37

Indications and Contraindications

Description of System Components

Operative Techniques for Loop Fixings (Type A)

Positioning

Incision and Exposure

Bony Preparation and Decision of Loop Size

Deformation and Installation

Case Illustrations

Case 1

Case 2

Case 3

Conclusion

Nitinol is an alloy of nickel and titanium that belongs to a class of materials called shaped memory alloys (SMAs). Nitinol was invented in 1962 by the U.S. Naval Ordnance Laboratory. The scientific team was seeking a nonmagnetic, high-hardness, noncorrosive material for hand weapons and tools. What they discovered was a relatively safer (nontoxic) SMA.¹

The team named the new alloy nitinol. The name represents its elemental components and place of origin. Ni and Ti are the chemical symbols for nickel and titanium. The nol stands for the Naval Ordinance Laboratory where it was discovered.

SMAs have interesting mechanical properties. Nitinol for example contracts when heated, which is the opposite of what standard metals do when heated. Not only does the alloy contract but it also produces thermal movement (expansion, contraction) 100 times greater than standard metals.

Another interesting property of SMAs is their shaped memory effect (SME). The alloy can be heat treated to remember a particular shape. If the shape is later bent and distorted, the alloy may be heated to regain its original shape. These characteristics (Table 37–1) can be used for internal stabilization and prosthetics of bone and ligament–cartilage structures of the spine.

The KIMPF-DI Fixing (CJSC KIMPF Company, Moscow, Russia) shape memory implant system for spine surgery is both biologically and mechanically compatible.²

This system comprises five types: (Fig. 37–1A–E).

Type A: Loop fixing type (Davydov shape memory loop)

Type B: Vertebral fixing

Type C: Intervertebral fixing Type

D: Fixing without loop

Type E: Endoprosthesis of intervertebral disks

Nitinol possesses a heterophase structure. This structure provides stable and appropriate characteristics and superelasticity, and it facilitates the shape memory effect.

Design of fixings ensures^2–4:

1. Mechanical behavior that is similar to the behavior of ligament–cartilage structures replaced or reinforced by fixings. Fixings have the following characteristics: range of self-adjusting compression and stiffness of counteraction to the functional loads.

2. Rapid, low-traumatic installation and reliable functional stabilization of spine elements.

This system has unique temperature characteristics. Preliminary deformation is done at temperatures not exceeding +10°C. Deformed shape is kept unchanged up to +26°C. Shape recovery occurs under heating up to +35°C.

Indications and Contraindications

The indications include2:

Type A: Installation by vertebral arches of the cervical, thoracic, and lumbar spine for the purpose of reinforcement of posterior ligament–cartilage structures. The use of fixing is indicated for compression fractures of vertebral bodies, degenerative-dystrophic affections, after operations on spinal marrow operations related with resection of arches or spinous processes of vertebrae (Fig. 37–1A) and for prevention of adjacent segment instability.

Type B: The vertebral fixing is intended for osteosynthesis and fixation of bone implants (Fig. 37–1B).

Type C: The fixing is intended for installation by spinous processes of thoracic and lumbar spine for reinforcement posterior ligament–cartilage structures in case of compression fractures of vertebral bodies and disruption of interspinous and supraspinous ligaments (Fig. 37–1C).

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Prosthetic Disk Nucleus Partial Disk Replacement: Pathobiological and Biomechanical Rationale for Design and Function Complications of Lumbar Disk Arthroplasty Tension Band System Cervidisc Concept, Six Years Follow-Up and Introducing Cervidisc II: DISCOVERY Rationale for Dynamic Stabilization MAVERICK Total Disc Replacement

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