Abstract:
An Intramedullary Distraction Osteotomy (IM DO) apparatus and corresponding methods are disclosed that allow for the patient or another to lengthen residual bone. The apparatus may be inserted into the intramedullary canal of the residual bone and may be lengthened through the application of a traction force. The apparatus protrudes from the body through a single percutaneous site. Lengthening of the amputated limb is achieved by the application of a controlled traction force that is generated by turning a lengthening knob external to the percutaneous site. One or more additional screw segments may be utilized to assist in limb lengthening. The traction force serves to separate a distal bone segment from a proximal bone segment at a specified, controllable rate, allowing new bone growth to fill in the resulting gap. Components of the apparatus provide support and alignment to the residual bone during both the lengthening and consolidation phases. External components of the apparatus may be removed after desired limb length has been achieved, reducing the risk of infection and improving patient mobility.

Description:
FIELD 
       [0001]    The invention described herein relates to the field of limb lengthening through the use of a surgically implanted device. 
       BACKGROUND 
       [0002]    Amputation of the arm or leg causes significant disability, the most effective treatment for which is replacement of the missing limb with a prosthetic device. However, amputations that result in short residual limbs pose significant problems for fitting and suspension of a prosthetic device, and control of the prosthesis is compromised because of the short length of the lever arm provided by the residual limb. This results in poor energy transfer between the limb and an attached prosthesis, as short lever arms generate less torque for a given force. This functional deficit is compounded when the lever arm is encased in very compliant tissue, such as a residual femur that is surrounded by the soft tissues of the thigh, which further impairs prosthesis control. Individuals with short residual limbs following leg amputation display greater gait asymmetries and gait changes than those with longer residual limbs (Bell et al. 2013). In addition, short residual legs reduce stability and balance when sitting and when performing transfers, such as getting on and off the toilet or into a car. Postural changes and compensatory mechanisms associated with use of short residual limbs can cause discomfort and injury to the spine or other body structures. 
         [0003]    Lengthening of a limb can be accomplished through Distraction Osteogenesis (DO), a process that starts by performing an osteotomy; a surgical procedure wherein a bone is cut into two segments, a proximal segment (nearer to the body) and a distal segment (further from the body). The two segments are then gradually separated by an applied traction force at an expansion rate such as 1 mm per day (Ilizarov 1990). After the bone has been cut, new bone starts to form in the resulting gap as a result of natural bone fracture-healing mechanisms. The period when new bone is forming is known as the distraction phase. When the desired length is reached, the distraction force is discontinued and the new bone ossifies and remodels into mature bone during the consolidation phase (Samchukov 2008). 
         [0004]    Current limb lengthening procedures that use DO rely on external devices (Ilizarov 1989) or fixators, which must be worn a minimum of 1 day for distraction and 2 days for consolidation for every millimeter of length gained, for a total of at least 3 days per millimeter of additional length. For example, to gain 75 mm of length, the patient would have to wear such a device for at least 225 days, or 7.5 months. Frequently, complications extend this timeline, such that it can sometimes be almost twice as long (Sakurakichi et al. 2002). Additionally, some external components of these devices must pass through the skin and attach to the bone at a minimum of 4 places, creating 4-8 percutaneous wounds that pose a considerable risk of infection. Thus an additional complication associated with use of these devices is infection and scarring at sites of skin penetration. Such complications are reported in up to 59% of patients (Paley 1990). Some studies show skin infection rates as high as 78-100% (Antoci et al. 2008). Infection rates decrease with fewer points of skin penetration (Brewster et al. 2010). 
