Abstract:
A device for effecting progressive elongation of a sectioned bone having no extracutaneous elements, and a method for using the device, are presented. The device, which includes a pair of telescopically engaged cylindrical members, is inserted into the medullary space of the bone, and one cylindrical member is affixed to each section of bone. Under the normal tortions experienced by the affected limb, a clutch mechanism is provided that causes the cylindrical members to be forced apart, separating the sections of bone, at which site new bone growth is stimulated. Rotations as small as 1 degree are sufficient to activate elongation. A mechanism is also provided for sensing and measuring the amount of elongation that has occurred extracutaneously. In an alternate embodiment, instead of the clutch mechanism, elongation is achieved by magnetically driving an internal component with an externally applied magnetic field.

Description:
This application is a continuation of international application number PCT 98/00065, filed Jan. 9, 1998, (status, abandoned, pending, etc.) pending; based on U.S. patent application Ser. No. 08/631,673 filed Apr. 9, 1996, now U.S. Pat. No. 5,704,939. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to surgical implements for use in the lengthening of bones, and more specifically to an apparatus and method for intramedullary skeletal distraction. 
     2. Description of Related Art 
     The problem of limb-length discrepancies resulting from congenital, postinfectious, and post-traumatic disorders is one that has received the attention of many researchers. Various devices have been known in the art that can be attached to the ends of a sectioned bone and made to lengthen progressively, the lengthening causing growth of bone tissue at the site of sectioning and thus a commensurate lengthening of the bone. The devices are then removed when the desire length is achieved or they may be left in place as an internal splint. 
     External distractors, usually comprising pins passing through soft tissue and bone, can carry non-negligible potential risks of injection, pain, and muscle contractures. One benefit, however, is the accessibility of this type of device to manipulation extracutaneously. 
     Several internal apparatus, designed to be placed within the medulla of a long bone, have been described. Intramedullary elongation devices have also been described in prior publications. 
     An attempt to obviate the need for directly contacting the elongation members has been made by Grammont et al. (U.S. Pat. No. 5,074,882 ; Trans . 37 th Ann. Mtg. Orthopaedic Research Soc ., Vol. 16, p. 657, 1991). As in previous prostheses, two telescoping tubes are used to stimulate progressive elongation of a limb. A related embodiment of the device and method to be discussed herein, the disclosure of which is hereby incorporated by reference, may be found in “intermedullary Skeletal Distractor and Method,” U.S. Pat. No. 5,505,733, issued to D. Justin and J. D. Cole. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an intramedullary skeletal distractor that elongates under the normal forces and torsions experienced in daily life and thus stimulates progressive elongation of a sectioned bone. 
     It is a further object of the invention to provide a device that has no extracutaneous elements. 
     It is another object of the invention to provide an elongation mechanism whose motion is effected with the use of a clutch and a threaded rod that together cause elongation under rotation in one direction and prevent shortening under rotation in the opposite direction. 
     It is an additional object to provide such a device having an elongation mechanism not subject to an axial load imposed by the patient&#39;s weight and tissue, such as in contracture. 
     It is yet a further object to provide such a device that emits an extracutaneously receivable signal indicative of an amount of lengthening caused by the elongation mechanism. 
     These and other objects of the invention are achieved by the device and method for elongating a bone. The device, an intramedullary skeletal distractor, is responsive to rotational oscillations during normal movement within the medulla of a bone. 
     The present distractor is for use in a medullary cavity of a bone, and comprises a first and a second cylindrical member dimensioned such that the second cylindrical member can slide into the first in telescopic fashion. Each member has a first end, a second end, and a bore, and the members are telescoped such that the first end of the second member is positioned between the first and second ends of the first member In use, the first and second cylindrical members are attached to the proximal and distal sections of a bone, respectively. 
     The device further comprises an elongated rod, also having a first and a second end, with a diameter dimensioned to slide within the bore of the second cylindrical member. The first end of the rod resides within the bore of, and is affixed to, the first cylindrical member. The second end of the rod resides within the bore of the second cylindrical member. 
