GB2492339A

GB2492339A - Alignment device for the knee

Info

Publication number: GB2492339A
Application number: GB1110915.4A
Authority: GB
Inventors: Sanjeev Agarwal
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-06-28
Filing date: 2011-06-28
Publication date: 2013-01-02
Also published as: GB201110915D0

Abstract

An alignment device to align femoral and tibial bones at a knee joint is disclosed. It comprises a femoral arm portion 101 and a tibial arm portion 103, which is connected to the femoral arm portion 101 by an intermediate section 105. The intermediate section 105 is perpendicular to both femoral and tibial arm portions 101, 103. The femoral and tibial arm portions 101, 103 subtend a fixed angle in the range 4-6Â° (Shown in Figure 1b). In a preferred embodiment, an adjustable arm 301 is slidably mounted on the intermediate section 105. Preferably, the adjustable arm 301 includes a body portion 303 which engages with the intermediate section 105 and an elongate arm 305 which engages with the knee joint. Optionally, a long axis of the elongate arm 305 is in a plane parallel to the plane of the long axis of the femoral or tibial arm portions 101, 103 and in a plane perpendicular to the plane of the long axis of the intermediate section 105.

Description

ALIGNMENT DEVICE

BACKGROUND

The knee is a large and complex joint in the human body which permits flexion and extension as well as some degree of internal and external rotation. The knee typically supports the whole weight of the body, and is therefore vulnerable to both acute injury and the development of conditions such as osteoarthritis and rheumatoid arthritis.

Knee replacement, or knee arthroplasty, is a surgical procedure to replace the weight-bearing surfaces of the knee joint. Typically, knee replacement surgery is performed in order to relieve pain and disability associated with conditions such as those mentioned above.

Knee replacement surgery can be performed as a partial or a total knee replacement. Typically, the surgery involves the replacement, by a surgeon, of any unhealthy or damaged joint surfaces of the knee with metal andlor plastic components which are designed to allow continued motion of the knee after surgery.

Due to its complex nature and the interplay between the various elements of the knee joint, ensuring that any components used in a partial or total replacement knee are properly aligned is critical. Part of this includes ensuring that the femur and tibia are aligned correctly when the replacement components are in situ since a small variation from the mechanical or anatomical axes of the leg can result in early failure of the prosthesis.

SUMMARY

According to an example there is provided an alignment device for aligning femoral and tibial bones at a knee joint, the device comprising a femoral arm portion, a tibial arm portion connected to the femoral arm portion by an intermediate section perpendicular to both femoral and tibial arm portions, and an adjustable arm slideably mounted on the intermediate section, wherein the femoral and tibial arm portions subtend a fixed angle in the range 4-6.

According to a further example there is provided an alignment device for aligning femoral and tibial bones at a knee joint, the device comprising a femoral arm portion, a tibial arm portion connected to the femoral arm portion by an intermediate section perpendicular to both femoral and tibial arm portions, wherein the femoral and tibial arm portions subtend a fixed angle in the range 4-6.

According to a further example there is provided a method for measuring rotational, translational and alignment characteristics of a prosthetic knee joint arranged between a femur and tibia, comprising providing an alignment device including: femoral and tibial arm portions connected by an intermediate section perpendicular to the femoral and tibial arm portions, and an adjustable arm slideably mounted on the intermediate section, inserting the femoral arm portion into the medullary canal of the femur with the tibial arm portion projecting outside of the knee joint between the femur and tibia, aligning the tibia with the tibial arm portion such that the tibia is parallel to the tibial arm portion in both the frontal and vertical planes, determining rotation using the adjustable arm by sliding the arm along the intermediate section into contact with the knee joint, and aligning the knee joint with the adjustable arm to correct rotation at the knee joint.

According to a further example, there is provided an adjustable arm portion for use with an alignment device.

