WO2014153525A2

WO2014153525A2 - Device for detection of internal body force on an implanted bar

Info

Publication number: WO2014153525A2
Application number: PCT/US2014/031480
Authority: WO
Inventors: Dr. Stephen KNISLEY
Original assignee: Old Dominion University Research Foundation,
Priority date: 2013-03-21
Filing date: 2014-03-21
Publication date: 2014-09-25
Also published as: WO2014153525A3

Abstract

A device is provided for measuring the progress of a treatment for pectus excavatum, the treatment incorporating an implanted elongated pectus bar having ends defining and end-to-end distance. The device includes a caliper for measuring the end-to-end distance of the pectus bar and a device for determining sternal force in part from the change in end-to-end distance.

Description

DEVICE FOR DETECTION OF INTERNAL BODY FORCE ON AN IMPLANTED BAR

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to and the benefit of U.S. Provisional Patent Application No. 61/804,020, filed March 21, 2013 and entitled "DEVICE FOR DETECTION OF INTERNAL BODY FORCE ON AN IMPLANTED BAR", the contents of which are herein incorporated by reference in their entirety.

FIELD OF THE INVENTION The present invention relates to implanted pectus bars for the treatment of Pectus

Excavatum, and more particularly to systems and devices for assessing the progress of treatment.

BACKGROUND

Pectus Excavatum (also known as sunken or funnel chest) is the most common chest wall deformity and affects 1 in every 1,000 children. In current practice to treat a patient with Pectus Excavatum, the bar is formed into an approximate bow-shape prior to implantation. The bar is implanted, which forces the sternum up and produces the desired chest shape. The bar is later removed, typically after many months, when it is believed that the chest has remodeled to the desired shape. Examples of pectus bar technologies can be found in US Patent Publications 20110184411 (McKenzie et al), 20060259141 (Roman et al), and 20040117016 (Abramson). The disclosures of these publications are incorporated fully by reference.

SUMMARY OF THE INVENTION A device is provided for measuring the progress of a treatment for pectus excavatum, the treatment incorporating an implanted elongated pectus bar having ends defining and end-to-end distance. The device includes a caliper for measuring the end-to-end distance of the pectus bar, and a device for determining sternal force in part from the change in end-to-end distance.

The device for determining sternal force can comprise a scale. The device for

determining sternal force can comprise a processor. The processor can determine a change in sternal force. The processor can compare the change in sternal force to a predetermined threshold, the threshold being selected to indicate completion of the remodeling procedure. The processor can determine the sternal force by processing the formula:

SL = [BD+4.58-(0.0403-LD)-(0.0721-SW)+(0.0217-BL)]/0.0197 where SL is the sternal load or force, in Newtons, BD is the bar displacement, or change in bar end-to-end distance produced by the sternal force, in mm, LD is the lateral distance or width of person between left and right sides of chest, in mm, SW is the sternum width, in mm, and BL is the bar length, in mm.

A method for measuring the progress of a treatment for pectus excavatum, can include the step of providing a device comprising a caliper for measuring the change in end-to-end distance of the pectus bar, and a device for determining sternal force in part from the change in end-to-end distance. The change in end-to-end distance can be measured. The sternal force can be determined from the change in the end-to-end distance. The pre-operative end-to-end distance can be measured, the implanted end-to-end distance can be measured, and at least one post-operative end-to-end distance can be measured.

The method can include, when the end-to-end distance indicates at least a 50% decrease in sternal force, removing the pectus bar. The device for determining sternal force can comprise a scale. The device for determining sternal force can comprise a processor. The processor can determine a change in sternal force. The processor can compare the change in sternal force to a predetermined threshold, the threshold being selected to indicate completion of the remodeling procedure. The relationship between the change in bar end-to-end distance and the sternal force can be determined by:

SL = [BD+4.58-(0.0403-LD)-(0.0721-SW)+(0.0217-BL)]/0.0197 where SL is the sternal load or force, in Newtons, BD is the bar displacement, or change in bar end-to-end distance produced by the sternal force, in mm, LD is the lateral distance or width of person between left and right sides of chest, in mm, SW is the sternum width, in mm, and BL is the bar length, in mm

A method for treating pectus excavatum in a patient, can include the steps of implanting a pectus bar into a patient, determining the end-to-end distance of the pectus bar after implantation, determining the end-to-end distance after a period of time following the implantation, determining the change in end-to-end distance over the period of time, and determining the change in sternal force from the change in end-to-end distance.

