Abstract:
An intramedullary fixation device for use in securing a trial in the medullary canal of a bone to determine the offset and orientation of a prosthetic implant for replacement of a joint articulating surface of the bone is disclosed. The fixation device comprises a body for receiving a trial and a fixation portion for engaging the trial. A system for use in surgical repair of a joint comprising a selection of prosthetic implants of various sizes, a selection of trials of various sizes corresponding to the sizes of the implants, a selection of fixation devices of various sizes corresponding to the sizes of the trials, a trial fixation device driver for inserting the fixation device and attached trial into the canal of a bone, and a trial device extractor for removing the fixation device from the resected bone is disclosed. Methods of using the fixation device and system of the invention are disclosed.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a prosthetic system for joint replacement, and more particularly to a trial fixation device for securing a trial in the medullary canal of a resected bone so that accurate measurements can be made for fitting a prosthetic implant. 
     BACKGROUND 
     Patients suffering from trauma or disorders causing severe joint pain often require surgical treatment involving complete or partial replacement of the affected joint. For example, prostheses for replacing all or a portion of a damaged or diseased knee, hip, and shoulder of a person are well known. 
     When reconstructing damaged or diseased joints with an artificial prosthesis, it is desirable to position the components of the prosthesis such that the structure and function of the properly functioning natural joint is replicated to the greatest degree possible. This involves consideration of several factors. For example, the components of the prosthesis must be inserted such that the patient has the desired limb length after surgery. It is also desirable that the range of motion of the joint after surgery is, to the extent possible, the same as that of a healthy joint. Some of the factors relevant to proper placement include insertion depth of the prosthesis components into the bone and rotational orientation of the prosthesis components. 
     During a shoulder replacement operation, at least a portion of the proximal section of the humeral shaft is replaced by a metal prosthesis. This prosthesis generally consists of two parts: a stem that is mounted into the medullary canal of the humerus, and a head component connected in some manner to the stem. The head component replaces the bearing surface of the humerus and articulates within the glenoid cavity of the scapula to allow movement of the shoulder. An example of a humeral prosthetic system is the Neer 3 System from Smith &amp; Nephew, Inc. 
     The stem and head component of a humeral prosthesis may be supplied in “modular” form, that is, as separate connectable components. Different stem sizes and head sizes in a modular implant design provide the surgeon with some degree of flexibility, which facilitates reconstruction of the original anatomy of the patient. 
     With a range of stem sizes and a range of head sizes available, the surgeon can choose a particular combination to suit the anatomy of each individual patient without having a large inventory of “integral” or “monoblock” humeral prostheses. For example, one patient may require a relatively small head and a relatively long stem. With a monoblock prosthesis, a wide range of stem lengths and/or diameters are required for each head size, whereas with a modular arrangement, a particular head may be used with a range of stem, sizes, and a particular stem may be used with a variety of head sizes. 
     Additional variations also arise because individual patients may require differing angles of inclination of the head relative to the stem and differing eccentricities between the axis of the head and the axis of the stem. Thus, for example, in one patient, the eccentricity may be posterior and in another patient, it may be anterior. 
     Various shoulder prostheses are disclosed in European Patent Publication No. EP-A 0 679 375; EP-A 0 712 617; French Patent No. FR-A 2 664 809; U.S. Pat. Nos. 3,694,820; 3,803,641; 4,045,825; 4,106,130; 4,179,758; 4,865,605; 4,919,670; 5,358,526; 5,549,682; 5,462,563 and 5,702,457; and PCT International Patent Publication No. WO 96/17553, the entirety of which are hereby incorporated by reference. 
     Before surgery to reconstruct a patient&#39;s shoulder with a humeral prosthesis, x-rays and x-ray templates are used to give an indication of the necessary height and size of the prosthesis. During surgery trial stems and heads are used by the surgeon to choose the appropriate offset height and retroversion for the humeral prosthesis. The trial stem is inserted into the medullary canal, the trial head is attached (in the case of a modular trial), and the shoulder is taken through a range of motion. The trial stem may be graduated at 5 mm intervals to facilitate the determination of the proper height for stem implantation. Typically, an alignment rod is used to check retroversion. 
     The trial implant position is critical for restoring the height of the humerus and the degree of retroversion. The height of the humerus effects the balance of the soft tissues. The soft tissues are attached to the prosthesis in a balanced manner to avoid subluxation and for a good range of motion. If the offset is too high, then the soft tissue tension is too tight and if the offset is too low, then the soft tissue tension is too lax. 