         [0005]    Because of their design, traditional external fixator DO devices are large and cumbersome. They interfere with the ability to wear clothing and to move around in bed, which affects sleep. The Ilizarov technique requires a cage that encircles the limb so that the patient must keep their limb in an abducted position, which is uncomfortable, reduces mobility, interferes with the use of crutches or wheelchairs, and impairs general function. External fixators, which are placed on the lateral side of the leg, also interfere with the use of crutches, use of a wheelchair, and general function. 
         [0006]    The prior art devices preclude an active lifestyle for several months, which may contribute to physical decline, depression, and other psychological consequences. Despite the advantages provided by a longer residual limb, the inordinate burden imposed on the patient by these devices and the relatively high rates of complication often limit the use of DO to lengthen residual limbs in amputees. Utilization of the prior art is often too difficult, physically and emotionally, for a patient with an amputation. 
         [0007]    Lengthening-over-a-nail (LON) is a technique for patients with intact limbs that decreases the time a patient needs to wear the external fixator device. During the distraction phase, the LON approach utilizes both an external fixator and an internal nail inserted into the medulla of the bone, known as an intramedullary nail or IM nail. The external device is removed during the consolidation phase; however, the IM nail remains in the bone to provide support. By decreasing the required wear time of the external fixator device, LON techniques have led to decreased rates of superficial infection from 36.2% with traditional external fixator devices to 1.4% with LON (Brewster et al. 2010). Thus, limiting the time that external, percutaneous components are required can decrease overall complications in addition to improving patient comfort and quality of life (Kocaoglu et al. 2004; Mahboubian et al. 2012). 
         [0008]    Several intramedullary devices for DO exist for patients (usually children) with intact limbs. The Intramedullary Skeletal Kinetic Distractor (ISKD) (Cole et al. 2001) (Orthofix Inc., Texas) is the only FDA-approved intramedullary DO device available in the United States at this time. These devices allow bone lengthening in patients with intact limbs, without the need for any percutaneous devices. However, the ISKD has been shown to produce variable rates of distraction, which increases the risk of non-union, pseudoarthrosis, or early consolidation (Mahboubian et al. 2012). Reviews of this and other devices have proven that poorly controlled distraction (e.g., lengthening &gt;1.5 mm/day, so-called runaway) is an important risk factor for poor bone formation (Kenawey et al. 2011). Most importantly, none of the available intramedullary DO devices will work for the residual limbs of amputees. They are all designed for intact bones as they operate by distracting the bone between the epiphyses (the normal bone ends), a technique that cannot be applied to an amputated bone, which lacks a distal epiphysis. 
       SUMMARY 
       [0009]    The present invention is directed towards an Intramedullary Distraction Osteotomy (IM DO) system, and corresponding methods, for lengthening a bone in the residual limb of upper or lower limb amputees. 
         [0010]    The foregoing and other aspects of the present invention will become more apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a cross-sectional diagram of the IM DO apparatus showing placement within a residual bone. 
           [0012]      FIG. 2  is a diagram of the IM DO apparatus showing anchor points of IM nail after insertion into a residual bone. 
           [0013]      FIG. 3  is a diagram of the nail guide(s) for the correct placement for (i) the bicortical screws that anchor the IM nail to the proximal bone, and (ii) the unicortical screws that anchor the distal bone segment, extension tube, and anti-rotation lock. 
           [0014]      FIG. 4  is a diagram showing the padded covering of the distal limb and protruding IM DO apparatus during the distraction phase. 
           [0015]      FIG. 5  shows the IM DO nail in situ during the consolidation phase, after removal of the percutaneous lead screw and other external components. 
       
    
    
       [0016]    Corresponding reference characters indicate corresponding elements among the view of the drawings. The headings used in the figures should not be interpreted to limit the scope of the claims. 
       LIST OF NUMERALS IN DRAWINGS 
       [0017]      
         [0000]    
       
         
               
               
             
           
               
                   
               
             
             
