For many years, stance control orthoses (SCOs) have been an orthotic option for patients with paralysis of the muscles that stabilize the knee. They enable the user to freely swing his leg in the swing phase but are locked for the stance phase, giving the patient the same degree of security as locked knee-ankle-foot orthoses (KAFOs). However, SCOs have not yet prevailed over locked orthoses to any great extent. This literature review will analyze whether any benefit can be scientifically verified for patients using SCOs compared with the locked KAFOs.
On November 8, 2010, a DIMDI database search was run to search eight scientific databases (BIOSIS Previews, EMBASE Alert, EMBASE, HECLINET, ISTPB + ISTP/ISSHP, Health Technology Assessment Database, SciSearch, and Medline) for the publications on SCOs using the following search terms:
- stance control orthos? 8 scokj horton
- free walk otto bock 9 neuro tronic w fior gentz
- e-mag active otto bock 10 utx ambroise
- e-knee becker 11 full stride safety stride becker
- stance control KAFO 12 neuromatic fior gentz
- stance control poliomyelitis 13 e-mag active KAFO
- sensor walk otto bock 14 swing phase lock basko
In addition to the publicly accessible databases, the prosthetic and orthotic journals Medizinisch-Orthopädische Technik (Medical Orthopaedic Technology), Orthopädie-Technik (Orthopaedic Technology), and Journal of Prosthetics & Orthotics and the references of the analyzed publications were searched for other relevant articles. First, the abstracts of all articles were analyzed. The articles that did not involve with the patient benefits of SCOs were excluded. The full text versions of all the remaining articles were analyzed.
The research in the databases, the journals mentioned, and reference lists of the analyzed articles yielded 171 articles after duplications were eliminated. Of these, 156 were excluded from the analysis because they were either purely technical articles or did not deal with SCOs. Ultimately, 22 articles remained for the final literature analysis, including 2 literature reviews.1,2
The studies included examined the following orthosis systems:
- Horton stance control orthotic knee joint (SCOKJ)2 – 7
- Stance control KAFO (not commercially available)8,10 – 13
- Dynamic knee brace system (commercially available only in the US as Sensor Walk® [Otto Bock USA])2,3,8,14 – 16,18,19
- KAFO with a joint unit that controls knee movements using a microcomputer—intelligent orthosis (not commercially available)20
- Swing phase lock—Basko HealthCare/Fillauer2,21
- Otto Bock FreeWalk2,21,22
- Becker E-knee2,21
- Ottawalk-Speed SCKO (not commercially available)2,23
- Ambroise UTX Swing2
- Dual stiffness knee joint (not commercially available)2
The methodological quality of the studies on the medical benefits of SCOs is limited. Generally, only single-arm intervention studies (before [locked orthosis] and after [SCO] comparison) with only a few patients are available; some articles even include individual case descriptions of just one to three patients.
KINEMATIC GAIT PARAMETERS
A number of studies demonstrated that an SCO allowed their examined patients almost physiological knee flexion movement during the swing phase. This functional benefit is described in literature with a clear, sometimes statistically significant increase in maximum knee flexion during the swing phase7,10,13 – 16,22 or with a greater range of motion (ROM) during the gait cycle.4,12,13,16 Both values approach the normal levels of physiological gait when an SCO is used (Table 1).
KINETIC GAIT PARAMETERS
Schmalz et al.22 evaluated the changes in kinetic gait parameters when using an SCO. The analysis of the sagittal knee moment during the stance phase indicated no changes on the orthotic side due to the still locked joint, which was also confirmed by Irby et al.16 However, on the sound side, when the knee joint of the orthosis is locked, only a slight flexion moment occurs in the first half of the initial stance phase. After about 18% of the gait cycle (start of the mid-stance phase), a greater extension moment takes effect, which is consistent with the kinematic characteristics. Using an SCO, the course of the sagittal knee moment is qualitatively equivalent to normal gait, although the amplitudes of the local extension and flexion peaks are reduced, as the orthotic joint is still locked.
