EP0424734A1 — Screw device for fixing prostheses to bones

Claim 1

Independent Claim 170 words

A screw device (10; 80) for fixing prostheses to bones, comprising a neck (12; 112) and a threaded shank (14), characterised in that the threaded shank (14) of the screw (10; 80) has a core (32, 34) of overall frusto-conical shape, the screw core (12; 112) being cylindrical and having a diameter equal to or just greater than the maximum diameter of the thread on the shank (14) of the screw, and the thread being of two different types, namely a first thread (26) of large pitch suitable for fixing into the trabecular bone tissue (52) and extending along that part (22) of the shank (14) which is intended to make contact with said trabecular tissue, and a second thread (28), which can be of the self-tapping type, and is intended to fix into that cortical part (54) of the bone opposite the part into which the screw is inserted, said second thread (24) having a number of starts which is a multiple of that of the first thread (26).

Claim 2

Dependent Claim 170 words

A screw device (10; 80) for fixing prostheses to bones, comprising a neck (12; 112) and a threaded shank (14), characterised in that the threaded shank (14) of the screw (10; 80) has a core (32, 34) of overall frusto-conical shape, the screw core (12; 112) being cylindrical and having a diameter equal to or just greater than the maximum diameter of the thread on the shank (14) of the screw, and the thread being of two different types, namely a first thread (26) of large pitch suitable for fixing into the trabecular bone tissue (52) and extending along that part (22) of the shank (14) which is intended to make contact with said trabecular tissue, and a second thread (28), which can be of the self-tapping type, and is intended to fix into that cortical part (54) of the bone opposite the part into which the screw is inserted, said second thread (24) having a number of starts which is a multiple of that of the first thread (26).

Claim 3

Dependent Claim 40 words

A screw device as claimed in claim 1, characterised in that the directrices forming the frusto-conical core (32) of the second screw thread (28) are parallel, but internal, to the directrices forming the core (34) of the first thread (26).

Claim 4

Dependent Claim 32 words

A screw device as claimed in claim 1 or 2, characterised in that the first thread (26) is of substantially trapezoidal cross-section whereas the second thread (28) is of substantially triangular cross-section.

Claim 5

Dependent Claim 29 words

A screw device as claimed in any one of the preceding claims, characterised in that the outer diameter of the first thread (26) is constant throughout its entire extension.

Claim 6

Dependent Claim 32 words

A screw device as claimed in any one of the preceding claims, characterised in that the first thread (26) is a single-start thread and the second thread (28) is a three-start thread.

Claim 7

Dependent Claim 45 words

A screw device as claimed in any one of the preceding claims, characterised in that on the lateral surface (23) of the neck (112) of the screw (80) there is provided a third self-tapping thread (128) having the same characteristics as the second thread (28).

Claim 8

Independent Claim 264 words

A method for applying the screw device claimed in any one of claims 1 to 6, consisting of: forming a precision hole (40) in the bone in the position in which said screw device (10; 80) is to be inserted, the hole comprising: a first more outer cylindrical portion (42) to receive the screw neck, this first portion having a diameter equal to or preferably slightly less than that of the unthreaded neck (12) of the screw (10), or slightly greater than the diameter of the core of the neck (112) if this latter is threaded; a second more inner frusto-conical portion (46) of transverse dimensions equal to or preferably slightly less than those of the core (34) of the first part (22) of the shank (14) carrying said first large-pitch type (26) of thread; and a third portion extending along the remaining length of the screw shank (14), this third portion (48) being relative to said second type (28) of screw thread and having transverse dimensions slightly greater than those of the core (32) of that part (24) of the shank (14) with said second type (28) of thread; tapping the second portion (46) of the hole (40) to obtain in it a female thread suitable for receiving the first thread (26) of the screw (10; 80); if said second screw thread (28) is not of self-tapping type, tapping said third portion (48) of the hole (40) to obtain in it a female thread suitable for receiving said second screw thread (28); completely screwing said screw (10; 80) into the tapped hole (40).

