Abstract:
Applicant&#39;s invention includes a prosthetic rib which is adjustable in length through relatively minor surgical procedures subsequent to initial implantation along with methods for using same in the treatment of chest wall deformities and scoliosis and in immobilizing fractured ribs. The prosthesis is designed for secure attachment to existing natural ribs in a manner which minimizes constricture thereof, provides substantial torsional stability, and permits the prothesis to accommodate traumatic impact thereto while resisting fracture of the associated natural ribs.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Applicant&#39;s invention relates to prosthetic skeletal devices primarily for use in humans. 
     2. Background Information 
     Presently, ribs which are missing due to trauma or congenital defect may be prosthetically replaced to a limited degree. The presently available prosthesis consists of one or more steel rods attached to and spanning vertically between existing natural ribs. This creates an artificial albeit perpendicularly oriented substitute for the missing ribs and vital protection for the cardiovascular and peripheral tissues. 
     The presently available prosthesis has significant limitations, the most notable of which when used in children is its inability to accommodate growth. As a child grows the distance between any two natural ribs increases. To prevent substantial disfigurement, possible injury to the spinal column, and constriction of the cardiovascular system, the radical surgical procedure of implanting the presently available prosthesis must be repeated periodically to implant longer prostheses. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a novel prosthetic rib which is adjustable in length. 
     It is another object of the present invention to provide an novel prosthetic rib which has means for secure attachment to existing ribs yet minimizes ischemia and accommodates benign movement and reorientation of the rib. 
     It is another object of the present invention to provide a prosthetic rib which accommodates traumatic impact in a manner which minimizes the risk of fracture of natural ribs to which the prosthesis is attached. 
     It is another object of the prevent invention to provide a prosthetic rib which provides an optimal balance between effective prosthesis and safety in implantation. 
     It is yet another object of the present invention to provide a prosthetic rib which may be indefinitely implanted in a child notwithstanding later growth of such child. 
     In satisfaction of these and related objectives, Applicant&#39;s present invention provides a prosthetic rib which is adjustable in length through relatively minor surgical procedures subsequent to initial implantation. The prosthesis is designed for secure attachment to existing natural ribs in a manner which minimizes constricture thereof, provides substantial torsional stability, and permits the prosthesis to accommodate traumatic impact thereto while resisting fracture of the associated natural ribs. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a number of implanted prosthetic ribs of applicant&#39;s design. 
     FIG. 2a is an elevational view of the prosthetic rib of Applicant&#39;s invention in a contracted configuration rib sleeve being shown as transparent. 
     FIG. 2b is a top plan view of the prosthetic rib of Applicant&#39;s invention in a contracted configuration with the rib sleeve being shown as transparent. 
     FIG. 2c is an elevational view of the prosthetic rib of Applicant&#39;s invention in an extended configuration. 
     FIG. 3a is a top plan view of the rib sleeve of Applicant&#39;s invention. 
     FIG. 3b is an elevational view of the rib sleeve of Applicant&#39;s invention. 
     FIG. 3c is a cross sectional view of the rib sleeve of Applicant&#39;s invention. 
     FIG. 4a is a top plan view of the rib shaft/rib shaft carriage attachment of Applicant&#39;s invention. 
     FIG. 4b is a partial elevational view of the rib shaft/rib shaft carriage attachment of Applicant&#39;s invention. 
     FIG. 5a is a perspective view of the inner surface of the distraction lock of Applicant&#39;s invention. 
     FIG. 5b is an elevational view of the inner surface of the distraction lock of Applicant&#39;s invention. 
     FIG. 5c is a perspective view of the outer surface of the distraction lock of Applicant&#39;s invention. 
     FIG. 5d is a perspective view of the distraction lock of Applicant&#39;s invention placed on a length of the rib sleeve. 
     FIG. 6a is a depiction of the rounded rod of Applicant&#39;s invention as it contacts the natural rib of a recipient. 
     FIG. 6b is a depiction of the an angular rob, a taught against by Applicant&#39;s invention, as it would contact the natural rib of a recipient. 
