This February, two related symposia at the world congress of the International Society for Prosthetics and Orthotics, in Hyderabad, India, addressed the latest thinking about gait biomechanics and the effect of ankle foot orthoses (AFOs).
“We were partly trying to get across the linkage between orthotics and prosthetics, and the importance of alignment,” said Elaine Owen, MSc, MCSP, a pediatric physical therapist at the Child Development Center in Bangor, North Wales, UK.
Owen specializes in children with neurological diseases, particularly cerebral palsy, and presented in both sessions.
This approach includes understanding the nature and function of rockers.
Owen draws a distinction between joint alignment and segment alignment; the former is the spatial relationship between the skeletal segments that constitute the joint, whereas the latter is the relationship between the two ends of any given segment (e.g., the foot, shank, or thigh).
“It’s all about how distal segment alignments dictate proximal segment alignments,” she said.
In practical terms, such insight helps researchers and clinicians analyze gait and modify either AFOs or prosthetic devices accordingly.
“The shank is reclined relative to the vertical at initial contact, then moves [through stance phase] to an inclined position,” Owen continued.
She emphasized, however, that the shank doesn’t maintain the same angular velocity throughout stance. Instead, it slows in midstance, where it is typically inclined 10° to 12°.
“If you’re treating a child who is learning to walk, or an adult with a neurological problem, you have to replicate that normal shank kinematic and reproduce that stable midstance position,” she explained.
According to Owen, many clinicians still teach standing with an aim toward keeping the shank vertical relative to the floor. Unfortunately, this makes balance more difficult. Instead, she said, the goal should be to recreate the slight forward lean that arises naturally during normal walking.
In presenting her findings, Owen described which alignment factors in an AFO-footwear combination (AFO-FC) help create the most efficient second rocker.
Owen noted that patients with stiffness in the knees and hips may need more midstance inclination from the AFO-FC, meaning a shank-to-vertical angle ranging from 15° to 19°.
Owen once had an epiphany about such matters while watching a woman learn to tightrope-walk in a park. The woman inclined her shank, put her knee over the middle of her foot, then carefully placed the other foot in front and transferred her weight.
Patients who find standing balance difficult need a stable platform, however, and in such cases the flat part of the shoe’s sole may be 110% of the shoe’s length.
“If you combine that with the right alignment of the shank, you can produce very stable standing, but you won’t be able to walk very far because it’s too stable,” Owen said.
If the children improve, the clinician can create a rocker to help produce heel rise at the right place in the gait cycle.
Owen noted that this is one realm in which her work with AFOs differs from that of prosthetists, in that the latter often use rounded, rocker sole shapes.
Studying and achieving such rocker effects was the subject of a presentation by Andrew H. Hansen, PhD, who is director of the Minneapolis VA Rehabilitation Engineering Research Program and associate professor of physical medicine and rehabilitation at the University of Minnesota.
“In the symposium, we discussed how able-bodied people walk, and focused on the effective rocker shapes we make when we walk,” Hansen said.
Hansen explained that an effective rocker involves the whole lower-limb system; the foot, ankle, and knee are subsystems examined for clinical and research purposes, but they all work together.
When individuals are walking, the radius of the shape is about a third of leg length, according to Hansen. But when people stand and sway, the rollover shape is flatter, with a radius roughly equal to the person’s height. The center of mass remains at the waist in either case, of course, so standing is inherently more stable.
Hansen’s examination of subsystems has clinical implications for the amputee population. For example, a patient with a below-knee amputation would require a prosthesis consisting of the ankle, foot, and shoe, so the clinician would focus on ankle-foot rollover shapes. In those with an above-knee amputation, the clinician should consider how the prosthetic knee will affect rollover shapes.
“We’re looking at these shapes and trying to use them to help us design better prostheses, to try and mimic those [natural rollover] shapes,” he said. “We can also use them to evaluate current components, to see how well they mimic the natural shapes.
Researchers have also used rollover shape to study the effectiveness of AFOs.9,10 The author of several such studies—and a collaborator of Hansen’s—is Stefania Fatone, PhD, BPO(Hons), a research associate professor of physical medicine and rehabilitation at Northwestern University’s Feinberg School of Medicine in Evanston, IL. At the ISPO conference, Fatone helped tie together the work by Owen and Hansen in addition to discussing her own.
