Patterns, Algorithms, and Designs—Revisiting Rotary Deformities

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By John T. Brinkmann, MA, CPO/L, FAAOP(D), and Deanna Fish, MS, CPO

Clinical tasks performed by prosthetists and orthotists on a daily basis require an in-depth and nuanced understanding of the interaction of diverse physiological, anatomical, biomechanical, and psychosocial factors. The varied ways in which these factors interact create unique presentations in individuals requiring orthotic management, and these profiles are often much more complex and challenging to manage than those of prosthetic patients. Understanding a patient's orthotic needs and making effective design and care program recommendations requires extensive training and experience. A significant element of lower-limb orthotic education involves entry-level knowledge about anatomical segments, joint function, the impact of specific pathologies, and other related topics. Training aspiring orthotists to apply that knowledge in specific clinical scenarios is more difficult. Recognizing common patterns of deformities facilitates the identification of specific deficits, biomechanical goals, and required design features. Orthoses can then be fabricated based on these observations and the criteria most important to each individual case, and effective orthotic care programs developed to optimize walking tasks in safe and efficient manners.

An important aspect of clinical training involves going beyond the basics and learning to recognize patterns of clinical presentations, allowing for more efficient and effective identification of individual biomechanical and pathomechanical priorities. Alex Kirlik, PhD, a computer science and engineering researcher at the University of Illinois, has investigated how individuals make decisions in dynamic environments. While his focus is human-machine interfaces, the time pressure and complexity of the dynamic tasks he studies match those encountered in orthotic clinical practice. According to Kirlik, "In complex, dynamic environments, a central achievement of learning may be to simplify tasks ‘by resorting to pre-established routines, heuristics and short-cuts'…as dynamic decision-­making becomes more skilled, individuals appear to rely more heavily on perceptual and pattern-recognitional heuristics and less on analytical strategies."1

Kirlik describes the importance of focusing on the correct perceptual information, and that, to be effective, training must focus not only on certain rules for decision-making, but on how to apply those rules appropriately in a dynamic situation. "In most tasks that can be described in such terms, knowledge of the rules is thought to be the key to effective performance. As a result, training programs are often designed to communicate and teach this rule-based knowledge explicitly. The second stage is often conceived as mere rule application. As a result, this stage of learning often is not explicitly trained but, rather, occurs through relatively unstructured hands-on practice."1

This may be an apt description of orthotic education, a process that begins with a highly structured formal education in foundational rules and principles, followed by a less structured residency where personal clinical experience dominates. According to Kirlik, "The major difference between novice and expert…may not concern the rules they know but, rather, their abilities to rapidly and accurately obtain information from the environment that allows them to deploy their abstract knowledge to particular cases."1 Clinical practice provides many opportunities to make meaningful connections between rules and principles learned in school and various patient presentations.

Nerollyn Ramstrand, PhD, conducted research on observational gait analysis (OGA) that confirmed the importance of recognizing patterns in the acquisition of OGA skills. She found that experienced clinicians performed OGA using a visual search strategy that emphasized the recognition of patterns. Her research also evaluated the effect of teaching novices to focus on searching for gait deviations commonly associated with a pathology (recognizing patterns) compared to teaching them to focus on specific cues that could be observed at different body segments in isolation. Ramstrand found evidence "that the pathology-based learning group responded more rapidly to OGA training and that the cue-based learning group did not adopt the search strategy that had been emphasised throughout their training program."2

During the late 1980s and early 1990s the clinical understanding of many orthotists was influenced by the Oregon Orthotic System (OOS) model of triplanar pathomechanics. OOS created a systematic approach to identifying and evaluating lower-limb static and dynamic alignments as well as a strategic approach to orthotic design. Understanding how this strategic model of orthotic management was developed can reinvigorate the advancement of orthotic theory related to triplanar control for a new generation of clinicians.

