JOHNSON, Justice.
This is a worker’s compensation case that has been the subject of a prior appeal {Horton I). Horton v. Garrett Freightlines, Inc., 106 Idaho 895, 684 P.2d 297 (1984). In its prior opinion this Court held that the Industrial Commission had retained jurisdiction of this claim for a future determination of permanent disability. The primary issue presented in this appeal is whether physical impairments that arose [913]*913after the work-related injury to the employee (Horton), but which were the result of physical conditions that pre-existed the work-related injury, should be considered by the Commission when making a determination of the degree of Horton’s permanent disability. The Commission concluded that these conditions should not be considered in determining the amount of compensation that Horton should receive. We agree, and affirm the Commission’s order determining the employer’s liability for Horton’s permanent disability.
In this opinion we also point out that the evaluation of permanent disability is only the first step in determining the amount of compensation to be awarded, for permanent disability. Any permanent impairment that exists at the time of the disability evaluation and that is the result of a work-related injury or of a physical condition that preexisted the work-related injury should be included in the evaluation. The second step in determining compensation for permanent disability is apportioning liability to the employer and to the Industrial Special Indemnity Fund (ISIF) as provided for in I.C. §§ 72-406 and 72-332. Applying these statutes to the facts as found by the Commission does not cause us to conclude that more liability should have been apportioned to Horton’s employer and its surety or to ISIF.
I.
THE FACTS AND PROCEEDINGS BEFORE THE COMMISSION.
The facts of this case from the time of the work-related accident in 1974 until the Commission denied Horton’s application for a hearing in 1983 are set forth in (he opinion of this Court in Horton I. 106 Idaho at 895-96, 684 P.2d at 297-98. Within two months after the decision of this Court in Horton I in July 1984, Horton quit working for Garrett Freightlines, Inc. (Garrett), because it became apparent that a total replacement of his right hip would be necessary. The total right hip replacement was performed in the fall of 1984. Following the replacement, Horton’s doctor did not give him a full duty work release. Horton’s union would not allow him to return to his job without a full release, and he has never returned to work for Garrett.
In the spring of 1984 Horton began to experience pain in his left shoulder and left leg or hip. In mid-December of 1984 Horton’s doctor noted degenerative changes in Horton's left hip. By late February of 1985 the doctor X-rayed Horton’s left shoulder and found severe arthritic changes. About that same time Horton complained to his doctor of back pain. By mid-March of 1985 the doctor noted early degenerative changes in Horton’s left hip. By July of 1986 the doctor had diagnosed degenerative arthritis in Horton’s right shoulder and a grade 1 spondylolisthesis and spondylolysis with the possibility of a herniated disk in Horton’s back.
In February 1986 Horton filed an application for a hearing with the Commission seeking a determination of the degree of his permanent disability. Horton’s doctor concluded that the only physical impairment he could relate to the 1974 work-related accident with the requisite degree of medical probability was Horton’s right hip impairment, and that Horton could not return to his former employment because of great pain in his shoulders and left hip. He rated Horton’s permanent impairment due to the condition of his right hip as equal to 30 percent of a whole person.
In September 1986 Horton was examined by a board certified orthopedic surgeon at the request of Garrett and its surety. This doctor found arthritic changes in Horton’s left hip on the basis of X-rays taken in August 1984 as compared to prior X-rays. He diagnosed Horton’s problems as osteoarthritis and avascular necrosis of the left hip, osteoarthritis of the right and left shoulder, and congenital spondylolisthesis of his low back. He rated Horton’s permanent impairment because of his right hip as equal to twelve percent of a whole person. In this doctor’s opinion, the 1974 accident caused all of Horton’s right hip permanent impairment, but none of the impairment to his left hip, to either of his shoulders, or to his back. The doctor testified that it was [914]*914Horton’s hereditary collagen makeup that was responsible for his osteoarthritis.