According to a further example, there is provided a method for measuring rotation at a knee joint, comprising providing an adjustable arm portion and using the adjustable arm portion to determine a measure of rotation of a knee joint in a total or partial knee replacement procedure.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment will now be described, by way of example only, and with reference to the accompanying drawings, in which: Figure Ia is a side view of an alignment device according to an example; Figure lb is a frontal view of an alignment device according to an example; Figure 2a is a side view of an alignment device according to an example when in situ; Figure 2b is a frontal view of an alignment device according to an example when in situ; Figure 3a is a side view of an alignment device according to an example; Figure 3b is a frontal view of an alignment device according to an example; Figure 4 is a schematic perspective view of an alignment device according

to an example;

Figure 5 is a block diagram depicting a method of measuring rotational, translational and alignment characteristics of a prosthetic knee joint according to an example; and Figure 6 is a schematic block diagram of an aspect of the alignment device according to an example.

DETAILED DESCRIPTION

The alignment of the knee with respect to the hip and the ankle is determined by measuring the angle between the mechanical axis of the leg and the longitudinal axis of the femoral shaft. The mechanical axis is defined as a straight line extending from the centre of the hip, through the centre of the knee to the centre of the ankle along the tibial shaft. When the natural alignment and orientation of the knee joint is disrupted, subsequent joint instability, imbalance and stress at fixation interfaces can occur. Correction of this type of damage can require surgical replacement of some or all of the affected knee joint.

Typically, knee replacement surgery involves exposure of the front of the knee allowing exposure of the distal end of the femur and the proximal end of the tibia. The ends of these bones are then accurately cut to shape using cutting guides oriented to the long axis of the bones. Metal components are then impacted onto the bone or fixed using a suitable cement or cement-less technique.

Normal alignment of the knee is typically considered to result from an anatomic tibio-femoral angle in the range 4° to 9° of valgus or from a mechanical axis that falls through the middle third of the knee joint. Some conventional knee replacement instruments have adjustments to enable measurement of this, but do not allow checking of alignment once bone cuts have been made. In addition, alignment of the knee in side profile should demonstrate that the knee is able to fully straighten after an operation. Conventional instruments do not have a system to measure this.

It is desirable that rotation of the femoral component and the tibial component should be closely matched. Errors of tibial rotation can lead to early failure and a high revision rate of a prosthesis.

Alignment is thus an important surgeon-controlled factor in determining the durability of a knee replacement since any significant variation from normal alignment will usually result in pain and discomfort for the patient as well as a tendency for components of the replacement joint to wear more quickly than otherwise.

In order to achieve acceptable alignment, the accurate placement of the components and the relative positioning of the knee joint with respect to the hips and ankle is key. According to an example, there is provided an alignment device for aligning femoral and tibial bones at a knee joint which permits various translational and rotational aspects to be measured and corrected. The device comprises a femoral arm portion, a tibial arm portion connected to the femoral arm portion by an intermediate section perpendicular to both femoral and tibial arm portions, and an adjustable arm slideably mounted on the intermediate section, wherein the femoral and tibial arm portions subtend a fixed angle in the range 4-6.

Figure Ia shows an alignment device according to an example in a side view. Figure lb is a frontal view of an alignment device according to an example. A femoral arm portion 101 is connected to a tibial arm portion 103 by an intermediate section 105. A connection between the tibial arm portion 103 and the intermediate section 105 is effected using a connector portion 107 which, in an example, permits the length of the tibial arm portion 103 extending away from the femoral arm portion 101 to be varied.

Connector 107 can be a housing with an internal profile which matches the shape of the arm portion 103, and which can include a screw or other suitable securing mechanism (not shown) for securing the tibial arm portion 103 in place at a desired length.

In figure la, the lowermost portion of the intermediate section which connects to the femoral arm portion 101 is shown as a flattened portion 109 which has a relatively thinner profile than the remainder of the intermediate section 105. The length, width and profile of portion 109 can be varied depending on various factors, including ease of manufacture and a desired stability or rigidity of the alignment device. Alternatively, the whole intermediate section can have a flattened or substantially flattened profile.

In figure ib, it can be seen that the femoral arm portion 101 and the tibial arm portion subtend an angle 0 when viewed from above (frontal view). In an example, 8=5.0 (subject to normal manufacturing tolerances, such as ±0.5 for example). The angle 0 can be any angle in the range 4-9.

