Interventions for the Management of Mandibular Coronoid Process Fractures: A Systematic Review

Abstract

Background

The fracture of the coronoid process of mandible is one of the rarest fractures seen and the paucity of literature on the topic reflects the same. Despite the low incidence rate, the complications maybe grave which is why proper management is important. The treatment is controversial also because of the absence of standardized treatment protocol. This systematic review aims to compare the outcome of various treatment modalities available.

Methods

Registered under PROSPERO: CRD42020200700. Systematic research was conducted across databases like PubMed, Google Scholar, Pro Quest, Wiley Online. All clinical studies done till January 2021 which included participants above 14 years of age were included. Case reports, case series and studies not mentioning the treatment plan were excluded. The studies were shortlisted by the authors based on the eligibility criteria. Risk of bias was assessed using the MINORS tool and JBI checklist.

Results

A total of five studies were included. Four were retrospective studies and one was a retrospective case-controlled study. Two studies reported high, two moderate and one low risk of bias. Various treatment modalities were reported for the management of coronoid process fractures including conservative management, ORIF and coronoidectomy. Most authors preferred conservative management in asymptomatic cases and surgical management in symptomatic cases.

Discussion

No randomized control trials were found on the topic. Majority of the articles were case reports. Conservative management was preferred in minimally displaced fractures of coronoid process. However, in presence of displaced coronoid process fractures causing impediment of mandibular function surgical management is preferred.

Introduction

Coronoid fractures account for only 0.6 to 4.7% of all facial fractures [1]. Even though mandibular fractures are one of the most common fractures of the maxillofacial region, the fracture of the coronoid process of mandible is one of the rarest fractures seen [2–4]. Clarkson, Wilson and Lawrie in 1946 during the second world war first described the fracture of coronoid process [5, 6]. The coronoid process constitutes the upward continuation of the anterior border of the mandible. It mainly gives insertion to the temporalis muscle and on the lateral aspect to the masseter muscle. The lines of stress also pass vertically on the coronoid process [7]. The rarity of this fracture is because of its protected position, deep under the zygomatic complex and the muscles overlying it [8]. High velocity road traffic accidents (RTA), falls, interpersonal violence, and explosions may result in coronoid fractures. Iatrogenic fractures are rare but mandibular third molar extractions and mandibular ramus sagittal split osteotomy may lead to the same [5, 9]. Coronoid fractures are usually simple, linear and minimally displaced. The displacement will be more in cases of injury to the periosteum, with the contraction of temporalis muscle [10].

Articles on management of coronoid fractures are sparse and controversial [5]. The treatment modalities include conservative management [11] in cases of minimally displaced fractures, coronoidectomy, open reduction and internal fixation (ORIF) [12], and splinting of temporalis muscle [1, 13].

To the best of our knowledge, this is the first systematic review on the management of mandibular coronoid process fractures. Despite the low incidence rate, the complications may be grave, like long-term pain with limited mouth opening, temporomandibular joint ankylosis or Jacob’s disease because of which proper management is crucial [1, 5, 7, 9, 10, 14–16]. The aim of this systematic review was to compare the outcomes of various treatment modalities available for treatment of mandibular coronoid fractures.

Methods

The review has been registered in PROSPERO; International prospective register of systematic reviews funded by National Institute of Health Research and produced by CRD (Centre for Reviews and Dissemination) an academic department of the University of York. The registration number of this review is CRD42020200700.

Information Sources

A comprehensive electronic database search was done for studies on coronoid fractures. The following databases were searched: PubMed, Google Scholar, Wiley online and Pro Quest. The last search was performed on 31st January 2021.

Search Strategy

Search strategy was developed using keywords related to “coronoid fracture of mandible”, “ORIF”, “conservative management”, “coronoidectomy”, etc. and was searched through the above databases (Table 1).

Table 1.

