JOINT FUSION PEG
The invention relates to a peg for joining two or more bones together at a joint for example the proximal interphalangeal joint of the toes, to a kit of parts including the peg, and to a method of fitting the peg to the joint.
A proximal interphalangeal (PIP) joint comprises a proximal phalanx and a middle phalanx. Current methods of correcting proximal interphalangeal joint deformities, such as hammer toe, involve resection of the distal condyles of the proximal phalanx and then fixation with K-wires or spike arthrodesis. Alternatively, no fixation is employed apart from tightly sewing the dorsal tissues together having first excised an ellipse of skin. The bones will then fuse together as healing takes place.
K-wires protrude from the tip of the toe, and are normally removed three and six weeks after fixation. The protrusion of the K-wire fixation from the tip of the toe causes a nuisance as normal shoes cannot be worn, and the tips of the wires have to be protected.
The toe is prone to infection around the protruding wire.
With spike arthrodesis, the middle phalanx is impacted onto a spike of proximal phalanx. Unfortunately, the application of a spike arthrodesis produces a bayonet deformity at the site of fusion which often leaves the toe looking swollen. Also, the spike arthrodesis is prone to tilt, with a loss of position, and the spike joining the distal and proximal phalanx together can break.
Where no fixation is employed, it is often still necessary to use K-wire in order to keep the bones straight while they fuse together. Additionally, the bones are prone to move relative to each other, especially when pushed by the other toes.
It is an aim of the present invention to improve the apparatus and method by which two bones are joined together at a joint, and particularly the proximal interphalangeal joint.
In a first aspect of the invention there is a peg for joining two bones together at a toe joint, the peg being substantially rigid and having two limbs, each limb being shaped to fit and positively engage with an internal surface of the bone defining an excavated intramedullary cavity such that on fitment of both limbs into the cavities, the bones are sufficiently rigidly held together, preventing relative motion and angulation of the bones, to facilitate the fusing of the bones together.
It will be appreciated that the peg gives a number of advantages. Firstly, since it does not need to be removed once the bones have grown together, there is no need for further medical intervention to remove it. Additionally, because it is internal, no part of the peg extends from the bones causing a nuisance of a site for infection. Further, since the peg is strong and relatively inflexible, it is unlikely to break and will support the bones as they knit together. Additionally, bayonet deformities are avoided. All of this leads to a much superior medical outcome to the treatment of any patient. Various other advantages will be understood from reading the specification.
It is intended that, once the bones are joined using the peg, the bones will fuse together through bone growth in order to reinforce the join between the two bones. Immediately after the bones have been joined, they might not actually be in contact with each other, fusion occurring over time.
Advantageously the peg is sufficiently rigid to prevent, or very significantly resist, bending forces, snapping and breakage. Also, when the peg is fitted to a joint, it prevents, or significantly resists, rotation and angulation between the bones of the joint by holding the bones sufficiently securely together, relative to each other: this also facilitates fusion between the bones.
Preferably one or more of the limbs tapers to aid insertion into the or each cavity.
Advantageously each tapered limb is shaped to readily fit the intramedullary cavity fomwd within one of the bones.
Preferably one or both of the limbs is conical or frusto-conical. Advantageously the cavity for receiving the limb is similarly, shaped facilitating the fit of the limb into the cavity.
Preferably, the two limbs are a distal limb and a proximal limb, the distal limb being shorter and wider than the proximal limb. This permits more secure engagement between the peg and the bones. A shoulder may be present between the limbs.
Preferably the distal limb is shaped to fit a cavity in the middle phalanx; the proximal limb may be shaped to fit a cavity in a proximal phalanx.
Preferably the surface of a part of each limb is textured or rough so that, on insertion of one limb into the intramedullary cavity of one of the bones, the surface of the limb positively engages with the surface of the bone defining the cavity. This allows improved stability between the bones being fused.
Advantageously, when the peg is fitted it stabilises the bones being fused. Since the peg is sufficiently rigid, it can resist bending forces, snapping and breakages. Also, when fitted to a joint the peg prevents rotation and angulation between the bones, by holding the bones sufficiently securely together. All these features facilitate the fusing of the bones.
Preferably the surface texture of at least one of the limbs includes one or more flanges whereby positive engagement between the surface of the bone and limb is achieved by a press-fit. Advantageously the limb would be easy to insert into a bone cavity.
