Unilateral external fixation device - Patent Review 4895141

Claims

What is claimed is:

1. An external fixation device for positioning and immobilizing the distal segment and proximal segment of a fractured bone to reduce the fracture, comprising:

a distal frame having means for clamping half pins insertable within the distal segment of the fractured bone, said distal frame being formed with a distal hinge element having an arcuate surface;

a proximal frame having means for clamping half pins insertable within the proximal segment of the fractured bone, said proximal frame being formed with a proximal hinge element having an arcuate surface matable with said arcuate surface of said distal hinge element of said distal frame;

means for interconnecting said distal hinge element with said proximal hinge element so that said mating arcuate surfaces thereof are movable relative to one another along a partially spherical-shaped surface defined by a radius of fixed length having an origin at approximately the center of the fracture to permit pivotal movement of said distal frame relative to said proximal frame for aligning the distal segment with the proximal segment of the fractured bone.

2. The external fixation device of claim 1 in which said distal frame and said proximal frame each include substantially non-cylindrical shaped rods formed with a non-cylindrical-shaped, central core of foam material and an outer wall of composite material.

3. The external fixation device of claim 2 in which said rods of said distal frame and proximal frame are elliptical or oval in shape.

4. The external fixation device of claim 1 in which said distal hinge element and said proximal hinge element are each substantially cup-shaped in cross section each having a convexly arcuate outer surface and a concavely arcuate inner surface, said concavely arcuate inner surface of said distal hinge element being slidable relative to said convexly arcuate outer surface of said proximal hinge element along said partially spherical-shaped surface defined by said radius of fixed length having an origin at approximately the center of the fracture to permit pivotal movement of said distal frame relative to said proximal frame.

5. The external fixation device of claim 4 in which said means for interconnecting said arcuate surface of said distal hinge element with said arcuate surface of said proximal hinge element comprises a hinge cap engagable with one of said convexly arcuate outer surface of said distal hinge element and said concavely arcuate inner surface of said proximal hinge element, a bolt insertable through said hinge cap and said distal and proximal hinge element s and a nut threadable onto said bolt for mounting said distal and proximal hinge elements in fixed relation to said cap.

6. The external fixation device of claim 1 in which said means for clamping half pins comprises:

a pin block formed with a threaded outer surface and an internal slot for receiving a rod portion of said distal frame or said proximal frame;

means for clamping said pin block to said distal frame or said proximal frame, comprising:

(i) a spacer insertable within said internal slot of said pin block, said spacer being formed with a first end engagable with said rod portion of said distal or proximal frames and a second end extending exteriorly of said internal slot in said pin block;

(ii) a clamping cap formed with a hollow interior defining a cylindrical wall terminating at a bearing surface, said cylindrical wall being formed with threads matable with said threaded outer surface of said pin block, said clamping cap being threaded onto said pin block so that said bearing surface contacts and forces said spacer against said rod portion of said proximal or distal frames to mount said pin block thereto;

a seat formed in said pin block;

pin clamping means movable means movable within said seat, said pin clamping means being formed with a throughbore defining a wall, said throughbore being adapted to receive a half pin;

means mounted in said pin block for contacting said pin clamping means and urging said wall of said throughbore against the half pin to clamp the half pin in position on said distal frame or said proximal frame.

7. The external fixation device of claim 6 in which said pin block is formed with a first bore and a second bore intersecting said first bore, said second bore defining an internal wall formed with threads, said pin clamping means comprising:

a projection mounted to said pin block within said first bore, said projection being formed with an arcuate surface facing said second bore;

a retainer insertable within said second bore, said retainer having an arcuate surface extending into said first bore and facing said arcuate surface of said projection, said arcuate surfaces of said retainer and said projection forming a seat;

a ball formed with a throughbore defining a cylindrical wall, a portion of said cylindrical wall being tapered radially inwardly, said ball being received within said seat and movable therein relative to said pin block;

a hollow sleeve insertable within said throughbore of said ball, said sleeve being formed with a radially inwardly tapering slotted end portion which mates with said radially inwardly tapered portion of said cylindrical wall formed in said bore, said sleeve being adapted to receive an end of a half pin;

a screw having a cylindrical stem connected to a head, said cylindrical stem being formed with external threads matable with said threaded second bore, said screw being threaded into said second bore so that said cylindrical stem forces said retainer against said ball, said tapered portion of said cylindrical wall of said ball being collapsed radially inwardly to clamp said slotted end portion of said sleeve against the half pin to retain the half pin within said pin block.