Biomechanical Patterns

The understanding of triplanar pathomechanics has evolved significantly over the last 50 years. In 1964, Henderson, Campbell, and others at the University of California Biomechanics Laboratory introduced the UCBL, a rigid, submalleolar foot orthosis for pes planus. In the late 1970s, Carlson and Berglund developed design improvements to improve stabilization of the subtalar joint. Their adaptation of the original UCBL design included an aggressive modification under the sustentaculum tali and anterior calcaneus that blended into the longitudinal arch and was intended to stabilize the hindfoot in the coronal and sagittal planes. In the early 1980s, inspired by these orthotic designs for foot and ankle alignment, Jean-Paul Nielsen, CP, began to create designs that focused on the role of forefoot alignment on the stability and alignment of the hindfoot. Supported by a 1987 publication by Shahan K. Sarrafian, MD, titled "Functional Characteristics of the Foot and Plantar Aponeurosis under Tibiotalar Loading," Nielsen further refined his clinical designs to strategically address the subtalar and midtarsal joints in the sagittal, coronal, and transverse planes.

As effective alignment and stabilization of the base of support was noted to create triplanar realignments of proximal joint structures, distinct patterns of deformities of the lower limbs were identified as external rotary deformities (ERDs), internal rotary deformities (IRDs), non-rotary deformities (NRDs), or skeletal deformities.3 Input from other sources and the success of collaborative clinical outcomes were used to established principles related to triplanar control of the lower limb. These principles were incorporated into orthoses fabricated by OOS, a subsidiary of Webb's K.E. Karlson, an O&P patient care company based in Portland, Oregon. The original OOS design included a laminated footplate, Becker double-action ankle joints, and laminated calf section with a solid pre-tibial shell. Over time, many different design variations evolved from this basic model. OOS was then acquired by Becker Orthopedic in 1997.

Clinical Algorithms

Forces generated through the limbs during walking exceed body weight and become exacerbated by joint deviations, deformities, and misalignments. The OOS system was based upon the application of serial three-point force systems effecting alignment changes to the five major joints of the lower limb in the three cardinal planes of motion. Forces applied to the midtarsal, subtalar, talocrural, knee, and hip joints address triplanar structural misalignments in combination with the functional deficits identified during bipedal ambulation. An integral part of the OOS model was an emphasis on derotating the foot and ankle complex, segmental alignment of the lower limb, application of serial three-point force systems, ground reaction versus structural stabilization, static and dynamic evaluation, gait training and therapy concepts, ligamentous pathomechanics, and modeling and remodeling concepts. Essentially, OOS developed an algorithm (a process or set of rules to be followed in calculations or other problem-solving operations) for managing common pathological presentations in orthotic practice. Elaine Owen, MBE, MSc, SRP, MCSP, describes algorithms as "analogous to identifying all the possible ingredients for a recipe and then choosing the optimal ingredients in the optimal sequence, in order, to achieve the desired result. Once written, the individual steps in the algorithms can be much more easily explained and understood…."4

When the need for detailed clinical training on the OOS algorithm was identified, Jean-Paul Nielsen, CP, and Deanna Fish, CPO, collaborated to create a three-day comprehensive training program on triplanar control and orthotic design for lower-limb pathomechanical conditions. Over time, other clinicians, including Cheryl Kosta, PT; Cheryl Hood, CPO; Bill Neumann, CPO; and Kyle Scott, CO, made significant contributions to these clinical training courses and materials. Ongoing feedback and collaboration with a national network of orthotic clinicians continued to advance the OOS theory and designs. OOS provided interdisciplinary clinical training programs on triplanar pathomechanics for about ten years. These programs were designed to provide the orthotist with a better understanding of triplanar pathomechanical conditions and to provide the physical therapist with strategies for improving static and dynamic balance and overall walking abilities.

As a result of these educational programs, many orthotists incorporated this approach into their practice and continued to evolve these clinical techniques. The OOS process of evaluation, segmental casting, fitting, and follow-up was very time intensive compared to other orthotic programs but was particularly effective with challenging patient profiles. Success also depended on the dissemination of this orthotic approach into the surrounding medical and rehabilitation communities. In many areas, orthotists were very successful in developing a clinical practice focused on expanding on these triplanar concepts and the OOS algorithm.

