257
JRRD
Volume 46, Number 2, 2009
Pages 257–268
Journal of Rehabilitation Rearch & Development
Engineering design review of stance-control knee-ankle-foot orthos
Terris Yakimovich, MASc;1 Edward D. Lemaire, PhD;1* Jonathan Kofman, PhD, PEng 21
Institute for Rehabilitation Rearch and Development, The Ottawa Hospital Rehabilitation Centre, Ottawa, Canada; 2Department of Systems Design Engineering, University of Waterloo, Waterloo, Canada
Abstract—Persons with quadriceps muscle weakness are often prescribed a knee-ankle-foot orthosis that locks the knee in full extension during both stance and swing phas of gait. Locking the knee results in abnormal gait patterns characterized by hip hiking and leg circumduction during swing. The stance-control knee-ankle-foot orthosis (SCKAFO), a new type of orthosis, has emerged that permits free knee motion during swing while resisting knee flexion during stance, thereby supporting the limb during weight-bearing. This article examines various SCKAFO designs, discuss the existing design limitations, and identify remaining design challenges. Several commercial SCKAFOs have been relead that incorporate different locking mecha-nisms. Preliminary gait studies have shown some devices to be promising; however, an important functional limitation in some SCKAFOs is dependence on specific joint angles to switch between stance and swing modes. Important design factors such as size, weight, and noi must be considered in new orthosis designs to ensure wide consumer acceptance.
Key words: assistive technology, design, gait, knee-ankle-foot orthosis, lower limb, orthosis, rehabilitation, stance, stance control, stance-control knee-ankle-foot orthosis.
大米面发糕
INTRODUCTION
Approximately 866,000 Americans u a lower-limb orthosis [1]. For people with isolated quadriceps weak-ness or paralysis, a standard knee-ankle-foot orthosis (KAFO) is typically prescribed to support the limb dur-ing locomotion. Many of the KAFOs support the limb by locking the knee in full extension throughout the gait cycle to prevent the leg from collapsing while weight-bearing.
While constraining the knee to full extension solves the body-weight support problem, straight-legged gait introduces other issues. During swing pha, KAFO urs must adopt unnatural gait strategies to bring their braced leg forward to prepare for the next heel or foot strike.Compensatory gait patterns include incread upper-body lateral sway, ankle plantar flexion of the contralateral foot (vaulting), hip elevation during swing pha (hip hike), or leg circumduction [2]. Lack of knee flexion during foot strike caus abrupt initial loading and disrupts the smooth progression of the center of mass (COM) of the body.
Abnormal gait patterns can lead to soft tissue and joint dysfunction of the hip and lower back, causing pain and loss of motion [3]. As well, walking with a fixed knee can decrea gait efficiency by 24 percent [4] and increa vertical displacement of the COM of the body by up to 65 percent [5]. The associated incread muscu-lar effort can lead to higher energy expenditure [6] and early fatigue for the KAFO ur during ambulation [4].Incread energy demand with the KAFO contribute
s significantly toward high KAFO rejection rates (between 60% and almost 100%) [6].
Abbreviations: AFO = ankle-foot orthosis, COM = center of mass, DKBS = Dynamic Knee Brace System, KAFO = knee-ankle-foot orthosis, SCKAFO = stance-control knee-ankle-foot orthosis.
*Address all correspondence to Edward D. Lemaire, PhD;Institute for Rehabilitation Rearch and Development, The Ottawa Hospital Rehabilitation Centre, 505 Smyth Road,Ottawa, Ontario, Canada K1H 8M2; 613-737-7350, ext 75592;fax: 613-737-4260. Email: a DOI:10.1682/JRRD.2008.02.0024
258
JRRD, Volume 46, Number 2, 2009
When the knee cannot flex, ascending and descend-ing stairs and inclined surfaces and walking onto curbs po challenges. Walking with a fully extended knee hin-ders balance correction when a ur stumbles, since the leg cannot flex to control fall direction and the braced limb cannot dampen the fall [7].
Attempts have been made to design a new orthosis that would improve gait over conventional locke
猪肉白菜饺子
邋邋遢遢d-knee KAFOs. However, veral difficult design challenges hindered efforts to solve this problem. Recently, a new type of KAFO has emerged on the orthotics market that allows wearers to flex their knee when swinging the leg forward while preventing knee flexion during weight-bearing. The new designs have been commonly labeled stance-control knee-ankle-foot orthos (SCKAFOs) in the orthotics community. SCKAFO designs must ensure proper functioning during stance and swing, as well as appropriate switching between weight-bearing and non-weight-bearing modes. This article examines the design challenges of the new SCKAFO devices and compares various design approaches.
