What is ORTHOSIS ?

• An orthosis is any device added to the body to stabilize or immobilize a body part , prevent deformity , protect against injury or assist with function

Some Basic Goals of Orthosis:-

• 1) To assist movement generally• 2) Maintenance or correction of body

segment alignment• 3) To aid rehabilitation from fractures

after the removal of a cast• 4) Assistance or resistance to joint

motion• 5) Protection against physical insult

WALKING• Walking is a complex process in which

the body segments move in many ways.

• To function efficiently, the lower extremity should have the ability to: 

• 1) support body weight during the stance phase 

• 2) rotate and coordinate the joints to achieve forward progression.

• 3) adjust limb length by flexing the knee during the swing phase 

• Normal walking requires muscular strength, joint mobility and coordination of the central nervous system.

• The absence of any of these capabilities can challenge a person's ability to walk.

• Yet impaired walking can be lessened by orthotic intervention.

Knee-Ankle-Foot Orthosis

• The term KAFO is an acronym that stands for Knee-Ankle-Foot Orthosis

• This device extends from the thigh to the foot

• It is generally used to control instabilities in the lower limb by maintaining alignment and controlling motion.

• These Instabilities can be either due to skeletal problems

• broken bones, arthritic joints, bowleg, knock-knee, knee hyperextension or muscular weakness and paralysis

. There are two very general categories of KAFOs: Metal designs and plastic and metal designs . The metal design consists of a metal structure shaped to the limb and furnished with leather at the points where the device makes contact with a person’s body.

• This is the more traditional of the two designs.

• The plastic device is custom molded to the person’s body with metal components in key structural areas only.

• The reason for the increased use of the plastic and metal design is that it is lighter in weight and is considered to be more cosmetic

Strength Maximum external load that can be withstand

Stiffness Stress/strain or force-to-displacement ratio

Durability (fatigue resistance)

Ability to withstand repeated loading

Density Weight per unit volume

Corrosion resistance Resistance to chemical degradation

Types of KAFO’s• Two types of KAFOs generally

are prescribed: eccentric (free-knee) joints or locked- (fixed-) knee joints. 

• Eccentric knee orthoses are stable in extension as long as the ground reaction-force vector passes anterior to the hinge axes. The eccentric hinge orthosis design provides limited stance stability and allows flexion/extension at all times

Materials and Methods• Logic-Controlled

Electromechanical Free-Knee Brace :-

• A small, lightweight, electronically controlled knee lock that can be installed on a conventional KAFO has been developed

• The system is composed of mechanical hardware and an electronic control system

• The mechanical hardware portion consists of a polypropylene orthotic design, a mechanical clutch and a clutch-release actuator solenoid. To adapt the electromechanical components to a standard orthosis, the medial-side knee hinge struts are left intact, and the lateral hinge is removed. Specifically fabricated stainless steel brackets connect the clutch mechanism to the lateral thigh and shank struts. The knee-hinge clutch mechanism is a wrap-spring clutch (a special class of overrunning clutches; an overrunning clutch allows torque to be transmitted from one shaft to another in only one direction of rotation). The assembly is, in effect, a band break connecting two cylinders placed end-to-end and rotating on a common axis (see Figure 2 ). The spring is fastened to the left-hand arbor and slips on the right-hand arbor. The backstopping, or locking-up, occurs when a torque is applied to the clutch, which tends to wrap the spring tightly onto the shaft while locking the shafts together. Conversely, when torque is applied to the opposite side, the spring unwraps from the shaft, allowing the shaft to slip easily in the opposite direction. A solenoid is used to control the clutch.

• The electronic control system is composed of digital logic-integrated circuits. A combination logic network monitors input data and produces electrical output commands based on the input states. The inputs to the control circuitry are signals generated by strategically located foot contact sensors. Based on the input, the controller algorithm generates an actuation signal that is sent to the solenoid for release of the clutch during the swing phase of gait.

Knee Motion

• Kinematic parameters were acquired using a computerized video motion analysis system (VICON ) with five infrared cameras. The spatial distribution of the cameras was optimized to yield reliable motion data bilaterally at the hip, knee and ankle. Reflective markers were placed on the subject's lower limbs to identify the relative rotations of the limb segments. Markers were placed on a sacral stick and bilaterally on the anterior/superior iliac spines, greater trochanters, lateral femoral condyles, lateral malleoli, calcanei and fifth metatarsal heads as well as on a 12-cm wand taped to the lateral aspect of the tibias. The motion analysis system was calibrated prior to each gait analysis. Video motion data were acquired over a 3-in length of a 9-in walkway to yield one complete gait cycle. One set of data corresponding to the standing position (static data) was recorded to calculate joint centers.

• After a brief orientation session, the subject was asked to walk along the walkway. At least five trials were conducted. The time and distance parameters were calculated and averaged, and the walking cycle that most closely typified the patient's gait was selected for further analysis. The selection was made by calculating the Euclidian norm for the deviation of velocity, cadence and step length from the average velocity, cadence and step length. The cycle with the smallest Euclidian norm was considered the representative cycle. The two-dimensional coordinates recorded by each of the cameras were reduced to a set of three-dimensional marker coordinates using the analytical software package (AMASS b) provided within the VICON system.

• Once the marker positions were computed, the rotation of the limb segments was calculated using software developed in the Motion Analysis Laboratory (6,7). The software was configured to calculate and display joint angles and deviations from normal gait at the hip, knee and ankle as a function of the gait cycle (8). Angular rotations were calculated about three axes of the hip, knee and ankle. The authors used Fourier analysis to quantitate wave forms and smooth the data. The gait cycles were manipulated (extended and compressed) to yield a normalized gait cycle. All gait events were expressed as a percentage of the gait cycle, irrespective of the actual time for a stride.

