Adaptive muscle stimulation technique

An embodiment of the invention resides in the apparatus and technique of dynamically measuring and storing a biological condition or disposition during the time that one set of conditions are imposed on a joint or body area and applying closed-loop therapeutic action so as to re-achieve that same biological condition or disposition during a subsequent time that another different set of conditions are imposed. Furthermore, dynamic potentials surrounding said joint or body area may be created, bolstered, and/or modulated through aspects of stimulation applied which are independent of those aspects utilized to counteract force incident on the joint or body area. Other embodiments are described herein.

BACKGROUND

When a skeletal joint is compromised, whether through injury, pathology, misalignment, overuse, or surgery, bracing is often necessary to provide support and possibly facilitate healing. Conventional external mechanical braces, however, have been shown repeatedly to cause muscle atrophy by supplanting normal muscle activity. In that this effect is antipathetic to the basic principles of rehabilitation, devices which actively stimulate the body's own musculature surrounding the compromised joint are increasingly being used for protection and/or rehabilitation. One of these devices may be worn throughout the day, constantly monitors the patient's movements, and responds to problematic joint circumstances by stimulating muscles in a manner which opposes the incident force causing the problem. A form of muscle stimulation used in these devices is electrical current.

These devices, however, rely upon pre-programmed templates for operational parameters, or learn physical conditions deemed problematic for the joint by either the patient or an attending medical practitioner. They are therefore inherently open-loop systems, responsive solely to physical conditions of the joint, without regard for direct or indirect effects of the dynamic muscle stimulation they provide. Not only does this open-loop nature necessitate programming applicable to a broad range of patients (as opposed to individualized therapy), it as well precludes adaptation by the device to incremental improvements made by the patient through use of the device. No attempt may therefore be made by such as system to regulate therapy toward a nominal state for that particular patient. Application of closed-loop techniques would allow these devices to continuously adapt to the individual patient on an ongoing basis.

The term ‘closed-loop’ is used herein to denote proportional control of a control system output (such as electrical muscle stimulation current), as a linear or non-linear function of one or more error terms. These error terms, as commonly practiced in the art, consist of deviations between a desired value of a measured input (command term) and the actual measured input.

Bones and joints both have been known for some time to exhibit piezoelectric properties. Following the discoveries that bones become stronger in adaptation to stress, and that physical stress induces localized currents in the bone, bone growth stimulators have been developed which apply controlled mechanical stress and/or electrical current to a damaged tissue area. Consistent with observed piezoelectric activity and stress-induced growth of bone and joints, electrical stimulation which imposes a DC bias has shown to accelerate tissue regeneration.

Piezoelectric activity is considered to be a minor contributor to natural electrical currents in and near joints. Each change in skeletal loading causes fluid flow through bone and particularly cartilage. Due to constituent charged particles, this fluid flow creates dynamic electrical currents which impose what are referred to as streaming potentials across the surrounding tissue. Streaming potentials have significance both from a diagnostic perspective, and in their capacity for fluid flow modulation. In addition to possible impact on cartilage hydration in eroded joints through imposed steaming potentials, control of chondrocyte migration has been shown to occur from imposed electrical potentials.

Diagnostic measurement of joint potentials under dynamic loading is taught in U.S. Patent Application Publication No. 20110034797, ‘Non-invasive measuring of load-induced electric potentials in diarthroidal joints’. Neither use of the subject matter of the application outside a diagnostic setting, nor therapeutic modulation of potentials discovered is addressed. Furthermore, the subject matter of the application does not address the relationships between the myriad force vectors possible during normal activity and the resultant streaming potentials. Vectors of incident forces upon a joint become much more significant when applied to joints comprised of multiple load-bearing surfaces.

To date, devices that stimulate bone and cartilage growth through electrical stimulation have relied either upon constant excitation or pre-programmed stimulation sequences. In contrast, piezoelectric activity and streaming potentials during normal patient activities are dynamic—polarities and magnitudes of the currents generated are resultant of incident forces, so constantly follow physical activity. Stimulation devices which are non-responsive to physical activity therefore are incapable of either mimicking or bolstering natural biological piezoelectric or streaming potential activity. In that it has been found that synchronizing muscle stimulation with volitional exertion, it is improved tissue regeneration may result from synchrony between physical stress and stimulation. To compound difficulty in bolstering or supplanting this electrical activity of a specific patient, huge subject response variances have been reported. This strongly implies that broad success of generalized stimulation will be less probable without adaptation to each specific case.

