The proposed method for implant marking and registration of reference axes enables comparison of prosthesis function between patients and studies.     

Pelvic stresses in vitro--I. Malsizing of endoprostheses

Seven embalmed human cadaveric hemi-pelves have been stripped of all soft tissues except the articular cartilage and instrumented with 25 strain-gauge rosettes on both the medial and lateral surfaces. Loads up to 2.5 kN were applied, without simulated muscle forces, to mimic the line-of-action of the resultant joint-force in a single-legged stance. In this parametric study, endoprostheses were studied at the 'correct' size and in sizes of 1 and 2 mm above and below the correct size. The correct size of endoprosthesis produced similar periacetabular stress data to those obtained with the normal femoral head; however, significant changes in stress on the medial and lateral aspects of the ilium suggested the correctly-sized spherical endoprosthesis had a different moment arm than its anatomical counterpart. Endoprostheses of 1 mm greater than the correct size caused major increases in the magnitude of both periacetabular and medial-wall stresses, while prostheses of +2 mm created dramatic and significant increases in magnitudes of these stresses. Endoprostheses smaller than the correct size caused only small but significant changes in the pattern of stresses up to -2 mm malsizing and, in particular, were associated with the disappearance of all periacetabular tensile stresses; however, stress data on the medial and lateral aspects of the ilium were more closely matched to the 'normal' for this -2 mm of undersizing.     

Stair climbing is more critical than walking in pre-clinical assessment of primary stability in cementless THA in vitro

Pre-clinical testing of hip endoprostheses is a mandatory requirement before clinical release. Inadequate loading conditions may lead to lower elastic and plastic interface movements than those occurring post-operatively in vivo. This study investigated the influence of patient activity on the primary stability of cementless prostheses with a special emphasis on active simulation of muscle forces. A loading setup, based on validated musculo-skeletal analyses, was used to generate the hip contact force during walking and stair climbing by transmitting muscle forces through the femur. In addition, a loading configuration which only generated the hip contact force occurring during stair climbing at the prosthesis head was simulated. CLS prostheses were implanted in 18 composite femora and subjected to cyclical loading. The relative micro-movements at the bone-prosthesis interface were determined and appeared to be extremely sensitive to the specific patient activity. Compared to walking, stair climbing generated higher micro-movements, with pronounced axial and rotational components. Stair climbing with the femur loaded by the resultant hip contact force only exhibited a characteristic valgus tilt of the stem with significantly lower interface micro-movements than under active simulation of muscle forces. The analyses suggest that stair climbing induced the highest mechanical instability at the bone-prosthesis interface, a level which may compromise the necessary osseointegration process. Active simulation of muscle forces considerably affects the primary stability of cementless hip endoprostheses. Pre-clinical in vitro tests should therefore simulate stair climbing and include muscle activity in the assessment of initial implant stability, otherwise micro-movements may be underestimated and the primary stability overestimated.     

Radiologic endovascular prosthesis of the renal arteries in patients with renovascular hypertension]

A high percentage of restenoses after roentgenovascular dilatation of the renal arteries laid the basis of a search for new therapeutic methods for these patients. Experiments on implantation of nitinol spiral endoprostheses showed their ability for long-term permeability of renal arteries, not causing their thrombosis and intimal spreading, destruction of formed elements of the blood, change in plasma proteins. Morphological investigations have shown rapid formation (during 14 days) of connective tissue neointima, covered on the side of the blood flow with the true vascular endothelium (ensuring a nonadhesive surface and laminar blood flow), around the coils of an endoprosthesis. This method after its experimental development started to be used in clinical practice. The authors reported the first experience in the clinical use of this method (12 patients with vasorenal hypertension). A 15-month follow-up revealed a stable antihypertensive effect in all patients.     

