Stability testing of a two miniplate fixation technique for mandibular angle fractures. An in vitro study

Treatment modalities for mandibular angle fractures

PURPOSE

Management of mandibular angle fractures is often challenging and results in the highest complication rate among fractures of the mandible. Optimal treatment for angle fractures remains controversial. Historically, treatment of mandible fractures included intraoperative maxillomandibular fixation (MMF) along with rigid internal fixation. More recently, noncompression plates miniplates, which produce only relative stability, have gained popularity. The absolute necessity of intraoperative MMF as an adjunct to internal fixation has also become controversial. The current trends in the management of simple, noncomminuted mandibular angle fractures are examined.

MATERIALS AND METHODS

A survey was submitted to North American and European AO ASIF (Arbeits-gemeinschaft fur Osteosynthesefragen Association for the Study of Internal Fixation) faculty in July 2001. Statistical analysis of results included both Fisher's exact and chi-square tests. Results were considered significant if P <.05.

RESULTS

One hundred ten of 127 potential responses were received (87%). Among 104 surgeons who treat mandible fractures, 86 (83%) treat more than 10 mandibular fractures per year. Preferred techniques for simple, noncomminuted mandibular angle fractures in this group were: single miniplate on the superior border (Champy technique) with or without arch bars (44 surgeons, 51%); tension band plate on the superior border and nonlocking, bicortical screw plate on the inferior border (11 surgeons, 13%); dual miniplates (9 surgeons, 10%); a locking screw plate on the inferior border only (6 surgeons, 7%), and 3-dimensional plates (5 surgeons, 6%). Eleven surgeons (13%) gave multiple answers. Although only 13% of surgeons surveyed primarily use the combination of tension band and nonlocking, bicortical screw plates, many surgeons (73%) continue to use this technique in certain circumstances. Within this group, 32 (51%) place screws in a neutral position, while 31 (49%) place screws in an eccentric position, resulting in compression. For simple noncomminuted angle fractures, the number of surgeons performing internal fixation without MMF were: 14 often (16%); 20 occasionally (23%); 17 seldom (20%); and 35 never (41%). Surgeons treating more than 10 versus those who treat less than 10 fractures per year, International versus North American faculty, and Oral and Maxillofacial surgeons (OMS) versus non-OMS surgeons were compared. Surgeons who treat more than 10 fractures per year favor the Champy technique over the tension band and bicortical plate combination (44 [51%] vs 11 [13%]), while those surgeons who treat less than 10 per year favor the tension band and bicortical plate combination over the Champy technique (9 [50%] vs 3 [17%]; P < .01, Fisher exact test). International faculty are less likely to use intraoperative MMF than North American faculty (29 [81%] vs 31 [43%]; P < .01, Fisher exact test). OMS surgeons are less likely to use the tension band and bicortical plate combination than non-OMS surgeons (22 [56%] vs 42 [90%]; P < .017, Fisher exact test).

CONCLUSION

This survey suggests an evolution in the management of mandibular angle fractures. A single miniplate plate on the superior border of the mandible has become the preferred method of treatment among AO faculty. When using large, inferiorly based plates more surgeons are now favoring neutral rather than eccentric screw placement. Intraoperative MMF is not considered mandatory by some surgeons in certain circumstances.

Three-dimensional finite element analysis used to compare methods of fixation after sagittal split ramus osteotomy: setback surgery-posterior loading

We used three-dimensional finite element analysis to compare the biomechanical stability of bilateral sagittal split ramus osteotomies fixed by lag screws with linear and triangular configuration, and double or single six-hole miniplates with monocortical screws after set-back operation. The three-dimensional finite element model contained 122,717 elements and 25,048 nodes. Posterior occlusal loads were simulated on the distal segments. MSC Marc software was used to calculate the stress fields on both the segments and the fixing appliances. We conclude that either triangular lag screw configuration or double miniplates led to better stability and lower mechanical stresses near the osteotomy than the linear lag screws or single oblique miniplates.

Analysis of complications in fractures of the mandibular angle—a study with finite element computation and evaluation of data of 277 patients

AIM

The purpose of this study was to compute the load on different osteosynthesis plates in a simplified model using finite element analysis, and to find out whether miniplates were sufficiently stable for application at the mandibular angle.

PATIENTS

Data from 277 patients with 293 fractures of the mandibular angle have been evaluated.

METHODS

A computation model using finite elements was established in order to compute mechanical stress occurring in osteosynthesis plates used for fixation of fractures of the mandibular angle. In the second part of this study, the data from all in-patients treated for fracture of the mandibular angle were evaluated retrospectively. Age and sex of the patients, cause of fracture, state of dentition, type of therapy as well as complications were noted.