Synchronization of stimulation to the gait cycle, for the purpose of impacting cartilage health, is explored in U.S. Pat. No. 8,060,210, ‘Methods for improving mobility and controlling cartilage matrix degradation of weight-bearing articular joints’. The subject matter of this patent addresses motor-level stimulation of antagonistic muscles in a timed fashion, so as to minimize pressure or moving friction, but makes no distinction between reduced joint forces through muscle contraction and charged particle migration through the joint tissue. In that timing, physical location, and stimulation waveforms required for joint force reduction may or may not differ substantially from those required for fluid flow modulation, the arbitrary application of waveforms before and/or after application of unspecified multiphasic stimulation, as taught therein, does not show independent fluid flow control.

U.S. Pat. No. 7,822,481 addresses adjustment of a therapy program in response to one or more sensed patient parameters, but does not describe stimulation intensity to be any direct function of patient activity or circumstance. Adaptation by stimulators to dynamic physical conditions can be found both in cardiac stimulators and neural stimulators used for pain masking, such as is disclosed in U.S. Pat. No. 7,822,481, ‘Therapy adjustment’. These devices alter one or more parameters of pre-programmed stimulation patterns in response to body position or inclination, activity level, etc. None of these devices, however, stimulate tissue as a direct function of dynamic physical conditions imposed on the stimulated area.

DETAILED DESCRIPTION

Various operations will be described as multiple discrete operations, in turn, in a manner that is most helpful in understanding the illustrative embodiments; however, the order of description should not be construed as to imply that these operations are necessarily order dependent. In particular, these operations need not be performed in the order of presentation. Further, descriptions of operations as separate operations should not be construed as requiring that the operations be necessarily performed independently and/or by separate entities. Descriptions of entities and/or modules as separate modules should likewise not be construed as requiring that the modules be separate and/or perform separate operations. In various embodiments, illustrated and/or described operations, entities, data, and/or modules may be merged, broken into further sub-parts, and/or omitted. The phrase “embodiment” is used repeatedly. The phrase generally does not refer to the same embodiment; however, it may. The terms “comprising,” “having,” and “including” are synonymous, unless the context dictates otherwise. The phrase “A/B” means “A or B”. The phrase “A and/or B” means “(A), (B), or (A and B)”. The phrase “at least one of A, B and C” means “(A), (B), (C), (A and B), (A and C), (B and C) or (A, B and C)”.

Although diagnostic measurement of joint potentials under dynamic loading in a clinical setting is addressed in U.S. Patent Application Pub. No. 20110034797, ‘Non-invasive measuring of load-induced electric potentials in diarthroidal joints’, modulation of the streaming potentials involved as a continuous patient resource (outside clinical settings) is included in an embodiment of the invention and facilitates tissue preservation and/or possibly regeneration when combined with protective measures, such as those afforded by surrounding musculature.

In addition to dynamic electrical activity within tissue with readily observable relationships to physical activity, longer-term dynamic electrical potentials have repeatedly been observed. In that this activity has often been associated with pathological states or recovery therefrom, modulation of dynamic potentials at very low frequencies is included in an embodiment of the invention.

In that ambulant muscle stimulators are most often applied to areas which have been physically damaged, extension past their current use for physical support, to encourage tissue hydration and regeneration, is addressed in an embodiment of the invention.

An embodiment satisfies a need whereby ambulant muscle stimulation may be modulated to both counteract forces incident on an area of a body in a closed-loop fashion, and to encourage tissue generation or regeneration by stimulating localized tissue in a manner highly consistent with individualized biological activity.

An embodiment of the invention resides in the apparatus and technique of dynamically measuring and storing a biological condition or disposition during the time that one set of conditions are imposed on a joint or body area and applying closed-loop therapeutic action so as to re-achieve that same biological condition or disposition during a subsequent time that another different set of conditions are imposed. Furthermore, dynamic potentials surrounding said joint or body area may be created, bolstered, and/or modulated through aspects of stimulation applied which are independent of those aspects utilized to counteract force incident on the joint or body area.

