Condylar Prosthesis for the Replacement of the Mandibular Condyle

Indications for the application of an alloplastic prosthesis for the replacement of the mandibular condyle are extremely rare. Whenever possible, the reconstruction of the mandibular joint should be performed with autogenous material. Under certain conditions, however, it may be necessary to use a metal prosthesis. During the 20 years between 1974 and 1994, we treated 17 patients with 21 alloplastic prosthesis, mostly made out of steel. At the moment the use of an AO/ASIF alloplastic joint prosthesis is now permitted in the United States because they are FDA approved, currently as a 2.4 mm titanium locking reconstruction plate with condylar head right and left as 3 16, 4 18, and 5 20 hole sizes, and 2.4 mm titanium condylar plates 8 holes right and left (see Chapter 22).1–11

the condyle is replaced. In our patient group only partial arthroplasties were performed.

Patients

Between 1974 and 1994 17 patients received 21 prostheses. There were 10 females and 7 males. The mean age was 43.5 years (range 16 to 81). The first prosthesis ever used in our unit was placed in 1974 (surgery performed by Prof. Spiessl). This prosthesis in a young female is now in place for 23 years. The average duration of the 21 prosthesis until 1994 was 8.7 years (range, 13 to 244 months) (Figure 32.2).

Material

In the past, the system consisted of a prosthesis designed to replace the condyle without an artificial fossa. The prosthesis comes in three different sizes. The condylar part is shaped either like a sphere or a barrel. It is connected to a short prebent plate that can be fixed with four-to-six 2.7 screws at the ascending ramus. For those patients in whom part of the lateral mandible together with the joint was replaced, a prebent reconstruction plate with a condyle on top of the vertical part was used (Figure 32.1).

Tests have been made with titanum-coated prostheses and special adaptable condyles in combination with the THORP system. The adaptable version had joints in between the plate and condyle. The purpose was to facilitate the placement of the artificial condyle in the glenoid fossa. Because of technical problems, this version is no longer used.

Indications

In the majority of our patients (9 of 17) and the majority of all condyles replaced (12 of 21), the procedure was necessary because of an ankylosis. Most of these ankyloses were posttraumatic. One patient suffered from a Morbus Bechterew (spondylarthritis ankylopoetica) and had developed over a period of 18 years a bilateral ankylosis. Her range of motion at the time of surgery was 2 to 1 mm interincisal distance. She now says, 11 years after surgery, that she feels like a newborn person.

In 4 of 21 reconstructed joints, the indication was a tumor or metastasis. In these patients the lateral mandible together with the ascending ramus was replaced by a reconstruction plate with condylar head (Figure 32.3). Since 1994, we have immediately reconstructed the condylar area in severely comminuted fracture situations in several patients (Figure 32.4).

Generally one distinguishes between a total and a partial arthroplasty. In a total arthroplasty the condyle is replaced together with an artificial fossa. In a partial arthroplasty only

In most of the operations, a two-site approach (preauricular and submandibular) was used. In ankylosis operations, the ankylotic mass was removed to create a thicker than normal

FIGURE 32.3 Indications for surgery for 21 joint replacements between 1974 and 1994.

pseudofossa to prevent the danger of a perforation of the artificial condyle through the base of the skull. An ipsilateral coronoidectomy was usually performed. In all other instances, whenever possible, the disc was left in place as a protection against perforation of the fossa. As a further measure against the danger of perforation we have always tried to place the prosthesis slightly inferior to the fossa. This, of course, is possible only if just for joint replacement. In those patients where

both the joint and the lateral mandible must be replaced, it is especially difficult to place the condyle correctly into the natural fossa and keep it there. However, we have seen postoperative displacements of the condyle into the temporal fossa without clinical consequences (Figure 32.5). Whenever possible, in all patients, intermaxillary fixation was applied during surgery to identify the optimal position for the prosthesis.

Results

Only in one patient with one prosthesis for an ankylosis in 1981 was the prosthesis removed 5 years later in another unit. The precise reasons are not known to us. Originally the patient suffered from an ankylosis with only 2- to 3-mm interincisal distance. One month after surgery his range of motion was 22 mm. He was very uncooperative and did not come back for postoperative control and exercises. As far as we could find out at the time of removal, the distance was 13 mm and no lateral or anterior motion was possible. Several further attempts under general anesthesia were undertaken to improve the range of motion after the removal of the prosthesis.

In general, lateral and anterior motions are almost impossible in patients with two prostheses. In those with one prosthesis, such motion is possible in a limited range.

FIGURE 32.4 Replacement of the left mandibular condyle after a comminuted fracture in this area and the mandibular body on the opposite side. The patient was a severe polytraumatized patient and is tetraplegic.

FIGURE 32.5 Replacement of the chin and right side of the mandible because of an osteosarcoma with a 2.7 reconstruction plate with condylar head. The condylar head is displaced laterally out of the fossa. The patient lives with good comfort, and the plate has been in place for over 3 years.

In summary, indications for an artificial joint with an alloplastic prosthesis are rare. Although in all of our cases partial arthroplasties without fossa replacement were performed, perforation through the glenoid fossa was not observed. Periodic follow-up is necessary because a perforation in the area of the fossa can be asymptomatic. In our view, under certain conditions, the indication for an alloplastic prosthesis is given for ankylosed joints. Additional conditions are severely traumatized joints and patients with tumors invading the mandible or the soft tissues in the area of the joint. If possible, the patients must be well informed and able to be cooperative. Reconstruction with autogenous material, if the local and general conditions permit, is always preferable.

References

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FIGURE 32.7 Bilateral condylar replacement with steel prosthesis because of ankylosis: (a) 10 months postoperatively; (b) 3 years thereafter. Note: Anterior and posterior bony apposition around the artificial condyle.

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