The Commission adopted the permanent impairment rating of Horton’s right hip provided by the doctor for Garrett and its surety over those of Horton’s physician. The Commission did so because in making his rating Horton’s doctor began with the assumption that all of Horton’s physical impairments should total 100 percent. He then assigned percentages somewhat arbitrarily to each of the individual impairments to achieve that result. The Commission also noted that Horton’s doctor had evidenced confusion as to the extent of the permanent impairment due to Horton’s right hip injury, sometimes assigning to it a rating of 50 percent of the whole leg and sometimes a rating of 50 percent of the whole person. The Commission pointed out that even when Horton’s doctor finally decided that the correct figure was 50 percent of the whole leg, he incorrectly calculated that a rating of 50 percent of the whole leg was equivalent to 30 percent of the whole person. Pursuant to I.C. § 72-428, the 50 percent of the whole leg rating was actually equivalent to only 20 percent of the whole person. The Commission also noted that Horton’s doctor had failed to take into account the decrease in total permanent impairment that takes place when separate permanent impairments are added together.
The Commission also had before it testimony of two private rehabilitation specialists — one employed by Horton’s attorney and one who saw Horton at the request of Garrett and its surety. The rehabilitation specialist employed by Horton’s attorney concluded that based on the totality of Horton’s physical impairments it was unlikely that Horton would find work within the geographic area of his employment by Garrett. This specialist did not attempt to disassociate the right hip condition from Horton’s remaining physical impairments. The rehabilitation specialist employed by Garrett and its surety concluded that based upon only the physical limitations resulting from Horton’s right hip replacement, Horton would be employable in regularly and continuously available employment, although not in heavy labor. This specialist also concluded that the physical impairments to the other portions of Horton’s body would preclude substantially more employment opportunities and would render Horton “for the most part” permanently and totally disabled. Based on this evidence the Commission concluded that as. a result of the 1974 work-related accident, Horton was permanently partially impaired to the extent of 12 percent of the whole person, and that considering Horton’s permanent physical impairment and nonmedical factors, Horton was permanently disabled as a result of the accident to the extent of 30 percent of the whole person. It is from this decision that Horton has appealed.
II.
IN APPORTIONING TO GARRETT OR ISIF THE COMPENSATION TO WHICH HORTON WAS ENTITLED FOR HIS PERMANENT DISABILITY IT WAS NOT NECESSARY TO CONSIDER THE IMPAIRMENTS TO HORTON’S LEFT HIP, HIS SHOULDERS, AND HIS BACK.
Horton asserts that all limitations and circumstances present at the time of an evaluation of disability should be included in the disability evaluation. In support of this position Horton cites I.C. §§ 72-425 and 72-430.
I.C. § 72-425 provides that the evaluation or rating of permanent disability “is an appraisal of the injured employee’s present and probable future ability to engage in gainful activity as it is affected by the medical factor of permanent impairment and by pertinent nonmedical factors provided in section 72-430, Idaho Code.” Horton argues that the Commission failed to assess properly his “present and probable future ability to engage in gainful activity” in light of the physical impairments that arose after the injury to his right hip. In refusing to include these limitations in its evaluation of Horton’s permanent disability the Commission referred to them as “unrelated permanent physical impairments.” [915]*915We conclude that the Commission correctly determined the amount of compensation to which Horton was entitled. However, we conclude that the Commission left out of its decision a necessary step in the process of reaching this result. The step that was left out of the Commission’s decision was the evaluation of Horton’s permanent disability taking into account his work-related impairment- and all of his physical impairments existing at the time of the evaluation and resulting from any condition that preexisted the injury to his right hip. We are convinced that in deciding the amount of the award of compensation for permanent disability the Commission simply stated its conclusion without setting forth the result of the initial evaluation of permanent disability outlined above..
Horton’s argument breaks down at the point where he concludes that if the Commission had determined that he were totally and permanently disabled as a result of all the physical impairments existing at the time of the evaluation, together with the nonmedical factors contained in I.C. § 72-430, that he would be entitled to compensation for total and permanent disability. With this conclusion we do not agree.