The external moments of the hip joint on the orthotic side show only slight differences between locked KAFOs and SCOs up to about 50% of the gait cycle. In the last part of the stance phase, unlike with a SCO, the extension moments are much higher than normal with a locked KAFO. An analysis of the torque of the sound hip also shows that joint loading of patients with a free swing phase orthosis is nearly physiological. If the two test situations are compared, higher joint stress can be measured during nearly the entire stance phase when the orthotic joint is permanently locked.22
Because of the changes in kinematic and kinetic gait parameters when walking with an SCO, compensatory movements, which were indispensable for walking with a locked knee joint, are reduced. Several studies showed in particular reduced pelvic obliquity on the orthotic side; in two studies to a statistically significant extent (Table 2).7,16 Schmalz et al. described a sound side pelvic obliquity when walking with a locked KAFO. At the start of the stance phase of the sound side, the pelvis must be raised sharply very quickly. This compensatory effect did not occur when using an SCO. The pelvic movement is qualitatively equivalent to a healthy comparison group.22
Another compensatory movement with a locked KAFO is a pronounced plantar flexion of the sound foot in the stance phase.4,16 The user attempts in this manner to gain more ground clearance on the orthotic side. Irby et al. described significantly reduced plantar flexion when walking with an SCO. The group of first-time orthosis users reduced plantar flexion with an SCO on average by statistically significant 2.5° (p = 0.04); patients with previous experience in using a locked KAFO on average by also statistically significant 1.4° (p = 0.02).16 Hebert et al. even reported that no plantar flexion at all occurred in the mid-stance phase with an SCO.14
The influence of an SCO on the reduction of plantar flexion seems to be clearly greater for first-time users than for experienced orthosis users. The reason for this is that experienced orthosis users have already internalized the gait pattern of the locked KAFO as a motor engram. Switching to an SCO requires a longer accommodation and training phase.3,15 This was also made clear in the article by Irby et al.16 in that the first-time orthosis users achieved a markedly greater range of knee motion of 55.2° ± 4.8° in the gait cycle using the SCO than the patients who had previously been fitted with a KAFO, who had a ROM of 42.6° ± 3.8°.
In summary, the results of the literature search show that the use of a SCO versus a locked KAFO can clearly reduce or even eliminate the necessity of compensatory movements. Because these movements serve mainly to ensure enough safety (ground clearance) when walking with a locked orthosis, this benefit is of great clinical significance to patients. The probability of suffering long-term sequelae as a result of strain to the musculoskeletal system is thus greatly reduced.
Metabolic parameters when walking with locked KAFO and SCOs were also studied and compared. The results of most studies (Table 3) show a tendency toward lower energy consumption when walking with an SCO; two studies even demonstrated statistically significantly reduced energy consumption.15,22 However, there are also studies that showed no difference in energy consumption between the two types of orthoses,4,7 yet one of these studies7 was conducted with healthy subjects and not patients. There are also discussions concerning energy consumption that patients may require a longer acclimation period for the SCO before the energy consumed while walking actually sinks.4,7,15
Only two studies analyzed muscle activity when walking with an SCO. In 1998, Suga et al. published a study in which they analyzed the electromyographic signals of the vastus medialis, rectus femoris, biceps femoris, and tibialis anterior muscles of healthy subjects and of subjects with muscular weakness. The muscle potentials were derived and compared under various orthotic conditions. The conclusion of the study was that both healthy subjects and patients with a paretic quadriceps muscle had clearly lower muscle activation when walking with an SCO than with a locked KAFO. Thus, the paretic musculature in patients was clearly less stressed by the SCO than by the locked orthosis.20 In a case study by Hebert et al., activation of the rectus femoris and vastus lateralis muscles of the sound side was evaluated. When the patient was wearing the SCO, unlike walking with a locked orthosis, there was no activation of the two muscles in the mid-stance and late stance phases. This change was explained by the lack of plantar flexion on the sound side in the mid-stance phase.4
All studies on time-distance parameters are presented in Table 4. In five of the six studies, the subjects' walking speed demonstrated statistically significant increases or at least showed an increasing tendency compared with a locked KAFO.3 – 5,16,22 By contrast, Yakimovich et al.13 observed reduced speed in their patients with an SCO, whereas Irby et al.16 observed this only in patients with previous KAFO experience. Overall, the gait pattern of patients walking with a SCO was consistently assessed as more symmetrical and natural.
Bernhardt et al.3 surveyed patients on their satisfaction with the various types of orthoses, both directly after fitting and after 3 months of acclimation. The patients were satisfied with stability during standing and walking and assessed it as somewhat better than with previous orthoses. At the initial survey, patients who had previously used a locked KAFO expressed an increase in safety when walking and a loss of safety when standing. After a 3 months accommodation period, this feeling was reversed. Overall, the SCO (Sensor Walk®) was perceived to be bulkier and heavier than the previous locked KAFO. However, many patients said that they would accept the greater weight of an SCO if it were reliable and walking with it were easier than with a locked orthosis.3
McMillan et al.5 also found a greater patient satisfaction with an SCO. With an SCO, patients found it easier to walk, and they were more mobile than with a locked KAFO.5 Two subjects from the study by Yakimovich et al.13 preferred the SCO because they perceived walking to be less strenuous, had to concentrate less, and found the SCO easier to control. The third patient preferred the locked KAFO, as he had to concentrate intensely on releasing the joint when initiating the swing phase. All three subjects indicated a greater measure of safety with the SCO.13
The methodological quality of the studies on the medical benefits of SCOs has the generally known deficits of studies in prosthetics and orthotics. There are only before and after comparisons with only very few patients; many articles describe only small case series of one to three patients. For this reason, potentially clinically relevant differences between the two types of orthoses did not reach the level of statistical significance in many studies. It must also be taken into consideration that the studies were conducted with many different SCO systems, which have some major technical differences. Switching between the stance and swing phase can be done using various technological mechanisms:
- Weight-activated SCO: E-Knee (Becker Orthopedics), SCOKJ (Horton), NeuroTronic W (Fior&Gentz), SensorWalk (Otto Bock USA)
- Position sensor-activated SCO: E-MAG Active (Otto Bock), Swing Phase Lock (Basko)
- Ankle-activated SCO: Free Walk (Otto Bock), UTX (Ambroise), Full Stride/Safety Stride (Becker Orthopedics), Neuromatic (Fior & Gentz)
In the weight-activated SCOs, the orthosis knee joint is locked for the stance phase as soon as weight is placed on the foot, registered through pressure sensors in the foot section of the orthosis. The joint is released for the swing phase when the foot no longer bears weight or the weight falls below a preset weight threshold or changes of weightbearing from the heel to the sole of the foot to the forefoot associated with walking are registered.
