Classifications

• • D—TEXTILES; PAPER
  • D07—ROPES; CABLES OTHER THAN ELECTRIC
  • D07B—ROPES OR CABLES IN GENERAL
  • D07B1/00—Constructional features of ropes or cables
  • D07B1/06—Ropes or cables built-up from metal wires, e.g. of section wires around a hemp core
  • D07B1/0673—Ropes or cables built-up from metal wires, e.g. of section wires around a hemp core having a rope configuration
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B17/00—Surgical instruments, devices or methods
  • A61B17/56—Surgical instruments or methods for treatment of bones or joints; Devices specially adapted therefor
  • A61B17/58—Surgical instruments or methods for treatment of bones or joints; Devices specially adapted therefor for osteosynthesis, e.g. bone plates, screws or setting implements
  • A61B17/68—Internal fixation devices, including fasteners and spinal fixators, even if a part thereof projects from the skin
  • A61B17/82—Internal fixation devices, including fasteners and spinal fixators, even if a part thereof projects from the skin for bone cerclage
• • D—TEXTILES; PAPER
  • D07—ROPES; CABLES OTHER THAN ELECTRIC
  • D07B—ROPES OR CABLES IN GENERAL
  • D07B5/00—Making ropes or cables from special materials or of particular form
  • D07B5/007—Making ropes or cables from special materials or of particular form comprising postformed and thereby radially plastically deformed elements
• • D—TEXTILES; PAPER
  • D07—ROPES; CABLES OTHER THAN ELECTRIC
  • D07B—ROPES OR CABLES IN GENERAL
  • D07B2201/00—Ropes or cables
  • D07B2201/10—Rope or cable structures
  • D07B2201/1028—Rope or cable structures characterised by the number of strands
  • D07B2201/1036—Rope or cable structures characterised by the number of strands nine or more strands respectively forming multiple layers
• • D—TEXTILES; PAPER
  • D07—ROPES; CABLES OTHER THAN ELECTRIC
  • D07B—ROPES OR CABLES IN GENERAL
  • D07B2201/00—Ropes or cables
  • D07B2201/10—Rope or cable structures
  • D07B2201/104—Rope or cable structures twisted
  • D07B2201/1048—Rope or cable structures twisted using regular lay, i.e. the wires or filaments being parallel to rope axis
• • D—TEXTILES; PAPER
  • D07—ROPES; CABLES OTHER THAN ELECTRIC
  • D07B—ROPES OR CABLES IN GENERAL
  • D07B2201/00—Ropes or cables
  • D07B2201/10—Rope or cable structures
  • D07B2201/104—Rope or cable structures twisted
  • D07B2201/1064—Rope or cable structures twisted characterised by lay direction of the strand compared to the lay direction of the wires in the strand