Referring now toFIG. 1, Terminal Swing101shows the end of travel forward of the right foot, in preparation for taking a step. Initial Contact102shows the right foot being planted, or loaded. Note that the left foot is as well load-bearing at this time. Loading Response103shows full loading of the right foot as the left foot leaves the ground. Midstance104shows the point of maximal gravitic load on the right foot. Terminal Stance105shows forward propulsion changing from the upper-leg muscles to the muscles of the lower leg. Preswing106shows the end of propulsion by the lower leg muscles, hence the end of ankle travel (plantarflexion), in preparation to swing the right leg forward for another step. Initial Swing107shows the right foot lifting from the ground and initial femur travel forward. Midswing108shows the end of femur travel with continuation of tibia travel forward.

From the previous delineations, it can be seen that the right leg supports body weight through Phases102,103,104,105, and106; but is in free space through Phases107,108, and101. It can also be seen that the femur and tibia are in higher axial alignment in Phase101than Phases107or108.

Controller204receives positional information in the sagittal and coronal planes of the femur from Accelerometer202, and of the tibia from Accelerometer203, respectively. Accelerometers202and203sense positions and motions in three axes. Controller204as well receives input from Electrodes206,207, and208. These inputs are used by Controller204to produce Medial Stimulation209and Lateral Stimulation210, both of which are applied as control inputs to Stimulation Amplifier205.

Referring now toFIG. 3, Position301shows sagittal position of the right femur, Position302shows coronal position of the right femur, Position303shows sagittal position of the right tibia, Position304shows coronal position of the right tibia, and Position Differential305shows right leg differential femur-tibia coronal position, all of the person proceeding through the gait phases ofFIG. 1. Phase markers306,307,308,309,310,311,312, and313show positions at gait Phases101,102,103,104,105,106,107, and108, respectively, all ofFIG. 1. Sagittal positions increase with motion in a posterior direction; coronal positions increase with motion in a lateral direction (abduction). Central axis marked for each Position indicates true vertical. (Horizontal dotted lines are plumb verticals in both sagittal and coronal planes.)

Although inertial forces will often exceed gravitic forces during normal activities, gravitic forces only are included herein in the interest of simplicity. It is assumed that the person depicted inFIG. 1and measured inFIGS. 3 and 5suffers medial condyle damage which results in collapse on that condyle when the knee is under compressive load. This collapse results in a lateral deflection of the knee, known as a varus deformity.

At Marker309, corresponding to Midstance104, ofFIG. 1, note that femur sagittal Position301and Tibia sagittal Position303are both mid-scale, indicating true vertical for both femur and tibia. Maximum gravitic axial force occurs at this inclination. Note as well that femur coronal Position302indicates largest lateral deflection and that tibia coronal Position304indicates medial deflection at Marker309, consistent with medial condyle collapse. The differential coronal Position305therefore indicates degree of varus deformity, maximum deformity being at Marker309as the leg withstands maximum gravitic axial force.

Note that at Markers312and313, corresponding to Initial Swing107and Midswing108ofFIG. 1, the femur swings slightly in the medial direction, shown in femur coronal Position302. This medial motion represents compensatory reaction taken against the previous lateral collapse.

Note however, that at Marker306, corresponding to Terminal Swing101ofFIG. 1, that femur and tibia coronal positions302and304achieve balance. This is presumably in response to full quadriceps firing, extending the tibia in preparation for landing the next step. With similar muscle activation, therefore, the primary physical difference between Markers306and307, corresponding to Terminal Swing101and Initial Contact102, ofFIG. 1, is compressive loading on the leg.

Lateral laxity in the proposed example results in the progressive varus deformity seen between Markers307and311in differential femur-tibia coronal Position305. A perfect hinge joint, however, would maintain a constant value in Position305, and a healthy knee may be expected to maintain a relatively constant value between at least Positions306and311, corresponding to Terminal Swing101and Preswing106ofFIG. 1. In other words, compressive force should create no (or little) significant coronal deviation from the differential Position305seen at Marker306. In that the differential coronal position is not impacted by loading, Terminal Swing101ofFIG. 1therefore represents an optimal target for differential position of the knee, regardless of laxity within the joint.

Referring now toFIG. 4, Accelerometer Output401, from Accelerometer202ofFIG. 2, and Accelerometer Output402, from Accelerometer203ofFIG. 2, are applied as inputs to Spacial Transforms403and404, respectively. Transforms403and404derive sagittal and coronal positions from said three-axis accelerometers, using techniques known to the art. Femur Sagittal Position405and tibia Sagittal Position407are applied as inputs to State Detector409, which continuously detects if Leg201ofFIG. 2is in the Terminal Swing Phase101or state, ofFIG. 1, and outputs this result as TSW State Indication410.

