Mandibular Reconstruction with the A-O Plate

Peter A. Hilger, MD, George L. Adams, MD

At the University of Minnesota and affiliated hospitals several methods of mandibular reconstruction have been used. From October 1978 through March 1984, 11 patients have undergone reconstruction with the A-0 plate technique. These patients had both traumatic and oncologic defects. All patients treated with this technique have achieved a solid mandibular arch. Included is a discussion of the theoretical advantages, preoperative prerequisites, and the operative technique. (Arch Otolaryngol 1985; 111:469-47 1)

Mandibular reconstruction is a complex task, as evidenced by the number of methods currently available.  No single  technique has clearly been established to be superior. There are three basic methods for reconstruction. The first, autologous bone brought in as a graft, includes the pectoralis myocutaneous flap with rib, the trapezius myocutaneous flap with the spine of the scapula, and free-flap transfers with microvascular anastomosis. The second method involves autologous bone held in position with a prosthesis. The particulate cancellous marrow (PCM) graft with titanium tray is an example of this method. The third general category of reconstruction involves bone grafting with autologous or homologous bone treated in some manner so as to make it tumor free or immunologically inert. This last technique is exemplified by the freeze-dried homologous mandibular reconstructive technigque described by Defries and autologous mandibular grafting with irradiated bone as described by Hamaker.

Each method has its own proponents and specific uses. Factors influencing the technique selected include the general status of the patient, the extent of bone and/or soft-tissue loss, location of the defect, dentition, previous irradiation, likelihood of recurrent disease, and the surgeon’s previous experience.

The objective of reconstructive surgery is to reestablish normal form and function. Not all patients who have lost a segment of the mandible due to trauma, infection, or tumor resection require, or are candidates for, osseous reconstruction. Fox example, not all patients who have had a composite resection including a portion of the mandibular angle and ascending ramus have been shown not to benefit from osseous reconstruction. It is clear that patient selection is a complex task and many authors have proposed criteria for surgery. Our objective is not to discuss all of the indications for surgery but to discuss our experience with the A-O (A-O indicates Arbeits Gemeinschaft für Osteosynthesefragen [Association for the Study of Internal Fixation]) plate technique that we have used for the past few years.

Interest in the A-0 plate technique for mandibular reconstruction was prompted by the favorable results we achieved with the dynamic compression plating system (DCP, EDCP) for mandibular fractures as reported at the thirds International Symposium of Facial Plastic and Reconstructive Surgery in 1979. Before we adopted the A-O plate technique as an option for mandibular reconstruction, most defects were repaired with the PCM method and noted an 88% success rate for 34 patients. Most of the failures in this group involved the symphyseal and body regions of the mandible.

These select patients for whom the PCM method ailed prompted a search for additional methods. We were attracted to the A-O plate technique because it has several theoretical advantages. Bony union is influenced by the degree of fragment immobilization and local blood supply. Approximately 80% of the bone grafted with the A-O plate technique is exposed to the surrounding vessels, as compared with 50% of the bone surface contained in the titanium tray with the PCM method. The screws selected for the A-O plate method engage both mandibular cortices, rather than one cortex as in the PCM method. This provides excellent immobilization. The A-O plate can be bent in three dimensions and thus contoured to fit the bony and soft-tissue defect, unlike the PCM tray that requires that the soft-tissue pocket be created to fit the tray. The bone grafts used with the A-O plate method are large, whereas the bone used for the PCM method must be small particles, and the larger bone fragments require fewer areas on bony union to create a solid mandibular arch. Finally, the A-O plate is applied to the facial cortex of the mandible, reducing the opportunity for intraoral exposure that can lead to graft loss.

TECHNIQUE

Mandibular Reconstruction, Technique - Minneapolis, MN
Fig 1. – There of several different reonstruction plates that are commercially available.

The details of the technique must be tailored for each case, but a general scheme has been followed for the patients in this series. Reconstruction is not attempted primarily. Adequate soft-tissue coverage, intraoral mucosal healing, resolution of any local infection, and completion of radiation therapy are achieved before bony repair is attempted. During this initial healing phase, when possible, the residual bony fragments are maintained in proper anatomic position with Kirschner wires or with an external fixation device. The soft-tissue pocket is developed and the residual and the residual bone debrided, exposing healthy bleeding bone before the graft material is harvested from the iliac crest. During this portion of the procedure fragment reduction is maintained with an external fixation device or intermaxillary fixation. The reconstruction plates are available in various lengths (Fig 1) and can be molded to fit the soft-tissue pocket with orthopedic plate benders (Fig. 2). This contrasts with the PCM method in which the soft-tissue pocket must be contoured to fit the preformed tray. The plate selected for each case is long enough to bridge the defect and overlap the remaining mandible, permitting placement of three or four screws in each fragment.

