Abstract:
A surgical jig for preparing a distal end of a femur during an orthopedic procedure comprising an engagement surface that accommodates at least a part of at least one of a patella and patella tendon.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of United Kingdom application number GB0602055.6, filed Feb. 1, 2006. The disclosure of the above application is incorporated herein by reference.  
       FIELD  
       [0002]     The present teachings relate to surgical jigs. In particular, the present teachings relate to surgical jigs for preparing a distal end of a femur.  
       BACKGROUND  
       [0003]     The statements in this section merely provide background information related to the present teachings and may not constitute prior art.  
         [0004]     When a knee joint becomes damaged or diseased, it is known to replace all or part of the knee joint with a prosthesis. A common form of prosthesis comprises a femoral component, which is attached to a distal end of a femur, and a tibial component, which is attached to a proximal end of a tibia. The femoral and tibial components may articulate directly or may be separated by a meniscal bearing component. The femoral component also articulates with a patella, which is secured in position by a quadriceps tendon and a patellar ligament.  
         [0005]     The articulation of a natural knee joint is stabilized by the action of medial and lateral collateral ligaments and anterior and posterior cruciate ligaments. Where possible, all of these ligaments are retained when a prosthesis is implanted, although in practice it is often necessary to remove at least the posterior cruciate ligament. It is desirable for tension in the knee ligaments after surgery to be balanced throughout the range of motion of the knee.  
         [0006]     The most complex component of a knee prosthesis is the femoral component, since it carries not only the condylar bearing surfaces, but also the patella bearing surface, which extends along an anterior face of the distal femur. Conventional femoral components require resection of the distal end surface of the femur and the anterior and posterior faces of the femur. They also usually require two chamfered cuts to be made at the distal end of the femur anteriorly and posteriorly. The correct positioning of the femoral cuts is vitally important to ensure equal tension in the ligaments after surgery.  
         [0007]     Conventional jigs for resecting the femur use as a reference an intramedullary rod. The cutting jig is mounted on the rod adjacent the resected femoral surface and may be moved in the anterior/posterior direction relative to the rod. In order to mount a conventional jig adjacent the distal surface of a femur, it is necessary to move the patella from its normal positional. The patella is either everted or subluxed in order to provide sufficient space for the jig. Once the jig is in the desired position, it is secured to the bone and the necessary cuts are made. The anterior/posterior position of the femoral cuts, and hence of the cutting jig, is vital in order to restore proper functioning of the knee and balance to the ligaments. Conventional jigs are provided in a range of sizes (usually five or six) in order to accommodate the range of knee sizes encountered.  
         [0008]     Balancing of the knee ligaments during surgery conventionally takes place in three stages. First, after the distal surface of the femur and the proximal surface of the tibia have been resected, the knee is placed in full extension and a spacer block is used to measure the gap between the bones. The ligaments are balanced with the knee in extension to achieve a rectangular gap between the adjacent bone surfaces and equal tension in the collateral ligaments. Then, with the knee in 90 degrees of flexion and the femoral cutting jig attached, the spacer is again inserted, this time between the proximal tibial surface and the posterior surface of the cutting jig. The aim is to achieve the same rectangular gap and equally tensioned collateral ligaments with the knee in 90 degrees of flexion as in extension.  
         [0009]     Balancing of the joint at this stage is complicated by the position of the patella. The quadriceps mechanism exerts a large force on the knee joint via the patella and the patella tendon. This force usually acts within the plane of articulation of the joint. However, with the patella either everted or subluxed to allow space for the femoral cutting jig, this force acts to skew the joint either laterally or medially. Correct balancing of the collateral ligaments at this stage is therefore extremely difficult.  
         [0010]     Finally, after the anterior and posterior resections have been performed, trial prosthesis components are attached to the femur and tibia and a trial reduction is performed. Only at this point can the tension of the ligaments be checked throughout the range of motion of the knee.  
       SUMMARY  
       [0011]     The present teachings provide for a surgical jig for preparing a distal end of a femur during an orthopedic procedure comprising an engagement surface that accommodates at least a part of at least one of a patella and patella tendon.  
         [0012]     The present teachings further provide for a surgical jig for preparing a distal end of a femur during an orthopedic procedure comprising a guide member, an engagement surface, an alignment member, and an adjustment system. The guide member has at least one tool guide. The engagement surface of the guide member accommodates at least a part of at least one of a patella and a patella tendon. The alignment member engages the guide member and the femur. The adjustment system moves the guide member relative to the alignment member.  
