Similar to most European countries, CMF surgery in Germany is the core specialty responsible for CMF injuries. Its unique characteristics comprise undergraduate dual-degree (MD plus DDS/DMD) requirements, five-year training standard, and full scopes of head and neck surgical practice [17, 18]. However, only 158 of 1914 (or 8.3%) German hospitals can offer CMF patient care [3, 4]. There has, therefore, been an upward trend in hiring one or two, either full- or part-time, CMF surgeons in the trauma unit of hospitals without a standalone CMF section. This circumstance has compelled many changes and challenges, i.e., CMF education is provided for other specialty trainees, while it is unapproved and unaccredited by the German Medical Council in all federal states. Rotational trainee sharing, hence, becomes essential in this organization model, and requires investigations concerning the benefit-risk appraisal including patient safety.

The key aim of this study was to determine whether trainees’ background influenced patient outcomes with regard to LHS and CFRCs. We hypothesized no outcome differences between the trainee groups. The results of this study accepted the null hypothesis, i.e., the coronal flap could be performed by TS-Rs as the primary surgeon with favorable clinical outcomes, after they had assisted in ≥ two coronal flaps performed by the skilled CMF surgeon. This finding suggests a steep (easy) learning curve of the procedure, i.e., an uncomplicated, non-technically demanding procedure. Experienced trainees in other surgical specialties can begin CMF trauma surgery in some circumstances (for example, when the CMF consultant surgeon is busy with other patient care) and may need the consultant only for skeletal reduction and fixation, and dental occlusion control, if they are properly trained. Our findings appear comparable to those of other works reported by staff surgeons in diverse specialties (Table 3), suggesting that well-trained trainees could operate this flap so well as staff surgeons do.

German medical education, especially residency training, remains highly variable. Previously, residents in this country were autodidactic, i.e., they could independently work from their mentors, i.e., staffs (“Facharzt/-ärztin”) and consultants (“Oberarzt/-ärztin”), and the departmental head. Nowadays, it is mandatory that at least one staff or consultant surgeon is present during major surgeries. Certain patient care such as minor surgeries and patient follow-ups may not require continuous guidance or supervision, if respective/related competencies have been achieved and reassured [31, 32]. The self-standing practice simply facilitates case-based learning, and in surgery, promotes operative skills, and encourages trainees to participate in a discussion, where relevant, with their mentors. This “learning by mentorship” format not only assures learner’s engagement, but adds deliberative tools, such as critical analysis, appraisal and problem solving to an individual patient. Moreover, it provides a practical application of theoretical knowledge passively gained from earlier lectures and seminars, and the cultivation of professionalism, i.e., confidentiality, competency and responsibility [33]. However, close mentorship was found to be linked to better resident’s satisfaction [32, 33]. A recent German survey showed very low satisfaction among otolaryngologic residents due to training quality, i.e., < 30% of residents were satisfied or very satisfied. The dissatisfaction mostly arose from limited supervision and low numbers of surgery cases [32]. It can therefore be implied that surgical educators must find the “middle path” to ameliorate the training quality.

In the real world, teaching surgeons are often pressured toward operating more and teaching less. Possible reasons are diminishing reimbursements, demanding high-quality outcomes including low complication rates and short LHS, and inefficiency of regulation and defensive practice. All pressures trample over surgical education and learner’s satisfaction [34]. The link between intraoperative independence (self-standing performance) and trainee’s satisfaction is beyond this study’s scope and requires further investigations.

One provoking factor is that too many residents, despite reduced workloads of the faculty surgeons, concurrently reduce operative volume for trainees. Apart from preference (e.g., toward facial aesthetic surgery for further career in private practice [35]), the perception of cases being “stolen” by one another may develop and subsequently curtails satisfaction of residents in training.

At the training end, residents and fellows are supposed to enter the exit examination. Surgical board certification examinations in Germany are unlikely to be based on practical competencies, but depend mainly on the examiners (i.e., neither rigid standard nor writing examination nor case presentation), and focus on the minimal number (“not” the quality) of performed procedures. It was the first author (P.P.)’s subjective experiences that some CMF surgeons were be able to pass the German board examination without an essential ability to perform basic procedures (i.e., without the need for help), for example, tracheostomy, orbital floor fracture repair, neck dissection, or extraoral draining of deep space infections of the neck. A possible explanation is that some CMF departments arrange very long ward works, for example, one CMF center in Saxony arranged a six-month ward rotation (with no involvement of surgery at all) for its trainees, which reduces the trainee’s operative skill and confidence during this long period of ward rotation. Some centers separated their trainees into subgroups, e.g., trainees in one CMF clinic in Hessen are divided into cleft-craniofacial and orthognathic, or head and neck tumor and reconstructive, or CMF trauma subgroups, according to the trainee’s interest and/or department’s organization. No or at least no wider competency across subgroups is gained and maintained and appears problematic. Trainees in the cleft-craniofacial and orthognathic subgroup often face difficulty in post-microsurgical monitoring in oncologic reconstructive patients, when the trainees work during the night shift, and trainees in the CMF trauma subgroup almost never perform a neck dissection by themselves (unpublished data).