PubMed search strategy

Serial no	Query	Search details	Results
1	ORIF	"ORIF"[All Fields]	2370
2	(Conservative management) OR (ORIF)	"Conservative treatment"[MeSH Terms] OR ("conservative"[All Fields] AND "treatment"[All Fields]) OR "conservative treatment"[All Fields] OR ("conservative"[All Fields] AND "management"[All Fields]) OR "conservative management"[All Fields] OR "ORIF"[All Fields]	90,693
3	(Coronoidectomy) OR ((conservative management) OR (ORIF))	"Coronoidectomies"[All Fields] OR "coronoidectomy"[All Fields] OR ("conservative treatment"[MeSH Terms] OR ("conservative"[All Fields] AND "treatment"[All Fields]) OR "conservative treatment"[All Fields] OR ("conservative"[All Fields] AND "management"[All Fields]) OR "conservative management"[All Fields] OR "ORIF"[All Fields])	90,918
4	(Mandibular coronoid process [Title/Abstract]) AND ((coronoidectomy) OR ((conservative management) OR (ORIF)))	"Mandibular coronoid process"[Title/Abstract] AND ("coronoidectomies"[All Fields] OR "coronoidectomy"[All Fields] OR ("conservative treatment"[MeSH Terms] OR ("conservative"[All Fields] AND "treatment"[All Fields]) OR "conservative treatment"[All Fields] OR ("conservative"[All Fields] AND "management"[All Fields]) OR "conservative management"[All Fields] OR "ORIF"[All Fields]))	11

Eligibility Criteria

All clinical studies; retrospective, prospective, randomized control trials, case control studies which included participants above 14 years of age were included. All studies published till January 2021 fulfilling the inclusion criteria were included.

Case reports, case series and the studies not mentioning the treatment plan were excluded. Studies which included participants below the age of 14 years were also excluded.

PICO guidelines:

P: Population—Patients aged 14 years and above treated for coronoid fractures either conservatively or surgically.

I: Intervention—Patients treated with Open Reduction and Internal Fixation, Coronoidectomy.

C: Comparator—Patients treated with conservative management and observation.

O: Outcome—pain, mouth opening and occlusion.

Selection Process

For initial selection of studies, the title and the abstract of the studies was reviewed keeping in mind the inclusion and exclusion criteria. After, the initial selection of studies based on the title and abstract, full text of studies was viewed by all authors.

Data Collection Process

A standardized data extraction form was prepared in Microsoft Excel with the help of an expert. Initially 3–4 entries were made in the Excel and it was reviewed by an expert. Any disagreement between the authors was resolved by discussion.

The following data were extracted:

• i.Aim of the study
• ii.Type of study design
• iii.Sample size
• iv.Demographics of the study population
• v.Time duration of the study
• vi.Presence of other associated fractures
• vii.
  Treatment modality used:

  1. Conservative: Observation or Inter Maxillary Fixation for 3–4 weeks
  2. Surgical: Open Reduction and Internal Fixation or Coronoidectomy
• viii.Outcomes measured—pain, mouth opening, occlusion
• ix.Complications of various treatment methods

Risk of bias assessment

Risk of bias in included studies was assessed using the MINORS tool for retrospective studies and JBI Checklist for case-controlled studies. All authors together assessed the included studies for assessment of risk of bias.

Results

After comprehensive search, a total of 27 studies after removal of duplicates were found. For initial selection of studies, the title and abstract of studies was viewed. Based on the inclusion and exclusion criteria five studies were included. Four were retrospective studies and one was a case-controlled study.

Of the 27 studies found, 20 were case reports [3, 8, 13, 17–33], one was a book chapter [34] and one was a radiological study [10] which did not mention the treatment plan.

Following data was extracted from the five included studies: (Table 2)

Table 2.

