Locomotion Rehabilitation Platform with Weight Bearing Relief for Knee Osteoarthritis

Adolfo Ávila Barón Engineering Department. Santo Tomás University

Tunja, Colombia aavila@ustatunja.edu.co

Margareth Alfonso Physiotherapy Department. Boyacá University

Tunja, Colombia mlalfonso@uniboyaca.edu.co

Pedro Enrique Jiménez Faculty of Medicine. Boyacá University

Tunja, Colombia pejimenez@ustatunja.edu.co

Abstract—Major kinematic changes occurring in gait pattern in patients affected by osteoarthritis of the knee are due to pain which brings decreased physical activity and life quality impairment. Decreased physical activity generated by pain results in lower energy consumption, body weight rise and increase in knee load and pain. Reduction in weight-bearing load to treat the pain of osteoarthritis is well documented. In Tunja (Boyacá-Colombia) a weight bearing relief device is used by researchers to promote physical activity controlling load and decreasing pain. A platform will be used to control locomotive rehabilitation and asses the ideal load relief on osteoarthritis knee to promote physical activity, body weight reduction and symptoms improvement.

Keywords- Keywords- gait, control, platform, osteoarthritis, load, Unweighting.

I. INTRODUCTION Osteoarthritis is a disease characterized by changes in

articular cartilage leading to biomechanical performance impairment, degeneration and pain and disability. Knee is one the most commonly affected joint with more than 30% of 60 years older people afflicted. A recent report of the World Health Organization indicates that osteoarthritis of knee is close to be the fourth most important cause of disability in women and the eighth one in males, with high annual costs attributed to this pathology [2]; it is assumed that around 2020, 11.6 people will have limitations due to knee osteoarthritis with annual expenses of 60 dollar billions around the world [3].

The most important symptom in osteoarthritis is pain, typically of mechanic character, appearing during gait and improving at rest, in severe cases can be present yet at rest. Other symptoms include: joint morning stiffness that can last up to 30 minutes, decreased range of motion, muscular retractions, crepitus, instability, joint effusion, etc. [4). Some researches show relation between structural and functional alterations and biomechanical changes in knee [5]. Pain is the basic reason leading to unconscious modification of stance and gait biomechanics to diminish load on the medial part of knee. Within processes investigation for knee osteoarthritis, it is necessary to design and use a rehabilitation platform that

facilitates the practice of physic activity to minimize the load on the joint, furthermore contributes to lose weight easier and retraining gait pattern, thus, these patients will be more functional on locomotion activities.

II. CHANGES IN GAIT CONSEQUENCES Some studies have shown differences in gait pattern

between adults with osteoarthritis and normal subjects demonstrating relevant changes in load transmission and function. Also differences between men and women were founded: men showed increased time in double support time, balancing phase and load response compared with women. On the other side, velocity and cadence were both decreased in osteoarthritic men and women compared with non affected people of the same age [6]. Kinematic gait analysis in osteoarthritic patients show more medial joint wear which modifies load transmission in all inferior limb: hip rotates externally during initial contact, knee goes into varus, foot supinates and load transmission during initial contact and metatarsal alignment is modified with a consequent slower and poor functional gait pattern [7].

Rheumatology’s American Association performed a research involving two patient groups: healthy subjects with medial pain induced by hialuronic acid injection and 161 patients with medial knee osteoarthritis, using a contact platform the gait was analyzed. Both groups developed a gait pattern with diminished support time and altered load bearing, less pronounced in in osteoarthritic patients. The researchers concluded that pain is the cause of the modified gait pattern in osteoarthritic knee [8].

The behavior of kinematic variables of gait has been described showing a relationship between decrease in gait velocity and reduction in range of motion of the knee particularly extension [9]. Another study shows that some early mechanic alterations may have etiologic implications but may be that some others represent secondary changes developed as compensatory mechanisms. Examples of such changes are: increase in varus and internal rotation during stance phase [10].