STANCE-CONTROL KNEE-ANKLE-FOOT ORTHOSIS INDICATIONS
An appreciable portion of the population using fixed-knee KAFOs has sufficient hip strength to benefit from a SCKAFO. SCKAFO prescription criteria typically require hip strength of at least Grade 3*. This includes people with multiple sclerosis, muscular dystrophy, polio, post-polio syndrome, spina bifida, incomplete spinal injury, unilat-eral leg paralysis and paresis, trauma, congenital defects, and isolated quadriceps weakness. Hip strength and con-trol requirements may decrea for some SCKAFO designs as prescribers gain experience with clinical u of the devices.
Some studies have suggested that orthos that allow uninhibited knee motion in swing improve gait kinematics and increa gait efficiency compared to conventional KAFOs. McMillan et al. analyzed gait patterns and heart rates of three subjects with lower-limb weakness walking with a SCKAFO built by Horton Technology, Inc [3]. The subjects participated in a ries of gait analysis and treadmill trials and an obstacle cour. The study reported faster walk-ing speeds, longer strides, fewer compensatory motions, incread mobility, and more symmetrical gait patterns when subjects walked with a SCKAFO than with a fixed-knee KAFO. Hebert and Liggins reported similar results for level ground walking by a post-poliomyelitis syndrome sub-ject using a Horton SCKAFO, although spatiotemporal parameters only showed small changes [8]. Zissimopoulos et al. investigated nine nondisabled subjects walking with the Horton SCKAFO in locked-extension, free-swing, and stance-control modes [9]. No significant difference in oxygen consumption was obrved between subjects walking with the SCKAFO in locked-extension mode and stance-control mode; however, subjects experienced clor to normal gait kinematics when walking with the SCKAFO in stance-control mode than in locked-extension mode.
Lehmann and Stonebridge investigated the effect of a SCKAFO on the oxygen consumption of two nondisabled subjects and two patients with spinal cord lesions [10]. Significant energy savings were
reported for nondisabled subjects at ambulation rates >73 m/min. However, energy expenditure improved little in both disabled subjects, since they did not have sufficient muscle strength to flex their knee adequately in the swing pha or sufficient hip flexor strength to reach normal walking speeds. Other SCKAFO-KAFO oxygen consumption comparisons with nondisabled subjects showed no significant differences [6,9]. Kaufman and colleagues showed a 1 mL/kg/mm improvement in oxygen consumption when a subject with post-polio syndrome ud a SCKAFO compared with a KAFO [6]. For nondisabled individuals, this change incread walking velocity 8 m/min.
Another study investigated the effect of a SCKAFO on lower-body kinetics and kinematics of eight novice KAFO urs and thirteen experienced KAFO urs [11]. Walking with the SCKAFO, the novice urs incread lf-lected walking velocity and stride length signifi-cantly compared with experienced urs. One explana-tion may be that the accommodation period with the Dynamic Knee Brace System (DKBS) may not have been long enough to overcome the learned walking strate-gies ud for the conventional KAFO. Both novice and experienced KAFO urs incread peak knee flexion in
*This value comes from prescription criteria provided by various manu-facturers in unpublished documents and manuals:
·Becker Orthopedics Stance Control Overview Guide II, p. 4.·Fillauer Swing Pha Lock Manual, p. 4.
·Horton Stance Control Knee Training Cour.
·Otto Bock Sensor Walk (bock.ca/cps/rde/xchg/ ob_us_en/hs.xsl/15994.html).
259 YAKIMOVICH et al. Stance-control knee-ankle-foot orthosis designs
swing and reduced compensatory motions such as plantar flexion of the contralateral ankle in stance (vaulting) and dynamic pelvic obliquity (hip hike). In another study, con-sumers found that the SCKAFO offered them greater stabil-ity while standing and walking compared with their original orthosis [12]. A study involving 14 participants walking with the DKBS, 3 months into an open-enrollment field trial, found that temporodistance measures improved significantly [13].
