Abstract
Fractures of the coronoid process are uncommon and can easily be missed. The purpose of this study was to classify the fracture patterns and explore the treatment options. This retrospective study included 39 patients with fractures of the mandibular coronoid process. Treatment protocols were developed based on the time of fracture, degree of mouth opening, location of the coronoid fracture, types of fracture, and other concomitant fractures. All patients were followed up for 12–60 months. Sixteen patients underwent conservative management and four of these patients developed progressive trismus, which improved significantly after removal of the coronoid process. Twenty-three patients underwent open reduction and internal fixation (ORIF) via the modified retromandibular approach. Follow-up data showed significant improvement in maximum mouth opening and symptoms (diet and pain) compared to their preoperative status. In summary, conservative management is first recommended for fractures of the coronoid process with minimal displacement or restriction of mouth opening. For patients with significant fracture displacement and limited mouth opening, or with concomitant fractures of the zygoma, zygomatic arch, or mandibular ramus, ORIF via the modified retromandibular approach through the anterior border of the parotid gland is an alternative treatment method.
Mandible fractures frequently occur at the mandibular condyle, angle, mental foramen, and the symphysis. Coronoid fractures are less common. Clarkson et al. first reported coronoid fractures among British troops during World War II in 1946. Today, coronoid fractures are commonly the result of traffic accidents and can less frequently result from falls, explosions, and local trauma. Iatrogenic coronoid fractures from mandibular third molar extraction and sagittal split osteotomy of the mandibular rami are rare.
It is generally accepted that coronoid fractures can be managed conservatively. A review of the literature revealed that reports on the management of coronoid fractures were sparse. Restricted mouth opening is one of the common clinical sequelae, due to inappropriate management of coronoid fractures causing adhesions of the fracture segments to the surrounding tissue. Surgery may be indicated in a few special cases, especially for those with significant displacement and those who are not good candidates for prolonged maxillomandibular fixation (MMF).
The traditional surgical approaches for coronoid fracture include extraoral and intraoral incisions. Preauricular incisions carry a higher risk of facial nerve injury. Although intraoral incisions have the advantage of a low incidence of facial nerve injury and no facial scar, special surgical instruments are required. This approach also carries the risk of injury to the pterygoid plexus and the internal maxillary artery, and results in limited surgical exposure. In the present study, we report the long-term follow-up results of 39 patients with coronoid fractures; patients were treated between 2005 and 2010. A treatment algorithm is proposed based on the degree of trismus, location of the coronoid fracture, and other concomitant fractures.
Materials and methods
Patients
A total of 1358 patients with mandibular fractures were treated between 2005 and 2010. Among them, 39 patients had coronoid fractures. Sixteen patients (20 sides) were managed conservatively, while 23 patients (29 sides) underwent open reduction and rigid internal fixation (ORIF) via a modified retromandibular approach. Detailed information including medical history, treatment methods, follow-up results, and pre- and post-treatment imaging studies were available for these patients. Patients who were lost to follow-up were excluded. The study was approved by the Institutional Review and Ethics Board of Sichuan University. Written informed consent was obtained from each patient.
Preoperative and postoperative data processing
Subjective data regarding pain and dietary consistency were collected using a standard visual analog scale both preoperatively and at each follow-up appointment. A scale of 1–10 was used for pain assessment (1 = least, 10 = worst) and a scale of 1–4 was used to measure swallowing function (1 = liquid diet, 2 = soft, 3 = restricted, 4 = normal). Objective data were collected by directly measuring the maximum inter-incisal opening (MIO), assessing facial nerve function and occlusal relationship, and analyzing fracture healing on plain X-ray films and computed tomography (CT) images. The collected information was entered into Microsoft Excel for review and analysis.
Treatment method: conservative management
Four patients with isolated coronoid fractures were treated with MMF for 1–2 weeks. Twelve patients had concomitant fractures of the zygomatic arch and other mandibular fractures that were treated with early ORIF. The coronoid fractures in these patients were not surgically treated.
Treatment method: operative management
The other 23 patients were treated surgically via a modified retromandibular approach ( Fig. 1 ). The skin flap was elevated in this plane up to the anterior border and the apex of the parotid gland. For fractures at the base of the coronoid process, the masseter muscle and mandibular periosteum were elevated off the mandible, in a plane between the parotid duct and the buccal branch, up to the ramus, to expose the base of the coronoid process. For fractures high up in the coronoid, the fracture site was exposed through a safe zone between the upper buccal branch and the zygomatic branch of the facial nerve. For comminuted fractures of the coronoid process, the fracture site was also approached between the zygomatic and buccal branches of the facial nerve. For combined fractures of the coronoid and mandibular ramus, the fracture sites were exposed by elevating the masseter muscle between the buccal and marginal mandibular branch of the facial nerve.
Once the fractures were reduced, a miniplate was placed along the anterior and posterior borders of the fractured bone, based on the stress trajectory of the mandible under physiologic conditions ( Fig. 2 ).
Statistical analysis
The statistical analysis was performed using SPSS 10.0 software (SPSS, Chicago, IL, USA). The paired-sample Student’s t -test was used to compare preoperative and the latest postoperative follow-up data. A P -value of <0.05 was considered significant.