     In one embodiment clutch means are positioned within the bore of the first cylindrical member upon the elongated rod. The clutch means is selectively responsive to rotation in a first direction, upon which it operates upon the second cylindrical member to effect elongating telescopic movement. Upon rotation in the opposite second direction, the clutch means locks the rod from rotating and thus prevents contracting telescopic motion. The clutch means are positioned out of the axial (longitudinal) kinetic chain of the first and the second cylindrical members and the threaded rod, thereby preventing the clutch means from experiencing an axial load during use. This confers the advantage of permitting a finer response to rotation, as the clutch means itself need not then be sufficiently robust to withstand such an axial load. 
     In one subembodiment, the clutch means comprises a first and a second clutch. The first clutch is positioned in the bore of the first cylindrical member between the first ends of the first and second cylindrical members. The first clutch has an outer periphery dimensioned to fit sufficiently tightly in the bore that movement is communicated between the first cylindrical member and the first clutch. The first clutch is also positioned upon the elongated rod and is constructed so that the inner diameter of the first clutch fits sufficiently tightly thereupon that motion in the first direction is communicated thereto and that motion in the second direction permits slippage therebetween. 
     The second clutch is positioned within the bore of the second cylindrical member and upon a threaded portion of the elongated rod. The second clutch also has an outer periphery dimensioned to fit sufficiently tightly in the bore that movement is communicated therebetween. When rotation of the elongated rod occurs in the second direction, slippage of the elongated rod within the second clutch is permitted, and the second clutch travels along the threaded portion, pushing the second cylindrical member away from the first cylindrical member. When rotation occurs in the first direction, slippage of the elongated rod within the second clutch is not permitted, the elongated rod rotates with the second clutch, slipping within the first clutch, and no lateral motion occurs. 
     In an alternate embodiment, means are provided in communication with the elongated rod for determining an amount of elongation that has occurred from the starting position. This determination can be made from an extracutaneous location (i.e., noninvasively). 
     In another embodiment, a rotation-effecting means is provided that is affixed to the elongated rod. This means, which may take the form of a magnetically susceptible material, is responsive to an extracutaneous signal to produce rotation. Thus elongation can be effected noninvasively and controllably from a location external to the device. 
     The method of using the first embodiment of the skeletal distractor comprises the following steps: The device is inserted into the medulla of a bone. The first cylindrical member is then affixed to the proximal section of bone, and the second cylindrical member, to the distal section of bone. Due to the precision of the clutch mechanism used herein, during the normal motions of daily life, sufficient torsion will typically occur to activate the clutch mechanism and effect elongation. When sufficient elongation has occurred in the bone, the device is removed. 
     The method of using the externally driven skeletal distractor comprises the step of causing an elongating telescopic movement between the first and second cylindrical members by effecting a rotation of the elongated rod rather than depending upon physiological torsions. 
     The features that characterize the invention, both as to organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description used in conjunction with the accompanying drawing. It is to be expressly understood that the drawing is for the purpose of illustration and description and are not intended as a definition of the limits of the invention. These and other objects attained, and advantages offered, by the present invention will become more fully apparent as the description that now follows is read in conjunction with the accompanying drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates the skeletal distractor (a) assembled and in its most shortened position and (b) in exploded view. 
     FIG. 2 is (a) a longitudinal view and (b) a longitudinal sectional view of the first cylindrical member. The views in (a) and (b) are rotated 90 degrees from each other along the cylindrical axis. 
     FIG. 3 is (a) a longitudinal view and (b) a longitudinal section view of the second cylindrical member. The views in (a) and (b) are rotated 90 degrees from each other along the cylindrical axis. 
     FIG. 4 illustrates the elongated rod. The views in  9 ( a ) and ( b ) are rotated 90 degrees from each other along the cylindrical axis. 