For position sensor-activated SCOs, at the end of the swing phase, the orthosis knee joint is locked for the stance phase at a certain angle relative to the ground (Swing Phase Lock) or to the patient's hip (E-MAG Active) and released for the swing phase at the end of the stance phase at a certain angle relative to the ground or to the patient's hip.
Ankle-activated SCOs are controlled by the relative movement of the tibia compared with the foot, whereby they are released for the swing phase at the end of the stance phase. The orthosis knee joint is locked when the nonweightbearing orthosis is fully extended at the end of the swing phase.
In addition, SCOs also differ as to the angle at which the knee joint of the orthosis can be locked for the stance phase. Most commercially available SCOs can lock the orthotic knee joint only when it is completely extended (e.g., Free Walk, UTX, E-MAG Active, Swing Phase Lock). These orthoses make it possible to stand safely on all surfaces, but walking safely is possible only on fairly level ground. On uneven ground, especially if it is very uneven, it can be very difficult to extend the knee joint of the orthosis completely to lock it for the stance phase. In addition, unlocking the joint for the swing phase becomes more and more difficult on increasingly uneven ground, so that walking on uneven ground with these SCOs can be described as only somewhat safe (slightly uneven ground) to unsafe (very uneven ground).
Some SCOs (e.g., E-Knee [Becker Orthopedics], SCOKJ [Horton], Neuromatic, Neuro Tronic W [both Fior & Gentz], SensorWalk [Otto Bock USA]) can lock the knee joint of the orthosis even when it is flexed. Some of these orthoses still allow the orthotic knee to be extended, whereby the lock remains activated in the flexion direction. These SCOs allow patients to stand and walk safely on both even and uneven ground. However, none of the SCOs allow the knee joint of the orthosis to be flexed when loaded and thus do not permit alternate ramp and stair descent.
The various SCO systems also pose very different demands on patients regarding the necessary residual functions and the coordination skills required for safely controlling the respective orthotic system. The manufacturer recommendations must be observed. Many patients who could in principle be fitted with a SCO, therefore, cannot be safely fitted with all available orthosis systems. The diversity of these product-specific demands on patients may contribute to the failure of SCOs to prevail to a larger extent over locked KAFOs. The selection of the most suitable orthosis system for the individual patient is challenging and ultimately requires precise knowledge of the specifications of all products available in the market. A major cause for the failure of fitting SCOs in practice is that an unsuitable or not optimally suitable orthosis system is selected for the individual patient. Test orthoses, which are offered by some manufacturers for their orthosis systems, can be a great practical help.
In the studies analyzed here, it is also uncertain whether the respective orthosis systems studied presented the best technical solution for all patients included or whether they could have been better served with another system. Therefore, it cannot be ruled out that the differences between SCOs and locked orthoses could have been much greater if the individual patients had been fitted with the optimal orthosis system.
In summary, it can be determined that despite the limited methodological quality of the studies, there are clear indications of a medical benefit from SCOs. The majority of publications tend to produce very similar results, which usually failed to reach the statistically significant level only due to the low number of patients. The medical benefit of a SCO can be described in three categories:
- More physiological gait pattern
- Reduction of compensatory movements
- Greater walking speed
- Lower energy consumption
- Greater patient satisfaction
BENEFITS FOR THE AFFECTED (ORTHOTIC) SIDE
- Knee flexion and greater ROM for the knee in the swing phase with greater ground clearance when walking
- Lower pelvic obliquity
BENEFITS FOR THE SOUND SIDE
- Plantar flexion to achieve greater ground clearance on the orthotic side is reduced to eliminated
- Elimination of pelvic obliquity in the stance phase
Further studies with better methodological quality are needed, especially with larger patient numbers and a randomized sequence of the orthotic interventions, to further support the previous results.
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