Patent Publication Number: US-9901331-B2

Title: Spacer block

Description:
CLAIM OF PRIORITY 
     This application is a continuation of U.S. patent application Ser. No. 14/034,076, filed on Sep. 23, 2013, the benefit of priority of which is claimed hereby, and which is incorporated by reference herein in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to knee arthroplasty. More particularly, the present disclosure relates to an instrument for use during a knee arthroplasty procedure, and to a method for using the same. 
     BACKGROUND 
     In a total knee arthroplasty (TKA) procedure, a patient&#39;s distal femur is resected and replaced with a prosthetic femoral implant, and the patient&#39;s proximal tibia is resected and replaced with a prosthetic tibial implant. The prosthetic femoral implant articulates with the prosthetic tibial implant to restore joint motion. 
     Many factors influence joint motion after the TKA procedure. The size and shape of each prosthetic implant will impact joint motion. Additionally, the location and orientation of each prosthetic implant, which is determined by the location and orientation of the corresponding bone resections, will impact joint motion. The tension or laxity of the surrounding soft tissue will also impact joint motion. For example, if the surrounding collateral ligaments are too tense, joint motion may be limited, but if the surrounding collateral ligaments are too lax, improper femoral rotation or femoral lift-off may occur. Also, the soft tissue balance around the joint will impact joint motion. 
     Different surgical philosophies have traditionally influenced TKA instruments and procedures. For example, a first, “measured resection” philosophy emphasizes bone resections while preserving the natural joint axis and soft tissue. A second, “soft tissue balancing” philosophy emphasizes soft tissue modifications while preserving bone. 
     OVERVIEW 
     This overview is intended to provide an overview of subject matter of the present patent application. It is not intended to provide an exclusive or exhaustive explanation of the invention. The detailed description is included to provide further information about the present patent application. 
     The present patent application provides an exemplary TKA instrument and procedure. The instrument can separate the patient&#39;s tibia and femur, in both extension and flexion, to place the knee joint in tension and to measure a gap and an angle therebetween. The instrument can include various modular accessories. The accessories can provide flexibility of usage throughout the TKA procedure. For example, the instrument can be used before resecting or otherwise manipulating the patient&#39;s knee joint to evaluate the natural knee joint and plan the TKA procedure, as well as after resecting or otherwise manipulating the patient&#39;s knee joint to evaluate and/or further plan the TKA procedure. The accessories can also allow each individual user to select accessories that accommodate his or her own surgical philosophy and the needs of the particular patient. The accessories can also allow the user to incorporate multiple surgical philosophies into a single surgical procedure, such as by comparing the potential outcome of one accessory with the potential outcome of another accessory. 
     According to an example of the present disclosure, a knee arthroplasty instrument can be provided for use in a patient&#39;s knee joint, which includes a tibia and a femur. The instrument can include a spacer tool and a spacer shim. The spacer tool can include a tibial component configured for placement against the tibia and a femoral component configured for placement against the femur. The tibial component can be structured to accept a shim to place the patient&#39;s knee joint in tension by separating the tibia and the femur. The shim can be removably coupled to the spacer tool to increase the effective height of the tibial component. 
     According to an example of the present disclosure, a knee arthroplasty method for a patient&#39;s knee joint can include: estimating a resection gap, selecting one of a set of spacer shims, attaching the selected spacer shim to a tibial component, inserting an instrument with the spacer shim attached into the resection gap to separate the tibia and femur to verify a joint gap and a joint angle prior to implantation of an artificial joint. 
     To further illustrate the knee arthroplasty system and method disclosed herein, a non-limiting list of examples is provided here: 
     In Example 1, a knee arthroplasty system for use in a patient&#39;s knee joint can be provided that includes a spacer block instrument including a base portion, a tibial component extending from the base portion and configured for placement against a tibia, and a femoral component configured for placement against a femur, wherein the femoral component is rotatably coupled to the tibial component. The system further includes one or more spacer block shims structured for removable attachment to the tibial component. 
