Impact of the COVID-19 pandemic on maxillofacial trauma surgery in Germany - implications from the national DRG database

Purpose The COVID-19 pandemic has affected the personal and social lives of millions of people and also impacted the etiological factors of midfacial trauma such as falls, interpersonal violence or traffic accidents. The aim of this study was to analyze the influence of the COVID-19 pandemic on maxillofacial trauma surgery in the German healthcare system. Methods Nationwide data regarding the national diagnosis-related-group (DRG) inpatient billing system used in all German hospitals was received from the German Federal Statistical Office. Various trauma-associated procedures of the Operation and Procedure Classification System (OPS), a German modification of the International Classification of Medical Procedures (ICPM), were statistically associated with different epidemiological factors between 2012 and 2021. Results A statistically significant decrease (p < 0.05) in surgeries regarding maxillofacial fractures was registered during the years 2020 and 2021. Young male patients had the largest decline in maxillofacial trauma surgeries during this period (p < 0.05). In contrast. elderly patients 80 years and older showed a dramatic increase in the frequency of fractures in both the midface and the mandible (p < 0.05). Conclusions During the COVID 19 pandemic there has been a shift in the number, composition and etiology of maxillofacial fracture surgeries. Measures of social distancing and personal risk avoidance had a societal positive effect on the frequency of facial injuries. This stands in contrast to the drastic increase in fractures of elderly people who should be protected primarily by the measures taken. These results can help to understand these influences better in future pandemics. Trial registration German Clinical Trials Register No: DRKS00032778.


Introduction
The COVID-19 pandemic caused by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has had an enormous impact on the life, behavior and habits of each individual as well as on the coexistence of society in general.Both personal and governmental measures have been taken worldwide to curb the spread of the virus and, Traumatic facial injuries are particularly common among young adult males [4,5].The most common causes are traffic accidents, falls, physical violence and sports injuries.These are subject to strong seasonal trends and fluctuations [3,6,7].Open reduction and internal fixation has become the standard procedure for fractures of most facial regions.Since the evidence for the superiority of surgical treatment in the area of mandibular condylar process fractures has been proven in the last two decades, conservative treatment with closed reduction and maxillomandibular fixation still plays a certain role [8][9][10].
Data from a single center study in Germany suggest a decline in frequency of traumatological cases between 2019 and 2020 in both facial fractures and facial soft tissue injuries [11].Local single center studies and regional multi center studies from different countries and continents have also shown a change in volume and a shift in the type and cause of facial injuries, despite to our knowledge there is no nationwide investigation representing a central European country like Germany [12].
The purpose of this study was to examine the nationwide impact of the COVID-19 pandemic on patients in need of surgical management of facial fractures in Germany.For this purpose, the regional, gender-specific and age-related distribution of patients with facial fractures who required inpatient open reduction and internal fixation in various anatomical regions of the midface and mandible were evaluated.

