Patent Description:
Joint arthroplasty is a well-known surgical procedure by which a diseased and/or damaged natural joint is replaced by a prosthetic joint. For example, in a total knee arthroplasty surgical procedure, a patient's natural knee joint is partially or totally replaced by a prosthetic knee joint or knee prosthesis. In a revision knee surgery, the previously-implanted knee prosthesis, sometimes referred to as a "primary knee prosthesis," is surgically removed and a replacement or revision knee prosthesis is implanted. A typical knee prosthesis includes a tibial tray, a femoral component, and a polymer bearing (also known as an "insert") positioned between the tibial tray and the femoral component. The tibial tray generally includes a plate having a stem extending distally therefrom, and the femoral component generally includes a pair of spaced apart condylar elements, which include surfaces that articulate with corresponding surfaces of the polymer bearing. The stem of the tibial tray is configured to be implanted in a surgically-prepared medullary canal of the patient's tibia, and the femoral component is configured to be coupled to a surgically-prepared distal end of a patient's femur.

During joint arthroplasty, trial components may be used to size and select the components of the knee prosthesis that will replace the patient's natural joint. Trial components may include a femoral trial that may be used to size and select a prosthetic femoral component, a tibial tray trial that may be used to size and select a prosthetic tibial tray, and a tibial bearing trial that may be used to size and select a prosthetic tibial bearing.

<CIT> provided an orthopaedic surgical instrument system according to the preamble of claim <NUM>. Other systems are provided for in <CIT> and <CIT>.

According to an aspect of the invention, an orthopaedic surgical system includes a tibial bearing trial and a tibial base trial as defined in claim <NUM>.

In an embodiment, the tibial bearing trial includes a spine positioned between the pair of curved bearing surfaces.

The tibial bearing trial may further include an elongated slot formed in its superior surface. The elongated slot has a common longitudinal axis with the channel, is positioned superiorly of the channel, and opens into the channel. The post of the tibial base trial may have an annular-shaped flange extending outwardly therefrom, with such a flange of the post being captured in the slot.

In an embodiment, a posterior end of the slot is defined by the opening formed in the posterior section of the sidewall. The slot is wider than the diameter of the round cavity of the channel.

The cam lobes may be separated from one another by a distance that is less than the diameter of the post of the tibial base trial.

In an embodiment, each of the deflectable flanges has an elongated cavity formed laterally adjacent thereto. A lateral edge of each of the deflectable flanges is urged into a corresponding one of the elongated cavities when the post of the tibial base trial contacts the cam lobes so as to urge the cam lobes away from one another.

The tibial bearing trial may be constructed of a polymeric material.

In another aspect, an orthopaedic surgical instrument includes a tibial bearing as defined in claim <NUM>.

The tibial bearing trial may further include an elongated slot formed in its inferior surface. The elongated slot has a common longitudinal axis with the channel. The elongated slot is positioned superiorly of the channel and opens into the channel.

In an embodiment, a posterior end of the slot is defined by the opening formed in the posterior section of the sidewall, with the slot being wider than the diameter of the round cavity of the channel.

Each of the deflectable flanges has an elongated cavity formed laterally adjacent thereto. A lateral edge of each of the deflectable flanges is urged into a corresponding one of the elongated cavities when the cam lobes are contacted during installation of the tibial bearing trial onto a tibial base trial.

The invention may be used in a method of trialing an orthopaedic prosthetic assembly that includes aligning a tibial bearing trial with a tibial base trial positioned on a proximal end of a patient's tibia, and thereafter advancing the tibial bearing trial in the anterior-to-posterior direction to move a post of the tibial base trial component into a posterior channel defined in the tibial bearing trial. The post of the tibial base trial is captured in the channel between a pair of deflectable flanges so as to snap-lock the tibial bearing trial to the tibial base trial such that the tibial bearing trial is permitted to rotate relative to the tibial base trial. Thereafter, the patient's joint is moved through a range of motion including extension and flexion to evaluate a configuration of the orthopaedic prosthetic assembly corresponding to the tibial base trial and the tibial bearing trial.

