This appeal is from a judgment based on a jury verdict which convicted John and Sherry Carpenter, husband and wife, on two counts of first degree criminal abuse. Sherry Carpenter was sentenced to five years imprisonment on each count, with the sentences to run concurrently. John Carpenter was sentenced to ten years imprisonment on each count. He was also found to be a second-degree persistent felony offender and his sentences were enhanced to twenty years imprisonment on each count, with the sentences to run consecutively for a total of forty years.
The questions presented on appeal are whether the evidence was insufficient; whether K.R.S. 508.100 is unconstitutionally vague; whether there was improper opinion testimony; whether there was irrelevant testimony which was prejudicial; whether the instructions were improper and whether the PFO conviction was proper.
*824On June 14, 1986, the Covington Life Squad responded to a call on a choking victim. The Carpenters told the squad attendant that their five-month-old baby had choked on green beans. At the hospital an X-ray taken of the child’s head showed severe brain damage caused by a blunt object. The medical witness testified that the injury had been caused by an extremely forceful blow which would be similar to a child falling from a second-story window. The evidence also indicated that the child suffered rib fractures which occurred on two separate occasions. There was no evidence of any green beans. Medical testimony indicated that as a result of the injuries, the child will probably remain severely impaired in a vegetated state for the rest of her life.
John Carpenter was charged on Count I with causing the child’s head injury of June 14, and also charged in Count II with causing the rib injuries between May 12 and June 14. He was convicted on both counts. Sherry was convicted on both counts pursuant to a permissive theory of criminal liability.
There was sufficient evidence of John’s guilt to withstand a motion for a directed verdict. John asserts that the evidence was insufficient as to Count I, but does not challenge Count II. Shortly before May 23, a witness saw John first shake the child and later throw her onto a bed in a fit of rage which resulted in the baby bouncing off the bed hitting her head. There was no dispute that on June 14, the date of the head injury, John and Sherry had exclusive control over the child. The head injury inflicted on June 14 was consistent with a blunt force blow and could not have resulted from an accident. The combination of these factors was sufficient for a jury to reasonably infer guilt on the part of John.
Kentucky’s criminal abuse statute, K.R.S. 508.100, is not unconstitutionally void for vagueness. At trial, the vagueness challenge was related to the use of the words “may” and “permit.” The principal question in such an inquiry is whether the statute gives suitable notice of prohibited conduct.
The Carpenters argue that the word “may” as used in K.R.S. 508.100(l)(b) does not provide a fair description of the prohibited conduct because virtually any conduct directed toward the child had the possibility of placing the child in a situation that may cause serious physical injury. A proper interpretation of the statute as a whole is that it does not apply to every situation where a child is injured but only to those instances where abuse is involved. Abuse is defined in K.R.S. 508.090(1). Similar attacks have been instituted, without success, on child abuse statutes in California and New Mexico where the statutes are similar to that of Kentucky. State v. Coe, 92 N.M. 320, 587 P.2d 973 (N.M.Ct.App.1978); People v. Beaugez, 232 Cal.App.2d 650, 43 Cal.Rptr. 28 (1965).
Now we turn to the use of the word “permit” in the statute. The pertinent part of K.R.S. 508.100(1) involved here punishes the person who, “intentionally abuses another person or permits another person of whom he has actual custody to be abused....” Sherry, but not John, argues that the jury was not properly instructed on all the elements of first-degree criminal abuse. She claims that the jury never learned of the element requiring intent. She also complains about the meaning of the word “permit.”
The instruction under which Sherry was found guilty on two counts, permitting another to commit child abuse, failed to require proof that she intentionally permitted the abuse. The word “intentionally” was used to define the act of a person inflicting the abuse but was erroneously deleted from the definition characterizing the action of the person permitting the abuse. Consequently, under the instructions Sherry could be convicted for the offense even though she had no intent to permit it. K.R.S. 502.020 provides that criminal responsibility may be imposed where a person having a “legal duty to prevent the commission of the offense, failed to make a proper effort to do so.” Neither the indict*825ment, nor the instructions, charge Sherry with criminal responsibility on this basis.
K.R.S. 508.100 punishes the person who intentionally abuses or permits a child in his or her actual custody to be abused. The statute does not repeat the term defining the culpable mental state required to convict before the word “permits.” As this Court stated in American Trucking Ass’n v. Com., Transp. Cab., Ky., 676 S.W.2d 785 (1984), “Where a statute is reasonably susceptible of two constructions, one of which will uphold the validity thereof, and the other would render it unconstitutional, the court must adopt the construction which sustains the constitutionality of the statute.” Id. at 789, 790.
If we interpret K.R.S. 508.100 as intending the intentional culpable mental state as applying only to the person inflicting the abuse and not to the person permitting the abuse, then the statute is necessarily either void for vagueness or overbreadth because the functional element, permitting, is unlimited. See Lanzetta v. New Jersey, 306 U.S. 451, 59 S.Ct. 618, 619, 83 L.Ed. 888 (1939), for a discussion of the concept of vagueness, and Musselman v. Commonwealth, Ky., 705 S.W.2d 476 (1986), for a discussion of the concept of overbreadth.
A proper culpable mental state must be supplied by statutory interpretation in order to provide for the constitutional basis for the statute. This constitutional principle of criminal responsibility was denied in the instructions relating to Sherry. The instructions defining permitting were similarly defective as to John, but because he was found guilty under the instruction as the person who actually committed the abuse, the erroneous instruction produced no prejudice as to him.
K.R.S. 508.100 is constitutionally proper if the word “intentionally” is construed to modify both abuse and permits. This is a logical construction because the legislature intended to impose criminal liability only if the accused were mentally culpable and because the internal structure of the three degrees of the offense of criminal abuse is the same. The only difference in the degrees was the insertion of the words “intentionally, wantonly or recklessly.”
The instructions should tell the jury what the constituent elements of permitting criminal abuse are. The jury could find Sherry guilty of criminal abuse in the first degree only if she intentionally permitted the abuse. Intent is an essential element and failure to instruct is prejudicial error. Watkins v. Commonwealth, Ky., 298 S.W.2d 306 (1957). Here the instructions authorized a conviction on the mental state of the person directly responsible for the abuse and not for the one who permitted the abuse.
The Carpenters were not substantially prejudiced by the introduction of opinion testimony that the injuries were intentionally caused. There was no question that the testimony was received from qualified experts. These opinions came from treating physicians who had experience in treating abused children. The objection to the testimony was based on the fact that the opinion invaded the province of the jury and not that the physicians were not qualified to render an expert opinion. Opinion testimony is admissible where it appears that the trier of fact would be assisted in the solution of the ultimate problem. Here the testimony aided the jury in determining that the injuries were not accidentally caused. Cf. Department of Highways v. Widner, Ky., 388 S.W.2d 583 (1965). We find no reversible error in the evidence concerning the Carpenters’ behavior at the hospital. John’s argument on the PFO instruction is unpreserved for appellate review and will not be considered under RCr 10.26, there being no palpable error or manifest injustice.
The judgment of conviction of John Carpenter on both counts is affirmed and the judgment of conviction of Sherry Carpenter on both counts is reversed and remanded for retrial.
STEPHENS, C.J., and COMBS and LAMBERT, JJ., concur. *826VANCE, J., concurs in result only. LEIBSON, J., files a separate opinion, concurring in part, dissenting in part, in which GANT, J., joins. LEIBSON, Justice,