FISCHEL, J.
The employee appeals from the decision of the administrative judge once again denying and dismissing his claim for § 34 benefits following remand of the case to the judge by the reviewing board for further subsidiary findings regarding the expert medical testimony presented. See Dirring v. Custom Deliveries, 6 Mass. Workers' Comp. Rep. 163 (1992).
On remand, the reviewing board required the judge to make further findings regarding her characterization of the medical opinion of the insurer's medical expert, Dr. Walsh. The parties stipulated that neither needed to offer further testimony (Dec. 2), and the judge filed a decision based on the existing record. In the remand decision, the judge addressed the effect of a May 11, 1989 MRI report on Dr. Walsh's previously stated diagnosis when the doctor was presented with the report for the first time at deposition. The judge found that while the doctor acknowledged the MRI test results indicated some evidence of herniation, the report did not dissuade him from his previous opinion that the employee was capable of gainful employment.
Dr. Walsh however, did change his diagnosis, testifying that his revised diagnosis was "MRI evidence of central disc protrusion at L5-S1 with slight lateral extension and marked nonorganic component to the patient complaints and chronic low back syndrome . . . [w]ith suggestion of light compression of the right S1 root" (Walsh Dep. pp. 38-39).
The employee argues on appeal that the decision distorts both the May 11, 1989 MRI test results and Dr. Walsh's response to the test results, and subscribes greater weight than is justified to the doctor's opinion following three examinations of the employee than to his response to the MRI report when confronted with it at deposition. It is an administrative judge's prerogative to determine the probative value of expert medical testimony. Amon's Case, 315 Mass. 210, 215 (1943); Rennie's Case, 357 Mass. 640, 644 (1970).
The judge found that while Dr. Walsh conceded on cross-examination that the MRI report indicated an objective finding of herniation (Dec. 2), the doctor stated that such evidence was but part of the evidence, including the employee's medical history and condition upon physical examination, that should be taken into consideration when rendering a diagnosis (Dec. 4). When presented with the MRI report, Dr. Walsh conceded that the result indicated objective findings and that some of the employee's complaints were consistent with "MRI evidence of central disc protrusion at L5-S1" (Dep. 37-38). However, he was not persuaded by the MRI report to change his ultimate opinion of lack of incapacity because he found only some of the employee's complaints were consistent with the test results and he considered the results but one element that must be interpreted "in light of the remainder of the history and physical" (Dep. 37-38). When asked whether he would expect pain in the right leg or in the back based on the May 11, 1989 MRI report, Dr. Walsh replied, "possibly" (Walsh Dep. 34). He declined to say "probably" when pressed by employee's counsel (Walsh Dep. 34), and remained unconvinced that the MRI finding provided sufficient evidence to draw a conclusion regarding the employee's work capacity without substantiation by history and physical examination (Walsh Dep. 44-45). The doctor did not find such substantiation and ultimately opined that the employee should "get on with his life and go back to work" (Walsh Dep. 36-37).
The judge's finding that in Dr. Walsh's opinion the symptoms of which the employee complained "did not correspond to the findings on the MRI," (Dec. 4), while not reflecting the extent to which the doctor found correlation for the employee's complaints, adequately reflects the expert's final opinion.
The judge adopted the opinion of Dr. Walsh and adequately characterized his opinion. The choice to credit one medical expert's testimony over that of another is the prerogative of the administrative judge. Moviette Brown v. Hellenic Nursing Home, 5 Mass. Workers' Comp. Rep. 98 (1991).
The employee argues that the judge substituted her own opinion for that of the medical experts when she interpreted the meaning of the words used in the MRI report, which she characterized as "ambivalent," (Dec. 3) where the doctors involved found no such ambivalence. (Employee brief p. 9) The judge cited a portion of the report wherein the physician stated, in part: "The S1 roots appear in normal position but the right S1 [root] appears slightly splayed in coronal plane suggesting some compression of the root" (Dec. 3) (emphasis added by administrative judge). The employee correctly points out that no medical expert opined that the language of the MRI report was ambiguous. Whether a root may be in normal position while slightly splayed in the coronal plane of the right S1 root is a matter beyond the lay expertise of an administrative judge, and exclusively the province of the medical experts. See Lovely's Case, 336 Mass. 512 (1957); Blanchard v. Norfolk County Agricultural School, 3 Mass. Workers' Comp. Rep. 242, 245 (1957).
The judge stated that the report gave an "impression" rather than a "conclusion," implying the report was thereby less persuasive. The judge noted that Dr. Walsh pointed out the difference between the two words. This is incorrect. When asked what was the "conclusion" of the MRI by employee's counsel, Dr. Walsh began his answer by stating "[t]he impression is . . .," merely echoing the language at the end of the May 11, 1989 report. The word "impression" is a medical term of art, not a sign of indecisiveness by the physician reviewing the test result as the judge seems to suggest.
While it would be error for a judge to substitute lay opinion for that of a medical expert under circumstances beyond lay expertise, any error is harmless in this case, where such error could not affect the final result. See La Plante v. Maguire, 325 Mass. 96, 98 (1949); Bendett v. Bendett, 315 Mass. 59, 65-66 (1943).
It is clear that the administrative judge chose to discredit the testimony of the employee as to his physical limitations, and instead credited the testimony of a private investigator. Determinations with regard to credibility are within the discretion of the administrative judge. Frazier v. Cumberland, 7 Mass. Workers' Comp. Rep. 36 (1993). See § 11C. In view of the judge's findings as to the lay evidence, no other conclusion can be sustained but that the employee could not succeed in his claim for weekly incapacity benefits. See S. Solomon Sons Trust v. New England Theatres Operating Corp., 326 Mass. 99 (1950). The Decision of the administrative judge is affirmed.
In her decision the judge found as follows:
Private Investigator, Mr. John Tuney, also followed the Employee from the IME exam to his home. The Employee walked gingery to the car, rode as a passenger for a while and then, walking in normal fashion, took the driver's seat and drove home to do his shovelling. Photographs of the employee were entered into evidence showing the Employee shoveling his walk and climbing into the bed of his truck to shovel; after having left the doctor's office complaining of pain and inability to do work. I specifically do not credit the Employee's testimony. I credit and adopt the evidence presented by Private Investigator Tuney. (Dec. 7-8)
Judges McCarthy and Wilson concur.