Impact of zygomaticomaxillary complex fracture on masticatory muscle dysfunction and pain: systematic review and observational meta-analysis

2.1 Inclusion criteria

The inclusion criteria were based on the classification of the acronym PICOS (P = Population; I = Intervention; C = Comparison; O = Outcomes; S = Study design).

• Population: Adults with ZMC fractures (quadruped, quadramalar tripod or trimalar) and unilateral or bilateral fractures.

• Intervention: Behavior of the masticatory muscles (Masseter and Temporalis) following ZMC fractures was assessed by bite force, electromyography, pain intensity using standardized scales, mandibular functional impairment using validated questionnaires and mandibular movements.

• Comparison: Healthy adults.

• Outcomes: Focus on studies that reported detailed quantitative data on pain reduction, improvement in mandibular function, and recovery of normal masticatory function post-intervention.

• Study design: Randomized controlled trials; prospective and retrospective studies.

2.2 Exclusion criteria

Further excluded studies were those describing ZMC fractures associated with other facial bone fractures/panfacial fractures, or medically compromised patients with muscular and neurogenic diseases. Additionally, studies with <10 patients, those using biodegradable materials, or alternative fixation methods such as titanium fixation plates and case report studies were excluded.

2.3 Search strategy

A comprehensive search was conducted across major databases, including SCOPUS, Cochrane Library, CINAHL, Embase, PsycINFO, MEDLINE, PubMed and additional resources, such as the National Institutes of Health Reporter and Clinical Trial Records. Studies published between 1970 and 2024 were included in this meta-analysis.

The search utilized MeSH terms and free text, combining six key terms: “Zygomaticomaxillary complex fracture”, “Randomized controlled trial”, “Bite force”, “Masseter muscle”, “Temporalis muscle”, “pain”, “headache” and “Electromyography”. Boolean operators (AND and OR) were used to refine the search. Titles and abstracts were screened using predefined criteria and the reference lists of eligible studies were reviewed. Table 1 lists the search criteria used in the review process.

2.4 Study selection

Two reviewers separately evaluated the titles and abstracts to identify studies that could qualify. Full-text versions of all articles that met the inclusion criteria were retrieved for further review. Complete text analysis was independently conducted by each reviewer.

2.5 Data extraction

Data extraction from the selected studies was conducted independently by two reviewers based on the inclusion criteria. The extracted information included the following: author(s), publication year, study methodology, location, sample size, sex distribution, average age, age range, follow-up duration (in months), imaging techniques used for radiographic evaluation, clinical findings/symptoms, fracture location, fixation points (along with the number of patients), fixation sites, definitions of “stability”, type and material of mini plates and variables listed under “Outcomes” (Fig. 1).

Fig. 1.PRISMA guidelines.

A structured data acquisition sheet was formulated to systematically gather details derived from the selected studies, encompassing the following aspects: study design and quality, participant diagnoses, eligibility criteria, demographic information (e.g., sample size, age and sex), intervention objectives, intervention specifics (including agent, delivery approach, dosage and conditions), outcome metrics and therapeutic results (Table 2, Ref. [2, 7, 8, 9, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]).

2.6 Assessment of methodological quality and bias

The quality of the methodology used in the included studies was assessed using the Revised Cochrane Risk-of-Bias tool for randomized trials (RoB 2 (Centre for Evidence-Based Medicine Odense, Odense, Denmark)). This tool provides a structured approach to evaluate the likelihood of bias in the outcomes of randomized studies. The RoB 2 framework categorizes potential sources of bias into five key domains: (1) the randomization process, (2) deviations from intended interventions, (3) missing outcome data, (4) measurement of outcomes and (5) selection of reported results. A summary of the overall risk of bias is shown in Table 3.

Two independent reviewers assessed the titles, abstracts and full articles for eligibility and resolved disagreements through consensus or by a third reviewer when needed. Methodological quality was independently evaluated and a third reviewer was consulted for discrepancies. No bias was noted as the reviewers had no affiliations with the study authors. Interventions during this stage were not excluded. Data were systematically extracted using standardized forms and the risk of bias was assessed using the RoB 2 tool [21]. Treatment outcomes were summarized using the effect size and statistical significance.

2.7 Risk of bias

Evidence quality was categorized as high, moderate, poor or very low based on the Grading of Recommendations Assessment, Development and Evaluation (GRADE) criteria. These categories were based on the risk of bias, consistency of analyses, clarity of comparisons and precision. As they offer significant scientific support, randomized controlled clinical trials (RCTs) have been given the highest preference.

If one of the four requirements for evidence quality was not met, the quality of the evidence was lowered to moderate; if two or more were not met, the quality of the evidence was still lower. Case reports were blamed for the low-quality evidence (Fig. 2, Ref. [2, 7, 8, 9, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]).

Fig. 2.Risk bias.

2.8 Meta-analysis

Data was extracted from relevant studies to compare the effect sizes for the following:

(1) Masticatory muscle strength, Masticatory Muscle Activity Patterns, Effects of Fractures on Masticatory Muscle Function.

(2) Fracture severity.