8. The external fixation device of claim 6 in which said pin block is formed with a threaded outer surface and an internal slot for receiving a rod portion of said distal or proximal frames, said means for clamping said pin block to said distal frame or said proximal frame comprising:

a spacer insertable within said internal slot of said pin block, said spacer being formed with a first end engagable with said rod portion of said distal or proximal frames and a second end;

a clamping cap formed with a hollow interior defining a cylindrical wall connected to a head portion, said head portion being fixedly mounted to said second end of said spacer, said cylindrical wall being formed with threads matable with said outer threaded surface of said pin block, said spacer being inserted within said internal slot and said clamping cap being threaded onto said pin block so that said first end of said spacer contacts said rod portion to mount said pin block onto said distal or proximal frame.

9. An external fixation device for positioning and immobilizing the distal segment and proximal segment of a fractured bone to reduce the fracture, comprising:

a distal frame having means for clamping half pins insertable within the distal segment of the fractured bone, said distal frame being formed with a distal hinge element having an arcuate surface;

a proximal frame having means for clamping half pins insertable within the proximal segment of the fractured bone, said proximal frame being formed with a proximal hinge element having an arcuate surface matable with said arcuate surface of said distal hinge element of said distal frame portion;

means for interconnecting said distal hinge element with said proximal hinge element so that said mating surfaces thereof are movable relative to one another along a partially spherical-shaped surface defined by a radius of fixed length having an origin at approximately the center of the fracture to permit pivotal movement of said distal frame relative to said proximal frame for aligning the distal segment with the proximal segment of the fractured bone;

compression-distraction means engagable with said pin clamp means of at least one of said distal and proximal frames for axially moving said pin clamp means relative to the longitudinal axis of the fractured bone, said pin clamp means axially moving one of the distal and proximal bone segments of the fractured bone connected thereto by half pins relative to the other of the distal and proximal bone segments.

10. The external fixation device of claim 9 in which said compression-distraction means comprises:

a threaded rod rotatably carried by said means for interconnecting said arcuate surface of said distal hinge element with said arcuate surface of said proximal hinge element;

a nut having internal threads matable with said threaded rod, said nut being movable axially along said threaded rod in response to rotation of said threaded rod;

yoke means interconnecting said nut with said pin clamp means of one of said distal and proximal frame portions, said nut contacting and moving said yoke means axially along said threaded rod, said yoke means in turn axially moving said pin clamp means and the distal or proximal bone segment connected to said pin clamp means by half pins.

11. The external fixation device of claim 10 in which said yoke means comprises a pair of spaced yoke elements connected by a leg member, each of said yoke elements having an upper end formed with a bore adapted to receive said threaded rod and a lower end formed with spaced arms adapted to straddle said distal or proximal frame portion, said yoke elements being spaced to capture said nut between said upper ends thereof and said pin clamping means between said lower ends thereof.

12. The external fixation device of claim 10 in which said distal frame and said proximal frame each include a rod portion connected to said distal hinge element and said proximal hinge element, respectively, said threaded rod being connected to one of said rod portions for mounting said compression-distraction means.

13. A method of positioning and immobilizing the distal segment and proximal segment of a fractured bone to reduce the fracture, comprising:

clamping one end of a half pin inserted within the distal segment of the fractured bone to a pin clamp carried by a distal frame of an external fixation device, said distal frame being formed with a distal hinge element having an arcuate surface;

clamping one end of a half pin inserted within the proximal segment of the fractured bone to a pin clamp carried by a proximal frame of said external fixation device, said proximal frame being formed with a proximal hinge element having an arcuated surface which mates with said arcuate surface of said distal hinge element for permitting pivotal movement therebetween;

positioning said distal hinge element and said proximal hinge element relative to the fracture so that said arcuate surface of said distal hinge element and said mating arcuate surface of said proximal hinge element pivot with respect to one another about a partially spherical-shaped surface defined by a radius of fixed length having its origin at the approximate center of the fracture of the bone so as to permit precise adjustment of the position of the distal segment at the fracture for alignment with the proximal segment.

