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Advanced prosthetic knee joint

This document discusses different types of prosthetic knee joints, including mechanical single-axis and polycentric knees, and computerized knees that use microchips, hydraulics, or pneumatics to control motion. It describes the evolution of prosthetic knees from simple pendulums to advanced mechanisms with microprocessor control. Key factors in prescribing the appropriate knee include the user's ability to control stability, flex the knee in swing phase, and walk at different speeds.

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Advanced Prosthetic Knee Joint KARTHIK M ANIL MPO 1ST BATCH
INTRODUCTION • It is the mechanical knee joint replica for anatomic knee functioning for any above knee prosthesis . • EVOLUTION - Prosthetic knees have evolved greatly over time, from the simple pendulum of the 1600s to those regulated by rubber bands and springs or pneumatic or hydraulic components. Now, some knee units have advanced motion control modulated through microprocessors.
CLASSIFICATION • The plethora of presently available prosthetic knee components can be divided into two groups based on how they are controlled: • Recent innovations that incorporate an onboard computer and the more familiar purely mechanical devices. • These categories then can be subdivided into generic functional classes based on the degree of stance phase stability and swing phase responsiveness offered by each type of knee mechanism
Prosthetic knee joint Mechanical Single axis Polycentric STABILIZING MECHANISM Manual Locking / Weight-Activated MOTION CONTROL Constant Friction Vs Variable Friction Computerized Hybrid knee mechanisms Microchip controlled Hydraulic Pneumatic STANCE PHASE CONTROL SWING PHASE CONTROL SWING PHASE CONTROL
Single-axis knee Joint • The single-axis knee, essentially a simple hinge, is generally considered the “workhorse” of the basic knee classes due to its relative simplicity, which makes it the most economical, most durable, and lightest option available. • LIMITATION - By virtue of their simplicity, the knees are free-swinging and have no stance control; amputees must use their own muscle power to keep them stable when standing. • To compensate for this, the single-axis knee often incorporates a constant friction control and a manual lock. The friction keeps the leg from swinging forward too quickly as it swings through to the next step.
Polycentric knee joint • The polycentric knee has two or more pairs of bars connecting the upper and lower portions of the unit. The bars pivot at both ends thus creating a moving center of rotation. • As the wearer bends the knee, the bars cross proximally and posteriorly, thereby changing the center or rotation and thus promoting knee stability during stance phase • Because four linkage bars connect the four axes, the polycentric knee also is referred to as a four-bar design.
Instantaneous Centre of Rotation (ICoR) • In most polycentric knee designs, the position of the ICOR moves anteriorly and distally as the knee flexes, following a curved pathway called the centrode. After the knee has been flexed a few degrees, the ICOR now falls in front of the GRFV, and the knee flexes automatically. • polycentric knee can provide inherent stability in early stance while still flexing easily in late stance during the preswing. Many users prefer this combination of inherent stability plus ease of voluntary swing phase initiation.
Various polycentric Knee Mechanisms
• As the knee flexes, the apparent or instantaneous centre of rotation between the thigh and shank changes in a manner which improves the stability characteristics of the knee and also allows an increased range of knee flexion. • Characteristics of stability (1) the instant centre of thigh-shank rotation, (2) the load line, (3) the brake moment or torque generated by the prosthetic knee, and (4) the hip moment which can be supplied voluntarily by the amputee.
The position of the load line at heel contact or at toe off may be related to the load P carried through the hip joint and the hip moment exerted by the amputee. An extension moment moves the load line ahead of the hip, a flexion moment moves it behind.
HYDRAULIC KNEE UNITS • Swing control • Hydraulic knee units regulate the swing of the shank according to the walker’s speed. • The unit has an oil-filled cylinder attached to the knee axis. A piston from the axis to the cylinder interior descends during early swing; this action forces oil to flow through narrow channels to provide frictional resistance.
MICROPROCESSOR CONTROLLED PROSTHETIC KNEES • Microprocessor knee units have electronic sensors that monitor the action of hydraulic knee units during swing and ground force during stance. Sensors measure angles, moments of force, and pressures at 50 or more times per second. • Adjustments can be made with a laptop or handheld computer. Software algorithms determine the phase of gait, automatically adjusting knee functions to approximate normal function.
MICROPROCESSOR CONTROLLED PROSTHETIC KNEES • First proposed concept by Kobe Steel researchers 2 decades ago, the clinical application of microprocessors controls to prosthetic knee mechanisms is a recent development. • 4 different microprocessor controlled knee prostheses using the sensor technology and the units generating internal resistances are available: 1. C-Leg 2. Adaptive 2 3. SynergyKnie 4. RheoKnee
C-Leg • The C-Leg system (Otto Bock, Germany) consists of a linear hydraulic unit including two independently adjustable valves for flexion and extension of the joint. • For identification of certain walking situations during the gait cycle, the prosthesis is provided with an ankle moment sensor (strain gauges) installed in the tube adapter and a knee flexion angle sensor. • An integrated algorithm calculates the valve positions required for adequate resistances. The working frequency of CPU is 50Hertz allowing adaptation of resistance each 20 ms.
