Patent Description:
Prosthetic tibial components for replacement knee joints typically comprise a tibial tray which is coupled to the tibia of a patient and forms a tibial plateau of the tibia. The tibial component may be a unicondylar tibial component of a partial knee replacement prosthesis which replaces the proximal surface of a medial or a lateral tibial condyle. Alternatively, the tibial component may be part of a total knee replacement prosthesis and may replace substantially the complete proximal surface of the tibia and form a tibial plateau of the medial and lateral tibial condyles.

Often, separate bearing components are coupled to the tibial tray, which may be fixed bearing components or mobile bearing components. Fixed bearing components may additionally comprise mobile portions which are trapped within the fixed bearing. Any fixed bearing components must be coupled to the tibial tray to prevent movement and brackets are often provided on the posterior regions of the tibial tray which couple to the bearing components. The bearing components may comprise a pocketed recess in the posterior region of the bearing to couple with the bracket. The posterior portion of the bearing may be heavily loaded during some knee articulations and if a pocket is provided in this location, reinforcement may be required. In some cases it may be undesirable to provide a pocket in the posterior region of the bearing, for example to improve the rigidity of the posterior portion of the bearing.

During an operation to implant a prosthetic tibial component, which comprises one or more fixed bearing components, the surgeon may select from several bearing components of different thicknesses and may trial fit a bearing component of one thickness before selecting another thickness of bearing component to finally implant. For example, the surgeon may determine that the first bearing selected was too thick and was applying undesirable load into the prosthetic knee joint. The surgeon may trial fit several bearing components before selecting a bearing component with the correct thickness. It is therefore desirable to allow coupling and decoupling of fixed bearing components to be as simple as possible during surgery.

<CIT> discloses a knee joint prosthesis assembly, including a femoral component, a unitary tibial component, a medial bearing, and a lateral bearing. The femoral component can have a medial and a lateral condyle portion connected by a patellar track portion. The femoral component can form an opening between the medial and lateral condyles. The unitary tibial component can have a medial portion that includes a first posterior engagement lip and a first outer securing lip. The tibial component can further include a lateral portion that includes a second posterior engagement lip and a second outer securing lip. The medial bearing can have a first posterior groove formed thereon that selectively engages the first posterior engagement lip and a first outer groove that selectively engages the first outer securing lip.

According to a first aspect of the present invention, there is provided a prosthetic assembly as set out in claim <NUM>. Optional features are set out in claims <NUM> to <NUM>.

According to a second aspect of the present invention, there is provided a method of securing bearing components to a prosthetic assembly, as set out in claim <NUM>. Optional features are set out in claim <NUM>.

To avoid unnecessary repetition of text in the specification, certain features are described in relation to only one or several aspects or embodiments of the invention. However, it is to be understood that, where it is technically possible, features described in relation to any aspect or embodiment of the invention may also be used with any other aspect or embodiment of the invention.

For a better understanding of the present invention, and to shown more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:.

With reference to <FIG>, a conventional prosthetic joint assembly <NUM> comprises a femoral component <NUM>, a tibial component <NUM>, a medial bearing component <NUM> and a lateral bearing component <NUM>. In use, the femoral component <NUM> is coupled to a distal end of a femur (not shown) and the tibial component <NUM> is coupled to a proximal end of a tibia (not shown).

The tibial component <NUM> comprises a tibial tray with a medial portion <NUM> and a lateral portion <NUM>. The medial and lateral bearing components <NUM>, <NUM> are coupled to the medial and lateral portions of the tibial component respectively. The medial and lateral bearing components comprise proximal bearing surfaces <NUM>, <NUM>, which engage cooperating bearing surfaces <NUM>, <NUM> on the femoral component <NUM>. The bearing surfaces <NUM>, <NUM>, <NUM>, <NUM> allow the prosthetic joint assembly to articulate and approximate the range of movement of a natural knee joint.

In the prosthetic joint assembly shown in <FIG>, the medial and lateral bearing components <NUM>, <NUM> are mobile bearing components, which are movably coupled to the medial and lateral portions <NUM>, <NUM> of the tibial component. This allows a high flexibility of movement of the joint. The prosthetic assembly <NUM> may also comprise an artificial ligament <NUM> which extends between the tibial component <NUM> and the femoral component <NUM>. The inclusion of the artificial ligament <NUM> provides stability to the joint and prevents undesirable articulations.

<FIG>, shows a tibial component <NUM> in accordance with an embodiment of the invention. The tibial component <NUM> comprises a tibial tray, which supports medial and lateral bearing components <NUM>, <NUM>. The medial and lateral bearing components are fixed relative to the tibial component <NUM>. Providing fixed bearing components <NUM>, <NUM> within the prosthetic assembly <NUM> improves the stability of the joint.