Rearch has shown improvements in mobility and walking with the SCKAFO compared with fixed-knee KAFOs. The results suggest a strong potential for wider prescription and SCKAFO u if the design meets impor-tant functional and cosmetic needs of orthosis urs. DESIGN CONSIDERATIONS
A SCKAFO should allow free knee motion in the swing pha and resist knee flexion at any knee angle in the stance pha. The orthosis should also allow urs to extend their knee at any time in stance mode to permit the ur to climb onto a curb or stair or to recover from a stumble. The ideal orthosis should also be quiet, have a very quick reaction time (<6 ms) when switching between stance and swing modes [14], be relatively inex-pensive to manufacture, function reliably for an apprecia-ble amount of time between rvicing (>6 mo) and recharging with an electric power source (at least 1 day of u, if electromechanical), and support a large gment of the potential ur population.
The SCKAFO has remained a challenging engineer-ing problem becau of the high-flexion moments that occur at the knee during normal walking cadence (1.04 Nm/kg body mass) [15], fast cadence (1.67 Nm/kg) [15], and stair climbing (1.71 Nm/kg) [16]. The knee joint, or other structural mechanism, must support the high-flexion moments. An ideal orthosis should also have minimal dimensions mediolaterally and anteroposteriorly and be as lightweight as possible. Since a regular KAFO can weigh 5 lb (2.3 kg), a SCKAFO should be at least as light as the typical KAFO. This design is a difficult chal-lenge, since knee-joint components that sufficiently resist failure and are sufficiently safe are not typically light and small. The following ction describes SCKAFO devices th
世人谓我恋长安at are on the commercial market or published recently in journals.CURRENT STANCE-CONTROL KNEE-ANKLE-FOOT ORTHOSES
Otto Bock Free Walk/Becker UTX
Manufactured by two different companies under two different names, Otto Bock HealthCare’s Free Walk and Becker Orthopedic’s UTX share the same ratchet/pawl design [17–18] (Figure 1). A spring-loaded pawl locks the knee automatically when the knee fully extends prior to heel strike (Figure 1(a)). A 10° ankle dorsiflexion angle caus a control cable connected to the pawl to pull down and dingage the lock (Figure 1(b)). Simulta-neous extension of the knee with 10° dorsiflexion is required to eliminate flexion moments about the knee and free the pawl from friction for dingagement.
Since full knee extension is required to engage the knee lock, the knee will be unsupported if flexed during limb load-ing. Limb loading on a flexed knee is common when urs walk on stairs, inclines, uneven ground, or during stumbling and relaxed standing. Since the dingagement mechanism requires 10° dorsiflexion, the device cannot be ud for patients with a fud ankle or biomechanical problems that limit dorsiflexion. The Otto Bock Free Walk/Becker UTX is the lightest and most cosmetically attractive of all commer-cial SCKAFOs; however, the delicate tubular steel structure
could concern urs who feel they need more support. Figure 1.
Otto Bock Free Walk/Becker Orthopedic UTX. (a) Spring-loaded pawl locks knee when full knee extension is attained. (b) Dorsiflexion of foot at end of stance pulls on control cable connected to pa
wl to dingage lock for swing.
260
JRRD, Volume 46, Number 2, 2009
Horton Stance Control Orthosis
过膝靴搭配
Horton Technology, Inc, produces the Horton Stance Control Orthosis (Figure 2), that features a locking mecha-nism modeled after a standard unidirectional clutch design and involves jamming an eccentric cam into a friction ring that is attached to the upper-knee joint (Figure 3) [19–22].*A thermoplastic stirrup shell (Figure 2) is positioned just below the thermoplastic ankle-foot orthosis (AFO) shell.The thermoplastic stirrup travels along the length of the orthosis and is attached to a pushrod that is attached to the eccentric cam.
Heel contact pushes the stirrup upward to engage the pushrod and drive the cam into the friction ring. The surface of both the hardened steel cam and friction ring is textured with microgrooves. The microgrooves eliminate slip between the friction ring and cam. When the cam is engaged, knee flexion caus the friction ring to load the cam, thereby locking the joint. Knee extension pushes the cam away from the friction ring, allowing uninhibited knee extension. During limb unloading, a spring pushes the push-rod down, the cam dingages, and the knee can move freely. An extension moment about the knee is required to eliminate impinging forces on the cam and dingage the joint. Attaching the pushrod to the heel of an articulated AFO ction can actuate the Horton Stance Control Orthosis locking mechanism. When the foot plantar flexes, the cam will push upward to engage the lock. A knob located on the side of each joint will switch the joints into one of t
hree functional modes: automatic stance/swing, constant free knee motion, and constant locked knee extension. The dif-ferent modes add versatility to the orthosis. Constant locked knee extension can add curity for orthosis urs walking in unsure surroundings, and the free knee motion mode facili-tates activities such as using the gas and brake pedals while a car is being driven.