RESULTS

In those tests, both the 1.0 mm miniplate and the 2.3 mm module plate were sufficiently stable. The rate of major complications (requiring revisional surgery with general anaesthesia) amounted to approximately 17% in comminuted fractures, or in non-compliant patients in which primary stability with a single miniplate did not appear sufficient, so that other osteosynthesis methods were used in addition. This rate was considerably higher than that in simple mandibular fractures. Simple fractures of the mandibular angle were just treated with one miniplate following Champy's guidelines strictly. In these fractures the rate of major complications was only 2.3%.

CONCLUSION

In comminuted fractures and in non-compliant patients, the use of a stronger osteosynthesis material should be considered while in all other cases application of a single 1.0 mm miniplate was regarded as sufficient for fixation using open reduction.

[Load resistance of mandibular angle fracturs treated with a miniplate osteosynthesis]

AIMS

The aim of this study was to evaluate the load resistance of mandibular angle fractures treated with a miniplate osteosynthesis according to Champy.

MATERIAL AND METHODS

We evaluated 22 completely dentate patients with fractures of the angle in addition to 15 controls. An electric test procedure for the determination of the load resistance between the incisors, canines and molars was carried out 1-6 weeks after treatment.

RESULTS

At 1 week postoperatively 90 N was registered between the molars while after 6 weeks this was 148 N. This revealed only 31% and 58% of the maximal vertical load found in the controls, respectively.

CONCLUSION

The minipate osteosynthesis according to Champy offers a secure method in the treatment of mandibular angle fractures with sufficient stability. Maximum voluntary bite forces were not registered during the time of healing.

Fixation of mandibular fractures with 2.0-mm miniplates: review of 191 cases

PURPOSE

Our goal was to study the use of 2.0-mm miniplates for the fixation of mandibular fractures.

PATIENTS AND METHODS

Records of 191 patients who experienced a total of 280 mandibular fractures that were treated with 2.0-mm miniplates were reviewed. One hundred twelve of those patients, presenting 160 fractures, who attended a late follow-up were also clinically evaluated. Miniplates were used in the same positions described by AO/ASIF. No intermaxillary fixation was used. All patients included had a minimum follow-up of 6 months. Demographic data, procedures, postoperative results, and complications were analyzed.

RESULTS

Mandibular fractures occurred mainly in males (mean age, 30.3 years). Mean follow-up was 21.92 months. The main etiology was motor vehicle accident. The most common fracture was the angle fracture (28.21%). Twenty-two fractures developed infection, for an overall incidence of 7.85%. When only angle fractures are considered, that incidence is increased to 18.98%. Although only 1 patient (0.89%) described inferior alveolar nerve paresthesia, objective testing revealed sensitivity alterations in 31.52% of the patients who had fractures in regions related to the inferior alveolar nerve. Temporary mild deficit of the marginal mandibular branch was observed in 2.56% of the extraoral approaches performed and 2.48% presented with hypertrophic scars. Incidence of occlusal alterations was 4.0%. Facial asymmetry was observed in 2.67% of the patients, whereas malunion incidence was 1.78%. Fibrous union, mostly partial, occurred in 2.38% of the fractures, but only 1 of those presented with mobility (0.59%). Condylar resorption developed in 6.25% of the fixated condylar fractures. Mean mouth opening was 42.08 mm.

CONCLUSION

The overall incidence of complications, including infections, was similar to those described for more rigid methods of fixation.

Bite forces in patients after treatment of mandibular angle fractures with miniplate osteosynthesis according to Champy

Maximal biting forces were evaluated in 22 patients with mandibular angle fractures treated with miniplate osteosynthesis according to Champy. An electric test procedure for evaluating the load resistance between the incisors, canines and molars was carried out 1 to 6 weeks following the treatment and additionally in 15 controls, too. This revealed that after surgical fracture treatment 1 week postoperatively only 31%, of the maximal vertical loading found in controls was registered. These values increased to 58% at the 6th week postoperatively.

A biomechanical evaluation of mandibular angle fracture plating techniques

PURPOSE

The purpose of this investigation was evaluate the biomechanical behavior of a vast array of fixation philosophies and techniques that address mandibular angle fractures.