     FIG. 7a is a partial perspective view of the rib sleeve carriage attachment of Applicant&#39;s invention. 
     FIG. 7b is a partial perspective view of the rib sleeve carriage attachment of Applicant&#39;s invention with the rods thereof bent as for initial implantation procedures. 
     FIG. 7c is a partial perspective view of Applicant&#39;s rib sleeve carriage attachment with the rods thereof encircling a natural rib of a recipient according to the teaching of Applicant&#39;s invention. 
     FIG. 7d is a cross sectional view of Applicant&#39;s rib sleeve carriage attachment with the rods thereof encircling a natural rib of a recipient according to the teaching of Applicant&#39;s invention. 
     FIGS. 8a and 8b are serial representations of the action of the Applicant&#39;s prosthetic rib in absorbing impact. 
     FIG. 9a is a perspective representation of a means of attachment not taught by Applicant shown to demonstrate the comparative stability of Applicant&#39;s preferred embodiment. 
     FIG. 9b is a partial perspective representation of one of Applicant&#39;s carriage attachments depicting the stability provided by the dual robs included therein. 
     FIG. 10 is a partial perspective representation of one of Applicant&#39;s carriage attachments depicting the stability provided by the dual rods included therein. 
     FIGS. 11a and 11b are elevational representations of one of Applicant&#39;s carriage attachments with the rods thereof affixed to the natural rib whereby the prosthetic rib projects perpendicularly from the rib surface. 
     FIGS. 11c and 11d are elevational representations of one of Applicant&#39;s carriage attachments with the rods thereof affixed to the natural rib whereby the prosthetic rib projects obliquely from the rib surface. 
     FIG. 12 is a representation of one of Applicant&#39;s carriage attachments with the rods thereof affixed to the natural rib is aligned with the vertical axis of the recipient&#39;s body notwithstanding the transverse projection of the natural rib. 
     FIG. 13 is a representation of the manipulation of the rods of Applicant&#39;s carriage attachments which permits inward adjustment of the over-all prosthetic rib. 
     FIG. 14a is a representation of the pliers used to adjust the length of an implanted prosthetic rib. 
     FIG. 14b is a representation of the tips of the pliers shown in FIG. 14a. 
     FIG. 14c is a representation of the pliers of FIG. 14a is position to adjust the rib shaft relative to the rib sleeve. 
     FIG. 15a is a representation of rods improperly spaced on a recipient natural rib. 
     FIG. 15b is a representation of rods properly spaced on a recipient natural rib. 
     FIG. 16a is a representation of an implanted sheet of medical elastomeric plastic material underlying Applicant&#39;s prosthetic ribs. 
     FIG. 16b is a representation of the sheet of medical elastomeric plastic material of FIG. 16a. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, the prosthetic rib of Applicant&#39;s invention is identified generally by the reference numeral 10. As is apparent from FIG. 1, multiple prosthetic ribs 10 will typically be implanted to span between existing natural ribs 12 to compensate for an abnormal absence of intervening natural ribs. 
     The prosthetic rib 10 is designed to be adjusted in length subsequent to implantation. The primary purpose of the adjustability being to accommodate growth of a child in whom the prosthetic rib 10 is implanted. 
     Referring to FIGS. 2a, 2b, and 2c, the prosthetic rib 10 comprises three principal components: a rib sleeve carriage attachment 14, a rib shaft/rib shaft carriage attachment 16 and a rib sleeve 18. The rib shaft/rib shaft carriage attachment 16 is a single object of unitary construction, but for discussion purposes may be divided between the rib shaft 16a and the rib shaft carriage attachment 16b. 
     Unless otherwise specified, all components of the prosthetic rib 10, except the rib sleeve 18, which is made of Titanium Alloy 64, are manufactured of Commercially Pure (CP) Titanium. The use of titanium is dictated by the strength and flexibility requirements for the components of the prosthetic rib 10 in light of the dimensions of such components. Other materials, such as surgical grade stainless steel, may be used in constructing the prosthetic rib 10, but at the expense of the optimum balance of benefits derived from titanium. 