Referring to <FIG> and <FIG>, the medial and lateral bearing components <NUM>, <NUM> comprise recesses 106a, 108a. The recesses 106a, 108a, are formed by slots provided in a medial face of the lateral bearing component <NUM> and a lateral face of the medial bearing component <NUM>. The slots extend from an anterior face of each bearing component to a posterior face.

As shown in <FIG> and <FIG>, the proximal bearing surfaces <NUM>, <NUM> of each bearing extend over the recesses 106a, 108a and are supported by a portion of the bearing component provided on a superior side of each slot. The inferior boundary of each slot is formed by distal walls 106b and 108b, which extends laterally from respective bearing components.

When assembled into the prosthetic assembly <NUM>, the recesses 106a, 108a, define medial and lateral passages <NUM>, <NUM> of the tibial component <NUM>. The passages <NUM>, <NUM> are provided at a substantially central location of the tibial component. As shown in <FIG>, the passages <NUM>, <NUM> extend from an anterior side of the tibial component <NUM> towards a posterior side of the tibial component.

The prosthetic assembly <NUM>, as shown in <FIG>, further comprises a retention clip <NUM>. In the example shown, the retention clip <NUM> is a substantially U-shaped clip comprising medial and lateral arms 110a, 110b and a body 110c extending between the arms. The retention clip <NUM> is configured to be received within the medial and lateral passages formed by the recesses 106a, 108a in the medial and lateral bearing components, e.g. the retention clip is configured to be inserted into the tibial component <NUM> in an anterior-posterior direction. The arms 110a, 110b are tapered at distal ends of the arms to ease alignment with the medial and lateral passages during initial insertion of the retention clip.

When inserted into the medial and lateral passages, the retention clip engages the tibial component <NUM> and the medial and lateral bearing components <NUM>, <NUM>. The arms of the retention clip are configured to apply loads to the medial and lateral bearing components in the medial and lateral directions respectively, which trap the bearing components against the tibial component <NUM>.

With reference to <FIG>, <FIG> & <FIG>, a medial attachment bracket <NUM> is provided on the medial portion <NUM> of the tibial tray <NUM> and a lateral attachment bracket <NUM> is provided on the lateral portion <NUM>. In the example shown in <FIG>, the medial attachment bracket <NUM> is provided on the medial edge of the medial portion <NUM> and the lateral attachment bracket <NUM> is provided on the lateral edge of the lateral portion <NUM>. However, it is equally envisaged that the medial and/or lateral attachment bracket <NUM>, <NUM> may be provided in other locations on the medial and/or lateral portion respectively. For example, the medial and/or lateral attachment bracket may be provided substantially centrally on the medial and/or lateral portion <NUM>, <NUM> of the tibial tray.

With reference to <FIG>, the medial and lateral bearing components comprise attachment recesses <NUM>, <NUM>. The medial and lateral bearing components are coupled to the tibial component <NUM> by translating the medial and lateral bearing components in a generally anterior-posterior direction relative to the tibial tray, such that the attachment recesses <NUM>, <NUM> engage the medial and lateral attachment brackets <NUM>, <NUM> respectively.

A boss <NUM> is provided on the tibial component <NUM> at a substantially central location on the tibial tray. The boss <NUM> is provided substantially between the medial and lateral passages <NUM>, <NUM>. The width of the boss is greater than the medio-lateral separation of the passages <NUM>, <NUM>, such that when the retention clip <NUM> is assembled in the prosthetic assembly <NUM>, the arms of the retention clip 110a, 110b engage either side of the boss <NUM>.

With reference to <FIG>, the boss <NUM> comprises medial and lateral interference portions 134a, 134b, which are configured to interfere with the distal ends of the arms 110a, 110b of the retention clip, when the arms are fully received within the passages <NUM>, <NUM>. A relief slot 110d is provided within the retention clip <NUM> to allow the medial and lateral arms to be displaced medially and laterally respectively, due to their interference with the boss <NUM>, without distorting the body 110c of the clip. The relief slot also reduces the stress at the locations on the retention clip <NUM> where the arms 110a, 110b join to the body 110c. When the arms 110a, 110b are displaced in this way, strain energy is stored within the arms and body 110a, 110b, 110c of the retention clip causing the arms of the retention clip to apply a clamping load to the boss <NUM>, e.g. the arms and body of the retention clip <NUM> are resilient. The clamping load provided by the retention clip on the boss acts to resist decoupling of the retention clip <NUM> from the tibial component <NUM>.

