TOOKEY, J.

Petitioners challenge the validity of OAR 811-015-0036, a rule adopted by the State Board of Chiropractic Examiners (the board) that authorizes chiropractic physicians to perform "dry needling." Petitioners assert that the rule exceeds the board's statutory authority, and they make several arguments to support that contention. We address only petitioners' first argument — that the challenged rule authorizes a technique that is not encompassed within the practice of "chiropractic," as defined by ORS 684.010(2) — which is dispositive. Because we conclude that dry needling does not fall within the practice of chiropractic, we declare OAR 811-015-0036 invalid.

Under ORS 183.400(1), "any person" may petition this court to determine the validity of a rule. In reviewing a rule challenge under that statute, we may declare the rule invalid only if we conclude that it violates constitutional provisions, exceeds the statutory authority of the agency that adopted the rule, or was adopted without complying with rulemaking procedures. ORS 183.400(4). Here, petitioners do not argue that OAR 811-015-0036 is unconstitutional or that its adoption was procedurally flawed; they assert only that the rule exceeds the board's statutory authority.

To determine whether a challenged rule exceeds the agency's statutory authority, we may consider only "the wording of the rule itself (read in context) and the statutory provisions authorizing the rule." Wolf v. Oregon Lottery Commission, 344 Or. 345, 355, 182 P.3d 180 (2008) (citing ORS 183.400(3)(a), (b)). Based on those sources, we consider whether the agency's adoption of the rule exceeded the authority granted by statute and, further, whether the agency "departed from a legal standard expressed or implied in the particular law being administered, or contravened some other applicable statute." Planned Parenthood Assn. v. Dept. of Human Res., 297 Or. 562, 565, 687 P.2d 785 (1984). In making that determination, we seek to discern the legislature's intent by examining the text and context of the relevant statutes and, if useful to the analysis, pertinent legislative history. See State v. Gaines, 346 Or. 160, 171-72, 206 P.3d 1042 (2009) (describing statutory analysis).

We begin with the statutory provisions authorizing the board to adopt rules related to the practice of chiropractic in Oregon. The board has the authority "[t]o enforce the provisions of [ORS chapter 684] and to exercise general supervision over the practice of chiropractic within this state," ORS 684.155(1)(b) and "shall from time to time adopt such rules as it deems proper and necessary for the administration of this chapter and the performance of its work," ORS 684.150(1). Thus, for the board to adopt a valid rule under ORS chapter 684, the rule must relate to the practice of "chiropractic." ORS 684.010(2) defines "chiropractic" as

Here, the challenged rule defines dry needling and explicitly states that the technique falls within the statutory definition of "chiropractic." The rule provides, in relevant part,

OAR 811-015-0036. Petitioners argue that dry needling does not fall within the statutory definition of "chiropractic" under ORS 684.010(2)(a) because it does not fall within any of the enumerated categories of treatment. Further, petitioners argue that, because dry needling does not fit within the definition of "chiropractic" in subsection (a), it cannot fall within the definition of "chiropractic diagnosis, treatment and prevention of body dysfunction" under subsection (b). (Emphasis added.) Respondents argue that dry needling fits within the statutory definition of "chiropractic" because it is a form of "physiotherapy" under ORS 684.010(2)(a),1 and it is performed for the "treatment and prevention of body dysfunction" under subsection (b).

As noted, when interpreting a statute, we seek to discern the legislature's intent by examining the text and context of the statute and, if useful to the analysis, pertinent legislative history. Gaines, 346 Or. at 171-72, 206 P.3d 1042. The question here is whether dry needling falls within the definition of "chiropractic" under ORS 684.010(2)(a) as a form of "physiotherapy." We begin by observing that the term "physiotherapy" was added to the law as an amendment in 1927, and there is no available legislative history relating to that amendment. However, based on the statute's text and context, we conclude that the dry needling technique does not fall within the intended meaning of "physiotherapy."

The term "physiotherapy" is not defined in ORS chapter 684 or other related statutes; thus, dictionary definitions can help us discern the term's plain, natural and ordinary meaning. See Gaines, 346 Or. at 175, 206 P.3d 1042. When "interpreting the words of a statute enacted many years ago, we may seek guidance from dictionaries that were in use at the time." State v. Perry, 336 Or. 49, 53, 77 P.3d 313 (2003); see also Hopkins v. SAIF, 349 Or. 348, 360-64, 245 P.3d 90 (2010) (interpreting the statutory term "arthritis" using Webster's Third New Int'l Dictionary and medical dictionaries that were in use when the statutory provision was enacted).

Citing Webster's Third New Int'l Dictionary, respondents assert that the term "physiotherapy" is synonymous with "physical therapy." See Webster's Third New Int'l Dictionary 1707 (unabridged ed 2002) (defining "physiotherapy" as ": PHYSICAL THERAPY"). Respondents point out that the term "physical therapy" is defined by Webster's as "the treatment of disease by physical and mechanical means (as massage, regulated exercise, water, light, heat, electricity)." Id. Based on that definition, respondents assert, without further explanation, that "[d]ry needling falls within the category of treatment by physical or mechanical means, i.e., of physiotherapy."