     The combined rib shaft 16a and rib sleeve 18 serve as the actual prosthesis. The robs 20 of the carriage attachments 14 and 16b serve as the attachment means for anchoring the prosthetic rib 10 to natural ribs 12 and will be discussed in detail hereinafter. 
     Referring again to FIGS. 2a, 2b, and 2c and also to FIGS. 3a, 3b, and 3c, the rib sleeve 18 may be described as an open, semi-oval with a lengthwise oriented channel 22 interrupting the lower surface of the rib sleeve 18. The presence of the channel 22 is in response to manufacturing cost limitations. It should be understood that a suitable alternative sleeve which lacks the channel 22 entirely (not shown in the drawings) would be acceptable for the purposes stated herein, but would be available, if at all, at a considerably higher price because of difficulties in manufacturing such a sleeve. 
     Referring again to FIGS. 2a, 2b, 2c, and also to FIGS. 4a and 4b, the rib shaft 16a is of solid construction and has a lengthwise oriented ridge (not visible in the drawings). The ridge is designed to mechanically interface with the channel 22 when the rib shaft 16a is telescopically received within interior lumen 24 of the rib sleeve 18 as it is designed to do. While the presence of the channel does tend to weaken the rib sleeve 18 in resisting axial rotation relative to the rib shaft 16a, or vice versa, when a torque is applied to either, the restraining action of the ridge&#39;s interface with the channel 22 compensates completely for any such tendency. Prior to incorporating the ridge into the rib shaft 16a design, experimentation revealed a marked tendency toward such rotation particularly when the prosthetic rib 10 was extended to near its maximum extent. 
     The rib shaft 16a and the rib sleeve 18 are formed whereby they jointly define a single arc having a constant radius of curvature regardless of the degree the rib shaft 16a is received within the rib sleeve 18. The rib sleeve&#39;s 18 and rib shaft&#39;s 16a radius of curvature may be adjusted in the manufacturing process according to the expressed preference of the responsible surgeon, as dictated by the physiology of the intended recipient. 
     Referring principally to FIG. 2a, 2b, 2c, 3a, 3b, 3c, 4a and 2b, the effective length of the prosthetic rib 10 is determined by the degree to which the rib shaft 16a is telescopically received within the rib sleeve 18. To secure the relative positions of the rib shaft 16a and the rib sleeve 18 once a desired length is attained, the rib shaft 16a has a plurality of evenly spaced holes 26 passing therethrough. The rib sleeve 18 has two holes 28 spaced complementarily to the holes 26 in the rib shaft 16a. The holes 28 in the rib sleeve 18 are situated on the outer face of the rib sleeve 18. The rib sleeve carriage attachment 14 also has one hole 30 passing through its sleeve engaging projection 14a. 
     The holes 26, 28, and 30 are oriented whereby a linear object may concurrently extend through one of holes 26 in the rib shaft 16a and one of the two holes 28 in the rib sleeve 18 when the rib shaft 16a is telescopically received within one end of the rib sleeve 18. Likewise, a second linear object may extend through hole 30 in the rib sleeve attachment carriage 14 and through the hole 28 in the rib sleeve 18 when the sleeve projection 14a is telescopically received and properly positioned within the other end of the rib sleeve 18. 
     Referring principally to FIGS. 5a, 5b, 5c and 5d, once the rib shaft 16a and the rib sleeve 18 are properly, relatively positioned, they are secured using a distraction lock 32. The distraction lock 32 includes a pin 34 long enough to extend through either holes 28 and 26 or through holes 28 and 30 when in position on the assembled prosthetic rib 10, but not long enough to extend beyond the termini of the gripper flanges 36. The tip of the pin 34 as well as the termini of the gripper flanges 36 are rounded. The limit on the length of the pin 34 and the just-referenced rounding are in satisfaction of safety concerns. Sharp edges and slender protrusions are to be avoided in anticipation of the distraction lock 32 possibly becoming dislodged after implantation and have been so avoided in Applicant&#39;s preferred embodiment of the distraction lock. 
