Orofacial Regeneration

(Customised Distraction Osteogenesis)

The Spiral Vector Distracter® - World Wide Patents Pending

Originally described by Ilizarov in the 1950’s in the lengthening of limb by the manipulation of callus following osteotomy, with external pins passing through the skin. DO was later adapted for advancement of the facial bones using both internal screw devices and external pin distraction devices. These devices were developed as a more simple alternative to complex composite flap reconstruction of the facial skeleton which involve long complex surgical multisited and multistaged procedures. In particular the area of the chin is technically very difficult to reconstruct. All distraction devices to date have a problem with precise choice of vector leading to deformity, and malocclusion. External pins cause skin necrosis and scarring as they are pulled through the tissues with their attached bone. These devices have a low mechanical advantage leading to bending and fracture of transcutaneous pins. Reconstruction of the curved vector of the chin is difficult especially with external pins and their associated frames and this leads to unwarranted soft tissue damage.

The Spiral Vector Distracter® - World Wide Patents Pending

A proposed internal Spiral Distraction Device is proposed which permits:

Accurate presurgical planning using rapid prototyping, reverse engineering and Engineering Assisted Surgery PrinciplesTM
The accurate translation of the surgical plan into the patient.
Selection of a predetermined vector for optimum jaw contour. An internal device using cord of chain distraction techniques and an external capstan / key mechanism.
Improved Mechanical Advantage, with less force required for distraction and less soft tissue injury.
A Spiral Distraction mechanism using sharpened shuttle devices to assist cleavage of the tissues.
Easy assembly and disassembly.
A mechanism to facilitate bony union and overdenture attachment in the midline.
Easy removal of the device from the patient..

Spiral Distraction

A customised spiral distracter bar is manufactured to produce a mandibular contour which is prognathic, i.e. Class III. This bar is inserted with a frictional lock mechanism into two skeletal anchorage plates located on the mandibular ramus.

Spiral Vector Demonstration

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The spiral paths of distraction. Please right mouse click to replay movie

Two sharp shuttle (S) are screwed to the mobile osteogenic fragments following osteotomies adjacent to the anterior mandibular defect.

The shuttle has razor sharp edges to cleave through the tissues, and is screwed to the advancing bone fragment with 2mm screws, represented by the elastic band.

A capstan device is located in the floor of the mouth. A traction cord is attached to each shuttle and runs in a groove within the spiral vector bar to pass through a midline aperture to the capstan mechanism.

Removable key attachments penetrate the skin below the chin

The elastic band located on the posterior aspect of the shuttle provides stability for the demonstration of the spiral vector.

Vertex View

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Note three point fixation of overdenture with dental implants to prevent relapse of new chin position

The spiral vector is designed to produce a Class III mandibular prognathism, which permits bending of the callous (indicated in red) for bony overlap in the midline with a normal (Class I) mandibular projection. Fixation in the midline is achieved with a single lag screw which doubles as an overdenture abutment.

The "neomentum" is stabilised using two additional overdenture abutments in the proximal mandible posterior to the osteotomy cuts. This gives three point fixation of the new chin position until the callous matures.

Using this protocol it is estimated that a 6 cm defect can be closed in 43 days. The spiral nature of the distraction facilitates removal of the spiral vector bar, which becomes the meat in the sandwich with bone above and below at the end point of distraction. This means that removal of the bar may be achieved with an anterior path of withdrawal, through a simple mental (chin) incision +/- a lip spilt approach.

Removal of Device

At the end point of spiral distraction, the key attachments are removed.

An appropriate chin incision is made to expose the anterior aspect of the spiral distracter.

The shuttle screws are removed from the adjacent bone in the leading edge of the neo-mandible.

A specially designed ring hammer is hooked around the back of the capstan and with a sharp tap the spiral vector bar is removed with an anterior path of withdrawal. The skeletal anchorage components in the mandibular ramus may be removed through appropriate neck incisions, or, if smaller in design, could be left in situ. The mandible at this stage is Class III, and the anterior free bone fragments are bent towards the midline until they overlap, at which point they are screwed together with a position screw(s) or lag screw(s). This fixation screw device could incorporate an overdenture attachment system which perforates the oral mucosa for denture attachment.

The use of this device is associated with reduced surgical trauma and operating time and has applications in other areas of the skeleton.

Engineering Assisted Surgery - The Future of Mandibular Reconstruction

Crestal (alveolar) or lingual application of the reconstruction bone plate with low profile designs of prosthetic attachment systems may overcome the problem of long term ulceration of the plate through the skin invariably seen with the lateral (buccally) placed plate.

This complication appears to be related to pressure effects on the overlying skin and subcutaneous tissues, and occurs after two years.

Plate fenestration can be treated very simply by rotation of a local flap of tissue to cover the plate; however hyperbaric oxygen may also be required to promote healing in those patients who have been prescribed post operative radiotherapy.

Spiral distraction

Spiral distraction may afford a novel solution to the difficult reconstruction of the anterior mandibular defect and floor of mouth. The distraction procedure involves reduced surgical trauma and is carried out without any additional reconstructive flap surgery. Mobilisation of the advancing osteogenic bone fragments has a secondary effect on attached soft tissues, which are also subjected to traction forces. It is to be noted that defects in the floor of mouth may close by packing alone - without the use of flap surgery, and it is likely that such closure may be accelerated by soft tissue traction secondarily related to spiral distraction of the mandible.

Customised Biologically Active Implants

Engineering Assisted Surgery™ techniques lithography may also be used to design and manufacture customised implants impregnated with hormones that will turn the implant into living bone, and this is a particular exciting application of this technology. The technique would require primary healing of soft tissue cover over the reconstruction, which places it at a disadvantage over exposed prosthetic implants which require no flap cover and operations requiring less surgical trauma for the patient.