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

Pre-contoured reconstruction plate fabricated via three-dimensional printed bending support

A mandibular continuity defect can be repaired using either a prosthetic device or autogenous bone. A titanium reconstruction plate can be used with a localized or vascularized flap over the defect of the mandible. Unfortunately, the plate may fail due to plate exposure, screw loosening, fracture, or infection, and will need to be removed. Plate exposure though the skin or mucosa is one of the main reasons for failure. In the present work, the authors introduced a lingually positioned reconstruction plate fabricated via three-dimensional printed bending support. This custom reconstruction plate can avoid plate re-exposure as well as reduce surgical errors and operation time.

Novel finite element-based plate design for bridging mandibular defects: Reducing mechanical failure

INTRODUCTION

When the application of a free vascularised flap is not possible, a segmental mandibular defect is often reconstructed using a conventional reconstruction plate. Mechanical failure of such reconstructions is mostly caused by plate fracture and screw pull-out. This study aims to develop a reliable, mechanically superior, yet slender patient-specific reconstruction plate that reduces failure due to these causes.

PATIENTS AND METHODS

Eight patients were included in the study. Indications were as follows: fractured reconstruction plate (2), loosened screws (1) and primary reconstruction of a mandibular continuity defect (5). Failed conventional reconstructions were studied using finite element analysis (FEA). A 3D virtual surgical plan (3D-VSP) with a novel patient-specific (PS) titanium plate was developed for each patient. Postoperative CBCT scanning was performed to validate reconstruction accuracy.

RESULTS

All PS plates were placed accurately according to the 3D-VSP. Mean 3D screw entry point deviation was 1.54 mm (SD: 0.85, R: 0.10-3.19), and mean screw angular deviation was 5.76° (SD: 3.27, R: 1.26-16.62). FEA indicated decreased stress and screw pull-out inducing forces. No mechanical failures appeared (mean follow-up: 16 months, R: 7-29).

CONCLUSION

Reconstructing mandibular continuity defects with bookshelf-reconstruction plates with FEA underpinning the design seems to reduce the risk of screw pull-out and plate fractures.

Mechanical stress in plates for bridging reconstruction mandibular defects and purposes of double plate reinforcement

PURPOSE

To evaluate the biomechanical performance of a commercially available bridging plate (2.4) as well as screws and bone simulating the reconstruction of hemimandibular defects and to indicate alternatives of reinforcement to prevent plate fractures either by strength or fatigue.

MATERIAL AND METHODS

Two common hemimandibular defects are investigated using computed finite element analysis (FEA) approach. Simplified and refined computational models are developed for the geometry of the screw. Conditions of non-locking and locking plate-screw interfaces are considered. Static loads of 120 N are applied. Von Mises stresses and fatigue are calculated. As reinforcement, a second complete or partial plate is placed onto the original plate.

RESULTS

Results demonstrate that reconstruction plates are often subjected to excessive stress that may lead to fracture either by strength or by fatigue. An attached complete or partial second plate is able to reduce stress in the plate, in screws and bone so that stress remains below the allowable limit of the materials.

CONCLUSION

A simplified technique of attaching a whole or sectioned second plate onto the original plate can reduce the stress calculated and may reduce the frequency of plate fractures for the patient's comfort, security and financial savings.

Pulled-out locking screw re-screwed spontaneously in anterior cervical decompression and fusion with the zero-profile implant system: A case report

RATIONALE

The zero-profile, standalone device (Zero-P, Synthes GmbH, Switzerland) has been reported to be an effective and safe treatment method with similar clinical outcomes compared with plate. Instrumental complications concerning Zero-P have been little reported. Considering the rarity, we present this amazing case to share with our spinal surgeons and instrument specialists.

PATIENT CONCERNS

A 46-year-old man patient presented to our hospital with neck and shoulders pain for 23 years, numbness and weak-ness of right hand for 6 months.

DIAGNOSES

Hypoesthesia in the right C6 and C7 roots distribution, myodynamia weakness of the right little finger was detected from physical examination. Two-level anterior cervical decompression and fusion (ACDF) using the Zero-P was performed via a classic right Smith-Robinson approach after induction of general anesthesia. Three months postoperative x-rays showed a good position of the implant. Six months postoperative x-rays showed a locking screw at the segment C6/7 pulled out. The patient was diagnosed as screw pullout after ACDF.

INTERVENTIONS

The patient was treated conservatively with regular follow-up as he was asymptomatic and no evidence of esophageal perforation was detected.

OUTCOMES

The patient was followed again and 24 months postoperative x-rays also showed the pulled-out locking screw had re-screwed spontaneously. The patient was noticed that a revision surgery was needed if symptoms occur. At present bony union is not reached but he is still asymptomatic.

