Non-invasive adjustable distraction system
A spinal distraction system includes a distraction rod having a first end and a second end, the first end being configured for affixation to a subject's spine at a first location, the distraction rod having a second end containing a recess having a threaded portion disposed therein. The system further includes an adjustable portion configured for affixation relative to the subject's spine at a second location remote from the first location, the adjustable portion comprising a housing containing a magnetic assembly, the magnetic assembly affixed at one end thereof to a lead screw, the lead screw operatively coupled to the threaded portion. A locking pin may secure the lead screw to the magnetic assembly. An o-ring gland disposed on the end of the housing may form a dynamic seal with the distraction rod.
1. A non-invasive adjustable distraction system comprising:
an implantable distraction rod having a first end and a second end, the first end being configured for subcutaneous affixation to a subject's bone at a first location, the implantable distraction rod having a second end containing a recess having a threaded portion disposed therein; and
an adjustable portion configured for subcutaneous placement relative to the subject's bone at a second location different from the first location, the adjustable portion comprising a housing containing a permanent magnet configured for rotation about a longitudinal axis of rotation, the permanent magnet contained within a magnetic assembly affixed at one end thereof to a lead screw via a locking pin passing transversely through both an aperture disposed in the lead screw and at least part of the magnetic assembly, the lead screw operatively coupled to the threaded portion, wherein the lead screw is substantially coaxial with the longitudinal axis of rotation of the permanent magnet and configured to permit at least some angular displacement of the lead screw relative to the longitudinal axis of rotation.
2. The non-invasive adjustable distraction system of claim 1 , wherein the locking pin comprises heat treated stainless steel.
3. The non-invasive adjustable distraction system of claim 2 , wherein the locking pin maintains structural integrity up to tensile loads of 124 lbs.
4. The non-invasive adjustable distraction system of claim 3 , wherein the locking pin maintains structural integrity up to tensile loads of 350 lbs.
5. The non-invasive adjustable distraction system of claim 1 , wherein the magnetic assembly comprises a first cup and a second cup configured to contain the permanent magnet, the first cup comprising a receptacle having an aperture dimensioned to receive the locking pin.
6. The non-invasive adjustable distraction system of claim 5 , further comprising a bearing disposed about the receptacle and within the housing of the adjustable portion.
7. The non-invasive adjustable distraction system of claim 1 , wherein rotation of the permanent magnet causes the lead screw to trace a cone-shaped envelope in the absence of contact with the threaded portion of the recess.
8. The non-invasive adjustable distraction system of claim 1 , wherein the permanent magnet comprises a cylindrical magnet.
9. The non-invasive adjustable distraction system of claim 1 , wherein the permanent magnet comprises a cylindrical magnet having a first length contained within a cavity formed between first and second cups, wherein the cavity has a length that is longer than the first length.
10. The non-invasive adjustable distraction system of claim 1 , wherein the threaded portion comprises a material that is different from the material of the lead screw.
11. The non-invasive adjustable distraction system of claim 10 , wherein the threaded portion comprises aluminum bronze.
12. The non-invasive adjustable distraction system of claim 1 , wherein the locking pin has a length of less than 0.2 inches.
13. The non-invasive adjustable distraction system of claim 1 , wherein the locking pin has a diameter of less than 0.04 inches.
14. The non-invasive adjustable distraction system of claim 1 , wherein the locking pin comprises 440C stainless steel.
15. The non-invasive adjustable distraction system of claim 1 , wherein the locking pin is heat treated and has a hardness of at least C58 Rockwell.
16. The non-invasive adjustable distraction system of claim 1 , further comprising an external adjustment device comprising first and second rotatable permanent magnets spaced apart from each other within a housing, the first and second rotatable permanent magnets operatively coupled to a motor disposed in the housing.