     In Example 2, the system of Example 1 is optionally configured such that each of the one or more spacer block shims comprises a spacer component and a handle portion, wherein the handle portion is structured to be positioned adjacent to the base portion of the spacer block instrument. 
     In Example 3, the system of any one of or any combination of Examples 1-2 is optionally configured such that the one or more spacer block shims comprises a plurality of spacer block shims, each of the spacer block shims defining a different shim height. 
     In Example 4, the system of Example 3 is optionally configured such that the shim height of each of the plurality of spacer block shims is between about 10 mm and about 13 mm. 
     In Example 5, the system of any one of or any combination of Examples 1-4 is optionally configured such that each of the one or more spacer block shims includes a connector structured to removably engage, in the alternative, the tibial component of the spacer block instrument. 
     In Example 6, the system of Example 5 is optionally configured such that the connector is a sliding joint. 
     In Example 7, the system of Example 6 is optionally configured such that the sliding joint is a dovetail joint. 
     In Example 8, the system of any one of or any combination of Examples 5-7 is optionally configured such that the connector includes a ball detent mechanism. 
     In Example 9, the system of any one of or any combination of Examples 1-8 is optionally configured such that the base portion of the spacer block instrument includes one or more channels extending through the base portion and configured to receive one or more alignment rods. 
     In Example 10, the system of Example 9 is optionally configured such that the handle portion of the one or more spacer block shims includes one or more channels configured to at least partially align with the one or more channels in the base portion of the spacer block instrument. 
     In Example 11, the system of any one of or any combination of Examples 2-10 is optionally configured such that the handle portion of the one or more spacer block shims includes a fin portion extending in a direction generally perpendicular to an axis of the spacer block instrument. 
     In Example 12, the system of Example 11 is optionally configured such that the fin portion is curved. 
     In Example 13, the system of any one of or any combination of Examples 1-12 is optionally configured to include a scale plate extending from the base portion and a pointer extending from the femoral component. 
     In Example 14, the system of Example 13 is optionally configured such that the scale plate includes an arcuate slot configured to at least partially receive the pointer, wherein the pointer travels within the arcuate slot as the femoral component rotates relative to the tibial component. 
     In Example 15, the system of any one of or any combination of Examples 13-14 is optionally configured such that the scale plate includes a numerical scale defining a range of joint angles. 
     In Example 16, a method of using a knee arthroplasty instrument to evaluate a resected knee joint can be employed that includes observing a resection gap between a distally resected femur and a proximally resected tibia, selecting a first spacer block shim from a plurality of spacer block shims, attaching the first spacer block shim to a tibial component of the knee arthroplasty instrument, and inserting the knee arthroplasty instrument into the resection gap, including positioning the tibial component and attached first spacer block shim adjacent to the proximally resected tibia and positioning a femoral component of the knee arthroplasty instrument adjacent to the distally resected femur, the femoral component being rotatable relative to the tibial component. The method further includes evaluating tension in the resected knee joint, including determining a first joint angle formed between the tibial component and the femoral component. 
     In Example 17, the method of Example 16 is optionally configured to include removing the knee arthroplasty instrument from the resection gap, detaching the first spacer block shim from the tibial component, selecting a second spacer block shim from the plurality of spacer block shims, attaching the second spacer block shim to the tibial component, reinserting the knee arthroplasty instrument into the resection gap, and evaluating tension in the resected knee joint, including determining a second joint angle formed between the tibial component and the femoral component, and comparing the first joint angle to the second joint angle. 
     In Example 18, the method of any one of or any combination of Examples 16-17 is optionally configured such that each of the plurality of spacer block shims defines a different shim height. 
     In Example 19, the method of any one of or any combination of Examples 16-18 is optionally configured such that determining a first joint angle comprises observing a scale plate extending from the knee arthroplasty instrument. 
     In Example 20, the method of Example 19 is optionally configured such that the scale plate includes an arcuate slot configured to at least partially receive a pointer extending from the femoral component. 
