The ALJ's award was very brief. The ALJ pointed out Dr. Wise's opinion that employee sustained 5\% permanent partial disability of the left knee; and Dr. Stuckmeyer's opinion that employee sustained 40 % permanent partial disability of the left knee. Without providing any additional findings or supporting analysis, the ALJ simply split the difference between the two ratings and concluded that employee sustained 22.5 % permanent partial disability of the left knee as a result of the November 19, 2010, injury.
While we acknowledge that the ALJ was not bound by the percentage estimates of the medical experts and was free to consider all of the evidence in determining the percentage of employee's permanent disability, ${ }^{2}$ we find that the ALJ's award of 22.5 % permanent partial disability of the left knee is not supported by competent and substantial evidence.
Dr. Wise provided his 5\% permanent partial disability rating based solely on the November 19, 2010, injury; whereas, Dr. Stuckmeyer provided his 40\% permanent partial disability rating based on a combination of the December 28, 2009, injury and the November 19, 2010, injury. Dr. Stuckmeyer did not attribute a specific portion of his 40\% permanent partial disability to the November 19, 2010, injury. In other words, the two doctors' ratings are not comparable because they are not based on the same set of variables. The ALJ did not even acknowledge this dissimilarity between the two doctors' ratings before simply splitting the difference "based on [employee's] credible testimony and evidence presented...."
We find that this distinction between the two doctors' ratings is crucial because "when a preexisting disability is present, the claimant is required to prove the extent of the preexisting disability so that such percentage can be evaluated against the disability percentage existing after the compensable injury." Bock v. City of Columbia, 274 S.W.3d 555, 560 (Mo. App. 2008), citing Plaster v. Dayco Corp., 760 S.W.2d 911, 913 (Mo. App. 1988). In Moriarty v. Treasurer of the State of Missouri, 141 S.W.3d 69 (Mo. App. 2004), ${ }^{3}$ the court held that when preexisting disability to the same body part is present, "[f]ailure to offer expert testimony regarding the percentage of disability derived from the compensable injury bars the claimant from recovering permanent partial disability benefits." Id. at 73, quoting Miller v. Wefelmeyer, 890 S.W.2d 372, 376 (Mo. App. 1994).
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[^0]: ${ }^{2} See Bock v. City of Columbia, 274 S.W.3d 555, 560 (Mo. App. 2008).
{ }^{3}$ Overruled on other grounds by Hampton v. Big Boy Steel Erection, 121 S.W.3d 220 (Mo. Banc 2003).
Of course, the aforementioned is premised upon the assumption that the matter is not within the realm of lay understanding. In deciding whether a matter is not within the realm of lay understanding and, therefore, requiring expert testimony, the court in Griggs v. A.B. Chance Co., 503 S.W.2d 697, 704-05 (Mo. App. 1973) held that the issue "depends upon whether the injury or injuries are 'sophisticated,' meaning requiring surgery or 'highly scientific technique for diagnosis.' And an additional injury to the same area is simply more likely to place the matter outside the realm of lay understanding."
In light of employee's two injuries to his left knee and subsequent surgical procedures to repair the same, we find that attributing a percentage of disability between the two left knee injuries is not within the realm of lay understanding and, therefore, an expert opinion attributing a specific percentage of disability to the November 19, 2010, injury is necessary for the Commission to arrive at a decision on this issue. Because Dr. Stuckmeyer's 40\% rating fails to attribute a specific percentage of disability to the November 19, 2010, we do not give it any weight in our determination. Dr. Wise's 5\% rating accounts solely for the November 19, 2010, injury and, therefore, is the only credible expert opinion we can rely on with respect to the nature and extent of employee's permanent partial disability.
As mentioned above, the ALJ was not bound by the percentage estimates of the medical experts and was free to consider all of the evidence in determining the percentage of employee's permanent disability. However, in this case, the ALJ simply listed a small portion of the evidence presented, failed to acknowledge Dr. Stuckmeyer's combination rating, and provided no legal analysis or rationale for her finding that employee sustained 22.5 % permanent partial disability of the left knee.
We find, based upon the credible medical expert testimony and opinions, the medical records, employee's testimony, and the record as a whole, that as a result of the November 19, 2010, injury, employee sustained 5\% permanent partial disability of the left knee. Employee failed to meet his burden of proving that he sustained more than 5\% permanent partial disability in his left knee.
With respect to employer's argument that the ALJ erred in awarding employee future medical care, we find that the competent and substantial evidence supports the ALJ's award of future medical care. Dr. Stuckmeyer provided the only medical opinion regarding the issue of employee's need for future medical care and stated that employee is "more likely than not predisposed to advancing degenerative arthritis in the left knee," and that "it is more probable than not that he will need to undergo a unicompartmental joint arthroplasty." Based upon Dr. Stuckmeyer's opinion and the record as a whole, we find that employee met his burden of proving a reasonable probability that additional medical treatment is needed and that the reasonable probability arises from the work injury.