INDEX SHOE

K960307 · Orthopedic Technology Research, Inc. · IRN · Jun 27, 1996 · Physical Medicine

Device Facts

• Record ID: K960307
• Device Name: INDEX SHOE
• Applicant: Orthopedic Technology Research, Inc.
• Product Code: IRN · Physical Medicine
• Decision Date: Jun 27, 1996
• Decision: SESE
• Submission Type: Traditional
• Regulation: 21 CFR 890.5575
• Device Class: Class 2

Indications for Use

The AccuTread™ Shoe is intended for use as a limb load monitoring device to monitor limited weight bearing during rehabilitation of patients with insults to their lower extremities.

Device Story

AccuTread™ Shoe is a shoe-like enclosure for patients with lower extremity insults requiring limited weight-bearing. The device monitors weight applied to the affected limb during rehabilitation. A lever mechanism in the wooden sole concentrates force onto a Force Sensing Resistor (FSR). The FSR, a polymer thick film device, decreases resistance as load increases. This resistance change modulates a 9.545 MHz carrier wave frequency, which is transmitted to a receiver. The receiver compares the signal to a physician-calibrated weight limit (30-130 lbs). If limits are exceeded, the device provides auditory, visual, or vibratory feedback. Physicians use the receiver to calibrate weight thresholds and select signaling modes. The device aids in protecting the extremity, ensuring compliance with prescribed weight-bearing programs, and providing patient peace of mind during ambulation.

Clinical Evidence

No clinical data. Bench testing only.

Technological Characteristics

Shoe-like enclosure with wooden sole; Force Sensing Resistor (FSR) polymer thick film sensor; 9.545 MHz amplitude-modulated transmitter; receiver with auditory, visual, and vibratory feedback; battery-powered (9V in shoe, 2xAA in receiver).

Indications for Use

Indicated for patients with lower extremity insults requiring limited weight-bearing rehabilitation. No specific age or gender restrictions provided.

Regulatory Classification

Identification

A powered external limb overload warning device is a device intended for medical purposes to warn a patient of an overload or an underload in the amount of pressure placed on a leg.

Special Controls

*Classification.* Class II (special controls). The device is exempt from the premarket notification procedures in subpart E of part 807 of this chapter subject to the limitations in § 890.9.

Predicate Devices

• Force Guard I (K882974)

Submission Summary (Full Text)

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K 960307

JUN 27 1996

SECTION 6: 510(k) SUMMARY

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# Premarket Notification

510(k) Summary of Safety and Effectiveness Information

## DATE OF SUMMARY PREPARATION

May 1, 1996

## MANUFACTURER

Orthopedic Technology Research, Incorporated
5731 Lyons View Pike
Suite 202-203
Knoxville, Tennessee 37919

Telephone: [phone]
Fax: [phone]

## MANUFACTURER CONTACT PERSON

David H. Gray
Vice President of Operations

## REGULATORY CORRESPONDENCE

Mr. Brian Cleary
Director of RA/QA
Hayes Medical, Inc.
819 Striker Avenue, Suite 10
Sacramento, CA 95834-5432

Telephone: [phone]

## PROPRIETARY DEVICE NAME

**AccuTread™ Shoe**

## COMMON NAME

Orthopedic Limb Load Monitor

## CLASSIFICATION NAME

Powered external limb overload warning device

## CLASSIFICATION REFERENCE

21 CFR, 890.5575

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# DEVICE PRODUCT CODE

89 IRN

# REGULATORY CLASS

In accordance with FDA classification of powered external limb overload warning devices as Class II devices, this device is a Class II device and is thus subject to "Special Controls".

# SPECIAL CONTROLS

At this time, Food and Drug Administration generated special controls and performance standards applicable to the AccuTread™ Shoe are not in force. Orthopedic Technology Research produces this device using available voluntary standards that are appropriate to the risk that Class II devices reasonably present. Materials and vendor certifications, in-house SOP's and ASTM standards are utilized as appropriate.

# INTENDED USE

The AccuTread™ Shoe is intended for use as a limb load monitoring device to monitor limited weight bearing during rehabilitation of patients with insults to their lower extremities.

# DEVICE DESCRIPTION

The AccuTread™ Shoe is a shoe-like enclosure, worn by patients having insults to their lower extremities. The device is intended for use to achieve benefits such as:

- protection of the affected extremity during the healing process,
- ease of mind during initial ambulation, and
- documentation of compliance or non-compliance to a prescribed weight bearing program.

These benefits derive from the patient's ability to know that he/she is not exceeding the correct amount of weight applied to the affected extremity as prescribed by their physician. The complete device consists of the following components:

- Shoe Body
- Sensor Unit
- Transmitter
- Receiver

# SUBSTANTIALLY EQUIVALENT PREDICATE DEVICES

Several commercially available devices are substantially equivalent to the AccuTread™ Shoe with respect to materials, intended use, and indications for use.

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Within the proposed class, the following device is most similar to the AccuTread™ Shoe and thus serves as the predicate device for comparison:

Force Guard I
Boulder Impact Monitors
K882974

## SUBSTANTIAL EQUIVALENCE COMPARISON

To begin, both the AccuTread™ Shoe and Force Guard I are intended to provide feedback to the patient to monitor prescribed limited weight-bearing. Thus, the indications for use of the two devices are identical.

The Force Guard I possesses a sensor footpad which can be placed into the provided slipper or, alternatively, into a loose-fitting slipper or shoe of the patient’s choice. The sensor footpad is designed to measure the force applied to the sensor by the plantar surface of the patient’s foot.