Comparison of in vivo measured loads in knee,hip and spinal implants during level walking

Walking is a task that we seek to understand because it is the most relevant human locomotion. Walking causes complex loading patterns and high load magnitudes within the human body. This work summarizes partially published load data collected in earlier in vivo measurement studies on 9 patients with telemeterized knee endoprostheses, 10 with hip endoprostheses and 5 with vertebral body replacements. Moreover, for the 19 endoprosthesis patients, additional simultaneously measured and previously unreported ground reaction forces are presented.The ground reaction force and the implant forces in the knee and hip exhibited a double peak during each step. The maxima of the ground reaction forces ranged from 100% to 126% bodyweight. In comparison, the greatest implant forces in the hip (249% bodyweight) and knee (271% bodyweight) were much greater. The mean peak force measured in the vertebral body replacement was 39% bodyweight and occurred at different time points of the stance phase.We concluded that walking leads to high load magnitudes in the knee and hip, whereas the forces in the vertebral body replacement remained relatively low. This indicates that the first peak force was greater in the hip than in the knee joint while this was reversed for the second peak force. The forces in the spinal implant were considerably lower than in the knee and hip joints.     

Oral health and oral implant status in edentulous patients with implant‐supported dental prostheses who are receiving long‐term nursing care

Aim: The aim of this study was to investigate oral health and oral implant status in a group of edentulous patients receiving long‐term residential or nursing care (LTC), all of whom had implant‐supported fixed or removable dental prostheses. Material and methods: A dental examination was performed on a total of 3310 patients receiving LTC and from this population 35 edentulous patients in whom dental implants had been placed formed the cohort for this study. All examinations were performed by a specialist in hospital dentistry and took place in the patients’ own home environment. Oral health was assessed by means of a protocol which evaluated oral hygiene status, possible oral mucosal inflammation and oral mucosal friction levels. Any problems with the implant‐supported prosthesis, implant mobility or other complications were also assessed. In addition, patients were asked about any oral symptoms and their usual oral hygiene procedures. Results: About half of the subjects (17/35) were registered as having no/mild inflammation with 18 of 35 having moderate/severe inflammation. Twelve of the 35 patients had good/acceptable oral hygiene and 23 of 35 had poor/bad oral hygiene. Twenty‐one of the 35 patients depended on help from the nursing personnel for their daily oral hygiene procedures. Obvious problems with food impaction were noted in 11 patients. A total of 229 implants had been placed in 43 jaws supporting 40 full arch‐fixed prostheses and three implant‐borne overdentures. There was no evidence of mobility or fractures of either the implants or the prostheses. Fifteen implants showed some exposed screw threads. Pus was exuding from one implant site and general peri‐implant gingival hyperplasia was noted in two patients. Twenty‐four patients were completely satisfied with the function and appearance of their implant‐supported prostheses. Two patients were totally dissatisfied. Conclusion: This study indicates that oral implant therapy can be considered as a treatment of choice in elderly patients, even if oral hygiene is sub‐optimal.     

Comparative tissue morphology in using prostheses from polypropylene and polytetrafluoretilen

To treat hernias, polymer net implants are widely used. We carried out a comparative study of the morphological picture of inflammation, cellular composition of tissues, and dynamics of scar formation in mice in using the implants Esfil and Uniflex under conditions of single and double introduction of cultivated fibroblasts and without fibroblasts in the area of disposition of the endoprostheses. A more expressed inflammatory reaction throughout the entire period of time was observed in implantation of the material Esfil. In using the material Uniflex, there was revealed a higher percent of fibroblasts than in using the Esfil prosthesis. Introduction of cultivated fibroblasts in using both materials modified the curve of dynamics of the inflammatory process by making it smoother. Use of the Uniflex endoprosthesis is preferable.     

Decompression of malignant biliary obstruction by duodenoscopic intubation of bile duct.

Interest is increasing in non-operative methods of relieving malignant obstruction of the bile duct, and drainage tubes and prostheses may be placed in the bile duct via the percutaneous transhepatic route. Two cases are described, however, in which a duodenoscope was used and the approach was via the papilla of Vater. This method allows temporary or permanent drainage tubes to be placed through malignant strictures. This endoscopic approach is less invasive and should be safer than that by the transhepatic route; furthermore, removing and replacing a blocked endoprosthesis should be easier. Further study is needed, as the procedure is technically more difficult and its role in managing biliary strictures has yet to be defined.     

