BackgroundVertebral compression fractures (VCFs) can cause significant pain and functional impairment, and their cumulative effect can lead to progressive morbidity. This single-arm, prospective feasibility trial, conducted at 4 clinical sites, was undertaken to evaluate the clinical outcomes associated with the use of an innovative vertebral augmentation device, the Kiva VCF Treatment System (Benvenue Medical, Santa Clara, California), in the management of symptomatic VCFs associated with osteoporosis.MethodsVertebral augmentation treatment was performed for persistent back pain symptoms in 57 patients (mean age, 71.9 ± 10.4 years), including 46 women, with radiologically confirmed VCFs; 36 of these patients (63%) had reached 12 months of follow-up at this data analysis. There were 51 one-level cases, 5 two-level cases, and 1 three-level case, representing 64 treated levels. Back pain severity and condition-specific functional impairment were evaluated with a standard 100-mm visual analog scale and the Oswestry Disability Index (ODI), respectively, before device implantation as well as at 6 weeks, 3 months, and 12 months.ResultsMarked clinical improvements were realized in back pain severity and functional impairment through 12 months of follow-up. The mean back pain score on the visual analog scale improved from 79.3 ± 17.2 before treatment to 21.9 ± 21.3, 21.9 ± 24.6, and 23.2 ± 23.3 at 6 weeks, 3 months, and 12 months, respectively. The mean decrease at 12 months was 49.9 ± 30.3 mm, or approximately 66% (P < .0001). Similarly, the mean ODI score improved from 68.1% ± 16.9% before treatment to 27.4% ± 17.2%, 23.8% ± 18.7%, and 23.3% ± 15.5% at 6 weeks, 3 months, and 12 months, respectively, representing a mean change of 39.2 ± 19.6 percentage points, or approximately 63%, at 12 months. Overall clinical success rates based on a 30% improvement in pain severity or greater and maintenance or improvement in the ODI were 91%, 88%, and 89% at 6 weeks, 3 months, and 12 months, respectively. The vertebral augmentation procedure required injection of a mean of 2.2 ± 0.12 mL of cement per vertebral body. There were 5 levels (8%) where cement extravasation was identified radiographically, and none were related to clinical symptoms.ConclusionsThese pilot findings are encouraging, suggesting robust and durable clinical improvement after this novel vertebral augmentation procedure in patients with painful VCFs.
Replacement of the Arg residue at position 82 in bacteriorhodopsin by Gln or Ala was previously shown to slow the rate of proton release and raise the pK of Asp 85, indicating that R82 is involved both in the proton release reaction and in stabilizing the purple form of the chromophore. We now find that guanidinium chloride lowers the pK of D85, as monitored by the shift of the 587-nm absorbance maximum to 570 nm (blue to purple transition) and increased yield of photointermediate M. The absorbance shift follows a simple binding curve, with an apparent dissociation constant of 20 mM. When membrane surface charge is taken into account, an intrinsic dissociation constant of 0.3 M fits the data over a range of 0.2-1.0 M cation concentration (Na+ plus guanidinium) and pH 5.4-6.7. A chloride counterion is not involved in the observed spectral changes, as chloride up to 0.2 M has little effect on the R82Q chromophore at pH 6, whereas guanidinium sulfate has a similar effect to guanidinium chloride. Furthermore, guanidinium does not affect the chromophore of the double mutant R82Q/D85N. Taken together, these observations suggest that guanidinium binds to a specific site near D85 and restores the purple chromophore. Surprisingly, guanidinium does not restore rapid proton release in the photocycle of R82Q. This result suggests either that guanidinium dissociates during the pump cycle or that it binds with a different hydrogen-bonding geometry than the Arg side chain of the wild type.
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