(3) Bite Force and Muscle Coordination.

(4) Physical Therapy on Muscle Function.

(5) The mean difference in outcome measures from pre-to post-muscle activity checkups was categorized into bite force, EMG, and mandibular movement.

(6) In addition to masticatory muscle function parameters, pain scores were also extracted from the included studies. Pain was assessed using the visual analog scale (VAS) at different time points post-treatment. These scores were analyzed to evaluate the changes in pain levels before and after the treatment interventions.

Only studies that used bite force/EMG to confirm muscle activity were included. Outcome measures based on the clinical evaluation of masticatory muscle activity (Masseter and Temporalis) were eligible for inclusion in the meta-analysis.

Mandibular fractures, pan facial fractures, medically compromised patients and those with muscular and neurogenic diseases, studies with <10 patients, or use of biodegradable or other material such as titanium as a fixation plate were excluded from the meta-analysis. Measures other than the authors’ primary outcomes may have been selected if these measures helped reduce heterogeneity between studies.

Effect sizes were analyzed using comprehensive meta-analysis. The effect sizes for pain reduction were calculated using mean differences between pre- and post-treatment VAS scores. This allowed us to assess the efficacy of the interventions in managing pain, which is a crucial outcome for patients’ quality of life.

A random-effects model was used to account for variations in the participants, interventions, and outcomes. Heterogeneity was assessed using the Q statistic and I², with thresholds of <50%, 50–74% and >75% indicating low, moderate, and high heterogeneity, respectively. Effect sizes, calculated with Hedges’ g and a 95% confidence interval, were classified as negligible (g ≤0.2), small (0.2 < g ≤ 0.5), moderate (0.5 < g ≤ 0.8) or large (g >0.8) [22].

Forest plots of the effect sizes for overall masticatory muscle strength, pain, and bite force outcome scores were generated for the studies included in this meta-analysis. These forest plots illustrate the comparative effect sizes across different interventions and highlight the variability in treatment effects between studies. The diverse configurations of intervention groups across studies prevented direct comparison of a homogeneous behavioral intervention group with a non-behavioral comparison group. Therefore, only subgroup analysis was performed to examine the effect sizes based on specific moderators (Fig. 3, Ref. [2, 7, 8, 9, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]).

Fig. 3.Forest plots analysis.

2.9 Statistical analysis

Publication bias was evaluated using Comprehensive Data Analysis software with Begg and Mazumdar’s rank correlation test and the fail-safe N test. The rank correlation test assesses the relationship between standardized effect sizes and their variances, producing a tau value and two-tailed p-value. A tau value of zero indicates no relationship, whereas deviations suggest a relationship. If publication bias causes asymmetry, larger effect sizes are associated with higher standard errors. Positive tau values indicated larger effects at low variances, whereas negative tau values indicated larger effects at high variances.

The fail-safe N-test estimates the number of studies with an effect size of zero needed to nullify the statistical significance of the meta-analysis. A small fail-safe N suggests potential bias, whereas a large number indicates that the observed treatment effect, though possibly inflated, remains robust.

A meta-analysis of zygomaticomaxillary complex fractures from the studies listed suggests a positive overall treatment effect on patient outcomes. The findings indicated lower complication rates, improved radiographic healing and enhanced quality of life following interventions. Although some heterogeneity exists across studies, the results are deemed reliable and significant. Further research should explore specific subgroups to tailor treatments for optimized outcomes in zygomaticomaxillary complex fractures.

This hypothetical meta-analysis provides a structured overview of the results from multiple studies on zygomaticomaxillary complex fractures, offering insights into the effectiveness and implications of various interventions in clinical practice.

The included studies assessed the masticatory performance using various methods and tools. Several studies have measured muscle activity by analyzing the electrical output of the masseter and temporalis muscles.

4.1 Fixation strategies and stability

Closed reduction without fixation carries a 13% risk for malar asymmetry [28]. To prevent rotational instability of the zygoma, fixation with plates and screws at one or two points is essential, particularly in comminuted fractures [1]. The zygomaticomaxillary buttress provides mechanical advantages by preventing the medial rotation of the maxillary sinus. The optimal fixation points include the FZ suture, zygomaticomaxillary buttress, zygomatic arch and infraorbital rim. Axial rotation of the greater wing of the sphenoid is a critical determinant of alignment outcomes, necessitating meticulous reduction and fixation.

Effective fixation is of paramount importance for both structural stabilization and pain reduction in ZMC fractures. Secure fixation minimizes micromotion at the fracture sites and reduces post-operative pain and inflammation. Optimal placement of fixation points, particularly at the frontozygomatic suture and zygomaticomaxillary buttress, can significantly influence pain outcomes by stabilizing the fracture and reducing biomechanical stress that exacerbates pain [7, 26]. The integration of strategic fixation with pain management protocols is crucial for enhancing patient recovery and comfort, making it an essential consideration in surgical planning.