Computer-designed prostheses for orbitocranial reconstruction

Three-dimensional imaging is an adjunct to preoperative evaluation and surgical management in some patients with complex anatomic defects of various etiologies. Deformities defined by conventional computerized tomography can be viewed as accurate three-dimensional images calculated from the original scan. The images are viewed on a high-resolution video monitor and can be photographed for a permanent record. A computer-controlled milling device can use these data to fabricate prostheses. The prostheses aid reconstructive surgery through use as an alloplastic implant, as a template to fashion autogenous bone grafts, or as a model for tissue removal. We have utilized three-dimensional imaging in combination with computer-assisted prosthesis manufacture in six patients with complex orbitocranial deformities. Four patients have undergone reconstructive surgery with satisfactory results and no complications thus far. The use of computer-designed prostheses adds a new aspect to orbitocranial reconstructive surgery that facilitates increased accuracy in the correction of anatomic defects.     

Effect of exogenous embryonic fibroblasts on ratio of collagens types I and III in tissues of mouse paraprosthetic capsule

At present, the use of synthetic prostheses is an obligatory condition of surgical treatment of extensive and giant ventral hernias. We have carried out a comparative investigation of the dynamics of the collagen Type I to Type III ratio in the mouse paraprosthetic region upon use of the implants Esphyl (polyethylene), Ecophlon (polytetrafluorethylene), and Uniflex (polyvinylidenfluoride) with or without single and twofold introduction of cultured fibroblasts into paraprosthetic region at different time periods. Use of staining with Sirius Red and polarization microscopy revealed that, at a short time period (10 days after endoprosthesis implantation), the fibroblast introduction and the multiplicity of their introduction do not affect the collagen type ratio. At later time periods (30–60 days after the endoprosthesis implantation), the collagen type I ratio increased with use of all materials. At all steps of the experiment, the collagen type I/III ratio was the highest in the case of use of the Uniflex endoprosthesis. The exogenous fibroblasts accelerate the increase in the collagen type I/III ratio to a greater degree during twofold than upon single introduction.     

胆管癌的光动力疗法

胆管癌(Cholangiocarcinoma CC)是一种罕见的胆道原发性恶性肿瘤,预后较差。根治性手术只适用于一小部分早期诊断的患者。姑息性的经皮或内镜下支架置入胆管引流术能通过减轻瘙痒,疼痛,和胆管炎的程度从而提高生活质量,但对于延长生存时间作用甚微。光动力疗法(PDT)是对于不能手术切除的CC的一种较新颖的局部微创性的姑息疗法。其原理是PDT中使用的光敏性分子能特异性的聚集在增生组织如肿瘤,在特定波长的光照下光敏剂激活生成活性氧类物质,从而选择性的导致肿瘤细胞的死亡。经过初步的可行性性研究和充满前景的前瞻性II期临床研究后,关于研究比较胆管支架置入联合光动力治疗与单纯胆管内支架置入的两组前瞻性随机对照试验已经发表。其中一组试验结果显示PDT组(493天)与非PDT组(98天)相比在中位生存期方面的显著优势(P0.0001),且PDT组患者的体力状态也明显改善。另一组试验也进一步明确了PDT治疗对于提高生存率方面的优势(PDT组630天而单纯支架置入组210天,P0.01)。整个治疗过程耐受性良好。有报道称PDT作为CC的辅助或新辅助疗法已取得了令人满意的结果,因此PDT可以被看作是治疗不能手术切除的胆管癌的一种标准性姑息治疗方法。     