The relationship between the change in bar end-to-end distance and the sternal force can be determined by:

SL = [BD+4.58-(0.0403'LD)-(0.0721'SW)+(0.0217'BL)]/0.0197 where SL is the sternal load or force, in Newtons, BD is the bar displacement, or change in bar end-to-end distance produced by the sternal force, in mm, LD is the lateral distance or width of person between left and right sides of chest, in mm, SW is the sternum width, in mm, and BL is the bar length, in mm. The end-to-end distance can be determined by a device comprising a caliper for measuring the end-to-end distance of the pectus bar. The method can include using a scale for determining sternal force in part from the change in end-to-end distance. BRIEF DESCRIPTION OF THE DRAWINGS

There are shown in the drawings embodiments that are presently preferred it being understood that the invention is not limited to the arrangements and instrumentalities shown, wherein:

Figure 1 is a schematic diagram of a device for the measurement of internal body force on an implanted bar.

Figure 2 is a schematic diagram of the device as used on a patient.

DETAILED DESCRIPTION This invention comprises a caliper that will be used outside of the body to measure the end-to-end distance of an implanted pectus bar. Caliper contact points can be provided to overcome effects of soft tissue thickness. A conversion algorithm can be provided that will convert the distance to a measure of the sternal force pushing on the central region of the bar.

Immediately after implantation, the pectus bar pushes upward on the sternum and there is an identical force of the sternum pushing down on the central region of the bar. In the remodeled state just prior to removal of the bar there will not be any sternal force pushing down on the bar, or this force will be greatly reduced.

The pectus bar will slightly straighten when subjected to central force similar to the sternal force pushing down on the central region of the bar. This straightening will increase the end-to-end distance of the bar. The amount of central force and the amount of end-to-end distance has been examined in a computer model and a bar subjected to realistic forces in a bench apparatus. The results showed there is a relationship between the amounts of central force and the end-to-end distances. The model showed that the relationship depends on the size of the bar and the location of supports on either side of the center that correspond to the left and right aspects of the rib cage.

The caliper scale can reflect sternal force, length units, or both. The relationship between the change in length and the sternal force is provided by formula (1) below: SL = [BD+4.58-(0.0403'LD)-(0.0721'SW)+(0.0217'BL)]/0.0197 (1) where SL is the sternal load or force, in Newtons, BD is the bar displacement, or change in bar end-to-end distance produced by the sternal force, in mm, LD is the lateral distance or width of person between left and right sides of chest, in mm, SW is the sternum width, in mm, and BL is the bar length, in mm. The caliper has a suitable measurement range, for example -30-60 cm, which the physician can use to measure the end-to-end distance between the pectus bar ends. The caliper can have sub millimeter resolution. The contact points of the caliper with the body can have tapered tips in order to contact the body surface near the pectus bar ends. The tapered tips will enable measurement of bar end-to-end distance with minimal errors caused by the thickness of soft tissue such as body fat and skin that cover the bar ends. The contact points of the caliper with the body can also have needles to penetrate through tissue to the bar to eliminate errors in patients where there is excessive fat.

The invention can be used in the diagnosis of chest tissue remodeling after surgical implantation of a pectus bar and before removal of the pectus bar for correction of chest wall deformity.