Claim 9

Dependent Claim 38 words

A bone tissue cutter, of the type cooled by sterile liquid which also serves the purpose of removing the bone shavings which form, characterised by comprising a cutting part (106) in the shape of an inverted "wedding cake".

Claim 10

Dependent Claim 38 words

A bone tissue cutter, of the type cooled by sterile liquid which also serves the purpose of removing the bone shavings which form, characterised by comprising a cutting part (106) in the shape of an inverted "wedding cake".

Claim 11

Dependent Claim 38 words

A reamer for obtaining a hole of the desired precision ready for tapping, characterised by having a relief angle suitable for cutting bone tissue and comprising means for conveying isotonic liquids into the cavity formed in the bone.

Claim 12

Dependent Claim 38 words

A reamer for obtaining a hole of the desired precision ready for tapping, characterised by having a relief angle suitable for cutting bone tissue and comprising means for conveying isotonic liquids into the cavity formed in the bone.

Claim 13

Dependent Claim 52 words

A reamer as claimed in claim 9, characterised in that the means for conveying isotonic liquids consist of a coaxial channel (146) which passes through the entire reamer (140), said channel (146) communicating with an isotonic liquid feed device and with lateral apertures (148) provided between the cutting edges of the reamer.

Claim 14

Dependent Claim 85 words

A method for forming in a bone a precision hole into which a screw device claimed in any one of claims 1 to 6 is to be inserted, consisting of: with the cutter (100) claimed in claim 8, forming a stepped cavity having diametrical dimensions less than or at the most equal to the corresponding dimensions of the required precision hole (40); and with the reamer (140) claimed in claim 9, manually reaming said stepped cavity to obtain the hole (40) with the required precision.

Claim 15

Dependent Claim 176 words

A tapper (60) for tapping a precision hole (40) previously formed in a bone, characterised by comprising a tapping thread (62) with a maximum diameter not exceeding that of the neck (12; 112) of the screw (10; 80), said tapping thread having the same number of starts and the same pitch as the first thread (26) of the screw (10; 80) and extending for the same length (22) as said first screw thread (26), the tapper end part (66), of length substantially equal to that of the second thread (24) of the screw (10; 80), being free of tapping threads and having transverse dimensions not exceeding those of the corresponding third portion (48) of the hole (40) if said second screw thread (28) is of self-tapping type, whereas said end part of the tapper has a tapping thread with the same number of starts and the same pitch as the second screw thread (28) if this second thread is not self-tapping; the tapper (60) having at least one discharge means (74; 174) for the organic liquids.

Claim 16

Dependent Claim 176 words

A tapper (60) for tapping a precision hole (40) previously formed in a bone, characterised by comprising a tapping thread (62) with a maximum diameter not exceeding that of the neck (12; 112) of the screw (10; 80), said tapping thread having the same number of starts and the same pitch as the first thread (26) of the screw (10; 80) and extending for the same length (22) as said first screw thread (26), the tapper end part (66), of length substantially equal to that of the second thread (24) of the screw (10; 80), being free of tapping threads and having transverse dimensions not exceeding those of the corresponding third portion (48) of the hole (40) if said second screw thread (28) is of self-tapping type, whereas said end part of the tapper has a tapping thread with the same number of starts and the same pitch as the second screw thread (28) if this second thread is not self-tapping; the tapper (60) having at least one discharge means (74; 174) for the organic liquids.

Claim 17

Dependent Claim 54 words

A tapper as claimed in claim 12, characterised in that the organic liquid discharge means are one or more longitudinal grooves (74) extending along the entire length of the tapper (60) to interrupt all of its threads (62) and involve part of its core (64), the outer edges (73) of said groove being rounded.

Claim 18

Dependent Claim 42 words

A tapper as claimed it, claim 12, characterised in that the organic liquid discharge means are a coaxial channel (174) which passes longitudinally through the entire tapper (160) and communicates with apertures (176) provided in the core part (164) of the tapper.

Claim 19

Dependent Claim 35 words

A method as claimed in claim 7, characterised in that the third portion (48) of the hole (40) is slightly longer than the corresponding lower part (24) of the shank (14) of the screw (10).

Screw device for fixing prostheses to bones

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