Long-term use of polyurethane breast prostheses: a 14-year experience

I have used polyurethane prostheses for the past 14 years, implanting 220 implants into 130 patients who desired breast reconstruction after subcutaneous mastectomy or cancer ablation or simply breast augmentation. I theorize that a polyurethane-covered implant resists contracture, retaining its compressibility because the fibroblasts proliferate into the polyurethane in many different directions. When the fibrils contract, the forces of contracture counterbalance one another, resisting contracture. However, when smooth prostheses are implanted, fibrils are directed in a circular fashion around the implant and naturally contract, leading to firmer breasts. There were 115 prostheses inserted following subcutaneous mastectomy, and 22 percent developed contracted capsules. Seven implants became exposed because of skin necroses; one was removed because of a Staphylococcus infection; and two patients developed a combination of polyurethane and silicone granulomas. These developed only with the earlier implant, where there was shedding of the polyurethane sponge layer and silicone bled from the low-viscosity silicone used in the earlier implants. No granulomas were noted with the currently used Surgitek Replicon implant. Eighty-five breasts were reconstructed after cancer ablation with polyurethane implants, and the contracture rate was 2.3 percent. Other complications were minimal. A smaller group of patients had augmentation mammaplasty, and 20 prostheses were placed in 10 patients. A 15 percent contracture rate was noted in this group. In this study, 82 percent of patients were followed for up to 14 years. Capsular contractures occurred in 30 implants between 1 and 11 years, for an average recurrence at 6.3 years. The overall contracture rate was 13 percent. Other complications were minimal. All implants were placed subcutaneously or subglandularly, and all were drained.     

High-tech hip implant for wireless temperature measurements in vivo

When walking long distances, hip prostheses heat up due to friction. The influence of articulating materials and lubricating properties of synovia on the final temperatures, as well as any potential biological consequences, are unknown. Such knowledge is essential for optimizing implant materials, identifying patients who are possibly at risk of implant loosening, and proving the concepts of current joint simulators. An instrumented hip implant with telemetric data transfer was developed to measure the implant temperatures in vivo. A clinical study with 100 patients is planned to measure the implant temperatures for different combinations of head and cup materials during walking. This study will answer the question of whether patients with synovia with poor lubricating properties may be at risk for thermally induced bone necrosis and subsequent implant failure. The study will also deliver the different friction properties of various implant materials and prove the significance of wear simulator tests. A clinically successful titanium hip endoprosthesis was modified to house the electronics inside its hollow neck. The electronics are powered by an external induction coil fixed around the joint. A temperature sensor inside the implant triggers a timer circuit, which produces an inductive pulse train with temperature-dependent intervals. This signal is detected by a giant magnetoresistive sensor fixed near the external energy coil. The implant temperature is measured with an accuracy of 0.1°C in a range between 20°C and 58°C and at a sampling rate of 2-10 Hz. This rate could be considerably increased for measuring other data, such as implant strain or vibration. The employed technique of transmitting data from inside of a closed titanium implant by low frequency magnetic pulses eliminates the need to use an electrical feedthrough and an antenna outside of the implant. It enables the design of mechanically safe and simple instrumented implants.     

Habilitation of Patients with Congenital Malformations Associated with Thalidomide: Surgery of Limb Defects

The deformities commonly seen in “thalidomide babies” are described. These vary from relatively uncomplicated radial-ray defects to complete phocomelia of all four extremities. It is suggested that the care of these children is best carried out in a clinic accustomed to dealing with juvenile amputee problems. A plea is made for very early fitting of upper-extremity prostheses (at approximately three months of age) in cases of unilateral upper-limb deficiencies. A “bucket” for sitting should be supplied for children with quadrilateral phocomelia to sit in when they reach seven or eight months of age. Children with severe upper-limb malformations will be candidates for some form of externally powered prostheses.     

