Bridging lower jaw defects with AO plates: comparison of THORP and 3-DBRP systems

Comparison of locking and non-locking reconstruction plate-screw system in lateral mandibular defects by finite element analysis

PURPOSE

The purpose of this study is to analyze and compare stress distribution on bone screws and plate systems in locking and non-locking screw-plates design in lateral mandibular defects.

MATERIAL AND METHODS

Solid mathematical model of mandible was created by three-dimensional finite elements analysis and 25 mm length of lateral resection (L defect) was performed on the model. Models were reconstructed with 2.4 locking and non-locking reconstruction plate system. Each masticator muscles attached to mandible were simulated as direction, attachment area and magnitude on 3D model to compare with reality. The stress formation on bone and hardware system were evaluated.

RESULT

The stress values on the cortical bone, plate and screw system were higher in conventional plate model than the locking system model. The highest stress values were measured in the proximal segment especially in conjunction with conventional screw system. Furthermore, the distribution of stress on the bone surface was more homogenous in the locking system.

CONCLUSION

It is evident that the use of the locking system in 25 mm length lateral mandibular defects provides an additional advantage over conventional systems in reconstruction models.

Bridging mandibular continuity defects with miniplates: an experimental study

Various miniplate fixation techniques were studied in dogs to determine whether the use of miniplate fixation provides sufficient stability in mandibular continuity defects. Continuity resections measuring 15 mm were made on the mandibles of 16 dogs and were bridged using 4 miniplate fixation techniques, each replicated 4 times. All dogs were placed on a normal diet throughout the postoperative period. Clinical and radiological examinations were carried out 6 weeks later. We found that the group with both double miniplates and bicortical screws was stable, whereas the groups utilizing either a single miniplate or monocortical screws were not. The results of this study indicate that using a combination of double miniplates and bicortical screws to bridge defects after mandibular resection produces stable and predictable results.

Adaquate fixation of plates for stability during mandibular reconstruction

PURPOSE

To determine the most appropriate plate fixation for dispersing the stress around screws in mandibular reconstruction.

MATERIAL AND METHODS

Forty-eight three-dimensional reconstructed mandibular models with Central (C) or right Lateral (L) defects were created and divided into three groups, fixed with: (1) two screws on each side, (2) three screws on the left side with the third (middle one) located distally, or (3) three screws on the left side with the third (middle one) located proximally. A 300N vertical load was applied to the left molar region. The maximum stress was calculated using a finite element method and statistically evaluated.

RESULTS

Stress was concentrated around the screw at the distal end of the mandibular halves on the loaded side ('crucial screw'). For the C defect, stress concentrated around the 'crucial screw' was greater when there were only two screws for fixation (20.55MPa) than when there were three screws (16.17MPa; p=0.022). No significant difference was found between the two groups with three screws for fixation. For the L defect on the other hand, stress on the 'crucial screw' was relatively greater when there were three screws for fixation (18.9MPa) than when there were only two screws for (12.83MPa; p=0.051). No significant difference was found between the two groups with three screws for fixation. As for the reconstruction plate, the stresses on the plates were not different among the various screw groups for fixation nor among the C and L defects.

CONCLUSION

This paradoxical result is explained by plate bowing. Thus in large defects screw positions should take into consideration the potential for plate bowing.

Primary oromandibular reconstruction using free flaps and thorp plates in cancer patients: a 5-year experience

BACKGROUND

Low-profile second-generation THORP titanium plates combined with soft tissues free flaps (forearm or TRAM) can be used for oromandibular reconstruction in patients with SCC in advanced stage (stage III-IV).

METHODS

To evaluate long-term stability and possible complications of this reconstructive technique, we recorded, retrospectively, data of 25 patients with posterolateral oromandibular defects after tumor resection collected during a 5-year period.

RESULTS

All free flaps were successfully transferred, although eight patients were initially seen with delayed hardware-related reconstructive complications: plate exposure in four patients and plate fracture in four patients.

CONCLUSIONS

Nowadays, the state-of-the-art treatment for mandibular defects is primary bone reconstruction with bone free flaps, but in selected cases (elderly patients, poor performance status, posterolateral oromandibular defects, soft tissue defects much more important than bone defects) the association with THORP plate-soft tissue free flaps represents a good reconstructive choice.

A comparative study on four screw-plate locking systems in sheep: a clinical and radiological study

Four mandibular screw-plate locking systems were studied in sheep. Three to four centimetres angular continuity resections of the mandible were performed and the defects bridged with pre-bent angular reconstruction plates fixed with four screws in the body part and three in the ramus. Each type was used four times. Clinical and radiological examinations were carried out 1 and 2 months later. All sheep were able to eat and ruminate normally throughout the postoperative period. Radiology revealed that 6/16 plates and 5/112 screws fractured during the follow-up period. In one type, no fracture occurred. Screw fracture was confined to just one reconstruction system. Six of 16 mandibles showed slight to moderate bone resorption under the plate. The results point to the internal shortcomings of the systems tested.

Use of a locking reconstruction bone plate/screw system for mandibular surgery

PURPOSE

This study examined the use of a locking reconstruction bone plate/screw system for use in mandibular surgery.

PATIENTS AND METHODS

All patients treated with a locking reconstruction bone plate/screw system for fractures of the mandible or continuity defects in an 18-month period were prospectively studied. Ease of use of the locking plate/screw system, characteristics of the fractures/defects, and complications were tabulated.

RESULTS

One hundred two locking bone plates were placed in 84 patients. Most patients (n=75) were treated for fractures of the mandible; there were eight continuity defects and one case of mandibular narrowing. There were no cases of malocclusion or difficulties encountered in using the plate/screw system. Loss of fixation was encountered in only one patient.

CONCLUSIONS

The use of a locking plate/screw system was found to be simple, and it offers advantages over conventional bone plates by not requiring the plate to be compressed to the bone to provide stability.

Fixation of vascularized bone grafts

In 24 patients, fixation of isolated or combined bone grafts has been performed exclusively with miniplates. Other than the lateral displacement of one osteomyocutaneous iliac crest graft, no complication occurred with regard to the fixation method chosen. In contrast to the clinical findings, our results of an animal experiment demonstrate less complications by fixation of vascularized bone grafts to mandibular angle defects (guinea pig) when THORP plates are used instead of miniplates. Whereas we consider miniplate fixation of vascularized bone grafts to be the method of choice, selected patients may require more stable fixation systems, especially when a high postoperative mobility may be expected or large amounts of the mandible including the condyle have to be reconstructed.