GB2484667A

GB2484667A - A device for measuring the length of bone cavities

Info

Publication number: GB2484667A
Application number: GB1017534.7A
Authority: GB
Inventors: Rajaram Lakshmipathy
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-10-18
Filing date: 2010-10-18
Publication date: 2012-04-25
Also published as: GB201017534D0

Abstract

A device for the measurement of the length of a bone comprises a shaft having a first end and a second end, the shaft comprising a series of graduations towards the second end thereof, the graduations comprising at least a portion of a material having a density suitable to absorb short-wave electromagnetic radiation, e.g. absorb x-rays. The shaft may be adapted to fit within a cavity of a long bone. The device may include a removable handle. A method of using the device to measure the length of a cavity in a bone is also claimed. The device may be used to determine the required length of an intramedullary nail.

Description

A Measurement Device The present invention relates to a measurement device. In particular, the present invention relates to a measurement device for use in the medical field, for example for the measurement of bones and/or orthopaedic implants and supports.

In orthopaedic surgery, it is important to be able to accurately measure the length of a patient's bones, particularly those which must be replaced or fixed following injury and/or degenerative disease, for example fractures. In certain surgeries, metal rods or nails must be inserted into a patient's bone to provide support for the regeneration of the bone at the site of a fracture. It is important that the length of the rod or nail is accurate. If the rod is too long and extends beyond the end of the bone, the end of the rod can cause irritation to the surrounding soft tissue. If the rod is too short, if for any reason the rod needs to be removed from the bone, for example to further stimulate regeneration of the bone due to non-union as in exchange nailing, it is very difficult to remove the rod from the bone and more invasive surgery would be required. For these reasons, there exists a need to provide an apparatus and method to accurately measure the length of the rod or nail prior to insertion thereof into the bone.

Currently, the only devices that are available to measure the length of patient's bones rely on the surgeon being able to read off a measurement accurately by eye from the device. However, in practical terms it is not possible for the surgeon to see the top of a patient's bone accurately because it is covered by soft tissue. Therefore, these prior art devices are highly prone to human error and magnification error. This is mainly due to the fact that these devices use an indirect measurement technique.

Other techniques for the determination of the required length of an intramedullary nail include inserting a rod of known length into the bone cavity and measuring the length of the rod that is left protruding from the top of the cavity. However, this technique is also an indirect measurement technique because the surgeon must determine accurately where the end of the cavity is.

Therefore, this technique suffers from the same disadvantages as that described above.

It is an object of the present invention to address these and other

disadvantages associated with the prior art.

According to a first aspect of the present invention, there is provided a measurement device for the measurement of the length of a bone, the device comprising a shaft having a first end and a second end, the shaft comprising a series of graduations towards the second end thereof, the graduations comprising at least a portion of a material having a density suitable to absorb short-wave electromagnetic radiation.

Preferably, the first end of the shaft comprises at least a portion of a material having a density suitable to absorb short-wave electromagnetic radiation, Preferably, the shaft comprises a material having a density suitable to allow at least a portion of short-wave electromagnetic radiation pass therethrough.

Preferably, the shaft comprises a plastics material.

Preferably, the graduations of the shaft comprise a metal. Preferably, the first end of the shaft comprises a metal. Preferably, the metal is impregnated within and/or on the shaft. Preferably, the metal is a medical grade metal, for example stainless steel, titanium, tungsten, aluminium, or the like.

Preferably, the short-wave radiation comprises x-rays.

Preferably, the shaft is adapted to fit within a bone cavity. Preferably, the bone cavity is a medullary cavity. Preferably, the shaft is adapted to fit within a cavity of a long bone, for example a bone in the leg or arm.

Alternatively, the shaft is adapted to fit within a bone cavity that has been enlarged by a drilling process or the like.

Preferably, the shaft is adapted to be passed into the bone cavity from one end of a long bone.

Preferably, the shaft is elongate. Preferably, the shaft has a longitudinal axis which runs along the length of the elongate structure.

Preferably, the shaft is substantially cylindrical in shape. Preferably, the shaft is substantially circular in cross-section taken perpendicular to the longitudinal axis thereof. Preferably, the shaft is a tube.

Alternatively, the shaft may be substantially "D" shaped in cross-section taken perpendicular to the longitudinal axis thereof. Preferably, the graduations are visible from the flattened surface of the "D" shaped cross-section.