     The holes 26 have been spaced in 10 mm intervals in anticipation of the likely growth intervals which will indicative an adjustment of the prosthetic rib 10. Such spacing is in recognition of the fact that only slight misalignment of the spinal column can result in discomfort and possible spinal cord injury. 
     Referring principally to FIGS. 2a, 2b, 2c, 4a 4b, 6a and 6b, both the rib sleeve carriage attachment 14 and the rib shaft carriage attachment 16b include two rods 20 at their respective ends. The robs 20 are round in cross section. The rods 20 have a cross sectional diameter of 2 mm in the preferred embodiment. 
     The rods&#39; 20 round cross sectional shape was chosen as a means for minimizing the biological trauma to the periosteum of the ribs 12 and to the inferior surfaces of the ribs 12 where the rods 20 have their primary contact therewith (to be discussed in more detail hereinafter). 
     The specific 2 mm diameter of the rods 20 was chosen after numerous alternative specifications were tested. A 2 mm diameter of CP Titanium has proven to provide the optimum balance between the flexibility necessary for safe manipulation during implantation and strength necessary for post-implantation stability. No other material tested in a 2 mm rod configuration and no other dimension in CP Titanium provided the preferred characteristics for the rods 20. 
     The rods 20 of the preferred embodiment are 76 mm in length. This length has been shown through experimentation to provide a quite acceptable degree of surplus length to facilitate the needed manipulation during implantation both to circumvent the natural ribs 12 at the basic level, as well as to adjust the orientation and position of the loops formed from the rods 20 in determining the over-all orientation of the prosthetic rib 10 within the patient. The indicated length does not, however, introduce excessive length which would impede maneuvering during implantation and require excessive bending to avoid surrounding tissues. 
     Referring principally to FIGS. 1, 7a, 7b, 7c and 7d, the rods 20 are during the implantation procedure manipulated by the surgeon to circumvent the appropriate natural rib 12. The path of the rods 20 about the natural rib 12 is essentially circular when properly implanted, even though the rib would be better described as oblong. This is an important aspect of practicing Applicant&#39;s invention for several independently significant reasons. The circular circumvention permits the carriage attachments 14 and 16b to pivot relative to the natural ribs 12. This is important, in part, because the carriage attachments 14 and 16b change orientation relative to the ribs 12 to which they are attached as the length of the prosthetic rib 10 is changed subsequent to implantation. 
     Referring principally to FIGS. 8a and 8b, the ability of the carriage attachments 14 and 16b to pivot is further important in allowing the prosthetic rib 10 to partially accommodate traumatic force which may occur in falls, etc. while not transferring the force to the natural ribs 12 in a manner which would likely fracture the natural ribs 12. If the carriage attachments 14 and 16b were rigidly attached to natural ribs 12, the carriage attachments 14 and 16b would apply a possibly damaging torque to the natural ribs 12 in response to a traumatic force to the rib shaft 16a and/or rib sleeve 18. This is substantially avoided by the circular path of circumvention suggested herein. Also, the relatively loose circumvention of the natural ribs 12 obviates the danger of rib ischemica at the site of contact between the rods 20 and the natural rib 12 surface. Still further, the gentle movement permitted by the preferred mode of attachment for the prosthetic rib 10 and brought about by normal movement of the recipient has the tendency to promote work hypertrophy thereby actually strengthening the natural rib 12. 
     When the prosthetic rib 10 is properly implanted and adjusted, the rods&#39; 20 principal contact with the natural ribs 12 are to inner surface areas of the natural ribs 12 relative to the intervening chest wall defect. In this manner, the rods 20 &#34;cradle&#34; the natural ribs 12 at a point of minimum contact as opposed to deleteriously compressing them. 
