The New Generation of AFOs

A Historical Perspective

As in the film Forrest Gump, orthoses were still commonly referred to as braces and were viewed more as restrictive apparatuses with only a minimal therapeutic benefit until a few years ago. They sometimes even resulted in serious complications for the patients.

The countless failures of orthotic treatments can frequently be traced back to the poor functionality of the components employed, which resulted in the poor functionality of the orthosis as a whole. This was exacerbated by the heaviness of traditional construction materials such as leather and steel. Without intelligent calculation systems to determine the expected loads, it was not possible to perform the necessary complex calculations to plan orthotic treatments precisely. As a result, the function, stability, and weight of the orthoses was often inadequate for the respective patients.

Challenges in making optimal use of new materials, innovative components, and intelligent calculation systems mean that failures are still commonplace in orthoses that are supplied to patients today. Rigid and heavy designs still represent the standard. Following negative experiences with inadequate and faulty orthoses, wheelchairs are unfortunately still the recommended treatment in certain cases of spinal cord injuries in many hospitals.

When the potential of orthotic treatment is not realized, patients who might be capable of an improved gait are locked in a fixed ankle-foot position. This, in turn, leads to ineffective gait training, resulting in a missed opportunity to restore the patients' physiological gait.

Requirements of AFOs

The aim of treating patients who are affected by neurological conditions with orthoses is to achieve the greatest possible approximation to the physiological gait. This goal requires both the orthosis as a whole and its individual components to have high functionality. As the orthosis is often subject to extreme loads, it is essential that it be constructed so as to be able to withstand them accordingly. Alongside high resilience, low weight is equally important for a successful orthotic treatment and the user's acceptance of the device.

Versatility in an orthosis is important in rehabilitation. The AFO must fulfill the purposes of medical aids and provide a therapeutic benefit. For instance, the device should support early gait training, be it with a walker, crutches, canes, or parallel bars.

While improvement in stance stability is most important during rehabilitation, the movements that a patient performs must also not be limited, or only to the smallest extent possible. This is the only means of ensuring that the success achieved during gait training is maintained beyond rehabilitation.

In his article about pediatric orthoses for children with cerebral palsy (CP), Grunt states that effective orthoses are essential in supporting physiotherapy as well as surgical treatment.¹ In some cases, the orthotic fitting needs to be complemented by orthopedic shoes or shoe modifications or adjustments. Years later, Novacheck et al. and Owen et al. mention that depending on the patient's pathological gait, the physician's requirements, and the goal of physiotherapy, the orthotist must produce an orthosis that provides the required lever effect.^2,3

Additionally, the result of surgery should be sustained with an orthosis that ensures correct alignment and an adjustable range of motion (ROM) without interfering with physiotherapy. This is the point where orthotists face practical difficulties because of a lack of options of adjusting orthoses to loading forces, sizes, activity levels, and required joint moments.

Limitations of Current Orthotic Treatments

Novacheck et al. mention the conflicting goals in the orthotic treatment of children affected by CP. "One orthosis may not be optimal to address all the goals. While a hinged AFO may help promote transitional activities from the floor to standing, it may also promote crouch gait while walking. Difference of opinion in goal setting can exist between physiatrists, physical therapists, and orthopedists."²

The choice of device depends also on the severity and the characteristics of the disease pattern. Some of the best-known orthotic treatment methods are summarized here, providing a critical view of their advantages and disadvantages.

Patients with CP may simply be treated with orthopedic inserts with a sensorimotor insole. This may also be integrated into a supramalleolar orthosis (SMO). The University of California Biomechanics Lab (UCBL) foot orthosis and SMOs provide hindfoot varus/valgus control and improve the foot-progression angle and stability in stance. If the Achilles tendon area is not covered, the SMOs also possess dynamic features. In comparison to AFOs, however, they do not passively control sagittal-plane ankle joint alignment.

Solid AFOs (SAFOs) made of polypropylene or carbon do not allow any movement in the ankle and are commonly used for patients with severe spasticity. The so-called floor reaction AFO (FRAFO) with ventral shell also blocks any movement of the anatomical ankle joint, in the interest of enabling knee extension in terminal stance.

Classical hinged AFOs block any plantarflexion and enable dorsiflexion with a defined pivot point in the anatomical ankle joint. They are commonly designed with elastomer spring joints without spring effect or dorsiflexion stop. The alternatively used coil springs in the joints do not have a high spring effect. AFOs with spring effect, referred to as posterior leaf spring AFOs, on the other hand, do not have a defined pivot point, a defined or adjustable ROM, nor an adjustable alignment. Carbon material provides a higher spring in contrast to similar AFOs made of polypropylene.