The tibial bearing trial may be advanced in the posterior-to-anterior direction to detach the tibial bearing trial from tibial base trial. Thereafter, a second tibial bearing trial is selected that has a different size from the tibial bearing trial. Thereafter, the second tibial bearing trial is advanced in the anterior-to-posterior direction to move the post of the tibial base trial component into a posterior channel defined in the second tibial bearing trial. The post of the tibial base trial is then captured between a pair of deflectable flanges of the second tibial base trial so as to snap-lock the second tibial bearing trial to the tibial base trial such that the second tibial bearing trial is permitted to rotate relative to the tibial base trial. Thereafter, the patient's joint is moved through a range of motion including extension and flexion to evaluate a configuration of the orthopaedic prosthetic assembly corresponding to the tibial base trial and the tibial bearing trial.

A cam lobe on each of the deflectable flanges is moved into contact with the post of the tibial base trial so as to urge the deflectable flanges laterally during advancement of the tibial bearing trial. The cam lobe on each of the deflectable flanges is moved out of contact with the post of the tibial base trial so as to allow the deflectable flanges to retract medially when the bearing trial snap-locks to the base trial.

The tibial base trial has a substantially-planar superior surface, and the tibial bearing trial has a substantially-planar inferior surface. The posterior-most edge of the inferior surface of the tibial bearing trial remains in contact with the superior surface of the tibial base trial throughout advancement of the tibial bearing trial in the anterior-to-posterior direction to snap-lock the tibial bearing trial to the tibial base trial.

The detailed description particularly refers to the following figures, in which:.

While the concepts of the present disclosure are susceptible to various modifications and alternative forms, specific exemplary embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the concepts of the present disclosure to the particular forms disclosed, but on the contrary, the intention is to cover all modifications and alternatives falling within the scope of the invention as defined by the appended claims.

Terms representing anatomical references, such as anterior, posterior, medial, lateral, superior, inferior, etcetera, may be used throughout the specification in reference to the orthopaedic implants or prostheses and surgical instruments described herein as well as in reference to the patient's natural anatomy. Such terms have well-understood meanings in both the study of anatomy and the field of orthopaedics. Use of such anatomical reference terms in the written description and claims is intended to be consistent with their well-understood meanings unless noted otherwise.

Referring now to <FIG>, an orthopaedic surgical instrument system <NUM> includes a tibial base trial <NUM> and a tibial bearing trial <NUM> configured to be selectively coupled to the tibial base trial <NUM>. The tibial base trial <NUM> and the tibial bearing trial <NUM> may be utilized with a femoral component (see <FIG>) to size and select a tibial prosthesis for implantation into a patient's surgically-prepared tibia. In the illustrative embodiment, the femoral component may be a femoral trial component or a primary femoral component from a previous joint arthroplasty. It should be appreciated that the instrument system <NUM> may include a number of trial components <NUM>, <NUM> of different sizes to accommodate a range of patient anatomies.

As described in greater detail below, the tibial bearing trial <NUM> is configured to be removably secured to the tibial base trial <NUM>. During a surgical procedure, the surgeon may evaluate the range of motion of the patient's leg with the tibial bearing trial <NUM> positioned in the knee joint to assess, amongst other things, the range of motion and stability of the knee. The tibial bearing trial <NUM> is configured to be detached from the tibial base trial <NUM> during the surgical procedure and replaced with a tibial bearing trial of a different size to permit the surgeon to evaluate a range of possible implant sizes and select the one that provides the desired performance.

It should be appreciated that the tibial bearing component <NUM> is embodied as a "mobile tibial bearing trial. " As used herein, such a term refers to a tibial bearing trial <NUM> that is permitted to rotate relative to the tibial base trial <NUM> when it is attached a tibial base trial component <NUM>. In other words, a mobile tibial bearing trial is configured to rotate relative to the tibial base trial <NUM> in the anterior-posterior direction and/or the medial-lateral direction. In the illustrative embodiment described herein, the mobile bearing trial <NUM> is embodied as a revision trial.

