COMPENSATORY EFFECTS OF FOOT DEFORMITY:

Transcription

1 COMPENSATORY EFFECTS OF FOOT DEFORMITY: Understanding the Nature of Foot Deformity and Imbalance BY KENDRICK A. WHITNEY, DPM, C.PED. 14 Pedorthic Footcare Association

2 The key to optimizing shoe and foot orthosis re-alignment therapies may lie in a better understanding of the true nature of foot deformity and the compensatory foot imbalances produced by specific tri-plane deformity. Human body balance is to a great extent a product of normal foot function. Were it not for a highly responsive load-receptor system in the foot, we would not appreciate our spatial position with reference to the ground. Except for the spine, the foot is the anatomical region that contains the greatest numbers of specialized proprioceptive nerve endings, which interact with the central nervous system via feedback loops that help to coordinate body movements, postural alignment and balance 1. Terrestrial two-legged primates possess a relatively high center of gravity and small base of area support. Such a situation requires a precise, continuous juggling action by the feet to maintain the torso centrally over and within the foot base of support. Thanks to our refined load-receptor system in the soles of the feet, we are aware of our position in space over the feet. When we shift our torso to either side, we are immediately conscious of an increased foot loading on the side or region of body shift. In a similar way, we are conscious of a torso shift forward or backward over the supporting feet. In other words, the load shifting tendency of our head, arms and torso (HAT) and our ability to sense the exact nature and extent of the change allows for a human body balancing mechanism of great precision. As the torso sways forward, the projected weight-load is transferred to the toes, which then react by a downward gripping motion that serves to counter the anterior body displacement. The long digital flexor muscles, in the posterior compartment of the legs, are activated via automatic reflexive reactions to arrest and correct the anterior body imbalance. The large Triceps surae calf muscles are likewise recruited as necessary in this process. Posterior body sway is counteracted by a reflexive activation of the dorsiflexor muscles in the anterior compartment of the legs and is accompanied by an observable upward retraction of the digits (Figure 1). CEP Read This Article, Take Survey to Earn Continuing Education Points Pedorthic Footcare Association (PFA) now offers Continuing Education Points (CEPs), approved by the American Board for Certification in Orthotics, Prosthetics & Pedorthics (ABC) and the Board of Certification/Accreditation International (BOC), via specially designated articles within Current Pedorthics magazine. To take advantage of the program, thoroughly read the adjacent article, Compensatory Effects of Foot Deformity, and then visit and click on the Continuing Education Opportunities tab to purchase the 10-question quiz associated with this article. CEP quizzes cost $25 for members and $35 for non-members. The quizzes are worth 1.0 Scientific or Business CEP, depending on the content. Successful completion of the quiz will result in 1.0 CEP reported directly to ABC and BOC at the end of each quarter. This article is the third CEP-eligible article in Current Pedorthics. Look for additional CEP-eligible articles in future issues of the magazine. If you have any questions, contact Lauren Kemp, PFA education coordinator, at (800) or info@pedorthics.org. Figure 1 Current Pedorthics May June

3 COMPENSATORY EFFECTS OF FOOT DEFORMITY Figure 2 From side to side, the feet are also responsive to lateral shifts of body apposition which can be identified by changes in foot position induced by appropriate collateral leg muscles. For example, a body shift toward the outer side of a supporting foot, produces a reactive supination of that foot by contraction of the supinator muscles (tibialis anterior and posterior). Figure 3 In single foot supporting function, this same muscle action moves the subtalar joint into inversion or eversion with an associated lateral or medial displacement of the lower limb column. Such rapid lateral and medial displacement of the lower limb column constitutes the juggling mechanism to which Dudley J. Morton referred 2. Whereas the relatively large superimposed body mass (HAT) is not easily moved from side to side, the supporting ankle is juggled by the appropriate foot muscles to maintain the precarious body balance (illustration). We have found that the well-aligned and balanced foot maintains a projected line of weight thrust that passes vertically through the supporting foot structure in the region of the middle cuneiform. This line of limb weight thrust extends from the superimposed hip joint to the central region of the supporting foot (Figure 2). Should a limb imbalance exist, that foot is found to be weak or otherwise impaired in one or more of eight possible vectors of imbalance (Figure 3). We have identified certain defects occurring in each of the eight vectors of foot imbalance associated with specific foot deformities. Anterior Vector The toes show a generalized downward gripping and the posterior calf muscles are visibly and palpably contracted. An increased forefoot loading is easily sensed. A posterior cavus foot-type will tend to produce this type imbalance as will the wearing of higher-heeled shoewear. The imbalance and its associated symptomatology may be negated with the use of lower or even negative heel type shoes. Anteromedial Vector A shift of the limb weight-thrust forward and medially may be caused by compensation of a forefoot varus foot condition. This type of imbalance may be better appreciated with a three-legged stool analogy wherein the front medial leg is short, the stool will tip forward and medial when any load is exerted (Figure 4). This vector of imbalance relates particularly to weakness or impairment of the first metatarsal segment. D.J. Morton brought attention to a syndrome that he characterized as a shortness, primary hypermobilility Figure 4 Figure 5 16 Pedorthic Footcare Association