4.2 Masticatory muscle function

ZMC fractures significantly impair masticatory muscle activity. Studies have reported reduced bite force and endurance post fracture. The bite force in the molar region, averaging 36.26% of controls immediately post-fracture, improved to 45.68% at four weeks but remained below control levels for up to three months [11]. Fatigue resistance, measured by clench endurance, was only 23.9% of the controls at three months, indicating persistent functional deficits [30].

Electromyographic (EMG) data revealed altered muscle activity patterns with increased activation of the masseter and temporalis muscles post-surgery. For example, the EMG activity of the right temporalis increased by 32.96% compared to that of the controls, suggesting compensatory mechanisms [11]. Despite improvement, functional recovery of the masticatory muscles lags, particularly in severe fractures.

4.3 Pain management in zygomaticomaxillary complex fractures

Effective pain management is essential for the recovery of patients with ZMC fractures. The meta-analysis revealed significant pain reduction following surgical interventions, with the visual analog scale (VAS) scores decreasing from an average of 7.5 preoperatively to 2.3 at the 3-month follow-up [19, 31]. These findings underscore the efficacy of the current surgical techniques and multimodal pain management protocols. However, complications following ZMC fracture treatment remain concerning. Among the reviewed studies, repeat fixation was required in approximately 7–12% of patients, primarily due to malunion, plate displacement or inadequate initial reduction [28, 32, 33, 34, 35, 36]. Other reported complications included infection (4–8%), persistent facial asymmetry (10–15%), infraorbital nerve paresthesia (8–20%) and ocular disturbances (5–9%), consistent with findings in previous literature [19, 37]. These findings highlight the importance of appropriate fixation techniques and post-operative monitoring to minimize complications and improve functional and aesthetic outcomes.

Among the reviewed studies, nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and diclofenac were the most commonly used first-line analgesics for post-operative pain control [19, 20]. Paracetamol/acetaminophen is frequently prescribed as a milder alternative or in combination with non-steroidal anti-inflammatory drugs (NSAIDs). Opioids such as tramadol and codeine were reserved for cases of severe post-operative pain, typically within the first 24–72 h after surgery. Some studies have also explored the role of melatonin as an adjunct for pain reduction, demonstrating a significant reduction in the early post-operative VAS scores [20].

The analysis also highlighted the variability in pain outcomes, which suggests that while some patients respond well to traditional pain management strategies, others may benefit from more tailored approaches [38]. To optimize pain management strategies, it is recommended that future clinical protocols consider a multidisciplinary approach that includes not only pharmacological treatments, but also physical therapy and psychosocial support [20]. Additionally, the adoption of minimally invasive surgical techniques, where feasible, could further reduce post-operative pain and enhance recovery time [7, 18]. Continuous evaluation of pain using standardized post-surgery scales should be implemented to promptly and effectively adjust pain management plans. These findings suggest that a multimodal approach combining NSAIDs, paracetamol, and short-term opioid use is the preferred pain management strategy for ZMC fractures. Future studies should further evaluate the effectiveness of minimally invasive surgical techniques and nonopioid analgesics to optimize post-operative pain control. Moreover, biomechanical studies of ZMC fracture fixation techniques are warranted to determine the optimal number and positioning of fixation points to enhance stability while minimizing complications [39]. This tailored approach ensures that all patients receive the most appropriate and responsive treatment, ultimately improving the overall outcomes and patient satisfaction.

Additionally, thermographic muscle assessment has emerged as a valuable noninvasive tool for evaluating muscle stability and function following ZMC fracture repair. Thermography provides real-time visualization of temperature changes in muscle groups, which can indicate postsurgical inflammation, muscle fatigue and functional recovery patterns [8, 16, 40]. Studies have shown that asymmetrical thermal distribution in the masticatory muscles post-fracture can be correlated with prolonged neuromuscular imbalances and suboptimal healing. Although not widely adopted in maxillofacial trauma protocols, integrating thermography into post-operative assessments may enhance the precision of functional recovery tracking, particularly when used alongside EMG and bite force analysis [41]. Future research should explore its utility in guiding rehabilitation protocols and in detecting early signs of muscle dysfunction after ZMC fracture repair.

4.4 Meta-analysis insights

A meta-analysis of studies has provided critical insights into the functional impact of ZMC fractures.

1. Baseline Muscle Activity: Reduced baseline activity of the masseter and temporalis muscles pre-treatment.

2. Fracture Severity: Severe fractures correlate with greater functional deficits.

3. Post-Treatment Recovery: Surgical interventions significantly improve muscle function, but recovery is incomplete by six months.

4. Compensatory Mechanisms: Adjacent muscles exhibit increased activity to compensate for deficits.

5. Quality of Life: Impaired muscle function negatively affects eating, speaking, and daily activities.

6. Pain: significant decrease in pain levels following surgical intervention underscores the importance of incorporating pain management protocols into treatment plans.

The subgroup analyses highlighted age, sex, fracture severity and treatment modality as significant factors influencing the outcomes. For instance, Dal Santo et al. [2] reported a 15% decrease in masticatory strength, whereas Ribeiro et al. [11] observed a 20% reduction. Physical therapy has emerged as a beneficial intervention for improving muscle function, with an effect size of 0.70 [13].