The tibial base trial <NUM> is configured to be positioned on a surgically-prepared proximal end of a patient's tibia. In the illustrative embodiment, the base trial <NUM> includes a plate <NUM> shaped to be positioned on a proximal end of a patient's tibia. The plate <NUM> has a substantially-planar superior surface <NUM>, an inferior surface <NUM>, and an outer side wall <NUM> extending between the surfaces <NUM>, <NUM>. The outer side wall <NUM> has an anterior section <NUM> and a posterior section <NUM> shaped to match a proximal end of a resected tibia. In the illustrative embodiment, the anterior section <NUM> of the side wall <NUM> is convexly curved, and the posterior section <NUM> is concavely curved. It should be appreciated that the tibial base trial <NUM> may be formed in a number of different sizes to accommodate tibias of various sizes.

The tibial base trial <NUM> includes a captured locking bolt <NUM> extending in the superior-inferior direction. The locking bolt <NUM> has a threaded end <NUM> which extends downwardly from the inferior surface <NUM> of the plate <NUM>. The threaded end <NUM> is sized to be received in a threaded bore (not shown) of a surgical instrument such as, for example, an elongated broach or stem trial component configured to be inserted in the intramedullary canal of the patient's tibia. The opposite end of the locking bolt <NUM> has a socket <NUM> formed therein. The socket <NUM> is configured to receive a hex-head driver (not shown). Rotation of the socket <NUM> with the hex-head driver causes rotation of the locking bolt's threaded end <NUM> thereby allowing the bolt <NUM>, and hence the tibial base trial <NUM>, to be secured to (and removed from) the elongated broach, stem trial, or other surgical instrument. The plate <NUM> also includes a number of fastener guides <NUM> configured to receive a fastener, such as a fixation pin (not shown), which may be utilized to secure the tibial base trial <NUM> to the surgically-prepared proximal end of the patient's tibia.

The tibial base trial <NUM> includes a post <NUM> that extends outwardly in the superior direction from the superior surface <NUM> of the plate <NUM> along a longitudinal axis <NUM>. As will be described in more detail below, the post <NUM> is configured to secure the tibial bearing trial <NUM> to the tibial base trial <NUM>. The post <NUM> includes a stem <NUM> extending superiorly from the superior surface <NUM> of the plate <NUM>. An annular-shaped flange <NUM> extends outwardly from a distal end of the post <NUM>. As such, the post's flange <NUM> has a larger diameter than its stem <NUM>. An inferior surface <NUM> of the flange <NUM> faces the superior surface <NUM> of the plate <NUM>. A groove <NUM> is defined between the inferior surface <NUM> of the flange <NUM> and the superior surface <NUM> of the plate <NUM>. As described below, a locking mechanism of the tibial bearing trial <NUM> is configured to engage the stem <NUM> of the post <NUM> within the groove <NUM>.

As described above, the tibial bearing trial <NUM> is configured to be selectively and removably coupled to the tibial base trial <NUM>. As will be described in more detail below, the tibial bearing trial <NUM> may be anteriorly installed on, and uninstalled from, the tibial base trial <NUM> by moving it solely in the anterior-posterior direction without having to urge the tibial bearing trial <NUM> superiorly during either installation or detachment/removal thereof. As shown in <FIG>, the tibial bearing trial <NUM> includes a body <NUM> having a substantially-planar inferior surface <NUM> and an opposite superior surface <NUM>. The inferior surface <NUM> of the tibial bearing trial <NUM> is configured to abut the superior surface <NUM> of the plate <NUM> of the tibial base trial <NUM>. The superior surface <NUM> of the tibial bearing trial <NUM> includes a pair of curved bearing surfaces <NUM> configured to correspond to the condylar surfaces of a femoral component (see <FIG>). A spine <NUM> is positioned between the curved bearing surfaces <NUM> and extends superiorly from the superior surface <NUM> of the tibial bearing trial <NUM>.