Water jet cutting for bones and bone cement--parameter study of possibilities and limits of a new method]

Water jet techniques have been used in industrial cutting, drilling and cleaning applications for more than 30 years. Plain water is typically used for the cutting of non-metallic materials. The addition of abrasive substances to the stream allows almost any material to be cut. The first medical applications were reported in the early 1980s, when the water jet was used to cut organs. The present study investigates the use of water jet cutting technology for endoprosthesis revision surgery. Bone and PMMA (polymethylmethacrylate) samples were cut at different pressures using an industrial water jet cutting device. Using plain water at 400 bar, PMMA was cut selectively without damaging the bone; above 400 bar, bone was also cut, but the cutting depths in PMMA were significantly greater (p < 0.05). Adding a water-soluble abrasive disaccharide to the water results in a significantly higher removal rate for both materials (p < 0.05), but selectivity is lost, although the differences in cutting depth between the two materials was significant (p < 0.05). With an abrasive, the quality of the cut was better for both materials. The water jet technology--in particular the abrasive technique--can be used to cut biomaterials such as bone and bone cement. The diameter of the jet is a great advantage when working in the confined area at the prosthesis interface. The cutting process is essentially cold, thus eliminating a thermal effect, and the jet reaction forces are relatively low. Accurate manipulation of the hydro jet nozzle is possible both manually and by robot. The results obtained show that it is possible to remove prostheses with this cutting technique, rapidly and with little damage to the surrounding tissue. Problem areas are the development of sterile pumps and the "depth control" of the jet.     

The interacting effects of temperature and plant community type on nutrient removal in wetland microcosms

Treatment wetlands can remove nutrients from inflow sources through biogeochemical processes. Plant composition and temperature play important roles in the nutrient removal efficiency of these wetlands, but the interactions between these variables are not well understood. We investigated the seasonal efficiency of wetland macrophytes to reduce soil leachate concentrations of total nitrogen and total phosphorus in experimental microcosms. Each microcosm contained one of six vegetation treatments: unplanted, planted with one of four species (Carex lacustris, Scirpus validus, Phalaris arundinacea and Typha latifolid) in monoculture or planted with an equal abundance of all four species. Microcosms were also subjected to two temperature treatments: insulated microcosms and microcosms exposed to environmental conditions. A constant nutrient solution containing 56 mg/l N and 31 mg/l P was added to all microcosms three times a week. Water samples were analyzed monthly for total dissolved nitrogen and total dissolved phosphorous. Microcosms exhibited a typical pattern of seasonal nutrient removal with higher removal rates in the growing season and lower rates in the winter months. In general, planted microcosms outperformed unplanted microcosms. Among the plant treatments, Carex lacustris was the least efficient. The four remaining plant treatments removed an equivalent amount of nutrients. Insulated microcosms were more efficient in the winter and early spring months. Although a seasonal pattern of nutrient removal was observed, this variation can be minimized through planting and insulation of wetlands.     

Complications after hip rearthroplastics with revision endoprosthesis

The stability of the revision endoprosthesis components is more difficult to achieve than in primary endoprosthesis due to large bone defects and/or decreased bone mass quality. That is the reason for more frequent complications for revision than in primary arthroplasty. The aim of this study was to investigate the frequency of complications in 122 patients who were operated with the revision endoprosthesis in the Department of Orthopedics in University Hospital Split in the period of 1998 to 2007 and accepted to participate in this study. There were 3 patients treated on bought hips. The average follow up time was four years (0.6-10.6). There were 32 (26.2%) males and 90 (73.8%) females. The average age was 70.66 +/- 7.63 years. The average time from operation to physical therapy was 3.53 +/- 2.56 days. There were 27 (21.6%) complications. The most common complication was infection in 9 (7.2%) cases. From those cases, 4 (3.2%) had superficial, and 5 (4%) had deep infection. From other complications, there were 5 (4%) endoprosthesis reluxations, 2 (1.6%) periprosthetic femur fractures, 5 (4%) urinary infections, and 6 (4.8%) other complications (lung mycroembolia, heart infarction, lumbal plexus lesion from L2, spinal cord infarction with paraplegia, pneumonia and severe sacral bed-sore). There were 10 (8%) re-interventions following the revision arthroplasty. The result was good or excellent in 80% of operated patients, satisfied in 17%, and bad in 3%. The revision hip procedures are characterized with a high complications incidence rate. Our results are comparable with the results from literature.