MATERIALS AND METHODS

A total of 150 polyurethane synthetic mandible replicas (Synbone, Laudquart, Switzerland,) were used in this investigation. Five controls and 5 each of 14 different fixation philosophies and techniques were subjected to vertical loading at the incisal edge and then repeated for contralateral loading in the molar region by an Instron 1331 (Instron, Canton, MA) servohydraulic mechanical testing unit. The fixation philosophies and techniques evaluated were the lag screw technique, monocortical superior border plating techniques with varying sizes of plates and screws, monocortical 2-plate techniques with varying forms of fixation, monocortical tension band systems with associated bicortical stabilization plates of various types, and various forms of reconstruction plates. Load/displacement data within a 0 to 200 N range were recorded. Yield load, yield displacement, and stiffness were determined. Mean and standard deviations were calculated, and statistically significant differences within and among categories were determined using an analysis of variance (P <.05). Second-order polynomial best-fit curves were also created for each group to further evaluate and compare the mechanical behavior.

RESULTS

For incisal edge loading, statistically significant differences (P <.05) were found for stiffness between some of the monocortical superior border fixation techniques, as well as for yield displacement between several forms of monocortical 2-plate fixation techniques. No other differences were found within categories or among the groups that best represented their categories. For contralateral molar loading, statistically significant differences existed within and among categories.

CONCLUSIONS

Under the conditions of this experiment, all systems met or exceeded currently identified postoperative functional requirements for incisal edge loading, but failed to meet them for contralateral molar loading.

A computer study of biodegradable plates for internal fixation of mandibular angle fractures

PURPOSE

This computer-based study was performed to determine the suitability of small biodegradable plate systems for mandibular angle fractures.

MATERIALS AND METHODS

In a 3-dimensional computer model of the mandible, fracture mobility and plate strain were calculated for bite forces applied on 13 bite points on the dental arch. The angle fracture was fixed with 2 polylactide (PLA) midiplates or with 2 PLA maxiplates. The first plate was positioned buccally on the external oblique ridge. Two positions of the second plate were studied: halfway up the height of the mandible or on the lower border. Maximum fracture mobility was set at a limit of 150 microm to enable undisturbed fracture healing. Maximum plate strain was set at the yield strain of PLA.

RESULTS

Fixation with the PLA maxiplates, with the second plate positioned halfway up the height of the mandible, resulted in fracture mobility below the set limit for all bite points. For the other PLA fixation strategies, fracture mobility exceeded the set limit. Fixation with the second plate positioned halfway up the height of the mandible generally resulted in less fracture mobility than with the plate positioned on the lower border. The yield strain of PLA was not exceeded in any of the fixation strategies.

CONCLUSIONS

Based on the computer model, 2 PLA maxiplates are suitable for fixation of mandibular angle fractures. One plate should be positioned buccally on the external oblique ridge, and the other should be positioned halfway up the height of the mandible.

Treatment of mandibular angle fractures with a malleable noncompression miniplate

PURPOSE

This study evaluated the results in patients treated for fractures of the mandibular angle with a single, thin, malleable miniplate designed for use in the midface.

PATIENTS AND METHODS

Forty-six patients with 51 fractures of the mandibular angle were treated by open reduction and internal fixation using one noncompression, thin, malleable miniplate and 1.3-mm self-threading screws placed through a transoral incision. No patient was placed into postsurgical maxillomandibular fixation. They were prospectively studied for complications.

RESULTS

Seven patients (15.2%) experienced complications. All were considered minor and did not require hospitalization. Three had asymptomatic fracture of the bone plate, but at the time of diagnosis the fracture had already healed and it required no treatment. Two patients had fracture of the bone plate with continued fracture mobility requiring maxillomandibular fixation. Three minor infections occurred requiring intraoral incision and drainage.

CONCLUSIONS

The use of this small bone plate for fractures of the angle of the mandible provided adequate fixation in most cases but was associated with an unacceptable incidence of plate fracture. However, the results also indicate that the fixation requirements for angle fractures is less than previously thought.

A three-dimensional study of bending and torsion moments for different fracture sites in the mandible: an in vitro study

The aim of the study was to determine and compare bending and torsion moments across mandibular fractures, for different positions of the bite point and different sites of the fracture. Three identical resin mandibles, each with a single fracture, were used. The fracture sites were in the angle, body and symphyseal regions. A polyethylene bone plate was used for fixation. Simulated bite forces were applied at 13 bite points. For each bite point, the displacements of the fragments were registered and converted into bending and torsion moments across the fracture. Positive bending moments were defined as those moments that caused compression at the lower border and tension at the alveolar side of the mandible; negative bending moments did the opposite. Angle fractures had relatively high positive bending moments. Body fractures had positive as well as negative bending moments and the highest torsion moments. Symphyseal fractures had negative bending moments only and relatively high torsion moments. It was found that angle, body and symphyseal fractures each have a characteristic load pattern. These load patterns should play a decisive role in the treatment of mandibular fractures with regard to number and positioning of plates.