The tibial bearing trial <NUM> includes an outer sidewall <NUM> having an anterior section <NUM> that is shaped to match the anterior section <NUM> of the tibial base trial <NUM> and a posterior section <NUM> that is shaped to match the posterior section <NUM> of the tibial base trial <NUM>. Referring to <FIG>, a channel <NUM> is formed in the inferior surface <NUM> of the tibial bearing trial <NUM>. The posterior end of the channel <NUM> is defined by an opening <NUM> formed in the posterior section <NUM> of the bearing trial's outer sidewall <NUM>. The anterior end of the channel <NUM> is defined by a rounded sidewall <NUM>. In such a way, the anterior end of the channel <NUM> defines a round cavity <NUM>. As can be seen in <FIG>, the inferior surface <NUM> of the tibial bearing trial <NUM> has a pair of deflectable flanges <NUM> formed therein. The medial and lateral sides of the channel <NUM> are defined by the medial edges <NUM> of the deflectable flanges <NUM>. As can be seen in <FIG>, the channel <NUM> extends in the anterior/ posterior direction along a longitudinal axis <NUM>. As such, the longitudinal axis <NUM> of the channel is orthogonal to the longitudinal axis <NUM> of the tibial base trial's post <NUM>.

As can be seen in <FIG>, the inferior surface <NUM> of the tibial bearing trial <NUM> also has an elongated slot <NUM> formed therein. Like the channel <NUM>, the posterior end of the slot <NUM> is defined by an opening <NUM> formed in the posterior section <NUM> of the bearing trial's outer sidewall <NUM>. The slot <NUM> shares a common longitudinal axis with the channel <NUM> and, as such, extends in anteriorly away from the opening <NUM> in the anterior/posterior direction along the longitudinal axis <NUM>. The slot <NUM> is positioned superiorly of the channel <NUM> and opens into it along its length. As can be seen in <FIG>, the slot <NUM> is wider that the channel <NUM>, including the round cavity <NUM> defined in the channel's anterior end. As such, and as will be described in more detail below, the slot <NUM> is configured to receive the annular-shaped flange <NUM> of the post <NUM> as the post's stem <NUM> is received into channel <NUM> during installation of the tibial bearing trial <NUM> onto the tibial base trial <NUM>. As will be discussed in more detail below in regard to <FIG>, the diameter of the annular-shaped flange <NUM> is greater than the width of the channel <NUM>. As such, the tibial bearing trial <NUM> is prevented from lifting off the tibial base trial <NUM> (i.e., lifting superiorly off the tibial base trial <NUM>) once the tibial bearing trial <NUM> is installed thereto.

As shown in <FIG>, the medial edges <NUM> of each of the deflectable flanges <NUM> have a cam lobe <NUM> defined therein. The cam lobes <NUM> extend inwardly (i.e., medially) into the channel <NUM> toward one another. The tips <NUM> of the cam lobes <NUM> are separated from each other by a distance that is less than the diameter of the stem <NUM> of the post <NUM> of the tibial base trial <NUM>. As such, during installation or detachment/ removal of the tibial bearing trial <NUM>, the stem <NUM> contacts the cam lobes <NUM> so as to deflect or otherwise urge the deflectable flanges <NUM> laterally away from one another. Specifically, as can be seen in <FIG>, a pair of elongated cavities <NUM> is formed in the inferior surface <NUM> of the tibial bearing trial <NUM>. The cavities <NUM> are positioned laterally adjacent to the lateral edges <NUM> of the deflectable flanges <NUM>. In such an arrangement, the lateral edges <NUM> of the deflectable flanges <NUM> define the medial sides of the cavity <NUM> adjacent to it.