The Horton Stance Control Orthosis is bulky, and the joints are relatively large by KAFO standards, with a mediolateral profile of 2.3 cm. While this design can lock at any knee angle, some urs may not tolerate the bulk of this SCKAFO.
Both mechanical actuation methods for the Horton Stance Control Orthosis can be problematic. Objects such as clothing, socks, or debris from walking outdoors can lodge between the foot and the stirrup. The two-layer thermoplastic foot shell may prevent the ur from don-
ning a shoe or the shoe may adverly affect the stirrup mechanism. The articulating ankle-driven pushrod option cannot be ud for urs with ankle mobility problems.The nsitive triggering mechanism may constrain urs to walk with a consistent step length and speed to achieve reliable engagement [9]. This SCKAFO can also fall out of the optimal performance-trimmed state, leading to unreliable locking performance.
Fillauer Swing Pha Lock
Fillauer, LLC, developed a novel gravity-actuated knee-joint locking mechanism for its Swing Pha Lock
*Drachlis D. Innovative knee brace moves a step clor to manufac-
turing with acceptance of final design. Marshall Space Flight Center
News Relea 98–032. 1998 Mar 5.
Figure 2.
Horton Stance Control Orthosis. Hatton BJ, Hatton DL, Wallace ZG.2003. Articulating knee supports. United States patent US 6635024.2003 Oct 21. AFO = ankle-foot orthosis.
261
YAKIMOVICH et al. Stance-control knee-ankle-foot orthosis designs
为什么qq空间打不开
orthosis [23]. As shown in Figure 4, a weighted pawl falls in and out of locking position, depending on the ur’s thigh angle.
When the hip is flexed with the thigh anterior to the body, as in terminal swing, the weighted pawl falls into the locked position to prevent knee flexion (Figure 4(a)).The knee must be fully extended fo
r the pawl to fall into this locked position. When the hip swings behind the body prior to the swing pha, the weighted pawl din-gages and the knee flexes freely (Figure 4(b)). An exten-sion knee moment is required to eliminate impinging forces on the pawl and allow the pawl to dingage freely. The hip angle required to engage and dingage the pawl is manually t on the joint head by an orthotist.Only one Fillauer Swing Pha Lock is mounted on the KAFO. The cond orthotic knee joint, mounted on the medial side of the KAFO, is a simple mechanism that us friction and a spring to regulate knee flexion in the swing pha [24]. A satellite switch, fixed to the proxi-mal end of the orthosis, switches the functional knee joint into one of three operational modes: manual lock, free
swing, and automatic lock/unlock [25]. Since the locking mechanism depends on limb-gment orientation, the Fil-lauer Swing Pha Lock is not effective for urs to curely climb stairs or walk on uneven ground.Becker Orthopedic 9001 E-Knee
The Becker Orthopedic 9001 E-Knee us a magneti-cally activated one-way dog clutch (Figure 5) [26]. The joint integrates two circular ratchet plates that are spring-biad apart. One of the ratchet plates is positioned within an electromagnetic coil. When pressure nsors below the foot detect foot contact, the electromagnetic coil is energized and the ratchet plates are forced together. When engaged, the ratchet plates allow relative angular motion in only one direction. In stance, knee flexio
n is resisted, while knee extension is still allowed.
宣传员Ratchet devices suffer from two inherent disadvan-tages. First, as in a houhold ratchet tool, the 9001 E-Knee generates a clicking sound when rotated under engagement, such as when urs extend their knee in stance. Cosmetics are often as equally important as func-tion for KAFO urs. If an orthosis looks or sounds unnatural, the orthosis may not be ud.
Second, unlike most friction-bad clutches, a ratchet device only has a finite number of locked positions. The 9001 E-Knee hous 60 ratchet teeth, thereby allowing
up to 6° of free-fall knee flexion before the joint locks关于国庆节
Figure 3.
Cross-ctional view of Horton Stance Control Orthosis locking mechanism—unlocked and in 90° knee flexion. Hatton BJ, Hatton DL,Wallace ZG. 2003. Articulating knee supports. United States patent US
6635024. 2003 Oct 21.
Figure 4.
Gravity-activated Fillauer Swing Pha Lock with pawl weighted by mass (M): (a) when thigh is anterior to ur’s body and knee is fully extended, weighted pawl falls into locked position; (b) with thigh posterior to ur’s body and knee extension moment, pawl falls out of engagement.