Next Generation Adjustable System Ankle Joint

A modern orthotic concept can be expected to be optimally adjustable to the patient's needs.

Both dynamic and static AFOs should be produced with an adjustable ankle joint to treat the pathological gait as well as provide the needed ROM. It is necessary to be able to adjust the orthosis to the gait pattern, since the position of the patient's foot during the production of the cast inevitably differs from its position under load. An adjustable ROM and exchangeable spring units make it possible to react to changes in the pathological gait that can occur during treatment.

Following this rationale, the German company FIOR & GENTZ developed a new adjustable ankle joint system, which was patented in 2013 and has been widely studied and used in Europe and elsewhere. The NEURO SWING system ankle joint provides three adjustments—spring force, orthosis alignment, and ROM—that can be changed separately and do not influence each other. It is fabricated in carbon fiber and Kevlar.

Advantages of the Modern Joint Design

Adjustable plantarflexion
As an effect of the traditional locked plantarflexion, excessive torque is applied to the lower leg and transmitted to the knee. This puts high demand on the quadriceps femoris muscle (similar to walking with a ski boot) and can cause an increased knee hyperflexion in patients with weak quadriceps and gastrocnemius muscles. If physiological plantarflexion is permitted by the orthosis, it may be used to treat insufficient muscles. Renata Horst, physical therapist and author of books about neuro-orthopedic rehabilitation, writes that the right cerebral connections are established via motor impulses, and single muscle groups are strengthened with targeted muscle training.⁴ This makes it possible to counteract the advancing muscle atrophy, as stated by Goetz et al.⁵

Physiological heel rocker function
Because of the anatomical pivot point, there is a lever arm at the hindfoot, which leads from the point of heel strike through the calcaneus to the ankle. On initial contact, the body weight triggers a passive foot dropping through this lever that is controlled by the eccentric work of the tibialis anterior muscle. Other orthoses, such as the posterior leaf spring AFO, do not allow this lever. The NEURO SWING system ankle joint enables the passive plantarflextion through the defined pivot point and the adjustable ROM in plantarflexion.This movement is controlled by the dorsal spring unit.

Adjustable ankle alignment
To provide the required lever effect, it is necessary to use an adjustable ankle joint. First, the orthosis can be aligned to match the patient's pathological gait, and second, it can be adapted when changes in gait occur. The NEURO SWING system ankle joint allows a fine adjustment of the orthosis as needed. Owen recommends determining the individual inclination of the lower leg, where a basic value should be 10-12 degrees of the shank-to-vertical Angle (SVA).³

Adjustable ROM
After surgery or in patients who are treated with antispasmodics, it may be necessary to partially or completely lock the ROM of an orthosis and only allow it again later during the course of the therapy. Thus, an ankle joint with an individually adjustable ROM must be mounted in the AFO. It may also make sense to treat patients with CP or stroke with a static AFO when physiotherapeutic success cannot generally be expected, or the foot is severely deformed.

High spring forces
The pathological gait of some stroke patients requires very high spring forces. The NEURO SWING system ankle joint achieves those with disc springs that are stacked to compact spring units, far exceeding the effects possible with conventional elastomer or coil spring joints. Two spring units placed opposite of each other have a positive effect on the user's sense of balance, which results in the stabilization of walking and standing.

Exchangeable spring units
The spring force in plantarflexion and dorsiflexion can be adjusted to the patient's pathological gait by using spring units of various strengths. This allows a greater range of adjustments than pre-loading springs in conventional AFOs with ankle joints such as an articulated metal AFO. This stored energy is returned from terminal stance on and supports heel lifts from the ground dynamically.

Pathological Gait Classification Systems for a Standardized Orthotic Treatment

The Amsterdam Gait Classification was developed especially for patients with CP at the Vrije Universiteit (VU University) Medical Center in Amsterdam. It classifies five types of gait according to their knee position and foot-floor contact in mid-stance (Figure 1). The classification is equally suitable for patients who are affected either unilaterally or bilaterally and is recommended for a standardized orthotic treatment.