14. The method of claim 13 in which said step of positioning said distal hinge element and said proximal hinge element comprises spacing said mating arcuate surfaces of said distal hinge element and said proximal hinge element at a distance from the center of the fracture of the bone which is approximately equal to the length of the radius having its origin at the center of the fracture.

15. The method of claim 13 in which said step of positioning said distal hinge element and said proximal hinge element comprises spacing said mating arcuate surfaces of said distal hinge element and said proximal hinge element at a distance from the center of the fracture of the bone in the range of about two inches to four inches.

16. The method of claim 13 in which said step of positioning said distal hinge element and said proximal hinge element comprises positioning the focal point of said arcuate surface of one of said distal hinge element and said proximal hinge element substantially coincident with a vertical plane extending through the center of the fracture of the bone transverse to the longitudinal axis of the bone.

BACKGROUND OF THE INVENTION

This invention relates generally to devices for the treatment of bone fractures in which soft tissue damage is present, and, more particularly, to a pre-assembled, unilateral external fixation device for controlled closed reduction of a bone fracture which is operable to apply controlled distraction and compression at the fracture site of the bone.

A variety of activities such as high speed travel and the widespread use of heavy machinery in industry have in recent years increased the frequency of severely compounded and infected long bone fractures, such as the femur, tibia, radius and ulna, with accompanying damage to the surrounding soft tissue. In order to properly manage the wound and prevent infection of the soft tissue, it is necessary to avoid covering the affected area except with appropriate dressings or skin grafts. Casts may not be used for the treatment of long bone fractures where soft tissue damage is present.

One early method of treatment of these cases, which is still used today, involves placing the patient in traction to completely immobilize the affected limb. As is well known, there are many problems attendant to long term confinement of a patient to a bed including necrotic pressure sores and muscle atrophy.

Another approach in the prior art for the treatment of such fractures involved the use of internal fixation devices such as bone plates which were secured directly to the bone. The problem with this method is that the fracture segments must be exposed to insert and affix the device, which increases the chance of infection of both the bone and surrounding soft tissue.

In order to limit the use of traction in the treatment of fractured bones with attendant soft tissue damage, and to avoid the use of bone plates and other internal fixation devices, research begun in the 1800's resulted in the development of external skeletal fixation devices. These devices generally comprise one or more retaining pins secured to the distal bone segment and proximal bone segment on opposite sides of the fracture, which are adjustably connected to a frame located externally of the affected limb.

One external fixation device commonly used today is the so-called Hoffmann system originally developed in the late 1930's. The Hoffmann fixation system includes two sets of self-drilling and self-tapping retaining pins, known as transfixing pins, each having a centrally located continuous thread. One set of two or three transfixing pins enters the soft tissue at one side of the fracture site, passes completely through the distal or proximal segment of the bone and then extends outwardly through the soft tissue on the opposite side. The same procedure is repeated for the other set of transfixing pins on the opposite side of the fracture. Each transfixing pin is connected at opposite ends to a frame which is adapted to permit translation and pivoting of the pins for properly aligning the distal and proximal segments. The frame is adjustable during the surgical procedure, and controlled distraction or compression may be applied post-operatively to maintain the bone segments in engagement and in alignment.

Different frame configurations have been employed for supporting the transfixing pins such as bilateral, triangular, circular and quadrilateral frames. See the discussion, for example, in Mears, Dana C. (1983) External Skeletal Fixation, The Williams & Wilkins, Baltimore, Chapter 1, pp. 1-41; Chao, E.Y.S., AN, K.N. (1982) Biomechanical Analysis Of External Fixation Devices For the Treatment Of Open Bone Fractures, Finite Elements in Biomechanics, John Wiley & Sons, Ltd. The above-described Hoffmann device, for example, employs a quadrilateral frame.

One problem with prior art external fixation devices employing bilateral, triangular, circular or quadrilateral frames involves the use of transfixing pins. As mentioned above, transfixing pins are first inserted into the soft tissue on the distal and proximal side of the fracture from one side of the injured limb. The surgeon can manipulate each transfixing pin around nerves and arteries in the soft tissue on one side of the limb until the transfixing pin contacts the bone and begins to enter the cortical bone. At that point, however, the path of the pin is fixed and no further manipulation is possible. There is a substantial risk of nerve and arterial damage as the pin passes through the bone and then into the soft tissue in a fixed path on the opposite side of the leg.