     Referring principally to FIGS. 9a, 9b and 10, the rods 20 number two for each of the carriage attachments 14 and 16b in satisfaction of some of Applicant&#39;s material objectives in designing the preferred embodiment. Most notably, dual attachment sites for the carriage attachments 14 and 16b, as opposed to a singular attachment site, provide substantial rotational stability for the prosthetic rib 20. As illustrated by FIGS. 9a and 9b, a single site of attachment will do little to stabilize the prosthetic rib 10 against even minor deflective forces while a dual attachment quite ably resists such force. Also, the cumulative mass of titanium needed for strength of the attachment to the natural ribs 12 can be divided between the two rods 20 as opposed to being embodied in a single, larger rod. Such a single rod would be too stiff to safely manipulate during implantation if it incorporated the same quantum of titanium as is divided between the two rods 20 of each carriage attachment 14 and 16b of the preferred embodiment. 
     It is noted that the use of three or more rods 20 is not recommended because of the associated consumption of surface space on the natural ribs 12 and the minimal additional stability which would be achieved. Because of a plurality of prosthetic ribs 10 will be required in most situations requiring any use of the prosthetic rib 10, conservation of natural 12 rib surface space is desired. 
     Referring principally to FIGS. 11a, 11b, 11c, 11d, and 12, a perhaps less apparent benefit of dual rods 20 with a certain degree of surplus length lies in the flexibility provided to the surgeon ni orienting the prosthetic rib 10 relative to the natural ribs 12 to which the prosthetic rib 10 is attached. As shown in FIG. 12, the portions of the ribs 12 to which a prosthetic rib 10 is attached are seldom precisely perpendicular to the desired lengthwise orientation of the prosthetic rib 10. By looping the rods 20 at different positions along their length, the over-all prosthetic rib 10 can be oriented in any desired manner. Particularly where the variance from a perpendicular orientation is notably pronounced, the duel rods 20 cooperate to minimize the chance of slippage along the natural rib 12. 
     Referring principally to FIGS. 11c and 11d, the surgeon may not want the prosthetic rib 10 to be oriented with the convexity of the rib shaft 16a and the rib sleeve 18 extending &#34;radially&#34; from the patient. The dual rods 20 permit appropriate three dimensional alignment of the prosthetic rib 10 without sacrificing stability of its attachment to the natural ribs 12. The loops formed from the rods 20 may be situated in an eccentric relationship whereby the respective carriage attachment 14 or 16b is directed obliquely relative to the path of the natural rib 12. 
     Referring principally to FIG. 13, there are occasions when anantomical considerations require that the maximum radial extension of the prosthetic rib 10 be reduced and that the respective origination and termination of the combined rib shaft 16a and rib sleeve 18 are accordingly adjusted medially relative to the outermost surfaces of the relevant natural ribs 12. The above-referenced surplus length of the rods 20 is further instrumental in permitting any such necessary adjustment as can be seen from the drawing. 
     The surgical procedure involved in implantation of the prosthetic rib is outlined as follows: 
     The patient is placed in a lateral decubitus position. The arm on the side of the procedure is free draped to allow for positioning during surgery. A longitudinal, curvi-linear incision is then made over the area of the chest wall defect and carried down to the level of the defect. The skin flaps are then developed proximal and distal and are retracted. The natural, vestigial ribs that are present proximal and distal to the chest wall defect are isolated. The prosthesis site is first selected posteriorly. The fully assembled prosthetic rib is then vertically positioned in the most posterior position of the chest wall defect, and the two rods extending from each carriage attachment are placed overlying the natural ribs and the sites are marked with a cutting cautery. The prosthetic rib is then removed and a clamp is used to pierce the intercostal muscle overlying the natural rib at each site with the lung safely held away from the camp. Thus, two holes are placed over the superior surface of the natural rib where the prosthetic rib will be placed. A similar procedure is repeated at the area immediately inferior to the natural, vestigial rib at inferior limit of the chest wall defect. 
     The prosthetic rib is replaced over the chest wall defect and the two rods of each carriage attachment are bent toward the chest wall cavity at a near right angle to the length of the assembled rib shaft and rib sleeve. The rods of the rib shaft carriage attachment are inserted partway through the incisions over the superior surface of the superior natural rib. The rods of the rib sleeve carriage attachment are inserted partway through the incisions under the inferior surface of the inferior natural rib. 