     FIGS.  5 ( a ) and ( b ) are cross-sectional views of two embodiments of the indicator mechanism with the piston (a) within the cutout and (b) entirely within the bore in the elongated rod. FIG.  5 ( c ) is a cross-sectional view of a further embodiment of the indicator mechanism having a pair of pistons. 
     FIG. 6 depicts an exploded view of the overrunning roller clutch used in the distractor. 
     FIG. 7 illustrates the skeletal distractor positioned within the medullary cavity of a bone. 
     FIG. 8 illustrates an alternate embodiment of the device having a bent first cylindrical member. 
     FIG. 9 is a perspective view of the keyring of the present invention. 
     FIG. 10 is an exploded view of the device having a magnetic position-indicating device. 
     FIG. 11 is a perspective view of the magnetically driven embodiment of the skeletal distractor, using (a) a static magnet or (b) an electromagnet, (c) an exploded view of the device, and (d) a cross-sectional view of the second cylindrical member. 
     FIG. 12 is a perspective view of the magnetic position-indicating device in place within a bone. 
     FIG. 13 is a perspective view of an alternate one-piece assembly of a roller clutch. 
     FIG. 14 is an exploded view of an alternate embodiment of the overrunning roller clutch. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments of the present invention will now be discussed with references to FIGS. 1-14. 
     Embodiment One 
     The intramedullary skeletal distractor, shown assembled and in exploded view in FIGS. 1 a  and  1   b , respectively, will be referred to generally by the reference numeral  10 . Device  10  comprises a first  20  and a second  30  cylindrical member, shown in cross section in FIGS. 2 and 3, respectively, an elongated rod  40 , shown in FIG. 4, and an indicator mechanism  50 , shown in FIG.  5 . In this embodiment the clutch means comprise a first clutch  60  and a second clutch  70  (FIG.  1 ), both overrunning roller clutches that permit rotation in one direction and lock movement in the other direction. It can be appreciated by one skilled in the art that other types of clutches may be substituted, such as spring, spiral-band, friction, magnetic, or sprag clutches. 
     In detail, first cylindrical member  20  (FIG. 2) has a first end  202 , a second end  204 , an outer diameter  206 , an inner wall  214 , an outer wall  216 , and a partial longitudinal bore  208 . Bore  208  communicates with second end  204  but does not proceed through to first end  202 . 
     Adjacent first end  202  is angled bore  212 , through which a screw  604  is inserted to anchor first cylindrical member  20  to a proximal section  602  of bone  60  (see FIG.  7 ). Angled bore  212  does not communicate with longitudinal bore  208 . In the preferred embodiment, angle  218 , measured from the cylinder axis of first end  202  to the axis of bore  212  is in the range of 45-60 degrees for the case of, for instance, a femur or a humerus. This angle permits the anchoring means to engage the thickest portion of bone and thus provide the greatest strength. 
     For the case of a tibia, a slightly different embodiment of first cylindrical member  80  is provided. As shown in FIG. 8, first end  802  of first cylindrical member  80  is slightly bent, typically at an angle  810  of approximately 10 degrees from the cylinder axis. The location of the bend  804  occurs between the first end  802  and the end of bore  808  closest the first end  802 . In this embodiment, instead of angled bore  212 , two diametric bores  806  and  808  are provided adjacent first end  802  through which a pair of screws may be inserted to anchor first cylindrical member  80  to the proximal section of the tibia. 
     Returning to FIG. 2, within first end  202  and communicating with angled bore  212 , but not communicating with longitudinal bore  208 , is threaded longitudinal bore  210 . Threaded bore  210  is utilized during insertion and retrieval of the device by threading an extension member (not shown) into bore  210 . Bore  210  is also used as a passageway for the insertion of a drill guide to assist in the correct placement of screw  604 . In an alternate embodiment, a nail may be used in place of screw  604 . With either a screw or a nail, bore  210  may also be used for a locking set screw  606  to secure the screw or the nail in place. 