     In order to accurately test the correct height of the trial stem, the trial stem is held in place in the medullary canal. Current methods of securing the trial stem in the medullary canal include packing gauze in the medullary canal around the trial stem to keep it in position. This method does not allow the surgeon an easy way to adjust the height, if the trial stem is found to be at the incorrect height, or provide a reliable method of keeping the trial stem in place during the range of motion test. 
     Another method is to use an extramedullary device to hold the trial stem in place. These extramedullary devices are big and bulky and prevent an effective range of motion being investigated during surgery and do not allow the surgeon to close the tuberosities and other soft tissue around the trial stem in order to check the balance of soft tissues. 
     SUMMARY 
     Methods, devices, and systems of this invention seek to provide a trial fixation device for use in complete or partial joint replacement and repair that secures a trial in the medullary canal of a bone. With the trial fixation device of the invention, the trial can be securely fixed in the bone canal, the trial can be put through a full range of motion, the balance of the soft tissues can be tested, and the height of the trial can easily be adjusted if necessary. 
     Methods, devices, and systems according to this invention more particularly provide an intramedullary trial fixation device designed to engage a trial and secure the trial in the canal of a bone, a prosthetic system for replacement or repair of all or a portion of the damaged joint, and methods for using the intramedullary trial fixation device to replace or repair a damaged joint. In one embodiment, the primary components of the trial fixation device are a body adapted to be received in the resected bone and adapted to receive a trial stem and a fixation portion attached to the body for engaging the trial stem. 
     An additional aspect of this invention is a surgical system that includes a selection of prosthetic implants of various sizes and shapes, a corresponding selection of trial prostheses, a corresponding selection of fixation devices, and a selection of devices for implanting and removing the fixation device. 
     Another aspect of this invention seeks to provide a method of using the trial fixation device for replacing or repairing all or a portion of a damaged joint and orienting the prosthesis to compliment the patient&#39;s natural anatomy. More particularly, this invention provides a method of replacing the proximal humerus and humeral head. 
     These and other features of this invention will become apparent after a review of the following detailed description of the disclosed embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded view of a fixation device according to one embodiment of this invention. 
     FIG. 2 is another exploded perspective view of the fixation device of FIG.  1 . 
     FIG. 3 is a perspective view of the fixation device of FIG.  1 . 
     FIG. 4 is another perspective view of the fixation device of FIG.  1 . 
     FIG. 5 is an exploded view of a trial stem and the fixation device of FIG.  1 . 
     FIG. 6 is a perspective view showing the fixation device and trial stem of FIG. 5, as engaged. 
     FIG. 7 is a side view of the fixation device and the trial stem of FIG.  5 . 
     FIG. 8 is a perspective view of the trial stem and the fixation device of FIGS. 6-7 implanted in the medullary canal of a bone. 
     FIG. 9 is a side view of a prosthetic implant according to one embodiment of this invention. 
     FIG. 10 is an exploded view of another embodiment of a fixation device of the invention. 
     FIG. 11 is a perspective view showing the fixation device of FIG. 10 engaging a trial stem. 
     FIG. 12 is a perspective view of a trial fixation device driver according to one embodiment of this invention. 
     FIG. 13 is a perspective view of a trial fixation device extractor according to one embodiment of this invention. 
    
    
     DETAILED DESCRIPTION 
     Methods, systems and devices according to embodiments of this invention seek to provide improved trialing during complete and partial joint replacement and repair. A trial fixation device of this invention may include a device that engages and secures a trial in a bone canal, such as a device including a body adapted to be received in a resected bone and a fixation portion attached to the body for engaging a trial stem. In one embodiment of this invention, the fixation portion comprises a first capture member attached to the body, a second capture member, and a first fastener adapted to move the second capture member towards the first capture member to engage the trial stem. The first capture member has a first aperture, the second capture member has a second threaded aperture, and the first fastener is a first tension bolt adapted to extend through the first aperture and thread through the second aperture so that when the first tension bolt is tightened, the second capture member moves toward the first capture member. The first capture member has a third threaded aperture and the second capture member has a fourth aperture and the device further includes a second tension bolt adapted to extend through the fourth aperture and thread through the third aperture so that when the second tension bolt is tightened the second capture member moves toward the first capture member to engage the trial stem. 