4 or marked proximal placement of the radial sesamoid bones. His simple and effective remedy was the use of a first ray platform, which restored first ray function by eliminating the compensatory anteromedial imbalance. Posterior Vector While anterior types of foot imbalance produce a forward shift of the body center of gravity, posterior types of foot imbalance such as that produced by an anterior cavus (forefoot equinus) cause a posterior shift as ground reactive forces dorsiflex the plantarflexed forefoot (Figure 5). Special thanks to Pilgrim Shoes for sponsoring this original lecture presentation at the 2010 North American Pedorthic Congress. Postero-Medial Vector Slightly more complex is the compensatory imbalance produced by a lateral column type of anterior cavus. This extremely common foot type causes a posterior shift of body balance plus an additional medial shift as well. Restoration of optimal body balance thus requires both heel elevation and a medial forefoot wedge via orthosis and/or shoe re-alignment therapy. We have built upon Dr. Morton s use of such restorative functional pads by developing a set of block balance pads and wedges fashioned from semi-rigid EVA material to be placed under one or more of the eight specific regions of foot imbalance. This series of block balance pads were developed originally by Alan K. Whitney, DPM, as a precursor to his in-shoe test balance padding techniques and more definitive foot orthosis therapy 3. Properly placed test balance blocks should restore the more centralized location of the vertical axis of limb loading with observable improvement of foot and limb alignment. The patient may also offer feedback as to the relative Current Pedorthics May June

5 COMPENSATORY EFFECTS OF FOOT DEFORMITY Figure 6 Figure 7 A general understanding of the nature of body balance helps to identify certain foot defects underlying a situation of imbalance. success of the test realignment that will certainly lead to more effective shoe and orthosis treatment outcomes (Figure 6). A general understanding of the nature of body balance helps to identify certain foot defects underlying a situation of imbalance. We have presented a few examples of foot defects producing body imbalance and have indicated the specific directions or vectors of resultant foot involvement. When one appreciates the nature and direction of the foot imbalance, appropriate test realignment pads or wedges can be introduced. We have devised a system of test balance pads and wedges, which help to identify and confirm the vector of foot and body imbalance (Figure 7). When a condition has been test confirmed a more permanent orthosis/shoe management program may be developed. References 1. Christensen, K.D., Adjunctive Therapies to the Adjustment Improving Proprioceptive Balance with Orthotic Support. Dynamic Chiropractic vol. 4, issue 17, Morton, D.J., The Human Foot, University Press, Columbia NY, Whitney, A.K., Biomechanical Footwear Balancing, Pennsylvania College of Podiatric Medicine, Philadelphia, PA, 1979 Kendrick A. Whitney, DPM, C.Ped., is a third-generation podiatric physician with more than 25 years of teaching and clinical experience as an associate professor in the Department of Podiatric Medicine and Orthopedics at the Temple University School of Podiatric Medicine (TUSPM). He is the director of the pedorthic pre-certification courses offered at TUSPM. He lectures at numerous national and international seminars and symposia on biomechanical applications and othosis realignment therapies and has numerous publications in peer reviewed journals and text books. 18 Pedorthic Footcare Association