     Bore  208  has three stages, which, proceeding from second end  204 , are first section  220 , having the largest diameter  222  and length  221 ; section  224 , having intermediate diameter  226 ; and third section  228 , having the smallest diameter  230  and having an octagonal internal wall profile in axial cross section. 
     Outer wall  216  has a tapered section  232  at second end  204 , through which is a pair of opposed slots  234  and  236 , having a width  238  for engaging keyring  95 , to be discussed in the following. 
     Second cylindrical member  30 , shown in detail in FIG. 3, has first end  302 , second end  304 , outer diameter  306 , longitudinal bore  308 , outer wall  310 , and inner wall  312 . Outer diameter  306  is dimensioned to slidably engage first section  220  of bore  208  in first cylindrical member  20 . Outer diameter  306  is further dimensioned to be larger than the diameter  226  of second section  224 ; therefore, the depth to which second cylindrical member  30  can be inserted into first cylindrical member  20  is determined by the length  221  of first section  220 . When assembled (see FIG.  1 ), first end  302  is inserted (after elongated rod  40 , vide infra) into bore  208  from second end  204  of first cylindrical member  20 . In the preferred embodiment, second end  304  is tapered  315  and has a rounded edge  313  to facilitate insertion. A pair of opposed slots,  314  and  316 , not communicating with bore  308 , run from adjacent second end  304  to a section  318  of first end  302 . Slots  314  and  316  have a width  315  perpendicular to the axis of second cylindrical member  30 . Near second end  304  is a pair of diametric bores  320  and  322 , proceeding through and having a larger diameter than the width  315  of slots  314  and  316 . Bores  320  and  322  are utilized for screws  607  and  608 , which secure member  30  to a distal section  610  of bone  60  (see FIG.  7 ). 
     Beginning from the second end  304 , bore  308  has three stages: first section  334 , having diameter  326 ; second section  336 , which is threaded, having diameter  338 ; and third section  340 , having diameter  342 . 
     Distal plug  90  (FIG. 1 b ) is dimensioned to fit into bore  308  of the second cylindrical member  30  at second end  304  and extends from second end  304  past the location of bore  320 . Distal plug  90  serves to strengthen the distal end and to block intramedullary tissue from entering bore  308  during insertion and elongation. Distal plug  90  also has a pair of circumferential bores  902  and  904  extending therethrough and communicating with bores  322  and  320 , respectively. 
     Keyring  95  (FIG. 9) is a cylindrical member dimensioned to be press fit onto the second end  204  of first cylindrical member  20 . Keyring  95  has an inner wall  952 , from which a pair of opposed protrusions  954  and  956 , each having a width  958 , extend into bore  960 . When assembled, protrusions  954  and  956  engage opposed slots  234  and  236  in first cylindrical member  20  and also opposed slots  314  and  316  in second cylindrical member  30 . The purpose of keyring  95  is to prevent excessive rotation of first  20  and second  30  cylindrical members and yet permit sufficient relative rotation to activate the clutches. Thus the width  958  of protrusions  954  and  956  must be dimensioned smaller than slot widths  238  and  315  to permit a relative rotation sufficient to activate the clutch mechanism and is also within the limits of natural anatomical limb rotations. In the preferred embodiment, a rotation of 3 degrees is permitted. 
     Elongated rod  40 , shown in FIG. 4, has a first end  402 , and second end  404 , length  408 , and diameter  406 . Extending from second end  404  is threaded portion  410  of rod  40 , dimensioned to mate with threaded section  336  of second cylindrical member  30 . Extending from first end  402  is nonthreaded portion  412 . Extending into nonthreaded portion  412  are partial  414  and full  416  diametric bores. When assembled (see FIG.  1 ), first end  402  resides within the full extent of bore  208  of first cylindrical member  20  and is threaded into threaded section  336  of second cylindrical member  30 , with which it is rotatably engaged and longitudinally extendable thereby, as will become apparent in the following. 