     In Example 21, the system or method of any one of or any combination of Examples 1-20 is optionally configured such that all elements or options recited are available to use or select from. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, like numerals can be used to describe similar elements throughout the several views. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document. 
         FIG. 1  is a perspective view of a knee arthroplasty instrument in accordance with an example of the present disclosure, the instrument including a base, a lower tibial component, an upper femoral component and a tibial spacer shim. 
         FIG. 2  is a top plan view of the instrument of  FIG. 1 , in accordance with an example of the present disclosure. 
         FIG. 3  is a cross-sectional view of a portion of the instrument taken along line B-B of  FIG. 2 , in accordance with an example of the present disclosure. 
         FIG. 4  is a distal end view of the instrument detailing alignment of key and keyway features, in accordance with an example of the present disclosure. 
         FIG. 5  is a distal end view of the instrument detailing an offset of the key and keyway features, in accordance with an example of the present disclosure. 
         FIG. 6  is an exploded perspective view of the instrument showing an example of a spring-loaded ball plunger attached to the lower tibial component, in accordance with an example of the present disclosure. 
         FIG. 7  is a bottom view of the upper femoral component showing an example of a detent channel, in accordance with an example of the present disclosure. 
         FIG. 8  is a perspective view of the tibial spacer shim of  FIG. 1 , in accordance with an example of the present disclosure. 
         FIG. 9  is a perspective view illustrating the removable attachment of the tibial spacer shim to the instrument of  FIG. 1 , in accordance with an example of the present disclosure. 
         FIG. 10  is an anterior elevational view of a knee joint in extension, in accordance with an example of the present disclosure. 
         FIG. 11  is an anterior elevational view of the knee joint in flexion, in accordance with an example of the present disclosure. 
         FIG. 12  is a perspective view of the instrument of  FIG. 1  with the tibial spacer shim positioned within the knee joint in extension, in accordance with an example of the present disclosure. 
         FIG. 13  is a perspective view of the instrument of  FIG. 1  with the tibial spacer shim positioned within the knee joint in flexion, in accordance with an example of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIGS. 1 and 2 , a spacer instrument  10  can be provided for separating a patient&#39;s tibia and femur and measuring a joint gap and a joint angle therebetween. Instrument  10  can include a base portion  12 , a handle portion  13 , a lower tibial component  14 , an upper femoral component  16 , a post  30  configured to couple femoral component  16  to tibial component  14 , and a tibial spacer block shim  18 . Base portion  12  can include one or more channels  40  extending at least partially therethrough and oriented generally perpendicular to a plane formed by tibial component  14  to allow for the use of one or more alignment rods in cooperation with instrument  10 . As will be discussed in further detail below, femoral component  16  and spacer block shim  18  can be removably attached to tibial component  14  using a suitable connection means. Tibial component  14 , femoral component  16  and spacer block shim  18  (see  FIG. 1 ) can be offset from base portion  12 , as shown in  FIG. 2 , to accommodate the patient&#39;s patella. 
     Femoral component  16  can be configured to rotate relative to tibial component  14 . More specifically, femoral component  16  can be configured to rotate relative to tibial component  14  about rotation axis A. As shown in  FIG. 2 , post  30  can engage with femoral component  16  at one or more locations along rotation axis A, and femoral component  16  can be configured to rotate about post  30 . In an example, the rotation axis A of femoral component  16  can be parallel to the longest dimension of the base portion  12 , such as a longitudinal dimension extending between a proximal end and a distal end of base portion  12 . 