A study by the American Society of Physical Medicine and Rehabilitation to investigate the gait patterns and reaction forces in the sagittal plane by means of a biomechanical force platform, 10 meters in length, in which variables such as speed, acceleration, determinants and phases of gait were analyzed, described the changes in gait pattern in patients with knee osteoarthritis. It showed that patients with knee osteoarthritis had significantly lower load compared with healthy adults; furthermore, double stance time expressed as a percentage of gait cycle was longer in the group of people with arthritic knee. The main conclusion of this study was that loss of joint mobility and muscle strength and altered proprioception, added to pain, contribute to deterioration in the gait pattern in this population [11]. In general a locomotion deficiency lead to increased energy expenditure during gait process, which may be caused by saturation of the aerobic metabolism capacity what reduces the autonomy of movement [12]. A joint degeneration causes a low speed gait and its consequence of decreased energy efficiency [13].

There is current evidence on the relationship between overweight and severity in symptoms of knee osteoarthritis. An investigation in which an exercise prescription plan and a low calorie diet were applied demonstrated a decrease in body weight, relief of pain and a better functional status [14]. Within characteristics more prevalent in patients with knee osteoarthritis, is evident the high rates of overweight, in part due to pain and decreased levels of physical activity and lower energy expenditure increasing body weight and loads on the involved joint. Weight control becomes more complex but the necessity to perform physical activity is not only to reduce body weight but also to diminish cardio vascular risk.

III. LOCOMOTION REHABILITATION PLATFORM Biomedical signals are spatial and temporal records of

electrical, electromagnetic or chemical activity produced by human organs. To obtain and adapt these signals and then transmit them properly without losing information is a challenge that engineers are facing, especially when human life depends on it. The electronic information reliability makes possible the control, such as mechanical systems, electronic systems, or mixed systems as industrial systems. But health security is relevant when people are using a device such a locomotion rehabilitation platform, and even more when it has wireless devices.

Figure 1. Design Phases of Locomotion Rehabilitation Platform.

The requirement for mechanical, computer and electronic designs must be combined to ensure safety and reliability; other design features should provide comfort and ease use for patients and who takes care of them. In the Figure 1, you can see each phase considered in this design.

The rehabilitation platform Dimensions was designed considering data from 15 older adults than 60 years of Tunja City in Colombia country, the data sample was taken using phases and determinants gait, lower limb length in centimeters real and apparent, also step length.

Different research institutes and business enterprises around the world, such as AEMEDI or ALTACRO designed their own rehabilitation platforms, some of them made their designs by climbers, others use bicycles or similar mechanisms, but general considerations in the rehabilitation and patient comfort are what make the difference on implementation. Considering Stride length such a variable which can modify the treadmill adjust.

TABLE I. STRIDE LENGTH AND LIMBS LENGTH

No RLLL ALLL SL

A1 85 79 86

A2 78 67 83

A3 86 80 79

A4 79 77 76

A5 81 80 77

A6 75 73 78

A7 76 73 79

A8 77 72 69

A9 82 76 80

A10 78 73 77

A11 79 75 74

A12 77 74 76

A13 78 75 80

A14 66 63 86

A15 84 80 83

Average 79 74 79

a. RLLL = Real Lower Limbs Length, measured in cm.

b. ALLL = Apparent Lower Limb Length, measured in cm.

c. LS = Step Length, measured in cm.

d. A = AdultSample of a Table footnote. (Table footnote)

Figure 2. Rehabilitation Platform design: this design includes some degree

of freedom, in particular treadmill adjust.

A. Stride length. Taking linear distance in meters between two events, equal

and successive in the same limb, usually the measurement is selected with the initial contact of one limb until the next initial contact of the same limb. The step length includes a short right and left step; the samples in Table I were taken over senior adults in normal gait conditions.

B. Platform Degrees of freedom. According to the patient height, weight and size, the

mechanical structure platform has a mobile support on the parallel bars with two degrees of freedom, as shown in Figure 4. The First degree of freedom allowing bars movement inside or outside of platform and second graduate bars height.

Figure 3. Mobile support and parallel bars: specify different adjust degree on the platform.

To improve the patient area movement on the platform, it is possible to move control device and treadmill along platform surface base as shown in Figure 2, thus the movement completes the third degree of freedom. This treadmill displacement and adjust depends on the patient stride length, it is shown in the Table II as control distance.

