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Cusick: Radtka Response Paper

On Orthotic Efficacy Research: A Critique of a Recently-Published Paper

by Beverly Cusick, PT, MS • (January 1998)

This paper is a condensed version of a response paper originally submitted for publication in Physical Therapy on July 7, 1997. This condensed version was submitted as a letter to the editor to Physical Therapy on December 3, 1997, and rejected by the editor on December 16, 1997.

The original Radtka article was published in Physical Therapy, Volume 77, Number 4: April 1997 (ppg 395-409).

Copyright 1998 by Beverly Cusick, PT, MS, COF. (866) 410-8062   |   info@gaitways.com

Topics:
On the Selection of Variables

On the Orthotic Devices Used

On the Scope of the Investigation

On the Research Method

On the Clinical Recommendations

On the Discussion

Author's Thanks

References

Introduction

We all know that clinical research is arduous at best, even with the aid of a computerized gait analysis lab. I fully appreciate and commend the effort expended to undertake any clinical research project. Such efforts can drive many of our rehabilitation management decisions. My thanks to all clinical researchers, and particularly to Sandra Radtka and her research team, for making the effort.

Having read most of the existing literature (published in the English language) on orthotic efficacy for children with cerebral palsy (CP), I am writing to discuss several elements which concerned me about the research report by Radtka, S.A., S.R. Skinner, D.M. Dixon, and M.E. Johanson (April 1997), in which they compare certain effects of two ankle-foot orthoses on selected gait features of 10 mildly-involved children with spastic diplegic and hemiplegic CP. I hope, in detailing these concerns, to encourage future researchers to find new approaches to efficacy research regarding rehabilitation strategies for children with CP.

Topics:
On the Selection of Variables

On the Orthotic Devices Used

On the Scope of the Investigation

On the Research Method

On the Clinical Recommendations

On the Discussion

Author's Thanks

References

Back to Top...

On the Selection of Variables...

Radiologic evidence of foot joint alignment: The biomechanical and kinesiologic relationships between joint alignment and muscle function - and between malalignment and muscle dysfunction or imbalances - is well-known. Thomas et al (1996) imposed changes in load-bearing joint alignment (using rigid tape) on 4 nondisabled adults, mimicking 3 configurations seen commonly in children with diplegic CP, and produced spatio-temporal gait characteristics and patterns of EMG output which closely approximated those reported for comparable children with CP.

Citing Ricks and Eilert's study, in which they determined that bone and joint alignment was not achieved in ankle-foot orthoses (AFOs) which are made at their facility, Radtka and others, hereafter referred to as "the researchers", omitted the variable of radiologic evidence of change in weight-bearing foot and ankle alignment. Had they perhaps exercised less bias and acknowledged the photographed, radiologic evidence of orthotically-induced improvement of foot joint alignment, presented by three other authors listed in their bibliography [Hylton (1989,1990) and Rosenthal (1984), listed by the researchers], they might have included foot joint alignment as a possible influence on outcome.

As I commonly see standard AFO's made with flat plantar surfaces, everted calcaneal sections and bulging medial midfoot support walls, fully accommodating pronation deformity while achieving 0 degrees at the ankle joint, I wonder if the solid AFOs issued by the researchers meet basic foot joint alignment criteria. Weightbearing X-rays would answer this question.

Distinguishing features of the DAFO style of orthosis include the way the foot is contained by the combination of contouring in the floor, thin "dorsal wings" which are usually closed by a strap over the instep, and a hallux adductor strap. I suggest that the foot-containment features of the modified DAFO versus the (virtually undescribed) solid AFO could be effectively evaluated and compared radiologically, and their comparative durability in this regard might also be considered at the end of the data-gathering period.

Topics:
On the Selection of Variables

On the Orthotic Devices Used

On the Scope of the Investigation

On the Research Method

On the Clinical Recommendations

On the Discussion

Author's Thanks

References

Back to Top...

On the Orthotic Devices Used: "...Solid, Dynamic, and No Ankle-Foot Orthoses..."

The title of this paper is perhaps misleading, as the typical pediatric rehabilitation clinician's working definition of a "dynamic" ankle-foot orthoses (DAFO) is the "free plantar flexion (PF)", posterior U-cut style, with a supra-malleolar-length shaft section. Other "dynamic" orthotic designs which restrict ankle motion - such as "the DAFO with PF stop" - require specific description. Given a photograph of the modified DAFO and none of the alternative, "solid AFO", the reader cannot competently compare the foot support features, shaft lengths and strapping systems of the two devices. As the proximal shaft trim lines are described for each device using different reference points on the limb, comparison is impeded.