Preferably, the cross-section perpendicular to the longitudinal axis of the shaft has a maximum diameter of less than the cavity in which the shaft is adapted to fit. Preferably, the cross-section perpendicular to the longitudinal axis of the shaft has a maximum diameter of between approximately 0.1 mm and approximately 6mm less than the cavity in which the shaft is adapted to fit, preferably between approximately 0.3mm and approximately 5mm less, most preferably between approximately 1 mm and 4mm less.

Preferably, the device comprises a handle at the second end thereof.

Preferably, the handle is removable from the device. Preferably, the handle comprises a sleeve that is slidable onto and off the second end of the shaft.

Preferably, the handle comprises gripping means for gripping the shaft.

Preferably, the handle comprises release means for releasing the handle from the shaft.

Alternatively, the handle may be integral with the shaft.

The device may be formed by injection moulding, extrusion, compression moulding, or any other suitable method. The graduations may be embedded within the shaft, or secured to the shaft during manufacture.

According to a second aspect of the invention, there is provided a method of measuring the length of a cavity within a bone, the method comprising the steps of: a) inserting a measuring device according to the first aspect of the invention into the cavity; b) exposing the end of the bone nearest to the second end of the measuring device to a source of short-wave electromagnetic radiation and producing an image of the radiation transmission pattern; and c) determining the length of the cavity by reading the graduations at the end of the bone on the short-wave electromagnetic radiation image of the bone.

The measurement method preferably provides direct measurement of the bone length, and therefore can be used to calculate the required nail length for each bone.

Preferably, the method further comprises the steps of exposing the end of the bone nearest the first end of the measuring device to a source of short-wave electromagnetic radiation and producing an image of the radiation transmission pattern to ensure that the measuring device is correctly positioned within the cavity and at the required distal end of the bone where the intramedullary nail has to fit.

All of the features described herein may be combined with any of the above aspects, in any combination.

For a better understanding of the invention and to show how the same may be brought into effect, a specific embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figures 1 a and b show a schematic plan view of the measurement device of the present invention and a cross sectional view through the handle of the device respectively; Figure 2 shows a schematic cross-sectional view of the measurement device of Figure 1 in position in the cavity of a bone; and Figure 3 shows a schematic plan view of an x-ray image of the measurement device of Figure 1 within a bone.

A measurement device 2 for measuring the length of a cavity of a bone 18 comprises an elongate shaft 4 and a handle 6.

The elongate shaft 4 has two ends. A first end 8 is operable to be inserted into the cavity of the bone 18. A second end 10 of the shaft is operable to remain outside the cavity. The handle 6 of the device is releasably securable to the shaft 4 at the second end 10 thereof.

The shaft 4 is substantially circular in cross-section. The shaft 4 can have a variety of diameters. The diameter of the shaft 4 may be between approximately 6mm and approximately 15mm. The length of the shaft 4 is preferably between approximately 240mm and approximately 420/440mm.

The shaft 4 may taper from the first end 8 to the second end 10. For example, in one embodiment of the invention, the shaft 4 may be approximately 7mm in diameter at the first end 8 and taper gradually to approximately 10mm at the second end 10. This tapering allows for a less hindered movement of the shaft 4 into the bone cavity 20. Furthermore, to also aid in insertion of the shaft 4 into the bone cavity 20, the shaft 4 may be curved. This allows the shaft 4 to be fed in from one side of the bone 18 using the peripheral edge of the cavity as a guide.

The shaft 4 is constructed from a plastics material, or other material that is operable to transmit X-ray radiation. Therefore, the shaft 4 is not visible, or is only faintly visible, on an X-ray image. The material is of surgical grade and may be either disposed of after use, or sterilised for re-use. Examples of suitable materials include Polyphenylsulfone, Polysulfone, Polythermide, Polycarbonate, Polypropylene, PM MA, Polyetherketone, Polyetheretherketone, and the like.

The first end 8 of the shaft is constructed from a metal material, or other material that is operable to absorb X-ray radiation. Therefore, the first end 8 of the shaft is clearly visible on an X-ray image. The material is of surgical grade and may be either disposed of after use, or sterilised for re-use. Examples of suitable metals include, but are not limited to stainless steel, titanium, tungsten, aluminium, and the like. The metal is impregnated within the plastic of the shaft.

The shaft 4 comprises a series of graduations 12 along its length, particularly towards the second end 10 of the shaft. The graduations 12 are set at specific intervals to measure the distance in mm from the first end of the shaft.

Preferably, the graduations 12 are set at 1mm intervals so that the distance from the first end of the shaft can be read to the nearest mm.

