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Structural response and relative strength of a laminated composite hip prosthesis: effects of functional activity.

To obtain a better appreciation for the structural performance of a laminated composite hip prosthesis (CP), we examined in situ prosthesis structural response and relative strengths as a function of walking and stair climbing using our previously developed analysis guidelines. Accordingly, we examined overall prosthesis structural response utilizing a global continuum level modeling approach and prosthesis relative strengths using a local microstructural (or ply-level) modeling approach. As a reference and control, we examined the structural performance of the intact natural femur (NAT) and a titanium alloy (Ti) based hip prosthesis. In terms of the overall structural response, i.e., the femur/prosthesis deformational response, stem/bone interfacial stress transfer, and calcar strain energy density restored, the performance of the CP prosthesis was moderately improved over that of the control Ti prosthesis and better approximates the NAT response. In terms of relative strength, we found that the neck of the CP prosthesis failed for all activities with the exception of the mid-stance phase of level walking. However, the prosthesis appears to have sufficient relative strength for function at positions distal to the neck of the prosthesis. While these results dampen enthusiasm for consideration of laminated composite hip prostheses designed with a shape based on a metal alloy implant, they indirectly support consideration of alternate hip prosthesis structural designs such as using a better supported prosthesis neck or utilizing metal/composite hybrid constructions. Importantly, our simulation and analysis approach could be utilized in the design of other laminated composite biomedical structural components.

Alloys↗

[Bladder compression caused by hip prosthesis displacement].

Case report of one patient with extrinsic vesical compression secondary to a displaced hip prosthesis. Interesting case due to increasing hip prosthesis surgery over the last few years involving, although not frequently, ureteral and vesical injuries of varying consideration which require early diagnosis and management.

Bone Cements↗

Arthroscintigraphic evaluation of the painful total hip prosthesis.

Arthroscintigraphy was performed in 19 patients with a painful total hip prosthesis by injecting both Tc-99m sulfur colloid and iodinated radiographic contrast material intra-articularly. Scintigraphic and radiographic results correlated exactly in 15 patients, with one false-negative scintigram, one false-positive scintigram, and one false-negative arthrogram. One patient was evaluated by scintigraphy alone. Although arthroscintigraphy is potentially more sensitive than conventional arthrography in the detection of femoral component loosening, acetabular component loosening cannot be evaluated by scintigraphy alone. A combination of scintigraphy and conventional arthrography appears to be the most accurate imaging method in the evaluation of hip prosthesis loosening.

Arthrography↗

Psoriasis is a risk factor for hip-prosthesis infection.

Risk factors for hip and knee prosthesis infection have been described, but not psoriasis. Eighty five infected patients from different centers and 202 non infected patients were included in a case-control study. Fifteen of 85 infected patients (17.6%), and 2 of 202 (1%) non infected patients had psoriasis. Odds ratio for infection in patients with psoriasis is 21.4 (4.7-195.5), and 39.7 (5.3-1718.8) in patients with hip prosthesis and psoriasis. No significant difference was found in patients with knee prosthesis. These data indicate that psoriasis is a risk factor for hip prostheses infection.

Case-Control Studies↗

Intrapelvic extraction of a total hip prosthesis. A case report.

A 69-year-old man with a total hip prosthesis, recurrent infection, and intrapelvic incarceration of the acetabular components required extraction of a long-stem total hip prosthesis through three incisions. Retroperitoneal intrapelvic extraction of the incarcerated prosthesis was necessary. This approach allowed removal of intrapelvically migrated components and the eradication of the infection. The patient had no signs of infection five years postoperatively.

Accidents, Traffic↗

Presumptive infection of a total hip prosthesis by Mycobacterium tuberculosis: a case report.

Infection of a total hip prosthesis by Mycobacterium tuberculosis (MT) is an uncommon complication. We report a patient with septic loosening of a total hip prosthesis with a presumptive diagnosis of MT infection. His previous history was negative to any form of tuberculosis, and there was no evidence of a primary focus on the radiological study of the chest. He was diagnosed initially as presenting aseptic loosening and revision surgery was performed. Six months after surgery, septic loosening was diagnosed. The prosthesis was then removed. The histological study showed caseum granulomas and acid-fast bacilli, and routine cultures of the synovial fluid were negative. Since only a positive Löwenstein culture would have confirmed the diagnosis with certainty, a presumptive diagnosis of MR infection was made based on the findings in the histological study. Tuberculostatic treatment was administered for 9 months. At six years follow-up no signs of infection are present, neither by clinical or radiological criteria.