However, by computing the relative shaft lengths as they are described, they could conceivably be more similar to than different from each other. If this is so, the investigation more accurately explores some effects on dynamic equinus gait of small variances in solid AFO shaft length, material thickness or rigidity, and foot enclosure properties. Furthermore, the flexibility of floor in the forefoot area of either orthotic device is not described, and therefore escapes consideration as a potential influence on propulsion moment and ensuing swing phase kinematics, and on limb rotation effects in stance and swing. (The modified DAFO toe area appears to prohibit sagittal-plane motion.)
Topics:
On the Selection of Variables

On the Orthotic Devices Used

On the Scope of the Investigation

On the Research Method

On the Clinical Recommendations

On the Discussion

Author's Thanks

References

Back to Top...

On the Scope of the Investigation

Kinematic vs. kinetic data

The researchers state that children with CP show kinematic, muscle firing and temporal-distance gait pathology. In recent years, several other researchers have advised us that force plate data and kinetics - elements of energy storage and release - are among the most functionally relevant components of gait analysis.(2,3,4,5)Force plate data, ground reaction forces, acceleration of body segments and of the center of mass, calculated joint moments, eccentric (negative) and concentric (positive) muscle action, all comprise components of kinetics. Concentric triceps surae action contributes about 45% of the accelerating moment to forward walking at early propulsion.(3,6) Therefore, the moment of muscle firing most important to the production of forward accelerating power in gait is heel-rise, at early propulsion (or third rocker).

The researchers did not obtain the data required to calculate joint angles or muscle firing status at propulsion, or to compute related ankle joint moments or power. Though they listed in their bibliography Berger and Dietz's study (1982), showing reduced triceps surae EMG activity in children with CP and equinus gait, they neither discuss it nor the well-documented, and possibly more significant problems of triceps surae weakness, reduced EMG activity in quadriceps and triceps surae, and reduced ankle joint power at propulsion shown by children with CP.(2,4,8)

Non-orthotic approaches to managing "functional equinus gait"

While this list is by no means complete, equinus gait management alternatives for children with CP currently include the following:

Preliminary restoration of adequate soft tissue extensibility: Sutherland et al (1988) report that children of age 7 years show [a median value of] 15 of maximum passive ankle DF ROM with knee extended. The researchers' subjects with 5 maximum DF therefore demonstrate muscle hypoextensiblity. Keeping the foot joints fully congruent, I typically measure maximum DF at nearer to 25 degrees in children of this age. L1 end range, or resting muscle length (a.k.a. "first catch", "functional, "initial" or "R1" end range), is the length at which actin and myosin filaments show optimum overlap for contractile force generation.(10,11)

I usually encounter L1 at > 0 DF in nondisabled, school-aged children. The researchers neither report resting (or functional) muscle length values, nor do they describe how (or if) ankle DF ROM was measured or reliability-tested. Ankle DF measurements can be inflated significantly by manually pronating the foot.

For many fully-ambulatory children with CP and equinus gait, resting muscle length has been functionally reduced, by adaptive mechanisms, at both hamstrings and triceps surae, even though the same tissues can be forcibly stretched further under maximum load.(,4,8,10,11) A fundamental key to reducing the pathomechanics of equinus gait, and compensatory stance-phase foot pronation or knee hyperextension (or both), is the restoration of adequate resting length of, and reduced stiffness through the range of elongation in, the triceps surae and hamstring muscles(12)

I find I can achieve this objective for children with mild involvement by using periodic (annual or biannual) serial casting, occasionally supplemented with neurolytic injections in the presence of clonus, and given compliance in using routine positioning to maintain hamstrings length and ankle dorsiflexion (DF) range of motion (ROM). Usually, wedging the heel and allowing upto 10 degrees of ankle PF to occur adequately protects the foot joints from pronatory strain, affords heel loading and allows tibial progression. Rarely, surgical lengthening is required.

As the modified DAFO used by the researchers bears no proximal shaft strap (does the standard AFO?), one might presume that the tibial shaft would progress during second rocker by virtue of the open anterior shaft section. The lack of evidence of any notable stance phase DF in the modified DAFO might be attributed to the subjects' lack of adequate triceps surae and hamstrings extensibility.

Neuromuscular electrical stimulation (NMES) to the functioning calf muscles: Carmick (1995) describes her experience using functional NMES to markedly reduce functional equinus in stance and gait for many ambulatory children with CP, using videotapes and foot print data to substantiate her observations.

