WO2010134078A1

WO2010134078A1 - An intramedullary nail device

Info

Publication number: WO2010134078A1
Application number: PCT/IL2010/000404
Authority: WO
Inventors: Mordechay Ilovich; Elik Chen
Original assignee: Orthogon Technologies 2003
Priority date: 2009-05-18
Filing date: 2010-05-17
Publication date: 2010-11-25

Abstract

The present invention provides a remotely operated intramedullary nail device designed to operate with substantially improved efficiency, accuracy, load tolerance, and reduced friction. In general, the intramedullary nail device comprise two telescopic arms configured such that one of the arms is movably disposed inside a cavity provided in the other arm, an actuation unit fixedly disposed in the internal cavity of one of the telescopic arms and adapted to be remotely actuated and produce rotary movements, and a ball-screw device comprising a ball-nut and a spindle rod engaged in it and adapted to mechanically link between the actuation unit and the telescopic arms.

Description

AN INTRAMEDULLARY NAIL DEVICE

Field of the Invention

The present invention relates to orthopedic intramedullary nails and devices. More particularly, the present invention relates to an accurate and reliable intramedullary nail device having improved efficiency and torque consistency.

Background of the Invention

U.S. patent no. 7,135,022 of the same applicant hereof, the entire disclosure of which is incorporated herein by reference, describes an intramedullary implantable nail operated by means of an externally applied magnetic field that is induced and controlled by an external magnetic coil. The telescopic intramedullary nail device in this patent includes and combines a magnetic pulling/pushing mechanism and a mechanical transfer mechanism that converts the internal induced linear (or axial) magnetic pulling/pushing force into an external force operated by linear (or axial) translation throughout a distracted/retracted telescopic arm. A mechanical transfer mechanism suitable for such intramedullary nail devices is described and claimed in international patent application no. PCT/IL2006/00888 (published as WO 2007/015239) , the entire disclosure of which is incorporated herein by reference.

Typically, such telescopic intramedullary nail devices which require axial or rotational or both movements of one of their telescopic parts relative to the other incorporate a rotational-to-axial or axial-to-rotational conversion mechanism, such as a power screw-nut (also known as power- screw) , for example. In most cases involving low to high level loads (10-200 kg) the execution of the relative motion between the telescopic parts requires a high moment of operation (e.g., 20 to 80 kgxmm) , which is typically difficult to obtain in intramedullary nail devices. High payloads, (e.g., of about, or greater than, 30kg) may cause damage to the nail's operation or non motion problems due to friction, and/or galling effects (roughening and formation of protrusions). These effects cause the intramedullary nail or the device to malfunction and may result in permanent damage.

It is an object of the present invention to solve the above mentioned problems and to provide an implantable intramedullary nail device capable of efficiently and accurately converting rotational moments into controllable, reliable and repetitive axial distraction or retraction force acting on the telescopic parts of the intramedullary nail device .

It is another object of the present invention to provide an implantable intramedullary nail device capable of operating under relatively high loads with substantially reduced friction and improved device longevity.

It is a further object of the present invention to provide a method and device for efficiently and accurately distracting or retracting a fractured bone.

Other objects and advantages of the invention will become apparent as the description proceeds. Summary of the Invention

The present invention provides a remotely operated intramedullary nail device employing a ball-screw device for converting rotary movements produced by actuator means provided therein into linear (axial) movements, which thus benefits from the efficiency, accuracy and low level of moments, permitted by the ball-screw device. The intramedullary nail devoice of the invention further assists to overcome the problems of operation under heavy loads (as defined above) , and provide a nail device which operation is very smooth, reliable, accurate, and which operates with substantially low friction. Additionally, the intramedullary nail device of the invention has improved device longevity in comparison to conventional screw-nut based intramedullary devices, and which can operate under relatively high loads without any damage caused to the intramedullary nail elements.

The inventors of the present invention surprisingly managed to configure a ball-screw device to permit its assembly in an intramedullary nail device for converting rotary movements produced by an actuation unit used inside the nail device into linear (axial) movements. The intramedullary nail device of the invention generally comprises two telescopic arms configured such that one of said arms (also referred to as the internal arm or movable arm) is movably disposed inside the other arm (also referred to as external arms or base element) . The telescopic arms preferably comprise internal cavities accessible via openings situated at their engaging ends. In treatment, each arm is fixedly attached to a segment of a fractured bone by means of fixation bores provide at their free ends, wherein the controlled accurate and repetitive axial distraction force acting on the nail's telescopic arms causes controlled mechanical axial distraction (movement) of the bone in limb elongation and/or the treatment of various skeletal deformities. Alternatively, the controlled retraction force acting on the nail's telescopic arms causes controlled mechanical axial compression (movement) of the bone in non union fixation treatments and/or the treatment of various skeletal deformities.

In general, the intramedullary nail device of the invention comprises two telescopic arms one or both of which comprising an internal cavity and an opening communicating the cavity, wherein the telescopic arms are configured such that one of the arms (the internal arm) is movably disposed inside the other arm (the external arm) such that their internal cavities communicate, an actuation unit fixedly disposed in the internal cavity of one of the telescopic arms and adapted to be remotely actuated and produce rotary movements, and a ball- screw device comprising a ball-nut and a spindle rod engaged in it adapted to mechanically link between the actuation unit and the telescopic arms.

The intramedullary nail device of the invention is a remotely operated orthopedic nail device which may be implemented comprising: a hollow base element (the external arm) having a closed end (the free end) and an open end (the engaging end) communicating with its internal cavity, the base element is capable of being fixedly attached at its closed end to a first bone segment; a movable arm (the internal arm) slidably disposed in the cavity of the base element and is capable of being fixedly attached to a second bone segment at its closed end; a remotely operated actuation unit fixedly attached inside the cavity of the base element; and a ball screw device mechanically linking between the actuation unit and the movable arm. Advantageously, the movable arm comprises an internal cavity, a closed end (the free end) and an open end (the engaging end) communicating with the internal cavity.