     Affixed to nonthreaded portion  412  of elongated rod  40  at first end  402  is indicator mechanism  50  (see FIG.  1 ), shown in detail in FIGS. 5 a  and  5   b . Indicator mechanism  50  comprises indicator housing  52 , piston  54 , and spring  53 . 
     Indicator housing  52  is a hollow octagonal element having an outer periphery  520  dimensioned to closely fit within third section  228  of bore  208  of first cylindrical member  20 . Indicator housing  52  also has a bore  522  that has four substantially identical cutouts  526  that are equally spaced radially (at 90 degrees from each other) about bore  522 , cutouts  526  having a radial extent  528 . Bore  522  further has a minimum diameter  524  over the bore  522  regions away from cutouts  526 . Minimum diameter  524  is dimensioned to encompass and closely engage nonthreaded portion  412  of elongated rod  40 . 
     Piston  54  and cutouts  526  are shaped so as to closely engage each other. The radial profile  542  of piston  54  has a sloping edge  544  and a substantially straight edge  546  approximately collinear with the radius of elongated rod  40 . The radial extent  548  of pistons  54  is greater than the radial extent  528  of cutouts  526 . Cutouts  526  have a radial profile  541  having a sloping edge  543 , which curves oppositely from curve  544 , and a substantially straight edge  545 . The sloping and straight edges of the piston and a cutout substantially align when the piston resides within the cutout. 
     When assembled (see FIG.  1 ), spring  53  is inserted into bore  414  in rod  40  and piston  54  is inserted into bore  414  atop spring  53 . Indicator housing  52  is then fit over first end  402  of rod  40  so that piston  54  resides in one cutout  526  and extends partially into bore  414 . It can be seen that relative rotation between indicator housing  52  and rod  40  is opposed in a first direction  548  toward straight edge  546 , but that it is possible in a second direction  549  toward sloping edge  544 . If rotation in second direction  549  is to occur, however, a sufficient torque must be exerted to overcome the coefficient of friction of the mechanism and the spring constant of spring  53 , so that spring  53  is compressed by piston  54  being pushed into bore  414 . When sufficient rotation in the second direction occurs so that pistons  54  reside completely within bore  414 , as shown in FIG.  5 ( b ), less torque is required to continue rotation. When a rotation of 90 degrees is achieved, piston  54  reaches the next cutout  526 , and an audible sound is emitted as piston  54  snaps into cutout  526  as spring  53  is released. 
     In a subembodiment, an audible sound may be a signal that sufficient forcible torque has been applied to overcome the resistance of the indicator mechanism and thus alert the patient that progressive elongation may occur. 
     In another subembodiment, a magnetic field may be applied to move the piston into the bore  714 , releasing the indicator mechanism. 
     In a further subembodiment as shown in FIG.  5 ( c ), the indicator mechanism  50 ′ comprises a pair of opposed pistons  54  and  54 ′ and a full diametric bore extending completely through the enlongated rod. In this configuration, the spring  53 ′ is held within the bore by the pair of pistons. The housing and the elongated rod rotate relatively to each other as previously described in the second direction from one pair of opposed cutouts to an adjacent pair of opposed cutouts. 
     It can be seen that further subembodiments may comprise different numbers of cutouts, also equally radially spaced. For instance, three cutouts would be spaced 120 degrees apart. Having the flexibility afforded by such a variety of indicator mechanisms permits one to custom design elongation parameters without altering any of the other elements. 
     Also affixed to nonthreaded portion  412  of elongated rod  40  is indicator bearing  55 , a cylindrical member having a longitudinal bore  552  dimensioned to closely engage nonthreaded portion  412  (see FIG.  1 ). Diametric bore  554  communicates with bore  416 , and locking pin  58  is inserted through bores  554  and  416 , retaining bearing  55  upon rod  40 . When assembled, bearing  55  resides within third section  228  of bore  208  in first cylindrical member  20 , further toward second end  204  than and adjacent to indicator mechanism  50 . 