In use, the femoral arm portion 101 is inserted into the medullary canal of the femur of a patient who is to undergo a partial or total knee replacement operation, thereby acting as a reference for the axis of the femoral bone.

Accordingly, femoral arm portion 101 has a length and profile which renders it suitable for insertion into the medullary canal. For example, arm portion 101 can be between 15-25cm in length, with a circular, elliptical or otherwise curved profile or another profile which renders the portion suitable for insertion and removal from the canal. The arm portion 101 and the device in general can be formed from a substantially inert metallic compound such as stainless steel for example or a disposable material, such as a material which is sterile and inert and is such that the device can be discarded after use if desired. Alternatively, different parts of the device can be made from different materials, with some parts being replaceable or disposable. Accordingly, parts of the device can be arranged to disconnect from other parts to permit replacement. For example, femoral arm portion can be a user replaceable component.

In situ, portion 109 is arranged to lie between the distal end of the femur and the proximal end of the tibia, and to project the tibial arm portion 103 clear of the knee joint which is undergoing replacement. Accordingly, the width and length of portion 109 is such so as to allow it to fit appropriately and project portion 103 clear of the knee joint. For example, the thickness of the portion 109 as shown in figure Ia can be between 1 and 5mm, and its length can vary from between 1-Scm.

The device can be removed and reinserted into the medullary canal multiple times during a knee replacement procedure in order to permit adjustments to bone or prostheses to be made. Insertion and removal can be effected whilst the knee joint under consideration is bent at an angle, such as 90 for example, thereby exposing the canal for insertion/removal.

Figure 2a is a side view of an alignment device according to an example when in situ. As can be seen, portion 109 lies between the distal end of the femur 201 and the proximal end of the tibia 203. Femoral arm portion 101 is inserted into the medullary canal of the femur. That is, a channel is made into the femur as part of the standard technique in knee replacement and the same channel can be used to insert arm portion 101. Line 205 depicts the long axis of the tibia when viewed from the side. In use, and when femoral arm portion 101 is in position within the femur, the tibial arm portion 103 is aligned with the axis 205 so that the two are parallel.

Specifically, the long axis of the tibial arm portion 103, depicted generally by line 207, is aligned with the long axis 205 of the tibia so that the two are substantially parallel. This results in vertical alignment of the knee joint -that is, alignment within a vertical plane with respect to the tibial axis.

Figure 2b is a view of an alignment device according to an example when in situ and viewed from above. Tibial arm portion 103 is aligned with the long axis of the tibia 205 such that, when viewed from above, the arm portion 103 and the long axis of the tibia 205 are substantially parallel.

Accordingly, the femur and the tibia then subtend an angle which is the same as the angle subtended by the femoral and tibial arm portions of the device. This results in frontal alignment of the knee joint -that is, alignment within a horizontal plane with respect to the tibial axis. A surgeon can easily assess and ensure that 207 and 205 are parallel, and hence that 101 and 205 will be parallel, which is one of the goals of a knee replacement.

The angle, as described above is selected in order to optimise the alignment of the knee with respect to the femur and tibia thereby allowing the anatomical or mechanical axis of the leg to be maintained in its natural position so that the replacement knee joint maintains a natural alignment thereby minimising joint instability and excessive stress and wear at contact points.

Alignment in the frontal and vertical planes as described above thereby results in an optimisation of the angle subtended by the femur and tibia (varus-valgus), and also of flexion-extension of the femur or tibia. Normal placement of the knee joint can therefore be obtained.

Figure 3 is a schematic block diagram of an alignment device according to an example. Similarly to the device described above with reference to figures la-b and 2a-b, device 300 includes a femoral arm portion 101 and tibial arm portion 103 disposed around an intermediate section 105 to maintain a fixed angle between the arm portions. An adjustable arm portion 301 is provided in movable engagement with intermediate section 105. The adjustable arm portion 301 can freely move up and down the intermediate section 105, and can optionally be locked in any one position on the intermediate section using a fixing mechanism (not shown), such as a screw which engages with the intermediate section 105 for example.