     Next, the lung is again retracted, the rib sleeve is disengaged from the rib shaft and from the rib sleeve carriage attachment so that both carriage attachments can be rotated so that the respective rods inside the chest cavity are brought out toward the surgeon for visualization in the chest wall defect. The rib shaft carriage attachments are sequentially held in place as the surgeon, using pliers or a suitable substitute, manipulates the rods to circumvent the natural ribs in a circular, minimally pitched spiral configuration with the most distal portion of each rod coming to closely juxtapose its proximal origin exterior to the chest cavity (See FIG. 15b). The only interthoracic portions of the carriage attachments are the curved, smooth surfaces of the rods. 
     Once the rods are configured about the natural ribs, the rib sleeve is re-engaged with the rib shaft and the engaging projection of the rib sleeve carriage attachment to allow final positioning of the prosthetic rib assembly. The radius and length of the rods are adjusted to provide final position of the actual over all prosthetic rib assembly. By appropriately bending and orienting the rods over-all position of the prosthetic rib assembly may be brought further into the chest wall defect to allow for clearance of neurovascular bundles of the arm. Also the loops formed of the rods can be adjusted to lie eccentrically to orient the rib shaft and rib sleeve in an anterior lateral or posterior lateral position. 
     Once final positioning of the first prosthetic rib assembly is attained, a suitable plurality of prosthetic ribs are implanted as just described in an anterior progression until the chest wall defect is adequately overlain. 
     In the implantation procedure, care is taken that the two rods of each carriage attachment are separated by an adequate distance to allow for blood supply of the natural rib between them (See FIGS. 15a and 15b). Once the desired number of prosthetic ribs are satisfactorily in position, distraction locks installed as previously described herein. 
     Referring to FIGS. 16a and 16b, a dacron, reinforced, Silastic sheet of at least 0.030 inch thickness is next measured to cover the chest wall defect and overlap it to a distance of approximately 2 centimeters in all dimensions. Slots are cut in the material where the carriages are piercing the chest wall and the center portion and the narrow strip of material should be threaded between the carriage shafts for each prosthesis. The silastic sheet is then placed underneath the prosthetic and provides an interface between the lung surface and the metal of the prosthesis. The periphery of the silastic sheet is sutured in each corner and, utilizing a zero proline suture, the plastic sheet is attached at two inch intervals along each prosthetic rib to tether it up to the external chest wall formed by the prosthetic ribs. Chest tubes are then inserted inside the thoracic cavity to fully expand the lugs and then the skin surface is closed in the usual surgical manner. 
     The surgical procedure involved in adjusting the length of the previously implanted prosthetic rib is outlined as follows: 
     The patient under general anaesthetic has an incision made in the scar from the original implantation. Once this is done the skin flap is minimally dissected down toward the distraction locks securing the rib shaft relative to the rib sleeve. Once distraction locks are located, they are removed from each of the prosthetic ribs except the central most one. Next, distraction pliers (shown in FIGS. 14a, 14b, and 14c) are engaged with the central most prosthetic rib and the last distraction lock is removed. The distraction pliers are used to lengthen the central most prosthetic rib to the desired extent to expand the affected chest cavity to the length of the normal chest cavity. Once this adjustment is performed, distraction locks are placed on all prosthetic ribs to secure their adjusted lengths and states. The silastic sheet&#39;s edges are drawn further to the edges of the actual borders of the chest wall defect and the proline suture which is tethering the silastic sheet to the undersurface of the ribs slides on top of the body of the prosthetic ribs. Once this is accomplished, a radiograph checks their final position and the skin gets closed in the usual fashion. No chest tubes are needed. 
     Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limited sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the inventions will become apparent to persons skilled in the art upon the reference to the description of the invention. It is, therefore, contemplated that the appended claims will cover such modifications that fall within the scope of the invention.