Bone anchored ear prosthesis

The management of microtia in Hemifacial microsomia is complicated by the need for reconstructive surgery for the surrounding facial anomalies. It is therefore sometimes difficult to decide which to do first. There is no clear rule. Often the decision will be made according to the individual case and the wishes of the parents and child.

The microtic ear in Hemifacial microsomia is commonly in an abnormal position. In general this can be managed by the excision of such remnants usually with primary repair and the construction of a prosthetic ear in an ideal position relative to the contralateral unaffected side. Sometimes attention has to be given to the augmentation of the surrounding soft tissues to achieve a good result. The presence of an malpositioned ear canal makes prosthetic rehabilitation more difficult and will need to be managed with assistance from the relevant otologist/ENT surgeon.

This illustration shows the ideal position for titanium implants in relation to the prosthetic ear.

We will describe 2 options for planning the procedure.

• An impression is taken of the normal ear and a plaster model made.
• A wax ear is manufactured as a mirror image of the ear model.
• Holes are made in the wax ear in the ideal position for the placement of two implants.

The ear is positioned on the affected side and moved around until its position is ideal and symmetric.

The sites for implant placement are marked on the skin with a pen using the wax template.

An impression is made of the abnormal side, a plaster model made and the implant positions marked on that model.

A plastic template (surgical drilling guide) is made on the model for use at the time of surgery.

A high definition CT-scan is obtained of the patient's whole head and face including both hard and soft tissues.

Planning is then carried out using computer assisted planning software using the following steps:

Step 1: A mirror image of the normal ear soft tissues is produced.

Step 2: The mirrored ear is overlayed on the affected side and moved until its position is ideal and symmetric.

Step 3: The virtual implants are planned on the 3D-virtual model.

A cross section is made through the implant holes and surrounding bone in the virtual model to check the quantity and quality of the surrounding bound (shown in red). If the bone is not of adequate thickness or of poor quality, other implant positions must be considered.

Step 4: When the implant positions and the bone stock around them are acceptable, a template or surgical drilling guide is designed. This is generally done on the virtual model, and then manufactured by rapid prototyping.

Surgery to insert the implants is carried out in
two stages in children but generally in one stage in adults. The rationale for this is that the bone in children is quite soft and primary loading of the implant should not be attempted.

Generally one must allow four months to elapses between the two stages to ensure adequate osseointegration of the implants.

The implants used are craniofacial flanged fixtures which are made of commercially pure titanium.

If an external guide is being used, the sites for the implants are marked on the skin and subcutaneous tissue using a long needle and ink. An incision is made through the skin and down to the periosteum posterior to the proposed site of the implant placement.

A flap of skin and subcutaneous tissue is raised exposing the underlying periosteum. If a bone fitting guide has been constructed this is then placed on the surface of the bone (although sometimes it can be placed over the periosteum instead). The implant sites are marked on the bone with ink. If an external guide has been used, the ink markings are identified.

If the periosteum has been left on the bone, a circle of periosteum is incised around each implant site.

A drill drilling sequence is then followed to prepare the osteotomies to receive the flanged fixtures. Chilled saline irrigation is used to minimize the risk of bone injury due to overheating.

The implants are now inserted using a drill at very low speed and hand tightened with a wrench.

If a two stage procedure is being carried out, cover screws are inserted in the implants to protect the internal holes within the implants from the ingrowth of bone or soft tissue.

The incision is closed in layers and the implants are left to osseointegrate undisturebed for
approximately 4 months.

Skin tags and/or skin ear remnants are not
normally removed until the second stage.

If a one stage procedure is carried out, the imlants are immediately loaded as described below.

If a one stage is being performed, the residual ear tags and ear remnants are excised. The skin flap is thinned to ensure that the skin around the implant abutments is thin and tightly bound to the bone.

If a two stage procedure is being carried out, the ear tags and ear remnants are excised. A skin flap is raised over the site of the implants and the implants are identified and checked for osseointegration. The cover screws are removed. The skin flap is thinned, replaced and sutured.

A biopsy punch is used to expose the implants. Titanium abutments are screwed into the implants.

It is sometimes preferable to replace the skin and subcutaneous tissues over the implant site with a split skin graft to ensure that the soft tissue covering the implants is thin and bound down to the bone minimizing the risk of chronic inflammation around the fixtures.

Healing caps are then screwed into the abutments to help retain the dressing.

Prosthetic treatment usually commences 4-6 weeks after the second stage.

Construction takes 2-3 days and the patient is present while the Prosthetist carves, fits and caracterizes the prosthesis.

The first stage is to construct a cast custom gold bar.

The bar is screwed into the abutments with gold screws.

With the bar in place, the next step is construction of the substructure.

This is made from hard plastic and holds the gold clips that attach to the bar. This substructure will be bonded into the silicone prosthesis.

The ear prosthesis is initially carved in wax to enable adjustments to the shape and fit to be made.

Once the position and shape are satisfactory, the edge of the wax prosthesis is closly adapted to the patients’ skin.

The wax pattern is then flasked to allow for the production of the silicon prosthesis.

The flask can be used to produce a number of duplicates of the prosthesis if needed.

Once the prosthesis fabricates the silicone prosthesis, it is fitted to the patient and any minor colour adjustments made.

The patient is shown how to attach and remove the prosthesis.

Magnets may also be used instead of a bar and clip arrangement to maintain the prosthesis.

These are typically bonded directly into the body of the prosthesis.

The sterile dressing placed over the skin incisions is maintained for a minimum of 48 hours. Thereafter routine wound care should be instituted around the fixtures.

Antibiotic prophylaxis is continued for 1-5 days depending on the nature, complexity, and duration of the surgical procedure.

Remove sutures from skin after approximately 5 days if nonresorbable sutures have been used.

Regular follow up examinations to monitor healing are required.

Avoid sun exposure and tanning to skin incisions for several months.