With reference to <FIG>, the tibial component <NUM> comprises a stem <NUM> having a stem recess <NUM>. The stem recess <NUM> is configured to receive a resilient element, such as a spiral spring <NUM>, as shown in <FIG>. In one possible arrangement, the spiral spring comprises a ligament anchor 144a configured to couple to the artificial ligament <NUM>. The spiral spring <NUM> is configured to apply tension to the ligament <NUM>. In one arrangement the tension in the ligament is adjusted to be substantially equal to the tension in a natural anatomical ligament. The spiral spring <NUM> comprises one or more projections (not shown) which are received within one or more grooves <NUM> provided in the stem recess <NUM>. Contact between the grooves <NUM> and projections allows the spiral spring <NUM> to extend and contract within the stem recess <NUM> as load is applied to the ligament <NUM>. As shown in <FIG>, <FIG> and <FIG>, the arms 110a, 110b of the clip <NUM> cover distal ends of the grooves <NUM>, and prevent the projections from being removed from the grooves whilst the retention clip is assembled. Consequently, the retention clip can be used to retain the spiral spring <NUM> within the stem recess <NUM>.

In a method of surgery for implanting the prosthetic assembly <NUM>, the femoral component <NUM> is implanted onto the distal end of the femur of a patient and the tibial component <NUM> is implanted onto the proximal end of the tibia of the patient. Bearing components <NUM>, <NUM>, of suitable thicknesses are selected and coupled to the tibial tray by sliding the bearing component in a generally anterior-posterior direction against the tibial component <NUM>, such that the attachment recesses <NUM>, <NUM> of the medial and lateral bearing components <NUM>, <NUM> engage the medial and lateral attachment brackets provided on the tibial tray.

Once the medial and lateral bearing components are assembled, the retention clip <NUM> is coupled to the prosthetic assembly <NUM> by inserting the medial and lateral arms of the retention clip 110a, 110b into the medial and lateral passages <NUM>, <NUM> respectively, until the arms of the retention clip engage the boss <NUM>, as described above.

When the retention clip <NUM> is assembled into the prosthetic assembly <NUM>, the medial and lateral arms of the retention clip 110a, 110b are deflected in the medial and lateral directions respectively, due to their interference with the boss <NUM>. The arms of the retention clip <NUM> engage the medial and lateral bearing components and apply loads to the bearing components in the medial and lateral directions respectively. The medial and lateral bearing components are thereby trapped against their respective attachment brackets <NUM>, <NUM>.

The distal walls 106b, 108b, which form the inferior boundaries of the recesses 106a, 108a, as described above, prevent the bearing components <NUM>, <NUM> from being displaced superiorly relative to the tibial component <NUM> and disengaging from the retention clip <NUM>. This ensures that the bearing components <NUM>, <NUM> remain coupled to the tibial component <NUM> during normal use, and are not able to dislocate during articulation of the joint.

Although interference between the arms 110a, 110b of the retention clip <NUM> and the boss <NUM>, as described above, prevents the retention clip <NUM> from detaching from the tibial component <NUM> during normal use, if it is desirable during an operation, a surgeon may remove the retention clip <NUM> and decouple either or both of the bearing components <NUM>, <NUM> from the tibial tray <NUM>, for example in order to fit bearing components of a smaller or larger thickness. As the retention clip <NUM> is installed into the tibial component in an anterior-posterior direction, the retention clip <NUM> may be removed or installed through a very small incision in the front of a patient's knee, in a minimally invasive surgical procedure.

In another arrangement (not shown), the boss <NUM> comprises one or more clip retaining portions, such as lugs, provided on the medial and lateral sides of the boss extending in the medal and lateral directions respectively. The retention clip comprises corresponding engagement portions, e.g. recesses, which receive the protrusions. Engagement between the retention clip recesses and the protrusions act to prevent the retention clip from disengaging from the boss.

In another arrangement, the clip <NUM> may comprise one or more protrusions which are received within one or more corresponding recesses provided on the boss <NUM>. In another arrangement, one or more clip retaining protrusions and/or recesses may be provided on the bearing components <NUM>, <NUM> and corresponding recesses and/or protrusions may be provided on the retention clip <NUM>, which are configured to engage the clip retaining protrusions and/or recesses provided on the bearing components <NUM>, <NUM>.

Claim 1:
A prosthetic assembly (<NUM>) comprising:
a tibial tray comprising:
a medial retaining bracket (<NUM>) positioned at a medial portion (<NUM>) of the tibial tray;
a lateral retaining bracket (<NUM>) positioned at a lateral portion (<NUM>) of the tibial tray; and
a boss (<NUM>) substantially centrally disposed on the tibial tray;
a medial bearing component (<NUM>);
a lateral bearing component (<NUM>); and
a retention clip (<NUM>) comprising a first arm (110a) and a second arm (110b),
characterised in that each of the first arm and the second arm extends anteriorly-to-posteriorly to engage opposite sides of the boss (<NUM>), the first arm configured to engage and trap the medial bearing component against the medial retaining bracket and the second arm configured to engage and trap the lateral bearing component against the lateral retaining bracket.