This invention generally relates to covers for medical implants and introducers for securing a cover to a medical implant and, more particularly, to covers, holders and introducers for acetabular cup implants.
The following descriptions and examples are not admitted to be prior art by virtue of their inclusion within this section.
Acetabular cup implants with large diameter bearings, such hip resurfacing arthroplasty (HRA) cups or large diameter total hip replacement (THR) cups, are a challenge to hold during implantation. The surgeon must forcibly impact the cup into a prepared, slightly undersized acetabular socket during fitting, whilst ensuring that the cup is implanted in the correct angle and orientation which is critical to function. Furthermore, it is essential to protect the super finished bearing surface from damage during this impaction process. Most conventional THR cups consist of an outer shell and separate bearing liner which is inserted after the metal shell is implanted. Therefore, the inside of the metal shell is used to provide holding features for an introducer shaft such as a screw thread or bayonet attachment. However, this area is not available on HRA cups or THR cups with pre-fitted liner because the inside surface forms the bearing surface. Furthermore, the outer surface is usually fully embedded in the bone socket. Previous HRA cup designs have attempted to solve this problem in various ways, but these have resulted in compromises to the designs, either by reducing bearing surface, or reducing outer fixation surfaces or by including holding features which caused snagging and aggravation of the soft tissue structures such as Psoas tendon in close proximity to the cup rim.
A new generation of HRA implants and large diameter THR’s utilizing non-metal bearing materials including zirconia toughened alumina ceramic (ZTA) and cross linked ultra-high molecular weight polyethylene (UHMWPE) pose bigger challenges for cup holding during implantation. In the case of ZTA, due to the constraints of the manufacturing process and hardness of the material, it is technically difficult and expensive to add small holding features sometimes present on metal hip cups. In the case of UHMWPE, it is critical for wear characteristics and material strength that full wall thickness is maintained, so holding features that reduce wall section would be undesirable. In addition, some new generation devices are intended for specific rotational alignment of asymmetric features on the cup which also add complication for cup holding and positioning.
Covers and introducers for medical implants as well as systems of such and methods of their use are provided. The following description of various embodiments of covers, systems, introducers, and methods is not to be construed in any way as limiting the subject matter of the appended claims.
Embodiments of a cover for a medical implant comprises a body portion and a seal. The body portion comprises a distal end and a proximal end. The proximal end comprises a region adapted for connecting to an introducer and the seal comprises at least one tab extending away in a proximal direction from the body portion.
Embodiments of a method of fixing a cover to a medical implant comprises adding a fluid to a region of the medical implant which will accept the cover, introducing the cover into the region of the medical implant such that the cover displaces the fluid until the cover abuts a surface of the medical implant, and adding additional force to the cover such that a seal of the cover is compressed between a body portion of the cover and the medical implant.
Embodiments of an introducer comprises a drive shaft, a connector hub, and a latching means to secure the connector hub to a cover for a medical implant.
Embodiments of a system comprises a cover for a medical implant and an introducer, wherein the cover is releasably fixable to the introducer.
Embodiments of a system comprises a medical implant and a cover releasably fixable to an inner surface of the medical implant.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the accompanying drawings in which:
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.
The present disclosure provides a cup holding solution which can be applied to any hip cup with large diameter bearing surface without the need for special holding features on the cup. It functions by establishing a hydraulic seal between a cover assembly and the cup implant which holds them together securely. The cover is connected via a separate mechanical connection to an introducer shaft which is used to position and forcibly impact the cup implant into the prepared acetabulum. Once fitted, the introducer is disconnected, leaving the cover still attached to the cup implant. The hydraulic seal between cover and cup implant is then broken by pulling a release tab on the cover enabling easy removal of the cover.
In United Kingdom patent document no. GB2552173A, a similar hydraulic seal is established between three elements, (1) the cup implant, (2) the cover and (3) the introducer, whereas on the latest invention it is established between only two elements, (1) the cup implant and (2) the cover. This provides several advantages, firstly, during implantation, the surgeon can remove and reconnect the Introducer from the cover without disrupting the hydraulic seal. This allows for checking of cup position in the acetabulum with the option of reattaching the Introducer to further advance or adjust cup position. Secondly, it is advantageous to be able to turn the cup implant when approaching the acetabulum to position asymmetric features on the cup rim to the intended positions to match the anatomy of the acetabular rim. Where a straight introducer shaft is employed, this can be done by rotating the entire assembly about the shaft’s axis, however where an offset shaft is employed it is desirable to turn the cup independently without influencing the shaft offset position, because, due to the constraints of surgical access, the offset shaft is positioned within a narrow window of available space within the surgical site. Furthermore, the optimum position for the offset varies depending on surgical approach and surgeon preference, so it is advantageous to position the offset shaft and cup rim rotational features independently of one another. It is easier to allow the cup with cover to turn independently of the introducer if the hydraulic seal does not rely on features on the introducer. A mechanism for rotating the cup via the introducer will be described later. Thirdly, because the hydraulic seal is contained within two elements, the required fluid volume is reduced, as is the likelihood of air bubbles remaining in the fluid system which reduce the holding force. And lastly, the non-return valve and releasing mechanism present on the previous invention are not necessary with the new invention so there and fewer components contributing to the hydraulic seal and less to go wrong.