Horton would also have us construe I.C. § 72-332 to require liability of ISIF for disability due to pre-existing permanent physical impairments where the impairments were manifested after the work-related injury but before the disability evaluation. Horton’s argument is premised on the portion of I.C. § 72-332(1) that refers to “an employee who has a permanent physical impairment from any cause or origin” and who “incurs a subsequent disability by an injury or occupational disease arising out of and in the course of his employment.” (Emphasis added.) Horton contends that this dictates that if a permanent physical impairment manifests itself before the disability evaluation takes place, it should be considered to have pre-existed the “subsequent disability.” We note first that immediately following the language cited by Horton the statute states that the liability of ISIF is established when “by reason of the combined effects of both the pre-existing impairment and the subsequent injury or occupational disease or by reason of the aggravation and acceleration of the pre-existing impairment” the employee “suffers total and permanent disability.” (Emphasis added.) This makes it clear that the impairment must pre-exist the injury. Thus, a reading of the statute as a whole gives us adequate reason to reject Horton’s simplistic approach. First American Title Co. of Idaho v. Clark, 99 Idaho 10, 12, 576 P.2d 581, 583 (1978). However, we consider Horton’s case to present a fundamental question about the determination of liability of employers and ISIF under our worker’s compensation law. Therefore, we feel compelled to address this issue in greater depth.
The first step in our analysis is to explore how an evaluation of disability relates to the apportionment of liability for permanent disability. To do so it is helpful to examine the history of our worker’s compensation law and how it has evolved since its inception. Much of the statutory and judicial history of worker’s compensation law in Idaho that is pertinent to our inquiry here was thoroughly presented by Justice Joseph J. McFadden, now retired, in Wilson v. Gardner Associated, Inc., 91 Idaho 496, 426 P.2d 567 (1967). We will refer to portions of the decision only, but we commend to all who are interested in this subject a thorough reading of the entire opinion.
In Wilson, Justice McFadden reviewed the statutes and cases in Idaho from 1921 until 1963 dealing with the liability of employers for disability and concluded:
In summary these various decisions lead to the conclusion that this court, prior to the enactment of S.L.1941, Ch. 155 (I.C. § 72-323) held there could be no apportionment of compensation as between industrial accident and pre-existing condition or disability. [Citations omitted.] Subsequent to enactment of this provision this court has recognized that apportionment of compensation is to be made as between disability caused by or resulting from industrial accident and disability caused, by or resulting from pre-exist-ing injury, disease or condition residual [916]*916from previous injury, and the ratio of apportionment is for the board’s determination.
Id. at 502, 426 P.2d at 573.
In 1968 this Court reaffirmed Wilson and stated: “In short, if a condition existed prior to the compensable accident, and made the resulting disability more serious than it might have been in the absence of the pre-existing condition, then the board must apportion the disability between the two.” Scott v. Aslett Construction Company, 92 Idaho 834, 840, 452 P.2d 61, 67 (1968).
The pertinent portion of I.C. § 72-323, as it existed until 1971 stated: “If the degree or duration of disability resulting from an accident is increased or prolonged because of a preexisting injury or infirmity the employer shall be liable only for the additional disability resulting from such accident.” This statute contemplated that the evaluation of disability would include pre-existing injuries or infirmities, but that the degree of disability determined by an evaluation of disability was not necessarily the degree of disability for which the employer was liable.
In 1971 the legislature recodified the worker’s compensation law in this state. 1971 Idaho Sess.Laws, ch. 122, p. 408. In this recodification the statute that had been previously known as I.C. § 72-323 became I.C. § 72-406. I.C. § 72-406(1) read then as it does today:
In cases of permanent disability less than total, if the degree or duration of disability resulting from an industrial injury or occupational disease is increased or prolonged because of a pre-existing physical impairment, the employer shall be liable only for the additional disability from the industrial injury or occupational disease.
The 1971 recodification also included a new-statute concerning the liability of ISIF. As enacted in 1971, I.C. § 72-332 read:
(1) If an employee who has a permanent physical impairment from any cause or origin, incurs a subsequent disability by an injury or occupational disease arising out of and in the course of his employment, and by reason of the combined effects of both the pre-existing impairment and the subsequent injury or occupational disease or by reason of the aggravation and acceleration of the pre-ex-isting impairment suffers total and permanent disability, the employer and surety shall be liable for payment of compensation benefits only for the disability caused by the injury or occupational disease, including scheduled and unscheduled permanent disabilities, and the injured employee shall be compensated for the remainder of his compensation benefits out of the special industrial indemnity fund.
(2) As used in this law, “permanent physical impairment” means any permanent condition, whether congenital or due to the injury or disease, of such seriousness as to constitute a hindrance or obstacle to obtaining employment or to obtaining re-employment if the employee should become unemployed.