One- or two-plate fixation of mandibular angle fractures?

Standard treatment of mandibular angle fractures with miniplates, according to the recommendations of Champy et al. (1976), consists of fixation with one plate at the superior border of the mandible ventral to the external oblique line. In certain constellations, a second miniplate at the lower mandibular margin may provide additional stability. In contrast, extremely high complication rates following two-plate fixation of mandibular angle fractures were reported by Ellis and Walker (1994). In a prospective randomized study, 31 consecutive patients were treated with 2.0 mm (mini) plates (Synthes Co., Switzerland). One group was treated with one plate, the other one with two plates. In none of the patients was intermaxillary immobilization used. Follow-up was performed 6 months postoperatively, consisting of clinical and radiographic examination. No significant differences (P = 0.74 for infection, and P = 1.0 for occlusal and postoperative sensory disturbance) in postoperative short- or long-term complications were found between the two groups. The results are compared with our experimental investigations presented at the annual congress of the Germany Society of Oral and Maxillofacial Surgery, 1995. Two-plate fixation may not offer advantages over single-plate fixation in general. However, individual fracture constellations may benefit from variation in plate(s) localization. Factors contributing to complications in mandibular angle fractures are discussed.

A three-dimensional study of loads across the fracture for different fracture sites of the mandible

The loads across the fracture depend on variables such as position of the fracture and the bite point. Up to now, no study has described systematically the influence of these two variables on these loads. The aim of this study was to describe and compare value and direction of the loads across the fracture for different positions of fractures in the mandible. In a three-dimensional model, bending and torsion moments and shear forces were compared for five mandibular fractures. The fractures were located in, respectively, the angle, posterior body, anterior body, canine and symphysis region. Positive bending moments were defined to give compression at the border, negative bending moments to give compression at the alveolar side of the mandible. The angle and posterior body fracture have high positive bending moments, small torsion moments and high shear forces. The anterior body, canine and symphysis fracture have high negative bending moments and high torsion moments with similar maximum values. The number of bite points with negative bending moments were different for all fractures. These bite points were always located on the fractured side. It is concluded that mandibular fractures can be divided roughly into two groups with similar load patterns across the fracture. One group consists of angle and posterior body fractures, the other group consists of anterior body, canine and symphysis fractures.

A comparison of mandibular angle fracture plating techniques

OBJECTIVE

The purpose of this investigation was to compare the conventional technique of mandibular angle fracture plating with two biomechanically dissimilar techniques in their abilities to resist vertical loads similar to masticatory forces.

STUDY DESIGN

Three groups of five synthetic hemimandibles with simulated fracture repairs were compared for their capabilities to resist vertical deformation. The conventional group was stabilized with a thin tension band system at the superior border and thick stabilization plate system at the inferior border. The nontraditional group was stabilized with a thick tension band system at the superior border and thin stabilization plate system at the inferior border. The two miniplate group was stabilized with a thin tension band system at the superior border and thin stabilization plate at the inferior border. A cantilever beam design was used. Testing was performed with an instron 8511.20 (Instron Corp., Canton, Mass.) mechanical testing device. The three groups were compared with a two way analysis of variance.

RESULTS

The forces resisted by the conventional group (167.6 +/- 18.2 N), the nontraditional group (156.3 +/- 33.9 N), and two miniplate group (154.0 +/- 18.4 N) were not statistically different (F = 0.44, p > 0.66). All failures occurred at the tension bands secured with monocortical screws.

CONCLUSIONS

Under the conditions described in this in vitro investigation, plate thickness or pattern made no difference. All failures in this experiment occurred with monocortical screws in the superior border tension band system.

Treatment of mandibular angle fractures using one noncompression miniplate

PURPOSE

This study evaluated the results in patients treated for fractures of the mandibular angle with a single miniplate.

PATIENTS AND METHODS

Eighty-one patients with fractures of the mandibular angle were treated by open reduction and internal fixation using one noncompression miniplate with 2.0-mm self-threading screws placed through a transoral incision. No patient was placed into postsurgical maxillomandibular fixation. They were prospectively studied for complications.

RESULTS

Thirteen patients with angle fractures (16%) experienced complications requiring secondary surgical intervention. Most of the complications (n = 11), however, were minor and could be treated in the office. Most commonly, intraoral incision and drainage and later removal of the bone plate were required. All patients with minor complications had clinical union. Only two complications required hospitalization for intravenous antibiotics and further surgery. One of these patients had a fibrous union requiring a bone graft.

CONCLUSIONS

The use of a single miniplate for fractures of the angle of the mandible is a simple, reliable technique with a relatively small number of major complications.