         [0013]     The present teachings also provide for a method of preparing a distal end of a femur, which articulates with a proximal end of a tibia and with a patella, using a jig having an alignment member in cooperation with a guide member. The method includes: resecting a distal surface of the femur; inserting the alignment member of the jig into the femur until a proximal surface of the guide member engages the resected femoral surface, a groove on the guide member being aligned in a substantially anterior/posterior direction; inserting a spacer between the proximal surface of the tibia and a posterior surface of the guide member; adjusting an adjustment system of the jig until the posterior surface of the guide member is flush against the spacer; positioning the patella in the groove of the guide member; and balancing the tension of ligaments joining the femur and the tibia.  
         [0014]     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     DRAWINGS  
       [0015]     The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.  
         [0016]      FIG. 1  is a perspective view of a surgical jig for use on the left knee of a patient;  
         [0017]      FIG. 2  is another perspective view of the jig of  FIG. 1 ;  
         [0018]      FIG. 3  is a perspective view of a mounting post of the jig of  FIG. 1 ; and  
         [0019]      FIG. 4  is a perspective view of an alignment member of the jig of  FIG. 1 . 
     
    
     DETAILED DESCRIPTION  
       [0020]     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.  
         [0021]     With reference to the Figures, a surgical jig  2  comprises a guide member  4 , an alignment member  6 , and a reference member  8 , comprising a mounting post  52  and a stylus  60 . An adjusting means  10  acts between the guide member  4  and the alignment member  6  to permit relative translational movement between the guide member  4  and the alignment member  6 . A plurality of tool guides  5  extend through the guide member to guide the bit of a drill (not shown).  
         [0022]     With reference particularly to  FIG. 2 , the guide member  4  comprises a substantially rectangular guide body  12  having a proximal surface  18 , a distal surface  20 , an anterior surface  19  and a posterior surface  21 . The proximal and distal surfaces  18 ,  20  terminate at upper, anterior edges  22  and lower, posterior edges  24 .  
         [0023]     The guide body  12  is divided into a mounting portion  14  and a guide portion  16 . The mounting portion  14  is disposed on the medial side  26  of the jig  2  and the guide portion  16  is disposed on the lateral side  28  of the jig  2 . In the illustrated embodiment, the medial side is to the left of the jig  2 , as viewed from the distal approach, but it will be appreciated that in a jig for use on the right knee of a patient, the medial side will be to the right side of the jig when viewed from a distal approach. The distal surface  20  of the guide portion  16  includes a longitudinal groove  30  that runs in a substantially anterior/posterior direction. In the illustrated embodiment, the groove  30  extends from the anterior edge  22  of the distal surface  20  and terminates adjacent to the posterior edge  24  of the distal surface  20 , thus defining a seat  32 . However, the groove  30  may extend the length of the guide body  12 , terminating at the posterior edge  24  of the distal surface  20 .  
         [0024]     A recess  34  extends across the proximal surface  18  of the guide portion  16 , opposite to the groove  30  in the distal surface  20 . The recess  34  extends the length of the proximal surface  18  from the anterior edge  22  to the posterior edge  24 . The recess  34  is defined by lateral and medial ridges  36 ,  38  that protrude from the proximal surface  18  of the guide portion  16 .  
         [0025]     The ridges  36 ,  38  curve toward each other, defining respective grooves  40 ,  42  at opposite sides of the recess  34 . A longitudinal slot  44  extends into the guide body  12  from the proximal surface  18  adjacent the medial ridge  38  and parallel to the recess  34 . The slot  44  is integral with a first cylindrical bore  46  that also extends the length of the guide body  12 .  
         [0026]     An adjusting screw (not shown) is located in the cylindrical bore  46  such that threaded portions of the screw protrude into the slot  44 . The adjusting screw is waisted between the threaded portions to form an annular groove in a central region of the adjusting screw. A grub screw  48  extends through the guide body  12 , engaging the groove of the adjusting screw and holding the adjusting screw captive within the cylindrical bore  46 , such that relative translational movement between the adjusting screw and the guide body  12  is prevented.  
         [0027]     A second cylindrical bore  50  extends through the mounting portion  14  of the guide body  12 . A mounting post  52 , as shown in  FIG. 3 , is received within the second cylindrical bore  50 . The mounting post  52  comprises a posterior section  54 , which is received within the second cylindrical bore  50 , and an anterior section  56 , which is of greater diameter than the posterior section  54 . A plurality of annular grooves  58  extends around the anterior section  56 . A stylus  60  is received within any one of the groves  58 .  