     An angle measuring means can be provided to measure an angle α between tibial component  14  and femoral component  16  about the rotation axis A. In an example, as illustrated in  FIG. 1 , the angle measuring means can include a scale plate  32  extending from base portion  12 . As further illustrated in  FIG. 1 , scale plate  32  can define an arcuate slot  34  configured to receive a pointer  36  extending from femoral component  16 . As femoral component  16  rotates relative to base portion  12  about axis A, pointer  36  can be configured to move along or through arcuate slot  34  of scale plate  32 . The angle α between tibial component  14  and femoral component  16  can be determined by reading the value from scale plate  32  that is adjacent to pointer  36 . When femoral component  16  is oriented parallel to tibial component  14 , pointer  36  can be centered in slot  34  corresponding to an angle α of 0 degrees. As femoral component  16  deviates from this parallel orientation, pointer  36  can move along slot  34  to a positive angle α greater than 0 degrees or a negative angle α less than 0 degrees. As discussed in further detail below, angle α can indicate a varus/valgus angle of the patient&#39;s knee joint and/or internal/external rotation of the patient&#39;s knee joint. 
     An angle rotation limiting means can be provided to restrict the angle of motion between tibial component  14  and femoral component  16  about rotation axis A. Referring to  FIG. 1 , femoral component  16  can include a femoral cover  90  with an outer surface  92  and an inner surface  94  (see  FIG. 3 ) that includes a rotation restriction portion  96  with one or more rotation restriction surfaces  98 . In an example, outer surface  92  and inner surface  94  can be located on circular arcs centered about axis A so that rotation of femoral component  16  about post  30  can result in similar rotation of femoral cover  90  about axis A. Tibial component  14  can include one or more restriction pocket surfaces  100  located on projection  102 , which can be connected to post  30  as shown in  FIG. 6 . Projection  102  can extend from base portion  12  via wall  104 . In an example, as femoral component  16  rotates about post  30 , the rotation angle α between tibial component  14  and femoral component  16  can be limited by the interference of a restriction surface  98  with a pocket surface  100 . As shown in  FIG. 3 , which is a cross-sectional view of a portion of instrument  10  taken along line B-B of  FIG. 2 , rotation angle α of femoral component  16  can depend on the arc length L of rotation restriction portion  96 . 
     Instrument  10  can include a set of modular accessories, examples of which are described further below. Instrument  10  and the accessories can be provided together as a system. In this manner, a surgeon or another user can select a first accessory from the system and attach that first accessory to instrument  10 . As the surgical procedure progresses, the surgeon can select a second accessory from the system and attach the second accessory to instrument  10 . In various examples, the first accessory can be left in place when the second accessory is attached to instrument  10 . In other examples, the first accessory can be removed from instrument  10  to accommodate the second accessory. A variety of different coupling mechanisms (e.g., dovetail joints) and locking mechanisms (e.g., keys, ball detents) can be used to selectively receive and retain the desired modular accessory on instrument  10 . Additional information regarding modular accessories for instrument  10  can be found in PCT Publication No. WO2013013094 to Claypool et al., entitled “Knee Arthroplasty Instrument,” the disclosure of which is incorporated herein by reference in its entirety. 
       FIG. 4  is a distal end view of instrument  10  detailing attachment of femoral component  16 , which can be considered a modular accessory that can be removably coupled to instrument  10 . In an example, a key  50  can be located on post  30  and a keyway  52  can be located in femoral component  16  as shown in  FIG. 4 . Alignment of keyway  52  with key  50  can allow a surgeon to slide keyway  52  over key  50  along axis A in a direction toward handle  13  until key  50  extends at least partially through femoral component  16  (see  FIG. 2 ) thereby locating femoral component  16  onto post  30  and allowing femoral component  16  to rotate freely about post  30 . 
       FIG. 5  is a distal end view of instrument  10  detailing an offset of the key  50  and keyway  52  features. As shown in  FIG. 5 , keyway  52  ordinarily remains offset from key  50  during rotation of femoral component  16  about post  30  so as to interfere with the motion of femoral component  16  along axis A, thereby preventing detachment of femoral component  16  from instrument  10  during use. Removal of femoral component  16  can be effected by rotating femoral component  16  about post  30  until keyway  52  is once again aligned with key  50  (see  FIG. 4 ), allowing a surgeon to slide femoral component  16  along axis A in a direction away from handle  13  for removal over post  30 . 
