Elevation of the flap to expose the underlying fracture can create a hard-to-reach area in certain locations, such as the midface to place screw exactly at 90° to the plate.
KLS Martin Company created an absorbable system with pins that are ultrasonically vibrated to fill the pilot hole with the pin material. A, Photomicrograph demonstrating how the head of the Sonic Weld pin (arrow) is ultrasonically vibrated to lock with the plate. This essentially fuses the head of the pin to the plate in a type of weld. B, Demonstration of how the Sonic Weld system ultrasonically vibrates the pin to fill the predrilled grooves in the pilot hole.
Weber-Ferguson and sublabial incisions were made and the soft tissue elevated off the midface to unveil the underlying bony skeleton. The nasomaxillary and zygomaticomaxillary buttresses and the zygomaticofrontal sutures were exposed. Fractures were initiated with the oscillating saw and completed with gentle tapping with an osteotome.
All specimens were tested in a similar manner with the Instron 8500. The testing device is able to detect and read the applied load at the plate-pin construct and record the force at which failure occurred.
Carron MA, Zuliani G, Pereira L, Abuhamdan M, Thibault A, Dau N, Bir C. Stability of Midface Fracture Repair Using Absorbable Plate and Screw System Pilot Holes Drilled and Pin Placement at Angles Other Than 90°. JAMA Facial Plast Surg. 2014;16(1):42-48. doi:10.1001/jamafacial.2013.1404
Conventional plating systems use titanium plates for fixation of fractures, with benefits of strength and biocompatibility. However, titanium plates require that screws be placed at a 90° angle to the pilot holes. In the midface, this becomes extremely difficult. Today, a variety of craniomaxillofacial osteosynthesis systems are available, including resorbable plating systems. Specifically, the KLS Martin Sonic Weld system ultrasonically fuses the plate and the head of the pin when placed and will fill the pilot hole grooves completely even at less than 90° angles, which provides a tremendous advantage in midface fracture repair.
To determine if the KLS Martin Sonic Weld system provides plate-screw construct stability in human heads even when placed at acute angles at the midface buttresses.
Design, Setting, and Specimens
Twenty cadaveric head specimens with the mandible removed were prepared by creating osteotomies in the midface buttresses bilaterally. Specimens were defleshed and placed in a 2-part testing rig to hold and position the head for testing in a standard material testing system. Testing was performed at the Wayne State University Bioengineering test laboratories, Detroit, Michigan, using an Instron device and high-speed camera. Specimens were plated on one side of the midface using the KLS Martin Sonic Weld system with pilot holes and pins placed at 90° angles. On the contralateral side, the buttresses were plated with the KLS Martin Sonic Weld system at 60°, 45°, and 30° angles. Data were collected using the TDAS data acquisition system and were compared with matched pairs within each specimen.
Main Outcomes and Measures
Ultrasonically vibrated pins placed into absorbable mini-plates at less than 90° angles with the KLS Martin Sonic Weld system were compared with the same amount of stress as the system placed at a 90° angle before demonstrating plate-screw construct failure.
Fifty-seven paired tests were collected, with 114 total tests. Twenty failures were due to bone breakage, and 94 fixations failed as a result of the plate-screw construct breaking. Fractures fixated with the ultrasonic absorbable plating system placed with screws at all tested angles failed at similar loads to our control plates with pins placed at 90° angles. These results lend the surgeon to successfully reduce fractures in the midface fragments in difficult-to-reach areas and possibly cut down on operative time while improving the chance of achieving a long-lasting adequate reduction.
Conclusions and Relevance
Although there is a measured difference in the laboratory, no clinical difference is observed because the maximum force is not usually encountered. Overall, the clinical scenario indicates absorbable plates to be a viable option in less accessible areas.
Level of Evidence
The zygomatic bone is important in the aesthetics and function of the midface and represents the most lateral and anterior structure of the midface. If the zygomatic bone is fractured, it may result in significant morbidity and functional impairment, including trismus, altered globe position, and infraorbital nerve damage. Manson et al1 developed a system that divides the fractures into low-, middle-, and high-energy injuries. Higher-energy injuries result in more severe fracture and comminution more likely requiring surgical treatment and stabilization. Conventionally, titanium plates are used for fixation of fractures. The benefits of titanium include its strength and biocompatibility. However, one of its weaknesses is that titanium plates require that screws be placed at a 90° angle to the pilot holes, which can become problematic in certain locations, such as the midface, where raising a flap tethered superiorly creates a situation in which drilling a 90° angle pilot hole with parallel screw placement becomes extremely difficult. Today, a variety of craniomaxillofacial osteosynthesis systems are available commercially, including resorbable plating systems. These resorbable plates are gaining popularity; however, to date, there are no randomized controlled clinical trials comparing these plates to titanium plates.2
Optimal healing after open reduction and internal fixation of craniofacial injuries requires methodical operative techniques. A well-known tenet is that pilot holes are made and screws are placed perpendicular to the plate to prevent screw-plate failure. This important technique is illustrated in textbooks and taught at training courses.3
Access to the fracture site is obtained by strategically raising soft tissue to minimize the chance of neurovascular injury. Exposing areas of the craniofacial skeleton are challenging due to soft-tissue limitations, especially to the nasolabial buttress and the zygomatic arch (Figure 1). It is difficult to drill pilot holes and place screws perpendicular to the plate, and soft tissue may be stretched considerably to facilitate the proper angle of instruments. With titanium mini-plates, the screw must be seated in the plate and bone near perpendicular for it to secure properly.