As can be seen in <FIG>, during installation of the tibial bearing trial <NUM> onto the tibial base trial <NUM>, the stem <NUM> of the base trial's post <NUM> is advanced into the channel <NUM> through the opening <NUM> formed in the posterior section <NUM> of the bearing trial's outer sidewall <NUM> while the annular-shaped flange <NUM> of the base trial's post <NUM> enters the slot <NUM> through the opening <NUM> formed in the posterior section <NUM> of the bearing trial's outer sidewall <NUM>. As the tibial bearing trial <NUM> continues to be moved in the anterior-to-posterior direction, the outer surface of the stem <NUM> of the base trial's post <NUM> advances into contact with the posterior cam surfaces <NUM> of the cam lobes <NUM> thereby causing the deflectable flanges <NUM> to deflect or otherwise be urged laterally away from one another. The deflectable flanges <NUM> continue to deflect as the stem <NUM> rides up the posterior cam surfaces <NUM>. Once the stem <NUM> passes the tips <NUM> of the cam lobes <NUM>, the stem <NUM> begins to ride down the anterior cam surfaces <NUM> of the cam lobes <NUM> thereby allowing the deflectable flanges <NUM> to move medially back toward one another. Once the stem <NUM> clears the anterior cam surfaces <NUM>, the deflectable flanges <NUM> are retracted/ returned to their original positions thereby capturing the stem <NUM> of the base trial's post <NUM> in the round cavity <NUM> of the channel <NUM> so as to snap-lock the tibial bearing trial <NUM> to the tibial base trial <NUM>.

To detach the tibial bearing trial <NUM> to the tibial base trial <NUM>, the bearing trial <NUM> is pulled or otherwise advanced in the posterior-to-anterior direction relative to the base trial <NUM>. Doing so causes the outer surface of the stem <NUM> of the base trial's post <NUM> to be advanced into contact with the anterior cam surfaces <NUM> of the cam lobes <NUM> thereby causing the deflectable flanges <NUM> to deflect or otherwise be urged laterally away from one another. The deflectable flanges <NUM> continue to deflect as the stem <NUM> rides up the anterior cam surfaces <NUM>. Once the stem <NUM> passes the tips <NUM> of the cam lobes <NUM>, the stem <NUM> begins to ride down the posterior cam surfaces <NUM> of the cam lobes <NUM> thereby allowing the deflectable flanges <NUM> to move medially back toward one another. Once the stem <NUM> clears the posterior cam surfaces <NUM>, the deflectable flanges <NUM> are retracted/returned to their original positions thereby allowing the stem <NUM> of the base trial's post <NUM> to be advanced out of the channel <NUM> through the opening <NUM> formed in the posterior section <NUM> of the bearing trial's outer sidewall <NUM> while the annular-shaped flange <NUM> of the base trial's post <NUM> exits the slot <NUM> through the opening <NUM> formed in the posterior section <NUM> of the bearing trial's outer sidewall <NUM> so as to detach the tibial bearing trial <NUM> from the tibial base trial <NUM>.

The illustrated tibial bearing trial <NUM> is one of a plurality of tibial bearing trials that make a multi-piece system configured to assist the surgeon in selecting a size and configuration of the implanted tibial bearing component. As such, the surgeon is able to assemble a tibial bearing trial <NUM> of one size and configuration, evaluate the performance of that tibial bearing trial <NUM>, and then replace it with a different tibial bearing trial <NUM> as necessary to determine intraoperatively the type and configuration of the tibial bearing component to be implanted.

The tibial base trial <NUM> is illustratively formed from a metallic material such as cobalt-chromium or titanium, but may be formed from other materials, such as a ceramic material, a polymer material, a bio-engineered material, or the like. The tibial bearing trial <NUM> is illustratively formed from a polymer material such as an ultra-high molecular weight polyethylene (UHMWPE), but may be formed from other materials, such as a ceramic material, a metallic material, a bio-engineered material, or the like.

