Overview

The C-Leg 4 Update microprocessor knee

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With over 100,000 fittings to date, the C-Leg is trusted by more users than any other microprocessor knee in the world1. And it&#;s no wonder: Studies show the C-Leg provides the exceptional reliability and performance users need to focus on what really matters &#; enjoying a healthy, active lifestyle.

From descending stairs and ramps, to navigating uneven terrain, to walking backward, the C-Leg dynamically adapts to a wide variety of everyday situations.

This legacy lives on in the C-Leg 4 Update. With an innovative design and exciting new features, the C-Leg 4 provides the known reliability, next-level personalization, and an easier, more intuitive user experience for both patients and professionals alike.

For Users

• New! Supported descent on ramps and stairs
• New! Improved stance release with short and quick steps
• New! Stumble Recovery Plus active at all times
• New! Increased support for sitting down
• New! Training function for stance release exercises!
• New! Choice between intuitive and deliberate stance
• New! More options for favorite activities with MyMode Plus
• New! Deep sleep mode to save battery
• New! Redesigned charger allowing one-handed operation
• New! Customizable shield cover
• New! Darker color option (Midnight Shadow)
• Safe backward walking
• More reliable swing and stance phase control
• User customized functions via the Cockpit app for Android and Apple iOS

For Professionals

• New! Training function for ensuring consistent stance release
• New! C-Soft Plus with video tutorials and presets to support the fitting process
• Delivered in Safety Mode until patient-specific data is entered. A recommendation is then provided.
• Standard 34mm, easily shortened tube adapters
• Access usage statistics when activated to see progress at each appointment for 6 months
• Can be connected to an osseointegrated, percutaneous implant system*

The C-Leg is available in multiple colors as well as a screw-top or pyramid adapter.

IP67 Rating: Water-resistant but not corrosion resistant. Protected from dust, sand, dirt, and temporary submersion in fresh water (up to 1m for 30min). Accidental water damage does not void the warranty.

1Wismer, N., Mileusnic, M., Sreckovic, I., & Hahn, A. (). First results on next generation C-Leg. Poster presentation at OTWorld, Leipzig, Germany

A mechanistic explanation for previously observed safety improvements with microprocessor-controlled prosthetic knees is needed. A repeated measures design of 15 subjects with unilateral transfemoral amputation was used to assess changes between baseline use of their standard of care, mechanical pros-theses, and a C-Leg microprocessor-controlled prosthetic knee. The primary outcome measures were sensory dependency scores for somatosensory, visual, vestibular, and visual preference, which were calculated based on a Sensory Organization Test. Falls during posturographic assessment were also recorded. Somatosensory system dependency significantly increased (p = 0.047) while using the C-Leg compared to a nonmicroprocessor prosthetic knee (NMPK). Reliance on visual with vestibular input and reliance on vestibular input alone were not significantly increased with C-Leg use (p = 0.41 and p = 0.15, respectively). When utilizing the C-Leg, there was a significant reduction in the average number of falls (p = 0.03). Hence, increased reliance on somatosensory input is a possible explanation for improved balance with use of a microprocessor prosthetic knee (MPK).

Microprocessor prosthetic knees (MPKs), specifically the C-Leg, reduce falls in transfemoral amputees (TFAs) ( 5 ). A recent literature review collectively confirmed that the C-Leg is safer than a nonmicroprocessor prosthetic knee (NMPK) ( 5 ). However, no mechanistic explanation for the safety improvements has been offered. Therefore, this study&#;s purpose was to determine if C-Leg use favorably increases sensory system utilization, thereby offering a mechanistic explanation for the previously observed safety improvements.

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The Equitest ® dynamic posturography balance platform (NeuroCom International, Inc., Clackamass, OR, USA) was utilized to assess sensory dependence. Specifically, the Sensory Organization Test (SOT) was used to distinguish afferent contributions of the visual, vestibular, and somatosensory systems to balance. Three consecutive trials in each of six combinations of visual and support surface conditions were collected while the platform and visual surroundings either remained stationary or swayed sagittally to match subjects&#; estimated center of mass excursions. Specifically, the six conditions were 1) eyes open with fixed surface, 2) eyes closed with fixed surface, 3) eyes open with sway-referenced visual surround, 4) eyes open with sway-referenced surface, 5) eyes closed with sway-referenced surface, and 6) eyes open with sway-referenced surface and visual surround. Individual and composite SOT scores are reported else-where ( 7 ). This study performed secondary analyses to derive sensory dependency scores ( ). Trials where subjects stepped or touched the wall to avoid falling received a zero score and were classified as a fall.

