In the past two years, a new class of gait enhancing knee ankle foot orthoses (KAFOs) has burst on the scene — stance control orthoses. This new generation of stance control orthoses (SCOs) allows knee flexion during the swing phase of gait and is changing the way orthotists treat patients.
History of Stance Control
Stance control orthoses are not a new concept by any means. Orthotists have been interested in the development of an orthotic stance control knee joint for literally centuries, said John Michael, MEd, CPO, FAAOP, president of CPO Services Inc. Michael estimates at least a dozen SCOs have appeared on the market in the course of his 30-year career, noting that all of them have disappeared for various reasons such as unreliability, prohibitive cost and mechanical inconsistency. In fact, up until January 2002, “the state of the art in orthotic management was that you locked the patient’s knee if they needed stability, and it stayed locked throughout the gait cycle,” said Michael.
What has happened during the past two years to radically change the state of the art in lower extremity orthotics? Four mechanical and one electronic stance control orthotic devices that enable patients with isolated quadriceps weakness to ambulate with a gait more closely approximating normal have been launched commercially in the United States since January 2002. In addition, a second electronic stance control knee joint is currently undergoing clinical testing.
While Michael attributes some of this recent activity in the SCO arena to today’s availability of better materials and better engineering, he also noted that there was a focused interest from the engineering community on tackling this difficult problem. This is in part fueled by the findings of a multidisciplinary panel on prosthetic-orthotic practice convened by the National Center for Medical Rehabilitation Research in 1992. The panel identified the lack of stance control knee joints for orthoses as a key area that desperately needed research and concluded that lower limb orthotic components had not “changed significantly in modern times.”
“Once that report was published by the federal government, there was an implied promise that there would be research funding available and that had never happened before,” said Michael. “Within the next 10 years, basically, multiple research groups around the world tackled this problem.”
The first stance control device to reach the orthotic market was Horton Technology’s Stance Control Orthotic Knee Joint® (SCOKJ), which became available commercially in January 2002. Otto Bock Health Care’s Free Walk Stance Control Knee/Ankle System followed closely in March 2002. Then, in the fall of 2002, Becker Orthopedic launched the UTX Swing KAFO and Fillauer announced it would begin distributing Basko Healthcare’s Swing Phase Lock (SPL) System in North America.
The primary goals — increased stability and an increased energy-efficient gait that more closely approximates normal gait — of all of these SCOs are the same, yet the orthoses differ from one another in design and construction. The broad indications for the orthoses also are similar and include isolated quadriceps weakness or absence, or leg paralysis or paresis. Candidates for an SCO include post-polio and multiple sclerosis patients, trauma patients and patients with unilateral paralysis or spinal cord injury.
However, as Michael noted in an article he recently coauthored, “It is important to note that SCOs are prescribed based on the biomechanical deficit, which is a lack of voluntary knee stability, and not on the basis of any particular medical diagnosis.”
Stance Control Orthotic Knee Joint
The first of the mechanical stance control devices to be launched, the SCOKJ consists of a knee joint and the mechanisms to activate it. The joint is available as a component part, and practitioners can fabricate the orthoses themselves, said Gary Horton, CO, FAAOP, of Horton Technology Inc. in Little Rock, Ark.
Horton began developing the SCOKJ in 1994 in collaboration with the National Aeronautics and Space Administration’s (NASA) Transfer of Technology program. He was actually working on another project when he was approached by a NASA team regarding a stance control type knee joint. Horton was immediately interested in the knee joint and began working on a prototype joint in collaboration with NASA at Marshall Space Center in Alabama.
However, the team was unable to adapt the technology they had developed to produce a marketable orthosis because the machining was too expensive to reproduce the prototype for testing, said Horton. The NASA team began redeveloping the orthosis to produce it at a reasonable price. That NASA project is still ongoing and a new prototype has recently been developed, noted Horton.
When he began working on the NASA project, Horton had the rights to the knee joint licensed to him. Because the stance control joint project was not a priority for the NASA scientists, who work on such projects as time permits, Horton assembled a team of his own to work in coordination with NASA. His team, which included a local engineer and a local machine shop, attacked the problem of producing a knee joint that was affordable, and eventually created a marketable version — the SCOKJ.