As we understand, the pressure applied to the inflated sensor footpad is transferred via a hollow tube to a bridge-type strain gage transducer contained in an electronics module worn around the ankle of the patient. Within the electronics module, this signal is then routed to a comparator, which then compares the received signal to a pre-set calibrated maximum weight limit (20, 30, 50, or 70 pounds). If the force applied to the sensor exceeds the pre-set weight limit, a repeating “bell-like” tone is emitted once per second to alert the patient that the prescribed weight limit has been exceeded.

The AccuTread™ Shoe consists of a shoe-like enclosure which houses the force sensing mechanism in the wooden sole of the shoe. This force sensing unit consists of a lever mechanism which concentrates the force applied at the metatarsal and/or heel area of the shoe to a force concentrating unit. The force concentrating unit then concentrates the forces to a single force measurement which is then distributed over a force sensing resistor (FSR).

The FSR is a polymer thick film (PTF) device which exhibits a decrease in resistance with an increase in the force applied to the active surface. Thus, as increased load is applied to the FSR, the resistance decreases, in turn resulting in an increase in the kilohertz frequency of the transmitted “amplitude modulated wave” described below.

The FSR is in turn coupled to a transmitter which converts the resistance characteristic into a frequency which is transmitted to the receiver for comparison to a pre-set target frequency representing the prescribed maximum weight limit. As weight is applied to the AccuTread™ Shoe, the transmitter emits a chopped carrier wave frequency at a constant 9.545 megahertz. This frequency is chopped at a rate of zero to three kilohertz, which is the “amplitude modulated wave”. The amplitude modulated wave is what varies as weight is applied (kilohertz increase with an increase in the applied weight).

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When the target frequency is detected, an alarm is emitted depending upon the signaling mode selected by the physician.

In directly comparing the two devices, it is important to note that the patient must wear the **AccuTread™ Shoe** throughout rehabilitation. This is unlike the Force Guard I, which allows the patient to alternatively place the footpad sensor in any loose-fitting shoe of their choice.

Another difference is in the weight limits that may be prescribed by the physician. The Force Guard I allows the physician to select only one of four pre-set maximum weight-bearing limits (20, 30, 50, and 70 pounds), whereas the **AccuTread™ Shoe** allows the physician to calibrate the device to any maximum weight limit within a 30 to 130 pound range.

The devices also differ in their means of alerting the patient when the prescribed weight limit has been exceeded. As described previously, the Force Guard I emits a repeating tone when the prescribed maximum weight limit is exceeded. The **AccuTread™ Shoe** instead allows the physician to prescribe any of three possible signaling modes to alert the wearer in such an instance. The three modes consist of an auditory, visual and vibrating mode. The physician thus may select the mode which will best serve the patient’s needs. Table 1 on the following page describes each of these alarm feedback mechanisms.

The visual feedback mode of the **AccuTread™ Shoe** further allows the physician to set a minimum weight limit to notify the patient that a desired minimum load is being applied to the affected limb. In this operating mode, the minimum and maximum weight limits are distinguished by separate green (minimum) and red (maximum) lights that are clearly labeled on the receiver.

To conclude, based on the design concept, use of well known materials, feature comparisons to the selected predicate device, and indications for use, Orthopedic Technology Research believes that sufficient evidence exists to reasonably conclude that the **AccuTread™ Shoe** is substantially equivalent to existing legally marketed limb load monitor devices.

Table 1 on the following page summarizes the relevant feature comparisons between the **AccuTread™ Shoe** and Force Guard I.

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TABLE 1: Feature comparisons between the AccuTread™ Shoe and Force Guard I

| | AccuTread™ Shoe | Force Guard I |
| --- | --- | --- |
| Intended Use | Intended for use to monitor limited weight-bearing during rehabilitation of patients with insults to their lower extremities by providing feedback to the wearer. | Intended for use to monitor limb load by sensing the amount of force applied to the plantar surface of the foot and to provide feedback to the wearer. |
| Feedback Mechanism | Auditory: receiver emits a "beep" (21 db) when pre-set maximum is exceeded.
Visual: green light when pre-set minimum is achieved; red light to alert patient that pre-set maximum has been exceeded.
Vibratory: receiver vibrates when pre-set maximum is exceeded. | Auditory: a repeating "bell-like" tone repeated once per second (75 db) when the selected load sensitivity is exceeded. |
| Summary Device Description | Shoe Body containing a sensor unit in the wooden sole to measure applied loads; separate receiver unit for calibration and to provide feedback to the wearer. | Non-skid slipper; pressure sensor footpad; electronics module to monitor weight-bearing and provide feedback to the wearer. |
| Force Measuring Mechanism | Pressure sensing unit housed in the sole of the shoe body. The measured force is transmitted to the receiver to provide feedback to the wearer. | Pressure sensor footpad connected to a separate bridge strain gage transducer contained in the electronics module. |
| Load Sensitivity | Physician calibrates the device to both a minimum and maximum prescribed load sensitivity within a 30 to 120 pound range. | One of the following four load sensitivities may be selected by the physician: 20, 30, 50, and 70 pounds. |
| Precision | Force Sensing Resistor (FSR) within +/- 5% | Factory set, +/- 5 pounds |
| Power | Receiver: two AA batteries.
AccuTreadShoe: 9 volt Battery | Electronics Module: 9 volt battery |
| Low Battery Indication | Receiver: yellow indicator light is activated when the receiver battery is low.
Shoe: the user is instructed to periodically check the shoe battery by applying enough weight to activate the selected signaling mode. | Electronics Module: a high frequency signal is emitted at twice the rate as the excess weight signal. |
| Manufacturer | Orthopedic Technology Research, Inc. | Boulder Impact Monitors, Inc. |
| 510(k) Number | N/A | K882974 |