               
                 100 
                 Proximal bone segment 
               
               
                 102 
                 Distal bone segment 
               
               
                 104 
                 Bicortical screws 
               
               
                 106 
                 Unicortical, screws 
               
               
                 108  
                 Intramedullary (IM) nail 
               
               
                 110  
                 Bone division site 
               
               
                 112  
                 Sealing plug 
               
               
                 114  
                 Friction nut assembly 
               
               
                 116  
                 Anti-rotation lock 
               
               
                 118  
                 Extension tube 
               
               
                 120  
                 Lead screw 
               
               
                 122  
                 Additional lead screw segment(s) 
               
               
                 124  
                 Lengthening knob 
               
               
                 126  
                 New bone 
               
               
                 128 
                 Pointed end cap 
               
               
                 130 
                 Distal nail guide 
               
               
                 132  
                 Nail guide end cap 
               
               
                 134 
                 Proximal nail guide 
               
               
                 136 
                 Residual limb 
               
               
                 138  
                 Padding 
               
               
                 140 
                 Bicortical screws 
               
               
                   
               
             
          
         
       
     
       DETAILED DESCRIPTION 
       [0018]    Referring to the drawings, embodiments of the device are illustrated and indicated numerically in  FIGS. 1-5 . The image of a human femur is used as an example in the drawings, although embodiments described herein could be used on a variety of upper limb and lower limb bones including, but not restricted to, the femur, tibia, fibula, humerus, radius, and ulna. 
         [0019]      FIG. 1  shows one embodiment of the invention installed in the residual bone of an amputated limb. The residual bone is cut (i.e., an osteotomy is performed) in an appropriate location (e.g., at position shown by dotted line  110 ) to obtain two separable bone segments: a proximal bone segment  100  and a distal bone segment  102 . An IM nail  108  and extension tube  118  are inserted through the intramedullary canal, and are shown passing through the proximal bone segment  100 , new bone  126  forming after surgery and during the lengthening procedure, and the distal bone segment  102 . 
         [0020]    The distal ends of the extension tube  118  and IM nail  108  exit at the distal end of the residual bone and protrude from a single percutaneous (e.g. through-skin) opening at the distal end of the limb. Locating the single percutaneous component at the distal end of the residual limb allows the patient to more easily wear normal clothes. The device shown at  FIG. 1  allows the patient to move in bed and use a wheelchair or crutches, improving the patient&#39;s sleep and mobility. Additionally, having only one percutaneous opening, as disclosed in  FIG. 1 , reduces infection risk. 
         [0021]    Bicortical screws  104  secure the IM nail  108  to the proximal bone segment  100 . The IM nail  108  has two grooves that run longitudinally on the outside of the nail, proximal to distal, from bicortical screws  104  to the distal end of the IM nail  108 , on opposite sides (such as the top and bottom) of IM nail  108 . Anti-rotation lock  116  comprises anti-rotation keys that fit into these grooves. The anti-rotation lock  116  is secured to the extension tube  118  by unicortical screws  106 . In this way, the anti-rotation lock  116  is operatively coupled to each of the IM nail  108  and the extension tube  118 . However, it should be apparent to one of ordinary skill in the art that other manners of operatively coupling the anti-rotation lock  116  to the IM nail  108  and the extension tube  118  could be used. Anti-rotation lock  116  may be made of metal such as steel or titanium. Unicortical screws  106  pass through each side (e.g., top and bottom) of the distal bone segment  102 , through specific holes in the extension tube  118 , and then thread into the anti-rotation lock  116 . This anchors said distal bone segment  102  to the extension tube  118 . Once secured, the keys in anti-rotation lock  116  ride in the linear grooves of the IM nail  108  and prevent relative rotation between proximal bone segment  100  and distal bone segment  102 . 