Orthotic Designs

Biomechanical requirements of walking include periods of flexibility and rigidity during initial loading and terminal stance, respectively. Balancing the flexibility and rigidity of each orthosis is required to optimize individual patient outcomes. Some flexibility at the foot and ankle could be addressed with the size, shape, placement, and materials of the sustentaculum tali modification (or ST pad). An ideal orthotic design would provide variable periods of rigidity and flexibility at specific joints during different phases of loading, while still controlling triplanar alignments and addressing the functional deficits encountered during walking. Material selection is critical to correct, hold, and prevent progression of further deformation, oppose forces under static and dynamic loads, and provide biomechanical opportunities for flexibility and stability. Early efforts with triplanar orthotic designs identified the deficiencies of using thermoplastic materials such as polypropylene or copolymer. While sagittal and coronal plane stability could be addressed, the inherent properties of the thermoplastic materials allowed excessive transverse plane motion. (This can be demonstrated by grasping the distal foot section and proximal calf section of a thermoplastic AFO and counterrotating the two segments.) Because of this, polyester resins were initially used to provide sufficient control in all three planes.

Over time, the laminated designs were further refined with the introduction of different fabrics (e.g., carbon, Kevlar, fiberglass, etc.) and improved acrylic and other resins. Contemporary material options offer even more opportunities to improve on the original design concepts and match each patient's static and dynamic needs.

Height, weight, activity level, degree of deformity, degree of correction, and many other factors should be considered relative to the structural needs of the orthotic design. Thermoplastic materials are not contraindicated but should be used strategically to best meet the needs of the patient. New materials, such as pre-preg carbon fiber laminates, present opportunities for structural stability and decreased weight of the orthosis. It is likely that advancements in 3D printing and material science will yield even more options for clinicians with the necessary training.

What's Next?

For decades, orthotists have used the principles described in the OOS to improve their patients' function and mobility. In recent years, orthotists implementing Owen's principles of AFO tuning and AFO-footwear combinations have influenced their patients' lives in similar ways. Clinicians can expect that models for understanding complex clinical presentations will continue to evolve. In her commentary titled "Call to Action: Clinical Algorithms for Prescription of Ankle-Foot Orthoses Are Needed," Owen states that "clinical algorithms which determine optimum designs for achieving particular goals aid decision-making and are probably the key to simplifying complex orthotic science for clinicians, family, and other carers."4

An understanding of patterns of deformities and presentations can help novice clinicians learn the basics of effective clinical care, and help all clinicians optimally manage complex functional impairments. Every clinician has the responsibility to continue to refine his or her clinical understanding based on information from a variety of credible sources. A further responsibility is to contribute to the body of knowledge of the profession by developing and sharing coherent descriptions of our clinical processes. These descriptions can help us address individual patient needs and facilitate communication with other members of the care team. According to Owen, "having joint knowledge and clinical pathways or algorithms that guide the decision-making of all members of the team" is an essential element of providing care in an integrated manner. Joint knowledge is important so that families are not given conflicting advice and to enhance their understanding of the reasoning behind the decisions that they will be contributing to, regarding choice of AFO type, design, alignments, and frequency of use."4 The art and science of clinical care will continue to improve as we respond to Owens' call to action: "Create teams, share knowledge, and write clinical algorithms…."4

John T. Brinkmann, MA, CPO/L, FAAOP(D), is an assistant professor at Northwestern University Prosthetics-Orthotics Center. He has more than 20 years of experience treating a wide variety of patients.

Deanna Fish, MS, CPO, is clinical outreach manager for Orthomerica Products and brings more than 35 years of experience in treating challenging lower-limb orthotic patients.


1.        Kirlik, A., N. Walker, A. D. Fisk, and K. Nagel. 1996. Supporting perception in the service of dynamic decision making. Human Factors 38(2):288-99.

2.        Ramstrand, N. 2000. Visual search strategies and decision making in observational gait analysis. Doctoral dissertation, LaTrobe University, Melbourne, Australia.

3.        Fish, D. J., and J. P. Nielsen. 1993. Clinical assessment of human gait. Journal of Prosthetics and Orthotics 5(2):39.

4.        Owen, E. 2019. Call to Action: Clinical Algorithms for the Prescription of Ankle-Foot Orthoses Are Needed: A commentary on "Physical Therapists' Use of Evaluation Measures to Inform the Prescription of Ankle-Foot Orthoses for Children with Cerebral Palsy." Physical & Occupational Therapy in Pediatrics  28:1-5.