The choice of two solid-ankle orthotic devices

Orthotic design options for children with CP have multiplied over the last 20 years, each design offering a unique set of biomechanical and functional features and influences. Therefore, the decision to compare a few gait features using 2 solid-ankle devices must exclude consideration of all the other orthotic designs now available for children with mild spastic CP.

The expanding field of orthotic design specifications and options

Given the following AFO design options (which is no doubt incomplete), even the most elaborate knowledge of the comparative contributions to selected features of gait and muscle action of only two design variations of a solid-ankle orthosis offers the rehabilitation team little guidance for making a client-oriented, orthotic prescription decision. New design components include:

  • Foot and Leg Enclosure: Dorsal instep extensions or "wings" wrap the lesser tarsus and metatarsal shafts in a thin, plastic ectoskeleton. The modified DAFO in the study by Radtka and others features dorsal wings. The same concept is maximized in the R-Wrap Orthosis, developed by John Russell, CP, BOCO [Collier Rehab Systems, Pleasant Hill, CA], which is a total-contact, ultra-thin orthotic packaging system with much in common in principle with serial casting.

  • Solid AFO Trim Lines and Alignment:Advancing trim lines: Trimming increasingly more plastic off of the area around the malleoli on a standard AFO, gradually converting a standard AFO to a posterior leaf spring design.

  • Posterior leaf spring: This is a DF-assist device for a drop-foot - vs. spastic supination - problem in swing phase of gait.

  • Shaft length alternatives: from ankle height to 3 cm. distal to the fibular head.

  • Tall shaft AFO with deep posterior U-Cut: This modified solid AFO presents clients with a variety of (slightly flattened ) shaft panel lengths and various strapping systems - rigid and elasticized - applied at various positions on the shaft to alter the available degrees of freedom at the ankle joint.

  • A flexible toe break: Able to bend freely at the metatarsophalangeal joints.

  • A full, calcaneal cut-out to allow direct contact between the client's plantar heel pad and the walking surface, intended to enhance proprioceptive and tactile sensory input.Various angles of ankle joint DF.

  • Articulation: Elasticized ankle DF assists applied to articulated AFOs that feature different motion stop capabilities, from no stop at all to 0 degrees of PF. The newly-developed R-Wrap, total enclosure, articulating AFO offers limited DF ROM.Modular, adjustable-component AFO, with dual-axis ankle joint, metal uprights, plastic cuff and an ankle-height, DAFO-style foot section.

Topics:
On the Selection of Variables

On the Orthotic Devices Used

On the Scope of the Investigation

On the Research Method

On the Clinical Recommendations

On the Discussion

Author's Thanks

References

Back to Top...

On the Research Method

Introducing orthotic conditions: The researchers describe the initial period of orthotic intervention (no orthoses) this way (page 398, column 2): "barefoot with no orthoses for initial 2-week period," followed by 1 month in solid AFOs, then "barefoot with no orthoses for second 2-week period," followed by 1 month in DAFOs with PF stop. Did the study group spend two, non-orthotic trial periods utterly unshod? Shoes are a potentially-influential research variable, and should be considered either in combination with orthoses or in isolation (14).

Had the researchers standardized and fully described the shoes worn by each child, noting all aspects of design style and configuration including the material of the upper (leather, canvas, or a combination); the heel height and shape (wedged, flared at the base, beveled at the contact point); the ankle-height; and the shape and flexibility of the toe break, their potential influence on outcome might be better understood.

The researchers presume that that after each orthotic intervention, a return to baseline status of EMG activity and gait kinematics can be expected to occur, and evaluated their test-retest reliability accordingly. Had they assessed test-retest reliability for all gait parameters prior to the initiation of the study, they could have avoided the possibility of having introduced a learning effect.(15)

The subjects: Hemiparetic and diparetic children were included in the same study, with no acknowledgment of the differences in their gait pathomechanics as they relate to their markedly different distributions of involvement. I might have found the results more meaningful had all of the subjects shared the same diagnosis.