Femur Coronal Position406and tibia Coronal Position408, output by Transforms403and404, respectively, are applied as non-inverting and inverting inputs, respectively, of Summer421. Summer421provides as output Femur-Tibia Coronal Differential414, which is shown in Trace305ofFIG. 3. Femur-Tibia Coronal Differential414is applied as signal input to Amplifier411, and TSW State Indication410is applied as enable input to Amplifier411, which gates Femur-Tibia Coronal Differential414to Filter412only during the times that State Detector409detects that the system ofFIG. 2is in Terminal Swing Phase101ofFIG. 1. The Target Coronal Differential413of Filter412therefore consists of the average Femur-Tibia Coronal Differential of Leg201ofFIG. 2during Terminal Swing Phase101ofFIG. 1.

Target Coronal Differential413is applied as input to Hysteresis Adder415, which adds a negative value, and Hysteresis Adder416, which adds a positive value.

The output of Hysteresis Adder415and Target Coronal Differential413are supplied as non-inverting and inverting inputs, respectively, to Amplifier417. The output of Amplifier417therefore is a value which increases as Femur-Tibia Coronal Differential exceeds Target Coronal Differential by the hysteresis amount of Hysteresis Adder415. The output of Amplifier417is output as Lateral Stimulation419, or209ofFIG. 2, and used to control lateral stimulation from Stimulation Amplifier205, also ofFIG. 2.

The output of Hysteresis Adder416and Target Coronal Differential413are supplied as inverting and non-inverting inputs, respectively, to Amplifier418. The output of Amplifier418therefore is a value which increases as Femur-Tibia Coronal Differential falls below Target Coronal Differential by the hysteresis amount of Hysteresis Adder416. The output of Amplifier418is output as Medial Stimulation420, or210ofFIG. 2, and used to control medial stimulation from Stimulation Amplifier205, also ofFIG. 2.

Referring now toFIG. 5, Position501shows coronal position of the right femur, Position502shows coronal position of the right tibia, and Position Differential503shows femur-tibia coronal differential of the right leg of the person ofFIG. 1. Lateral Stimulation504and Medial Stimulation505show amplitude of stimulation to be applied to the lateral and medial side of Leg201ofFIG. 2, respectively. Phase markers506,507,508,509.510,511,512, and513show positions at gait Phases101,102,103,104,105,106,107, and108, respectively, all ofFIG. 1. Coronal positions increase with motion in a lateral direction (abduction). Central axis marked for each Position indicates true vertical. The heavy dotted line of Position503represents the Target Femur-Tibia Coronal Differential413ofFIG. 4, which can be seen to be the same as the femur-tibia coronal differential shown in Position503at Marker506, corresponding to Terminal Swing101ofFIG. 1. (Dotted horizontal lines on501and502are coronal plumb vertical, assuming the leg is abducted from vertical. Heavy dotted horizontal line in503is zero Femur/Tibia coronal deviation. Dotted horizontal lines on504and505are also zero.)

Note that beyond a small error, representing the hysteresis value of Hysteresis Adder415ofFIG. 4, Lateral Stimulation504increases, overshoots, and settles to a constant value as femur-tibia coronal differential exceeds Target413ofFIG. 4. After Marker511, Lateral Stimulation504can be seen to return to zero as Differential503converges on Target Differential413ofFIG. 4. Note that Medial Stimulation505then increases as Differential503falls below Target Differential413ofFIG. 4by a small error representing the hysteresis value of Hysteresis Adder416ofFIG. 4, but falls to zero as Differential503again approaches Target Differential413ofFIG. 4.

Thus, the embodiment ofFIG. 2provides a hysteretic closed-loop system utilizing the lateral and medial muscles of Leg201ofFIG. 2as actuators. This is in contrast to conventional systems, wherein open-loop muscle stimulation only is in use. In further contrast to conventional systems, the embodiment can be seen to continuously update an optimal command term for this closed-loop system from biological input of the person using an embodiment of the invention. Resultantly, the embodiment can be seen to not only adapt to the specific user of the embodiment of the invention, but furthermore adapt to ongoing changes in that specific user without external intervention.