Advantageously the surface of the limb need only have a flange on one or two regions of the limb. Preferably these regions are on opposing sides of the limb; more preferably along the full length of the limb. This pushfit texture is preferably on the proximal limb.
It is preferred that the flange include a shallow ramped surface which bears against bone during insertion, and that it further includes a sharply projecting surface which resists removal of the peg. Thus, the shallow ramp, whilst resisting the insertion of the limb to some extent causes a "cutting cone" of excavated bone providing a slot which resists rotation and movement of the limb within the bone once fitted. The sharply projecting surface acts like a barb in opposing removal of the limb from the excavated cavity.
It is also preferred that there are a plurality of flanges on a limb, the flanges being angularly aligned along the surface of the limb, and it is further preferred that the flanges are angularly aligned along the surface in two longitudinal lines.
The surface of one or each of the limbs may include one or more oblique ridges, which may form a texture, whereby a positive engagement between the surface of the bone the limb is achieved by screwing and impacting the limb into the cavity within the bone.
Advantageously the limb is easy to fit in the cavity, when a push-fit is not practical and a good fixture between the bones is required. Advantageously this texture facilitates secure fitting by a simple screwing impacting action on the limb when inserted in the cavity within the bone. Preferably the texture covers most of the surface of the limb and is preferably located on the distal limb of the peg.
One or both of the limbs may be smooth on its superior and inferior surfaces.
The limbs of the peg may be angled relative to each other such that on fixation fusion is encouraged to occur with the bones located relative to each other in an optimised position. Preferably in the optimised position, the limbs are mutually opposed to each other. Alternatively, the peg may be straight, enabling the joint being fused such as a proximal interphalangeal joint, to be fused in a straight position.
Preferably, after fitting of the peg, the peg self-fixates to the bones. Advantageously, no supplementary fixture, internal or external, is required to secure the device to the bones.
The surface of the peg could be made of a biocompatible material. Normally, the peg will not require removal. Preferably the material is a bioseparable material or a hydrophilic material or both. Advantageously these materials may help to lock the peg in place. More preferably the material is a bioceramic, such as a polylactic acid or tricalcium phosphate. Such a material favours bone union or at the very least a solid fibrous fusion.
In a second aspect of the invention there is a kit of parts for fitting a peg, the kit comprising: at least one excavating tool shaped to excavate an intramedullary cavity of a phalanxand a peg according to the first aspect of the invention, the limbs of the peg dimensioned to fit the cavities excavated in the proximal and middle phalanx.
Preferably, the kit comprises a first excavating tool shaped to excavate an intramedullary cavity of a proximal phalanx, and a second excavating tool shaped to excavate a intramedullary cavity of a middle phalanx.
In a third aspect of the invention there is a method of fitting a joint fusion peg between a proximal phalanx and a middle phalanx, the peg having a proximal limb and a distal limb, the method comprising the steps of: (1) excavating the intramedullary cavities of the proximal phalanx and the middle phalanx, the proximal limb being dimensioned to fit the intramedullary cavity in the proximal phalanx; (2) push fitting and/or impacting the proximal limb into the proximal intramedullary cavity within the proximal phalanx; and (3) compressing and/or screwing the distal limb into the intramedullary cavity within the middle phalanx.
An embodiment of the invention will now be described by way of example only with reference to the drawings in which:- Figure 1 is a sectional plan view of a peg fitted to a proximal interphalangeal toe joint, showing the peg, the proximal phalanx and the middle phalanx; Figure 2 is a side view of the peg shown in Figure 1 prior to insertion; Figure 3 is a top pian view of the peg shown in Figure 2; Figure 4 is a perspective view of the peg shown in Figures 2 and 3; and Figure 5 is a perspective view of a proximal phalanx having a peg fitted to it ready for impaction of the distal limb of the peg into an intramedullary cavity of a middle phalanx.
A preferred embodiment of the invention is described below for use in maintaining the surgical correction of deformities of the proximal interphalangeal (PIP) joints of the toes. It is a device aimed at joining the bones to allow fusion in the optimum position.
It is not a joint replacement. In view of the elongate shape of the device, it is referred to
in the specification as a peg.