         [0028]     With reference particularly to  FIG. 4 , the alignment member  6  comprises an attachment portion  62  and an intramedullary (IM) rod  64 . The attachment portion  62  comprises a body  66 , lateral and medial projections  68  and  70  and an engagement arm  72 . The projections  68 ,  70  and the engagement arm  72  each extend the length of the body  66  in a substantially anterior/posterior direction. The engagement arm  72  carries on its medial face a thread  74 , which may be a rack. The IM rod  64  is formed integrally with the attachment portion  62  and extends from a proximal side of the body  66  of the attachment portion  62  at an angle that is chosen to replicate the natural valgus angle of the average patient. A range of alignment members may be provided, each having a different angle formed between the IM rod  64  and the body  66  of the attachment portion  62 . An appropriate alignment member may then be selected according to the requirements of a particular patient.  
         [0029]     In an assembled condition of the jig, as illustrated in  FIGS. 1 and 2 , the attachment portion  62  of the alignment member  6  is received within the recess  34  of the guide body  12 . The lateral and medial projections  68 ,  70  are received within the lateral and medial grooves  40 ,  42  of the recess  34 . The engagement arm  72  is received within the slot  44  such that the rack  74  on the engagement arm  72  protrudes into the first cylindrical bore  46 . The rack  74  engages the threaded portions of the adjusting screw (not shown).  
         [0030]     The adjusting screw is prevented from translational movement relative to the guide body  12  by the interaction of the grub screw  48 , the guide body  12  and the annular groove on the adjusting screw. Rotation of the adjusting screw therefore causes both the adjusting screw and the guide body  12  to be moved along the rack  74  of the engagement arm  72 , thus translating the guide body  12  in the anterior/posterior direction relative to the alignment member  6 . Rotation of the adjusting screw is effected by means of an Allen key or other device.  
         [0031]     In use, the jig  2  may be employed in conjunction with a plurality of differently sized cutting blocks. The cutting blocks are sized according to the corresponding size of femoral prosthesis, and include guide portions for guiding a saw in making the required anterior, posterior and chamfered cuts to the distal end of the femur.  
         [0032]     Prior to use, the jig  2  is placed in an assembled condition and the stylus  60  is removed. Following standard proximal tibial resection and distal femoral resection, the knee is placed in extension and an appropriately sized spacer is selected, permitting tension of the relevant soft tissues to be checked. The knee is then placed in 90° of flexion and the IM rod  64  of the jig  2  is inserted into the medullary canal of the femur until the proximal surface  18  of the guide body  12  is flush with the resected distal surface of the femur.  
         [0033]     The selected spacer is introduced into the gap between the posterior surface  21  of the guide body  12  and the resected tibial surface. The adjusting screw is rotated causing the guide body  12  to translate relative to the IM rod  64 , and hence the femur, until the posterior surface  21  of the guide body  12  is flush with the spacer. The stylus  60  is attached to a selected one of the annular grooves  58  on the mounting post  52  such that an end of the stylus  60  is adjacent the anterior femoral cortex. The anterior/posterior position of the guide body  12  is then finely adjusted by rotation of the adjusting screw until the end of the stylus  60  is in contact with the anterior femoral cortex.  
         [0034]     Prior to fixing the position of the jig  2  with respect to the femur, a partial reconstruction of the knee is effected. The patella is returned from its everted or subluxed position and placed to rest in the groove  30  of the jig  2 . The tension of the soft tissues may then be checked with the force exerted by the quadriceps mechanism acting in its correct anatomical direction. Further, the tension of the soft tissues may be checked throughout the range of motion of the knee with the jig  2  still in place, as the patella is able to track within the groove  30 . Fine adjustment of the position of the jig may be conducted as necessary.  
         [0035]     Once the correct position of the jig has been ascertained, guide holes are drilled through the guides  5  of the jig  2  and into the resected femoral surface. The jig  2  may then be removed and replaced with an appropriately sized cutting block. The size of cutting block may be selected to correspond with the annular groove  58  on the which the stylus  60  was mounted. The cutting block is attached to the femur using the guide holes drilled through the guides  5  in the jig. Anterior, posterior and chamfered cuts may then be made in the standard manner.  
         [0036]     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.