KLS Martin Company created an absorbable system with pins, which ultrasonically vibrated the pin to fill the pilot hole grooves created by the drill with the pin material. The material fills the grooves completely even at less than 90° angles and behaves analogous to screw threads. The KLS Martin Sonic Weld system ultrasonically fuses (or welds) the head of the pin to the plate, creating a very stable plate-screw construct (Figure 2). This provides a tremendous advantage in hard-to-reach midface areas because pilot holes may be drilled at less than 90° angles and the plate screw construct will maintain stability, unlike its titanium counterpart. The 2 properties of the absorbable system may help overcome the issue of achieving stability when perpendicular placement would be difficult.
The goal of our investigation was to test the strength of the plate-pin construct at acute angles. Our hypothesis was that the plate-pin construct will have the same failure load for acute pin angles as perpendicular pin angles.
Twenty fresh-frozen cadaver heads were provided by the Department of Biomedical Engineering at Wayne State University, Detroit, Michigan. Specimens were frozen at the Biomedical Engineering Laboratory at Wayne State University and thawed to room temperature before preparation. The institutional review board at Wayne State University approved the study.
The cadaver heads were prepared by creating osteotomies in the midface buttresses bilaterally. Fractures were created with an oscillating saw at the nasomaxillary (NM) and zygomaticomaxillary (ZM) buttresses, which were exposed with a Weber-Ferguson and sublabial approach, and the zygomaticofrontal (ZF) suture, which was exposed via a bicoronal approach. We also tested the zygomatic arch by creating a fracture at its midpoint. Fractures were initiated at the midpoint of the zygomatic arches and at the ZF, ZM, and NM sutures and completed with a 2-mm osteotome. All dissections and fractures were performed by the same investigators (L.P., M.A.) to ensure consistency (Figure 3). Data were compared as matched pairs within each specimen and statistically analyzed.
KLS Martin Sonic Weld absorbable plates and pins were used in this study. Standard KLS Martin Sonic Weld midface hardware was chosen with 1.0-mm-thick pins and 2.0-mm-thick plates. All fractures were plated with 2 holes on either side of the fracture line. After immersion in the water bath, plates were adapted to the fracture site in accord with the manufacturer’s recommendations. A handheld battery-operated mini-driver was used to make the pilot holes. Aluminum blocks at 60°, 45°, and 30° angles were used as drill guides to ensure the pilot holes were drilled at a consistent angle.
Twenty cadaver head specimens were used with the left hemi-face of each head as a control. Pilot holes were drilled and pins placed at a 90° angle to the plate surface. All experimental right hemi-faces had zygomatic arches plated at 45° angles. Of the 20 right-sided NM buttresses, 10 were plated with pilot holes and pins placed at 60° angles and 10 were placed with pilot holes and pins at 30° angles because simultaneous ZF suture and ZM buttress fractures in the same hemi-face would cause instability and likely lead to testing error. To test the strength of the plate-screw construct at only the ZF suture or only the ZM buttress (both were not tested on the same hemi-face), 10 heads were used to test the ZF suture and 10 heads were used to test the ZM buttress. Of the 10 ZF sutures tested, 5 right hemi-faces were plated at 60° angles and 5 were plated at 30° angles. Of the 10 ZM buttresses tested, 5 right hemi-faces were plated at 60° angles and 5 were plated at 30° angles (Table 1).
Specimens were placed in a 10-cm-deep container of wet sand. Specimens could be manipulated so the test load could be applied normally to each site. A quasi-static load was applied using a 0.63-cm diameter rod with a length of 4.55 cm at a rate of 0.1 cm/s by a load frame control panel tensile testing (Instron 8500) device (Figure 4). Once the specimen was in place, the wet sand was packed around the specimen to prevent motion. Specimens were observed under load and the test terminated when a failure occurred with breakage of the plate-screw construct or the bone. All failure types were considered in the results and are listed in Table 2.
The position and load were recorded at 2000 Hz using a TDAS data acquisition system (DTS). Failure was noted in the data when the load reached a local maximum, regardless of the failure mode.
