Distraction device for moving apart two bone sections

Details Distraction device for moving apart two bone sections Distraction device for moving apart two bone sections

1999-12-09

2001-06-12

Mancene, Gene (Department: 3732)

Surgery

Instruments

Orthopedic instrumentation

C606S090000, C606S060000

Reexamination Certificate

active

06245075

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a traction apparatus for moving apart two parts of a bone, in particular for bone extension or to bridge a bone gap, comprising a medullary pin which can be introduced into the medullary space of a bone and which has two parts respectively securable to one of the two bone parts and moveable axially apart, a drive unit which drives a drive shaft and a device for converting the rotational movement of the drive shaft into a relative axial movement of the two parts of the medullary pin.
The use of a medullary pin as part of such a traction apparatus is known from document DE 39 21 972 C2. This apparatus serves in particular for the extension of tubular bones or the bridging of defects after comminuted fractures, or an inflammatory bone process or after the removal of tumors in the area of longer tubular bones. This known apparatus already has considerable advantages in comparison with external traction apparatuses in which the bone parts are connected outwardly through the skin to an adjustable frame, since through this a continuous danger of infection is present due to the entry of germs and also an unfavorable application of force is present.
The manner of operation of the known medullary pin is such that by moving the two parts of the medullary pin apart from one another the two parts of the bone can be moved slowly apart from one another, with the gap which thereby forms between the two bone ends continuously being bridged by newly forming bone substance as a result of the slow advance. In this manner bone can not only be extended in that bones are separated and subsequently drawn apart after drilling and insertion of the medullary pin into the medullary space, but rather bone gaps can also be bridged in that a bone piece separated from a bone end adjacent to the gap is moved from the one end of the gap to the other. Accordingly the end of a bone stub, i.e. a bone with a missing bone end, can also be extended.
Important in an apparatus of the initially named kind is that the movement of the bone parts apart from another takes place slowly in order to provide adequate time for the formation of bone substance and for the adaptation of the surrounding tissue.
SUMMARY OF THE INVENTION
The invention is based on the object of setting forth a traction apparatus of the initially named kind which is characterized by a high operational reliability which enables a constructional size which is as small as possible with at the same time a high degree of efficiency of the drive apparatus.
This object is satisfied in that the drive shaft drives planetary rollers which are held on orbits on which drive grooves on their outer circumference engage in corresponding drive grooves of a hollow body surrounding the planetary rollers, with at least the drive grooves of the hollow body or of the planetary rollers being formed as thread grooves in order, on a rotation of the drive shaft, to displace the hollow body axially relative to the latter.
The traction apparatus of the invention is characterized by a high degree of efficiency of its driving device. In this way a high operational reliability is ensured on the one hand and a small constructional size of the apparatus is made possible on the other hand, since the drive device can be made relatively small despite the high forces that are required. The traction apparatus of the invention is thus particularly suited for implantation into the body of the patient being treated.
For the driving of the planetary rollers the drive shaft is preferably provided with a pinion-like outer toothing which meshes into an outer toothing present at each planetary roller alongside the drive grooves. Another possibility lies in rotationally fixedly connecting the drive shaft to a cage rotatable in the hollow body and in which the planetary rollers are journalled. The second variant is simpler from the design viewpoint, but the transmission ratio of the gear stage is missing.
In accordance with a further design of the invention the hollow body surrounds the drive unit in telescope-like manner and forms a part of the medullary pin. This leads to a small constructional size of the traction apparatus, which can also be used with small and short bones as a result of the small length of the medullary pin which can be achieved thereby.
In accordance with further embodiments of the invention the drive unit can be fixed relative to one bone and the hollow body can be made extensible, or, however, the hollow body can be fixed to one bone and the drive unit with the planetary rollers and an axially loadable pin mounted coaxially to the hollow body can be extendible. The second variant has the advantage that the hollow body of larger diameter can be arranged in the proximal end of a tubular bone while the pin of smaller diameter can be arranged in the distal end, where less space is present. The loading by the introduction of the medullary pin is thereby reduced.
By providing a cardan joint between drive motor and hollow body the medullary pin can advantageously also be of hollow design. In particular a hollow body forming part of the medullary pin can be provided with bends.
Through the provision of a bend of the medullary pin the latter can be anatomically matched to the medullary space of a bone. The impairing of the bone by the traction apparatus is hereby reduced. Together with the small constructional size of the medullary pin made possible by the invention the medullary pin can also be designed so that it can be inserted into the medullary space of a medullary pin with out drilling open the bone substance. A weakening of the bone is hereby avoided, or at least reduced.
In accordance with a further design of the invention the hollow body drives the piston of a hydraulic pump by which the medullary pin can be driven. The drive device can in this manner be accommodated separately from the medullary pin and in particular implanted into the patient's body. This design also enables a design of the medullary pin with curvatures. It is advantageous in this respect to form the medullary pin as a piston-cylinder unit. One part of the medullary pin forms the piston which can be driven by the hydraulic pump.
In accordance with a further embodiment of the invention the drive unit includes an electric motor which can preferably be inductively supplied with energy, in particular by the coupling in of high frequency energy. In just the same way it is however also possible to drive the electric motor by an implantable energy store. In both cases it is ensured that no danger of infection exists through parts which are lead outwardly, for example connection wires of the traction apparatus.
In accordance with a further design of the invention a force measuring device and/or a path measuring device for the movement of the medullary pin and implantable in the body of the patient is provided. Through this measuring device the bone build-up process can be monitored and recorded without the patient having to be x-rayed and thus without the danger of a thereby produced burden for the patient.
In accordance with a further embodiment of the invention a strain gauge is provided as the force measuring device, whereas the path measuring device can for example operate potentiometrically. Another advantageous possibility lies in using an encoder adapted to the motor or a Hall sensor. The transmission of the measurement signals outwardly can for example take place by means of a telemetry system.
The determining parameters of the moving parts of the apparatus of the invention for the relationship between the speed of rotation of the drive shaft and the axial path of the hollow body can be summarized as follows in an equation resolved in accordance with the path of displacement:
S
ax
=
U
a
·
(
PS
·
1
d
wa
+
d
wr
-
Pr
·
d
gs
d
gr
·
d
gr
)
·
d
wa
·
d
gr
d
gr
+
d
wr
In this equation
S
ax
=axial path of the hollow body
U
a
=number of rotations of the drive shaft
Ps=

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