List of included studies

Year	1985	2013	2014	2015	2017
Author	Rapidis	Shen	Boffano	Kale	Zhou
Type of study	Retrospective	Retrospective	Retrospective	Retrospective	Case Control
Year of data collection	1971–1980	2005–2010	2001–2010	2008–2013	2000–2009
Sample size	52	39	21	11	25-Case group 869-Control group
Unilateral/Bilateral	3-bilateral	10-bilateral	Not mentioned	2-bilateral	All unilateral
Associated fractures	12-isolated coronoid process fracture 23-mandibular fracture 10-ZMC fracture 2-LeFort II fracture 4-alveolar fracture	4-isolated coronoid process fracture 17-mandibular 18-midface	11-mandibular 16-midface fractures 1-frontal bone	1-Lefort II 7-mandibular 3-zygomatic arch	7-mandibular fractures 23-midface fractures 8-dental injuries 1-isolated coronoid process
Age	14–89 years	22–58 years	19–77 years	28–55 years	17–56 years
M/F	40-M 12-F	26-M 13-F	16-M 5-F	9-M 2-F	21-M 4-F
Etiology	38-RTA 10-assault 4-other	not mentioned	7-RTA 6-Assaults 6-Fall 2-Sports Injury	11-RTA	17-RTA 3-Assault 3-Fall
Treatment	44-IMF for up to 4 weeks 2-ORIF and Transosseous wiring 6-no treatment	16-conservative management with IMF for 1-2 weeks 23-Surgical management	All were treated with conservative management (observation or IMF not specified)	6-Conservative management using IMF for 3 to 4 weeks 5-ORIF	19-Coronoidectomy 5-Conservative management modality not specified 1-Declined treatment
Follow up	not mentioned	12–60 months	not mentioned	6 months	Not mentioned
Complications	Not mentioned	4-Jacob's disease 6-mandibular deviation towards fractured site on opening at the end of 1 wk., corrected at the end of 1-3 m 2-weakness in eye closure at the end of 1 wk., recovered 1–3 m later 1-air leakage when blowing cheek at end of 1wk, corrected 1–3 m later	Not mentioned	No complications	Not mentioned

The risk of bias for the four retrospective studies was done using the MINORS tool: (Table 3)

Table 3.

Risk of bias using MINORS tool for retrospective studies [35]

MINORS tool	Rapidis 1985	Shen 2013	Boffano 2014	Kale 2015
1. A clearly stated aim	0	2	2	2
2. Inclusion of consecutive patients	2	2	2	2
3. Prospective collection of data	1	2	2	2
4. Endpoints appropriate to the aim of the study	0	2	1	2
5. Unbiased assessment of the study endpoint	0	1	1	1
6. Follow-up period appropriate to the aim of the study	0	2	0	2
7. Loss to follow up less than 5%	0	2	0	2
8. Prospective calculation of the study size	0	0	0	0
Total	3/16	13/16	8/16	13/16

0 = not reported 1 = reported but not adequate 2 = reported and adequate

A study having a full score of 16 was considered as having low risk of bias, score in the range of 12–16 was considered having medium risk of bias and scores below 12 as having high risk of bias (Table 4).

Table 4.

Risk of bias using JBI checklist for case control studies [36]

JBI checklist for case control study	Zhou 2017
Were the groups comparable other than the presence of disease in cases or the absence of disease in controls?	Yes
Were cases and controls matched appropriately?	Yes
Were the same criteria used for identification of cases and controls?	Yes
Was exposure measured in a standard, valid and reliable way?	Yes
Was exposure measured in the same way for cases and controls?	Yes
Were confounding factors identified?	Unclear
Were strategies to deal with confounding factors stated?	No
Were outcomes assessed in a standard, valid and reliable way for cases and controls?	Unclear
Was the exposure period of interest long enough to be meaningful?	Yes
Was appropriate statistical analysis used?	Yes

The risk of bias was ranked as high when the study reached up to 49% of “yes” scores, moderate when the study reached from 50 to 69% of “yes” scores, and low when the study reached more than 70% of “yes” scores.

Two studies were found to have high risk of bias, two had moderate risk of bias and one study had low risk of bias.

