Section 287.020.3 RSMo defines "injury" and sets forth a two-part test for determining when an injury arises out of and in the course of employment.
(1) In this chapter the term "injury" is hereby defined to be an injury which has arisen out of and in the course of employment. An injury by accident is compensable only if the accident was the prevailing factor in causing both the resulting medical condition and disability. "The prevailing factor" is defined to be the primary factor, in relation to any other factor, causing both the resulting medical condition and disability.
(2) An injury shall be deemed to arise out of and in the course of the employment only if:
(a) It is reasonably apparent, upon consideration of all the circumstances, that the accident is the prevailing factor in causing the injury; and
(b) It does not come from a hazard or risk unrelated to the employment to which workers would have been equally exposed outside of and unrelated to the employment in normal nonemployment life.
Arising Out of and in the Course of Employment -- §287.020.3(2)
Section 287.020.3(2) (a) -- Prevailing Factor Test
The legislature defined the prevailing factor for us. "The prevailing factor" means, "the primary factor, in relation to any other factor, causing both the resulting medical condition and disability." §287.020.3(1) RSMo.
"Primary" means, "first in rank or importance." "Factor" means, "something (as an element, circumstance, or
influence) that contributes to the production of a result." Substituting the above dictionary definitions into the statutory definition, the prevailing factor is the most important influence, in relation to any other influence, in causing both the resulting medical condition and disability.
The definition clearly requires a comparison of the strength of causative influences giving rise to employee's injury. Before embarking on such a comparison, I must first determine if employee's fall contributed to causing employee's resulting medical condition and disability. If it did not, there is no need to proceed.
Returning to the dictionary we find: "Cause," the verb, means, "to serve as cause or occasion of: bring into existence." [5] "Cause," the noun means, "a person, thing, fact, or condition that brings about an effect or that produces or calls forth a resultant action or state." [6] "Result" means, "to proceed, spring or rise as a consequence, effect or conclusion: come out or have an issue: TERMINATE, END - used with from or in <an injury ing from a fall>" [7] "Condition" means, "the physical status of the body as a whole <good $\sim>< poor \sim>$ or of one of its parts usu. Used to indicate abnormality <a serious $\sim>< disturbed mental \sim>$." [8]
The administrative law judge's conclusion that the resulting medical condition is the underlying bone on bone disease is erroneous. It is clear from the testimony of the medical experts that the bone on bone disease already existed as of the date of the accident. The experts variously described the physical status of employee's knee before the injury as having a "bone on bone disease process," "advanced degenerative arthritis," or "degenerative changes." The experts agree that this condition pre-existed the work accident and that the degenerative condition was not changed by the blunt trauma of the fall. That is, employee had bone on bone arthritis before the accident and employee had that same bone on bone arthritis after the accident. The degenerative joint disease is not the "resulting medical condition." [9]
So, what physical status arose as a consequence of the fall? Employee's knee progressed from manageably painful to extremely painful as a consequence of striking his knee on February 1, 2006. Employee's body progressed from not needing a total knee replacement to needing a total knee replacement as a consequence of the increase in pain resultant from the impact of the fall. The medical experts agree that the fall contributed to bringing into existence employee's resulting condition of needing a knee replacement. Dr. Stuckmeyer said, "[t]he indication fo