The N.A.P. Gait Classification (Figure 2)⁴ describes the knee position in mid-stance as a compensation for the talus position to enable a simple assessment of the pathological gait. Two gait types are being distinguished, one with hyperextension and one with hyperflexion, each either with an inversion or an eversion of the lower ankle joint.

The Amsterdam and N.A.P. Gait Classifications make it possible to classify CP and stroke patients quickly according to their gait patterns. This facilitates interdisciplinary communication, selection of the right treatment, standardized orthotic treatments, and quality control.

The recommended orthosis is customized according to the pathological gait, weight, manual muscle test, the available ROM, and activity level.

Planning the Orthosis and Componentry Selection

In daily practice, selection of orthotic componentry and material is often informed by personal experience, preference, and weight reference but without a solid or consistent consideration of the loading forces during gait.

A software orthosis configurator selects the optimal combination of system components based on patient data. The system selects the correct ankle size, spring forces, and componentry. Moreover, by requiring precise information and using an elaborate calculating system, the configurator also gives recommendations for the foot piece, dorsiflexion stop, orthosis type, orthosis shells and, depending on the chosen configuration, further orthosis-specific details.

Research and Publications

The effectiveness of the new-generation ankle joint, specifically the NEURO SWING system, has been investigated in a wide range of studies. Representative of the published works, the findings of a large-scale Dutch study by Kerkum et al. in which 32 children with spastic CP were treated with the NEURO SWING system ankle joint, are listed here.⁶

• Increasing of lower-leg incline, joint angle, and joint moments in mid-stance via increasing of pitch
The insertion of wedges under a rigid AFO (tuning) leads to a significant increase in the lower-leg incline and the knee and hip flexion in mid-stance and a significant increase in the knee flexion moment in mid-stance.

• Increasing of joint moments in mid-stance via increasing foot piece rigidity
Increasing the rigidity of the foot piece leads to a significant reduction in the knee flexion moment in mid-stance.

• The mechanical properties of the NEURO SWING system ankle joint
As the spring units of the NEURO SWING system ankle joint are interchangeable, the AFO can be adapted to reflect the patient's individual gait. The design gives the spring units a threshold value below which there is no movement in the mechanical ankle joint (compaction of spring units) when there are only small moments in the anatomical ankle joint. This threshold value supports knee extension at the beginning of the stance phase.

• The optimal spring force for CP patients with increased knee flexion in mid-stance
The red and yellow spring units of the NEURO SWING system ankle joint are best suited for children with CP who present with increased knee flexion in mid-stance (gait type 4 and 5). The yellow spring unit offers an optimal balance of spring force and freedom of movement and makes the best contribution to improving the push-off with the resulting high energy return. The red spring unit standardizes the joint angle the most efficiently with its relatively high spring unit and low freedom of movement.

• Reduced energy consumption when walking with an AFO and optimal spring force
Thanks to the optimal spring force, the patient can significantly reduce his energy consumption when walking with an AFO compared with walking wearing just shoes. This is due to the improvement of the joint angle and moments in the stance phase rather than the supporting of the push-off.

• Improved knee angle and lower-leg incline when walking with an AFO and optimal spring force
The optimal spring force makes it possible to significantly reduce CP patients' excessive knee flexion in mid-stance when walking with an AFO and the lower-leg incline is significantly reduced when walking with an AFO compared with walking wearing just shoes.

• No time needed to get used to the new AFO
After acclimating to the AFO, no further improvement is noted in the important gait parameters (time-distance parameter, joint angles, and joint moments). As such, no time for getting used to the appliance needs to be provided in routine clinical practice.

The Future of AFOs

In the past decades, O&P has seen amazing developments in prosthetic technology, but only recently has the research and development focus shifted to the orthotics world. Notwithstanding the challenges of contending with an outdated reimbursement system that was designed around products and concepts from many decades ago, it is an exciting time to be an orthotist.

The NEURO SWING Adjustable System Ankle Joint is a prime example of next generation orthotics, inspired and validated by scientific research, and supported by scientific evidence and clinical outcome measurements. As such, the technology strengthens our role as expert care providers and active members of the rehabilitation team who play a pivotal role in achieving the best possible results for our patients.

Santiago Muñoz, CPO, FAAOP, is president and CEO of Equation Orthotic Technologies and clinical educator specialist of Fior & Gentz. He can be reached at santiago@equationortech.com.