         [0022]    The extension tube  118  may include a microbial barrier system. In one embodiment, the microbial barrier system includes a sealing plug  112  that is inserted into extension tube  118  prior to surgery to prevent entry of microbial contaminants. In one embodiment this sealing plug  112  comprises a short cylinder with two or more O-rings that fit into shallow grooves in extension tube  118  around the circumference of the plug. When the O-rings are inserted into the extension tube  118 , they form a tight seal with the extension tube  118  which prevents infectious agents from entering the extension tube  118 . In other embodiments of the microbial barrier system, the distal part of extension tube  118 , between the sealing plug  112  and the friction nut  114 , may be filled with gel or other substance containing anti-microbial agents, such as iodinated petroleum jelly. 
         [0023]    The extension tube  118  has metal (such as steel or titanium) threading at its distal end. After surgical insertion of the extension tube  118 , a friction nut assembly  114  is screwed onto this threading on extension tube  118 . A lead screw  120  is threaded through the friction nut assembly  114  and metal threading at the distal end of the extension tube  118  until the proximal end of lead screw  120  reaches the sealing plug  112 . The friction nut assembly  114  applies friction to the lead screw  120  so that it is not easily or accidently turned and is tight enough to prevent most material from entering the distal end of the extension tube, thus keeping the distal end of the extension tube relatively clean. 
         [0024]    The distal end of the lead screw  120  has internal threading, into which a lengthening knob  124  may be screwed. Lengthening knob  124  is used by the patient or another person to distract or lengthen the limb. In one embodiment, the mechanism regulating the expansion rate between the IM nail  108  and extension tube  118  comprises lengthening knob  124 , which can be turned in stepwise fashion and at varying, but accurately controlled rates according to the clinical needs of the patient. The degree of bone lengthening can be accurately measured by markers on the extension tube  118  or by counting the number of turns of the lengthening knob  124 . The lengthening knob  124  can be made to turn in only one direction to prevent the patient from inadvertently backing out the lead screw  120 . 
         [0025]    Lengthening knob  124  turns the lead screw  120 , which in turn pushes on the sealing plug  112 , which pushes on the IM nail  108 . The IM nail  108 , held in place by bicortical screws  104 , does not move. As a result, the extension tube  118  is pulled distally by the lead screw  120  turning through the threads at the distal end of extension tube  118 . The extension tube  118  is prevented from rotating by the keys in the anti-rotation locks  116  that fit into longitudinal grooves in the IM nail  108 . As extension tube  118  slides over the IM nail  108 , the distance between the proximal bone segment  100  and distal bone segment  102  is increased and new bone  126  forms within as a result of the body&#39;s natural healing mechanisms. In this embodiment, the lead screw  120  is operatively coupled to the IM nail  108  through the lead screw&#39;s application of force upon sealing plug  112 . It should be apparent to one of ordinary skill in the art that other manners of operatively coupling the lead screw  120  to the IM nail  108 , so as to allow for bone distraction, could be used. 
         [0026]    If desired, additional lead screw segments  122  can be attached to the lead screw  120 . Use of one or more additional lead screw segments  122  allows lead screw  120  to be shorter, limiting the distance that the IM DO device must initially protrude distally from the residual limb, while still allowing for substantial lengthening of said limb. In one embodiment, the lead screw  120  enables limb lengthening, until the distal end of the residual limb nears lengthening knob  124 . Then the lengthening knob  124  may be removed and an additional lead screw segment  122  may be threaded onto the lead screw  120 , effectively lengthening lead screw  120 . The distal end of additional lead screw segment  122  includes threading or other means known in the art for attachment to another additional lead screw segment  122 . Lead screw  120  and any additional lead screw segments  122  together make up the lengthening screw of the IM DO system. The lengthening knob  124  then may be re-mounted at the end of the additional lead screw segment  122 , allowing limb lengthening to continue. 
         [0027]    Embodiments of the invention allow for regulated expansion of the new bone  126 . In one embodiment, markings on the lengthening knob  124  can be used to provide accurate measures of daily bone extension. Alternatively, the length of exposed lead screw  120  and any additional lead screw segments  122  can be measured to determine the total amount of bone/limb extension. The rate of expansion can be controlled by the frequency at which the lengthening knob  124  is turned and degree to which said knob  124  is turned. The rate of expansion can thus be determined and controlled for each individual patient. 