Prior to the enactment of I.C. § 72-332 in 1971 the liability of ISIF had been very limited. When ISIF was created in 1927, its liability was limited basically to cases where an employee who had previously lost a hand or a foot subsequently lost another hand or foot in an industrial accident, or where an employee who had previously lost an eye subsequently lost the other eye in an industrial accident. 1927 Idaho Sess. Laws, ch. 106, § 6, p. 136, 142. In those cases the employer was only liable for the permanent partial disability caused by the subsequent industrial accident. ISIF was liable for the remainder of the compensation that would have been due the injured employee “if the subsequent injury itself had been the cause of his permanent total disability.” Id. Although recodified in 1955 (1955 Idaho Sess.Laws, ch. 250, p. 556-58) this formulation of ISIF’s liability continued basically unchanged until the re-codification of the entire worker’s compensation law in 1971.
Recently, this Court has reaffirmed that ISIF “was created for the purpose of encouraging employers to hire handicapped persons, ‘with the obligation only to pay compensation for an industrial injury to the [917]*917handicapped person such amount as the employer would have had to pay an employee who had not been handicapped with the Indemnity Fund assuming responsibility for the balance of the total permanent disability.’ Royce v. Southwest Pipe of Idaho, 103 Idaho 290, 294, 647 P.2d 746, 750 (1982).” Mapusaga v. Red Lion Riverside Inn, 113 Idaho 842, 847, 748 P.2d 1372, 1377 (1987).
The history of I.C. § 72-406 and its predecessor I.C. § 72-323, when read together with I.C. § 72-332 as enacted in 1971, convinces us that the intent of the legislature in 1971 was to continue the scheme established by the legislature in 1941 for apportioning liability for disability that was the result of a work-related injury or disease and a pre-existing impairment. The only significant addition that the legislature made in the scheme for apportioning liability for total permanent disability was to expand the liability of ISIF. Under I.C. § 72-332 ISIF became liable for a portion of total permanent disability for which the employee had not been entitled to receive compensation from the employer under I.C. § 72-323, as it existed before the 1971 re-codification.
This historical review puts in perspective the two-step process of (1) evaluating permanent disability as prescribed in I.C. §§ 72-425 and 72-430 and (2) apportioning the liability for permanent disability as prescribed in I.C. §§ 72-406 and 72-332. In evaluating permanent disability under the first step of this process all physical impairments that were caused by the work-related injury and by all pre-existing impairments or physical conditions should be taken into account. Otherwise, there would be no determination of disability that would permit an apportionment for pre-existing impairments under I.C. §§ 72-406 and 72-332. Here, this conclusion dictates that the Commission should have included the impairments to Horton’s left hip, his shoulders, and his back in making its evaluation of the degree of his total and permanent disability. The conditions that caused these impairments existed at the time of the injury to Horton’s right hip. Whether any of these impairments would lead to liability of Garrett and its surety or ISIF depends on the second step in the process outlined above — apportionment under I.C. §§ 72-406 and 72-332.
Horton is entitled to have applied to the determination of the liability for his permanent disability the law as it existed at the time of his work-related injury in 1974. Royce v. Southwest Pipe of Idaho, 103 Idaho 290, 293, 647 P.2d 746, 749 (1982). Under I.C. § 72-406, which has not been amended or subjected to any new interpretation since 1974 that would affect the result in this case, if Horton were evaluated to have a permanent disability less than total, Garrett would be liable only for the disability resulting from the injury to Horton’s right hip. This would include the effects of the arthritis that eventually caused the replacement of the hip. Garrett would not be liable for any disability caused by impairments to the left hip, the two shoulders, or the back. Therefore, if the disability evaluation in this case had included the impairments to the left hip, the shoulders and the back and had rated the permanent disability at less than total, the Commission’s award of compensation against Garrett equivalent to thirty percent of a whole person would have been correct.