Adjustable arm portion 301 can include a body portion 303 for engaging with the intermediate section 105, which can include a hole with an inner profile which matches that of the intermediate section 105 and/or portion 109, thereby allowing it to freely slide over those parts of the section 105.

In an example, the adjustable arm portion includes an elongate arm 305 which is arranged so that its long axis is in a plane parallel to the plane of the long axis of the femoral arm portion 101 and perpendicular to the plane of the long axis of the ritermediate section 105 (including pordon 109).

Elongate arm 305 can be circular, rectangular, square or elliptical in cross section for example, or have any other suitable cross section which maintains rigidity of the arm 305. In the alternative, arm 305 can be in the form of a disc shape, such as a hemispherical disc which resides in the same plane as the aforementioned long axis for example. Further alternatively, adjustable arm 301 can be of any suitable shape or configuration such that there is a portion which, when brought into contact with a knee portion such as a femoral component of a knee replacement, is arranged to indicate rotation of that portion or component. That is, arm portion 301 is arranged to measure rotation of a knee portion at the distal end of the femur or the proximal end of the tibia, or at both if two such arm portions are provided (in which case, each arm portion can be independently moveable with respect to one another and the intermediate section 105). As depicted in figure 3, arm portion 301 is arranged to measure rotation at the distal end of the femur.

In use, femoral arm portion 101 is introduced in the medullary canal of a femur of a patient who is to undergo knee replacement arthroplasty. As mentioned, the portion 101 can be introduced and removed multiple times as desired. The femoral arm portion 101 therefore acts as a reference for the axis of the femoral shaft. Tibial arm portion 103 has a length that is sufficient to permit measurement of the angle between the femoral and the tibial shaft external to the joint. In an example, long axes of the femoral and tibial arm portions subtend a fixed angle of 5 in a first plane, and are parallel in a second, orthogonal plane, thereby permitting alignment of the femur and tibia in two directions -that is, according to an example, alignment in the vertical direction and alignment in the horizontal direction, or alignment of the knee joint from a frontal view and from a side view. The intermediate portion 105 has a length sufficient to displace the tibial arm portIon 103 clear of the knee joint whilst remarIing fixed to the femoral arm portion 101. Accordingly, in situ, a device according to an example is used to align the femoral and tibial shafts of the leg in order to ensure a desired alignment for a knee joint.

When the femoral arm portion 101 is in situ, adjustable arm portion 301 can be used to measure femoral or tibial rotation. In an example, such measurement is performed once alignment of the shafts in the horizontal and vertical planes has been performed. The arm portion 301 is moved along the intermediate section 105 until elongate arm portion 305 comes into contact with a portion of the knee joint or the distal end of the femur.

That is, according to an example, the arm 301 is slid towards arm 101 until elongate arm 305 contacts the femur component on both medial and lateral ridges. This will give a surgeon an accurate assessment of the rotation of the femoral component. At this stage, the position of the arm 103 will indicate the rotational axis of the femur. The tibial rotation should be matched to arm 103 by rotating the tibial component until the anteroposterior axis of the tibial component passes through the arm 103.

The anteroposterior axis of the tibial component is marked on trial components used in modern knee replacement surgery. Accordingly, femoral and tibial rotation can be matched, thereby minimising risk of early failure through rotational misalignment.

Figure 4 is a schematic perspective view of an alignment device according to an example. The device of figure 4 is provided in situ, and as such the femoral arm portion 101 is depicted by a dotted line to demonstrate the fact that it has been inserted into the medullary canal of a femur. Intermediate section 105 projects tibial arm portion 103 clear of the knee joint.

Adjustable arm 305 is shown in a lowered position where it abuts one or more portions of the knee joint, such as the medial and lateral ridges as described above.