The above published patent application describes a means for establishing low pressure in the fluid (or maintaining it under suction). Experience has shown that this is not essential, because a sufficient holding force is achieved by allowing excess fluid to escape from the sealed cavity and preventing air or fluid from re-entering. For this reason, the latest invention does not include description of a similar means to lower pressure. Furthermore, the above publication states that while it is desirable to use fluid to establish the holding force, it also functions without fluid, where only air is present in the sealed cavity, but that the holding force is reduced. It is also the case with the latest invention that it functions without fluid but with reduced holding force.
In this document emphasis is placed to the hydraulic seal between cup implant and cover. A description of the third element, the introducer is included for context. The cover and introducer may be supplied as sterile single use devices. However, alternatively they may be supplied as re-useable devices providing, they are decontaminated, cleaned, and sterilized before each use.
The main function is to establish a holding force between cup implant and cover which can be released once the cup implant is positioned correctly and without undermining the fit of the cup in the acetabular socket. The mating surfaces of cup implant and cover must be in full contact with one another to transfer the impaction force from the Introducer to the cup implant while being fitted into a slightly undersized acetabular socket by impacting the introducer with a surgical hammer. At the same time, the cup implant and in particular the super-finished bearing surface must be protected.
The cover includes a seal component (such as silicone rubber) and a cover body. In some arrangements, including preferable configurations, a connector (e.g. in the form of a snap-ring) can also be utilized. Interactions between the cover and cup implant are responsible for, (a) allowing excess fluid to escape enabling full contact between mating surfaces (b) establishing and maintaining a hydraulic seal, holding them together and (c) allowing the hydraulic seal to be disrupted, for removal of the cover once the cup is implanted correctly.
In use, the cup implant is filled with a fluid (e.g. sterile water) and the cover is rotationally aligned and pressed together with the filled cup implant. Either the cover and cup are pressed together separately, or the cover is first fitted to the introducer before being pressed onto the cup implant. As they are pressed together excess fluid is expelled around a portion of the seal until the mating surfaces contact one another. If assembled separately, the cup implant with cover are then fitted onto the introducer. The cup implant is then transferred to the surgical site via the introducer and aligned correctly prior to impaction into the acetabular socket by hammering the end of the introducer. During cup fitting, the introducer can be removed and reconnected from the cup with cover for inspection and assessment of position by the surgeon whilst the hydraulic seal remains intact. Once positioned correctly, the cover is removed from the cup by gripping and pulling one of the seal tabs protruding upwards from the cup rim, either using a finger grip or with the aid of forceps. Only light pulling force is required as will be described below.
To maintain the hydraulic seal a number of portions (typically three, although two, four, five, or more can also be utilized) of the seal are being compressed between the cover body and cup bearing surface including the areas adjacent to the tabs and one other. Elsewhere there is slight clearance for the seal between the cover body and cup bearing surface. This allows excess fluid to be expelled on assembly and in this region the hydraulic seal is maintained by the edges of the seal pressing against the bearing surface. Thus, a hydraulic seal is maintained all round either by compression of the seal or by its edges being in contact. The edges of the seal are biased towards contacting the bearing surface because the sealing (e.g. silicone) part, typically being cut from a flat sheet, is being deformed into a spherical shape whilst trying to return to its free shape through its resilient nature. This causes not only the seal edges, but also the outer seal surfaces adjacent to edges to be in contact with the bearing surface forming an effective fluid tight or airtight seal.
The seal is disrupted by pulling the tabs because, as the silicone stretches, it becomes thinner beyond the amount it is being compressed, opening up a small gap for air to enter the sealed cavity and disrupting the seal. It takes only light force to stretch the tabs and they can be stretched inwards (towards the center of the cup) therefore avoiding forces which tend to pull against the cup fixation.