In one aspect the present invention is directed to an intramedullary nail device capable of being remotely operated comprising two telescopic arms each comprising an internal cavity and an opening communicating (accessing) the cavity, the telescopic arms are configured such that one of the telescopic arms is movably disposed inside the other arm such that their internal cavities communicate; an actuation unit fixedly disposed in the internal cavity of one of the telescopic arms and adapted to be remotely actuated and produce rotary movements; and a ball-screw device comprising a ball-nut and a spindle rod engaged in it adapted to mechanically link between the actuation unit and the telescopic arms.

According to one preferred embodiment the actuation unit is placed inside the cavity of the arm in which the movable internal arm is disposed i.e., inside the external arm (the base element) . The ball-nut of the ball-screw device may be attached to the movably disposed internal arm and the spindle rod of the ball-screw device may be rotatably attached to the actuation unit. The intramedullary nail device may further comprise clutch means and/or gear means adapted to mechanically couple between the actuation unit and the ball- screw device.

According to another preferred embodiment of the invetion the intramedullary nail device may further comprise a coupling shaft configured to be received in the cavity of the internal arm and transfer rotary movements from the actuation unit to the ball-screw device. Preferably, the coupling shaft comprises an internal cavity accessible via an opening provided in its free end, the ball-nut of the ball-screw device is preferably attached to the coupling shaft, and the spindle rod of the ball-screw device is preferably fixedly attached to the internal arm concentrically inside its internal cavity. The device may further comprise clutch and/or gear means adapted to mechanically couple between the actuation unit and the coupling shaft.

Preferably, the actuation unit is adapted to be activated by an externally applied magnetic field. Alternatively, the actuation unit may employ a piezo ceramic motor or rotary motor adapted to be activated by external wireless power sources (e.g., RF radiation).

The implantation and insertion procedure of the intramedullary nail device may be substantially similar to procedures employed with commercially available intramedullary nail devices. For example, procedures described in PCT/IL2006/00888 and/or US patent No. 7,135,022, or slightly modified implantation procedures, may be employed. Though similar treatment protocol may be used, preferably, the distraction/retraction procedure employed with the intramedullary nail device of the invention is somewhat different as the body part (e.g., limb) including the treated bone of the patient has to be inserted into the a ring shaped electromagnetic coil having a circular opening. Thereafter, the patient enables the coil's control system which activates a pulsating magnetic wave at a frequency generally in the range of 0.5-2 Hz. In bone lengthening procedures the duration of such session is preferably no more than few minutes.

The fixation procedure of the telescopic arms is also substantially similar to the method referenced hereinabove. For non-union problems the nail device preferably induces compression forces in order to eliminate any callus strain or activate vibration in-between the two fractured bone facets. Another approach is a combination of controlled compression regime accompanied by vibration.

Brief Description of the Drawings

The present invention is illustrated by way of example in the accompanying drawings, in which similar references consistently indicate similar elements and in which:

Fig. 1 schematically illustrates an embodiment of an intramedullary nail device of the invention comprising a ball-screw device wherein the ball nut of the ball-screw device is linearly guided;

Fig. 2 illustrates possible structure of a ball screw device which may be used in the intramedullary nail device of the invention;

Fig. 3 schematically illustrates an embodiment of an intramedullary nail device of the invention comprising a ball-screw device wherein the screw (spindle) part of the ball-screw device is linearly guided and the ball-nut is rotated;

Fig. 4 schematically illustrates an embodiment of the invention employing unidirectional clutch means for preventing backwards motion; and Fig. 5 schematically illustrates one possible implementation of the actuator unit used in the intramedullary nail device of the invention.

It is noted that the embodiments exemplified in the Figs, are not intended to be in scale and are in diagram form to facilitate ease of understanding and description.

Detailed Description of Preferred Embodiments

Intramedullary nails are often used to fixate fractured bones in the field of traumatic orthopedic or for cosmetic purposes. The nails are inserted into the medullar cavity of the bone and are fixated by different types of screws like self tapping, to the fractured bone segments. A telescopic nail is a type of intramedullary nail capable of axially or rotationally, or axially and rotationally, distract or retract its telescopic segments one relative to the other, and in this way apply tension or compression forces (with or without rotational movement) between two bone fragments to which the telescopic parts are attached. The linear distraction (i.e., applying tension stresses onto callus) nails are used for distraction osteogenesis method wherein the bone is being lengthened gradually and bone formation starts to consolidate between the two bone segments. Retraction nails are designed to apply forces in the opposite direction (i.e., applying compression stresses onto the callus) , and in this way create compression stress regime between the two fractured bone segments .

Intramedullary nails may be also used for carrying out stimulation treatments during callus formation, in accordance with Carter & Blenman (BME/ME 456 Biomechanics http: //www. engin. umich. edu/class/bme456/bonefracture/bonefract ure.htm) methodology teaching that mechanical stimulus is a key factor of new tissue build up. The sinusoidal vibration, acting between the two bone fragments to which the mail segments are attached, intensifies vascular supply which permits direct bone formation. In other words; bone consolidation period is shorten. The sinusoidal vibration displacements may be in the range between lμm to 200μm, and the freguency about 0.1Hz to 40Hz.

However, the conventional friction type lead screw intramedullary nails currently used for carrying out such treatments may degrade stimulus reliability since these devices may become jammed due to their poor mechanical efficiency.

Distraction (tension) nails are designated for limb elongation, deformities correction, cosmetic (limb lengthening), oncology (amputated bones due to cancer), etc.

Compression nails or stimulation nails are designated for nonunion bone fixation treatments (non consolidation of the fractured bone) .

Both types (distraction and compression) of nails are constructed from a stationary part and a moving part. Typically, during displacement, the moving linearly guided part (telescopic arm) is being actuated by means of a screw and nut mechanism. Hence; introduction of a relative rotary motion between the nut and the screw results in a linear translation when the non rotated section is linearly guided. Under axial payloads the friction torque between the nut and the screw threading is increased which deteriorates the

"screw-nut" mechanism efficiency, and which over time may result in device malfunction and even permanent damage of its "screw-nut" mechanism.

The most popular and inexpensive threading type, of the nut and screw mechanism, is the one in which the teeth flank surfaces interacts with each other and creates sliding friction between them (unified, ACME, buttress etc. threading) .

