What Is A ‘Normal’ Foot?
Podiatrists commonly use the terms “normal” and “abnormal” to describe foot structure and foot function. We might look at a set of plain film radiographs and note that one foot has a hallux valgus angle that we call “normal” while the contralateral foot has a hallux valgus angle that we call “abnormal.” We might also do gait examinations in our office and tell one patient that his gait appears normal while in another patient, we may say that her gait appears abnormal.
Regardless of how many times we use the terms “normal” and “abnormal” in our discussions with patients or other physicians, or in our lectures or written articles, these terms do not mean the same thing to all podiatrists. One podiatrist might think that an individual with only 7 degrees of ankle dorsiflexion with the knee extended during clinical examination has “normal” ankle dorsiflexion while another podiatrist might think that only 7 degrees of ankle dorsiflexion is “abnormal.”
One of the problems regarding the terms “normal” and “abnormal” within the podiatric profession may have come from one of the earliest textbooks on podiatric biomechanics, Biomechanical Examination of the Foot, Volume 1. Merton Root, DPM, William Orien, DPM, John Weed, DPM, and Robert Hughes, DPM, published their book on biomechanical examination of the foot in 1971 and described a set of eight “Biophysical Criteria for Normalcy,” which they considered to be ideal values to allow normal foot function. Many podiatrists still commonly use these criteria to determine whether a foot is normal or abnormal.
A few of the “criteria for normalcy” proposed by Root and colleagues include that the distal one-third of the leg is vertical, the subtalar joint rests in its neutral position and the calcaneal bisection is vertical during bipedal stance. Does this mean that when an individual stands with his calcaneus inverted 3 degrees from vertical that his foot is “abnormal”? Yes, it does, using the strict biophysical criteria for normalcy proposed by Root and colleagues.
The issue with the biophysical criteria for normalcy that Root and coworkers proposed over three decades ago is that scientific research has never shown these criteria to be either ideal or an average range of foot and lower extremity structural parameters within the healthy human population. This lack of research evidence within our profession supporting what exactly constitutes normal and abnormal structure and function causes confusion, and impedes professional communication since no two podiatrists can agree as to what a normal and abnormal foot exactly looks like or functions like.
With these facts in mind, the question that begs to be answered is whether we, as a profession, should be using the terms “normal” and “abnormal” to describe ideal foot and lower extremity structural parameters where only one ideal structural alignment can mean that the foot is “normal”? Do we use only one numerical value to describe any measurable parameter of the human body and then consider that one numerical value to be “normal” while all the other values are “abnormal”? Do we say that the only “normal” hematocrit for an adult male is 45 percent while hematocrits of 43 percent and 47 percent are “abnormal”? Do we say that the only “normal” fasting blood glucose test is 85 mg/dL and it is “abnormal” when it is either 75 or 95 mg/dL? Of course, we don’t.
In medicine, ranges of normal describe the accepted range of numerical values in healthy individuals, whether these numerical values are referring to blood tests, nerve conduction velocities or bone density tests. The rest of the medical world realizes that due to the diversity within the human population, there exists a range of measurable biological parameters within which individuals can live and function without disease or disability. They base these values on multiple scientific research studies on large groups to determine an average range of numerical values within healthy individuals. They do not limit their descriptions of “normal” to mean only one numerical value that is a theoretical ideal with not a shred of scientific research to support it.
The podiatric profession needs to collectively research and redefine the ranges of “normal” and “abnormal” foot structure and foot and lower extremity function. We can no longer rely on unsupported theories from over 30 years ago to define an ideal “normal” foot structure and foot function. We need to respond to this glaring lack of basic research in foot structure and function, if for no other reason than for the sake of our academic and professional integrity.
Dr. Kirby is an Adjunct Associate Professor within the Department of Applied Biomechanics at the California School of Podiatric Medicine at Samuel Merritt University in Oakland, Calif. He is in private practice in Sacramento, Calif.