Definitions

• the present invention relates to a metal cable and, in particular, to a cable for use in surgical procedures.
• a stiff stainless steel wire filament is moulded into a shape and pulled or pushed around the bone.
• the stiff wire is fastened by tightening together the free ends of the wire as described for example in U.S. patents 2,455,609 (Scheib), 1,304,620 (Steinkoenig) and 914,182 (Pfeffer).
• a mechanical operation simultaneously tightens and fastens the loop.
• this stiff wire is not ideal since it may cause serious and irreparable damage to the underlying soft tissues, and for this reason a more flexible cable would be preferable.
• metal wire filament may, at first sight, be obviated by the selection of alternative non-metallic materials for the filament.
• polymers or fibre reinforced composites might seem particularly suitable because of the way in which they have been successfully applied to a large number of other situations.
• polymers are prone to stretching, and fibres have a tendency to splinter. Neither of these characteristics are acceptable in this particular application.
• wire comprising surgical grade stainless steel e.g. ASTM F138 specifying 316 stainless steel, a material which is compatible with human tissue, has been preferred.
• the wire has to be strong enough to withstand the high strains which may be encountered during the surgical procedure, a factor which tends to necessitate an increase in the diameter of the wire.
• the wire has to be strong enough to withstand the high strains which may be encountered during the surgical procedure, a factor which tends to necessitate an increase in the diameter of the wire.
• by increasing the diameter to provide basic tensile strength there is an unavoidable loss in flexibility.
• an improved wire which has the strength and flexibility required by the surgical procedures.
• a metal cable comprising a plurality of individual wire filaments; the wire filaments comprising stainless steel and having a diameter in the range 0.0005 inches to 0.005 inches (approximately 13um to 127pm).
• the important mechanical properties of the metal cable are strength and flexibility.
• the strength depends upon the overall size of cable, the number of individual wires in the cable, and the type of material from which the wires are made.
• a cable that undergoes repeated and severe bending must have a high degree of flexibility to prevent premature breakage and failure due to fatigue. Greater flexibility in the cable is obtained by using small wires in larger numbers.
• groups of wire filaments are twisted together in a first helical direction around a central wire filament to make a strand.
• a plurality of strands are twisted together in a second helical direction around a core strand to make a strong, flexible cable.
• the first helical direction has the opposite sense to that of the second helical direction. If the wires in the strands lay in the opposite direction to that of the strands in the cable, then any filament failure is more likely to occur on the outer surface of the cable where it may be detected before catastrophic failure ensues.
• the cable has a 19x7 configuration with each of the nineteen strands consisting of seven wire filaments.
• the diameter of each wire filament is 0.0025 inches (64 ⁇ m), and the diameter of the cable after swaging is 0.033 inches (0.84mm).
• the combination of a 19x7 configuration with wire filaments of diameter 0.0025 inches (64 ⁇ m) results in a cable with a highly desirable strength versus flexibility ratio.
• Figure 1 shows a cross-section through a cable according to the invention in the unswaged condition
• Figure 2 shows an enlarged individual strand in cross section according to Figure 1;
• Figure 3 shows a configuration for a 19 x 7 cable
• Figure 4 shows a configuration for a 7 x 7 cable
• Figure 5 shows schematically a beam deflection test
• Figure 6 shows graphically the results of beam deflection tests.
• the cable comprises a plurality of strands 10.
• Each strand 10 comprises a plurality of wire filaments 20.
• Eighteen strands 10 are arranged substantially symmetrically about a central core strand in two concentric rings. Therefore the cable consists of nineteen strands altogether.
• Each strand consists of seven individual wire filaments 20. Therefore there are one hundred and thirty three (133) wire filaments in the cable cross-section.
• the cable designated a 19x7 cable, may be manufactured in the following way:-
• the individual wire filaments are produced by wire drawing.
• Drawing is the process by which metallic wire is pulled through a die in the presence of lubricants to create wire of a diameter equal to that of the die.
• There are several parameters in the drawing process which ultimately affect the strength, ductility, and flexibility of the wire. For example, differences in the drawing speed may effect the degree of strain hardening imparted to the material and thus the yield strength of the wire.
• the wire is drawn from a diameter of about 0.020 inches (0.5mm) in a series of drawing steps until it is typically 0.0025 inches (64 ⁇ m) in diameter.
• the very thin drawn wire is received on spools which are placed in a stranding machine.
• the wire is first "stranded" into 1x7 helical strands (i.e.
• Closing is the term which describes the stranding of strands to form the final cable in a process which is similar to the wire stranding process itself.
