TMJ - Joint Replacement System

A Intermedic Technology Ltda, representa no Brasil alguns dos maiores fabricantes mundiais de implantes cirúrgicos.

Desde 1996, ano de fundação, a confiança, tecnologia e presteza no atendimento fez dela uma das maiores e melhores empresas do país no ramo cirúrgico.

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Abaixo um post sobre um sistema de prótese da ATM fabricado pela W.Lorenz.

 

Pré-operative

After satisfactory induction of general nasotracheal anesthesia, the patient is prepped and draped in the usual manner. Twenty-six and twenty-four gauge stainless steel wires are used to place Ivy loop fixation wires in both the maxilla and the mandible, so that during the critical time of condylar prosthesis screw placement, the patient can be placed in inter-maxillary fixation.

1) Incisions

A standard endaural incision is made with dissection along the tragal cartilage down to the joint space itself, avoiding any damage to the upper trunk of the facial nerve. The root of the zygoma is identified and periosteum is stripped off to expose the zygoma. The dissection is then carried down to expose the capsule of the joint.

A modified posterior mandibular incision is then made approximately two finger breadths below, and posterior to, the angle of the mandible. This is truly a retro mandibular incision, which allows better visualization of the entire ramus and also permits rapid access to the terminal branch of the superficial carotid if any troublesome hemorrhage is encountered from the internal maxillary artery during the condylectomy. Dissection is carried through to the subcutaneous tissue until the marginal mandibular branch of the facial nerve is identified and retracted superiorly. Dissection is then carried in a plane between the anterior border of the sternocleidomastoid muscle and the submandibular gland. The facial artery and vein can be ligated at this time and then the aponeurosis between the masseter and pterygoid muscle is identified and incised. After stripping off the masseter muscle, the surgeon should be able to have full visualization of the lateral ramus up to the neck of the condyle.

 

2) Exposure of the Joint

Attention is then directed back to the joint itself where an incision is made along the posterior root of the zygoma and a full-thickness mucoperiosteal flap is elevated to expose the entire lateral surface of the glenoid fossa and the capsule of the joint itself. The neck of the condyle is isolated with condylar retractors and a two step condylectomy is performed.

 

 

3) Perfoming the osteotomy

A 1mm fissure burr is first used to make a traditional condylectomy cut at the level of the sigmoid notch. After the condyle is removed, the angle of the mandible is grasped securely with bone holding forceps and the ramus is pushed superiorly so that more of the superior ramal stump is visualized in the endaural exposure. This allows the second osteotomy to be performed, which is approximately 5mm below the sigmoid notch and can include the coronoid to be removed in a single section osteotomy. This is necessary to accommodate the thickness of the Lorenz glenoid fossa implant.

 

 

 

4) Preparing for the Fossa Prosthesis

 

A specially designed, large diamond burr is used to flatten the articular eminence. This removes the majority of the variability in the glenoid fossa. The end of the burr has a radial shape, which matches the medial radial surface of the fossa component.

 

 

 

 

 

5) Occlusion Placement

Surgical wounds are now packed with antibiotic-soaked sponges. (Irrigant for the entire case is antibiotic infused solution). The surgeon now re-enters the oral cavity and places the patient in the optimum desired occlusion with secure twenty-six and twenty-four gauge inter-maxillary wires. IMF screws can also be used as an alternative.

6) Sizing and Implantation of the Fossa Prosthesis

The surgeon changes his/her gown and gloves to place the fossa implant. The fossa trial (sizer) can now be used to assess the initial fit of the prosthesis, with the goal to have a tripod stable fit of the fossa with minimal dead space. At this point, the surgeon can determine which of the three sizes of the fossa prosthesis would best allow a minimum of four 2.0mm zygomatic screws to be placed. The difference between sizes is strictly in the flange area for screw placement options. The articular surface is identical between sizes. It is extremely important to reduce the bone on the medial surface of the glenoid fossa adequately enough to allow proper seating of the medial edge of the fossa prosthesis. ensure that the fossa is positioned so that it is approximately parallel to the Frankfurt-Horizontal line. This avoids an anterior-posterior or medio-lateral tilt to the implant.

Once the proper fit is achieved, two 2.0mm screws are used for the initial fixation.

7) Fitting of the Mandibular Component

The mandibular trial (sizer) is used to assess whether a 45mm, 50mm, or 55mm prosthesis will be used. It is also used to determine whether an optional narrow component or offset component are appropriate. There is unlimited size interchangeability between the mandibular components and the fossa components. The trial also allows the surgeon to determine whether the large diamond burr or rasp need to be utilized to contour the lateral surface of the ramus so there is a flush fit of the mandibular component against the ramus. The specially designed diamond rasp can be also used to radius the edge of the resected ramus. The mandibular implant and trial should not be bent in any way.

8) Range of Motion

Once the head of the permanent mandibular prosthesis is positioned in the mid portion of the glenoid fossa, two 2.7mm screws are placed temporarily to secure the prosthesis. When drilling the holes for the ramus prosthesis, it is important to approximate the position of the inferior alveolar nerve to avoid any damage while placing the screws. If desired, a drill guide is available to assist in drilling. Once the prosthesis is placed temporarily, and the wounds are covered with sterile drapes, the surgeon then goes back into the oral cavity and removes the intermaxillary fixation. The mandible should be put through a reasonable range of motion with an interincisal opening of 30 to 35mm to assess the mechanical functioning of the joint, and to look for any subluxation, dislocation, or mechanical obstruction. If there is any question that the patient has increased muscle tone under a light anesthetic, it may be necessary to request that the anesthesiologist administer a short acting muscle relaxant to make sure that there is proper mechanical joint function with a reasonable range of motion. If, under full muscle relaxation, there appears to be significant impairment to range of motion, it maybe important to assess whether a coronoid-ectomy is necessary or whether further stripping of the soft tissue attachments would be appropriate. If the range of motion and the occlusion are satisfactory, the maxillary and mandibular fixation wires could be removed at that time and an occlusive dressing is placed over the oral cavity.

9) Final Screw Placement

The remaining screws are then placed with a minimum of six screws recommended for securing the mandibular component. The implant may not be bent and great care should be taken to not scratch or damage the articular surface of the mandibular component.

Closure

The surgical wounds are then irrigated with antibiotic solution; the deep layers of the wounds are closed with 3-0 chromic, the subcutaneous layer is closed with 4-0 chromic, and the skin incisions are closed with 5-0 nylon. The pressure dressing is applied. At the end of the procedure, all of the fixation wires of the maxilla and mandible are removed, and the patient is extubated.

 

 

Rehabilitation and Follow Up

A regimen of jaw exercises is recommended after one day post-op and should be continued until maximum opening is achieved, or for at least six weeks. The post-operative evaluation form must be filled out at the prescribed follow-up intervals.

 

 

CREDITS : W. Lorenz - TMJ - Joint Replacement System (www.lorenzsurgical.com)