       FIG. 6  is an exploded perspective view of instrument  10  illustrating femoral component  16  detached from tibial component  14 .  FIG. 7  is a bottom view of femoral component  16  after removal from instrument  10 . Together,  FIGS. 6 and 7  depict exemplary features that can allow femoral component  16  to be removably coupled to tibial component  14 . 
     In an example, instrument  10  can include a ball detent mechanism to removably couple femoral component  16  to tibial component  14 . A ball detent mechanism can include, but is not limited to, a spring-loaded ball plunger component in combination with a cavity located on an adjacent component. In an example, tibial component  14  can include a spring-loaded ball plunger  82  as shown in  FIG. 6  and femoral component  16  can include a detent channel  80  located on inner surface  94  of femoral cover  90  as shown in  FIG. 7 . With reference to  FIGS. 6 and 7 , femoral component  16  can be removably coupled to tibial component  14  by sliding femoral component  16  over post  30  along axis A toward handle  13  whereby the spring biasing force of spring-loaded ball plunger  82  engages detent channel  80  so that motion of femoral component  16  along axis A can be impeded. Femoral component  16  can thereafter be removed from tibial component  14  by applying an axial force to femoral component  16  along axis A in a direction away from handle  13  to overcome the spring biasing force applied by spring-loaded ball plunger  82  to channel  80 , thereby releasing femoral component  16  for sliding removal over post  30 . 
       FIG. 8  is a perspective view of spacer block shim  18  removed from instrument  10 . In an example, spacer block shim  18  can also be considered a modular accessory that can be removably coupled to instrument  10  In use, spacer block shim  18  can be removably coupled to tibial component  14  thereby increasing the overall effective thickness of tibial component  14 . Spacer block shim  18  can be coupled to tibial component  14  to perform various functions, such as to adjust tension of soft tissue in the knee. Spacer block shim  18  can include a spacer component  64 , a connector  66 , and a shim handle portion  68  with a distal end  84  and a proximal end  86 . As illustrated in  FIG. 8 , spacer component  64  can be configured to extend from proximal end  86 . In an example, spacer component  64  can be substantially of the same size and shape as tibial component  14 . However, in various examples, spacer component  64  can be provided in different shapes, sizes and thicknesses to vary the overall effective thickness of tibial component  14 . Thus, in an example, a plurality of spacer block shims  18  having spacer components  64  with different thicknesses can be provided for selection by the surgeon or user. 
     Shim handle portion  68  can be structured for placement adjacent to a tibial side  70  of base portion  12  (see  FIG. 1 ). In an example, shim handle portion  68  can be configured with the same general shape as tibial side  70  of base portion  12 . However, shim handle portion  68  can assume any suitable shape. Shim handle portion  68  can include one or more channels  72  that can align with the one or more channels  40  of base portion  12  to allow for the use of one or more alignment rods in cooperation with instrument  10 . As illustrated in  FIG. 8 , shim handle portion  68  can include a fin portion  74  that can extend away from a plane formed by shim handle portion  68  and away from tibial side  70  of base portion  12 . In an example, fin portion  74  can be of a curved construction as shown in  FIG. 8 , and can extend generally perpendicular to the plane formed by shim handle portion  68 . However, fin portion  74  can be provided in different shapes, sizes, thicknesses and locations along shim handle portion  68 . 
     Spacer block shim  18  can include any suitable means that allow spacer block shim  18  to be removably coupled to tibial component  14  of instrument  10 , such as coupling means that allow spacer block shim  18  to slide linearly relative to tibial component  14  during engagement. In  FIG. 9 , for example, spacer block shim  18  can be removably coupled to tibial component  14  by a sliding engagement via one or more tongues  60  of connector  66  and one or more corresponding grooves  62  of tibial component  14 , where tongues  60  on connector  66  are sized to slide into the corresponding grooves  62  in tibial component  14  along axis A. In another example, the sliding engagement of spacer block shim  18  and tibial component  14  can alternatively or additionally utilize a ball detent mechanism between spacer block shim  18  and tibial component  14 . The ball detent mechanism can include features similar to the spring-loaded ball plunger  82  and the detent channel  80  previously described. 