The Adaptive2 • The Adaptive2 (Blatchford, Great Britain) comprehends a combination of a linear pneumatic and hydraulic unit working in parallel up to a knee flexion angle of approximately 35°. Exceeding - resistance of the hydraulic unit drops to a minimum. • Knee bending moments - strain gauge sensor located posterior to the knee rotation axis, the position of the piston - stroke sensor. • Motorised valves are implemented to adjust the resistances of the hydraulic (stance phase) and pneumatic unit (swing phase) in knee flexion direction. Extension stop is adjustable by a manual valve
SynergyKnie • (Nabtesco, Japan) consists of a combination of a hydraulic and pneumatic unit. The rotation hydraulic is primarily used to produce the resistances in flexion direction during stance phase. • A mechanical polycentric mechanism detecting rear and forefoot load during gait cycle allows switching from basic friction to a higher value manually adjustable. • The linear pneumatic unit adapts the flexion resistance for swing phase flexion by a motorised valve based on information provided by a position sensor located at the piston and a time counter. Extension stop is manually adjustable by a needle valve
RheoKnee • RheoKnee (Össur, Island) • A rotation hydraulic unit according to a magnetorheological concept is realised here. • Resistance in both flexion and extension direction is produced by changing the magnetic field and resulting change of fluid viscosity. • Force and moment sensors (strain gauges) installed distally to the joint chassis and a knee flexion angle sensor provide information with a frequency of 1000 Hertz. An adaptive control algorithm regulates the rate of resistances.
Prescription Criteria • The prescription of prosthetic components is not yet completely scientific, although the amount of data obtained increases with each new published study. But it now is possible to rule out specific components as being unlikely to benefit a patient with an amputated limb based on a biomechanical analysis of that person's goals and capabilities. • Rehabilitation team discussion then can be limited to those plausible alternatives components most likely to be clinically useful to the specific user.
Q,s for Prescription • The clinic team can determine each individual's stance and swing control needs by answering four questions. • Can this person be expected to use their remaining neuromuscular capacity to:(1) control prosthetic knee stability under all circumstances; (2) flex the prosthetic knee in a controlled manner during preswing; (3) walk with a prosthesis at differing speeds; and (4) walk with a prosthesis at a moderate or faster pace?
• Single axis designs - Those patients who can control voluntarily the stability of the prosthesis under all conditions may use one of the basic single axis designs. The remaining majority should be offered one of the more stable knee mechanisms according to their functional needs. • Manual locking knee - few patients who are totally unable to control the knee, perhaps because of a CVA affecting the amputated limb, may require a manual locking knee. Whenever possible, however, patients should be offered the opportunity to master a prosthetic knee that will bend during swing phase.
• Constant Friction - recent amputation and feeble patients whose overall physical condition will restrict them to very slow walking speeds may find a friction brake stance control mechanical knee sufficient. But slow preswing activation - not recommended for more active users. • Polycentric joint - offer excellent inherent stability in combinations with ease of knee flexion for swing phase clearance, making Polycentric knees the preferred choice for most patients needing some degree of stance stability who are otherwise in reasonably good health. • long residual limb usually will prefer the special class of four-bar knee prostheses designed to improve sitting cosmesis.
• Swing phase control - If the patient with an amputated limb is expected to vary their walking speed, then mechanical swing control devices will be insufficient and fluid control should be considered. • The smaller and lighter hydraulic units and pneumatic cylinders usually are sufficient for slow to moderate cadence walking, and often are prescribed for smaller stature individuals, including women and children. Larger, more powerful hydraulic swing phase controls are particularly appropriate for the taller individual, the more active ambulator, and for those who participate in competitive sports events.
• Microprocessor/Hybrid Knee - Specific indications for presently available microprocessor controlled knee prostheses have not yet been established. Because their long term durability is not yet fully documented, the ability of the user to return for follow-up adjustments or servicing is certainly an important consideration at this time. • In general, it seems that those amputees who would be reasonably good ambulators with conventional technology will derive the greatest benefits from such sophisticated knee controls
REFERENCE 1. Michael, John W. MEd, CPO Modern Prosthetic Knee Mechanisms, Clinical Orthopaedics and Related Research: April 1999 - Volume 361 - Issue - p 39-47 2. Comparative Biomechanical Analysis of Current Microprocessor Controlled Prosthetic Knee JointsM. Bellmann1, T. Schmalz, S. BlumentrittOtto Bock HealthCare GmbH, Department of Research/Biomechanics, Duderstadt, Germany 3. THE KNUD JANSEN LECTURE, Above-knee prosthetics, C. W. RADCLIFFE, Prosthetics and Orthotics International, 1977, I, 146-160