WO1998040024A1

WO1998040024A1 - Screw with threaded head for bone fragment osteosynthesis

Info

Publication number: WO1998040024A1
Application number: PCT/FR1998/000417
Authority: WO
Inventors: Jean-Alain Colombier
Original assignee: Biotech International (S.A.R.L.)
Priority date: 1997-03-11
Filing date: 1998-03-04
Publication date: 1998-09-17
Also published as: AU6838198A; FR2760628B1; FR2760628A1

Abstract

The invention concerns a screw with threaded head for bone fragment osteosynthesis, characterised in that it comprises a distal part (1) provided with a cylindrical thread (2) and a proximal part (3 ) provided with a conical thread (4) with its diameter increasing in the direction of the proximal end of said screw, and the conical thread (4) pitch (P) of the proximal part (3) is smaller than the cylindrical thread (2) pitch (P') of the distal part (1).

Description

Screw with threaded head for osteosynthesis of bone fragments.

The present invention relates to a threaded head screw for osteosynthesis

or coaptation of bone fragments.

The object of the invention is more particularly intended to allow the

coaptation of small bone fragments such as those of the foot or hand. In this

interesting application, the screw according to the invention makes it possible in particular to produce

osteosynthesis of the bones of the carpus, tarsus, metacarpal, metatarsal,

malleolus, etc. It is more particularly advantageous for the implementation

orthopedic techniques such as the treatment of Hallux Valgus by

Scarf osteotomy, or other osteotomy techniques, for example depending on the

Weil method.

However, it is emphasized that the screw according to the invention can also be

used to reduce / compress bone fragments from other parts of the skeleton.

There are, on the market, cannulated or non-cannulated screws for osteosynthesis of small bone fragments.

A first type of these screws which can be distinguished as being screws

single thread fairly close to ordinary screws, consists of a threaded distal part and a proximal part which can be either a head with plane support, or a head with conical support. In both cases, the compression force depends on the number of turns imposed on the screw, once the head is placed in contact with the upper cortex. The surgeon must therefore assess the tightening torque

necessary in order to estimate the compression force transmitted to the bone fragments. We

understands that any error of assessment can have unfortunate consequences on

the result of the reduction / compression intervention or for the integrity of

bone fragments for which osteosynthesis is desired.

In addition, this type of screw does not generate any anti-loosening effect.

We also know (US-A-4,175,555, FR-A-2,699,065, EP-0.695.537,

osteosynthesis screws with double thread and differentiated pitch. These screws are made up

a distal threaded part and a proximal part or head also threaded, but

whose pitch is slightly less than that of the distal part, which thus provides,

during screwing, a compression effect between the two bone fragments to be maintained

One against the other. All these screws include a proximal part or head

provided with a cylindrical helical thread.

Although larger in diameter than the body, the threaded heads of this

type of screws which generally only have three or four turns, only offer

that a weak axial mechanical resistance. As a result, it is difficult to obtain a satisfactory compression force on poor quality bones, with the risk

to see the head tear off the proximal thread from the bone.

In addition, once inserted, a screw of this type cannot be replaced in place of another by an intraoperative situation, in the event that a radiographic examination would reveal that the length of the screw used is not

conforms to that which is desirable.

The object of the invention is in particular to remedy the drawbacks

aforementioned known single thread or double thread and pitch screws

differentiated.

According to the invention, this objective is achieved by means of a screw comprising a

distal part provided with a cylindrical thread and a proximal part or head

with a conical thread whose diameter grows towards the end

proximal of said screw.

According to a second characteristic arrangement of the invention, the pitch of the

conical thread of the proximal part is smaller than that of the thread

cylindrical of the distal part.

Double thread with differentiated pitch allows reduction / compression

controlled or "pre-programmed".

The threaded conical head ensures good proximal support while being buried,

which authorizes the use of the screws according to the invention in the articular zone. The threaded conical head also makes it possible to replace a screw in an intraoperative situation, by

a screw of different length. In this case, the new screw can behave

like a conical head screw with a single distal thread. The above goals, features and benefits, and more,

will emerge more clearly from the description which follows and from the appended drawings in which:

Figure 1 is an elevational view of a first example configuration

of an osteosynthesis screw according to the invention, more particularly adapted to the execution

of osteotomies according to the Weil technique.

Figure 2 is an axial sectional view of this screw.

Figure 3 shows the profile of the thread of the conical thread of the part

proximal of the screw.

Figure 4 is an elevational view of a second example of

conformation of an osteosynthesis screw, more particularly suitable for

realization of phalangeal osteotomies.

Figure 5 is an axial sectional view of this screw.

Figure 6 is an elevational view of a third example of

conformation of an osteosynthesis screw, more specifically intended for osteotomy

from Scarf.

Figure 7 is an axial sectional view of this screw.

Reference is made to said drawings to describe advantageous examples, although in no way limitative, of making the screw intended to allow the coaptation, with compression, of two bone fragments, according to the invention. This screw can be made of any biocompatible material such as titanium,

or a material that is both biocompatible and biodegradable.

According to a first arrangement characteristic of the invention, this screw is

remarkable in that it comprises a distal part 1 provided with a thread

cylindrical 2 and a proximal part or head 3 provided with a conical thread 4 of which

the diameter increases in the direction of the proximal end of said screw.

The generatrices of the conical thread 4 of the proximal part 3 form,

for example, an angle α of the order of 16 °, relative to the axis of the screw.

On the other hand, this conical thread includes, for example, three to five turns.