A repeated measures experimental design was utilized. Except for knee mechanisms, prosthetic components were unchanged. This eliminated confounding socket-fit issues, foot properties, and accommodation to anything beyond the prosthetic knee. Subjects were first tested using NMPKs and then retested with a C-Leg. The study prosthetist [certified by the American Board for Certification in Orthotics, Prosthetics & Pedorthics (Alexandria, VA, USA) and by Otto Bock HealthCare for C-Leg fittings] evaluated subjects using observational gait assessment and made necessary adjustments to optimize alignment [confirmed with a L.A.S.A.R. (Laser Assisted Static Alignment Reference) posture tool (Otto Bock HealthCare)] and function. Following initial testing, subjects used the C-Leg until they stated that they were accommodated ( 9 ).

There was a statistically significant 33% reduction in the number of falls when using the C-Leg (p = 0.03). NMPK use resulted in 21 falls among seven fallers (average, 1.4 ± 2.3 falls per person) compared with 14 falls among four fallers (average 0.9 ± 2.1 falls per person) while utilizing the C-Leg. This comparison&#;s effect size was small.

There was a significant 3% increased reliance on somatosensory system input (p = 0.047) while using the C-Leg compared to NMPK. Reliance on visual with vestibular input and reliance on vestibular input alone were both greater (3%, p = 0.41, and 1%, p = 0.15, respectively) with C-Leg use but were not significant ( ). The four sensory dependency comparisons ( ) had small effect sizes (Cohen&#;s D < 0.20).

DISCUSSION

We hypothesized that sensory reliance would be limited to the somatosensory system. Thus, it was first necessary to determine if C-Leg utilization increased activity. The project&#;s first phase used doubly labeled water to demonstrate increased total daily energy expenditure associated with movement, whereas no significant difference in locomotion energy efficiency between knee conditions occurred (8). Our literature review revealed similar findings where only two of eight articles reported statistical improvements in energy efficiency associated with C-Leg use (5). Increased activity level with C-Leg utilization is uncorroborated through step-counting, which does not consider stepping intensity such as sloped terrain ambulation, leaving this assertion unresolved (5).

Using dynamic posturography, the project&#;s second phase determined that balance improved with C-Leg use (7). Furthermore, many studies corroborate improved safety with utilization of this device (5). Yet, a mechanistic explanation for these safety and balance improvements was lacking until this study was performed.

This study demonstrates that somatosensory system dependence increases significantly with C-Leg use. Vrieling et al. indicated that prosthetic side somatosensory input can increase with the weight-bearing aspect of balance maintenance (14). As subjects used the C-Leg and experienced fewer falls, confidence likely increased, contributing to increased prosthetic reliance. This is further corroborated by Kaufman et al.&#;s findings that weight-bearing symmetry improved while walking with a C-Leg compared to NMPKs in this same cohort (6). Nederhand et al. explain that an amputee&#;s continued weight-bearing symmetry improvement is attributable to central reorganization, including decreased reliance on active cognition and visual input (11). Our results confirm decreased visual reliance because we did not find significant increases in visual or vestibular dependence. Ultimately, balance improved as evident by previously reported improved SOT scores and further substantiated by a grade B recommendation of the C-Leg as a safer prosthetic knee (5,7).

Potentially confounding is the prosthetic foot/ankle. Nederhand et al. indicate that amputees can use passive prosthetic ankle stiffness to &#;fine-tune&#; ankle torque as an ankle strategy during balance (11). Prosthetic feet were not standardized in this experiment. Nevertheless, ankle kinetic gait symmetry improved with C-Leg use (6). Perhaps weight-bearing confidence was improved, and, as Vrieling et al. indicate, an ankle strategy may be employed by micromanaging ankle moments via axial weight bearing (14).

Confidence also plays an important role by increasing axial prosthetic loading and thus somatosensation (14). We believe increased confidence comes from utilizing the stumble recovery feature and subjects&#; knowledge that their knee is more stable. This can be partially corroborated because stumble recovery was effective when subjects were tripped and had fewer stumble events (1,5). There is presently not a clear and direct linkage between stumble recovery proficiency and increased confidence, although one study demonstrated improved Activities-Specific Balance Confidence scores with C-Leg utilization (12).

Several authors report improved balance may result from a learning effect associated with repeated postural control assessments when time between tests ranged from days to a month (4,15). Our subjects were only tested twice with a mean accommodation of 4.5 ± 2.0 months between tests. Further, the two prosthetic knee mechanisms differ considerably, requiring different stump motor strategies. Therefore, a learning effect can be ruled out.

Limitations

We attempted to optimize external validity in order to answer an important clinical question to determine if balance improved. The experimental conditions&#; sequence was not randomized. The NMPK was tested first because subjects were already accommodated to it and because this sequence best mimics clinical situations where amputees transition from NMPK to MPK. Unfortunately, there was no opportunity for long-term follow-up to determine if sensory inputs and activity levels stabilize, because studies with lesser quantities of training show structural cortical changes relative to balance performance (13). Finally, differing component properties may impact balance and activity levels so future studies should consider controlling them (11).

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