Aged↗

[Use of x-ray computed tomographic data for the concept of a custom-made hip prosthesis. Exploratory approach].

A custom-made hip prosthesis has to allow to improve the arthroplasty's longevity. In a Computer Aid program Conception (CAD) of such an implant, it becomes necessary to control the accuracy of the 3-D data given by CT Scans. The method employed is based on the comparison between 3-D data given by CT Scans and by photogrammetry. The study was made with a human pelvis including femoral head, without soft tissues. The CT Scans data have been given by automatic extraction of osseous outlines on two hundreds sections (1.5 mm thickness). The photogrammetry data have required five stereocouples for the whole pelvis and four stereocouples for the hip joint (femoral head and cotyle). There nine stereocouples have provided 37,213 points of reference. The comparison between the two sorts of informations shows that the error made in CT Scans acquisition was varying between 0.65 and 1.60 mm. This error is smaller when the outlines are simple, like the femoral diaphyse. The error decreases if we reduce the field size of CT Scan acquisition. These results confirm literature data. But this study has allowed to demonstrate validity of 3-D CT reconstruction. Scanography looks like the best present way of data acquisition. The dimensional précision is sufficient to define the endo-osseous outline, but it must be preserved at the moment of the extraction of this outline. Therefore this extractive can't be manual and must be made directly with processing data given by scanography.

Hip Prosthesis↗

Survivorship of hip prosthesis in primary arthrosis: influence of bilaterality and interoperative time in 45,000 hip prostheses from the Finnish endoprosthesis register.

We studied the influence of bilaterality and interoperative time on survivorship of the hip prosthesis. The material consisted of 45,000 (3,153 bilateral) total hip arthroplasties and 38,000 patients operated on for primary osteoarthrosis, using data from the Finnish Endoprosthesis Register between 1980 and 1999. Cox regression analysis showed that male sex, young age, uncemented prosthesis and time of surgery (first 10-year period) were significant risk factors for aseptic loosening. We found no difference between the survivorship of the first bilateral and that of unilaterals, but second bilaterals survived better than the unilaterals. Bilateral prostheses survived better when the second prosthesis was implanted during the first postoperative year. The risk of loosening of a bilateral prosthesis increased when the second prosthesis was implanted a few years later. Survivorship of bilateral prosthesesin a 1-stage bilateral operation was about the same as in those operated on within the first postoperative year. Better survivorship of the second bilateral can cause bias in per hip survivorship analyses. In bilateral cases, the second hip should be operated on as soon as possible or be considered for a 1-stage bilateral procedure.

Aged↗

[Therapy of burst ceramic head of a hip prosthesis].

The therapeutical possibilities in case of fracture of a ceramic head ball of a hip prosthesis system are discussed. A seventy year old patient suffered a fracture of a ceramic ball of a cemented hip prosthesis with polyethylene cup, ceramic ball and metal stem without trauma after one year after implantation. During operative revision a marked destruction of the gliding plane of the polyethylene cup by craters and an extreme metallose because of wear of the metal conus far into the bone bed of the acetabulum was found. The reason for the very seldom occurring fracture of the ceramic ball are minimal differences in the ascent grade of the metal conus of the stem and the corresponding connection of the ceramic ball. The broken ceramic ball should be substituted by a metal ball.

Aged↗

A noncemented total hip prosthesis.

Although total hip arthroplasty stabilized by cement has been a great step forward, loosening is becoming more and more frequent and constitutes a significant problem. This is a report of the design of a non-cemented prosthesis in which fixation of the prosthesis is secured by the in-growth of newly-formed bone into the irregularities of the metal. In more than 2000 cases with a follow-up of 5 1/2 years, this fixation design proves to be sound. The complications are relatively rare and the results are generally good.

Aged↗

Original surface replacement total hip prosthesis with alumina ceramic prosthetic head without cement.

We have developed a surface replacement total hip prosthesis of H.D.P. socket to ceramic head type having a polycrystal alumina ceramic prosthetic head and without bone cement for fixation. The strength test was done on this hip prosthesis, and comparative studies were made between the metal prosthetic head and the ceramic prosthetic head, using calculation models prepared in consideration of friction and the prosthetic head's inside diameter. Besides, the cadaver femur was replaced by the prosthetic head, and the impact test and the fatigue test by means of repeated loading were done. As we could consequently confirm that it could be fully used for clinical practice, we have manufactured various instruments to be used for surgery, and we are now actually practicing it.

Aged↗

Loosening of the cemented hip prosthesis. The importance of heat injury.