Screw-nut mechanism efficiency prescribes the relationship between an input rotary torque and the output thrust distraction/retraction force and vice versa. Typically, the frictional lead screw efficiency of the screw-nut mechanism is in the range of 20% to 25%, where ball screw exceeds efficiency rate at the range of 70%. It applies that it could push/pull axial forces which are 2 to 3 times greater in magnitude than the forces applicable with frictional screws.

The inventors hereof are not aware of previous work or study employing ball-screw devices in orthopedic devices. In fact, ball-screw devices in general are not suitable for use in implants due to size and biocompatibility limitations. Furthermore, when this type of mechanism is implanted inside a living body various considerations ought to be addressed in order to gain higher efficiency magnitudes such as: biocompatible materials, no lubrication, limited driving power source, volume. It was found during the inventors' work and research that ball-screw devices may be adapted, or specially designed, for use in intramedullary devices, and other such implants. For example, by employing sealing techniques and appropriate sizing of the ball-screw, enable the use of such ball-screw devices in orthopedic implants.

When the conventional friction sliding type screw mechanism is employed to distract/retract axial payloads, its efficiency typically deteriorates due to problems known as seizing or galling or just high friction. The limitations which have been mentioned above confine the ability of such devices to compete with higher axial loading above 15kg to 30kg. In addition, due to intensive abrasion the screw efficiency is deteriorating drastically over time, typically until it becomes jammed. This fact is limiting the range of travel which is predominantly required for distraction nails (typically up to 50mm of travel) .

In the intramedullary nail of the present invention the sliding frictional threaded type screw is replaced by a high efficiency ball screw mechanism adapted for use in orthopedic implants, such as intramedullary distraction nail devices. It was found that with the nail device of the invention employing a ball-screw device the range of travel is less restricted and the nail device can perform up to a 100mm axial stroke.

Fig.l schematically illustrates one possible configuration of an intramedullary nail device 100 according to a preferred embodiment of the invention. Intramedullary nail 100 comprises a base element 101 configured to telescopically receive a movable arm 102 in cavity 101c formed along a substantial length of base element 101. Movable arm 102 is designed to be movably engaged in cavity 101c for allowing it to progressively slide thereinside in inward and outward directions, preferably employing linear guiding means 106. Base element 101 is preferably an elongated and hollow element comprising a closed end 101b and an open end comprising an opening 101p through which its internal cavity 101c is accessed. Base element 101 may comprise fixation bores 101a passing along its width near its closed end 101b for attaching it to a bone section, preferably to a stationary bone section. The closed end 101b of base element 101 may include a taper adapted to assist in its insertion and attachment in the bone section. An actuation unit 103 fixedly disposed in internal cavity 101c of base element 101 near its closed end 101b is adapted to be remotely operated and rotate a spindle rod 104 rotatably attached to it at one end and extending along a substantial length of cavity 101c. As exemplified in Fig. 1 the free end 104f of spindle rod 104 may protrude outside of cavity 101c via opening 101p of base element 101.

Movable arm 102 may also be an elongated and hollow element comprising a cavity 102c passing along substantial portion of its length. Movable arm 102 may comprise fixation bores 102a passing along its width near its closed end 102b for attaching it to another bone segment, and its internal cavity 102c may be accessed via opening 102p provided at its open end, which is disposed inside the internal cavity 101c of base element 101.

In this preferred embodiment of the invention a ball-screw device 105 is attached over the external lip 102e of opening 102p of movable arm 102 such that recirculation balls 105b of ball-screw device 105 are engaged in balls tracks (also referred to as screw tracks or threads) 104t provided in spindle rod 104. In this way rotary movements (referenced by arrow 108) of spindle rod 104 are translated into axial inward or outward movements (referenced by arrow 109) of movable arm 102.

As exemplified in Fig. 1 linear guiding means 106 may be placed between the outer surface of movable arm 102 and the internal surface of cavity 101c of base element 101, near the opening 101p to said cavity 101c. However, linear guiding means 106 may be additionally or alternatively placed at different locations along the length of cavity 101c. Linear guiding means may be implemented utilizing numerous profiles of keys, or pins, configured to slide in a slot formed in the internal wall of cavity 101c. Additionally or alternatively, the cross-sectional shape of the cavity 101c in base element 101 and the cross-sectional shape of movable arm 102 may be machined in a "D"-like shape, such that the straight sections of these "D" shaped elements prevents them from rotating one relative to other. Alternatively, the cross-sectional shapes of cavity 101c and of movable arm 102 may be configured in square or rectangular shape, suitable for preventing rotations of movable arm 102 inside cavity 101.

Base element 101 and movable arm 102 are preferably cylindrical elements, but as discussed above, they (and their cavities) may of course have other cross-sectional shapes suitable for their telescopic engagement and movability. The length of base element 101 may generally be in the range of 30 to 300 mm and its diameter may generally be in the range of 5 to 18 mm. The length of movable arm 102 may generally be in the range of 10 to 200 mm and its diameter may generally be in the range 4 to 17 mm. However, base element 101 and movable arm 102 may be designed in different lengths and diameters according to requirements imposed by the type of the fractured bone and the age of the treated subject. Ball-screw actuators are typically employed in applications requiring accurate positioning, high speed and low friction (e.g., aircrafts, missiles, CNC machines, and other machinery) . Typical ball-screw devices are mechanical devices capable of efficiently translating rotational motion into linear motion, or vice versa, and they tend to be rather bulky, due to the recirculation paths required for their ball bearings. In a typical ball screw device a threaded shaft (also referred to herein as a spindle or spindle rod) provides a spiral raceway for ball bearings which acts as a precision screw. The nut internal diameter is also engraved with spiral raceway for the ball bearings to re-circulate. The balls are trapped between the threaded rod and the nut raceways and recirculate during nut or spindle rotation. In this way, instead of possessing sliding friction regime, the intramedullary nail device of the present invention gains rolling friction type, which is quantified with lower coefficient of friction at the range of 1 to 2 magnitudes.