Referring now toFIG. 6, three-axis Accelerometers602and603are affixed or held in place in the coronal plane over the femur and tibia, respectively, of Leg601, presumably a human left leg. Electrodes606and608are affixed or held in place in the sagittal plane at the meniscus, directly over the medial and lateral margins, respectively, of the knee of Leg601. Electrode607is affixed or held in place in the coronal plane, centered on the femur, proximal to the knee. By the orientations shown, it can be seen that electrical potentials created at or around the medial meniscus are differentially presented to Electrodes606and607, and that electrical potentials created at or around the lateral meniscus are differentially presented to Electrodes608and607. Note thatFIG. 6differs fromFIG. 2in placement of Electrodes606and608, which have been moved in a distal direction so as to highlight a specific aspect of an embodiment of the invention.

Controller604receives as input accelerations in three axes of the femur from Accelerometer602and accelerations in three axes of the tibia from Accelerometer603. Note that information regarding both gravitic and dynamic accelerations is provided by said Accelerometers.

Both static and dynamic potentials occurring on the surface of Leg601are provided to Controller604by Electrodes606,607, and608. Direct coupling to Controller604, to facilitate inspection of both direct and alternating voltage potentials on the surface of Leg601, is assumed. It is assumed that Controller604has adequate processing capability to continuously quantify vectored forces magnitudes, through modeling techniques known to the art, incident upon the knee of Leg601, using acceleration information in three axes each from Accelerometers602and603. Being in receipt of both Accelerometer602and603inputs, said processing capability, and Electrode606,607, and608inputs, it can be seen that Controller604has available requisite inputs and capability to ascertain relationships between vectored forces incident upon the knee of Leg601and the resultant streaming potentials biologically created within Leg601. It is also assumed that Controller604is possessed of adequate memory to store these relationships so ascertained.

Electrodes606,607, and608may as well be driven by Muscle Stimulator605, which may provide stimulation currents to said electrodes under control of Medial and Lateral Stimulation Commands609and610, respectively, issued from Controller604. Presumably Stimulator605will provide differential current between Electrodes606and607in response to Medial Command609from Controller604, and differential current between Electrodes608and607in response to Lateral Command610from Controller604. Independent, simultaneous, and time division multiplexing are among the output stimulation capabilities.

Electrodes606,607, and608therefore serve as both input and indirect output connections to and/or from Controller604. While Stimulator605is providing a current output, voltage measured by Controller604will be representative of the impedance presented by Leg601to Stimulator605. While Stimulator is not providing current, the voltage measured by Controller604will be representative of residual stimulation charge or potentials biologically created, such as piezoelectric or streaming potentials.

Controller604presumably utilizes a constant frequency source, as is commonly practiced, allowing temporal calculations, such as integration, derivation, and/or filtering to be performed upon inputs and/or outputs.

Although differential potentials and currents of medial and lateral condyles only are disclosed herein for the sake of simplicity, other embodiments may include one or more electrodes, using potentials and/or currents across any two or more electrodes or electrode groups.

Note that components shown inFIG. 6are preferentially situated on or near Leg601, allowing the wearer to move without encumbrance. This facilitates use outside a clinical setting, during normal daily activities of any user.

It can therefore be seen that Controller604is possessed of both vectored forces incident upon the knee of Leg601during normal activity of the knee of Leg601, and resultant streaming potentials biologically generated by Leg601during these same activities. It can as well be seen that Controller604is capable of independent stimulation between at least any two of Electrodes606,607, and608. This combination of input and output capability therefore facilitates potential to modulate biologically-generated streaming forces around the knee of Leg601during normal activities. Bipolar stimulation capability is used in some embodiments, facilitating application of time-variant positive and/or negative gradients between electrodes. Positive current, negative current, or alternating current with or without positive or negative integrated charge is therefore available across any electrode pair.

Referring now toFIG. 7, three-axis Accelerometers702and703, corresponding to Accelerometers602and603, respectively ofFIG. 6, provide sensor input to Signal Conditioner701. Electrodes705,706, and707, corresponding to Electrodes605,606, and607, respectively, ofFIG. 6, acquire and provide relative surface potentials at each shown location of Leg601as input to Signal Conditioner701. Signal Conditioner701performs necessary modifications, such as attenuation, filtering, limiting, compensation, and/or conversion upon one or more input signal shown, and may perform more advanced functions, such as integration or differentiation. Conditioned Signals711, consisting of conditioned version of all input signals described above, is provided by Conditioner701as input to Processor704.