     Consider one example of a device according to one embodiment of this invention. FIGS. 1 and 2 illustrate an exploded view of an intramedullary trial fixation device  10  according to one embodiment of the present invention. FIGS. 3 and 4 illustrate perspective views of the trial fixation device  10 . The trial fixation device  10  includes a fixation portion  12  and a body  14 . The fixation portion  12  includes a first fastener  16 , a first bias  18 , a first capture member  20 , a second fastener  22 , a second bias  24 , and a second capture member  26 . 
     The first capture member  20  has two apertures—an inner, smooth aperture  28  and an outer, threaded aperture  30 . The second capture member  26  has two apertures—an inner, threaded aperture  32  and an outer, smooth aperture  34 . The capture members  20 ,  26  have opposite fingers  36 ,  38  at the inner end of each capture member. 
     The first capture member is attached to a collar  40  on the body  14 . The second capture member  26  is not attached to the body  14  and its position is determined by the fasteners  16 ,  22 . The fasteners  16 ,  22  in the embodiment shown in FIGS. 1-4 are tension bolts. In other embodiments, any suitable fastener may be used. As shown in FIGS. 3 and 4, the first fastener  16  extends through the inner, smooth aperture  28  and is threaded in the inner, threaded aperture  32 . The second fastener  22  extends through the outer, smooth aperture  34  and is threaded in the outer, threaded aperture  30 . 
     Tightening either fastener moves the second capture member  26  toward the first capture member  20  and loosening either fastener moves the second capture member  26  away from the first capture member  20 . As the first fastener  16  is tightened or loosened, the second fastener  22  slides through the outer, smooth aperture  34 . As the second fastener  22  is tightened or loosened, the first fastener  16  slides through the inner, smooth aperture  28 . For example, when the first fastener  16  is tightened the outer, smooth aperture  34  of the second capture member  26  slides over the second fastener  22  allowing the second capture member  22  to move closer to the first capture member  20 . The first bias  18  and second bias  24  are placed around the fasteners  16 ,  22  between the capture members  20 ,  26  and serve to keep the second capture member  26  from becoming loose and sliding back and forth. In the embodiment of FIGS. 1-4, the biases  18 ,  24  are compression springs. In other embodiments, any suitable biasing element may be used. 
     While above described embodiment of the fixation portion  12  uses two fasteners, one of skill in the art understands that one fastener could be used. FIGS. 10 and 11 illustrate an embodiment of a fixation device  100  using one fastener  101 , in the illustrated embodiment, a tension bolt. As shown in FIGS. 10 and 11 a capture member connector  102  is attached to the first capture member  104  and slidably extends through an outer aperture on the second capture member  106 . The capture member connector  102  adds stability to the fixation portion. 
     The fixation portion illustrated in the Figures is designed to work with the Neer 3 and Modular Neer 3 trial stems from Smith &amp; Nephew, Inc. One of skill in the art understands that the fixation portion could be configured a variety of different ways to secure a Neer 3 or Modular Neer 3 trial stem and different trial stems to the fixation device. For example, a radially compressing semi-circular clamp fitting within the collar at the top of the device could close around the diameter of the implant, thereby providing fixation. Also, a tight fitting but compressible liner could be used in the distal portion of the device to control height, rather than a clamping mechanism. Also, a clamping mechanism devised to attach to the medial fixation fin rather than the lateral fixation fin could be used to attach the device to the trial stem. 
     As shown in FIGS. 1-4, the body includes a collar  40  around the proximal end to which the fixation portion  12  is connected. Two rotation prevention fins  42  extend from the collar  40  down the sides of the body  14 . The proximal section of the body  14  includes a medial trial fin slot  44  and a lateral trial fin slot  46 . The distal end of the body includes a trial stem sleeve  48 . In one embodiment, a friction liner  50  is affixed to the interior surface of the trial stem sleeve  48 . In one embodiment, the friction liner  50  is made of plastic, but in other embodiments may be made of any suitable material. One of skill in the art understands that the body can be configured a variety of different ways to accommodate a Neer 3 trial stem or different trial stems. 
     The preferred method of manufacturing the fixation device is machining. Although other methods, such as casting, could be used. 
     FIG. 5 illustrates an exemplary intramedullary humeral trial stem  52  that can be used with the intramedullary trial fixation device. The trial stem  52  includes a humeral trial head plateau  54  with a humeral trial head attachment post  56  affixed on the proximal side of the plateau. A humeral trial head (not shown) is attached to the humeral trial head attachment post  56  for modular trial stems. Monoblock trial stems have an attached humeral trial head. 