• the strands are layed in the left hand direction.
• the result is a cable, as shown in the drawing, comprising nineteen strands with seven wires in each strand, i.e. 19x7 cable.
• the cable is subjected to a stress relieving heat treatment. The stress relief helps the material maintain its helical shape and decreases its natural tendency to unwind. This process is repeated after the closing phase for the same reason.
• the cable undergoes a swaging operation which creates flats or longitudinal facets on the wire. Care must be taken not to crush or distort the wires unintentionally. Swaging smoothes out the wire and helps ensure a uniform cross sectional area. It is of paramount importance to ensure that the cable is free of sharp edges and burrs. For this reason, any free end of cable must be carefully prepared.
• the lay of the wires in the strands is opposite to that of the strands in the cable.
• Cross-laying has an advantage in that any failure of the cable usually begins on the outer surface of the cable and may therefore be detected.
• failure typically initiates on the inner wires and is not noticed until catastrophic failure occurs.
• the latter form of laying does result in a marginal increase in flexibility of the wire. Therefore, particular situations dictate which type of lay is preferred depending upon whether maximum reliability or maximum flexibility is required.
• the cross-section of the cable in Figure 3 shows two concentric rings of strands.
• the outermost shell of strands may not be required.
• the loss of twelve strands in the cable would greatly reduce its ultimate tensile strength. However, this would be compensated by a significant increase in flexibility.
• the resulting cable i.e. 7x7 configuration may have sufficient flexibility and strength for use as a suture in certain surgical procedures.
• the diameter of the cable is controlled by the diameter of the individual wires in each strand, and also by the number of strands in the cable.
• the 19x7 configuration can comprise wires of diameter in the range 0.0005 to 0.005 inches (13 ⁇ m to 127 ⁇ m) with a tolerance of ⁇ 0.0001 inches ( ⁇ 2.5 ⁇ m). The lower limit of this range is controlled by practical limitations.
• the corresponding cable diameter, in the unswaged condition, would be in the range 0.022 to 0.075 inches (0.56mm-1.9mm).
• the 7x7 configuration could employ wires of similar dimensions, although only wires in the range 0.0005 to 0.0025 inches (13 ⁇ m-65 ⁇ m) would be suitable for the intended application.
• the corresponding cable thickness, in the unswaged condition, would be in the range 0.0045 to 0.022 inches (0.114mm-0.56mm).
• wire filaments of diameter 0.0025 inches (64 ⁇ m) in a 19x7 configuration results in a cable possessing good flexibility and strength.
• the diameter of such a cable after swaging is 0.033 inches (0.84mm).
• Other construction patterns, besides a 19x7 configuration, using wire filaments of appropriate diameters could be used to give a cable of diameter 0.033" (0.84mm) as is illustrated in table 1.
• the 7x7x3 notation represents a cable with seven groups of seven strands where each strand has three wire filaments). However, some of these alternatives may not have adequate strength and others may not have sufficient flexibility.
• the diameter of the wire filament decreases so the flexibility of the resultant cable increases.
• the 19x7 configuration with wire filaments of diameter 0.0025" (64 ⁇ m) has a particularly advantageous strength v flexibility ratio.
• a sample 50 is clamped such a length "1", where 1 is 1.00 inches (25.4mm) projects horizontally from the clamp 51.
• a range of loads 52 are applied to the unsupported protuberant end of the sample to produce a variety of deflection readings.
• the maximum deflection "d" at the tip of the sample is measured and recorded provided that, when the load is removed, the sample returns to the horizontal starting position.
• the graph of figure 6 plots deflection against load applied for the different samples.
• the gradient of each slope obtained gives a relative indication of the flexibility of the sample.
• the 19x7 cable shows a gradient of 2.37; the 19x19 cable shows a gradient of 0.77; and the monofilament wire shows a gradient of 0.02.
• both the 19x7 and 19x19 cables are considerably more flexible than monofilament wire.

Landscapes

• Health & Medical Sciences (AREA)
• Orthopedic Medicine & Surgery (AREA)
• Surgery (AREA)
• Life Sciences & Earth Sciences (AREA)
• Heart & Thoracic Surgery (AREA)
• Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
• Engineering & Computer Science (AREA)
• Biomedical Technology (AREA)
• Neurology (AREA)
• Medical Informatics (AREA)
• Molecular Biology (AREA)
• Animal Behavior & Ethology (AREA)
• General Health & Medical Sciences (AREA)
• Public Health (AREA)
• Veterinary Medicine (AREA)
• Surgical Instruments (AREA)
• Ropes Or Cables (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=10717691

Family Applications (1)

Country Status (4)

Families Citing this family (6)

Family Cites Families (8)

• 1992
  • 1992-06-24 GB GB9213449A patent/GB2268198A/en not_active Withdrawn
• 1993
  • 1993-06-24 WO PCT/GB1993/001328 patent/WO1994000064A1/en not_active Ceased
  • 1993-06-24 EP EP93913425A patent/EP0684792A1/de not_active Ceased
  • 1993-06-24 JP JP6502161A patent/JPH07508193A/ja active Pending

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events