• Energy Expenditure Measurement• Energy expenditure testing was conducted on an electronically controlled treadmill.

During testing, the subject wore his customary shoes and was required to maintain an erect walking posture without walking aids.

• The subject was studied using the orthosis in both locked and unlocked configurations. Data were collected at treadmill grades of 0- and 5-percent incline. Walking velocities ranging from 15 to 80 in/mm (the functional range of walking speeds in adults) were tested. The average slow and fast walking speeds in adults ages 20-59 years range from 43 to 106 in/mm (9).

• The subject breathed through a suspended mouthpiece that allowed vertical, lateral and forward/backward movement with changes in head position. Gas samples were analyzed for oxygen content. A mass spectrometer (Perkin Elmer) and a volume turbine (Sensor Medics) were interfaced with commercially available software (Firstbreath) to calculate energy consumption variables on a breath-by-breath basis. The mass spectrometer was interfaced to the mouthpiece via a known length of capillary tube, precalibrated for lag time. Prior to the test, the mass spectrometer was calibrated with precision gases.

• Once physiological steady state was reached, data collection commenced. (Steady state was determined by observing the slope of the oxygen consumption rate and was reached within two minutes for all conditions.) All gas volumes were corrected to standard values of temperature, saturation and pressure (STPD). Standard protocols for energy expenditure measurement were followed (10,11).

• Energy expenditure during walking was expressed by three parameters (12). The rate of oxygen consumption (1702) is the amount of oxygen consumed per minute (ml/kg/min). The oxygen consumption rate indicates the intensity of sustained exercise and is related to the length of time exercise can be performed. The energy cost per meter (ml/kg/m) describes the amount of oxygen needed to walk a unit distance and indicates physiologic work. The energy cost equals the oxygen consumption rate divided by the speed of walking.

• A comparison of the energy cost per meter to an averaged value for normal walking enabled the authors to determine gait efficiency. Normal values for energy expenditure were taken from the literature. Energy expenditure data for normal gait on a level surface were available from Waters (9) and Bobbert. The relationship between energy consumption and speed during normal walking on a slope was taken from Bobbert (13). Gait efficiency was defined as the ratio of the energy cost for an able-bodied individual divided by the energy cost for the patient. Since the energy cost for the patient is nearly always greater than normal, the gait efficiency is less than 100 percent depending on the degree of disability. Thus, gait efficiency is a measure of the patient's rate versus an able-bodied individual's rate of energy expenditure at comparable speeds (9).

• For accurate measurements, the oxygen consumption rate (ml/kg/mm) must be distinguished from energy cost (ml/kg/m). The oxygen consumption rate indicates the intensity of physical effort during exercise and is a time-dependent parameter. Energy cost is not time-dependent. A high oxygen consumption rate indicates a high intensity of exercise. On the other hand, a high energy cost indicates a high degree of gait disability.

• Joining Technology• Materials used to join the uprights, joints and cuff components

together are typically rivets and screws made from aluminum, copper, brass or steel. Because the softer aluminum, copper, and brass rivets must be larger than steel rivets to achieve the same strength, larger holes are needed to accommodate the softer rivets within the uprights. In the orthoses, the larger holes in respect to the dimension of the metal uprights weaken the upright. Although recommendations have been made for their application,seldom is attention paid to the spacing of the fastening component or the edge distance. Conversely, the larger holes in softer plastic cuff material help distribute the load over a wider area making a better metal-plastic joint.

• Basic knowledge of the material properties used in orthotics is essential for achieving a robust design with minimal fabrication costs.

• Application: • Since there are many different reasons to use a KAFO, there are many

different designs. • Each design has its own special features and its own specific way to be

put on properly. • The orthotist providing the device will instruct the patient on the

proper way to put the • KAFO on at the fitting to make best use of the design features of the

device.

• The following instructions are for putting on a basic plastic KAFO with metal uprights:

• 1. While sitting, position the thigh and the leg inside the KAFO (See Figure 4).

• 2. Position the heel completely back into the plastic of the KAFO (See Figure 5).

• 3. Secure the Velcro strap across the instep (See Figure 6). • 4. Continue fastening the Velcro straps up the leg and the thigh

(See Figure 7). The • foot can then be inserted into the shoe. If necessary, the insole

of the shoe can be • removed to allow for more room for the foot portion of the

KAFO.

• Wearing Schedule: • On the first day you receive the brace, begin by wearing for only 1 hour. After 1 hour, • remove the brace and check your skin for red marks. Some small, light red marks may

be • noticed on the skin that should go away in 20 to 30 minutes after removing the brace. • Slight redness is common over the instep and under the ball of the foot. If the red

marks • do not go away in 20 to 30 minutes or if you notice any scratching, bruising, or

blistering, • do not put the brace back on. Call immediately to schedule an appointment with your • orthotist. • If the skin is ok, wait at least 1 hour and then put the brace back on for 1 hour at a time • for the rest of the first day, checking the skin after each hour. • On the second day, put the brace on for 2 hours. After 2 hours, remove the brace and • check the skin. If the skin is ok, put the brace back on for 2 hours at a time for the rest

of • the day, checking the skin after every 2 hours. If your skin is ok, gradually increase • wearing time by 1 hour each day, checking the skin after each wearing time.