LESSONS

Pulled-out screws re-screwed spontaneously are rare but it does occur. Insertion angle may affect the stability of the Zero-P device, and the repeated micro-motion may be the critical reason of the screw pull-out and re-screwing. The management of screws pull-out after ACDF remains individualized and a revision surgery is not necessary for every patient. Conservative treatment such as orthosis and regular follow-ups may be suitable for some asymptomatic patients.

Reconstruction plates used in the surgery for mandibular discontinuity defect

OBJECTIVES

The purpose of this study was to analyze the survival rate of reconstruction plates that were used to correct mandibular discontinuity defects.

MATERIALS AND METHODS

We analyzed clinical and radiological data of 36 patients. Only discontinuous mandibular defect cases were included in the study. Reconstruction plate survival rate was analyzed according to age, gender, location of defect, defect size, and whether the patient underwent a bone graft procedure, coronoidectomy, and/or postoperative radiation therapy (RT).

RESULTS

Plate-related complications developed in 8 patients, 7 of which underwent plate removal. No significant differences were found in plate survival rate according to age, gender, location of defect, defect size, or whether a bone graft procedure was performed. However, there were differences in the plate survival rate that depended on whether the patient underwent coronoidectomy or postoperative RT. In the early stages (9.25±5.10 months), plate fracture was the most common complication, but in the later stages (35.75±17.00 months), screw loosening was the most common complication.

CONCLUSION

It is important to establish the time-related risk of complications such as plate fracture or screw loosening. Coronoidectomy should be considered in most cases to prevent complications. Postoperative RT can affect the survival rate and hazard rate after a reconstruction plate is fitted.

Evaluation of fracture healing and subimplant bone response following fixation with a locking miniplate and screw system for mandibular angle fractures in a sheep model

This study aims to establish a mandible fracture model, and to review fracture healing following fixation with a locking miniplate system. Eighteen 2-year-old sheep were divided into three groups of six. Each animal had a single fracture that was anatomically reduced and internally fixed by a single 4-hole plate with two monocortical screws each side of the fracture. The fractures were internally fixed with poorly contoured conventional miniplates or poorly contoured mini-locking plate or well contoured conventional miniplates. Two sheep in each of the three groups were killed at 2, 4 and 8 weeks after surgery. The mandibles were radiographed then decalcified specimens were reviewed microscopically. No clinical difference was observed between the groups. All fractures were at an advanced stage of bony union by 4 weeks. Fracture union appeared radiographically more advanced with the locking plate system. This study established a protocol for simulating a fracture model for the study of fracture healing. A more advanced stage of union was seen for fractures internally fixed with locking plates/screws than with a conventional system. The observations suggest the purported biological benefits of locking miniplate system do exist.

Skeletal stability after mandibular setback surgery: bicortical fixation using a 2.0-mm locking plate system versus monocortical fixation using a nonlocking plate system

PURPOSE

This study was conducted to compare the time-course changes in condylar long-axis and skeletal stability after sagittal split ramus osteotomy (SSRO) with bicortical plate fixation versus monocortical plate fixation.

PATIENTS AND METHODS

Of a group of 40 Japanese patients diagnosed with mandibular prognathism, 20 underwent SSRO with bicortical plate fixation using a locking plate system and the other 20 underwent SSRO with monocortical plate fixation using a conventional plate system. The time-course changes in condylar long-axis and skeletal stability were assessed through axial, frontal, and lateral cephalograms.

RESULTS

Significant differences were found between the 2 groups in changes of the left condylar angle between the initial and 1-month measurements (P = .0454) and in ANB between the 1- and 3-month measurements (P = .0206); however, no significant differences were found between the 2 groups in the other measurements in each time interval.

CONCLUSIONS

Our findings suggest no significant differences in postoperative time-course changes between bicortical plate fixation using a locking plate system and monocortical plate fixation using a conventional plate system.

Biomechanical testing of different osteosynthesis systems for segmental resection of the mandible

PURPOSE

This investigation assessed the mechanical behavior of 3 different locking and nonlocking reconstruction systems-Unilock 2.4, Reconstruction 2.4, and Reconstruction 2.7-with regard to plate and screw fracture.

MATERIALS AND METHODS

Five different plate/screw configurations (Unilock 2.4-locking screws, Unilock 2.4 -conventional screws, Reconstruction 2.4-conventional screws, Reconstruction 2.7-conventional screws, and Unilock 2.4-locking screws with a 1-mm gap; Synthes, Umkirch, Germany) were tested on synthetic mandibles. All mandibles were resected on the left side between the canine and third molar, reconstructed, and loaded cyclically between 30 and 300 N up to 250,000 cycles or until screw or plate failure occurred.