During the 14th International Congress of the Turkish Association of OMF/CMF surgeons in 2007, Daniel M. Laskin [36], a former professor of Virginia Commonwealth University, VA, USA (deceased), presented the CMF scopes of practice in three levels: (1) areas of expertise, which are oral pathology/medicine (including basic knowledge in oral mucosal diseases, temporomandibular joint [TMJ] disorders and orofacial pain/headache, and CMF radiology), dentoalveolar and preprosthetic surgery (including dental implantology), and CMF traumatology, (2) areas of competence involving orthognathic surgery, TMJ surgery, and local reconstructive surgery, and (3) area of familiarity consisting of cleft-craniofacial surgery, regional reconstructive surgery, oncologic surgery, and esthetic surgery [36]. Because OMF/CMF surgery outside Europe is dentally based and often located in dental schools, it is unknown whether the Laskin’s scope classification is applicable to medically based CMF surgery in Europe. We refer interested readers to the complete lists of German CMF surgeons’ tasks detailed by Pitak-Arnnop [4, 18] and Pitak-Arnnop et al.[17]

To promote the “drilling warriors for future battlefields” in German surgical training, the “surgical sub-step” concept has been developed. This concept acquires surgical skills as a part of more complex operations that might be too difficult for trainees at the time, e.g., tracheostomy by a second-or-third-year resident, and vascular anastomosis by fourth-or-fifth-year trainees during a complex head and neck reconstruction after extensive tumor resection. The concept can be easily implemented in a surgical department based on an individual basis and increases resident’s satisfaction [37].

DaRosa et al. [38] described that the levels of teaching practical surgical skills should advance from 1) “assisting” (show and tell stage) to (2) “smart help,” to (3)“dumb help” (i.e., I can do all parts of the surgery, albeit with some hesitation or even floundering, but requiring only “passive” assistance from the consultant; consistent with the Peak of “Mount Stupid” in the Dunning-Kruger effect curve [the first author, P.P.,’s interpretation]), and (4) finally to “performing alone”. Surgical sub-steps (apart from wound closure and bandaging, which are common sub-steps for trainees and medical students) can be adapted to all of these levels and open possibility to gain competency before advancing to self-performing the whole surgery. The German Young Surgeons Working Group („Chirurgische Arbeitsgemeinschaft „Junge Chirurgen “, CAJC) currently plans the continuous sub-step registry in order to improve training quality and measure effects of the awareness campaigns. With this continuous registry, the proposed sub-step concept will hopefully be applied more often in the operating theater in this country [37].

Last but not least, the high percentage of males over females (M:F) in this study can result from the selection bias, or the real-world ratio of M:F in surgery, or both. Statistically, the ratios of M:F consultant surgeons in the UK and overall surgeons in Germany were found to be only ~ 8:1 and ~ 3.5:1, respectively (available from https://www.rcseng.ac.uk/careers-in-surgery/women-in-surgery/; https://www.derstandard.de/story/2000134267964/studie-zu-gender-effekt-maenner-chirurgie-fuer-patientinnen-gefaehrlich; accessed on November 29, 2022). Some of us (A.N., K.S., N.S., P.P.) found the meaningful associations between female CMF surgeons and low scientific productivity and limited progress in academic surgical career [39]. Women in CMF surgery is therefore an important issue for future research.

Prior studies often compared outcomes between surgeries performed by skilled staff surgeons vs. those by trainees [5, 34]. The strength of our study is, thereby, the use of objective measures to evaluate outcomes using the coronal flap as a part of CMF injury patient care to argue for or against the “surgical sub-unit” learning concept. This study has, however, limitations which merit discussion. First, its retrospective design hampers identification of clinical-/operator-related factors that could affect the treatment outcome. Second, possible selection bias may exist, i.e., relatively easy cases were assigned to trauma trainees, leading to favorable outcomes. Third, high volume of CMF injuries could increase trainees’ skills and success rate of the surgery, albeit performed by novice trainees. Accumulation of clinical experience at hospitals with high patient volume, taught by a skilled, qualified surgeon, may reduce the learning curve in surgery, and probably, interfere the study’s generalization or external validity especially in a small trainee cohort (n = 5 in each study arm) [5]. Fourth, the post hoc power based on CFRCs was < 50%, suggesting the high possibility of the beta error. However, to reach the post hoc power of 100, we would have needed the 11-fold increased sample size, i.e., in a 22-year interval of data collection. Multicentric studies could exponentially increase the sample size, but inter-operator variables such as surgeon’s skill and experiences could be problematic, and the study would have suffered from poorer internal validity instead. Compared to previous studies in the literature, 97 coronal flaps for CMF trauma in two years, indeed, indicate the very high hospital volume. Moreover, statistical significance by intentional adjustment of the sample size is considered as scientific misconduct [40].