In an example, the body of adjustable arm portion can be retrofitted to an existing alignment device. For example, the body portion can include a cut out or similar (not shown) which enables the body of the adjustable arm portion to be fitted onto an intermediate section or similar of an alignment device such as an alignment device described above. The body portion can also include a suitable fastening mechanism for securing the adjustable arm portion to an intermediate section, such as screw which can engage with the intermediate section when the adjustable arm portion is in the desired position for example.

Figure 5 is a block diagram depicting a method of measuring rotational, translational and alignment characteristics of a prosthetic knee joint according to an example. In block 501 an alignment device is provided such as that described above with reference to figures la-b, 2a-b and 3a-b.

In block 503, a femoral arm portion of the device is inserted into the rnedullary canal of the femur with the tibial arm portion projecting outside of the knee joint between the femur and tibia. In block 505 the tibia is aligned with the tibial arm portion such that the tibia is parallel to the tibial arm portion in both the horizontal/frontal and vertical/side planes.

In block 507, femoral rotation is determined using an adjustable arm, such as by sliding the arm down the intermediate section so that it comes into contact with the femoral portion of the knee joint, or a femoral portion of a prosthetic knee component. In block 509, the femoral portion of the knee joint is aligned with the adjustable arm to provide normal alignment of the femur with respect to the knee joint.

Figure 6 is a schematic block diagram of an aspect of the alignment device according to an example. A mark 601 on tibial arm portion 103 is used in order to determine a post-arthroplasty variation from a pre-arthroplasty measurement of the distance between the tibia and the mark 601. The mark can be a laser etched mark for example, and in an example can be 20cm from portion 107 on the tibial arm portion 103. In use, the distance between the position marking 601 and the top of the tibia is measured to provide a first measurement (pre-arthroplasty measurement) of the knee joint in its normal state of alignment. Once femoral and tibial cuts have been made for replacement components, and following alignment of the knee joint as described above, the distance between the position marking 601 and the top of the tibia is measured to provide a second measurement (post-arthroplasty measurement). Typically, such a surgical measurement is more accurate than a clinical measurement. Accordingly, using the position marking 601 can provide a more accurate determination for alignment during the process of arthroplasty. A deviation from the first measurement when the second measurement is taken can provide an indication that further alignment and/or adjustment of the position of any replacement components may be required. This can also include the requirement for further adjustments to be made to the cuts in the femur and/or tibia.

