Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
2000-01-07
2001-03-20
Philogene, Pedro (Department: 3732)
Surgery
Instruments
Orthopedic instrumentation
C606S054000, C606S059000, C606S057000, C606S053000
Reexamination Certificate
active
06203548
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a distraction apparatus for holding a fracture during the healing process, comprising screws or pins for insertion into a bone at points proximal and distal relative to a fracture site, and a pair of springs which can be connected externally between the screws or pins at spaced positions thereon, which springs act respectively as a compression spring and an extension spring between the screws or pins.
BACKGROUND OF THE INVENTION
The invention has been developed especially in connection with the problems that are encountered in cases of fractures of the wrist or lowermost in the radius, one of the bones of the forearm, a very common fracture. Usually, fairly good results are achieved with plaster treatment, but it is known that in 10-20% of cases this results in an unacceptable malalignment or malunion, especially fore-shortening. If there is presumed to be a danger of such malalignment or malunion, it is known to use external fixation. Transcutaneous screws are then screwed into the radius above the fracture and into the second metacarpal bone, and the alignment is locked by means of lockable universal joints, rods etc. At least two screws are used in each bone. When this technique is employed, the fracture lowermost in the radius is fixed indirectly because both the wrist joint and the joints in the campus are between the bones which are fixed with the screws. Despite this, this known method has proven to be adequate, and healing with a good alignment is usually achieved. However, the joints become stiff, and osteoporosis is a common complication. This causes considerable problems of rehabilitation and often a lasting reduction of mobility in wrist and finger joints, and there is therefore a certain degree of scepticism with respect to this method in the medical profession.
The drawbacks outlined above can be avoided if a distraction apparatus or fixator is used which permits the patient to move the joints during treatment.
Various fixators or distraction apparatus are known which seek to achieve this. For instance, No. 170 513 makes known an external bone fixation device which consists of fixation rods connected to bone fixation pins capable of being inserted into the bone, and an articulation part which joins the two rods. This known fixation device enables the patient to carry out some mobility exercises with the broken joint. DE 43 13 767 makes known a fixation device which includes a hinge member allowing limited joint movements.
U.S. Pat. No. 4,628,919 makes known an external fixation device which includes two articulatedly connected rods, attached to respective bone pins. This known device allows a certain freedom of movement in the wrist joint.
U.S. Pat. No. 5,437,666 makes known an external fixation device for osteosynthesis, which device includes bone fixation pins and connecting rods having a central disk articulation, and the device enables motion of the wrist joint about three axes.
Similarly, U.S. Pat. No. 5,437,667 makes known a fixation device for a distal fracture of the radius. Here too, a hinge mechanism is used which allows motion that does not differ from the normal kinematic motion of the wrist.
U.S. Pat. No. 5,047,865 makes known a distraction device where two bone fixation pins are interconnected by means of two springs which act as a compression spring and an extension spring, respectively. The device is especially intended for intra-articular fracture dislocations of fingers.
SUMMARY
In the case of fractures of the wrist it is correct to apply tractive forces to fractures, but it has been found that it is also very important to be able to provide the right moments at the wrist fracture.
One of the objects of the invention is thus to provide a distraction apparatus or fixator which makes it possible to balance the relation between choice of spring forces and distances for mounting points so that aligning moments are obtained at the fracture. Such aligning moments will help in the enhanced alignment and healing of the fracture site.
According to the invention, an apparatus is therefore proposed as mentioned in the introduction, which apparatus is characterised in that the springs are spring force adjustable and are connected in fixed receiving members in a respective frame part which carries the screws or pins, wherein the compression spring closest to the fracture site when the apparatus is in use is inclined relative to the exterior extension spring and the underlying bone so that the compression spring closest to the fracture site when the apparatus is in use is connected at a greater distance from the bone proximally than distally, reckoned along the screws or pins.
Although the new apparatus is intended primarily for fractures of the wrist where the type of fracture is of a nature such that it is desirable to use moments in addition to tractive force from the springs, the invention can of course also be used for other fractures wherever the apparatus might be suitable.
In each frame it is advantageous to construct a socket-type receiving member for the compression spring and insertion-type receiving member for the extension spring.
According to one variant, in each frame part there may advantageously be a socket-type receiving member for the compression spring and a hook-type receiving member for the extension spring.
When a hook-type receiving member is provided for the compression spring, this may be secured to or made as an integral part of a cylindrical body arranged slidably in a bore in the respective frame part, the cylindrical body having a keyhole-like cross-bore for interaction with a narrowed portion on a pin or screw.
The cylindrical body may be spring-loaded in the bore.
Each frame may advantageously have a bore with associated stud for securing interaction with a screw or pin.
An especially practical embodiment of the apparatus according to the invention would be one where the compression spring comprises a coil spring fixed in a surrounding split sleeve housing, wherein a first housing part is made in the form of a bottom sleeve wherein an outer bottom end is designed for connection of one end of the spring, and a second housing part, telescopic relative to the first housing part, is made in the form of a nut sleeve in threaded interaction with a threaded portion on a rod whose end is designed for connection.
In a practical embodiment of this kind, the extension spring may advantageously comprise a coil spring fixed in a surrounding split sleeve housing wherein a first housing part is made in the form of a bottom sleeve wherein an outer bottom part is designed for connection of one end of the spring, and a second housing part, telescopic relative to the first housing part, is made in the form of a bottom sleeve wherein an outer bottom part is designed for connection of the other end of the spring and a nut body is screwed onto the second housing part, which nut body has a pin which projects in through a slot in the second housing part and is secured to the attached coil spring end.
REFERENCES:
patent: 2391537 (1945-12-01), Anderson
patent: 5074865 (1991-12-01), Fahmy
patent: 5437666 (1995-08-01), Tepic et al.
patent: 5941877 (1999-08-01), Viegas et al.
patent: 6007534 (1999-12-01), Gonzalez et al.
patent: 6010501 (2000-01-01), Raskin et al.
Abelman ,Frayne & Schwab
Philogene Pedro
Prototech AS
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