As noted, the term "physiotherapy" was added to the law in 1927. At that time, The American Illustrated Medical Dictionary defined "physiotherapy" as "[t]he use of natural forces, such as light, heat, air, water, and exercise, in the treatment of disease." W.A. Newman Dorland, The American Illustrated Medical Dictionary 801 (11th ed 1922). Similarly, A Practical Medical Dictionary defined "physiotherapy" as "physiatrics," which in turn was defined as "[t]he use of natural forces in the treatment of disease." Thomas Lathrop Stedman, A Practical Medical Dictionary 775, 774 (7th rev ed 1922). Those definitions would suggest that physiotherapy uses "natural forces" similar to "light, heat, air, water, and exercise."2

We now turn to the context of the statute. Petitioners contend that dry needling cannot lawfully be considered physiotherapy in Oregon because physical therapists in this state are not authorized to practice that technique. The essence of petitioners' argument is that, because the term "physiotherapy" is synonymous with "physical therapy," the statutes regulating the practice of physical therapy in Oregon, set forth in ORS chapter 688, provide helpful context for interpreting the term "physiotherapy" in ORS 684.010(2)(a). In this instance, we decline to consider the definitions and rules relating to the practice of physical therapy, because the term we seek to define in this case is "physiotherapy," not "physical therapy." Even if we were to conclude that the legal definition of "physical therapy" excludes dry needling (which we do not decide here), we would not be compelled to conclude that the legislature intended for the two different terms to have the same legal meaning.

We do find other provisions of the same statute helpful to our analysis. Perry, 336 Or. at 55-56, 77 P.3d 313. When the legislature added the category of physiotherapy to the definition of "chiropractic" in 1927, it also added the categories of "electrotherapy" and "hydrotherapy." See Or. Laws 1927, ch. 450, § 3.3 Electrotherapy was defined at the time as "[t]he employment of electricity in the treatment of disease[,]" and hydrotherapy was defined as "[t]reatment of disease by means of water applied in various ways[.]" Stedman, A Practical Medical Dictionary at 308, 468. The addition of physiotherapy, electrotherapy, and hydrotherapy to the definition of "chiropractic" indicates an expansion of the practice to include not just "that system of adjusting with the hands the articulations of the bony framework of the human body," but also treatment methods that include other tools and sources of energy — those involved in physiotherapy (light, heat, air, water, and exercise), electrotherapy (electricity), and hydrotherapy (water).

With that understanding of the text and context of the statute, we turn to the question whether dry needling is a form of "physiotherapy," as that term is used in ORS 684.010(2)(a), and is therefore "chiropractic." The challenged rule defines dry needling as "a technique used to evaluate and treat myofascial trigger points that uses a dry needle, without medication, that is inserted into a trigger point that has been identified by examination * * * with the goal of releasing/inactivating the trigger points, relieving pain and/or improving function." OAR 811-015-0036(1). A "trigger point" is a small, sensitive area that, when stimulated, gives rise to a reaction elsewhere in the body. Webster's at 2444 (defining "trigger point" as "a small trigger area[,]" where a "trigger area" is defined as "a sensitive area of the body stimulation of which gives rise to reaction elsewhere in the body * * *"). The term "myofascial" refers to a sheet of fibrous tissue surrounding and separating muscle tissue. Stedman's Medical Dictionary 1173, 647 (27th ed 2000) (defining "myofascial" as "[o]f or relating to the fascia surrounding and separating muscle tissue[,]" where "fascia" is defined as "[a] sheet of fibrous tissue that envelops the body beneath the skin; it also encloses muscles and groups of muscles, and separates their several layers or groups"). Thus, plainly stated, dry needling is the insertion of a needle, without medication, into the tissue surrounding or separating the muscles within an identified, sensitive area, to relieve pain or improve function.

Based on that definition of dry needling, the question reduces to whether the insertion of a needle into the tissue surrounding a muscle uses a "natural force" similar to "light, heat, air, water, and exercise" — that is, whether a needle is a natural force. We conclude that it is not. A needle used in dry needling is neither "natural" nor is it a "force." In contrast to light, heat, air, water, and exercise — as well as the electricity and water used in electrotherapy and hydrotherapy — a needle is a man-made object. Moreover, although the use of natural forces may involve man-made objects and devices, we find nothing in the definition of physiotherapy suggesting that the practice of physiotherapy would include the application of a man-made object directly to the internal tissues of a patient.

Because dry needling is not a form of physiotherapy, and respondents do not contend that it falls within any other category of treatment listed in ORS 684.010(2)(a), we conclude that dry needling is not within the practice of chiropractic. Thus, the challenged rule exceeds the scope of the board's statutory authority and is invalid.

OAR 811-015-0036 held invalid.