As well as being able to apply or withstand high thrust loads, ball-screw devices operates with these high thrust loads with minimum internal friction. Ball-screw devices are typically made to close tolerances and are therefore suitable for use in situations in which low moment, high precision and low friction operation is required. In these configurations the ball bearings and the ball-nut assembly acts as the nut while the threaded shaft (the spindle) is the screw.

Fig. 2 illustrates a possible ball-screw device 105 suitable for use in the intramedullary nail device of the present invention. As seen ball-screw device 105 comprises a ball nut 105n having helical nut cavities 105v in which recirculation balls 105b are held and re-circulate, and a return channel 105c passing along the length of ball nut 105n, through which recirculation balls 105b return to the beginning of their circulation path. Other possible configuration of ball-screw device 105 may be similarly used.

For medical applications the ball screw device is preferably assembled of: balls bearings, threaded shaft (spindle), ball nut, and balls bearings recirculation return plate (a cover or a trajectory forcing the ball bearings to leave their raceway trajectory in-between the nut and the screw and return backwards to the starting point of the recirculation cycle) , all of which may be made of stainless steel, titanium alloys, biocompatible ceramics or any other biocompatible steel. Non biocompatible materials may be similarly used; in a properly sealed internal compartment.

The ball nut (105) external diameter may generally be in the range of 4 to 16 mm, the ball screw (spindle 104) diameter may generally be in the range of 2 to 10mm, and the screw pitch of ball tracks 104t may generally be in the range of 0.5 to 3 mm. The movable telescopic arm (102) (or base element 101, depending which part is fixated to the stationary bone segment) is preferably capable of being displaced from 0.01 to a total displacement length of about 120 mm, while the base element (101) (or movable arm 102, depending which part is fixated to the stationary bone segment) is preferably capable of being retracted from 0.01 to a total retraction length of about 15 mm.

The length of the spindle rod 104 of ball-screw device 105 may generally be in the range of 10 to 140 mm, and the length of its ball nut 105n may generally be in the range of 5 to 25 mm. This technology may be applied either in a form wherein the part of the nail device which comprises the ball nut 105n is linearly (or axially) guided (i.e., integrated within the telescopic movable arm 102, as shown in Fig. 1) and linearly translates when the spindle rod 104 is rotated, or alternatively, in a form wherein the part comprising the spindle rod (204, in Fig. 3) is linearly guided and linearly translated when the ball nut (205n) is rotated, as shown in Fig. 3.

More particularly, intramedullary nail device 200 shown in Fig. 3 is similarly comprised from a base element 201 comprising a cavity 201c in which a movable arm 202 is slidably disposed. These telescopic elements (201 and 202) similarly and respectively comprise openings (201p and 202p) through which their internal cavities (201c and 202c) may be accessed, linear guiding means 206 placed between the outer surface of the movable arm 202 and the internal surface of the cavity 201c of the base element 201, and closed ends (201b and 202b) comprising fixation bores (201a and 202a) , as described with reference to Fig. 1. The actuation unit 203 disposed inside cavity 201c comprises a rotatable rod 203r to which base section 207b of coupling shaft 207 is fixedly attached, such that any rotary movement of rod 203r is transferred to coupling shaft 207. Coupling shaft 207 is configured to be received inside cavity 202c of movable arm 202 and it comprises an internal cavity 207c configured to receive a potion of length of the spindle rod 204 which is concentrically and fixedly attached inside cavity 202c to the movable arm 202. Ball-screw device 205 is attached over the external lip 207e of coupling shaft 207, such that the recirculation balls 205b in its ball nut 205n are engaged in balls tracks 204t of spindle 204. In this way rotary movements (referenced by arrow 208) of rod 203r are transferred by coupling shaft 207 to ball nut 205n of ball-screw device 205 and translated into axial inward or outward movement (referenced by arrow 209) of movable arm 202.

The spindle 104 (in nail device 100) or the ball nut 205n (in nail device 200) may be driven employing rotational means such as but not limited to: rotational ratchet, rotational unidirectional clutch, gear head, piezo motor, dc motor or any type of electrical/manual driving mechanism, Ferromagnetic or magnetic elements which are capable of being remotely activated externally by means of magnetic field, NiTi shape memory arrangement, inflation, or the like.

Typical ball-screw devices suffer from poor self locking quality in comparison with conventional sliding frictional screw mechanisms. As a result, when the driving torque is disabled, the ball screw mechanism ability to sustain the compression/tension loads and keeping the movable arm in position is degraded. Hence; under compression load the ball nut may slide backwards over the spindle (or forwards when under tension loads) . Therefore, it is an option, and in certain implementations required, to equip the driving mechanism with a self locking measure such as an electromagnetic/magnetic break, a unidirectional clutch, a pair of unidirectional clutches, an index mechanism, a ratchet mechanism, or any controlled/non controlled breaking mechanism, configured such that when the driving torque is disabled the telescopic movable arm (102 or 202) remains in place.

Fig. 4 illustrate an embodiment 400 of the intramedullary nail device of the invention wherein the actuation unit 103 placed in cavity 101c of base element 101 is mechanically coupled to spindle 104 by means of a unidirectional clutch 133 adapted to prevent nail's backwards motion, which may occur under a certain axial load due to the low friction of the ball-screw device 105. Nail device 400 is substantially similar to nail device 100 described with reference to Fig. 1, and thus it will not be discussed herein in details for the sake of brevity. As exemplified in Fig. 4 spindle 104 may be mechanically coupled to unidirectional clutch 133 by means of (optional) gear head 134 used for amplifying the actuator input rotary torque in order to get higher output force vs. input torque ratio.

As will be appreciated by those skilled in the art, in certain configurations gear head 134 may be able to sustain the loads and prevent sliding of the ball nut over the spindle, and in such cases nail device 400 may be implemented without unidirectional clutch 133.