The SCOKJ is a double knee joint system consisting of both medial and lateral knee joints, and the cable that activates the joint is plastic rather than metal. The SCOKJ has three operating modes: automatic stance control, locked or unlocked. The joint is able to block flexion at any degree, which Horton said is the key difference from the other mechanical stance control devices on the market.
“Whenever you have heel contact, the SCOKJ will block flexion,” said Horton. “It does not lock the knee, it blocks flexion at that point at whatever degree of flexion the knee is in, and it will still let the knee go into extension. That is what I think makes the SCOKJ the most unique.”
Because of the complexity of the knee joint, Horton Technology requires orthotists to undergo a training program prior to purchasing the components. The training program, which is conducted by Michael, includes reviewing the biomechanics of normal and pathologic gait; learning the principles and functions of the SCOKJ; fabricating, fitting and adjusting the SCOKJ; and evaluating, selecting and educating patients. To date, Horton estimates more than 500 certified practitioners in the United States and Canada have completed training to fit the SCOKJ.
The second stance control device to reach the U.S. orthotic market was Otto Bock Health Care’s Free Walk Stance Control Knee/Ankle System. The Free Walk is a complete KAFO constructed out of tubular stainless steel. The locking mechanism is a steel braided cable located in the single tubular steel sidebar that runs from the ankle joint to the knee, said Kelly Clark, CO, an orthotic clinical specialist for Otto Bock in Minneapolis.
The Free Walk originated from a design of Dr. Nils Van Leerdam of the Netherlands, who originally collaborated with Otto Bock. However, in late 2001, that collaboration ceased to exist, and Otto Bock proceeded with the U.S. launch of the Free Walk in March 2002 after making some design changes, said Clark.
The knee joint of the Free Walk automatically locks prior to initial contact when the patient’s knee is fully extended. In terminal stance, an extension moment of the knee in conjunction with 10 degrees of dorsiflexion movement of the ankle will disengage the locked knee mechanism. The Free Walk is available in two versions depending on the weight of the patient: the L/R-80 for patients weighing up to 175 pounds and the L/R-120 for patients weighing up to 265 pounds.
Because the Free Walk is constructed from tubular steel and requires special tools for bending, central fabrication is required. Although training is not required for fitting the orthosis, practitioners are strongly encouraged to attend a workshop offered by Otto Bock, said Clark. Some materials, including a CD or videotape, that highlight indications, contraindications and patient assessment are provided to practitioners upon request. However, Clark notes, “In hindsight, a lot of the practitioners who didn’t take the course and proceeded with fitting and then later sat in on our course have said, ‘I wish I would have taken the course first. It would have made things easier.’”
The third stance control device to become available commercially in 2002 was the UTX Swing KAFO. Originally designed by Nils Van Leerdam and introduced by Ambroise Holland at the 1998 International Society for Prosthetics and Orthotics Congress in Amsterdam, Becker Orthopedic acts as the authorized U.S. representative for the UTX.
Because the UTX germinated from the same project as the Free Walk, the two orthoses have a similar look, said Gary Bedard, CO, FAAOP, clinical marketing manager for Becker Orthopedic. However, as with the Free Walk, the UTX has evolved, with several different versions currently available.
“Within the UTX family of orthoses, there are several stance control ones that have options pertaining to patients’ weight, valgus and varus instability and recurvatum, and then there is also a stable model that does not allow free motion during swing phase,” said Bedard.
The UTX Swing orthosis consists of a single tubular stainless steel sidebar with a cable running inside the distal side member from the ankle to the knee. As the knee reaches full extension, a ratchet engages to stabilize the knee, and at the end of stance phase as the ankle dorsiflexes, the cable unlocks to allow flexion.
The UTX Swing comes in two versions depending on patient weight: the UTX Swing 80 is for patients weighing up to 175 pounds and the UTX Swing 120 is for patients weighing up to 265 pounds. The Fs Swing orthosis is a slightly modified version designed for added valgus control in the coronal plane and can be assembled with either the UTX Swing 80 or 120, said Bedard.
Bedard notes that like most of the mechanical stance control orthoses or knee joints available at this time, certain muscular requirements are needed on the side of the patient in order to operate the mechanical joint to allow it to unlock.
“With the UTX, you need hip extensor control in order to neutralize the forces across the orthotic knee joint to allow the knee to then go into swing phase or free motion during swing phase,” said Bedard.