In addition to the outer edges of the seal interacting with the cup, the inner edges must also form a seal with the cover body to make a fully sealed cavity. This can be achieved by sandwiching the inner seal edge between the cover body and the connector where present (e.g. snap-ring), compressing the silicone, and forming an effective secondary seal. Other ways of forming a secondary seal are well known to the skilled person and can include e.g. the seal element being bonded to the cover body (e.g. via a heat bond, adhesive bond, etc.) or by over-moulding the seal to the cover. Alternatively, an effective seal can be made by stretching the smaller diameter central hole of the seal into a groove of larger diameter on the cover, similar to stretching an o-ring into an o-ring groove on a shaft.
The cover also incorporates features to enable secure fitting of the introducer via a latching mechanism and a rotational drive feature so that the cup with cover can be rotated around the introducer axis. This is beneficial to align the cup rim features as intended to the anatomical features of the acetabular rim without fully rotating the introducer. The springloaded latch engages automatically as the introducer is assembled into the cover, it can then be rotated via an adjustment knob and locked in a certain rotational position. To disengage the introducer from the cup with cover, the knob is pulled back towards the operator which unlatches it.
Embodiments of covers for medical implants as well as systems, introducers and methods for their use are provided as follows:
A cover for a medical implant, the cover comprising a body portion and a seal, the body portion comprising a distal end and a proximal end, the proximal end comprising a region adapted for connecting to an introducer and the seal comprising at least one tab extending away in a proximal direction from the body portion. The at least one tab can be manipulated to deform the seal. The body portion may include at least one raised portion between the proximal and distal ends that assists in maintaining contact between the cover and the medical implant when in use. In some cases, the at least one raised portion is two raised portions. In some arrangements, there is at least one further raised portion approximately equidistant from the at least one raised portion. In some configurations the proximal end of the body portion comprises at least one slot configured to allow the at least one tab to pass through a respective slot. In some cases, there is a raised portion adjacent each of the at least one slot of the body portion. In some configurations, the seal extends over the at least one raised portion. The seal can comprise a plurality of, such as but not limited to two, tabs. The seal may be removably attachable to the body portion. The seal may be fixedly attached to the body portion at a region of fixed attachment, and wherein said region of fixed attachment forms an air- and/or watertight, or a substantially air- and/or watertight, seal between the seal and the body portion.
The body portion may be dimensioned in a region away from the region of fixed attachment to provide clearance between it and the seal, thereby allowing the seal to move towards and away from the longitudinal axis of the cover. In some arrangements the cover further comprises a connector which connects the seal to the body portion. The distal end of the body portion can be profiled at a connector region to accept the connector. The connector region can be profiled to retain the connector, optionally wherein the connector comprises projections which interact with a rim on the connector region. In some cases, the medical implant is a cup implant, and the cover is profiled to fit within the cup. The body portion comprises a rim, optionally wherein the rim is contoured, and optionally wherein the rim is contoured to match a rim contour of the medical implant. In some arrangements the seal is contoured to match a contour of a rim of the body portion. In some arrangements the rim of the seal sits distally from a rim of the body portion except for at the at least one tab.
Also provided is a method of fixing a cover to a medical implant, the method comprising: (i) optionally (e.g. if a liquid is being used instead of air) adding a fluid to the region of the medical implant which will accept the cover; (ii) introducing the cover into the region of the medical implant such that the cover displaces the fluid, until the cover abuts the surface of the medical implant; and (iii) optionally adding additional force to the cover such that the seal is compressed between the body portion and the medical implant. The method can further comprise releasing the cover from the medical implant, the additional steps comprising: (iv) manipulating the one or more tabs on the seal in order to disrupt the seal between the cover and the medical implant; and (v) removing the cover from the medical implant.
There is also provided a system comprising a cover for a medical implant and an introducer, wherein the cover is releasably fixable to the introducer, the introducer comprising a drive shaft and a connector hub, the introducer comprising latching means to secure the connector hub to the cover, optionally wherein the connector hub comprises a rim that engages with a complementary valley in a cover for a medical implant.
This is also provided a system comprising a medical implant and a cover, wherein the cover is releasably fixable to an inner surface of the medical implant.
Also disclosed herein is an introducer comprising a drive shaft and a connector hub, the introducer comprising latching means to secure the connector hub to a cover for a medical implant. The connector hub may comprise a rim that engages with a complementary valley in a cover for a medical implant. In some cases, the latching means is moveable with respect to the drive shaft. The drive shaft may be offset from a longitudinal axis of the connector hub. In such arrangements, the introducer comprises an impact shaft for transferring load from a handle region of the introducer to the connector hub, the impact shaft being distinct from the drive shaft. In some cases, the drive shaft is independently moveable with respect to the impact shaft such that the drive shaft can be rotated and/or moved towards and away from the connector hub (in some cases parallel to the longitudinal axis of the drive shaft).