The method of the invention measures the change in bar displacement from x-rays or from a caliper or other suitable measuring instrument, yielding the ΔΒϋ in mm. The ΔΒϋ value is multiplied by a value determined empirically from ASL/ABD values as measured from representative patients in a particular age group. This will yield a value for the change in sternal load that occurred in the time interval between the bar measurements

The values for ASL/ABD for each of the various age groups are based on finite element model results that incorporate reported measurements of the bar sizes, sternal widths and lateral widths of the person for each of the age groups, or when a measurement for a certain age has not been reported, estimates of these measurements using curves fitted to the reported measurements as a function of age that produced the minimum-square-error. The units are Newtons/mm. Such methods are discussed in "Analysis of Bar Deformation Under Sternum Forces During Surgical Correction of Pectus Excavatum in Children," Old Dominion University, 2012, the disclosure of which is hereby incorporated fully by reference. An example of end-to-end displacements with sternal load is shown in Table 1 below:

Table 1 : FEA results of the horizontal displacement (mm) of the Pectus bar under different loading conditions

A set of ASL/ABD values for different age groups is provided in Table 2 below:

TABLE 2

Age ASL/ABD

6 year old 105.5

8 year old 81.2

10 year old 72.9

12 year old 54.1

14 year old 43.6

16 year old 36.3

18 year old 30.1

Values for the ΔΒϋ for a sternal load, and ASL/ABD can be determined empirically for different pectus bar characteristics such as material thickness, geometry and the like.

Example: A 10 year old patient is measured using x-rays or an instrument such as a caliper to determine show that the bar's ends became closer together by 2.2 mm. This ΔΒϋ or 2.2 mm is multiplied by 72.9 Newton/mm = 160 Newtons. The sternal force has decreased by 160 Newtons (ASL=160 Newtons).

The decrease in the sternal force is compared to a threshold decrease in sternal force to determine the progress of the treatment. The decrease in sternal force can be at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 100%. An indication that the sternal force is zero or that the decrease in sternal force has passed the threshold would be an indication the remodeling process has been completed.

A device according to the invention can measure the progress of a treatment for pectus excavatum. The treatment incorporates an implanted elongated pectus bar having ends defining and end-to-end distance. The device includes a caliper for measuring the end-to-end distance of the pectus bar and a device for determining sternal force in part from the change in end-to-end distance. The device for determining sternal force can be a scale. The device for determining sternal force can alternatively be a processor.

A method for measuring the progress of a treatment for pectus excavatum, includes the step of providing a device comprising a caliper for measuring the change in end-to-end distance of the pectus bar, and a device for determining sternal force in part from the change in end-to- end distance. The change in end-to-end distance is measured. The sternal force is determined from the change in the end-to-end distance. The pre-operative end-to-end distance can be measured, the implanted end-to-end distance can then be measured, and at least one postoperative end-to-end distance can be measured. When the end-to-end distance indicates 0 sternal force or a significantly reduced sternal force, the pectus bar can be removed. The device for determining sternal force can be a scale that has been scaled to produce sternal force as a function of ΔΒϋ, or a processor that has been suitably programmed.

A method for treating pectus excavatum in a patient includes the step of implanting a pectus bar into a patient. The end-to-end distance of the pectus bar after implantation is measured. The end-to-end distance after a period of time following the implantation is then measured. The change in end-to-end distance over the period of time is determined from the measurements. The change in sternal force is determined from the change in end-to-end distance. The end-to-end distance can be determined by a device comprising a caliper for measuring the end-to-end distance of the pectus bar. The device can further comprise a scale for determining sternal force in part from the change in end-to-end distance. A caliper according to the invention is shown in Figures 1-2. The caliper includes a support 1 for grasping and manipulating the caliper. An adjuster 2 is used to adjust the distance between contact points with the ends of the pectus bar so as to determine end-to-end distance and from that the change in end-to-end distance or ΔΒϋ. A suitable readout scale 3 or force indicator 4 can be provided to indicate the change in length or the change in sternal force. The indicator can be in units of length or converted to units of sternal force using the methodology of the invention. Force limiters 5 and displacement transducers 6 can be provided. A force signal output 7 provides an indication that a force signal is being generated. The contact points 8 of the caliper with the body can have tapered tips or needles in order to contact the body surface near the pectus bar ends. Electrical circuitry 9 can be provided to perform the various functions of the caliper.

