Goals of Foot Orthosis Therapy

About a year ago at a national podiatric seminar, I was invited to be a member of a panel of biomechanics "experts" discussing biomechanics and foot orthosis issues. It was my great fortune that in this panel of two podiatrists, two biomechanics researchers and one pedorthist, was included one of the foremost experts in the world on lower extremity biomechanics, Dr. Benno Nigg. Dr. Nigg is chairman of the Biomechanics Laboratory at the University of Calgary, Canada, and over the past two decades he and his co-researchers have published some of the finest research in the field of foot and lower extremity biomechanics. During our panel discussion, many of the questions focused on foot orthoses. Questions were asked regarding when they should be used, how they should be designed, what biomechanical measurements were important in designing the orthosis, and for what conditions they were useful for. One of the specific questions asked of Dr. Nigg was how a podiatrist should decide what specific type of foot orthosis would be best for an individual. As this question was asked of Dr. Nigg, I was expecting him to provide an exceedingly long list of biomechanical parameters which could be measured, tests which could be performed, and the research findings to back up his opinions. Quite to my surprise, and much to my pleasure, he gave a very simple answer to this most basic question. He said that the podiatrist must decide first what the goal of the foot orthosis is for the patient before the most effective foot orthosis can be designed for that patient. At the time of the panel discussion, I did not realize the true significance of Dr. Nigg’s words. However, in giving it much thought over the past year, it has become more apparent to me that Dr. Nigg’s statement is one of the most profound truths regarding foot orthosis therapy that I have heard in a long time. If you were to ask me the same question which was asked of Dr. Nigg after I had just graduated from my four years of podiatry school at the California College of Podiatric Medicine in 1983, I most likely would have answered, with great confidence, that the goal of foot orthoses was to make the patient walk with their subtalar joint (STJ) in the neutral position. In fact, I wouldn’t be surprised that at least 50-75% of the practicing podiatrists in the nation would also agree that the goal of foot orthoses should be to simply try and make the patient stand, walk or run closer to the STJ neutral position. Why do most podiatrists, young and old, believe that the main goal of foot orthoses is to make the foot function closer to the STJ neutral position? It is because these ideas have been taught in the podiatric colleges across the nation for over twenty years. It is based on the teaching and writings of Drs. Root, Weed and Orien who, for many years, emphasized that the ideal functioning position of the foot is the STJ neutral position. They introduced the eight "Biophysical Criteria for Normalcy" in which one of the criteria for normalcy was that "the subtalar joint rests at its neutral position" (Root, M.L., W.P. Orien, J.H. Weed, and R.J. Hughes: Biomechanical Examination of the Foot, Volume 1, Clinical Biomechanics Corporation, Publishers, Los Angeles, 1971, p. 34). Whether or not Drs. Root, Weed and Orien intended for their teaching and writings to be interpreted this way, it has been quite obvious to me that in meeting hundreds of podiatrists over the years in my lectures both nationally and internationally, that most of them believe that the goal of foot orthosis therapy is to simply attempt to get the foot to function closer to the STJ neutral position. It is clear to me that this narrow-minded approach to foot orthosis therapy is not only an ineffective means of allowing the podiatrist to design the best foot orthoses for their patients, but it also leads to a high rate of orthosis failure. In other words, in the patients I have seen both in my own practice and from other podiatrists, this "STJ neutral" goal of foot orthosis therapy has led to numerous orthosis failures where the patient is either unable to tolerate the foot orthosis or has developed painful lower extremity or back symptoms which prevent them from wearing their prescribed foot orthosis. The beauty of Dr. Nigg’s claim is that it is such a logical and common sense idea that the podiatrist should first decide on what the goal of foot orthosis therapy is before they embark on making foot orthoses for a patient. In nearly all instances, patients who will be receiving foot orthoses come to the podiatrist with a complaint which is causing them pain or disability which has a mechanically based etiology. For example, the patient may be walking or exercising more than normal, may be too heavy, may be carrying heavier loads at work, may have worn improper shoes, may have walked on a surface which they were unaccustomed to, and/or may have significant biomechanical abnormalities of the feet and/or lower extremities. What then is the goal of the foot orthoses which will be made for this patient? Is the goal of foot orthosis therapy simply to attempt to make the STJ function closer to the neutral position during gait? No! Is the goal of foot orthosis therapy to relieve the patient’s plantar heel discomfort but then cause them peroneal tendinitis or lateral ankle instability in the process? Of course not! Unfortunately, if your only goal of foot orthosis therapy for these patients who suffered from plantar fasciitis was to make them stand and walk in the STJ neutral position, then you would certainly be causing a high percentage of these individuals to suffer from symptoms which are caused by excessive supination moments acting across the STJ axis, such as peroneal tendinitis and lateral ankle instability. What then do I believe to be the general goal of foot orthosis therapy? The goal of foot orthosis therapy should be to reduce the pathologic loading forces on the injured structural components of the body in order to allow healing of the injured structures, to prevent new injuries from occurring, and to promote more efficient dynamics of the body during weightbearing activities. In other words, not only must the doctor focus on which anatomical structure is injured in the patient but also must determine what pathological loading forces are occurring on that specific structure to cause the injury. For example, in plantar fasciitis, the injury occurs from excessive tensile forces on the medial band of the plantar fascia. In hallux limitus, the injury mechanism is excessive interosseous compression forces acting on the dorsal aspect of the first metatarsal head. In a second metatarsal midshaft stress fracture, the injury occurs due to excessive bending moments acting on t he second metatarsal during weightbearing activities. Secondly, the doctor must determine how to design the foot orthosis to reduce these pathological loading forces to allow more rapid healing of the injured structure, prevent further injury to it in the future, and prevent injury to some other area of the body when the foot orthoses are worn. Of course, these are not always simple matters to accomplish due to the complex interactions of the multitude of factors which cause lower extremity biomechanical injuries to occur. However, if the podiatrist can strive toward this goal when they are contemplating prescribing foot orthoses, then the increased clarity of thought which results in the decision making process will greatly help the podiatrist design more effective foot orthoses for their patients. Kevin A. Kirby, D.P.M. Director of Clinical Biomechanics