Materials and methods
The national diagnosis-related groups (DRG) inpatient billing system includes data from all hospitals in Germany that use the DRG system.More than 99% of inpatient treatments in Germany are covered.Hospitals are required by law to provide comprehensive information about hospital care, including patient demographics, diagnoses, comorbidities, complications and procedures.
Surgical procedures from the years 2012 to 2021 were coded according to the Operation and Procedure Classification System (OPS), a German modification of the International Classification of Medical Procedures (ICPM).All diagnoses were coded according to the German version of the International Classification of Diseases and Related Health Problems, 10th Edition (GM ICD-10).Detailed lists of all procedures regarding facial fractures per year (coded 5-760, 5-761, 5-762, 5-763, 5-764, 5-765, 5-766 and 5-767 in the German procedure classification OPS) were provided by the German Federal Statistical Office (Statistisches Bundesamt -Destatis.Genesis-Online.Data licence by-2-0).The dataset contains all inpatient procedures regarding maxillofacial fractures performed in Germany within the observational period classified by year, gender, age and federal state.Maxillofacial procedures per year (PPY) were calculated and reported as median and range.In addition, population-adjusted rates of maxillofacial trauma surgeries per 100 000 inhabitants were calculated using population data also provided by the German Federal Statistical Office.In order to overcome seasonal influences, the fracture incidence was analyzed per year.Procedures were grouped according to the years 2012-2019 as pre-COVID years and 2020-2021 as COVID years.Cumulative incidences of COVID-19 were provided by the Robert-Koch-Institut [13].The normality of the distribution of continuous variables was tested by Kolmogorov-Smirnov test.Continuous variables with normal distribution were presented as mean and standard deviation; non-normal variables were reported as median and range.Means of 2 continuous normally distributed variables were compared by independent samples Student's t-test.Mann-Whitney U test was used, respectively, to compare means of variables with group sizes smaller than five or not normally distributed.Categorical data was presented through frequencies and percentages.The differences were considered significant at p < 0.05.Two-sided p-values were presented unless otherwise noted.Statistical analysis was performed using IBM SPSS Statistics Version 29.0 (IBM Deutschland GmbH, Böblingen, Germany).This trial was registered at German Clinical Trials Register (https:// www.drks.de)No: DRKS00032778.

Regional differences
Looking at the 16 federal states individually the number of maxillofacial trauma surgery procedures ranges from 19.0 (Brandenburg) to 57.8 (Bremen) per 100 000 inhabitants prior to COVID-19 (Table 2; Fig. 4).During the pandemic there was a decline in facial fracture surgery found in 14 of 16 federal states, 8 of which were statistically significant ranging from − 2.9% in Saxony to -26.3% in Saarland.An increase in interventions can be seen in Rhineland-Palatinate (+ 5.5%) and Berlin (+ 10%), both without statistical significance.There was no correlation to regional cumulative incidence of COVID-19.
In comparison changes within the pandemic were weak with an overall decrease of 2.8% between 2020 and 2021.
Only fractures of the mandibular ramus and condylar head (+ 2.7%) and fractures of the frontal sinus (+ 3.2%) showed a slight increase between 2020 and 2021.
In our study, young adolescent and adult males from 15 to 34 years are the main group suffering from facial fractures, representing 32% of all registered maxillofacial trauma procedures.During the COVID-19 outbreak there was the highest absolute and relative decrease from 7076 PPY to 5688 PPY (-25.8%,p < 0.05) in this subgroup and representing 58,6% of the overall decline in maxillofacial fracture procedures (Fig. 3).The second most affected group, males aged 35-59, showed the second largest absolute decrease from PPY 5688 to PPY 5044 (-11.3%, p < 0.05).Both males and females over 80 years are the only subgroups showing an increase in facial fracture associated procedures from The median annual number of inpatient facial injury associated diagnoses, including patients with conservative and soft tissue injury inpatient treatment, decreased by 19.7% during the pandemic.As a shift in conservative and soft tissue injury treatment from the inpatient to the outpatient sector is likely within the situation of scarce medical resources in the pandemic and the number of facial injury associated diagnoses is not necessarily related to the severity of the injury or the number patients affected, this number has to be interpreted with caution when interpreted as a surrogate for the number of underlying traumatic events.
Our results were in accordance with other studies describing a decrease of maxillofacial fractures after the COVID-19 outbreak.Salzano et al. describe a decrease in maxillofacial fractures in an Italian multicenter study [17].De Boutray et al. show a decreased incidence of maxillofacial trauma requiring surgery in a French multicenter study [18].This is in accordance with the experience of multiple single center studies in different European countries [11,