RESULTS

No screw fractures were observed. All plates fractured close to the distal fragment. The Unilock plates fixed with locking screws withstood significantly more cycles until failure than the Reconstruction plates 2.4 fixed with conventional MF-Cortex screws. No significant differences were found in the other groups. Only 2 of the 34 plates tested, both of the Reconstruction 2.7 system, reached the runout limit.

CONCLUSIONS

Unilock plates fixed with locking screws have a higher long-term stability than the Reconstruction 2.4 system. A 1-mm gap between the plate and mandible does not lead to early screw failure in the Unilock 2.4 system with locking screws. The Reconstruction 2.7 system seems superior if well contoured, because 2 of those plates reached the runout limit; however, this system is not as easy to handle as the 2.4 systems, and good contouring is difficult to achieve. Therefore, we consider the Unilock 2.4 system with locking screws the best choice.

Analysis of complications after reconstruction of bone defects involving complete mandibular resection using finite element modelling

BACKGROUND

In a retrospective study, risk factors for complications after the bridging of mandibular defects using reconstruction plates were reviewed. Especially the loosening of the plate-screw-mandible complex should be analyzed with a finite element model in order to reduce plate complications in future.

PATIENTS AND METHODS

We examined 60 patients who underwent a treatment with reconstruction plates after tumor resection during a period of 10 years. The problem of screw loosening was additionally reviewed by means of a finite element study, and a model for the loosening process was developed.

RESULTS

Our postoperative examination showed that 26 patients suffered from complications that required an early removal of the plate. These complications were oral or extraoral plate exposures, the looseness of screws with or without plate displacement, and plate fractures. Thereby, we noticed that maxillary and mandibular areas of opposing teeth, the size of the mandible defect, and the crossing of the orofacial midline are all risk factors for plate complications. On the basis of the finite element model, a modified arrangement of the screws was derived. Hence, a new type of resection plate was established.

CONCLUSIONS

By repositioning the screw holes along the long axis of the plate, the transition from tensile force to torque force of the screws in the screw-plate-bone complex can be minimized. Thereby, the complication of screw loosening will be considerably reduced.

Fracture of titanium plates used for mandibular reconstruction following ablative tumor surgery

PURPOSE

The purpose of this study was to identify reasons for fracture of titanium mandibular reconstruction plates, when used to bridge lateral mandibular defects after ablative tumor surgery.

MATERIALS AND METHODS

Sixteen titanium reconstruction plates from sheep mandibles were examined to identify reasons for the plate fractures. The broken plates and the seemingly unbroken plates were examined separately. The plates were removed from the mandibular bone and inspected by dye penetrant examination, metallography, optical microscope, scanning electron microscope, and energy dispersive X-ray spectrometer. Furthermore, axial load fatigue tests were performed in two different environments, air and physiologic salt solution, 0.9% NaCl, to compare titanium behavior in air and the human body.

RESULTS

The site of crack initiation was the inner curvature of the reconstruction plate, and the cracks initiated as a result of stress concentration in the shoulder fillet of the plate. The cracks grew in a cyclic manner under masticatory loading of the mandible and the plate. The plate fracture occurred by means of fatigue. The corrosive environment did not affect the failure of the titanium plate, and the fracture was not caused by hydrogen embrittlement. The results revealed that the fatigue properties of the plates may have been impaired by the residual stresses generated in plate bending.

CONCLUSIONS

Adjustive bending of the plates, in the surgical operation, may thus be an important cause of fracture of the reconstruction plates, because of generated residual stresses, which affect the mean stress in fatigue loading. To make the plates function without failure the plates should match closely with the three-dimensional shape of the mandible, to avoid any bending in the operative phase.

Failure Strength of 2.0 Locking Versus 2.0 Conventional Synthes Mandibular Plates: A Laboratory Model

PURPOSE

This laboratory study compared the performance of locking versus nonlocking Synthes (Synthes, Paoli, PA) 2-mm mandibular fixation plates. The purpose of the study was to determine if there are physical or mechanical properties to support the use of one rigid fixation device over the other.

MATERIALS AND METHODS

A bovine rib model was selected for this study because they closely approximate characteristics of the human mandible. Two experimental groups composed of 10 locking and 10 nonlocking 2-mm plates were secured to randomly selected osteotomized bovine ribs using 10-mm monocortical screws. The specimens were loaded using a 4-point bending system to the point of failure using a MTS model 309.00 servo-hydraulic testing system (MTS Systems Corp, Eden Prairie, MN) with a custom fabricated fixator. The data was obtained with TestStar 2 version 4.0 and TestWare Sx 4.0 software (MTS Systems Corp), and analyzed to determine if there was any difference in performance between the 2 mandibular plate designs.