The graduations 12 are formed by impregnating the plastics shaft 4 with a metal material, similarly to the first end 8 of the shaft. The metal graduations 12 therefore absorb X-ray radiation and are visible on an X-ray image. The metal may be impregnated within the plastic during extrusion of the plastic shaft 4 or afterwards. Alternatively, the metal may be a coating on the plastic, or etched into the plastic.

Graduations 12 at certain distances from the first end may be highlighted 14 by being larger or more visible than the surrounding graduations 12. The highlighted graduations 14 are at approximately 15mm intervals. These intervals correspond to widely available lengths of intramedullary nails.

Therefore, it is easy for the user to see which length intramedullary nail would be most suitable for each bone cavity.

The handle 6 is made from a plastics or metal material that is operable to be sterilised for multiple use. The handle 6 is configured to allow the device to be held easily, i.e. the handle is ergonomic. This ensures that the measuring device may be easily inserted and removed from the bone cavity.

The handle 6 is removably attachable to the shaft. The handle 6 comprises gripping means 16 such that the handle remains fixed on the shaft until removed by the user. The gripping means 16 comprises a spring which biases a gripping arm towards the shaft when the handle is in place on the shaft. The handle 6 is released from the shaft by compressing the spring to move the gripping arm away from the shaft. The handle 6 can then be slid off the end of the shaft.

In use, the first end 8 of the measuring device is inserted into a medullary cavity 20 as shown in Figure 2. The device 2 is passed down into the cavity 20 until the first end 8 of the shaft reaches the end of the cavity 22.

An X-ray image of the first end 8 of the shaft is then obtained to see if the shaft 4 is positioned correctly at the end of the cavity 22. The metal impregnated into the first end 8 of the shaft shows up clearly on the X-ray image and the positioning of the first end 8 of the shaft can be seen in relation to the bone cavity 20.

If any adjustments are needed to correctly position the shaft 4, these are made and the position of the first end 8 of the shaft re-checked.

Once the first end 8 of the shaft has been determined to be in the correct position, an X-ray image of the second end 10 of the shaft is taken such that the end of the bone cavity nearest the second end 10 of the shaft can be seen in the image, as shown in Figure 3. The image clearly shows the metal graduations 12 impregnated into the shaft 4.

The user is then able to accurately determine the length of the intramedullary nail required for insertion into the bone cavity 20 by reading off the graduation 24 closest to the end of the bone cavity 20 from the X-ray image. Therefore, the user can directly measure the length of the bone cavity.

The device of the present invention provides an accurate and direct way of measuring the length of a bone cavity, and therefore, of an intramedullary nail required to be fitted into the bone cavity. The user can rely on accurate imaging of the bone to determine the length of the cavity. This is a great improvement over the current methods of measurement which rely on the user being able to see the end of a bone by eye which can not be done since the end of the bone is covered with soft tissue.

The device of the present invention, being an intramedullary device, also avoids magnification error which is seen with current measurement methods.

Current measurement methods are susceptible to an incorrect anterior-posterior measurement being read instead of a correct lateral measurement.

With the device of the present invention, measurements are read only on the lateral view of the leg on the X-ray image. This inherently avoids the misjudging of the length of the leg measured by using an anteroposterior view.

The device of the present invention will lead to a reduction in wastage of time and materials that result from wrongly sized intramedullary nails being inserted into bone cavities and needing to be replaced. Furthermore, the device of the present invention will save patients from having to undergo additional, painful surgeries to correct mistakes that have been made through surgeons not being able to accurately determine the correct length intramedullary nail required for their bones.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise.

Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s).