         [0028]      FIG. 2  refers to a cross-section of one embodiment of the IM DO system showing the initial stages of an IM DO procedure. The IM nail  108  and extension tube  118  with the seal plug  112  can be inserted into the bone from either the proximal end or the distal end of the residual bone and can be inserted either before or after the osteotomy. In one embodiment, the surgeon drills an appropriately sized hole through the femoral neck, into the intramedullary canal, and through the canal to the end of the remaining femur. The osteotomy is then performed just distal to the trochanters, breaking the bone into two segments. 
         [0029]    The IM nail  108 , extension tube  118 , anti-rotation lock  116 , sealing plug  112  and pointed end cap  128  are kept in a sterile container until prior to the surgery, when they are assembled in a sterilized manner. The surgeon inserts the pointed end cap  128  into the proximal femur and pushes the sterile assembly all the way through the proximal bone segment, the distal bone segment, and finally out the end of the limb through a small percutaneous hole cut in the soft tissues. The pointed end cap  128  facilitates passage of the sterile assembly through the bone and soft tissue with minimal damage to said tissues and keeps material out of the sterile assembly. In addition, the pointed end cap  128  helps the surgeon to feel the end of the device in order to know where exactly to cut the small percutaneous hole. 
         [0030]    Once the IM DO device is in place, a proximal nail guide  134  (see  FIG. 3 ) is threaded into place in a threaded hole at the proximal end of the IM nail  108 . This guide is used to place the bicortical screws  104 . With the IM nail  108 /extension tube  118  assembly protruding from the end of the residual limb, the extension tube  118 , sealing plug  112  and anti-rotation lock  116  are at their fully compressed position, with the holes in the extension tube  118  aligned with the keys in anti-rotation lock  116  and at the correct position within the distal bone segment  102 . A distal nail guide  130 , shown in  FIG. 3 , is attached to the distal end of the extension tube  118  to enable accurate placement of the unicortical screws  106 . In one embodiment, the distal nail guide  130  is held in place by a nail guide end cap  132  which screws into the end of the extension tube  118 . A notch on the nail end guide cap  132  prevents the distal nail guide  130  from rotating with respect to the extension tube  118 . The surgeon then uses the distal nail guide  130  to surgically place the unicortical screws  106  through the cortex of the distal bone segment  102 , through the holes in the extension tube  118  and into the anti-rotation lock  116 . After the unicortical screws  106  have been placed on one side of the distal bone segment  102 , the nail guide end cap  132  can be removed and the distal nail guide  130  may be rotated 180 degrees about the extension tube  118 . The dotted outline in  FIG. 3  shows the distal nail guide  130  in fully-rotated position. The nail guide end cap  132  is then screwed back into the end of the extension tube  118 , and the notch serving to hold the nail guide  118  in place is rotated 180 degrees from its previous position in order to prevent rotational movement, as previously described. In an alternative embodiment, a second distal nail guide, rotated 180 degrees from the first distal nail guide  130  so that the second distal nail guide is positioned according to the dotted outline in  FIG. 3 , may be used instead of a rotating nail guide. 
         [0031]    The distal bone segment  102  is anchored by unicortical screws  106  (or other appropriate anchoring) to the proximal end of the extension tube  118  using the distal nail guide  130 . Once placement has been determined, distal nail guide  130  is removed. Unicortical screws  106  pass through the bone cortex on opposite sides (e.g., top and bottom as shown in  FIG. 2 ) and through holes in the extension tube  118  and then thread into anti-rotation lock  116  located within the proximal end of the extension tube  118 . The distal bone segment  102  is thus anchored to the extension tube  118  by unicortical screws  106 . The anti-rotation lock  116  prevents rotation of the extension tube  118  with respect to the IM nail  108 . From one to four distal unicortical screws can be used. Bicortical screws  104  could be inserted into proximal bone segment  100 , as shown in  FIG. 3 , from the lateral side of the limb or otherwise as known in the art. 