     A stem  58  is formed on or affixed to the distal side of the humeral head plateau  54 . The proximal end of the stem  58  may have graduated laser markings  60  to allow for stem positioning in the humerus. A medial fin  62  extends from the distal side of the humeral head plateau  54  to the stem  58 . Two lateral fins  64  are included on the stem opposite the medial fin  62 . The lateral fins  64  and the medial fin  62  replicate the fixation fins on a humeral prosthetic implant. 
     FIGS. 6 and 7 illustrate an embodiment of the fixation device  10  engaging the trial stem  52 . The trial is secured in the fixation device  10  by locking the fixation portion  12  on the trial stem  52 . In the embodiment shown in FIGS. 6 and 7, the trial is inserted into the fixation device  10  through the trial stem sleeve  48  so that the fingers  36 ,  38  of the capture members  20 ,  26  engage the lateral fins  64  of the trial stem  52  and the friction liner  50  engages the stem  58 . The lateral fins  64  of the trial stem  52  fit in the lateral trial fin slot  46  and the medial fin  62  of the trial stem  52  fit in the medial trial fin slot  44 . The friction liner  50  keeps the height of the trial stem  52  constant until the fixation portion  12  engages the trial stem  52 . The position of the trial stem  52  is adjusted by unlocking the fixation portion  12 , moving the trial stem  52 , and locking the fixation portion  12  to re-engage the trial stem  52 . 
     FIG. 9 illustrates an exemplary humeral prosthetic implant  70 . The prosthesis has a humeral head  72  and a stem  74  extending from the head. The prosthetic implant  70  could be modular or monoblock. A medial fixation fin  76  extends from the humeral head to the stem and includes a fixation hole  78 . Two lateral fixation fins  80  are formed on the proximal part of the stem  74 . The lateral fixation fins are in a sixty degree angle to each other positioned in a way that they align with the bicipital groove, giving the correct retroversion for the prosthesis. The lateral fixation fins each have four holes  82  allowing for the anatomical fixation of the tuberosities with sutures. 
     In cases of three or four part fractures of the proximal humerus or severe osteoarthritis, a humeral prosthetic implant like the one illustrated in FIG.  9  and described above is used to repair the shoulder. Initially, during surgery the humerus is prepared according to established surgical technique, which may include resecting the proximal portion and may include reaming the medullary canal. An appropriate trial stem is placed into the fixation device. The fixation portion of the fixation device is locked onto the trial stem. As shown in FIG. 8, the fixation device  10  and attached trial stem  52  are introduced into the medullary canal until the collar of the fixation device is flush, or as close as possible, to the bony surface of the humerus  90 . A trial fixation device driver can be used to lock the fixation device to the trial stem. FIG. 12 illustrates an embodiment of a trial fixation device driver. The fixation portion  12  of the fixation device  10  is unlocked and the height of the trial stem  52  is adjusted to the desired position based on the use of x-rays and x-ray templates before surgery. Once the trial stem  52  is adjusted to the desired position, the fixation portion  12  is locked onto the trial stem  52 . The fixation device  10  illustrated in FIGS. 1-7 has two fasteners  16 ,  22  to allow easy access to the fasteners for use in left and right shoulder procedures. 
     A trial head is placed on the trial stem and the range of motion of the shoulder is evaluated. If the range of motion is satisfactory, the position of trial height is noted by observing the marks  60  on the trial stem in relation to the device or the surface of the humerus. If desired, the trial stem  52  is marked with a pen at the appropriate position. If the range of motion is not satisfactory, the fixation portion  12  is unlocked and the height of the trial stem  52  adjusted until an acceptable position is reached. The trial stem  52  and fixation device  10  are then removed. If the device  10  does not come out with the trial stem  52 , a trial fixation device extractor can be used to lever the device out of the humerus. FIG. 13 illustrates an embodiment of the trial fixation device extractor. The humeral prosthesis is marked at the same position as the trial stem in order to indicate the correct offset for the prosthetic implant. Cement may be inserted medullary canal. The prosthetic implant  70  is placed in the canal at the marked height. The tuberosities and other soft tissue are then connected to the prosthetic implant. 
     The disclosure of devices and processes as recited above is not intended to limit the scope of the present invention. A person of skill in the art understands that various fixation portions can be used with different intramedullary fixation device body structures to accommodate different stem geometries. A person of skill in the art understands that, while the embodiments of the fixation device are described in terms of a prosthetic implant for a humerus, the fixation device could be used with other prosthetic devices.