     First clutch  60 , the structure of which is shown in FIG. 6, has an outer periphery  620  dimensioned to fit sufficiently tightly within the second section  224  of bore  208  of first cylindrical member  20  that rotational motion can be communicated therebetween. In an alternate embodiment, as shown in FIG. 10, first clutch  60  screws into a threaded portion in the second section  224  of bore  208 , and is held in place by a retaining bushing  64 . First clutch  60  further has an inner diameter  604  dimensioned to closely engage nonthreaded portion  412  of elongated rod  40  and also communicate rotational motion therebetween. When assembled, first clutch  60  is mounted on nonthreaded portion  412  between indicator bearing  55  and threaded portion  410 . First clutch  60  permits slippage between rod  40  and first cylindrical member  20  when rotation occurs in a first direction and communicates rotation therebetween in the second direction. 
     Second clutch  70 , identical in structure to first clutch  60  shown in FIG. 6, has an outer periphery  702  dimensioned to fit sufficiently tightly within widest section  340  of second cylindrical member  30  that rotational motion can be communicated therebetween. Second clutch  70  further has an inner diameter  740  dimensioned to engage threaded portion  410  of rod  40  and move longitudinally therealong. The directionality of second clutch  70  permits locking between rod  40  and second cylindrical member  30  when rotation occurs in the first direction; rotation in the second direction causes rotational slip, thus allowing linear movement between rod  40  and member  30 . When the device  10  is fully assembled, rotation in the second direction causes second clutch  70  to move along threaded portion  410  of rod  40  toward second end  404 , and consequently threaded portion  410  moves in a longitudinal direction out of threaded section  336  of bore  308  in second cylindrical member  30 . Such relative longitudinal movement serves to push second cylindrical member  30  out of the bore  208  of first cylindrical member  20 , elongating device  10 . 
     In detail, clutches  60  and  70  comprise cylindrical clutch housing  702 , clutch cage  704 , end cap  706 , four clutch springs  708 , and twelve clutch rollers  710 . 
     Clutch housing  702  has a bore  711  having inner surface  712 , a first end  701 , and a second end  703 . Inner surface  712  has sixteen asymmetrically shaped radial cutouts  713  having a gradual slope  714  in a first direction and a sharper slope  716  in a second direction. 
     Clutch cage  704  comprises a first ring-shaped end  718  and a second ring-shaped end  720  spaced apart by four equally spaced support members  722  affixed to the facing surfaces  719  and  721  of ends  718  and  720 , respectively. Each of these facing surfaces  719  and  721  has a circumferential channel  726  and  727 , respectively, therein. Second end  720  is dimensioned to slide within first end  701  of clutch housing  702 ; first end  718  is larger than clutch housing  702  and thus will not slide past first end  701  of clutch housing  702 . 
     Each clutch roller  710  comprises a substantially cylindrical member having a first  734  and a second  736  narrowed end. One set of three clutch rollers  710  resides between adjacent support members  722 , the first ends  734  positioned within channel  727  and second ends  736  positioned within channel  726 . When assembled, with cage  704  within housing  702 , clutch rollers  710  are biased against sharper slope  716  by springs  708 , which are mounted on support members  722 . Rollers  710  cannot rotate in the second direction past the sharper slope  716  of the housing, but they can rotate in the first direction past the gradual slope  714 . This selective rotational ability provides the clutch directionality. 
     To complete the assembly, end cap  706 , having a depending lip  738  dimensioned to fit within housing bore  711 , is placed over housing  702  at second end  703 . 
     Since both clutches  60  and  70  are overrunning roller clutches, very small rotations can effect elongation. In practice, torsions as small as 1 degree, well within the range of normal physiological movement, will cause elongation of device  10 . Therefore, no external manipulation is necessary, and, rather than the several larger elongations per day required of previously disclosed devices, small progressive longitudinal increments can occur throughout the day, a more desirable situation for stimulation of bone growth. The only external manipulation required is that necessary to release the indicator mechanism  50 . In practice, for human subjects, the device is designed to permit 0.20-0.25 mm of elongation per 90 degree rotation of the elongated rod  40 , and manipulation to release this mechanism is recommended four to six times per day, for a total elongation of 1 mm per day. 