All the five included studies mentioned the demographics of the patients [7]. There was a male predilection seen in all the studies. Out of total 148 patients included in the study, 112 patients were males and 36 were females with a ratio of 3.11:1. In most of the studies coronoid process fracture was commonly seen in the 4th decade of life, except for one where it was commonly seen in the 6th decade of life [1].

The incidence of coronoid fractures was less than 4% in all studies, ranging from 0.89 to 3.58% [1, 9, 37, 38].

Only four [1, 5, 7, 14] of the five studies raised the etiology of the fractures, most common etiology being motor vehicle or road traffic accidents (73 out of 114) followed by assault (19 out of 114) and fall (9 out of 114). The least common was sports injury, only two of the 114 cases.

All the studies stated about the presence of associated fractures. Out of the 163 coronoid process fractures evaluated in all studies, 65 of them were associated with mandibular fractures, 72 were associated with midface fractures, 12 were associated with dentoalveolar injuries, one with frontal bone fracture and 17 were isolated coronoid process fractures.

All five studies mentioned the treatment provided, a total of 148 patients with coronoid process fracture were evaluated. A total of 30 were treated by Open Reduction and Internal Fixation, 92 were treated conservatively, and no treatment was given to seven patients. A study [9] advocated the removal of the coronoid process, they treated 16 patients out of the 25 patients included in their study by coronoidectomy.

Two studies [1, 14] reported 3–4 weeks of IMF, whereas one study [9] reported 1–2 weeks of MMF. One study [5] did not mention the duration of MMF.

One study reported the following complications: deviation of mandible to the fractured side on maximum mouth opening which returned to normal after 1–2 months was seen in total of six out of 23 cases, two patients in the same study showed eye weakness and air leakage on blowing cheeks 1-week postoperatively and they recovered completely after 1–3 months. Malocclusion was seen in three out of 23 patients. Two patients reported with injury to the zygomatic branch and two patients reported with injury of the buccal branch [1].

The maximum interincisional opening was more than 37 mm in study by Shen et al. [9] In the study by Kale et al. [14] the maximum mouth opening in case of conservative management was 46 mm and in case of Open Reduction and Internal Fixation was 48 mm (Fig. 1).

Fig. 1.

PRISMA flow diagram [39]

Discussion

Coronoid process fractures are rare. Not only because of its anatomical position but also because it often is left undiagnosed. It is often left undiagnosed because it is superimposed on the radiographs taken regularly like OPG. Also, isolated fractures of the coronoid process are mostly asymptomatic. Most common symptoms include restricted mouth opening [9], limitation of mandibular movement, swelling in the zygomatic arch region [14, 40]. Intra orally, there may be ecchymosis or mild swelling of soft tissues in the retromolar area [14]. Lateral crossbite though rarely seen in association with coronoid process fractures is self-correcting after 1–2 weeks and is mainly caused because of muscular spasm [14]. The ideal radiograph to view coronoid process fractures is the standard occipitomental view or 15° occipitomental view [41]. However, the diagnosis has become much easier with the advent of CT scan [28].

There are no definitive guidelines available for the treatment of these fractures, leading to variability in treatment and thus more confusion as to how should coronoid fractures be treated; conservatively or surgically?

Natvig et al. [17], Oliveira et al. [42] advocated no treatment for intramuscular fractures as spasm of temporalis muscle is sufficient to hold the fragment till healing and IMF for submuscular fractures. Oliveira et al. in case of submuscular fracture, where the fragment is large and impedes mandibular function suggested ORIF and Transosseous wiring [23].

Kruger, Converse and Kazanjian & Converse suggested conservative treatment for minimally displaced fractures [3, 43]. Thoma advised intraosseous wiring of fragment through intraoral incision [3]. Dingman, Natvig, Walker advocated IMF as minimal treatment [3]. In case of significant displacement, Kruger suggested ORIF and intraosseous wiring. If reduction is not feasible then coronoidectomy was advocated by him [3]. Rapidis et al. believed tear of the periosteum lead to significant displacement due to the pull of temporalis muscle [14, 44].