The bone graft is harvested from the iliac crest and consists of cancellous bone with a cortical cap. Several fragments are required for large defects, while a single fragment is suitable for smaller defects. Screws are used to secure the grafts to the plate when several bone grafts are used. When only a single graft is needed it is often possible to wedge it firmly between the mandibular stumps without directly securing it to the plate (Fig 3).

Mandibular Reconstruction, Technique, Minneapolis, MN
Fig. 2. – Countoring of reconstruction plate achieved with orthopedic plate bender.
Mandibular Reconstruction, Technique | Minneapolis, MN
Fig. 3. – Reconstruction platre secured to mandible with cortical and cancellous bone filling mandibular defect.

In all cases three or four screws are used to fix the plate to each mandibular fragment. The screws are available in various lengths and should be long enough to engage both mandibular cortices. The screw holes are created with a hand drill and the tapped to prevent bone necrosis and loosening of the screws and plate. A closed drainage system is used and the external fixation device or intermaxillary fixation removed at the end of the procedure.

RESULTS

Reconstruction with the A-O plate was attempted for 11 patients from October 1978 through March 1984. All but two patients who underwent reconstruction have been followed up for at least one year, and the average length of follow-up was four years.

The patients in this study were treated at St Paul Ramsey Hospital, the University of Minnesota Hospitals, and the Minneapolis Veterans Administration Hospital. All of the patients had sustained a full-thickness mandibular defect. The size of the defects ranged from 2 to 17 cm, and five of the patients had lost greater than 60% of the mandible. In all cases at least a portion of the defect involved the body and/or symphyseal areas. As previously noted, our past experience with the PCM method demonstrated that these were the most difficult areas to repair. Five patients had traumatic defects. Six patients had defects secondary to oncologic surgery. Four of these patients had radiation therapy before reconstruction was attempted, and three patients had osteoradionecrosis.

One patient referred for osteoradionecrosis did not have the residual fragments anatomically positioned. The ascending ramus was displaced medially and superiorly, and the temporalis, medial pterygoid, and masseter muscles were fibrosed. During the surgical procedure, when the ramus was mobilized, the oral cavity was entered. This was the only case in which this occurred and the procedure was terminated and reconstruction was deferred. Based on our series of patients who underwent reconstruction with the PCM method, the mandible is not grafted when intraoral exposure occurs. In two cases the plate was placed without a bone graft. However, in eight cases iliac bone we harvested was used with the plate. This latter approach is favored because the surgeon can remove the plate at a later date, should it become necessary, and yet maintain a solid mandible.

All ten grafts had a solid mandibular arch with the plate still spanning the defect. Most of the patients were edentulous or had few teeth, preventing an accurate assessment of occlusion. With one exception, the six patients grafted for a defect related to tumor treatment were edentulous. Two of the edentulous patients were able to wear dentures and have satisfactory mastication and occlusion. Occlusion in the group of patients with traumatic defects is equally as difficult to assess because most of the patients were edentulous or lost the dentate portion of the mandible. None of the patients have developed intraoral exposure of the graft. However, the plate became exposed extraorally in one patient treated for an oncologic surgical defect. This occurred in an area of thin soft-tissue coverage with in the area of previous radiation therapy. Neither the plate nor the bone graft were removed. A regional pedicle flap was used to cover the defect and the wound healed satisfactorily.

COMMENT

We have been impressed with the results achieved thus far with the A-O plate in view of the fact that most of the patients had unfavorable conditions for grafting. Several patients had radiation therapy before grafting and all of the defects involved the anterior portion of the mandible, an area with a higher incidence of failure.

This technique has several theoretical and practical advantages. With it, more bone is exposed to the local blood supply, excellent immobilization is possible, the graft can be more precisely contoured to fit the defect, and the lateral location of the plate reduces the risk of intraoral exposure.

It is important to reemphasize that this technique has been used as a delayed rather than primary method of reconstruction and it is our preferred technique for some, but not all, patients with mandibular defects. Those patients who have inadequate soft tissues in the area of the defect should have this problem improved with local or regional flaps before grafting, or they can be treated with other techniques such as free or pedicled osteomyocutaneous flaps.

References

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