The upper side 4a of the thread of the conical thread 4 is perpendicular or

substantially perpendicular (slope of the order of 3 °) to the axis A of the screw, while

its lower side 4b is oriented obliquely relative to said axis (Figure 3).

On the other hand, the lower side 4b forms an angle (β) of the order of 35 ° to 40 °, of

preferably 38 °, with the upper side 4a.

Preferably, the distal 1 and proximal 2 threaded parts are

separated by a smooth cylindrical section 5.

The screws according to the invention have a variable length depending on the

interventions for which they are intended, this length being, for example,

between 10 and 28 mm. As a simple example, - the distal part 1 of a screw for osteotomy

of Weil, can have a length corresponding to approximately 46% of the length

total of the screw; - its smooth section 5, a length corresponding to approximately 31%

the length of the screw; - and its proximal part 3 with conical thread, a length

corresponding to 23% of the length of the screw. So if you consider, as

for example only, a screw for the Weil osteotomy with a length of 13 mm,

the length of its distal part may be 6 mm, that of its smooth section of

4 mm, and that of its conical threaded head 3 mm.

According to another characteristic arrangement of the invention, the pitch P of the

conical thread 4 of the proximal part or conical head 3 of the screw, at a height

slightly less than that of the pitch P 'of the cylindrical thread 2 of the distal part

1 of said screw.

As examples only:

- the pitch P of the conical proximal thread 4 of the self-compression screws

perforators for the implementation of the Weil technique, which generally have

a length between 11 and 14 mm, can have a height of 0.6 mm, then

that the pitch P 'of their distal cylindrical thread 2, can be 0.8 mm;

- the pitch P of the conical proximal thread 4 of the cannulated compression screws

for phalangeal osteotomy or for osteosynthesis of the scafoid, which have

generally a length between 12 and 28 mm, can have a height of

0.8 mm, while the pitch P 'of their distal cylindrical thread 2, can be 1 mm; - the pitch P of the conical proximal thread 4 of the cannulated compression screws

for the Scarf technique, which generally have a length of between 10 and

22 mm, can have a height of 1.05 mm, while the pitch P 'of their thread

distal cylindrical 2, has a height of 1.25 mm.

It follows from the above examples that the difference in height between

the steps P and P 'can advantageously be of the order of 0.20 mm.

The head of the screw is shaped so as to allow it to be driven in

rotation by means of an appropriate and standard instrument. For example, head 3 of

the screw is provided, in a manner known per se, with an axial hexagonal recess 6, intended

to receive the hexagonal drive end, of a tool or

suitable operation (screwdriver or other), for example 1.5 mm hexagon on flats

for Weil and phalangeal osteotomy, or 2 mm hex on plates for Scarf.

The osteosynthesis screw according to the invention can be of the "cannulated" type, that is to say

say provided with an axial channel 7 extending from one end to the other of said screw, for

the passage of a pin.

The conical thread 4 of the head of the screw may advantageously include

at least one notch 8 oriented along one of its generatrices, and giving the

conical head 3 of the screw a self-tapping action during screwing; so

preferred, the conical thread has two or three notches 8 regularly

spaced. However, it is also emphasized that the conical thread 4 could include

more than two or three cuts, for example four cuts 90 ° apart.

On the other hand, in a manner known per se, the cylindrical thread 2 of the part

distal 1, could also include, at least over a portion of its length,

one or more notches 9 (FIG. 4) oriented parallel to the axis of the screw and

cutting two or three extreme turns of said screw.

Claims

1. - Screw with threaded head for osteosynthesis of bone fragments, characterized in

that it comprises a distal part (1) provided with a cylindrical thread (2) and a

proximal part or head (3) with a conical thread (4) whose diameter increases

towards the proximal end of said screw.

2. - Screw according to claim 1, characterized in that the pitch (P) of the thread

taper (4) of the proximal part (3) is smaller than the pitch (P ') of the thread

cylindrical (2) of the distal part (1).

3. - Screw according to claim 1, characterized in that the difference in height

between the pitch (P) of the conical thread (4) of the proximal part (3) and the pitch (P ') of the

cylindrical thread (2) of the distal part (1) of the screw, is of the order of 0.20 mm.

4. - Screw according to any one of the claims 1 to 3, characterized in that

the generatrices of the conical thread (4) of the proximal part (3), form a

angle (α) of the order of 16 ° relative to the axis of the screw.

5. - Screw according to any one of claims 1 to 4, characterized in that

the conical thread (4) of the proximal part (3) consists of three to five

turns.

6. - Screw according to any one of claims 1 to 5, characterized in that the

upper side (4a) of the thread of the conical thread (4) is perpendicular or

substantially perpendicular to the axis (A) of said screw, while its lower side

(4b) is oriented obliquely with respect to said axis.

7. - Screw according to claim 6, characterized in that the upper sides (4a)

and lower (4b) of the thread of the conical thread (4) form, between them, an angle (β) of

on the order of 35 ° to 40 °, for example an angle of 38 °.

8. - Screw according to one of claims 1 or 2, characterized in that it comprises

an intermediate smooth cylindrical section (5) disposed between its distal parts (1)

and proximal (3) threaded.

9. - Screw according to any one of claims 1 to 8, characterized in that the

conical thread (4) of its proximal part (3) comprises at least one notch (8)

oriented along one of the generatrices of said conical thread.

10. - Screw according to claim 9, characterized in that the conical thread (4)

of its proximal part (3) comprises two or more than two notches (8)

regularly spaced.