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PubMed1986

[Urinary concentration of cobalt and chromium in patients with a non-cemented total hip prosthesis].

The concentrations of cobalt and chromium have been measured in the urine of 22 patients who had received uncemented hip prostheses made from cobalt, chromium and molybdenum alloy, and in 21 patients who had not received prostheses, using absorption spectrophotometry. The results were statistically analysed using the Wilcoxon test. The levels of cobalt in the urine in the patients with uncemented prostheses did not show a significant increase, indicating that there is no greater risk of cobalt toxicity. The concentration of chromium was significantly raised (p less than 10(-2) in the urine of patients with uncemented prostheses, and in three of these patients significant corrosion had occurred.

Adult↗
PubMed2002

Faulty design increases the risk of neck fracture in a hip prosthesis.

From October 1993 to May 1994, we performed 35 total hip arthroplasties (20 women) using a Charnley type modular 28 head manufactured by Medical Tee Brazil. 9 fractures through the neck of the stem prostheses occurred, all but 1 in men, after mean 4 (0.3-6) years. All fractures were due to an inadequate confluent radius causing abnormal transmission forces through the neck. The higher the load (men, heavy body weight), the greater the risk of fracture. The metallographic, chemical and microhardness analyses showed no abnormalities. We ascribe these fractures to faulty design of the stem prosthesis.

Aged↗
PubMed2001

HIDE: a new hybrid environment for the design of custom-made hip prosthesis.

This technical note describes a new software environment (HIPCOM design environment, HIDE) for the design of custom-made total hip replacements. These devices are frequently designed using general-purpose mechanical computer-aided design (CAD) programs using a set of bone contours extracted from the computer tomography (CT) images as anatomical reference. On the contrary, the HIDE system was developed to let the operator directly design the stem shape onto the CT images in a single-step operation. The operator can directly import CT data in DICOM format or use special functions to reconvert to a digital stack, the CT images printed on a radiological film. Once the stack of CT images is loaded, the operator can design the implant shape by imposing control sections directly on the CT images. The interpolation of these control sections produces the basic 3D shape of the custom-made stem. The shape is then exported to the CAD-computer-aided manufacturing (CAM) program to refine the design and to generate the part program to manufacture the implant with a CNC tooling machine. Using HIDE, the duration of design steps it affected was reduced by more than 50% with respect to the standard method in use at the manufacturer site. HIDE also improved the accuracy and the repeatability of the whole procedure. The learning curve became flat after only ten cases. These good results were achieved because of the integration of the vectorial description of the prosthetic component with the raster description of the CT data that allowed the designer to use all details available in the CT images.

Computer-Aided Design↗
PubMedDate not supplied

[Diagnosis of hip prosthesis loosening--sensitivity of clinical parameters].

AIM: In order to establish a strategy for early diagnosis of aseptic loosening of total hip arthroplasty (THA) physical examination, patient's assessment and radiographs were analysed. METHOD: Pain, self assessment, physical examination and mobility were examined according to a standard examination protocol in 428 hips of 297 patients after cementless total hip arthroplasty (THA). These findings were compared with the radiographic finding of the hip. Sensitivity and specifity of objective and subjective parameters were analysed. RESULTS: The clinical outcome of THA's is assessed by pain and physical examination. Nearly all hip scores are based on these parameters. In this study sensitivity and specificity of all parameters analysed were unsatisfactory compared with the radiographic finding. Although we found some correlations between clinical and radiological data, clinical data alone are not sufficient for exclusion of THA loosening, especially for loosening of the acetabular component, as there was no clear distinction between the group of radiographically loosened (43 acetabular cups and 4 stems) and intact endoprostheses. CONCLUSION: We conclude, that physical examination and pain history are not sufficient to exclude loosening of cementless THA's. Radiographic examination is essential for the assessment of THA's, even in painfree patients.

Aged↗
PubMedDate not supplied

Hip prosthesis revisions with LS stem: indications and results.

The authors present a study that includes 350 patients affected with loosening of hip arthroplasty and submitted to revision with a Wagner LS stem at the 4th Division of the Rizzoli Orthopaedic Institute. Several different types of cotyle (Fitek, Wagner, Standard Cup, cemented cotyle with support ring, Octopus system) were used depending on the anatomopathologic findings, combined with autoplastic grafts. Staging and grading of loosening were based on the four G.I.R. grades. A clinical evaluation of results was based on the Merle D'Aubigné parameters modified by Charnley. For radiographic evaluation the De Lee Charnley areas were studied for cotyle, the Gruen areas for the femoral stem. Overall, good results were obtained in 175 patients, fair in 137, poor in 38.

Adult↗
PubMed1993

[Prevention of thromboembolic complications with adapted low-dose of antivitamins K after total hip prosthesis].

This study reports the efficacy in the prevention of thromboembolic complications of adapted low-dose oral anticoagulants following total hip replacement. 750 patients undergoing total hip replacement received oral anticoagulants as exclusive drug prophylaxis for thromboembolic complications. These patients were considered preoperatively not to present any particular risk for the development of postoperative thrombosis. Anticoagulant therapy was commenced on the evening of the operation. Eleven pulmonary embolisms (1.5 per cent) were observed, but none of them were fatal. The risk of thrombosis was evaluated in 100 of these 750 patients by means of bilateral venography of the lower limbs: 21 patients developed distal thrombosis (sural veins) and 2 patients developed proximal femoral thrombosis. Only one haemorrhagic complication occurred in the 750 patients of this series. The prothrombin profile determined in the patients developing thrombosis or pulmonary embolism was not significantly different from that of the patients free of any thromboembolic complications. Although oral anticoagulants appear to be particularly effective for the prevention of fatal pulmonary embolism, it is not clear that their efficacy is directly related to the prothrombin time.

4-Hydroxycoumarins↗
PubMed2006

Migration and cyclic motion of a new short-stemmed hip prosthesis--a biomechanical in vitro study.

BACKGROUND: Uncemented, short-stemmed hip prostheses have been developed to reduce the risk of stress shielding and to preserve femural bone stock. The long-term success of these implants is yet uncertain. Prerequisite for osseointegration is sufficient primary stability. In this study the cyclic motion and migration patterns of a new short-stemmed hip implant were compared with those for two clinically successful shaft prostheses. METHODS: The prostheses were implanted in paired fresh human femura and loaded dynamically (gait cycle) with increasing load (max 2,100 N) up to 15,000 cycles. Relative displacements between prosthesis and bone were recorded using a 3D-video analysis system. FINDINGS: The short stem displayed a biphasic migration pattern with stabilisation at maximum load. Initial migration was predominantly into varus and was greater than that for the shaft prostheses. Failure occurred in cases of poor bone quality and malpositioning. Cyclic motion of the short prosthesis was less than that for the shaft prostheses. Surface finish showed no effect. System stiffness for the new stem was lower than for the shaft prostheses. INTERPRETATION: The new stem tended to migrate initially more than the shaft prostheses, but stabilised when cortical contact was achieved or the cancellous bone was compacted sufficiently. Bone quality and correct positioning were important factors for the short stem. The lower cyclic motion of the new stem should be favourable for bony ingrowth. The lower system bending stiffness with the new implant indicated a more physiological loading of the bone and should thereby reduce the effects of stress shielding.

Adult↗