Processor704, through algorithms known to the art, transforms conditioned accelerometer X, Y, and Z inputs from Conditioned Signals711into a standardized reference coordinate system, such as Euler angles, rotation matrices, or quaternions. Leveraging the constant mass of skeletal members concerned, in conjunction with definitions of internalized physiology of the knee of Leg601ofFIG. 6, Processor704as well calculates both vectored gravitic and inertial forces imposed on the joint being treated from conditioned accelerometer inputs. In the example shown inFIG. 6, Processor704may calculate axial force magnitudes imposed upon both the medial and lateral condyles of the knee of Leg701.

At appropriate times, such as at initial use of an embodiment of the invention or upon recognition of previously unseen movement or force conditions, Processor704determines and stores the mathematical relationship between joint movement and/or force, such as calculated axial condylar forces of the knee, and conditioned potentials measured at any one or more of Electrodes705.706, and707. In that the time constants of fluid flow within the joint, and hence the streaming potentials so generated, may be much longer than those of the causal forces, temporal aspects of this determined relationship or alternately of any or all elements of Conditioned Signals711may be calculated as well.

Calculated relationships between joint movement and/or force and measured electrode potentials are stored, preferably as coefficients, in Processor704memory. Read/write access to these stored relationships is provided through External Input/Output Interface713, optionally with different access restrictions between user and provider access. These relationships may therefore be read for joint diagnostic purposes, modified, or written directly by the user and/or provider, through External Interface713.

For each relationship between incident forces and streaming potentials so calculated and stored, Controller604may be, through modification via External Interface713, in possession of a desirous modification to be performed upon the calculated relationship. Input of desired relationship modifications to Controller604may be through any means known to the art, such as wired, wireless, infrared, etc. Examples of desired modification input may be direct input through an external computer by a health practitioner, notification of painful activity by the patient through wireless means, or detection by contemporaneous Controller software of unbalanced streaming potentials within the joint. Combined input forms of desired modifications, such as use of a practitioner-supplied scalar in conjunction with patient-identified pain, are anticipated.

In subsequent normal operation, Processor704, in response to predetermined, user-specified, and/or heuristically-determined conditions of one or more constituents of Conditioned Signal711, determines and controls stimulation current to be applied at one or more electrode locations through output of Medial and Lateral Stimulation Commands709and710, which correspond to Stimulation Commands609and610ofFIG. 6, which are provided as input to Stimulator712. At least one characteristic, such as intensity, of each element of Stimulation Commands709and710is calculated directly from at least one said stored relationship, as excited by one or more of joint movement and/or force. In other words, in an embodiment each stimulation output is a known function of a joint movement and/or force.

Stimulator712, under control of Command709and/or710, delivers dynamic individually-controlled stimulation currents to one or more of Electrodes706,707, and/or708. Stimulation outputs may be of any topology capable of sinking and/or sourcing controlled current and/or voltage, although bilateral controlled current is preferred. To facilitate optional measurement of skin surface potentials, ability to control output impedance of Stimulator712outputs is advantageous. Currents applied by Stimulator712to Electrodes706,707, and/or708then stimulate underlying tissue of Leg601ofFIG. 6in a localized fashion.

Following theFIG. 6example, an embodiment may calculate medial condylar axial force within the knee of Leg601ofFIG. 6from Accelerometer702and703inputs, measure concurrent differential voltage between Electrodes706and7707, calculate and store the average dynamic causal relationship between the two, allow provider modification of this stored causal relationship, and subsequently provide stimulation current between Electrodes706and707which follow this modified causal relationship, as controlled by dynamic calculated medial condylar axial force within the knee of Leg601ofFIG. 6.

Causal relationship modifications may be in any form, such as a simple multiplier, gain and span, or quadratic form; and may originate from any source, such as a medical practitioner, the patient wearing the device, or even additional software executed by an element of Controller604.

Model801provides structural definitions and constants of the appropriate joint to Model Resolver802, which, under excitement of Conditioned acceleration inputs ultimately from Accelerometers602and603ofFIG. 6, provides dynamic Medial Axial Force812and Lateral Axial Force814as outputs. Medial Force812is supplied as input to both Root Finder804and Polynomial Solver807; Lateral Force814is supplied as input to\ both Root Finder805and Polynomial Solver808.