     In an alternate embodiment of the clutch construction, shown in FIG. 14, the clutch  61  has a cylindrical clutch housing  612 , a clutch cage  614 , an end cap (not shown), eight clutch springs  618 , and eight clutch rollers  610 . The principle of operation is identical to that described for clutches  60  and  70 , except that there is one clutch spring  618  for every clutch roller  610 . 
     Another alternate embodiment of the roller clutch is shown in FIG. 13, which illustrates a one-piece roller/spring/cage assembly  62  that is dimensioned to be inserted into housing  702 . In this assembly  62 , which can be made, for example, by laser cutting or metal injection molding, the generally cylindrical “cage” portion  622  of the structure is fenestrated, having openings  624  in which the spring portions  626  and roller portions  628  are supported by interconnections between each other and, for the spring portions  626 , with the cage portion  622 . 
     In this clutch  62  design a first end  625  of each leaf spring  626  joins the roller  628  near the center thereof. A second end  627  of each leaf spring  626  joins a longitudinal section  621  of the cage  622  also near the center thereof. Each roller portion  628  is supported only by the leaf spring&#39;s first end  625 , thereby permitting some movement relative thereto. Under tension, the clutch operates in similar fashion to those discussed above, in that the roller portions  628  are restrained from rotating in the second direction by the shape of the housing  702  and are permitted to rotate in the first direction. In this case, however, the roller  628  do not rotate fully; rather, they turn slightly, exerting a force on the leaf springs  626 . The spring portions  626  comprise a loop of metal having sufficient flexibility to permit clutch rotation under physiological conditions but sufficient stiffness to restrain free motion. 
     In the embodiment shown in FIG. 13, there are  13  roller/spring units. While this number is meant to be exemplary and nonlimiting, it should be noted that the. construction of the clutch must strike a balance: The fewer the rollers, the larger they are in diameter, which limits the diameter of the elongated rod and the wall thickness of the cylindrical members; the greater the number of rollers, the smaller they are in diameter, which permits either the elongated rod or the wall thickness of the cylindrical members to be greater and, thereby, stronger. However, if the number of rollers becomes too large, the clutch would be unmachineable and too weak; therefore, a workable range is likely from 8 to 16 rollers for this embodiment, although this is not intended as limiting, as new materials might indeed make it possible to achieve operable clutches having a larger number of rollers. 
     The method of utilizing the above-described device comprises the following steps (see FIG.  7 ): An incision at the head of the sectioned bone  60  to be treated is made, through which the distractor  10  is inserted into the medulla of the bone. The first  20  and the second  30  cylindrical members are affixed by screws  604 ,  607 , and  608  to the proximal  602  and distal  610  sections of the bone  60 , respectively. When are torsional movement in the first direction occurs, the second clutch moves along the threaded portion of the elongated rod, pushing the second cylindrical member away from the first, elongating the device. Successive rotations continue to telescope the device until 0.25 mm elongation is reached, at which point the indicator mechanism locks against further elongation. At the end of quarter-day, either a second party or the patient him/herself forcibly rotates the limb until the piston is pushed within the bore in the elongated rod and clutch movement can occur again. When the limb has been stimulated to grow at bone section point  601  to the length desired, the distractor is removed from the bone  60  or left in place as an internal splint. 
     Embodiment Two 
     In a second embodiment  12 , shown in FIG. 10, means are provided that are in communication with the elongated rod  42  for determining from an extracutaneous location an amount of elongating telescopic movement that has occurred between the first  20  and the second  30  cylindrical members from a predetermined starting position. This movement-determining means comprises a signal-producing means, wherein the signal produced is indicative of a rotational position of the elongated rod  42 . 