RESULTS

Overall, there were no statistically significant differences between the locking and conventional 2-mm mandibular plate. Of the 20 samples tested, 1 (nonlocking) had a unique early screw failure (pullout) inconsistent with any other samples and was not analyzed. Of the remaining 19 samples, 17 produced a yield failure, bend, or stretch rather than a plate fracture. Both of the plate fractures occurred in the nonlocking plates. Although the data suggested that this mode of failure was more common in nonlocking plates, the difference between both groups in the mode of failure did not achieve statistical significance (chi2 = 2.0, P = .16). Thus, yield was the predominant mode of failure for both types of devices. The force at which each device failed was also similar in both groups. The force of failure for the nonlocking plates was 559.9 N (SD = 247.9), whereas the locking plate failure strength was 637.8 N (SD = 276.3; t (17) = 0.6, P = .53). The results indicated that there was no suggestion that one plate might be stronger than the other.

CONCLUSIONS

In this laboratory model, no significant differences were found between the 2 types of mandibular plates. Although studies have shown the locking system to be more rigid, this study suggested that the type and degree of failure are more likely related to bone quality and surgical technique when using the 2-mm mandibular plate. Additional prospective studies are needed to correlate these results in patient 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.

Reconstruction of large defects postmandibulectomy for oral cancer using plates and myocutaneous flaps: a long-term follow-up

A series of 28 consecutive cases of mandibular reconstruction by means of reconstructive plates and myocutaneous flaps were reviewed. In all cases mandibular resection was indicated for treatment of squamous cell carcinoma of the oral cavity: 25 pelviglossomandibulectomies (resulting in large defects from the angle of the mandible), 2 Commando operations (resulting in lateral defects) and 1 anterior sectional mandibulectomy (resulting in an anterior defect). Tumour stages were T1-T2 (4 cases) and T3-T4 (24 cases). Success was defined as plate maintenance 6 months' postoperatively/postradiotherapy. The overall success rate was 32.2%. Lateral-centre-lateral (L-C-L) defects had 32% success, L (lateral) defects had 50% success and in the single case of a C (centre) defect, the plate was not maintained. Stainless steel reconstruction plates showed a similar success rate as titanium plates (30% versus 34%). In cases not submitted to radiotherapy there were more maintained plates than in cases that received radiotherapy (45.5% versus 23.6%). Reconstruction plates are not effective in bridging large defects of the resected mandible. Only in selected cases that are not eligible for microvascular free flaps should plates and myocutaneous flaps be considered as an option for mandibular reconstruction.

[Experiences in the treatment of midfacial fractures using a fixed-angle osteosynthetic system. Biomechanical results]

AIM

Fixed-angle osteosynthetic systems are characterized by mechanical "locking" of the osteosynthetic screw and plate. These systems have found increasing acceptance and use for osteosynthetic fixation and temporary reconstruction of the mandible. The aim of this study was to investigate the applicability and performance of fixed-angle systems in the treatment of midfacial fractures.

MATERIAL AND METHOD

A newly developed fixed-angle osteosynthetic plate system (smart lock) was compared to a conventional system using fresh human skulls. The iatrogenically produced zygomatic fractures of the human skulls were treated by osteosynthesis and biomechanically tested. Furthermore, in a dynamic test series, an artificial bone was subjected to an alternating force of 15 N of up to 1,000,000 cycles. The new screws and plates were subjected to further biomechanical tests.

RESULTS

The tests using the fixed-angle implants revealed that an increase of stability of up to 40% can be expected after osteosynthetic fixation. Furthermore, the plates resisted 1,000,000 cycles of alternating forces, whereby the conventional systems failed after 170,000 cycles on the average.

CONCLUSION

Fixed-angle systems, due to their construction, provide a high degree of stability even in thin bones of the midface. They appear to be promising for the treatment of midfacial fractures.

Material analysis of AO plate fracture cases

PURPOSE

The clinical observation of fracture cases and material evaluation of fractured titanium plates were performed to investigate the causes of fracture.

PATIENTS AND METHODS

Fracture of titanium plates occurred in 4 patients of the 110 mandibular reconstructions. We clinically and experimentally evaluated plate fracture cases among cases in which primary reconstruction using titanium plates was performed after the mandibular resection.

RESULTS

Titanium plate fracture was frequently observed in L-type defect cases in which angle-type plates were used, and fracture mainly occurred in the anterior region of the mandibular angle. Material analysis suggested that the occurrence of fracture can be prevented by eliminating constricted parts on the internal side of the plates.