As with the Free Walk, the UTX is available only through central fabrication. Becker also offers a training seminar for practitioners who use the UTX family of orthoses, but does not require practitioners to attend the seminar. Bedard said that practitioners can fit the orthoses using the general guidelines they follow for fitting conventional KAFOs.
Swing Phase Lock
The final stance control device to hit the U.S. orthotic marketplace in 2002 was the Swing Phase Lock (SPL). The SPL, which is manufactured by Basko Healthcare in the Netherlands and distributed in North America by Fillauer, is a pendulum or balance type locking joint and operates using gravity.
“The SPL has a balance that is affected by gravity so at different phases of gait, that balance either rocks forward or backward,” said Gerry Stark, BSME, CP, FAAOP, director of education and technical support for Fillauer. “Just before heel strike, the pendulum rocks backward locking the knee, and at the end of stance phase, the pendulum rocks forward, unlocking the device.”
The SPL system consists of two parts: the lateral side is the Swing Phase Lock and the medial side is a Swing Phase Control unit. A remote control unit completes the system and is “a cable system attached to the locking mechanism that sets that balance into various positions,” said Stark. The remote control device, which can be fixated proximally on the orthosis or worn on the patient’s belt loop, has three settings: manual lock, manual unlock or automatic locking mode.
Stark notes that an extension moment is required to lock and unlock the device. If there is any flexion moment or flexion load on the device, it won’t release. Stark adds that one advantage of the SPL is the range at which the joint locks and unlocks can be adjusted by the orthotist.
The SPL can be custom fabricated by practitioners. While Fillauer offers workshops on fitting the SPL, practitioners are not required to attend before fabricating orthoses for patients. The reason for this is the SPL is “aligned almost the same as any other knee orthotic joint,” said Stark. However, he added that it is advisable for clinicians to attend one of the workshops to learn some of the nuances of the knee. He noted it is important to have torsional stability with the SPL because only one side of the knee is locked.
The Next Generation: Electronic SCOs
Just as the flurry of SCO activity began to slow down toward the end of 2002, the next generation of SCOs arrived on the scene this past January when Becker Orthopedic’s E-Knee became the first commercially available electronic SCO. Noting that the E-Knee allows orthotists to provide limb function in a dynamic manner for the first time, Bedard described electronic SCOs as the “holy grail for orthotists.”
Based on a design by Jonathon Naft, CP, the microprocessor-controlled E-Knee has three main components. One of the components is a foot sensor that fits between the orthosis and the patient’s foot or shoe. The foot sensor works in coordination with an intelligent controller to determine whether or not the patient is weight bearing. If the sensor determines the patient is weight bearing, the E-Knee will lock at any degree of flexion. In addition, the E-Knee does not require the patient to have hip extension, in contrast to the SCOKJ, which is the only one of the mechanical stance control devices that has the ability to lock at any degree of flexion.
“The E-Knee has the capability of sensing if the patient is placing weight on the affected limb and then to lock at any degree of flexion,” said Bedard. “Once it has locked, it has the ability to extend that knee but prevent flexion, so it’s similar to a one-way clutch when the locking mechanism is engaged and has sensed that the limb is weight bearing.”
The clinical applications for the E-Knee are broader than for the mechanical SCOs, enabling the orthosis to be used by patients who have a higher level of physical disability. Bedard notes that “there are less physical restrictions in the clinical application of this orthosis compared to the mechanical stance controlled orthotic knee joint. You can clinically apply the E-Knee to a patient who has a completely flail lower limb, and still allow that patient enhanced gait benefits from having free motion during stance phase.”
The E-Knee is available as a central fab item in a complete KAFO or as a component set for fabrication in the local O&P lab. However, unlike the UTX, practitioners must complete a qualification course before fitting patients with the E-Knee orthosis. The course is designed to give practitioners a working knowledge of the orthosis and includes technical exercises that practitioners would not be required to do in practice.
A second electronic stance control device, Horton Technology’s Smart Knee, is currently undergoing clinical testing. The Smart Knee is a battery-operated, microprocessor-controlled version of the SCOKJ, and while testing has demonstrated the Smart Knee works as reliably and effectively as the SCOKJ, Horton said, “The problem is it has added weight and more expense. Those are two big issues right now.”