Discussion
The COVID-19 pandemic was a worldwide challenge for all societies and everybody's personal life.Measures of social distancing, individual safety precautions and hygiene were proven to be effective means in prevention of viral spread in most countries worldwide [14].Also, in Germany, depending on the incidence, strict lockdowns and social distancing were imposed in order to slow down the spread of the COVID-19 infection by home quarantines, residence regulations, nationwide and regional curfews, cancellation of community events and the restriction of local and long-distance public transport.Elective health treatments have been temporarily suspended or postponed in favor of caring for affected patients and conserving human resources [15,16].
During the COVID-19 pandemic maxillofacial trauma procedures in Germany declined by 10.7%.This applies equally to the years 2020 and 2021, between which the number of interventions fell only slightly by 2.8% which might be a consequence of the pandemic wave and their associated worldwide known phenomenon [37,38].Regarding the different anatomical regions, the largest decreases were seen for lateral midfacial fractures, orbital fractures and frontal sinus fractures.In contrast, the decline of mandibular fractures was more moderate.This could be a consequence of the different etiological factors influenced by the COVID-19 pandemic, especially concerning interpersonal violence and traffic accidents, which are also influenced by geographic location, population density, economic status, and cultural differences [3].The regional analysis of the data shows that the decline in facial fractures is a nationwide effect that is not restricted to just a few cities, regions or centers.The 19 -22].Also in the USA and Australia a decrease in facial fractures was reported in single center evaluations [23][24][25][26][27], despite there also being studies in the USA suggesting no significant change in facial trauma incidence, maybe due to a less restrictive policy of social distancing after initial lockdown compared to European countries [28,29].In Asian and Middle Eastern countries, specifically in India, South Korea and Jordan a decline in maxillofacial trauma surgeries was also described [30][31][32][33].Non-maxillofacial fractures like ankle, hip or distal radius fractures were described to show a reduced incidence as well [34][35][36].Reduced trauma associated admissions to primary care centers is a violence associated facial fractures and injuries while the pandemic [25,27,[40][41][42].Although there are some studies describing a higher proportion of interpersonal violence in the incidence of facial injuries in France, Italy and the USA [18,22,23].
As road traffic accidents are the second most common cause of facial fractures the decline in road traffic accidents involving personal injury to a historic minimum is a second mechanism explaining a decline in facial fractures in Germany [43].This is supported by data from France, Italy, Jordan and India [18,19,22,33,40,42].
The restriction of social and societal life naturally also has an impact on private and professional contacts and could explain a decrease in facial fractures due to sports injuries and work accidents as other important causes of fractures [39,44].This was also described in studies from Australia, France and South Korea [18,25,32].
In elder people, falls are the most common cause of facial fractures, which are insignificant in other age groups [39].The significant increase in facial fractures in the age group lack of correlation to the cumulative regional COVID-19 incidence shows that the reduction in facial fractures is not due to the regional infection load but rather to the measures taken and their social effects.
Interpersonal violence was found to be the main cause of fractures in both the mandibular and midface regions especially among young men [3,39].In our data the decline of fractures in young male adolescents and adults between 15 and 34 years is representing more than 50% of the overall decline of maxillofacial fracture procedures.This may indicate that during the COVID-19 pandemic 2020-2021 the reduction of interpersonal violence is one of the main reasons for the reduced incidence of maxillofacial fractures.This thesis is also supported by the rather moderate, non-significant decline of fracture reductions in women for whom physical violence is not the most prominent cause of facial fractures.This also explains a significant shift to a more balanced gender ratio [3,39].Several single-and multicenter studies from different countries like Australia, Finland, India and the UK show a reduction in interpersonal or who use other reimbursement schemes could not be included.As reimbursement of trauma cases for hospitals in the DRG system covers more than 90% of the German population, we believe, however, that the dataset covers the vast majority of treatments.Another limitation is the completeness of the dataset itself, which provides information at only an aggregated level and in limited detail without information about a specific cause or severity of the injury; therefore, a more advanced analysis including anamnestic and diagnostic information was not possible in this scale using reimbursement data.This would, however, be interesting to evaluate further the impact of the COVID-19 pandemic on maxillofacial trauma care in detail.
To the best of our knowledge, this study is the first to examine the influence of the COVID-19 pandemic on the incidence and distribution of facial fractures at a national level in Germany.It can contribute to an analysis of the influence of legislative and personal measures to combat the pandemic on the associated shift in the genesis of facial fractures.The description of positive and negative effects can contribute to the future addressing of risk groups both during and outside of pandemic situations.For this purpose, the investigation of the direct influence of the measures on the causes of facial fractures should be expanded.