CONCLUSIONS

The causes of fracture were thought to be the use of plates under the conditions of comparatively frequent repeated application of stress or fatigue fracture caused by stress concentration, depending on the form of the plate.

Infections associated with locking reconstruction plates: a retrospective review

PURPOSE

In this study, we examined the incidence of infection with the use of a locking reconstruction bone plate/system.

PATIENTS AND METHODS

All patients, treated with a locking reconstruction bone plate/screw system for mandible fractures in the Oral and Maxillofacial Surgery service over a 28-month period at a level I trauma center, were evaluated through a retrospective chart review by independent examiners. The use of a locking reconstruction plate was determined by the attending staff involved in the patient's care. Patient population included single, bilateral, and comminuted fractures. Patient characteristics were noted and include dentate versus edentulous, smoking history, and history of previous infection.

RESULTS

Fifty-six locking bone plates were placed in 42 patients. Eight (19%) of the patients were infected before treatment. A persistent infection remained in 3 of these 8 patients (37.5%). Two patients (5.8%), with 3 fracture sites (6.4%) developed postoperative infection that required further intervention. All 5 of the patients who were infected after surgery were heavy smokers. History of preoperative infection and smoking appear to be significant factors in the etiology of postoperative infection. All postoperative infections resolved successfully with local measures and with no loss of fixation.

CONCLUSION

The use of locking reconstruction plates can facilitate the management of complicated fractures; however, it does not eliminate complications. Postoperative infections are related to numerous factors, including preoperative incidence of infection, smoking, and proper use of the plates.

Does plate adaptation affect stability? A biomechanical comparison of locking and nonlocking plates

PURPOSE

The purpose of this investigation was to determine whether the degree of plate adaptation and effects of locking influenced the mechanical behavior of the plate/screw/substrate system for 2.0-mm monocortical superior border plates and 2.4-mm reconstruction plates secured at the inferior border intended to stabilize simulated mandibular angle fractures.

MATERIALS AND METHODS

A total of 130 polyurethane synthetic mandible replicas (Synbone, Landquart, Switzerland) were used in this investigation. Five controls each, for incisal edge and molar loading, as well as 5 samples each for 2.4-mm locking and nonlocking reconstruction plates and 2.0-mm locking and nonlocking monocortical superior border plates, intimately adapted (0.0-mm offset), 1.0-mm offset and 2.0-mm offset were subjected to loading at the incisal edge and molar region with an Instron 1331 (Instron Corp, Canton, MA) servohydraulic mechanical testing unit. Load/displacement data were recorded, and yield load, yield displacement, and stiffness were determined. Mean and standard deviation values were calculated. Statistically significant differences were determined for the effects of locking and degree of plate adaptation using a 1-way analysis of variance (P <.05). For differences within categories and among groups, a Sheffé multiple-comparison test was performed. First-order polynomial best-fit curves were created for each group to further evaluate and compare the mechanical behavior.

RESULTS

There were no statistically significant differences (P <.05) for yield load, yield displacement, and stiffness within the 2.4 and the 2.0 locking categories for both molar and incisal edge loading. For the 2.4 nonlocking category, there were statistically significant differences for yield load, yield displacement, and stiffness between the 0.0-mm offset group and both the 1.0-mm and 2.0-mm offset groups for both molar and incisal edge loading but not between the 1.0-mm and 2.0-mm groups. For the 2.0 nonlocking category, there were statistically significant differences for yield load, yield displacement, and stiffness between both the 0.0-mm and 1.0-mm offset groups and the 2.0-mm offset group for both molar and incisal edge loading but not between the 0.0-mm and 1.0-mm groups.

CONCLUSIONS

The degree of adaptation (amount of offset) affected the mechanical behavior of the nonlocking systems evaluated. It did not affect the locking systems. Failure occurred as an "all-or-nothing" pattern.

Mandibular reconstruction: a clinical and radiographic animal study on the use of autogenous scaffolds and platelet-rich plasma

This paper reports on an experimental animal study evaluating a method of mandibular reconstruction. After a successful pilot study, 28 goats underwent a continuity resection of the mandibular angle. Primary reconstruction was carried out using specially designed osteosynthesis plates and screws. The defect was bridged by the original cortical scaffold, filled with an autogenous bone graft from the iliac crest. To accelerate bone healing, platelet-rich plasma (PRP) was mixed with the particulate bone graft in 14 goats. All goats had uneventful healing. The osteosynthesis plates and screws withstood immediate loading for periods varying from 3 weeks to 3 months. The use of PRP appeared to enhance bone healing considerably.