The cemented hip arthroplasty is one of the most successful orthopedic operations. However, the results do deteriorate with time because of mechanical loosening. Some hips with obviously loose prosthetic components are not painful. This discrepancy between symptoms and radiographic evidence of loosening has caused uncertainty about the diagnostic criteria that should be applied. This uncertainty has in turn led to confusion about the basic cause of loosening. The aims of this presentation were to find a favorable definition of loosening and to investigate the etiology of mechanical loosening of the cemented hip prosthesis. The diagnostic criteria of contrast and radionuclide arthrography, bone scintigraphy, and roentgen stereophotogrammetric analysis (RSA) were evaluated in 14 symptomatic hip arthroplasties examined by these methods. Loosening was found to be best defined as migration; regardless of diagnostic criterion, all loose prosthetic components were migrating, but no nonmigrating component was loose. The development of the radiolucent zone was analyzed in a simple model consisting of 6 cases of giant-cell tumor of bone successfully treated by curettage and cementing. In locations where the cement filling adjacent to cancellous bone was concave, a considerably wider zone developed. There was a positive correlation between the width of the zone and the volume of cement. The radiolucent zone in this model could be explained by heat injury during the polymerization of bone cement. The pattern of migration of the components in 20 cemented hip prostheses was studied with RSA and with conventional radiography over a period of 2 years postoperatively. Eleven acetabular and three femoral components migrated. After an initial 4-month period of rapid migration, most components migrated slowly. The initial rapid migration could be accounted for by the resorption of a layer of necrotic bone following heat injury during the polymerization. The less frequent migration of the metallic femoral component as compared with the polyethylene acetabular component could be explained by the metal acting as a heat sink. Radiographic examination was found to be unsatisfactory as a means of detecting mechanical loosening during the first 2 postoperative years. RSA, on the other hand, was capable of revealing migration as early as 4 months postoperatively. Migration of the components in 16 hip prostheses was studied with RSA for 1 year postoperatively following randomized use of low- and high-viscosity cement. As regards prosthetic migration, no difference was detected between the two types of cement; low-viscosity cement did not improve prosthetic fixation.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetabulum↗

Dose attenuation through a titanium alloy hip prosthesis.

The problem of dose perturbation due to hip prostheses during pelvic irradiation can be significant. Dose attenuation by a commonly used titanium alloy hip prosthesis was measured. Depending on the energy of the radiation beam and the thickness along the prosthesis, the attenuation was between 32% and 64%. This attenuation effect should be considered in treatment planning, especially in a patient with bilateral hip prostheses and when undergoing treatment for prostate cancer where the tumor typically lies between prostheses.

Alloys↗

[Changes in bone density of the femur after cement-free implantation of a modular hip prosthesis with a long shaft].

Until now, no reports exist on the existence of femoral bone loss after hip arthroplasty using long-stem cementless prostheses in elderly patients. In a prospective evaluation the amount of bone loss (stress-shielding) after implantation of a long stem hip prosthesis in patients with femoral neck fractures (group A) or pertrochanteric femoral fractures (group B) was examined. Eleven patients (five from group A and six from group B) were treated with a long-stem modular hip prosthesis (MHP). Change of bone mass was evaluated using quantitative computed tomographie (QCT) immediately following and at six months (group A and B) and twelve months (group A) after implantation of the prosthesis. Clinical results, expressed with the modified Harris Hip Score, and relative changes of bone mass were compared with mean periprosthetic bone mass of the femur after operation. After implantation of the MHP, the maximum decrease of mean femoral bone mass was 19.1% at six months and 20.2% at twelve months for group A and 29.5% at six months for group B. Bone loss in the proximal periprosthetic area was higher than in the distal part. There was no correlation between baseline values of bone mass and the amount of stress-shielding or clinical outcome.

Aged↗

Hip aspiration: a cost-effective and accurate method of evaluating the potentially infected hip prosthesis.

PURPOSE: The accuracy of fluoroscopy-guided hip aspiration in the diagnosis of infection in hip prostheses was evaluated. MATERIALS AND METHODS: Results from 147 preoperative aspiration cultures were compared with results of operative cultures. The relative costs of aspiration and nuclear medicine studies were also compared. RESULTS: With the operative culture results as the standard, sensitivity of hip aspiration was 92.8% and specificity was 91.7%. The negative and positive predictive values were 99.2% and 54.2%, respectively. Aspiration arthrography costs approximately 20% as much as complementary technetium sulfur colloid-indium-111 granulocyte scans, the most accurate nuclear medicine study used to evaluate potentially infected hip prostheses. CONCLUSION: Hip aspiration is an accurate and cost-effective method of evaluating the potentially infected hip prosthesis.

Bacteria↗