Fig. 5 schematically illustrates an implementation of an implantable magnetically activated axial actuator 80a, suitable to be used as actuation unit 103 in the intramedullary nail devices on the invention. Actuator 80a comprises a reciprocating driver comprising stationary and movable magnetic/ferromagnetic elements, lla-lln and 1Oa-IOn respectively, a movable rod 122 linked to a hollow member 18 via reciprocating plunger 12, returning spring 13, and hollow coupling element 20. Rotating pivot 23 may be connected directly to the hollow coupling element 20, or via a gear 21. Upon removal of the magnetic field the ferromagnetic elements are demagnetized and returning spring 13 pushes backward the reciprocating plunger 12 and the movable rod 122 backwards to their initial position. A ratchet mechanism, comprising a first ratchet section 18c and a second ratchet section 19a, is provided between the connected surfaces of hollow plunger 18 and ratchet 19. Teeth engagement spring 27 is provided in order to allow ratchet 19 to slide back and forth into the interior of hollow coupling element 20, thereby enabling disengagement of the ratchet sections whenever the counter rotations of hollow member 18 occur, and of course, to enable restoring teeth reengaged of the ratchet sections during the next cycle reciprocating motion.

The mechanical amplification of the magnetic force induced by the magnetic field and transformed into mechanical movements by the magnetic/ferromagnetic elements is obtained via the helix mechanism (which converts the magnetically induced linear movement into rotary movement and further on by the planetary gear head.

Axial actuator 80a comprises an elongated hollow body 9 used for housing the units and devices utilized in axial actuator 80a. In a preferred embodiment the reciprocating driver is implemented by one or more pairs of stationary magnetic/ferromagnetic elements 11 and movable magnetic elements 10, wherein magnetic elements 11a, lib,..., Hn, are affixed to the inner wall of body 9, and movable magnetic elements 10a, 10b,..., 1On, are affixed to movable rod 122 slidably centered thereinside.

Stationary magnetic/ferromagnetic elements 11 are configured to provide a concentric passage suitable to slidably comprise movable rod 122. Each stationary magnetic element 11 preferably occupies a circumferential cross-sectional area of hollow body 9 while providing a passage thereinside, where the passage of the adjacent stationary magnetic elements 11 are centered about the longitudinal axis of elongated body 9.

Stationary magnetic elements 11 are preferably distributed over a longitudinal section of body 9 in equal distances therebetween, and movable magnetic elements 10 are preferably distributed along movable rod 122 in corresponding distances therebetween, such that corresponding pairs of stationary and movable magnetic elements ({10a, lla}, {10b, lib},...) are obtained. In this way movable rod 122 may be moved horizontally, as exemplified by arrow 7, by applying a magnetic field along the longitudinal axis of elongated body 9, which in turn cause attraction forces to develop between each pair of stationary and movable magnetic elements 11 and 10.

Elongated body 9 is preferably a hollow cylindrical body manufactured from a non-magnetic material such as S.S316LVM or Titanium alloy. Its length is generally in range of 30 mm to 400 mm, preferably about 100 mm. The outer diameter of body 9 is generally in the range of 6 mm to 12 mm, preferably about 10 mm, and its inner diameter in the range of 4 mm to 8 mm, preferably about 7 mm. Stationary magnetic elements 11 are preferably cylinderical shape elements manufactured from ferromagnetic or magnetic material, such as carbon steel or industrial Ferromagnetic alloy, preferably from VACCOFLUX 50, SAElOlO, SAE1018, or SAE1020, Carbon steel. The diameter of stationary magnetic/ferromagnetic elements 11 is determined to allow fitting thereof in the hollow interior of elongated body 9. Stationary magnetic/ferromagnetic elements 11 preferably comprise a hollow bore, aligned with the longitudinal axis of elongated body 9, wherein said bore is configured to allow movable rod 122 to move therethrough, for example, said bore may be in the range of 1 mm to 3.5 mm, preferably about 2 mm.

Movable rod 122 may be manufactured from Stainless steel or Titanium alloy, preferably from S.S316LVM. The length of movable rod 122 is generally in range of 20 mm to 80 mm, preferably about 30 mm, and its diameter is generally in range of 1 mm to 3 mm, preferably about 1.5 mm. The distance between pairs of magnetic/ferromagnetic elements (e.g., the distance between magnetic element 10a and 10b) along the longitudinal axis of elongated hollow body 9 is generally in range of 6 mm to 20 mm, preferably about 11 mm. The gap between the stationary magnetic/ferromagnetic elements 11 and the movable magnetic/ferromagnetic elements 10 is generally in range of 0.4 mm to 2 mm, preferably about 1.2 mm, and the magnetic force applied during operation of the actuator may bring said elements to come into contact.

As exemplified in Fig. 5, one end tip of movable rod 122 contacts the base 12a of reciprocating plunger 12. Reciprocating plunger 12 is slidably centered in elongated body 9 by means of collar 17 and bearing (or roller) 14 which are affixed to the inner wall of elongated body 9. Collar 17 is engaged with the body section 12c of reciprocating plunger 12, wherein said body section 12c comprises a returning spring 13 disposed thereover and between said collar 17 and said base 12a. Bearing 14 engaged in a horizontal groove 12b provided on the outer surface of base 12a, prevents rotational movements thereof and utilized to provide linear guidance thereto. This assembly of reciprocating plunger 12 and returning spring 13 is efficiently used as a motion transformer to transfer the axial movements of movable rod 122, and to return movable rod 12 backwards to its initial position when the applied magnetic force is reduced or zeroed, thereby restoring the gap between the stationary and movable magnetic/ferromagnetic elements 10 and 11.

One end of body section 12c is attached to base 12a of reciprocating plunger 12 while its other end is slidably engaged in the hollow interior of base section 18a of hollow member 18. One or more rollers 16 provided on body section 12c are engaged in corresponding helical grooves 18d provided on the inside wall of the hollow interior of base section 18a. Alternatively, grooves 18d may be implemented as helical slits passing from the outer surface of base section 18a into its hollow interior.

Hollow interior of base section 18a of hollow member 18 should be respectively configured to allow body section 12c of reciprocating plunger 12 perform the entire axial movements forwarded thereto by movable rod 122. An annular groove 18b is provided over the outer surface of hollow member 18 for rotatably centering it in the internal space of elongated hollow body 9 by means of bearings (or rollers) 8 affixed to the inner side wall of elongated hollow body 9. This linkage between reciprocating plunger 12 and hollow member 18 by means of said rollers 16 and helical groove 18d translates the axial motion of reciprocating plunger 12 into an angular motion of hollow member 18.