Root Finders804and805as well receive as inputs conditioned electrode potential presumably ultimately from Electrodes606(Medial) and608(Lateral) ofFIG. 6. From said force and potential inputs, Root Finder804provides as output dynamic Calculated Relationship815between modeled axial force incident upon the medial condyle of the joint and resultant potential imposed by dynamic elements within the knee at Electrode606ofFIG. 6. Similarly, Root Finder805provides as output dynamic Calculated Relationship816between modeled axial force incident upon the lateral condyle of the joint and resultant potential imposed by dynamic elements within the knee at Electrode608ofFIG. 6. Specific algorithms used within Root Finders804and805may vary from simple division to more complex iterative methods such as Brent's Method, depending upon the order of the overall system, as is known in the art. Relationship Outputs815and816of Root Finders804and805, respectively, are presumably in coefficient form, appropriate to the order, but may be expressed in any form known to the art, such as coefficients of gain/span (Ax +B) or quadratic form.

Note that temporal aspects are optionally included in Calculated Relationships815and816, which may therefore include determined time constant and optionally filter order between application of axial force on a knee condyle and resultant voltage subsequently measured at one or more electrodes. Temporal aspects of his relationship may be expressed and stored in any form known and practiced in the art, such as FIR or IIR coefficients.

At appropriate points in time, such as while a user performs a painful action or upon demand of a health practitioner, Relationships815and/or816are stored in Memory806for subsequent use.

Due to the myriad action and force combinations possible in any human joint, it is assumed that multiple Relationships may be stored in Memory806, to be accessed appropriately to the current activity of the wearer, as is commonly practiced in the art.

Relationships so stored in Memory806may be viewed or displayed by external devices through External Interface813, which may be implemented through any physical medium in use, such as wired, wireless, infrared, etc. External acquisition of said relationships is intended for diagnostic use by the user or health practitioner. For example, External Interface813may consist of a wireless physical layer, accessible by a wireless hand-held device on which Relationships from Memory806may be viewed and/or edited. In another embodiment, External Interface813may consist of an internet-compatible physical layer with a web page server, such as apache2; facilitating data visibility and editing capability through any web browser. Although not required for all embodiments, there is encryption of otherwise insecure data exchange with other embodiments of the present invention.

Calculated Relationships stored in Memory806may as well be changed or directly written through External Interface813, and/or by additional software executing within Processor704ofFIG. 7. Any edited Relationship thus stored in Memory806therefore represents a Desired Relationship, to be used for control purposes described below.

Medial Force812and Lateral Force814are as well supplied as inputs to Solver807and808, respectively. Solver807also receives as input Desired Relationship817from Memory806, which may be an unaltered or altered version of Calculated Relationship815from Root Finder804. Similarly, Solver808also receives as input Desired Relationship818from Memory806, which may be an unaltered or altered version of Calculated Relationship816from Root Finder805.

Under dynamic excitation of Medial Force812as described, Solver807outputs Desired Potential819to Pulse Width Modulator821, which resultantly provides Medial Stimulation Command809to Stimulator605ofFIG. 6. Stimulator605then provides modulated stimulation current to Electrode606ofFIG. 6, as described above. Similarly, Solver808, under dynamic excitation of Lateral Force814, outputs Desired Potential820to Pulse Width Modulator822, which resultantly provides Lateral Stimulation Command810to Stimulator605ofFIG. 6. Stimulator605then provides modulated stimulation current to Electrode608ofFIG. 6, as described above. Although shown as pulse width modulators, Modulators821and822may use any modulation form, such as pulse density, pulse position, frequency, or even amplitude.

Although voltage and current are used interchangeably above for simplicity, physiology is known to present complex impedances. It is assumed that compensatory measures are to be taken within Processor704, presumably through analog circuitry or executable software to normalize measured potentials with imposed currents.

Thus, in various embodiments it can be seen that streaming potentials biologically created within Leg601ofFIG. 6, as transcutaneously measured, may be subsequently modulated by Stimulator105ofFIG. 1, as the wearer of the embodiment of the invention proceeds through normal activities.

Referring now toFIG. 9, Trace901shows tibial Sagittal Position of Leg601ofFIG. 6through stance phase of a gait cycle, with value directly proportional to anterior position. Traces902and903show axial Medial and Lateral Condylar Forces, respectively. Traces904and905indicate Streaming Potentials imposed on the medial and lateral sides of the knee, as presented to Electrodes606and608, respectively, relative to Electrode607, all ofFIG. 6. The X axis ofFIG. 9indicates linear time.