The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

A Measurement Device Claims 1. A measurement device for the measurement of the length of a bone, the device comprising a shaft having a first end and a second end, the shaft comprising a series of graduations towards the second end thereof, the graduations comprising at least a portion of a material having a density suitable to absorb short-wave electromagnetic radiation.
2. The measurement device as claimed in claim 1, wherein the first end of the shaft comprises at least a portion of a material having a density suitable to absorb short-wave electromagnetic radiation.
3. The measurement device as claimed in any preceding claim, wherein o the shaft comprises a material having a density suitable to allow at least a portion of short-wave electromagnetic radiation pass 1 therethrough.
4. The measurement device as claimed in any preceding claim, wherein the shaft comprises a plastics material.
5. The measurement device as claimed in any preceding claim, wherein the graduations of the shaft comprise a metal.
6. The measurement device as claimed in any preceding claim, wherein the first end of the shaft comprises a metal.
7. The measurement device as claimed in claim 6, wherein the metal is impregnated within and/or on the shaft.
8. The measurement device as claimed in claims 6 or 7, wherein the metal is a medical grade metal: including stainless steel; titanium; tungsten; aluminium; or the like.
9. The measurement device as claimed in any preceding claim, wherein the short-wave radiation comprises x-rays.
10. The measurement device as claimed in any preceding claim, wherein the shaft is adapted to fit within a bone cavity.
II. The measurement device as claimed in claim 10, wherein the bone cavity is a medullary cavity.
12. The measurement device as claimed in any preceding claim, wherein is the shaft is adapted to fit within a cavity of a long bone, for example a bone in the leg or arm.
13. The measurement device as claimed in any preceding claim, wherein the shaft is adapted to fit within a bone cavity that has been enlarged by a drilling process or the like.
14. The measurement device as claimed in claims 10 to 13, wherein the shaft is adapted to be passed into the bone cavity from one end of a long bone.
Is. The measurement device as claimed in any preceding claim, wherein the shaft is elongate.
16. The measurement device as claimed in any preceding claim, wherein the shaft has a longitudinal axis which runs along the length of the elongate structure.
17. The measurement device as claimed in any preceding claim, wherein the shaft is cylindrical in shape.
18. The measurement device as claimed in any preceding claim, wherein the shaft is circular in cross-section taken perpendicular to the longitudinal axis thereof.
19. The measurement device as claimed in any preceding claim, wherein the shaft is a tube.
20. The measurement device as claimed in any preceding claim, wherein the shaft is "D" shaped in cross-section taken perpendicular to the longitudinal axis thereof.
21. The measurement device as claimed in claim 20 wherein the r graduations are visible from the flattened surface of the "D" shaped o cross-section. a)
22. The measurement device according to claims 18 to 21, wherein the cross-section perpendicular to the longitudinal axis of the shaft has a maximum diameter of less than the cavity in which the shaft is adapted to fit.
23. The measurement device according to claims 18 to 22 wherein the cross-section perpendicular to the longitudinal axis of the shaft has a maximum diameter of between approximately 0.1mm and approximately 6mm less than the cavity in which the shaft is adapted to fit.
24. The measurement device according to claims 18 to 22 wherein the cross-section perpendicular to the longitudinal axis of the shaft has a maximum diameter of between approximately 0.3mm and approximately 5mm less than the cavity in which the shaft is adapted to fit.
25. The measurement device according to claims 18 to 22 wherein the cross-section perpendicular to the longitudinal axis of the shaft has a maximum diameter of between approximately 1mm and approximately 4mm less than the cavity in which the shaft is adapted to fit.
26. The measurement device as claimed in any preceding claim, wherein the device comprises a handle at the second end thereof.
27. The measurement device according to claim 26, wherein the handle is removable from the device.
28. The measurement device according to claims 26 to 27, wherein the o handle comprises a sleeve that is slidable onto and off the second end of the shaft. r
29. The measurement device according to claims 26 to 28, wherein the handle comprises gripping means for gripping the shaft.
30. The measurement device according to claims 26 to 29, wherein the handle comprises release means for releasing the handle from the shaft.
31. The measurement device according to claim 26, wherein the handle may be integral with the shaft.
32. The measurement device as claimed in any preceding claim, wherein the device is formed by injection moulding, extrusion, compression moulding, or any other suitable method.
33. The measurement device as claimed in any preceding claim, wherein the graduations are embedded within the shaft.
34. The measurement device as claimed in any preceding claim, wherein the graduations are secured to the shaft during manufacture.
35. A method of measuring the length of a cavity within a bone, the method comprising the steps of: a) inserting a measuring device according to the first aspect of the invention into the cavity; b) exposing the end of the bone nearest to the second end of the measuring device to a source of short-wave electromagnetic radiation and producing an image of the radiation transmission pattern; and c) determining the length of the cavity by reading the graduations at the end of the bone on the short-wave electromagnetic radiation C imageofthe bone. a)
36. The method as claimed in claim 35, wherein the method provides direct measurement of the bone length.
37. The as claimed in claims 35 or 36, wherein the method is used to calculate the required nail length for each bone.
38. The method as claimed in claims 35 to 37, wherein the method further comprises the steps of exposing the end of the bone nearest the first end of the measuring device to a source of short-wave electromagnetic radiation and producing an image of the radiation transmission pattern.
39. The method as described in claims 35 to 38 in accordance with any of claims 1 to 34.
40. The measurement device as described with herein reference to thedescription and accompanying figures. r Co a) r