Prosthetic Disc Nucleus: Treatment ..

This study documented the presence of large areas of strain maxima adjacent to the implant for all modes of loading. We have previously performed a similar analysis on a fixed-core TDR and evaluated the von Mises strains of the cancellous bone. The results of that study indicated that strains typically remained under 1% after implantation, with the exception of a small area during flexion. This is likely the result of the larger contact surface area for a TDR compared with the Fernström sphere, especially at 0 mm of subsidence. This is further indicated by the decreasing area of strain maxima that was observed for increasing levels of subsidence. As the implant nested further into the cancellous bone, the area of contact increased, which resulted in a more distributed load. Even though increased subsidence resulted in reduced areas of strain maxima, the fully nested models still depicted strains substantially greater than the intact state. Despite the large areas of strain maxima above 1% documented for all modes of loading, the clinical results depict reasonable levels of subsidence and satisfactory clinical outcomes., This suggests that the initial strains experienced by the bone after implantation may not be relevant when one is investigating long-term subsidence of spinal arthroplasty devices. Alternatively, the disparity between the clinical outcomes and high peak strain documented in this study may be explained by increased load bearing in the annulus fibrosus. Specifically, because the Fernström prosthesis maintains the majority of the annulus, continued subsidence may offset the axial loading from the device to the surrounding annulus. The current model did not take this phenomenon into consideration.

with the prosthetic disc nucleus PDN ..

The Prosthetic Disc Nucleus (PDN) 1, ..
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An intervertebral disc nuclear prosthesis ought, ..

Nuclear replacement is an emerging surgical treatment for degenerative disc disease (DDD) and low back pain (LBP). While clinical experience is most extensive with the prosthetic disc nucleus PDN (Raymedica, Minneapolis, Minnesota), strict indications apply for the implantation of this device. The purpose of this study was to ascertain what percentage of patients treated surgically for degenerative disc disease with other surgical procedures would have been candidates for nuclear replacement implantation.

The PDN prosthetic disc-nucleus device

The major complication found with use of the previous PDN generational products is posterior device herniation causing compressive radiculopathy, which usually requires revision, consisting of removal of the device and placement of a smaller one, TDR, or a fusion., , – In the earliest and latest series this complication occurred in 8–12% of the patients, respectively., , , However, in the interim, extrusion rates were as high as 26% and 38%, because the risk factors for extrusion were not completely appreciated. A series with no herniation in 45 patients has been reported, albeit with only two-thirds of the patients returning for a 6-month follow-up and with use of the nuclear replacement device for a different indication (adjunct to microdiscectomy for disc herniation). In face of potential complications, not all patients with DDD would qualify for nuclear replacement. Careful patient selection is stressed by all authors as essential for surgical and clinical success., , –

PDN® Prosthetic Disc Nucleus
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when the prosthesis was damaged ..

Following the soft nucleus replacement materials, which were described in 1977 (polyurethane) and 1978 (silicone), the Prosthetic Disc Nucleus (PDN) (Raymedica, Inc., Minneapolis, MN) prosthesis was first implanted in 1996. It comprises a polymeric hydrogel encased in a high-tenacity polyethylene jacket that allows the device to absorb fluid and expand in height.18 In the meantime, there has been an evolution from the stiff PDN to the PDNSOLO (Raymedica, Inc., Minneapolis, MN) and lastly HydraFlex (Raymedica, Inc., Minneapolis, MN).

of the disc blur the nuclear ..

This study evaluated the differences in von Mises strain in the vertebral cancellous bone for PEEK and CoCr implants. Radiolucent PEEK implants provide the ability to visualize the surrounding bone and soft tissues during diagnostic imaging, but the biomechanical effects are not fully understood. We hypothesized that the use of a PEEK Fernström prosthesis versus a CoCr prosthesis would have a negligible effect on bone strain. However, we noticed a small reduction in the peak strain values. Results from our study indicated increased peak von Mises strain in the vertebral body cancellous bone for the CoCr implant (14.7%) compared with the PEEK implant (12.9%) when no subsidence of the device was modeled. This is consistent with results from a previous finite element study that documented a reduction in endplate stresses between PEEK and titanium interbody spacers. Those authors concluded that the reduced stresses may result in a lower likelihood of subsidence. However, they did not report stresses in the endplate for an intact scenario. Whereas our study predicted a slight reduction in strain for a PEEK implant, both the PEEK and CoCr implants resulted in a substantial increase in peak strain and area of strain maxima compared with the intact state. In addition, this study indicated that increasing levels of subsidence result in a reduction of the differences between PEEK and CoCr, further suggesting that there may be limited biomechanical advantage to using PEEK for this application. Furthermore, the reductions in peak strain that resulted from increased subsidence or conformity of the endplate to the device still resulted in peak strain much higher than that documented in the intact condition. The results from this study suggest a high subsidence likelihood for either a PEEK or CoCr spherical prosthesis.

Abrev engleza | Heart | Intravenous Therapy

When we analyzed the Fernström prosthesis, peak effective strain in the cancellous bone during compression occurred just beneath the surface adjacent to the endplateimplant interface, with values of 0.48%, 12.9%, and 14.7% for the intact model, model implanted with PEEK and 0 mm of subsidence, and model implanted with CoCr and 0 mm of subsidence, respectively. Peak effective strain reduced to 4.0% and 4.6% at 2 mm of subsidence for the PEEK and CoCr implants, respectively. At 4 mm of subsidence, the peak effective strain was 2.7% and 3.0% for the PEEK and CoCr implants, respectively. Compressive loading resulted in strain maxima at the implant-endplate interface for both CoCr and PEEK implants (). Qualitatively, the PEEK implant resulted in a slight decrease in the size of the strain maxima. Both the PEEK and CoCr implants resulted in a decrease in strain maxima with increasing subsidence. During 0 mm of subsidence, the strain maxima occurred directly adjacent to the implant. At 2 mm of subsidence, the strain maxima in the superior vertebrae radiated out from the anterior and posterior portions of the endplate-implant interface, which resulted in an area of reduced strain maxima near the most superior portion of the implant. At 4 mm of subsidence, the strain maxima occurred at the anterior and posterior portions of the endplate-implant interface in both the superior and inferior vertebral bodies.