A second major problem with prior art external fixation devices, such as the Hoffmann device, is that the frame elements for supporting the transfixing pins are not preassembled but must be assembled during the surgery. An assortment of clamping elements and adjustment mechanisms forming the Hoffmann frame are provided in separate pieces and must be fitted together and then clamped to the transfixing pins during the surgical procedure. Unless a surgeon has great familiarity with a particular unassembled frame device, there may be a reluctance to employ an external fixation device at all.

One purpose of external fixation devices is to enable patients to move about and reduce the incidence of necrosis and other problems caused by confinement to bed. Many of the frame designs for securing transfixing pins, including the Hoffmann quadrilateral system and circular frames such as shown in U.S. Pat. Nos. 4,365,624 and 4,308,863, are extremely bulky and make it difficult for the patient to walk or otherwise move about. In addition, bulky metal frames often cover the fracture site and obstruct x-rays. While the transfixing pins must be firmly secured to apply the necessary force to the bone segments, it is desirable to make the frame as light as possible without obstructing the fracture site.

Another disadvantage of prior art external fixation devices is the difficulty in adjusting the position and force exerted by the retaining pins, both during and after surgery. During a surgical procedure and post-operatively, external fixation devices must be capable of adjusting the transfixing pins to vary the position of the bone segments and to control distraction and compression at the fracture site. It is often desirable to make relatively minor corrections of the position or force exerted by a set of retaining pins on one side of the fracture. However, in the Hoffmann quadrilateral fixation device and others, movement of the frame elements to adjust the position of one set of transfixing pins in any direction requires adjustment of other frame elements associated with the other set of transfixing pins. This unduly complicates post-operative adjustment procedures which further reduces the willingness of physicians to employ such devices.

Some of the problems with external fixation devices employing transfixing pins have been eliminated by unilateral fixation devices which consist of a single frame element located on one side of the injured limb having pin clamps to secure half pins mounted in the distal and proximal bone fragments. Half pins extend into only one side of the extremity and thus avoid the problem of damage to the soft tissue on the opposite side which can be caused by transfixing pins. Additionally, unilateral fixation devices are generally lighter in weight and present less of an obstruction to the affected area than other external fixation devices. Examples of unilateral external fixation devices include the "Shearer" external fixation system commercially available from Chas. F. Thackray Limited, Leeds, England and the "AO-ASIF" tubular external fixator commercially available from Synthes, Paoli, Pa.

One problem with unilateral fixation devices of the type described above is that they do not, provide the desired stability to prevent movement of the bone segments relative to one another, particularly axial rotation and transverse subluxation of the bone segments. In addition, fine or relatively slight adjustment of the position of the bone segments at the fracture is difficult with prior art unilateral fixation devices.

In a typical surgical procedure for an injury of the type described above, gross adjustment of the bone segment positions is made manually, usually by manipulating the distal bone segment. But it is desirable to make fine adjustments in the position of the segments once the fixation device is in place. Preferably, such fine adjustment is obtained by manipulating the frame or the pin clamps of the fixation device which are connected to the half pins inserted within either the proximal or distal bone segment. Unfortunately, any adjustment of the position of the bone segments obtained by moving either the frame or the pin clamps carried by the frame in prior art unilateral devices results in substantial movement of the bone segments at the fracture site. This prevents fine or precise adjustment of the position of the bone segments and can lead to incorrect anatomical alignment thereof.

SUMMARY OF THE INVENTION

It is therefore among the objectives of this invention to provide a single bar, unilateral fixation device for positioning and immobilizing the distal segment and proximal segment of a fractured bone to reduce the fracture, which provides for fine or precise adjustment of the relative position of the bone segments at the fracture, which is compact, light weight and stable, and which can accommodate fractures at the proximal, middle distal and distal portions of the bone.

These objectives are achieved in a unilateral external fixation device which comprises a distal frame and a proximal frame, both formed of light weight composite material, which carry pin clamps adapted to mount the outer end of half pins inserted within the segments of a fractured bone. The distal frame and proximal frame are formed with mating hinge elements which pivot relative to one another along an "arcuate" hinge surface, i.e., a porti