Nevertheless, to their credit, and unlike most other orthotic efficacy researchers, they disclose a few details regarding their 10 subjects' collective musculoskeletal and ambulatory status, recent surgical history (none in the "past year", presumably meaning the year prior to the data-gathering period), their ages, ambulatory status (independent without devices), evidence of ROM limitations at 3 joints, spasticity scores, and orthotic management prior to the study. Half of the study group wore articulated AFOs prior to the study. To apply the results to the management of my clients, I would need to learn these additional things:

  • Unique anthropometric features, particularly exceptions to average height and weight for age.
  • Surgical history prior to the year preceding the study.
  • Hip abduction ROM at resting length ("first catch" or L1) in hip extension.
  • Torsional status at the femur(s) and tibio-fibular unit(s).
  • Thigh/foot angles with feet aligned in full congruity.
  • Foot progression angle problems, such as in-toeing, out-toeing, or "windblowing" to one side.
  • The features of spinal and pelvic alignment in all 3 planes, in stance and gait.
  • Foot supination or pronation during stance and swing phases of gait.
  • Isolated, active ankle DF ROM with knee extended or flexed.
  • Antigravity muscle strength of the hip extensors, quadriceps, hamstrings and triceps surae in functional context and in isolation, including weightbearing joint angles in static stance and a count of full-height, unilateral heel rises.
  • Quantified standing balance on 2 feet, one foot, and either foot.
  • Endurance, quantified on level and inclined treadmill.

Replicability: Other researchers could not replicate this project, for lack of relevant orthotic and shoe design specifications; and for lack of instruction as to the procedures used to apply EMG surface electrodes to the calf musculature while wearing the orthoses, and to apply contact foot switches to the shoes (exterior sole surface? interior floor?).

The use of equipment: Contact-closing foot switches were placed along and taped to the plantar surfaces of the feet for tests without AFOs, and to (an undisclosed surface on) the shoes for tests with orthoses. Had the researchers attached the foot switches to the shoes for all four test conditions, and accounted for the influence of the shoes as a non-orthotic condition, the resulting data would more closely address the influence of the orthoses as super-imposed variables.

To collect kinematic data, the researchers attached reflective markers to the orthoses and the shoes, presumably on the assumption that the orthoses securely hold the hindfeet, and that the shoes securely seat the orthoses without pistoning or displacement. The researchers evidently did not justify their marker placements. Shoes worn over orthoses are often 2 or more sizes too big for the child, to accommodate the added size of the orthotic device. As a solid-ankle orthosis cannot be expected to remain stable in a shoe, I regard the results based on kinematic data as dubious. And, though most gait analysis labs are equipped with force plates, none was used in this study, so ankle moment and power at propulsion was not assessed.

Data Analysis: Presuming the recorded data is accurate, the determination that both orthoses showed positive influences on stride length, cadence and magnitude of PF in stance phase of gait, compared with no orthoses, is noteworthy. However, the averaged data comparing the effects of the two orthotic conditions shows that two AFOs, which apparently differ little from each other in basic design and shaft length, also differ little from each other in their influence on gait pathomechanics. Statistically, no effects on walking speed were noted comparing the three conditions.

Topics:
On the Selection of Variables

On the Orthotic Devices Used

On the Scope of the Investigation

On the Research Method

On the Clinical Recommendations

On the Discussion

Author's Thanks

References

Back to Top...

On the Clinical Recommendations

Apparently, the researchers used individual outcome data to generate orthotic prescriptions for individual subjects, disregarding the statistical means and trends shown by the entire group. If this is the researcher's modus operandi, then why strive to collect statistical data about groups which loses its significance when taken in individual context?

For 5 of the subjects, the modified DAFO was recommended on the basis of "clinical examination of individual subjects", the elements of which are not detailed. It seems that the consumer's preference for features of cosmesis and weight, and perhaps comfort, also drove this prescription decision - 3 factors which were not evaluated. Previous use of an articulated orthosis - successful or otherwise - was dismissed evidently, as no subjects received one after the study.

Topics:
On the Selection of Variables

On the Orthotic Devices Used

On the Scope of the Investigation

On the Research Method

On the Clinical Recommendations

On the Discussion

Author's Thanks

References

Back to Top...

 

On the Discussion

I agree with the researchers that their results are not generalizable. I will add that randomized, controlled trials, examining a few responses to a narrow field of interventions, will inevitably grant the rehabilitation team little useful information if they desire optimum functional effects, as children with CP present elaborate and unique constellations of coping strategies, cognitive capabilities and, with a few common trends, lower-extremity skeletal geometry, joint alignment, joint stability, muscle strength, selective muscle control, muscle length-tension relationships and physiologic adaptations, foot loading patterns, balancing skills, gait strategies, foot deformities, and levels of physical endurance.

Is the underlying goal of conducting orthotic efficacy research for this population to streamline the clinical problem-solving/ orthotic prescription process by offering busy rehabilitation clinicians short-cut, statistics-driven solutions to complex, unique problems?