Alternatively, bearing 8 may be implemented without a corresponding groove 18b, but with one or more concentric ball bearings arranged in tandem, wherein the axes of said bearings coincides with the axis of hollow member 18.

Reciprocating plunger 12 may be manufactured by lathing or mold casting in a cylindrical shape from a stainless steel or Titanium alloy, preferably from S.S316LVM. The diameter of the base 12a of reciprocating plunger 12 is generally in the range of 4 mm to 8 mm, preferably about 7.5 mm, and the diameter of its body section 12c is generally in the range of 2.5 mm to 6.5 mm, preferably about 6 mm. These dimensions can be larger or smaller depending on the outer and inner diameters of the rods .

Hollow member 18 is coupled to gear and unidirectional clutch unit via a ratchet mechanism implemented by the coupling of a driving ratchet element 18c (first ratchet section) , attached to (or formed on) a cross-sectional surface of hollow member 18, and a driven ratchet element 19a (second ratchet section) attached to (or formed on) the base of ratchet 19. For example, said ratchet sections, 18c and 19a, may be implemented by a radial saw profile tooth arrangement (not shown) provided on opposing faces of said elements, and configured such that rotations of converter 18 resulting from movements forwarded by movable rod 122 establish coupling therebetween, while the rotations in the opposite direction (counter rotations), caused by the return of reciprocating plunger 12 due to teeth engagement spring 27, breaks said coupling due to the sliding of the saw tooth ramps. Said sliding of the saw tooth ramps results in axial motions of ratchet 19, the body section 19b of which is received in a coupling element 20.

Motion converter 18 may be manufactured by lathing, milling, EDM (Electro Erosion) , or mold casting, in a cylindrical shape, from stainless steel or Titanium alloy, preferably from S.S316LVM. The length of hollow member 18 is generally in the range of 6 mm to 8mm, preferably about 7 mm, its diameter is generally in the range of 6 mm to 8 mm, preferably about 7.5 mm, and the angular motions it performs are generally in the range of 4° to 12° , preferably about 6.4°.

As illustrated in Fig. 5, the cross section of body section 19b of ratchet 19 is smaller than the cross section area of the driven ratchet element 19a, which defines an annular recess between driven ratchet element 19a and coupling element 20, wherein teeth engagement spring 27 resides. The hollow base 20a of coupling element 20 is configured to receive an end portion of body section 19b of ratchet 19 thereinto and any axial movements thereof during the sliding of the saw tooth ramps. Returning teeth engagement spring 27 retract portion of said body section 19b from the interior of hollow base of coupling element 20, thereby restoring the coupling between ratchet elements, 18c and 19a.

Backwards angular motion of ratchet 19 is prevented by means of friction like 0-ring seal, the shape of the interacted teeth's profile angle (moderate), and the unidirectional clutch. A sliding pin 19c, provided on body section 19b of ratchet 19, transfers the angular displacements of driven ratchet element 19a to coupling element 20. The hollow interior of coupling element 20 receives body section 19b of ratchet 19 and sliding pin 19c provided thereon is received in horizontal groove 20b, thus allowing ratchet 19 to move back and forth, linearly guided, while the ratchet teeth of ratchet elements, 18c and 19a, are being engaged/disengaged during their rotation. Ratchet 19 may be manufactured by lathing, milling, EDM (Electro Erosion) , or mold casting, in a cylindrical shape from stainless steel or Titanium alloy, preferably from S.S316LVM. The diameter of driven ratchet element 19a of ratchet 19 is generally in the range of 6 mm to 8 mm, preferably about 7.5 mm, and its length is preferably about 2 mm. The diameter of body section 19b of ratchet 19 is generally in the range of 4.5 mm to 6.5 mm, preferably about 5.5 mm, and its length if preferably about 5 mm.

Coupling element 20 may be manufactured by lathing or mold casting in a cylindrical shape from stainless steel or Titanium alloy, preferably from S.S316LVM. The outer diameter of hollow base 20a is generally in the range of 6 mm to 8 mm, preferably about 7.5 mm, and its length is preferably about 6 mm. The inner diameter of hollow base 20a is generally in the range of 5 mm to 7 mm, preferably about 6 mm, and its length is preferably about 6 mm. The diameter of coupling portion 20c of coupling element 20 is generally in the range of 2 mm to 8 mm, preferably about 5 to 7.5 mm, and its length is preferably about 7 mm.

The rotations transferred by coupling element 20 are received via coupling portion 20c thereof in gear 21. The chassis 21a of gear and unidirectional clutch 21 is affixed to inner wall of elongated hollow body 9, and a stationary part 22a of thrust bearing element 22 is affixed on its cross section surface. The rotating part 22b of said thrust bearing element 22 is affixed to the base 23a of rotating shaft 23. Thrust bearing element is designed to absorb external shocks and payload axial force which may be delivered via rotating shaft 23. A cross sectional portion area of said base 23a is coupled to the output shaft 21b of gear 21, where said output shaft 21b outputs rotational movements received via coupling portion 20c and which are transformed by transmission elements (not shown) of gear 21. An annular groove may be formed on the circumference of said base 23a in which 0-ring 23b may be mounted for sealing elongated hollow body 9. O-ring 23a may be implemented by a single, or a pair of, silicone 0-rings mounted in grooves provided in base 23a of rotating shaft 23.

Gear and unidirectional clutch 21 may be a type of planetary gear head (e.g., 16/1 of Faulhaber group), its diameter is generally in the range of 6 mm to 8 mm, preferably about 7.5 mm, and its length is preferably about 6 mm. The unidirectional clutch is preferably an "off the shelf" unidirectional clutch, such as manufactured by INA integrated in a gear and unidirectional clutch 21. Thrust bearing element

22 may be implemented by F3-8M manufactured by SAPPORO PRECISION INC.

Rotating pivot 23 is preferably configured to implement the spindle (104 in Fig. 1) or rotatable rod (204 in Fig. 3) of ball-screw device (105 or 205) used for translating the rotational motions received via gear 21 into linear movements, as described in details hereinabove. Similarly, rotating pivot

23 of magnetic actuator 30a may be configured to implement clutch input shaft (133s in Fig. 4) .