I.C. § 72-332 was amended in 1981. The amended version of the statute and the decision of this Court interpreting it are not applicable here, since Horton’s accident occurred in 1974. In Gugelman v. Pressure Treated Timber Co., 102 Idaho 356, 360-61, 630 P.2d 148, 152-53 (1981), this Court interpreted the statute before its amendment in 1981. Gugelman construed the portion of the statute referring to a “permanent physical impairment” to mean “any permanent condition which reasonably could constitute a hindrance or obstacle to obtaining employment or reemployment.” This Court also interpreted the pre-1981 version of the statute to require that before a pre-existing physical impairment could constitute a hindrance to employment “the condition must be manifest.” Royce, 103 Idaho at 294, 647 P.2d at 750. In Royce the Court stated: “ ‘Manifest’ means that either the employer or employ[918]*918ee is aware of the condition so that the condition can be established as existing prior to the injury.” Id. (Emphasis added.) This makes it clear that for ISIF to be liable for any portion of an employee’s total permanent disability, there must, be a permanent physical impairment that pre-exist-ed the work-related injury.
Applying these standards to the apportionment of Horton’s disability, we are unable to find any way in which ISIF could be liable to Horton, even if Horton were determined to be totally and permanently disabled, based in part, on the impairment of his left hip, his shoulders, and his back. Horton’s asymptomatic arthritis and spondylolisthesis had not manifested themselves at the time of the injury to his right hip. Although these underlying conditions were in existence, there is no evidence that either Horton or Garrett were aware of the conditions, as required by Royce. Therefore, even if Horton had been evaluated to be totally and permanently disabled, none of the liability could have been apportioned to ISIF.
Horton cites the decision of this Court in Bowman v. Twin Falls Construction Co., Inc., 99 Idaho 312, 581 P.2d 770 (1978) in support of his position that the Commission should have considered his current medical status at the time of the evaluation, regardless of origin, when it determined his entitlement to disability benefits. Bowman is not in conflict with our decision here. In Bowman the employee was determined by the Commission to be permanently and totally disabled because of pulmonary emphysema and congestive heart failure. However, the Commission denied any compensation to the employee on the ground that the employee’s occupation was not a major contributing factor to his pulmonary disease, and that the disease was not contracted or incurred during his employment and was not due to the nature of his occupation. This Court reversed the denial of compensation on the ground that where the employee’s “ ‘working conditions’ contributed, even slightly, to a disability which is total and permanent, such permanent and total disability is fully compensable.” 99 Idaho at 312, 581 P.2d at 770. Justice Bistline, writing for the majority, said:
Bowman became totally and permanently disabled because his work environment aggravated or accelerated a pre-existing disease or condition_ When one’s employment aggravates, accelerates or “lights up” a pre-existing disease so that total permanent disability results, the employee is entitled by statute to 100% disability benefits.
Id. at 315, 316, 581 P.2d at 773, 774. (Emphasis added.)
Here, the only evidence of aggravation, acceleration, or “lighting-up” was with regard to Horton’s arthritis in his right hip. The Commission correctly awarded Horton compensation for the permanent disability to that hip, including the effects of the pre-existing arthritis. However, with regard to Horton’s left hip, his shoulders, and his back, there is no evidence that these conditions were aggravated, accelerated, or “lighted-up” by his employment or by the injury to his right hip.
Our decision here is also consistent with the decision in Royce. There, a colloid cyst was present in the claimant’s brain prior to the work-related accident. Prior to the accident, “neither claimant nor anyone else had any indication that the cyst existed.” 103 Idaho at 295, 647 P.2d at 751. This Court noted that the medical testimony indicated that “the head trauma sustained by claimant in the accident triggered the onset of clinical symptoms.” Id. Based on these, facts this Court concluded that ISIF was not liable for any of the total and permanent disability that the Commission found the claimant to have and affirmed the conclusion that the employer and its surety were liable for the full amount of the claimant’s disability benefits.
The obvious difference between Royce and this case is that only the pre-existing arthritic condition of Horton’s right hip was affected by the work-related injury. So far as the record here shows, the pre-ex-isting condition of Horton’s left hip, his shoulders, and his back were not affected by the work-related accident and injury. [919]*919Therefore, Garrett is not liable for Horton’s total permanent disability.
