Nickel-titanium shape memory alloy (Nitinol) has properties that could be very useful in surgical applications. Thermal shape memory, superelasticity, and high damping properties make such alloys behave differently compared to other implant metals. There has previously been a lack of sufficient evidence on the biocompatibility of Nitinol. The purpose of this study was to evaluate general soft tissue response and biocompatibility to Nitinol in vivo, and to clarify neural and perineural responses, previously unreported. Seventy-five rats were randomized into three groups. Test specimens were implanted into paravertebral muscle and near the sciatic nerve. A comparison was made between Nitinol, stainless steel, and Ti-6Al-4V. The animals were euthanized at 2, 4, 8, 12, and 26 weeks after implantation. General morphologic and histologic observations were made under light microscopy. Semiautomatic computerized image analysis was used to measure the encapsule membrane thickness around the implants. The muscular tissue response to Nitinol was clearly nontoxic, regardless of the time period. The overall inflammatory response to Nitinol was very similar to that of stainless steel and Ti-6Al-4V alloy. There were no necroses, granulomas, or signs of dystrophic soft tissue clacification. The immune cell response to Nitinol remained low. Only a few foreign-body giant cells were present. The detected neural and perineural responses were also clearly nontoxic and nonirritating with Nitinol. No qualitative differences in histology between the different test materials could be seen. At 8 weeks, the encapsule membrane of Nitinol was thicker than that of stainless steel (mean 62 +/- 25 microns vs. 41 +/- 8 microns). At the end of the study, the encapsule thickness was equal to all the materials tested. We concluded that Nitinol had good in vivo biocompatibility after intramuscular and perineural implantation in rats in the 26-week follow-up. Based on the results of the present study, Nitinol appears to have good potential for clinical use.
The purpose of this study was to explore systematically the effect of the imaging parameters changeable by the user in spin-echo (SE) imaging sequences to minimize image distortion when imaging joint prostheses. A titanium alloy hip joint prosthesis was studied at I.O.T. The SE imaging parameters were bandwidth/pixel(BW/ p), TE, strength of encoding gradients (matrix size), echo train length (ETL), and direction of phase and frequency encoding. The effect of ETL in rapid acquisition relaxation enhanced (RARE) sequences was also evaluated with a turbo-SE sequence using a different ETL with the same TR and an effective TE. It is concluded that an optimized image quality can be achieved in SE imaging by using a high bandwidth/pixel value (at least 130 Hz/pixel), a high resolution matrix (256-512), sequences with multiple refocusing, and a frequency-encoding axis parallel to the long axis of the prosthesis. The degree of distortion is reduced with this optimized technique.
In 24 patients with total hip replacement using a short anatomic femoral stem, bone mineral density (BMD) was measured after a 7-year follow-up using dual-energy X-ray absorptiometry. The contralateral side was used as a control. The BMD on the side of the prosthesis was lower by a mean of 7% than that on the control side. The difference was greatest in the area of the calcar and laterally and proximally around the stem. BMD at the metaphyseal and diaphyseal areas were the same as on the contralateral side. The bone loss around the proximal aspect of the stem may be related to the proximal porous coating. It is concluded that stress shielding can be diminished by appropriate design of the femoral component.Résumé Chez 24 patients avec arthroplastie de la hanche utilisant une tige fémorale anatomique courte on a mesuré les densités minérales osseuses (DMO) par absorptiométrie biénergétique aux rayons X après un suivi de 7 ans. Le côté controlatéral a été utilisé comme té-moin. Du côté de la prothèse, la DMO était en moyenne 7% plus faible que du côté témoin. La plus forte diffé-rence fut enregistrée dans la région du calcar et latérale-ment autour de la partie proximale de la tige. Les DMO des zones métaphysaires et diaphysaires n'étaient pas différentes de celles enregistrées du côté contralateral. La perte osseuse autour de la partie proximale de la tige est peut-être due à l'enrobage poreux proximal. La conclusion est que le report de contrainte peut être réduit par la conception de la tige prothétique.
Some harmful and unpleasant complications are possible after discography. Antibiotic prophylaxis and stiletted needles should be used. Magnetic resonance imaging is the best radiologic procedure to image the complication, and surgery must be performed as soon as possible.
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