Calling the Smart Knee “still a work in progress,” Horton said ways to make it lighter and more cost efficient are being researched. In addition, Horton noted the Smart Knee “does not function any better for our patients right now than the one we have [the SCOKJ].” While a launch date has not yet been set for the Smart Knee, Horton expects the SCOKJ will be able to be retrofitted electronically.
Hurdles to Overcome
Several hurdles must be overcome before the use of SCOs becomes widespread. The first and perhaps largest hurdle involves reimbursement. Because SCOs represent new technology and a new class of orthoses, Medicare reimbursement currently is nonexistent. All four SCO manufacturers applied for L-codes from the Centers for Medicare and Medicaid Services by the April 1 deadline of this year, said Stark, who noted that the current L-code system doesn’t necessarily reward innovative designs.
A ruling is expected this month, with an effective date of January 2004 if L-codes are granted. In the meantime, Michael said that “some insurance companies allow a request for prior approval and will tell you up front whether they will cover it or not.” Other third-party payers require the orthosis to be custom made and custom fit, with the patient paying for the orthosis before the payer agrees to cover the cost.
Michael added that L-codes would have “a significant impact on the growth of this kind of care because if patients knew up front if it was or was not covered, they could make a more intelligent decision than at the current time.”
Clark agrees, citing the current lack of reimbursement from Medicare as one of the biggest snares.
“When a practitioner sees this, they love the technology, but then in order to have a business, you have to get paid. If that is going to be a big problem, they will think twice before going down this road,” said Clark.
Another hurdle to overcome is the lack of clinical data and experience as well as the associated difficulties that exist with any new medical technology.
“The hardest aspect with all of these new joints is having the practitioners out in the field cross the threshold of understanding, of being able to match the patient’s physical limitations to the benefits or the performance criteria of the orthotic joints themselves,” said Bedard. “That is the biggest threshold to cross at this point in time, because all of these products represent a quantum leap in terms of lower extremity orthotic management.”
“In the past, we’ve only been able to provide a static type of orthosis that did not have any gait enhancing capabilities,” said Bedard. “But for the first time, practitioners now have a potpourri of choices, and of course now they have a potpourri of decisions that they have to make of which component will best suit the clinical presentation of their patient.”
Michael concurs, noting the immediate challenge for orthotists is to understand when a stance control device would be optimal for a patient and when it would not. While there appears to be broad agreement regarding which patients are primary candidates, it is far less clear which patients are marginal candidates or not candidates at all.
Another aspect to consider is that because SCOs enable orthotists to regulate gait, it follows that orthotists will now need to learn more about how they want to regulate gait, said Stark. Previously, the state of the art in orthotic management was a locked knee, which precluded patients from ambulating with any semblance of a normal gait and obviated this need.
Finally, while the development of several stance control devices now offers the orthotist several choices in lower extremity orthotic management, it also has created “a new awakening or a blossoming of products that offer gait enhancement capabilities” that did not exist before, said Bedard. He maintains that practitioners should not limit themselves to looking at this range of products and thinking only of stance control because “some offer swing control, some offer load resistance control and some offer range of motion control in a dynamic fashion.”
Bedard believes that as practitioners become accustomed to this new technology, the terminology will broaden. He prefers to think of this group of products as enhanced gait orthoses because they enhance a patient’s gait in some manner and offer patients a dynamic action they have never had before.
Michael agrees that these initial concepts are in a period of rapid evolution. He predicts that additional and more advanced concepts will follow, ultimately revolutionizing the way orthotists think about KAFOs and the way they provide that care. He believes that in the future, “We’ll look back retrospectively and we’ll see this as the decade of stance control orthoses.”
Regardless of whether one prefers to call this generation of orthoses either stance control or gait enhancing orthoses, one thing is certain — the concept has finally arrived and is here to stay.
For more information:
- Michael JW, Bowker JH. Prosthetics/orthotics research for the 21st century: summary 1992 conference proceedings. Journal of Prosthetics and Orthotics. 1994;6:100-107.
- Michael JW, McMillan AG, Kendrick K. Stance control orthoses: history, overview and case example of improved KAFO function. Alignment. Canadian Association of Prosthetists and Orthotists. 2003.
- Travolta RL. Stance control revolutionizes knee bracing. Biomechanics. August 2002. Available at: http://www.biomech.com/db_area/archives/2002/0208.stancecontrol.bio.shtml. Accessed August 12, 2003.