In operation the caliper is placed over the pectus bar 10 being measured and the patient's chest 11. The end-to-end distance is measured, and from this the change in end-to-end distance from an initial measurement can be determined. This change or ΔΒϋ is used to determine the change in sternal force or ASL. This determination can be made from a table or graph, or through a scale provided on the caliper or by a processor that is provided with the caliper or separate from the caliper. This will provide an indication of the progress of the remodeling procedure. Also, the caliper can be used to determine when the ends of the pectus bar have returned to an initial position or the sternal force has passed below a threshold, indicating an absence or very significant reduction of the sternal force and that the remodeling procedure has been completed or is near completion. This invention can be embodied in other forms without departing from the spirit or essential attributes thereof, and according reference should be made to the following claims to determine the scope of the invention.

Claims

CLAIMS What is claimed is:

1. A device for measuring the progress of a treatment for pectus excavatum, the treatment incorporating an implanted elongated pectus bar having ends defining and end-to-end distance, the device comprising:

a caliper for measuring the end-to-end distance of the pectus bar; and,

a device for determining sternal force in part from the change in end-to-end distance.

2. The device of claim 1, wherein the device for determining sternal force comprises a scale.

3. The device of claim 2, wherein the device for determining sternal force comprises a processor.

4. The device of claim 3, wherein the processor determines a change in sternal force.

5. The device of claim 4, wherein the processor compares the change in sternal force to a predetermined threshold, the threshold being selected to indicate completion of the remodeling procedure.

6. The device of claim 3, wherein the processor determines the sternal force by processing the formula:

SL = [BD+4.58-(0.0403'LD)-(0.0721'SW)+(0.0217'BL)]/0.0197 where SL is the sternal load or force, in Newtons, BD is the bar displacement, or change in bar end-to-end distance produced by the sternal force, in mm, LD is the lateral distance or width of person between left and right sides of chest, in mm, SW is the sternum width, in mm, and BL is the bar length, in mm.

7. A method for measuring the progress of a treatment for pectus excavatum, comprising the steps of:

providing a device comprising a caliper for measuring the change in end-to-end distance of the pectus bar, and a device for determining sternal force in part from the change in end-to- end distance;

measuring the change in end-to-end distance; and,

determining the sternal force from the change in the end-to-end distance.

8. The method of claim 7, wherein the pre -operative end-to-end distance is measured, the implanted end-to-end distance is measured, and at least one post-operative end-to-end distance is measured.

9. The method of claim 7, wherein when the end-to-end distance indicates at least a 50% decrease in sternal force, removing the pectus bar.

10. The method of claim 7, wherein the method comprises using a scale to determine sternal force.

11. The method of claim 7, wherein the method comprises using a processor to determine sternal force.

12. The method of claim 11, wherein the processor determines a change in sternal force.

13. The method of claim 12, wherein the processor compares the change in sternal force to a predetermined threshold, the threshold being selected to indicate completion of the remodeling procedure.

14. The method of claim 11 , wherein the relationship between the change in bar end-to-end distance and the sternal force is determined by:

SL = [BD+4.58-(0.0403'LD)-(0.0721'SW)+(0.0217'BL)]/0.0197 where SL is the sternal load or force, in Newtons, BD is the bar displacement, or change in bar end-to-end distance produced by the sternal force, in mm, LD is the lateral distance or width of person between left and right sides of chest, in mm, SW is the sternum width, in mm, and BL is the bar length, in mm

15. A method for treating pectus excavatum in a patient, comprising the steps of: implanting a pectus bar into a patient; determining the end-to-end distance of the pectus bar after implantation;

determining the end-to-end distance after a period of time following the implantation; determining the change in end-to-end distance over the period of time; and

determining the change in sternal force from the change in end-to-end distance.

16. The method of claim 15, wherein the relationship between the change in bar end-to-end distance and the sternal force is determined by:

17. The method of claim 15, wherein the end-to-end distance is determined by a device comprising a caliper for measuring the end-to-end distance of the pectus bar.

18. The method of claim 15, wherein the device further comprises a scale for determining sternal force in part from the change in end-to-end distance. The method of claiml5, wherein when the sternal force has decreased by at least 50%,