The applicable standard of practice and such a defendant’s failure to meet said standard must be established in such cases by such a plaintiff by testimony of one (1) or more knowledgeable, competent expert witnesses, and such expert testimony may only be admitted in evidence if the foundation therefor is first laid, establishing (a) that such an opinion is actually held by the expert witness, (b) that the said opinion can be testified to with reasonable medical certainty, and (c) that such expert witness possesses professional knowledge and expertise coupled with actual knowledge of the applicable said community standard to which his or her expert opinion testimony is addressed; provided, this section shall not be construed to prohibit or otherwise preclude a competent expert witness who resides elsewhere from adequately familiarizing himself with the standards and practices of (a particular) such area and thereafter giving opinion testimony in such a trial.