When seeking disability benefits with respect to a work-related injury, the claimant has the burden of proof to show that a disability resulted and the extent of such disability." *Zimmerman v. City of Richmond Heights*, 194 S.W.3d 875, 878 (Mo. App. 2006)(internal citations omitted). The claimant needs to prove "the nature and extent of any disability by a reasonable degree of certainty." *Id.*
Proof of the extent of disability is not required to be made with mathematical exactness, nor is the Industrial Commission bound by the percentage estimates or other testimony of medical experts. Hall v. Spot Martin, Inc., 304 S.W.2d 844, 854 (Mo. 1957). It is the duty and special province of the Commission to weigh all the evidence and reach its own conclusion as to the percentage of disability suffered. Haggard v. Synder Constr. Co., 479 S.W.2d 142, 145 (Mo. App. 1972); ABB Power T \& D Co. v. Kempker, 236 S.W.3d 43, 52 (Mo. App. 2007).
The administrative law judge found that while Dr. Musich's opinion was sufficient to demonstrate and certify that employee had a disability from the last injury, it was insufficient to show the percentage of disability and that it was "impossible to determine the extent or percentage of disability that claimant sustained from the last back injury separate from earlier back injuries." We disagree.
Dr. Musich noted that employee "was awarded a 35\% permanent partial disability of the body as a whole" and the record also shows employee settled his claim with employer for 35 % permanent partial disability of the body as a whole. The Second Injury Fund was not a party to these settlements, and remained free to litigate issues conceded by employer. Hoven v. Second Injury Fund, 414 S.W.3d 676, 680 (Mo. App. 2013). The settlement agreement is, however, relevant evidence that the Commission may consider regarding percentage of disability. Id., citing Conley v. Treasurer of Missouri, 999 S.W.2d 269 (Mo. App. 1999).
Dr. Musich testified that since the last injury, employee had continuing complaints of left leg pain, numbness, burning, and tingling where he had no symptoms in his left leg before; had bladder dysfunction that was not present before the 2009 injury; and was taking Vicodin where employee took no narcotics prior to the 2009 injury. Dr. Musich in his report of September 25, 2012, also identified the January 16, 2009, injury as the prevailing factor in the development of acute low back pain, discogenic pain, lower extremity radicuopathy, and a symptomatic neurogenic bladder. Additionally, employee credibly testified that after the January 2009 accident, he had increased problems walking, sitting, lying down, bending, lifting, squatting, climbing, and long distance driving.
Because proof of permanent disability need not be established with mathematical precision, because we are in no way constrained by medical testimony expressed with such precision, and (applying strict construction) absent any statutory language that requires disability be expressed in mathematical terms, we conclude it is not necessary that physicians certify permanent disability in mathematical terms. Rather, we believe the burden of proof of permanent disability can be sustained by providing