Rapidis [14] and Delantoni [24] advocated IMF for up to 3–4 weeks for patients presenting with malocclusion and severe pain. No treatment if displacement is minimal and occlusion is satisfactory. ORIF and intraosseous wiring if the fractured fragment is large and affects the mandibular function. In case the fractured fragment is displaced towards the temporal fossa, he advocated no treatment, as in most cases function will be restored after acute phase [24].

Shen et al. [9] in cases requiring surgical management preferred extraoral approaches (modified retromandibular approach) [45–47] over intraoral approaches. Even though the risk of facial nerve injury was more with extraoral approaches, the modified retromandibular approach along the anterior border of parotid gland is a relatively safer zone. Intraoral approaches have their own limitations, like, limited exposure, injury to pterygoid plexus, maxillary artery and requirement of special surgical instruments.

One of the main aims in treatment of coronoid process fractures is to prevent the union of the fractured coronoid process with the zygomatic arch, also called as Jacob’s disease. Oliveira et al. [23]; Halazonetis et al. [48] and Baliga et al. [28] suggested aggressive physical therapy to avoid Jacob’s disease. Oliveira [23] has suggested a protocol for the same:

Relaxation of masticatory muscles (thermotherapy with dry heat) for 20 min followed by manual massage for 3 min (increases blood supply and helps in elimination of metabolic residues). Mandibular exercises like mouth opening with tongue on palate to increase muscular coordination, manual traction to prevent deviation to non-affected side and promote lateral movements to affected side and functional therapy (chewing) are then done. This protocol is to be followed for 3 months to prevent Jacob’s disease [23]. Walker however advised against physical therapy as increased movement may increase the displacement and delay union [49].

Based on the summarization of the data from the included studies, we have recommended the following protocol: (Fig. 2)

Fig. 2.

Treatment protocol for management of coronoid process fractures

Limitations

Though this study has included all the articles published till January 2021, yet the number of articles on the topic are not adequate. A meta-analysis could not be performed as the data on preoperative and postoperative measurements was scarce.

Implications

Deciding upon the appropriate treatment modality for coronoid process fractures presents a challenge to oral and maxillofacial surgeons worldwide. Though the literature available on this topic is scarce; in this systematic review an attempt has been made to aggregate all the scientific literature available on the topic, so as to help surgeons make a better-informed decision.

Furthermore, it is recommended to conduct randomized studies on the topic, so as to obtain strong scientific evidence. But conducting randomized control trials on coronoid process fractures is difficult and will span over a period of several years owing to its rarity. Hence, a protocol for reporting and treatment should be established which can be followed worldwide with a multicentric study and the results obtained after following the protocol can be published. The protocol depending on the results obtained can be modified over time.

We recommend using the SCARE 2020 Guidelines [50] for reporting of Case Reports and the PROCESS Guidelines [51] for reporting of Case Series.

Conclusion

The most common treatment modality for management of coronoid process fractures based on all the studies included was conservative management by IMF. The least common treatment modality was coronoidectomy. Surgical management was indicated only when there was impaired mandibular function. Extraoral approaches were preferred in the studies that managed the fractures surgically. A lack of information and standardisation was found in the studies done on the management of the coronoid process fractures making a large multicentred randomized control trial is an absolute necessity.

Author Contribution

The idea for the article: TPK, RP. Literature search: RP, TPK, SMK. Data analysis: RP, TK, SMK, HP. Draft: RP, TK, SMK, HP. Revision: RP, TK, SMK, HP.

Funding

The authors did not receive support from any organization for the submitted work.

Declarations

Conflict of Interest

All authors declare that they have no conflict of interest.

Consent to Participate’ and/or ‘Consent to Publish

Not applicable as this is a systematic review.

Ethics Approval

This is a systematic review registered under PROSPERO: CRD42020200700.

Research Involving Human Participants and/or Animals

Not applicable as this is a systematic review.

Informed Consent

Not applicable as this is a systematic review.