The shape and size of the peg takes into account the anatomy of the intramedullary cavities of the bones to be fused. The design features of the peg are aimed at controlling angular deformity, rotation and any pistoning movements that are liable to occur at the site of intended fusion. The peg, once fitted, needs to control rotation and angulation by holding the two bones together at the site of the intended fusion.
The preferred embodiment of the peg 1 is shown in Figure 1. In this embodiment, the peg 1 is straight with a long thin conical shaped proximal limb, and a shorter wider conical shaped distal limb 3. The surface of the proximal limb 2 is smooth on its superior and inferior surfaces and includes flanges 4 at its sides. The flanges 4 permit a press-fit of the proximal limb 2 to lock it into position in an intrarnedullary cavity of a proximal phalanx, preventing rotation. The surface of the distal conical limb 3 of the device is scored with oblique ridges 5 that lock the limb 3 in place in the intramedullary cavity of a middle phalanx when it is fitted, by manually screwing and impacting it.
The oblique ridges 5 are similar in structure to the ridges that would be found on a workshop file giving sufficient abrasiveness that it will be fitted securely within the middle phalanx. Other surface patterns and irregularities could be used instead. This device notably differs from other known pegs or pins, which all have smooth surfaces.
This difference allows the shape and surface of the peg 1 to provide maximal stability.
Each of Figures 2, 3 and 4 show the peg 1 prior to being used. More detail of the flanges 4 can be seen. The flanges are shaped to be similar to an intersecting cylinder with a shallow ramped surface 6 which is curved and angled such that it does not generate too much resistance to the insertion of the proximal limb into the proximal phalanx. However, as the proximal limb 2 is pushed into the proximal phalanx, it will excavate additional bone in order to create a channel within which the flanges will be securely located preventing rotation of the limb within the proximal phalanx.
The flanges also include a sharply projecting surface which resists removal of the peg.
It has an effect similar to that of a barb, and the surface may be dished. Resistance to removal from the proximal phalanx is generated by the edge between the shallow ramp surface 6 and the sharply projecting surface 7.
Additionally, where the two limbs join there is a shoulder 8 which is caused by the difference in diameter of the two limbs and which forms an abutment which prevents the proximal limb 2 from being inserted too far into the proximal phalanx.
Referring now to Figures 1 and 5, the fixation of the peg 1 proximally and distally are different. Proximally, the longer proximal limb 2 of the peg is inserted into the diaphysis or the midshaft of the proximal phalanx 9, which is the longer bone of the proximal phalanx 9 and middle phalanx 10. Distally the peg 1 will be inserted in the body of the middle phalanx 10 which is the smaller of the two bones and which has greater anatomical variability. The proximal longer limb 2 of the peg is inserted first and will consequently have greater stability.
Before the peg 1 is fitted to the joint, the proximal phalanx 9 is first reamed with a conical reamer. This excavation determines the size of the implant. The reamer will have a matched but shorter reamer for excavating the middle phalanx 10, where a subchondral plate should be preserved, apart from where it is penetrated by the reamer.
The limb 3 of the peg going into the middle phalanx 10 should be as long as possible.
The distal limb 3 of the implant might need to be trimmed to suit a particular patient, but should not be truncated any more than is necessary.
As well as the pair of reamers, a punch is required to impact the peg into the proximal phalanx 9. The impaction of the distal conical limb 3 of the peg into the middle phalanx 10 is achieved by manual compression with a twisting action, to screw it home.
The device is made from a bioceramic material such as polylactic acid and tricalciun phosphate composite which may favour bone union, although solid fibrous union is still considered a good result. Of course any other biocompatible material including bioabsorbable material or a hydrophilic material could be used. As it is made from a biocompatible material, the peg should not require removal.
The peg 1 is designed to be dimensioned to fit any of the PIP joints of the toes.
After the peg 1 has been fitted to a PIP joint the toe to which it is fitted has a normal contour and it is fused to be straight. The fixation is also as rigid as possible, permitting early wound healing with minimal swelling and an early return to the use of the toe in normal footwear.
In preparation of the peg 1 before surgery, the peg is made of a material that permits trimming, if necessary.
The fixation of the device to the joint is sufficiently strong that no supplementary fixation, internal or external, is required. Fixation is capable of being satisfactory without the use of bone cement or the like.