     An exemplary method of using instrument  10  will now be described with reference to  FIGS. 10-13 . The order of the following steps can vary depending on factors such as the surgeon&#39;s preference, the patient&#39;s bone quality, the state of the patient&#39;s surrounding soft tissue, and the types of prosthetic implants being used. 
     First, the surgeon can perform pre-operative planning. The planning step can involve taking X-rays or other images of the patient&#39;s knee joint  200  and selecting prosthetic implants to accommodate the patient&#39;s needs, for example. 
     Next, as shown in  FIGS. 10 and 11 , the surgeon can expose tibia  202  and femur  204  of the patient&#39;s knee joint  200 . The exposing step can involve incising the patient&#39;s skin, incising the patient&#39;s joint capsule, and removing osteophytes, for example. 
     With the patient&#39;s knee joint  200  now exposed, the surgeon can use instrument  10  to separate tibia  202  and femur  204  of the patient&#39;s knee joint  200  to a predetermined tension, and to plan and identify the desired bone resections of tibia  202  and femur  204 . With the patient&#39;s knee joint  200  tensioned in extension ( FIG. 10 ), the surgeon can plan and identify a proximal tibial resection  206  and a distal femoral resection  208  that will produce a desired gap G and angle α therebetween. The extension angle α can be referred to as a varus/valgus angle. With the patient&#39;s knee joint  200  tensioned in flexion ( FIG. 11 ), the surgeon is able to plan and identify the proximal tibial resection  206  and a posterior femoral resection  210  that will produce a desired gap G and angle α therebetween. The flexion angle α can be referred to as an internal/external rotation angle. Gap G and angle α between tibia  202  and femur  204  can be selected based on the patient&#39;s age, the patient&#39;s bone quality, the state of the patient&#39;s surrounding soft tissue, the types of prosthetic implants being used, and other factors, for example. 
     Tibia  202  and femur  204  can be resected using suitable cut guides. For example, the Minimally Invasive Surgery (MIS) Tibial Cut Guide Assembly, which is available from Zimmer, Inc. of Warsaw, Ind., can be used to form the proximal tibial resection  206  in tibia  202 . Suitable cut guides can also be used to form the distal femoral resection  208  and the posterior femoral resection  210  in femur  204 . 
     In addition to evaluating bone resections, the surgeon can also evaluate soft tissue resections, releases, or other soft tissue operations that would impact gap G and angle α between tibia  202  and femur  204 . For example, if the surgeon desires a balanced angle α of 0 degrees between tibia  202  and femur  204 , the surgeon can release or otherwise relax ligaments on one side of the patient&#39;s knee joint  200  (e.g., the medial side) relative to the opposing side of the patient&#39;s knee joint  200  (e.g., the lateral side). As another example, if the surgeon desires a larger gap G between tibia  202  and femur  204  without resecting additional bone from tibia  202  or femur  204 , the surgeon can release or otherwise relax ligaments around the patient&#39;s knee joint  200 . 
     According to an example of the present disclosure, knee joint  200  can be prepared such that gap G and angle α between tibia  202  and femur  204  are the same or substantially the same in extension ( FIG. 10 ) as in flexion ( FIG. 11 ). In this example, a three-dimensional space can be maintained between tibia  202  and femur  204  in extension and flexion. For example, a surgeon implanting a prosthetic femoral implant having equally thick distal and femoral condyles can prepare an extension gap G that is the same as the flexion gap G, while a surgeon implanting a prosthetic femoral implant having distal and femoral condyles of different thicknesses can prepare an extension gap G that varies the flexion gap G to account for the different thicknesses. When angle α is 0 degrees, such that the proximal tibial resection  206  is parallel to the distal femoral resection  208  in extension ( FIG. 10 ) and the posterior femoral resection  210  in flexion ( FIG. 11 ), the three-dimensional space between tibia  202  and femur  204  will be substantially rectangular in shape in extension and flexion. It is also within the scope of the present disclosure that the surgeon may tolerate differences between the extension angle α ( FIG. 10 ) and the flexion angle α ( FIG. 11 ), such as differences of 1 degree, 2 degrees, 3 degrees or more. 