Statistical analysis was conducted by using Predictive Analytic SoftWare (version 18) created by SPSS, Inc. One-tailed, paired t tests were conducted by using the ideal fixation on the left hemi-face (90° angle) as the control and the contralateral fixation as the test. Due to the limited number of tests, a bootstrapping test was conducted to validate the t tests. P < .05 was considered statistically significant.
A total of 57 paired tests were collected (114 total tests). Three tests could not be included in the analysis due to a lack of failure in the test system. Results included failures from plate-pin failure or bone breakage. Twenty failures were due to bone breakage, and 94 fixations failed as a result of the plate-screw construct breaking (Table 2).
Comparison of the 57 available paired fixations provided a statistically significant difference between the test and the control groups (P = .03). The P value for the bootstrapping test was also significant (P = .03).
However, once the data were separated into subgroups based on fracture location, fixation angle, or both, the failures of the experimental and control groups were no longer significantly different. The mean for control and test failure loads for each of the groups are given in Table 3. In all but 1 case, the mean failure load for the control group was higher than the test group. The ZM location and 60° angle group had 5 paired tests. The mean (SD) for the control group was 395.25 (217.94) newtons (N) and for the test group was 416.25 (302.91) N.
Proper reduction and fixation are critical in treating facial fractures. Titanium is an excellent material because of its rigidity and stability.4,5 Anatomical restrictions make some areas difficult to access for perpendicular screw-plate placement. A system that maintains stability at acute pin/screw angles would require less exposure and reduce surgical time.
When comparing all fracture sites on right and left hemi-faces, the constructs with acute angles were not as strong as those fracture sites placed at 90° angles. However, comparing each specific fracture site to its opposite control, subgroup analysis did not show any statistically significant difference in stability of either control or experimental sites. A larger sample size could enhance the statistical power of our study. However, the mean force that resulted in failure of the plate-bone complex was 285.08 N in the test group and 354.97 N in the control group. These forces exceed the mean force exerted by the masseter muscle (250 N) in healthy patients.6 This is the main force that displaces the reconstructed zygomatic complex fracture. The masseter and medial pterygoid muscles are responsible for 60% of the maximum molar bite force.7 The masseter force in patients experiencing posttrauma is reduced to 25 to 50 N, and all data collected exceeded this force with the exception of 1 control test.7 This is a preclinical study using cadaver head specimens in controlled conditions; therefore, these findings should be validated by a clinical study using the KLS Martin Sonic Weld system in patients with ZM complex fractures to assess the results and complications.
In conclusion, although there is a measured difference experimentally, all the failure force data from the absorbable plates with screws at acute angles exceed the masseter force in patients after surgery. Because this is the primary force displacing the zygomatic complex, it can be assumed that the resorbable plates with screws placed at acute angles provide sufficient stability. In addition, the titanium mini-plates can be used on easily accessible buttresses, and the absorbable plates can be used in less accessible areas. Overall, the clinical scenario indicates absorbable plates to be a viable option in less accessible areas.
Accepted for Publication: May 22, 2013.
Corresponding Author: Michael A. Carron, MD, Division of Facial Plastic Surgery, Department of Otolaryngology, Wayne State University School of Medicine, 4201 St Antoine, 5E-University Health Center, Detroit, MI 48201 (firstname.lastname@example.org).
Published Online: October 24, 2013. doi:10.1001/jamafacial.2013.1404.
Author Contributions: Dr Carron had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Study concept and design: Carron, Zuliani, Pereira, Abuhamdan, Bir.
Acquisition of data: Carron, Zuliani, Pereira, Abuhamdan, Thibault, Dau.
Analysis and interpretation of data: Carron, Pereira, Abuhamdan, Thibault, Dau.
Drafting of the manuscript: Carron, Pereira, Abuhamdan.
Critical revision of the manuscript for important intellectual content: Carron, Zuliani, Pereira, Thibault, Dau, Bir.
Statistical analysis: Pereira, Abuhamdan, Dau.
Obtained funding: Carron, Zuliani, Pereira.
Administrative, technical, and material support: Carron, Pereira, Abuhamdan.
Study supervision: Carron, Zuliani, Pereira, Bir.
Conflict of Interest Disclosures: None reported.
Funding/Support: This study was funded by the KLS Martin Company. KLS Martin Sonic Weld plates and pins were provided in addition to $5000 used only for biomechanical laboratory testing equipment and personnel time.
Role of the Sponsor: KLS Martin Company had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.
Previous Presentations: This study was presented at the Michigan Otolaryngological Society Annual Meeting; July 22, 2011; Grand Rapids, Michigan.
Additional Information: This research won first place for resident research at the Michigan Otolaryngological Society Annual Meeting in 2011.
Correction: This article was corrected online October 24, 2013, for an error in the last column heading in Table 1 under column heading Right Fracture Site (Test) entry.