Results
Coronoid fracture accounted for 2.9% of all mandibular fractures (39/1358). The average age in this study group was 38.7 years (range 22–58 years). There were 26 male and 13 female patients. The fracture had occurred more than 4 weeks prior to presentation at the clinic for eight patients, while the other 31 patients came to the clinic within 4 weeks of fracture. Twenty-nine patients had unilateral and 10 patients had bilateral coronoid fractures. An isolated coronoid fracture was seen in four patients (10.3%), whereas 17 patients (43.6%) had concomitant fractures at other sites of the mandible and 18 patients (46.1%) had other concomitant fractures in the mid-face. Patients were followed up postoperatively for 12–60 months.
Conservative management was employed in 16 patients, including 12 with linear fractures and four with comminuted fractures. Among them, 13 were fresh fractures and three were old fractures. Four patients had isolated coronoid fractures, seven had other mandibular fractures, and five had concomitant zygomatic arch fractures. There was a significant ( P < 0.05) improvement in mouth opening and swallowing function in patients with linear and fresh fractures after the treatment ( Table 1 ). In four patients (one comminuted fracture, one with other mandibular fractures, and two with zygomatic arch fractures), the mobility of the temporomandibular joint (TMJ) decreased with progressive trismus after 6–12 months of conservative management. X-ray images showed superior extension of the coronoid segment. Surgical exploration through an intraoral incision revealed extensive adhesions of the coronoid process to the surrounding tissue. Excision of the coronoid process significantly improved mouth opening ( Fig. 3 ).
| Fracture classification | Number | Preoperative | Postoperative | ||||
|---|---|---|---|---|---|---|---|
| MIO (mm) | Pain | Diet | MIO (mm) | Pain | Diet | ||
| Fracture type | |||||||
| Linear fracture | 12 | 24.7 (4.3) | 4.2 (1.1) | 2.5 (0.8) | 38.8 (2.2) * | 3.5 (1.7) | 3.3 (0.5) * |
| Comminuted fracture | 4 | 16.3 (3.8) | 4.2 (1.5) | 2.3 (0.4) | 25.0 (3.6) | 3.3 (0.9) | 3.5 (0.4) |
| Nature of fractures | |||||||
| <4 weeks | 13 | 23.9 (5.0) | 4.1 (1.0) | 2.4 (0.7) | 37.4 (5.6) * | 3.4 (1.6) | 3.3 (0.4) * |
| >4 weeks | 3 | 16.7 (4.5) | 4.6 (1.6) | 2.3 (0.5) | 26.7 (1.5) | 3.5 (1.1) | 3.5 (0.5) |
| Additional midfacial and mandibular fracture | |||||||
| Simple coronoid fracture | 4 | 26.5 (4.5) | 4.3 (0.9) | 2.0 (0.7) | 40.3 (3.2) | 2.7 (0.6) | 3.5 (0.3) |
| Additional mandibular fracture | 7 | 23.6 (4.5) | 4.1 (1.2) | 2.7 (0.8) | 37.8 (2.2) | 4.0 (2.0) | 3.1 (0.5) |
| Associated midfacial fracture | 5 | 18.0 (5.1) | 4.3 (1.3) | 2.4 (0.5) | 28.0 (7.4) | 3.2 (0.8) | 3.5 (0.4) |
Twenty-three patients underwent surgery, including 19 with linear fractures and four with comminuted fractures. Among them 18 were fresh fractures and five were old fractures. Ten patients had fractures at other sites of the mandible and 13 had concomitant zygomatic arch fractures. Follow-up results showed that there was a significant improvement in maximal mouth opening, swallowing, and pain symptoms ( P < 0.05) following surgical treatment in all patients with different fracture patterns ( Table 2 ).
| Fracture classification | Number | Preoperative | Postoperative | ||||
|---|---|---|---|---|---|---|---|
| MIO (mm) | Pain | Diet | MIO (mm) | Pain | Diet | ||
| Fracture type | |||||||
| Linear fracture | 19 | 19.3 (5.2) | 6.9 (1.9) | 2.2 (0.6) | 38.2 (1.5) * | 2.7 (0.8) * | 3.5 (0.3) * |
| Comminuted fracture | 4 | 18.8 (3.5) | 7.8 (1.3) | 1.7 (0.3) | 38.3 (1.5) | 2.4 (0.8) | 3.5 (0.5) |
| Nature of fractures | |||||||
| <4 weeks | 18 | 18.8 (4.2) | 7.3 (1.6) | 2.1 (0.6) | 38.1 (1.5) * | 2.5 (0.7) * | 3.5 (0.4) * |
| >4 weeks | 5 | 20.8 (7.0) | 6.0 (2.3) | 2.2 (0.7) | 38.4 (1.1) | 3.0 (0.9) | 3.4 (0.3) |
| Additional midfacial and mandibular fracture | |||||||
| Additional mandibular fracture | 10 | 18.2 (4.3) | 6.8 (1.7) | 2.4 (0.7) | 38.1 (1.4) * | 2.6 (0.7) * | 3.5 (0.3) * |
| Associated midfacial fracture | 13 | 20.0 (5.2) | 7.2 (1.9) | 2.0 (0.6) | 38.2 (1.5) * | 2.6 (0.8) * | 3.5 (0.4) * |
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