     In view of the foregoing, instrument  10  can be used to measure the natural gap G and angle α between tibia  202  and femur  204  in extension and flexion, and to plan or identify the proximal tibial resection  206 , the distal femoral resection  208 , the posterior femoral resection  210 , and/or any soft tissue resections that will produce a desired gap G and angle α between tibia  202  and femur  204  in extension and flexion. Additionally, after resecting or otherwise manipulating knee joint  200 , instrument  10  can be used to verify the desired gap G and angle α between tibia  202  and femur  204  in extension and flexion. Therefore, instrument  10  can be used before and/or after resecting or otherwise manipulating knee joint  200 . 
     The use of instrument  10  to measure gap G and angle α between tibia  202  and femur  204  is described further with reference to  FIGS. 12 and 13 , for example. In  FIG. 12 , instrument  10  is illustrated as being used with the patient&#39;s knee joint  200  in extension. Proximal tibial resection  206  has already been formed in tibia  202 , and distal femoral resection  208  has already been formed in femur  204 . Thus, in the illustrated example of  FIG. 12 , instrument  10  is being used to verify the resected gap G and the resected angle a between tibia  202  and femur  204 . A first spacer block shim  18  can be removably coupled to tibial component  14  of instrument  10  so that first spacer block shim  18  contacts the resected tibial surface when the instrument  10  is inserted into the resection gap G. The first spacer block shim  18  can be preselected with knowledge of the resected gap G to verify the desired resected gap G and resected angle α have been achieved. 
     After attaching first spacer block shim  18  to instrument  10 , first spacer block shim  18  can be placed against proximal tibial resection  206 . Femoral component  16  can be coupled through post  30  to tibial component  14  and placed against distal femoral resection  208 .  FIG. 12  shows an embodiment of femoral component  16  that can include spacing portion  212 , indicator portion  214  and pad portion  216 . Indicator portion  214  can terminate in pointer  36 . Pad portion  216  can be thicker than indicator portion  214  and spacing portion  212 .  FIG. 13  shows an embodiment of femoral component  16  where spacing portion  212  does not include pad portion  216 . With tibial component  14  and femoral component  16  of instrument  10  positioned to separate tibia  202  and femur  204 , the surgeon can check the extension gap G between proximal tibial resection  206  and distal femoral resection  208 . Also, the surgeon can measure the extension angle between proximal tibial resection  206  and distal femoral resection  208  by referencing scale plate  32  on base portion  12  and pointer  36  on femoral component  16 . 
     Where the resulting tension in the knee is deemed to be insufficient, instrument  10  can be removed from the resection gap G, first spacer block shim  18  can be removed from instrument  10  and a second spacer block shim that is incrementally larger than first spacer block shim  18  can be removably attached to instrument  10 . Thereafter, instrument  10  can be reinserted into the resection gap G as described previously. Where the resulting tension in the knee is deemed to be excessive, instrument  10  can be removed from the resection gap G, first spacer block shim  18  can be removed from instrument  10  and a second spacer block shim that is incrementally smaller than first spacer block shim  18  can be removably attached to instrument  10  and thereafter reinserted in the resection gap G as previously described. 