In her own research, Fatone is examining the rollover shapes exhibited by patients with pathologies such as stroke and CP, and how orthotic devices affect them.
She noted that in stroke patients, neuromuscular impairment often leads to an equinovarus foot posture, so that the patients make contact with the ground either with the foot flat or with the forefoot.
According to Fatone, Elaine Owen is determining how to affect those third and fourth rockers, as noted above, via her sole shapes.
The AFO-FC approach has as its fundamental biomechanical goal the control of segment kinematics.
One problem with the analyses performed so far, she noted, is that they haven’t been adequately systematic. Researchers haven’t taken one AFO and modified it incrementally; rather, they’ve changed the whole system.
Another issue is how well the research in children with CP will translate into patients with other conditions such as poststroke impairment.
The treatment goals are the same, in any case—better gait biomechanics and safer, more efficient ambulation with lower risk of falls.
“The diagnosis isn’t the thing that gets you there; it’s what impairments you want the orthosis to address,” she said.
Yamamoto and her colleagues have used the AFO in clinical applications, research, and gait training of stroke patients.
Yamamoto noted that the new AFO has limitations; it doesn’t work well in patients with very limited walking ability, for example, so in those cases she and her colleagues use knee-ankle-foot orthoses (KAFOs) for gait training. On the other hand, the AFO-OD appears to have a wide range of clinical applications.
“It was developed for stroke patients, but we’ve found that it improves the gait of patients with other diseases such as incomplete spinal cord injury, spina bifida, and peripheral nerve paralysis,” she wrote.
Is there a quack in the house?
During the second symposium, Elain Owen set an alarm on her iPad to let her know when she had a minute left to speak. The alarm, as suggested earlier, emitted the sound of a loudly quacking duck.
The quacking startled everyone when it began, but Owen quickly discovered that she couldn’t turn it off. People in the audience began to laugh, and the laughter spread. Owen, flustered, put the iPad in the corner, but it kept quacking, and by then everyone, including the presenter, was laughing so hard it was impossible to go on.
In this match, ultimately, Australia defeated Wales: Stefania Fatone (originally from Melbourne) strode forward, grabbed the iPad, and escorted the unruly duck out into the hall.
1. Perry J. Normal and pathologic gait. In: Hsu J, Michael J, Fisk J, eds. AAOS Atlas of Orthoses and Assistive Devices. 4th ed. Philadelphia: Mosby Elsevier; 2008.
2. Owen E. The importance of being earnest about shank and thigh kinematics, especially when using AFOs. Prosthet Orthot Int 2010; 34(3):254-269.
3. Owen E. From stable standing to rock and roll walking. Presented at International Society of Prosthetics and Orthotics 2013 World Congress, Hyderabad, India, February 2013.
4. Hansen A, Childress D, Knox E. Rollover shapes of human locomotor systems: effects of walking speed. Clin Biomech 2004;19(4):407-414.
5. Hansen A, Childress D. Effects of adding weight to the torso on rollover characteristics of walking. J Rehabil Res Dev 2005; 42(3):381-390.
6. Hansen A, Childress D. Effects of shoe heel height on biological rollover characteristics during walking. J Rehabil Res Dev 2004; 41(4):547-554.
7. Wang C, Hansen A. Responses of able bodied persons to changes in shoe rocker radius during walking: changes in ankle kinematics to maintain a consistent rollover shape. J Biomech 2010; 43(12):2288-2293.
8. Hansen A. The quest to improve rocker effects in O&P. LER 2010;2(4):35-39.
9. Fatone S, Hansen A. Effect of ankle-foot orthosis on rollover shape in adults with hemiplegia. J Rehabil Res Dev 2007;44(1):11-20.
10. Fatone S, Sorci E, Hansen A. Effects of clinically prescribed ankle-foot orthoses on ankle foot rollover shapes: a case series. J Prosthet Orthot 2009;21(4):196-203.
11. Fatone S. “Rocking with Orthotics.” Presented at International Society of Prosthetics and Orthotics 2013 World Congress, Hyderabad, India, February 2013.
12. Yamamoto S, Masako F, Tadashi Y. Change of rocker function in the gait of stroke patients using an ankle foot orthosis with an oil damper: immediate changes and the short-term effects. Presented at International Society of Prosthetics and Orthotics 2013 World Congress, Hyderabad, India, February 2013.