At Time Marker906, heel strike occurs, indicating initial loading. Resultantly, both medial and lateral condylar force immediately increase, as seen in Traces902and903, respectively. As the leg progresses through stance phase, however, oscillation between medial and lateral forces can be seen in Traces903and904, typical of knee instability caused by excessive laxity. Although negative-going streaming potentials can be seen in both Traces904and905as stance phase is entered after Marker906, Medial Potential904is seen to deviate less and more slowly than Lateral Potential905, in spite of the fact that Medial Force902exceeds Lateral Force903at this point by a visible margin.

At Time Marker907, the foot is no longer weight bearing, as indicated by force cessation in both Medial Force902and Lateral Force903. After Marker907, Medial Potential904and Lateral Potential905both move slowly in a positive direction, indicating reversal of fluid flows induced by axial force while loaded.

Attenuation and slow response of streaming potentials is repeatedly seen in joints with compromised cartilage. Potentials shown in Trace904between Markers906and907for the indicated force of Trace902therefore could indicate that Leg601ofFIG. 6has an eroded medial condyle. In that streaming potentials are induced by flow of fluids containing charged particles, loaded fluid flow through the medial cartilage of Leg601ofFIG. 6is therefore presumed to be deficient.

Referring now toFIG. 10, Trace1001shows tibial Sagittal Position of Leg601ofFIG. 6through stance phase of a gait cycle, with value directly proportional to anterior position. Traces1002and1003show axial Medial and Lateral Condylar Forces, respectively. Traces1004and1005indicate Stimulation Currents to be imposed by the an embodiment of the invention on the medial and lateral sides of the knee, as presented to Electrodes606and608, respectively, relative to Electrode607, all ofFIG. 6. The X axis ofFIG. 10indicates linear time.

(FIGS. 9 and 10include horizontal dotted lines that are sagittal plumb vertical in901/1001, and zero in the other traces. Further, traces904/905are potentials at the electrodes (without stimulation) that are measured (input connections to604, which become811).1004/1005are the composite potentials resultant of the body doing what is shown inFIG. 9, and the stimulation.FIG. 10depicts applying a current, to the electrodes, which modifies the potentials already on those electrodes, making traces1004and1005.)

At Time Marker1006, sharp increases can again be seen in Medial Force1002and Lateral Force1003, at initial loading. Note, however, that the initial forces indicated in Traces1002and1003result in immediate negative currents applied to both Electrodes606and608ofFIG. 6, shown in Trace1004and1005, respectively. Current applied to Electrode606ofFIG. 6can be seen in Trace1004to decrease non-linearly with decreasing force in Trace1002until Time Marker1007, at which point current returns to zero. Current applied to Electrode608ofFIG. 6can be seen in Trace1005to quickly decrease non-linearly in opposing fashion to Trace1004, attaining zero current before Time Marker1007.

Note that the force oscillation between Medial Force1002and Lateral Force1003between Markers1006and1007is diminished from that shown inFIG. 9. Stability has in this example been improved by simultaneous stimulation current to both medial and lateral sides of the knee upon loading at Time Marker1006.

Stimulation Current1004shows continuous current application to medial Electrode606ofFIG. 6, non-linearly proportional to Medial Force1002, until force cessation at Marker1007. The purpose of this current is to encourage fluid flow through the medial cartilage, in spite of mechanical damage to the joint. The rapid Stimulation Current1005diminution shown during Lateral Force1003loading can be seen to cease modulation of natural streaming potentials after the initial stabilization current at Marker1006.

Time constants, polynomial and filter orders, modulation forms, and streaming potential modulation strategies are all anticipated to be varied widely without departing the scope of embodiments of the invention as described herein.

By the preceding disclosure, individualized streaming potentials in and/or around a compromised joint or body part can be seen to be modulated in a therapeutic fashion by embodiments of the present invention. Through direct adaptation to the individual user, use of embodiments of the invention need not be constrained to clinical settings. It can furthermore be seen that potentials in and around the joint may be dynamically modulated.

Although shown in conjunction with electrical stimulation, alternate stimulation means, such as magnetic stimulation, are anticipated. Embodiments of the invention can be seen to be amenable to any control means known to the art, such as analog and/or digital electronic, pneumatic, or hydraulic control.