Conclusion
Trauma surgery experienced a dramatic change worldwide during the COVID-19 pandemic.This has also been observed in Germany with a drastic decline in the surgical treatment of facial fractures accompanied by a significant increase in the frequency of fractures in the COVID-19 risk group of elderly people (+ 80).Measures of social distancing and personal risk avoidance had a societal positive effect on the frequency of facial injuries.However, this is contrasted by the drastic increase in fractures in the group that is most dependent on social support and basically should rather be protected by the measures taken.
of 80 years and more (+ 23.5%, p < 0.05) and the increase in the average age suggests a significant increase in falls, possibly as a result of social distancing, social isolation and lack of social support of older people in the context of the COVID-19 outbreak.This is consistent with results describing the negative effect of social distancing on the physical and mental health of older people during the pandemic [45].A pandemic-associated increase in facial injuries caused by falls is described in several publications from Australia, UK, India and Italy [17,19,20,25,27,40,42].
This study is subject to certain limitations, which are mainly related to the dataset that was available for analysis.First, the specific reimbursed OPS codes only represent fractures treated by open reduction and internal fixation in the analyzed years.Fractures treated non-surgically are not included in the dataset.Second, the study only includes trauma cases performed during a hospital admission that led to the billing of a DRG.Patients treated as outpatients 8 ± 21.6 years before the pandemic to 48.4 ± 22.0 years during the 2020-2021 pandemic years (p < 0.05).In children aged 0-14 years treatment frequency decreased by 9.3% from 437 PPY (396-509) to 396 PPY (385-403) (n.s.).Young adolescents and adults aged 15-34 years showed the largest decrease in facial trauma surgery by 22.5% from 8187 PPY (7745-9210) to 6260 PPY (6240-6280, p < 0.05).In the age group 35-59 years the number of fracture repairs decreased from 7663 PPY (7542-7954) to 6896 PPY (6698-7095), corresponding to a decrease of 9.9% (p < 0.05).In the age group 60-79 years surgical fracture reduction decreased only slightly from 4357 PPY (4115-4700) to 4261 PPY (4175-4346) by 1.8% (n.s.).Remarkably, the incidence of fracture repairs in the age group over 80 years increased against the trend by 23.5% from 1653 PPY (1411-1980) to 2023 PPY (2012-2033) (p < 0.05).Overall the median annual number of inpatient facial injury associated diagnoses (ICD10-S01 -ICD10-S02) also including soft tissue injuries and conservative inpatient treatment decreased from 55,401 between 2012 and 2019 to 44,469 in 2020 and 2021 (-19.7%;p < 0.05).

Fig. 1
Fig. 1 Age-gender-diagram of facial fracture associated procedures per year before and after the COVID-19 outbreak

Fig. 2
Fig. 2 Total numbers of facial fracture associated procedures per year from 2012 to 2021.There were statistically significant changes found after the COVID-19 outbreak (2020-2021) for midfacial fractures,

Fig. 3 (
Fig. 3 (A) Absolute number of facial fracture associated procedures prior to and after the COVID-19 outbreak in the different age groups (B) Relative percent change of facial fracture associated procedures prior to and after COVID-19 outbreak in different age groups

Table 1
Median numbers and range of facial fracture associated procedures per year prior to and after the COVID-19 outbreak in Germany (p-value according to * Mann-Whitney-test and ° student's t-test)