I find no problem-solving data more enlightening than a thoroughly-gathered body of the existing musculoskeletal factors and functional strategies impacting each child's ambulatory skills. I look forward to the day when researchers define in detail the kinesiological, biomechanical and functional context into which a management modality is introduced and assessed; compare an inclusive array of applicable management strategies brought to the same, well-defined context; and measure efficacy in terms of the most functionally-relevant parameters, including, for the ambulatory groups, energy efficiency and effective prevention of degenerative joint disease.

Topics:
On the Selection of Variables

On the Orthotic Devices Used

On the Scope of the Investigation

On the Research Method

On the Clinical Recommendations

On the Discussion

Author's Thanks

References

Back to Top...

 

Author's Thanks

A parting thanks to the researchers, whose project has inspired me question many aspects of orthotic efficacy in general, and to strive for excellence and higher standards of clinical research in my own practice.

Beverly Cusick PT, MS, COF

305 Society Drive
Suite C-3
Telluride, CO 81435
info@gaitways.com
(866) 410-8062 • Fax: (866) 886-7736

Topics:
On the Selection of Variables

On the Orthotic Devices Used

On the Scope of the Investigation

On the Research Method

On the Clinical Recommendations

On the Discussion

Author's Thanks

References

Back to Top...

References:

  1. Thomas, S.S., Moore, C., Kelp-Lenane, C., Norris,C. Simulated gait patterns: the resulting effects on gait parameters, dynamic electromyography, joint moments, and physiological cost index. Gait & Posture.1996;4:100-107.

  2. Gage, J.R.,. DeLuca, P.A., Renshaw, T. Gait analysis; principles and applications - emphasis on its use in cerebral palsy. J. Bone Jt. Surg.1995; 77-A(10):1607-1623.

  3. Winter, D.A. Energy generation and absorption at the ankle and knee during fast, natural and slow cadences. Clin.Orthop. Rel.Res.1983;197:147-154.
  1. Olney, S.J., Wright, M.J. Cerebral palsy. In S.K. Campbell (Ed.) Physical therapy for children. Philadelphia, PA: W.B. Saunders. 1994;489-523.

  2. Ounpuu, S., Davis, R.B., DeLuca, P.A. Joint kinetics: methods, interpretation and treatment decision-making in children with cerebral palsy and myelomeningocele. Gait & Posture.1996;4:62-78.

  3. Gage, J.R. Clinical use of kinetics for gait pathology in cerebral palsy. Gait & Posture.1994;2(1):36-37.

  4. Berger, W., Quintern, J., Dietz, V. Pathophysiology of gait in children with cerebral palsy. Electroenceph. Clin. Neurophysiol. 1982;53:538-548.

  5. Dietz, V., Berger, W. Cerebral palsy and muscle transformation. Devel. Med. Child Neurol.1995;37:180-184.

  6. Sutherland, D.H., Olshen, R.A., Biden, E.N., Wyatt, N.P. Anthropometric measurements and developmental screening. In D.H. Sutherland et al 1988: The development of mature walking. New York, NY: Cambridge University Press.1988;33-54.

  7. Gajdosik, C.G., Gajdosik, R.L. Musculoskeletal development and adaptation. In S.K. Campbell (ed.) 1994: Physical therapy for children. Philadelphia, PA: W.B. Saunders Company.1994;105-126.

  8. Reimers, J. Contracture of the hamstrings in spastic cerebral palsy: a study of three methods of operative correction. J. Bone Jt. Surg 56-B:1;102-109.

  9. Boyd, R. How do physiotherapists achieve these [orthotic] aims? In D.N. Condie (Ed.)1995: Report of a consensus conference on the lower limb orthotic management of cerebral palsy. (Held November10-12, 1994) Borgervaenget 7, 2100 Copenhagen-0-, Denmark: Int'l Soc. Prosth. Orthot.1995;66-82.

  10. Carmick, J. Managing equinus in children with cerebral palsy: electrical stimulation to strengthen the triceps surae muscle. Devel. Med. Child Neurol.1995;37:965-975.

  11. Silverstein, L. Selby-. Gait assessment of children to enhance evaluation of foot and ankle function and treatment efficacy. In R. L. Craik and C.A. Oatis (Eds.)1995: Gait analysis: theory and application. St. Louis, MO: Mosby.1995;388-393.

  12. Major, R.E. Current orthotic practice in relation to the improvement of gait efficiency. In D.N. Condie (Ed.)1995: Report of a consensus conference on the lower limb orthotic management of cerebral palsy. (Held November 10-12, 1994) Borgervaenget 7, 2100 Copenhagen-0-, Denmark: Int'l Soc. Prosth. Orthot.1995;175-180.

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