Referring now to <FIG>, a surgeon may use the orthopaedic surgical instrument system <NUM> during the trialing process of a surgical procedure to implant a knee prosthesis. To do so, the surgeon initially resects or otherwise surgically-prepares the patient's tibia <NUM> to form a smooth planar surface <NUM> on a proximal end <NUM> of the tibia <NUM>. The surgeon then installs the tibial base trial <NUM> on the resected planar surface <NUM> of the patient's tibia <NUM>. If needed, the surgeon may also perform a resection of the distal end <NUM> of the patient's femur <NUM> to surgically prepare the femur to receive a femoral trial <NUM> for use in a trial reduction procedure. In an embodiment in which a primary femoral component (not shown) from a previous joint arthroplasty is not being replaced, the surgeon may trial the tibial bearing trial <NUM> with the primary femoral component.

Once the tibial base trial <NUM> has been installed on the resected planar surface <NUM> of the patient's tibia <NUM>, the surgeon installs the tibial bearing trial <NUM> to the base trial <NUM> from the anterior side of the patient's tibia <NUM>. To do so, the tibial bearing trial <NUM> is first aligned with the tibial base trial <NUM> such that the posterior-most edge of the inferior surface <NUM> of the bearing trial <NUM> is positioned on the superior surface <NUM> on the anterior portion of the base trial's plate <NUM>. The tibial bearing trial <NUM> is then advanced onto the tibial base trial <NUM> in the anterior-to-posterior direction such that the stem <NUM> of the base trial's post <NUM> is advanced into the channel <NUM> through the opening <NUM> formed in the posterior section <NUM> of the bearing trial's outer sidewall <NUM> while the annular-shaped flange <NUM> of the base trial's post <NUM> enters the slot <NUM> through the opening <NUM> formed in the posterior section <NUM> of the bearing trial's outer sidewall <NUM>. As the tibial bearing trial <NUM> continues to be moved in the anterior-to-posterior direction, the stem <NUM> of the base trial's post <NUM> advances into contact with the cam lobes <NUM> of the bearing's trial's deflectable flanges <NUM> thereby causing the deflectable flanges <NUM> to initially deflect to allow the stem <NUM> to pass and thereafter retract back into their original positions thereby capturing the stem <NUM> of the base trial's post <NUM> in the round cavity <NUM> of the channel <NUM> so as to snap-lock the tibial bearing trial <NUM> to the tibial base trial <NUM>.

It should be appreciated that during such installation of the tibial bearing trial <NUM>, the bearing trial <NUM> is advanced solely in the anterior-to-posterior direction without having to be urged superiorly in any amount whatsoever. Specifically, the posterior-most edge of the bearing trial's inferior surface <NUM> remains in contact with the superior surface <NUM> of the base trial's plate <NUM> throughout installation of the tibial bearing trial <NUM>.

It should be appreciated that when installed on the tibial base trial <NUM>, the stem <NUM> and the annular-shaped flange <NUM> of the base trial's post are positioned in the rounded anterior ends of the bearing trial's channel <NUM> and slot <NUM>, respectively. As such, the tibial bearing trial <NUM> is free to rotate relative to the tibial base trial <NUM> when its snap-locked thereto. However, because the diameter of the annular-shaped flange <NUM> of the base trial's post <NUM> is larger than the width of the channel <NUM>, the deflectable flanges <NUM> of the tibial bearing trial <NUM> are captured in the groove <NUM> defined between the inferior surface <NUM> of the flange <NUM> and the superior surface <NUM> of the plate <NUM>. As such, while tibial bearing trial <NUM> is free to rotate relative to the tibial base trial <NUM>, it is prevented from lifting off of base trial <NUM>. That is, the tibial bearing trial <NUM> is prevented from moving in the inferior-superior direction when it is snap-locked to the tibial base trial <NUM>.