Claims

<claim-text>CLAIMSWhat is claimed is: 1. An alignment device for aligning femoral and tibial bones at a knee joint, the device comprising: a femoral arm portion; a tibial arm portion connected to the femoral arm portion by an intermediate section perpendicular to both femoral and tibial arm portions; and an adjustable arm slideably mounted on the intermediate section, wherein the femoral and tibial arm portions subtend a fixed angle in the range 4-6.</claim-text> <claim-text>2. An alignment device as claimed in claim 1, wherein the adjustable arm includes a body portion to engage with the intermediate section and an elongate arm to engage with the knee joint.</claim-text> <claim-text>3. An alignment device as claimed in claim 2, wherein a long axis of the elongate arm is in a plane parallel to the plane of the long axis of the femoral ortibial arm portions.</claim-text> <claim-text>4. An alignment device as claimed in claim 2, wherein a long axis of the elongate arm is in a plane perpendicular to the plane of the long axis of the intermediate section.</claim-text> <claim-text>5. An alignment device as claimed in any preceding claim, wherein a length of the tibial arm portion extending past the intermediate section isadjustable.</claim-text> <claim-text>6. An alignment device as claimed in claim 2, the elongate arm to determine internal or external femoral rotation at the knee joint.</claim-text> <claim-text>7. An alignment device as claimed in any preceding claim, wherein the intermediate section is flattened at the joint with the femoral arm portion to project the intermediate section from the knee joint.</claim-text> <claim-text>8. An alignment device as claimed in any preceding claim, wherein the intermediate section has a length sufficient to displace the tibial arm portion clear of the knee joint.</claim-text> <claim-text>9. An alignment device as claimed in any of claims I to 7, wherein the intermediate section has a length sufficient to displace the tibial arm portion clear of the knee joint such that the distance between the tibial arm portion and a tibial bone for the knee joint at a position 20cm from the joint between the intermediate section and the tibial arm portion is in the range 5-30cm.</claim-text> <claim-text>10. An alignment device as claimed in any preceding claim, where at least the femoral and tibial arm portions are made from stainless steel or a disposable material.</claim-text> <claim-text>11. An alignment device as claimed in any preceding claim, wherein the femoral and tibial arm portions and the adjustable arm can be disjoined from the intermediate section to permit sterilisation.</claim-text> <claim-text>12. An alignment device as claimed in any preceding claim, further comprising a position marking on the tibial arm portion to enable a surgical measurement of the distance between the tibial arm portion and the tibial shaft to be taken.</claim-text> <claim-text>13. An alignment device as claimed in claim 12, wherein the position marking is 20cm from the intersection of the tibial arm portion with the intermediate section.</claim-text> <claim-text>14. A method for measuring rotational, translational and aHgnment characteristics of a prosthetic knee joint arranged between a femur and tibia, comprising: providing an alignment device including: femoral and tibial arm portions connected by an intermediate section perpendicular to the femoral and tibial arm portions, and an adjustable arm slideably mounted on the intermediate section; inserting the femoral arm portion into the medullary canal of the femur with the tibial arm portion projecting outside of the knee joint between the femur and tibia; aligning the tibia with the tibial arm portion such that the tibia is parallel to the tibial arm portion in both the frontal and vertical planes; determining rotation using the adjustable arm by sliding the arm along the intermediate section into contact with the knee joint; and aligning the knee joint with the adjustable arm to correct rotation at the knee joint.</claim-text> <claim-text>15. A method as claimed in claim 14 further comprising: measuring the distance between the tibia and the tibial arm portion at a position in the range 15-25cm from the intersection of the tibial arm portion and the intermediate section to provide a measure of pre-arthroplasty alignment of the knee joint.</claim-text> <claim-text>16. A method as claimed in claim 14 further comprising: measuring the distance between the tibia and the tibial arm portion at a position in the range 15-25cm from the intersection of the tibial arm portion and the intermediate section to provide a measure of intra-or post-operative alignment of the knee joint.</claim-text> <claim-text>17. A method as claimed in claim 15 or 16 wherein the position is determined using a pre-existing position marking on the tibial arm portion of the alignment device.</claim-text> <claim-text>18. A method as claimed in any of claims 14 to 17, wherein aligning the tibia includes aligning the tibia along the anatomical axis defined by the femur and tibia.</claim-text> <claim-text>19. A method as claimed in any of claims 14 to 16, wherein aligning the tibia results in a tibio-femoral angle of between 4-9 of valgus or a mechanical axis which falls through the middle third of the knee joint.</claim-text> <claim-text>20. An alignment device for aligning femoral and tibial bones at a knee joint, the device comprising: a femoral arm portion; a tibial arm portion connected to the femoral arm portion by an intermediate section perpendicular to both femoral and tibial arm portions, wherein the femoral and tibial arm portions subtend a fixed angle in the range 4-6W.</claim-text> <claim-text>21. An adjustable arm portion for an alignment device as claimed in any of claims I to 13 or 20, comprising an elongate arm to engage with the knee joint.</claim-text> <claim-text>22. An adjustable arm portion as claimed in claim 21, further comprising a body portion to engage with the intermediate section.</claim-text> <claim-text>23. A method for measuring rotation at a knee joint, comprising: providing an adjustable arm as claimed in claim 21 or 22; and using the adjustable arm to determine a measure of rotation of a knee joint in a total or partial knee replacement procedure.</claim-text> <claim-text>24. A method as claimed in claim 23, further comprsng correcting rotation of the knee joint using the measure.</claim-text> <claim-text>25. An alignment device substantially as hereinbefore described with reference to and as shown in the accompanying drawings.</claim-text> <claim-text>26. A method substantially as hereinbefore described with reference to the accompanying drawings.</claim-text> <claim-text>27. An adjustable arm portion substantially as hereinbefore described with reference to and shown in the accompanying drawings.</claim-text>