Rotating pivot 23 may be manufactured from stainless steel or Ti alloy, preferably from S . S316LVM, its diameter may generally be in the range of 5 mm to 7.5 mm, preferably about 7 mm, and its length is preferably about 50 mm.

The magnetic actuation scheme described hereinabove may be used to implement a reciprocating motion device (e.g., for oscillation purposes) operating with lower force magnitudes (e.g., up to 10Kg pushing/pulling force). Such reciprocating motion device may be implemented using pairs of magnetic/ferromagnetic elements ({10a, lla}, {10b, lib}... {10n, lln}) and a movable rod (122) and returning spring (13), as described above. The motion converters, ratchet mechanism and gear and clutch devices are not needed in such implementation. Furthermore, the magnetic actuation may be implemented using various magnetic/ferromagnetic elements arrangements using 3 such elements in tandem, for instance 2 moving ferromagnetic/magnetic elements and one stationary.

Magnetic actuator 30a (actuation units 103 and 203) may also comprise a monitoring feedback device for measuring directly or indirectly the axial/rotary movements of the actuator and output corresponding indications. For example, the monitoring feedback device may be implemented by one of the following options :

1. RF Transmission - A standard miniature RF transmitter may be located inside the actuator. Said RF transmitter may be energized via a small battery and transmit system displacement (rotary or linear) to an external monitor. A RF antenna can be located external to the actuator.

The rotary or linear displacement measuring may be carried out using a rotary chopper disc (disc with many slots) passing through an opto-coupler device (Infra red solid state diode illuminating a receiver) capable of counting the received pulses. Similarly, a capacitance proximity sensor, a Hall Effect proximity switch, a mechanical switch, or a rotary or linear encoder, may be used in such implementation to provide readout of the measured movements. 2. An internal Buzzer alert may be used to provide indication relating to the measured movements. The buzzer may be located inside the actuator, such that whenever it is indicated that the required elongation was accomplished the buzzer is energized and generates an audible signal that may be sensed by an external microphone located outside the body of the treated subject.

3. A mechanical internal feedback scheme may utilize to lock the Ferro-magnets/magnets actuation system whenever a complete elongation cycle (e.g., 0.25mm) is accomplished. In this way, an external microphone may be used to sense that no internal impact noise is created and stop the elongation. An additional electro-magnetic field or internal mechanism may be used to actuate the locking index into a disable position in which it is ready for the next elongation treatment.

EXAMPLE

The configuration of nail device 400 shown in Fig. 4 has been actually tested by the inventors that proved that there is a great feasibility to employ a ball screw mechanism inside an invasive implantable nail and get a significance pushing force with minimum input torque (with average energy amplification 75-100). Nail device 400 may be comprised from a rotary actuator (103) (in the tested device an electro magnetically actuator was used, as described in PCT/IL2006/00888 ) , a unidirectional roller ramp clutch (133) , a planetary gear head (134) , and finally the ball screw (104) which is causing the ball nut (105n) to move linearly. Unidirectional clutch 133 may be implemented by a type of Sprag clutch comprising an outer ring (not shown) having a series of ramps on their inside diameter, needle rollers which are retained and guided by a plastic cage to form the clamping elements. The needle rollers may be held in their correct position by means of springs. The clutch input shaft (133s) is mechanically coupling rotary movements to the planetary gear (134) , and therethrough to the driving rotary mechanism (the spindle 104 and ball nut 105) . The clutch housing (outer ring) is preferably clamped to the nail chassis (i.e., to base element 101) .

Whenever a back drive rotation occurs by the screw and the gear, the needle rollers, which are constantly pressed by the preloaded springs towards the ramps, are geometrically jammed confronting the ramps and therefore no backwards motion occurs. On the other hand, when the input shaft is driven forward, the clutch rollers function like any other needle rollers bearing and they are freely rotated around their axes.

During the experiment an INA unidirectional drawn cup roller clutch was used of the HF 0406 KF type, which general dimensions are: input shaft diameter 4mm, total length 6mm, outer ring external diameter 8mm and the permissible max torque=1.76 [Nxm] . The clutch functionality was tested during hundreds of cases and always proved to work in accordance to the nail device requirements.

Additional details

Internal nail mechanism - the actuation unit was implemented based on the configuration shown in Fig. 5 (as described in PCT/IL2006/00888) . In this configuration the nail is activated non-invasively by an external magnetic field which magnetized a pair of Ferro-magnetic elements which are attracted to each other under the magnetic field pulse. The linear attraction displacement is then converted into a reciprocating rotary motion, ratchet mechanism to construct a continuous rotation, a unidirectional clutch to prevent backwards rotational drift and provide a self locking and breaking mechanism, a planetary gear head to boost the output torque and a screw and nut mechanism driving a linear guided telescopic arm which consequently perform a distraction/retraction linear displacement .

Lead screw testing procedure

Static test - A pneumatic cylinder, calibrated to activate a thrust force at a magnitude of a 100kg was used.

The ball screw/unified screw testing apparatus contained a linearly guided telescopic arm, a ball-nut integrated within the arm, a spindle rod supported by a thrust bearing and an input shaft which rotates the spindle. The minimum input torque which is required to push the telescopic arm forward in this example was monitored by a torque meter.

Unified threading (sliding friction) testing screw

Screw external diameter - 3.5mm

Screw pitch - 0.4mm

Screw material - hardened stainless steel

No lubricant was used during the experiment

Ball screw (rolling friction) testing screw

Ball screw external diameter - 4mm

Ball screw pitch - lmm

Material - hardened stainless steel Test results

Using the Ball screw

- Torque required to push a 100kg payload - 22 [kgxmm] .

Ball screw calculated efficiency - 72%.

Measured torque figures have shown consistency in numerous numbers of testing cycles.

Using a Unified screw

- Torque required pushing a 100kg payload - 35 - 60 [kgxmm] .

- Screw calculated average efficiency - 0.25.

- No consistency has been monitored. In many occasions the screw was jammed.