In some arrangements the introducer comprises a means to bias the drive shaft towards the connector hub and, in some cases, the bias comprises a spring. The means to bias the drive shaft towards the connector hub may be independent from the latching means. The drive shaft has a distal end (i.e. the end at the connector hub) which may comprise an adaptor which allows the drive shaft to engage with and rotate a cover for a medical implant while at an offset angle, such as a ball drive end optionally with square sides. The drive shaft may be parallel to the longitudinal axis of the connector hub. The drive shaft of the introducer can act as an impact shaft for transferring load from a handle region of the introducer to the connector hub. In some arrangements the latching means is biased towards the connector hub, optionally wherein said bias is only present when the latching means is moved away from said connector hub. Some configurations have the connector hub comprising an anti-rotation feature, such as a projection. In some cases, the projection interacts with a complementary recess in the cover for the medical implant.
In use, the cup implant [24] typically is removed from sterile packaging and placed on a flat surface. It is then filled with fluid (e.g. sterile water) [28] as shown in
If assembled separately, the cup implant with cover are then fitted onto the introducer. With the hydraulic seal established, the cup implant can be transferred to the surgical site and manipulated into the pre-prepared acetabular socket [37] of the pelvis [36] in as shown in
A simulation of the effect of stretching one of the tabs is shown in
The embodiment of the introducer [34] shown in
The latch sub-assembly [45] incorporates housing [49] which incorporates latch [50] for retaining the cover, a rotating drive shaft [51] for rotating of the cover about the long axis of the introducer and a latching means such as a cam lever [52] to lock rotating drive shaft in a certain position. The drive shaft has an adaptor at its distal end to allow rotation of the cover whilst the drive shaft is off set. In the depicted arrangement this adaptor is shown as a ball drive end [53] with square sides which engages into recessed square drive feature [3] on the cover. The ball drive end [53] is similar to a standard ball ended Allen key which allows the tool to be used at an angle off-axis to the screw, except that the Allen key ball drive has hexagonal sides and this has square sides. In this case, the ball drive end allows the rotation drive shaft to be off axis relative to the axis of cover rotation. This is necessary due to the offset shape of the introducer shaft. Alternatively, the ball drive end [53] and mating recess [3] on cover body [1] could be hexagonal, or star shaped or any shape which allows rotation via and off-axis drive shaft.
Latch sub-assembly [45] is free to slide a short distance in the direction parallel to the drive shaft axis, while the position of spring holder [46] is fixed (e.g. by a rivet nut) so that the spring [47] biases the Latch sub-assembly towards hub [44]. This allows latch [50] and ball drive [53] to engage and disengage from the cover. When the cover is assembled together with the introducer, hub [44] engages into cover recess [4]. The latch and ball drive are driven back in direction of arrows [54] by cover boss rim [13] until the latch and ball drive drop into their respective engagements. This occurs automatically under the spring force as the operator pushes them together. To disengage and release the cover the operator must first pull the latch sub-assembly via the knob on drive shaft [51] a distance (e.g. 3-4 millimeters) against the spring force in direction of arrow [54] in
An alternative configuration of the introducer with a straight shaft [55] is shown in
The cover is universal so that it will accommodate either straight or offset introducers depending on surgeon preference. The cover may be supplied sterile for single-use or could be cleaned, re-sterilized and re-used several times. Those skilled in the art will appreciate that it is advantageous to have a commonly designed cover to fit both straight and offset introducers to improve compatibility and reduce instrument inventory.
It will be appreciated to those skilled in the art having the benefit of this disclosure that this invention is believed to provide covers for medical implants as well as systems, introducers, and methods of their use. Further modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as the presently preferred embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description of the invention. Changes may be made in the elements described herein without departing from the spirit and scope of the invention as described in the following claims.
Number | Date | Country | Kind |
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2010525.0 | Jul 2020 | GB | national |
The present application is a continuation-in-part application of International Application No. PCT/GB2021/051753 filed Jul. 9, 2021, which designates the United States and claims priority to United Kingdom Patent Application No. 2010525.0 filed Jul. 9, 2020.
Number | Date | Country | |
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Parent | PCT/GB2021/051753 | Jul 2021 | WO |
Child | 18094016 | US |