Although not asserted by Horton, one member of this Court has suggested that Garrett and its surety should be liable for the full extent of Horton’s disability based on the premise that “an employer takes an employee as he finds him.” Wynn v. J.R. Simplot Co., 105 Idaho 102, 104, 666 P.2d 629, 631 (1983). This concept in our worker’s compensation decision can be traced to language contained in McNeil v. Panhandle Lumber Co., 34 Idaho 773, 793, 203 P. 1068, 1075 (1921): “[I]t m.ay truly be said that our compensation law makes no distinction between wise and foolish, skilled and unskilled, healthy and unhealthy employees.” There, the claimant lost the sight of his right eye as the result of a detached retina that occurred while he was performing labor for the lumber company. The claimant had lost the sight in his left eye eight years before. The industrial accident board awarded him compensation for total permanent disability to be paid by his employer. This was before the establishment of ISIF and before apportionment was adopted by statute. As applied in Wynn, this concept of taking an employee as the employer finds him, caused this Court to reverse a decision of the Commission in which the claimant was denied benefits where he suffered a ruptured cervical disc. The Commission based its decision on the claimant’s history of nonwork-related activities including being a rodeo performer. The Commission found that the claimant’s spine had “become predisposed to the injury which he ultimately sustained.” Wynn, 105 Idaho at 104, 666 P.2d at 631. This Court concluded: “The injury produced the symptomatology and the disability from which claimant suffered.” Id. at 105, 666 P.2d at 632. See also, Bowman, 99 Idaho at 315, 581 P.2d at 773.
The facts here are distinctly different. The injury to Horton’s right hip did not produce the symptomatology and the disability to Horton’s left hip, his shoulders, and his back. These impairments arose independently. They were, as the Commission said, “unrelated.”
III.
THE COMMISSION CONSIDERED PERTINENT NONMEDICAL FACTORS IN DETERMINING THE DEGREE OF PERMANENT DISABILITY.
Horton contends that in arriving at the degree of his permanent disability, the Commission did not consider pertinent nonmedical factors provided for in I.C. § 72-430. This contention is refuted by the specific findings and conclusions of the Commission.
The nature of Horton’s physical disablement, the first nonmedical factor listed in I.C. § 72-430, was discussed extensively in the Commission’s findings. The disablement that is referred to in the statute clearly is the disablement that was caused by the work-related injury. The statute cannot reasonably be read to refer to disablement that resulted from some non-work-related injury or condition. To do so would emasculate the statutory procedure established in I.C. §§ 72-406 and 72-332 for apportionment of liability. If disablement from a pre-existing condition that was not apportionable to the employer under I.C. § 72-406 or to ISIF and the employee under I.C. § 72-332 could then become a “nonmedical factor” under I.C. § 72-430, the distinction between medical and nonmedical factors in our worker’s compensation system would have been destroyed.
There may be some confusion as to what conditions may be considered as nonmedical factors under I.C. § 72-430 because of the decision in Mapusaga. There, this Court allowed the claimant’s mental disorder to be treated as a personal circumstance under I.C. § 72-430. In our view, Mapusaga stands for the proposition that a mental disorder that is not accompanied by physical manifestations may be included as a nonmedical factor in a disability evaluation. It does not stand for the proposition that physical conditions such as those that caused the impairments to Horton’s left hip, his shoulders, and his back are nonmedical factors. Horton’s hereditary [920]*920collagen makeup that was responsible for his osteoarthritis and his congenital spon-dylolysthesis that was responsible for the condition of his back are medical factors, not nonmedical factors.
The Commission considered Horton’s occupation, his age at the time of the accident causing injury, and his age at the time his right hip condition stabilized. The Commission’s findings also detailed the efforts of Horton through the Pocatello Job Service to obtain other employment and the opinions of the rehabilitation specialists concerning the re-training and employability of Horton.
In its decision the Commission concluded: “Considering together Claimant’s permanent physical impairment and nonmedical factors, the commission concludes that Claimant is permanently disabled as the result of the industrial accident to the extent of 30 percent of the whole person.” It is clear that the Commission- considered the pertinent nonmedical factors in making this determination. The Commission determined that Horton was permanently partially impaired to the extent of 12 percent of the whole person and increased the permanent disability rating to 30 percent after reviewing the nonmedical factors.
We adhere to our often stated rule' that we will not disturb the Commission’s findings of fact when they are supported by substantial and competent, though conflicting, evidence. Kindred v. Amalgamated Sugar Co., 114 Idaho 284, 291, 756 P.2d 401, 408 (1988).
IV.
CONCLUSION.
The order of the Commission is affirmed.
Costs to respondents.
No attorney fees on appeal.
SHEPARD, C.J., and McQUADE and WALTERS, JJ., Pro Terns., concur.