Test analysis

The ball screw efficiency was found to be about 3 times greater than the efficiency obtained using the unified screw. The results show input torque consistency at any phase of the experiment even after a fatigue test (1 million cycles at 145/14.5 kg compression sinusoidal loading). On the other hand, the friction type screw tends to jam and during running the required invested input torque increased at each cycle. Therefore it is preferable, in many orthopedic applications, to integrate in orthopedic devices a ball screw mechanism that enables to provide accurate and reliable high level of distraction, rotation or compression forces. The integration of the ball screw mechanism provides reliable long life orthopedic devices that can easily me actuated under external non-invasive magnetic fields.

The tested ball screw

The tested ball screw device used comprised a spindle 4mm in diameter, manufactured by "Thomson" (a US company) . The "off the shelf" version of the ball screw device was not adequate to fulfill the nail's technical specifications and geometrical confinement's requirements for the following reasons:

1. The nut external diameter was 11mm (the nail's tube inner diameter requirement is 8mm only) ;

2. The max. permissible axial payload was 84kg (nail's specified pushing force is 100kg) ;

3. The parts were made of stainless steel but not biocompatible;

4. In accordance to standard commercial ball screws' manufacturers the ball race ways should be lubricant with grease otherwise their performance (efficiency) would be degraded.

In order to justify the engineering and the capital investment that is associate with the development of biocompatible ball screw the following the actions were performed:

1. The ball screw was disassembled;

2. The nut external diameter was grinded to comply with the nail's inner diameter (8mm);

3. A testing jig was designed and produced in order to evaluate the ball screw in the utmost conditions, hence, minimizing artifacts such as parasite friction, by journaling all rotational parts with ball bearings.

The ball screws (2 pieces) were tested numerous times and under or following payload test have shown remarkable performances as follows:

1. Static test during distraction 100kg - at a 100kg axial payload, 50mm stroke, there was no change in the applied torque which has required rotating the ball screw and pushing the nut forward against the payload. This type of testing has been repeated for at least 100 times where no degradation of nail performance has been monitored.

2. Ball screw efficiency - Following a degreasing treatment, which dries out the existing of any lubricant from the interacting surfaces, the calculated efficiency was 72%. This fact implies that the nail could be activated with input torgue which is lower at about 3 times less than a friction type unified screw.

3. Fatigue test - A specially made fixture was designed and produced in order to dynamically test the system at an "INSTRON" computerized dynamometer located at the Technion institution, Haifa, as follows:

Number of cycles - 1,350,000

Cycle frequency - 3Hz

Sinusoidal compression forces - 147kg to 14.7kg

Force direction - axially to the nail axis

Fatigue test results:

• No mechanical damage have been detected.

• The nut was running smoothly under no load condition.

• At a 100kg static test along 50mm of travel for several times, no degradation was monitored in the ball screw efficiency; hence 72%.

4. Max static test

The nail's testing fixture was axially imposed by a 270kg payload.

The results:

• No breakage or mechanical damage was monitored.

• The ball screw efficiency remains intact. Conclusions :

1. A miniature ball screw is capable of functioning under nail pay loading conditions;

2. Dry environment did not inflict upon the requirements from the nail;

3. The nail, relatively slow rotary pace (6 degrees/sec), doesn't require the utmost conditions, like automatic machinery, because dynamic payloads are minimized.

The above examples and description have of course been provided only for the purpose of illustration, and are not intended to limit the invention in any way. As will be appreciated by the skilled person, the invention can be carried out in a great variety of ways, employing more than one technique from those described above, all without exceeding the scope of the invention.

Claims

1. An intramedullary nail device capable of being remotely operated comprising:

Two telescopic arms each comprising an internal cavity and an opening for accessing said cavity, said telescopic arms are configured such that one of said telescopic arms is movably disposed inside the other arm such that their internal cavities communicate;

An actuation unit fixedly disposed in the internal cavity of one of said telescopic arms and adapted to be remotely actuated and produce rotary movements; and

A ball-screw device comprising a ball-nut and a spindle rod engaged in it mechanically linking between said actuation unit and said telescopic arms.

2. The intramedullary nail device according to claim 1 wherein the actuation unit is placed inside the cavity of the arm in which the movable internal arm is disposed.

3. The intramedullary nail device according to claim 2 wherein the ball-nut of the ball-screw device is attached to the movably disposed internal arm, and wherein the spindle rod of said ball-screw device is rotatably attached to the actuation unit .

4. The intramedullary nail device according to claim 3 further comprising clutch means adapted to mechanically couple between the actuation unit and the ball-screw device.

5. The intramedullary nail device according to claim 3 or 4 further comprising gear means adapted to transfer the rotary movements to the ball-screw device.

6. The intramedullary nail device according to claim 2 further comprising a coupling shaft configured to be received in the cavity of the internal arm and transfer rotary movements from the actuation unit to the ball-screw device.

7. The intramedullary nail device according to claim 6 wherein the coupling shaft comprises an internal cavity accessible via its free end, and wherein the ball-nut of the ball-screw device is attached to the coupling shaft, and wherein the spindle rod of said ball-screw device is fixedly attached to the internal arm concentrically inside its internal cavity.

8. The intramedullary nail device according to claim 7 further comprising clutch means adapted to mechanically couple between the actuation unit and the coupling shaft.

9. The intramedullary nail device according to claim 7 or 8 further comprising gear means adapted to transfer the rotary movements to the coupling shaft.

10. The intramedullary nail device according to claim 1 wherein the actuation unit is adapted to be activated by an externally applied magnetic field.

11. The intramedullary nail device according to claim 1 wherein the actuation unit employs a piezo ceramic motor or rotary motor adapted to be activated by an external wireless power sources.

12. An intramedullary nail device capable of being remotely operated comprising: a hollow base element having a closed end and an open end communicating with the internal cavity, said base element is capable of being fixedly attached by its closed end to a first bone segment; a movable arm slidably disposed in said cavity of said base element and comprising a closed end and an open end, said movable arm is capable of being fixedly attached to a second bone segment by its closed end; an actuation unit fixedly attached inside the cavity of said base element and capable of being remotely operated; and a ball screw device mechanically linking between said actuation unit and said movable arm.