     In a specific embodiment, the signal-producing means comprises a magnet  43 , such as a rare-earth magnet, having a pole (N-S) axis  432  oriented generally diametrically relative to the elongated rod  42 . The magnet  43  must be rotationally constrained relative to the elongated rod  42 , so that a movement of the elongated rod  42  is communicated to the magnet  43  and the magnetic field is thereby indicative of the rotational position of the elongated rod  42 . 
     As shown in FIG. 10, the elongated rod  42  has a partial longitudinal bore  422  from the second end  424 , within which the magnet  43  is dimensioned to reside. Close engagement is provided by a plug  44  that tightly encompasses the magnet&#39;s second end  434  and fits within the bore  422  sufficiently tightly that rotational movement is communicated between the magnet  43  and the elongated rod  42 . 
     Within the normal range of physiological movements, it is expected that the magnet  43  will rotate fully approximately twice per day, and that a measurement will be taken every four hours with, for example, an electronic Hall-effect sensor  49 , which detects the direction and magnitude of the magnetic field (FIG.  12 ). A microprocessor  48  in communication with the sensor  49  counts each time the field changes from north to south and relates that to one-half of the thread pitch, which gives a measure of the lengthening that has occurred. Alternately, a sensor could be worn by the patient continually and checked as often as desired. 
     Embodiment Three 
     In this embodiment of an intramedullary skeletal distractor  14  (FIG. 11 a-d ), the first  20  and second  32  cylindrical members and the elongated rod  42  are essentially as described above. However, here the rod  42  is coupled to the second cylindrical member  32  so that a relative rotational movement of the rod  42  is translated into a relative axial movement between the rod  42  and the second cylindrical member  32 . 
     Specifically, the rod  42  has a threaded portion  426  that is positioned to engage a complementarily threaded portion  362  of the second cylindrical member&#39;s bore  334 . Thus a rotation of the rod  43  effects a longitudinal movement between the rod  42  and the second cylindrical member  32 . 
     This embodiment  14  further comprises a rotation-effecting means affixed to the elongated rod  42  that is responsive to an extracutaneous rotation-producing signal. In a specific embodiment, the rotation-effecting means comprises a material responsive to a magnetic signal, such as a magnet  45 , so that an extracutaneous circumferentially directed magnetic signal causes a rotation of the responsive material and a corresponding rotation of the elongated rod  42 . 
     In order to retain the elongated rod  42  within the bore of the first cylindrical member  20 , a bushing  64  is provided that screws into a position adjacent the first cylindrical member&#39;s first end  202 . The bushing  64  is dimensioned to fit over the elongated rod&#39;s first end  421  but not in movement-producing contact. A retaining screw  63  is then inserted into a threaded bore  423  in the rod&#39;s first end  421 , serving to retain the bushing  64  in surrounding relation to the rod  42 . 
     The method of using this embodiment of the invention, therefore, comprises the step of delivering a magnetic signal from a second magnet  47  to the magnet  45 . The magnetic signal should have a circumferential component that is sufficient to drive the magnet  45  and rod  42  rotationally. Operationally, the second magnet  47  is positioned extracutaneously next to the limb containing the distractor  14  and is rotated in a direction to achieve lengthening (shown as a movement of the magnet  47  counterclockwise in FIG.  11 ). 
     In the foregoing description, certain terms have been used for brevity, clarity, and understanding, but no unnecessary limitations are to be implied therefrom beyond the requirements of the prior art, because such words are used for description purposes herein and are intended to be broadly construed. Moreover, the embodiments of the apparatus illustrated and described herein are by way of example, and the scope of the invention is not limited to the exact details of construction. 
     Having now described the invention, the construction, the operation and use of preferred embodiment thereof, and the advantageous new and useful results obtain thereby, the new and useful constructions, and reasonable mechanical equivalents thereof obvious to those skilled in the art, are set forth in the appended claims.