TABLE II. MAXIMUM AND MINIMUM RANGES ACCORDING STRIDE

Part limbs Treadmill Platform Vertical Adjust

Platform Rotational

Adjust

Measure Stride length (cm)

Control distance

(cm)

support height

(cm)

Rotation Angle (degrees)

Max. 74 80 cm 90 0

Min. 86 92 cm 105 45 Out

a. Control distance: distance measured from the medium hip to the platform control .

b. Rotation Angle: angle measured from vertical support position to external rotation.

c. support height: : distance measured from treadmill to support

IV. WEIGHT AND SPEED CONTROL USING AN ADAPTABLE FUZZY SYSTEM

There are different “Adaptive Fuzzy Systems” (AFS), one fuzzy controller called linguistic Self-Organizing Controller (SOC), it has many applications based on rule base changes. Others AFS type is the “Fuzzy Model Reference Learning Controller” (FMRLC) and WSAFC Wang Adaptive Fuzzy Controller which use Lyapunov theorem, all these methods are based on ruler changes and no proof completely that will result in a stable closed-loop system especially for critical systems. We consider that a Adaptive Fuzzy Logic System which modify fuzzy sets as happen in the project named “Mobile Robot Using Adaptable Fuzzy Control on a Digital Signal Processor”[16], It is an successful and proved strategy for using on platform control.

Known the Fuzzy System characteristics, our main objective is to control weight and desired speed, next figure describes a fuzzy control, it uses a reference model, this model produces an ideal output which will be used as input on Adaptive fuzzy Control, finally an output parameter will be used by fuzzy system controller as signal input to control the platform system. Platform has two inputs, weight and speed electrical signals, these are variables obtained by patient weight sensor and treadmill speed sensor. We could get many outputs if we take different human body parameters, but in this part of the system, cardiac rhythm and knee pain are the main variables. Pain parameter has many individual characteristics, because each patient has her own pain range but it has to be measured with the same scale, however weight parameter is easy to take despite its fluctuations, this input is only an electrical signal of a strain gage.

Figure 4. Adaptable Control Model Reference.

V. FUZZY SETS INPUTS AND OUTPUTS To introduce this fuzzy logic system it is necessary to know

the constitutive parts of Locomotion Rehabilitation Platform, it permits related Fuzzy logic systems with fuzzy sets design [17]. The sensors as strain gauge or electrodes measure the variables which correspond to different fuzzy set inputs. The output variable named speed has five fuzzy sets, one of them is Low speed as shown in figure 5 and others are Low-Media, Media, High-Media and High speed.

Figure 5. Figure 5. Fuzzy system characteristics

This control was tested using Unfuzzy software[17], which has the main adjust variables for Speed Output are: sets, variable definitions and defuzzyfier.

Input variable as the pain has five fuzzy sets: very low, low, medium, high, very high, but this pain test depends of verbal communication with each patient, however this variable is evaluated over fuzzy logic system as a discrete variable over a common scale. Here can be used the advantage of having an adaptive control system, “flexible fuzzy sets” as it is related in chapter IV.

VI. STATISTICAL RESULTS IN THE LOCOMOTION REHABILITATION PLATFORM

Figure 6 shows three Probability graphs about the patient pain. Each color describes a discharge weight case.

Figure 6. Probability plot of PPFS-CW, PAFS-CW, NDW

PPFS-CW: Platform Proportional System. PAFS-CW: Platform Adaptive Fuzzy System. NDW: No Unweighting.

Red line: using an adaptive fuzzy system to control with 20% unweighting.

Black line: using 10% constant unweighting.

Green line: No Unweighting.

Red graph shows how patient pain is lower than other cases. Then the adaptive fuzzy system applied on a locomotion platform contributes to lose weight easier and retraining gait pattern on patient with knee osteoarthritis.

VII. MATERIALS AND METHODS Longitudinal panel design and analysis [15], the same

group of participants is measured and observed with the different download weight: 90%, 80% and 100% of body weight thus analyze the variables which our study aims. Probability sampling is applied: Women over age 60 diagnosed with bilateral knee osteoarthritis, overweight, who underwent evaluation of gait pattern using the locomotive rehabilitation platform, with different downloads weight; at three different times, the first being evaluated with 80% of body weight, the second with 90% of body weight and a third time with 100%, then there will be a walk in the locomotive rehabilitation platform of 30 minutes at 0,5 m/s speed and 0 degree of tilt, then, It is tested and evaluated: the gait characteristics (walking phases, kinematic variable, motion range, speed, acceleration) in addition patient of the pain, through Verbal Analogue Scale, after that, the symptoms and functional limitation by the WOMAC questionnaire.

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