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1. WO1996016608 - VERTEBRAL INSTRUMENTATION ROD

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[ EN ]

CLAIMS
1. Vertebral instrumentation rod (5) for the early fixation of an unstable spine, in its growth phase, in patients suffering from muscular dystrophy, characterized in that this rod comprises a first part, being a lumbosacral part (6), which is rigid in all directions, a second part, being a dorsal part (7), which is rigid in a frontal plane (Ox, oz), in order to prevent scoliosis, and flexible in a sagittal plane (Ox, Oy), and these two parts, of different profiles, are connected via a dorsolumbar transition zone (8) which is profiled in a progressive manner so that its second moment of area remains as constant as possible in the said zone.
2. Rod according to Claim 1, characterized in that the lumbosacral part (6) is cylindrical and has a roughened surface (9), the dorsal part (7) is of rectangular cross-section, the greater length (13) of which extends in the frontal plane (Ox, Oz), the transition zone (8) having a cross-section which becomes progressively rectangular and decreases starting from the end of the cylindrical part with its thickness (e) in the frontal plane (xz) which diminishes progressively, whereas its width (1) in the sagittal plane (xy) increases progressively, the profile of this transition zone thus being such that its second moment of area remains substantially constant over the entire length of this transition zone.
3. Rod according to Claim 2, characterized in that the thickness (e2) of its dorsal part (7) diminishes progressively from the transition zone (8) to its free end, whereas the width (1) of this dorsal part, in the frontal plane (Ox, Oz), increases progressively in order to ensure easy positioning, then decreases progressively as far as its free end.
4. Rod according to Claim 2, characterized in that the roughened surface (9) of the cylindrical part (6) is interrupted before the start of the transition zone (8), from which it is separated by a zone (11) having a smooth surface.

5. Rod according to Claim 2, characterized in that, d being the diameter (in mm) of the cylindrical part (6) and I the second moment of area of its section, the rigidity R of the said cylindrical part is directly proportional to the second moment of area
I = π d4 / 64 (in mm4)
and b being the length in the frontal plane (Ox, Oz) of a section of the rectangular part of the rod, that is to say the thickness of the latter, and h its width in the sagittal plane (Ox, Oy), the rigidity of this rectangular part is directly proportional to the second moment of area (I) which, during flexion/extension movements in the sagittal plane, is
I z = b h3 / 12,
in that the resistance of the cylindrical section is proportional to the modulus of resistance on flexion:
I / v = π d3 / 32 (mm3)
and similarly the resistance in the rectangular section
- in the sagittal plane I z / v = b h2 / 6
- in the frontal plane I y / v = h b2 / 6, in such a way that a high resistance of the rod in the sagittal plane corresponds to a high modulus of resistance on flexion
Mf = Iz / v = b h2 / 6,
in that a low rigidity of the rod in the sagittal plane corresponds to a relative flexibility on flexion, hence o a low second moment of area:
I f = I z = b h3 / 12
a high resistance of the rod in the frontal plane corresponds to a high modulus of resistance on flexion
Ms = I z / v = b h2 / 6
and a high rigidity in the frontal plane corresponds to a high second moment of area
I s = I y = h b3 / 12
6. Rod according to Claim 5, in which, by giving priority to the rigidity, b and h are defined by the following relation:


7. Rod according to Claim 5, in which, by giving priority to the resistance, h and b are defined by the relations below:


8. Instrumentation for the fixation of the spine, in its growth phase, in patients suffering from muscular dystrophy, characterized in that it comprises two vertebral rods (5) equipped with means for attachment to the spine, and each rod comprises a first part, being a lumbosacral part (6), which is rigid in all directions, a second part,, being a dorsal part (7), which is rigid in a frontal plane (Ox, oz), in order to prevent scoliosis, and flexible in a sagittal plane (Ox, Oy), and these two parts, of different profiles, are connected via a dorsolumbar transition zone (8) which is profiled in a progressive manner so that its second moment of area remains as constant as possible in the said zone.