     In  FIG. 13 , instrument  10  is illustrated as being used with the patient&#39;s knee joint  200  in flexion. Proximal tibial resection  206  has already been formed in tibia  202 , and posterior femoral resection  210  has already been formed in femur  204 . Thus, as shown in  FIG. 13 , instrument  10  is being used to verify the resected gap G and the resected angle α between tibia  202  and femur  204 . A first spacer block shim  18  of instrument  10  can be placed against proximal tibial resection  206 . Femoral component  16  can be coupled through post  30  to tibial component  14  of instrument  10  and placed against posterior femoral resection  210 . With first spacer block shim  18  and femoral component  16  of instrument  10  positioned to separate tibia  202  and femur  204 , the surgeon can verify that the flexion gap G of  FIG. 13  is the same as or substantially the same as the extension gap G of  FIG. 12 . Also, the surgeon can verify that the flexion angle α of  FIG. 13  is the same as or substantially the same as the extension angle α of  FIG. 12 . Although  FIGS. 12 and 13  only show distal femoral resection  208  and posterior femoral resection  210  in femur  204 , other resections (e.g., chamfer cuts and an anterior cut) may also exist in femur  204  when instrument  10  is in use. 
     Where the resulting tension in the knee is deemed to be insufficient, instrument  10  can be removed from the resection gap G, first spacer block shim  18  can be removed from instrument  10  and a second spacer block shim that is incrementally larger than first spacer block shim  18  can be removably attached to instrument  10 . Thereafter, instrument  10  can be reinserted into the resection gap G as described previously. Where the resulting tension in the knee is deemed to be excessive, instrument  10  can be removed from the resection gap G, first spacer block shim  18  can be removed from instrument  10  and a second spacer block shim that is incrementally smaller than first spacer block shim  18  can be removably attached to instrument  10  and thereafter reinserted in the resection gap G as previously described. 
     If necessary, the patient&#39;s knee joint  200  can be manipulated to adjust the measured gap G and/or the measured angle α between tibia  202  and femur  204 . For example, if the surgeon determines that the flexion gap G of  FIG. 13  is too small compared to the extension gap G of  FIG. 12 , the surgeon can cut a deeper posterior femoral resection  210  to increase the flexion gap G of  FIG. 13 . The surgeon can also make any necessary ligament adjustments to balance the soft tissue around knee joint  200 . For example, the surgeon can release the patient&#39;s posterior cruciate ligament (PCL), which has been shown to increase the flexion gap G relative to the extension gap G. 
       FIGS. 12 and 13  depict post-resection use of instrument  10 , with instrument  10  being positioned against resected bone surfaces of tibia  202  and femur  204 . As discussed above, instrument  10  can also be used pre-resection, with instrument  10  being positioned against natural, un-resected bone surfaces of tibia  202  and femur  204 . In this pre-resection condition, instrument  10  can communicate the pre-resection gap G and the pre-resection angle α between the natural, un-resected bone surfaces in extension and flexion. The surgeon can predict the post-resection values by combining the pre-resection values with the planned resections. For example, the surgeon can estimate the post-resection gap G by adding the planned resection depths to the corresponding pre-resection gap G. 
     The above Detailed Description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention can be practiced. These embodiments are also referred to herein as “examples.” Such examples can include elements in addition to those shown or described. However, the present inventors also contemplate examples in which only those elements shown or described are provided. Moreover, the present inventors also contemplate examples using any combination or permutation of those elements shown or described (or one or more aspects thereof), either with respect to a particular example (or one or more aspects thereof), or with respect to other examples (or one or more aspects thereof) shown or described herein. 
     In the event of inconsistent usages between this document and any documents so incorporated by reference, the usage in this document controls. In this document, the terms “a” or “an” are used, as is common in patent documents, to include one or more than one, independent of any other instances or usages of “at least one” or “one or more.” 
     In this document, the term “or” is used to refer to a nonexclusive or, such that “A or B” includes “A but not B,” “B but not A,” and “A and B,” unless otherwise indicated. In this document, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Also, in the following claims, the terms “including” and “comprising” are open-ended, that is, a system, device, article, composition, formulation, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. 
     The above description is intended to be illustrative, and not restrictive. For example, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments can be used, such as by one of ordinary skill in the art upon reviewing the above description. The Abstract is provided to comply with 37 C.F.R. §1.72(b), to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may lie in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description as examples or embodiments, with each claim standing on its own as a separate embodiment, and it is contemplated that such embodiments can be combined with each other in various combinations or permutations. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.