         [0032]    After bone segments  100  and  102  are secured and distal nail guide  130  is removed, the friction nut assembly  114  (see  FIG. 1 ) is threaded onto the end of the extension tube  118  and locked in place. In one embodiment, friction nut assembly  114  comprises a friction nut, with a set screw running through the side of the friction nut for locking. The lead screw  120  is then threaded through the friction nut assembly  114  and extension tube threading until it firmly presses the sealing plug  112  against the IM nail  108 . The lengthening knob  124  is then mounted on the distal end of the lead screw  120 . 
         [0033]    In one embodiment, the lead screw  120  in the distal end of the extension tube  118  may be screwed in or out by a lengthening knob  124 . As described above, turning the lengthening knob  124  moves the extension tube  118  in a distal direction while lead screw  120  pushes against the sealing plug  112  and IM nail  108 , which is anchored to the proximal bone segment  100 , thus placing tension on the distal bone segment  102  and pulling it away from the proximal bone segment  100 . This process progressively generates a gap between bone segments that becomes filled with new bone  126 . The IM nail  108  stabilizes said new bone  126  and, in combination with the anti-rotating lock  116 , maintains correct alignment of the proximal ( 100 ) and distal ( 102 ) segments of the residual bone. In another embodiment, the turning knob  124  only allows turning in one direction, so that the patient cannot accidently turn the lead screw  120  backwards. 
         [0034]      FIG. 4  shows the system in place within the residual limb  136 . After wound care and extension adjustment, a padding  138  is placed over the protruding components of the system to prevent the external component of the IM DO system from causing irritation of injury to the patient&#39;s other limb or body, to provide a more normal limb diameter for patient comfort, and to shield the IM DO system from sudden impact or other damage. The padding  138  is readily removable to allow access to the lengthening knob  124  and percutaneous wound. The padding  138  may also extend over the distal limb. Padding  138  may be made from foam or another suitable material. 
         [0035]      FIG. 5  shows the IM nail  108  contained entirely within the residual limb  136  during the consolidation phase. The length of the IM nail  108 , lead screw  120 , and additional screw segments  122  is such that the distal end of the IM nail  108  will be coincident with the distal end of the distal bone segment  102  when the final desired length has been achieved. Once the residual bone has reached the final desired length, certain components may be removed. The lead screw  120  and any additional lead screw segments  122 , the extension tube  118 , and sealing plug  112  can be removed by removing the unicortical screws  106  and pulling the extension tube  118 , with its contents, distally out of the end of the limb. After removal of the extension tube  118 , the distal bone segment  102  is re-anchored to the distal end of the IM nail  108  using bicortical screws  140 . The distal nail guide  130  can be used if desired. The distal wound may be closed by the surgeon. The new bone  126 , which formed in the gap generated by the expansion procedure, is allowed to remodel and ossify into mature bone, with the continuing additional support of the IM nail  108 . The IM nail  108  remains in place to provide structural support to the bone during the consolidation phase and may provide sufficient strength to allow the treated limb to begin weight-bearing activities earlier in the consolidation phase. In this manner, there are no percutaneous devices protruding through the patient&#39;s skin during the long consolidation phase. When the consolidation phase is complete and the patient has a longer limb with a mature bone, the IM nail and any remaining components can be surgically removed, if desired. 
         [0036]    The embodiments described herein provide several advantages for lengthening an amputated limb. Such advantages, in addition to those already described, include: limited damage to a patient&#39;s soft tissue, limited points of skin penetration, more accurate control of lengthening, adequate stabilization of the limb during the consolidation phase, and sufficient increase in limb length to allow for improved prosthetic fitting and function. Removal of the IM DO components after the lengthening phase of treatment allows healing of the percutaneous wound, which further reduces infection risk. Positioning the lead screw  120  at the distal end of the residual limb improves the overall comfort of the user and reduces interference with daily life activities such as wearing clothing, mobility, and sleep. In addition, no external or percutaneous device is required during the consolidation phase, thus further reducing effects on daily life activities. The IM nail  108  supports the residual bone during the lengthening (distraction) and consolidation phases and may allow earlier return to use of the residual limb for weight bearing activities and prosthesis use. It should be understood that any advantage described herein is not intended to limit the scope of the invention.