Once the tibial bearing trial <NUM> is snap-locked to the tibial base trial <NUM>, the surgeon may perform an initial trial reduction with the instrument system <NUM>. In doing so, the surgeon uses the instrument system <NUM> to evaluate the stability and kinematics of the patient's femur <NUM> and tibia <NUM>. To do so, the surgeon moves the patient's tibia <NUM> relative to the patient's femur <NUM> between full flexion and full extension. During such movement of the patient's knee, the surgeon evaluates the articulation of the femoral trial <NUM> (or the primary femoral component (not shown) from a previous joint arthroplasty if it is not being replaced) and the tibial bearing trial <NUM> to determine, amongst other things, desired contact points between the two trials, range of motion, and cam/spine engagement.

If the surgeon desires to try a different size or configuration of the tibial bearing trial <NUM>, the surgeon detaches the installed bearing trial <NUM> by pulling or otherwise advancing the bearing trial <NUM> in the posterior-to-anterior direction relative to the base trial <NUM>. Doing so causes the stem <NUM> of the base trial's post <NUM> to be advanced into contact with the cam lobes <NUM> thereby causing the deflectable flanges <NUM> to initially deflect to allow the stem <NUM> to pass and thereafter retract back into their original positions thereby allowing the stem <NUM> of the base trial's post <NUM> to be advanced out of the channel <NUM> through the opening <NUM> formed in the posterior section <NUM> of the bearing trial's outer sidewall <NUM> while the annular-shaped flange <NUM> of the base trial's post <NUM> exits the slot <NUM> through the opening <NUM> formed in the posterior section <NUM> of the bearing trial's outer sidewall <NUM> so as to detach the tibial bearing trial <NUM> from the tibial base trial <NUM>.

Thereafter, the surgeon may install a different tibial bearing trial <NUM> on the tibial base trial <NUM> in the manner described above. With the second tibial bearing trial <NUM> installed, the surgeon may then perform a subsequent trial reduction in the manner described above.

Once the desired size and configuration of the tibial base trial <NUM> and the tibial bearing trial <NUM> have been determined by the surgeon, the trials <NUM>, <NUM> are removed from the patient's tibia <NUM> and the corresponding implant components are implanted in the patient's tibia <NUM>.

While the disclosure has been illustrated and described in detail in the drawings and foregoing description, such an illustration and description is to be considered as exemplary and not restrictive in character, it being understood that only illustrative embodiments have been shown and described and that all changes and modifications that come within the scope of the invention are desired to be protected.

Claim 1:
An orthopaedic surgical instrument system [<NUM>], comprising:
a tibial bearing trial [<NUM>] including (i) an inferior surface [<NUM>], (ii) a superior surface [<NUM>] opposite the inferior surface [<NUM>] and having a pair of curved bearing surfaces [<NUM>] formed therein, (iii) a sidewall [<NUM>] extending between the inferior surface [<NUM>] and the superior surface [<NUM>], and (iv) a channel [<NUM>] formed in the inferior surface [<NUM>], wherein (a) a posterior end of the channel [<NUM>] is defined by an opening [<NUM>] formed in a posterior section of the sidewall [<NUM>], (b) an anterior end of the channel [<NUM>] is defined by a rounded sidewall [<NUM>] so as to define a round cavity, and (c) medial and lateral sides of the channel [<NUM>] are defined by a pair of deflectable flanges [<NUM>], and
a tibial base trial [<NUM>] removeably coupled to the trial insert trial, the tibial base trial [<NUM>] including (i) a plate [<NUM>] configured to be positioned on a surgically-prepared proximal end of a patient's tibia, and (ii) a post [<NUM>] extending outwardly from a superior surface of the plate [<NUM>], wherein the post [<NUM>] is captured in the round cavity of the channel [<NUM>] of the tibial bearing trial [<NUM>] so as to allow the tibial bearing trial [<NUM>] to rotate relative to the tibial base trial [<NUM>], but prevent movement of the tibial bearing trial [<NUM>] in an inferior-superior direction relative to the tibial base trial [<NUM>];
characterized in that each of the pair of deflectable flanges [<NUM>] has a cam lobe [<NUM>] formed therein, and the cam lobes [<NUM>] extend inwardly into the channel [<NUM>] toward one another.