REFERENCES

1.        Grunt, S. 2007. Geh-Orthesen bei Kindern mit Cerebralparese. Paediatrica 18(6):30-34.

2.        Novacheck, T. F., G. J. Kroll, and G. Gent et al. 2009. Orthoses. In: Gage JR et al. (ed.): The Identification and Treatment of Gait Problems in Cerebral Palsy, 2nd edi­tion. London: Mac Keith Press, p. 327-348.

3.        Owen, E. 2010. The Importance of Being Earnest about Shank and Thigh Kinematics especially when using Ankle-Foot Orthoses. Prosthetics and Orthotics International 34(3):254-269.

4.        Horst, R. 2005. Motorisches Strategietraining und PNF. Stuttgart: Georg Thieme.

5.        Götz-Neumann, K.  2006. Gehen verstehen. Ganganalyse in der Physiotherapie. Stuttgart: Georg Thieme.

6.        Kerkum, Y. L.  2015. Maximizing the efficacy of ankle foot orthoses in children with cerebral palsy. Dissertation. Vrije Universiteit medical center Amsterdam.

Other Resources

1.        Becher, J. G. 2002. Pediatric Rehabilitation in Children with Cerebral Palsy: General Management, Classification of Motor Disorders. Journal of Prosthetics and Orthotics 14(4):143-149.

2.        Brehm, M. A. 2007. The Clinical Assessment of Energy Expenditure in Pathological Gait. Dissertation. Vrije Universiteit/medical center Amsterdam.

3.        Döderlein, L. 2007. Infantile Zerebralparese. Diagnostik, konservative und operative Therapie. Darmstadt: Steinkopff.

4.        Gage, J. R. 2009. Gait Pathology in Individuals with Cerebral Palsy. Introduction and Overview. In: Gage JR et al. (ed.): The Identification and Treatment of Gait Problems in Cerebral Palsy, 2nd edition. London: Mac Keith Press, p. 65.

5.        Gage, J. R, et al. 2009. Section 5. Operative Treatment. In: Gage JR et al. (ed.): The Identification and Treatment of Gait Problems in Cerebral Palsy, 2nd edi­tion. London: Mac Keith Press, p. 381-578.

6.        Graham, H. K., A. Harvey, and J. Rodda et al.  2004. The Functional Mobility Scale (FMS). Journal of Pediatric Orthopaedics 24(5):514–520.

7.        Krämer, J. 1996. Orthopädie. 4th edition. Berlin: Springer.

8.        Molenaers, G., and K. Desloovere. 2009. Pharmacologic Treatment with Botulinum Toxin. In: Gage JR et al. (ed.): The Identification and Treatment of Gait Problems in Cerebral Palsy, 2nd edition. London: Mac Keith Press, p. 363-380.

9.        Novacheck, T. F. 2008. Orthoses for cerebral palsy. In: Hsu JD, Michael JW, Fisk JR (ed.): AAOS Atlas of Orthoses and Assistive Devices, 4th edition. Philadelphia: Mosby/Elsevier, p. 487-500.

10.     Õunpuu, S., and P. Thomason, and A. Harvey. 2009. Classification of Cerebral Palsy and Patterns of Gait Pathology. In: Gage JR et al. (ed.): The Identification and Treatment of Gait Problems in Cerebral Palsy, 2nd edition. London: Mac Keith Press, p. 147-166.

11.     Peacock, W. J. 2009. The Pathophysiology of Spasticity. In: Gage JR et al. (ed.): The Identification and Treatment of Gait Problems in Cerebral Palsy, 2nd edi­tion. London: Mac Keith Press, p. 89-98.

Websites

1.        A Concept for the Orthotic Treatment of Gait Problems in Cerebral Palsy - fior-gentz.de.

www.fior-gentz.de/fileadmin/user_upload/pdf/handbuecher/PR0221-GB_CP-Handbuch_Englisch.pdf. Accessed 15 Sep 2018.

2.        CP Guide - fior-gentz.de.

www.fior-gentz.de/fileadmin/user_upload/pdf/handbuecher/EN_CP_Guide.pdf. Accessed 20 Sep 2018

3.        Guide to Spinal Cord Injuries - fior-gentz.de.

www.fior-gentz.de/fileadmin/user_upload/pdf/handbuecher/EN_Spinal_Cord_Injuries_Guide.pdf. Accessed 16 Sep 2018.

4.        Stroke Guide - fior-gentz.de.

www.fior-gentz.de/fileadmin/user_upload/pdf/handbuecher/EN_Apoplexy_Guide.pdf. Accessed 21 Sep 2018.