Comparison of skin elasticity and stiffness of the thoracodorsal artery perforator flap and commonly used flaps in head and neck reconstruction

Background Reconstruction of oral and maxillofacial defects requires soft and ductile flaps. Thoracodorsal artery perforator flap (TDAP) has good plasticity, but it is not widely used in the repair of oral and maxillofacial defects. The main aims of this study are to compare the skin elasticity and hardness of various free flaps commonly used in reconstructive surgery, and to explore the advantages and disadvantages of TDAP.Methods The elasticity and stiffness of the most commonly used free flaps in our department were measured by ElastiMeter and SkinFibroMeter. The elasticity and stiffness values of TDAP, anterolateral thigh flap, anterior medial femoral flap and forearm flap were measured respectively.Results The elasticity of TDAP was the lowest among all flaps, and the difference was statistically significant, except for the forearm flap (p = 0.000; p = 0.000; p = 0.06). The stiffness of TDAP was the lowest among all skin flaps, and the difference was statistically significant (p = 0.000; p = 0.000; p = 0.000).Conclusions TDAP is indeed suitable for reconstruction of head and neck defect, especially oral and oropharyngeal defect. Due to the ductile texture of TDAP, it is very conducive to the recovery of the morphology and function of oral and oropharyngeal organs.


Introduction
Oral and oropharyngeal cancers are among the most common cancers of the head and neck, accounting for nearly 4% of all cancer cases 1 . Surgical treatment is common for such cancers, and repair of tissue defects following tumour resection is critical. For both aesthetic and functional reasons, the oral, maxillofacial-head and neck areas are extremely important. If defects in these regions are not promptly repaired, adverse effects may include impaired speech, chewing and swallowing disorders and psychological problems due to disfigurement.
With the development of microsurgical techniques, free flaps are commonly used as a tissue source for the repair of oral, maxillofacial-head and neck defects [2][3][4] . As there are more than a dozen free flaps that can be used, choosing the correct flap is important for successful reconstruction 5 . The ideal free flap for reconstructing head and neck defects should have a high success rate, simple preparation, constant vascular anatomy, few donor site complications, sufficient diverse tissues and a vascular diameter similar to that of the neck and maxillofacial vessels. Investigators around the world have made great efforts to determine the most appropriate free flaps for repairing head and neck defects 6 .
The aims of this study are threefold: (i) to share our experience using thoracodorsal artery perforator flaps (TDAPs) to repair oral and maxillofacial defects, (ii) to compare the skin elasticity and hardness of various free flaps commonly used in reconstructive surgery and (iii) to explore the advantages and disadvantages of TDAPs.  Table 1. Post-surgery, aesthetic result, swallowing function and speech function were assessed by two surgeons. Aesthetic result for the oral and maxillofacial region was rated as 1 = unsatisfactory, 2 = satisfactory or 3 = excellent.

Methods
Swallowing function was rated as 1 = unable to swallow, 2 = liquid or soft food or 3 = normal. Speech function was rated as 1 = slurred speech, 2 = intelligible speech or 3 = normal speech. These ratings are presented in Table 2. and muscle flaps can be prepared. The donor wound was closed by direct suture after preparation of the complete flaps. If the wound tension was too large, a local random skin flap was used for repair. Ren's anastomosis 3 was used for microscopic artery anastomosis, and end-to-end or end-to-side anastomosis was used for microscopic venous anastomosis.

Measurement of flap elasticity and stiffness
The elasticity and stiffness of the flaps were measured by ElastiMeter (Suppelement Figure 1) and SkinFibroMeter (Suppelement Figure 2), respectively. The ElastiMeter and SkinFibroMeter probes were briefly (0.8 and 0.5 s, respectively) pressed perpendicularly against the skin. Each elasticity and stiffness value was calculated as the mean of five successful consecutive measurements at the same site. Previous readings were listed under the most recent value, and the values were mathematically modelled using 3D computational finite element analysis, with the final value displayed on the main screen. If the force applied or duration of measurement was incorrect, the message 'USER ERROR' was displayed and the measurement was repeated. We measured the skin elasticity and stiffness of the most commonly used free flaps (anterolateral thigh flap, anterior medial femoral flap and forearm flap) and TDAPs.

Statistical analysis
Data were analysed using SPSS 19.0 software (SPSS, Inc., Chicago, IL, USA). The χ 2 test or Fisher's exact test were used to analyse the data, as appropriate. A p-value < 0.05 was considered to indicate a statistically significant difference.

Results
Of the 38 TDAPs transferred, all 38 survived; 1 showed postoperative vascular crisis, but completely survived after treatment. The overall survival rate was thus 100%. Of the 38 flaps, the largest single flap area was 7.5 × 15 cm 2 , whereas the smallest was 4 × 5 cm 2 .
The perforator vessels of 86.8% 33/38 flaps were derived from the thoracic dorsal artery and 13.2% 5/38 from the lateral thoracic artery. The arterial vascular diameter was 0.8-2.5 mm, the venous vascular diameter was 1.5-2.2 mm and the vascular pedicle length ranged from 6 to 12 cm, with an average of 8.5 cm. The vascular pedicle most commonly comprised one artery and one vein (32 cases), followed by one artery and two veins (6 cases). The number of perforations ranged from 1 to 3, with an average of 1.8. The skin flaps were between 0.8 and 3 cm thick, averaging 1.6 cm. Of the 38 flaps, 12 were used to repair the tongue, 9 to repair the oropharynx, 8 to repair the bucca area, 8 to repair the floor of the mouth and 1 to repair the mandible (Table 1) respectively. The stiffness of TDAPs was the lowest among all skin flaps, and the difference was statistically significant (p = 0.000; p = 0.000; p = 0.000, Figure 4).
Complete elasticity and stiffness results are presented in Table 2.

Discussion
Various defects may occur following radical resection of head and neck tumours, and a considerable portion of these defects requires free flap repair 7-9 . The quality of repair directly affects patients' postoperative recovery and quality of life. There are two key factors that affect the quality of repair, namely, the surgical skill and clinical experience of the surgeon and the correct flap selection 5, 10-12 . Oral and oropharyngeal mucosa is soft, and the function of the relevant organ is very complex and sophisticated. Therefore, when repairing oral or pharyngeal defects, a ductile skin flap should be used whenever possible. Only in this way can a patient's oral oropharyngeal morphology and function be restored. This TDAPs can well meet the demand of softness for head and neck defect repair. Our study is the largest application of TDAPs to repair head and neck defects in mainland China at present. Meanwhile, we also reported a pedicle double island TDAP for the first time.
Stable, quantitative measurements of skin hardness and elasticity have long been lacking 13,14 . In this study, we used the ElastiMeter and SkinFibroMeter in a novel way to measure the elasticity and hardness of the skin flap, demonstrating that these tools can quantitatively evaluate skin elasticity and stiffness. The ElastiMeter and SkinFibroMeter also have the advantages of being highly sensitive, portable and accurate. Unlike diagnostic methods based on skin biopsy and puncture, ElastiMeter and SkinFibroMeter measurements are non-invasive and do not damage skin structures, thereby reducing patient anxiety. In addition, the wireless data collection system uses DMC software, enabling real-time data acquisition and storage. The measurement process is simple, requiring only depression of the operation button and adjustment of the power and velocity of the probe. The site of measurement was the donor site of the flap, not the flap.This can avoid measurement errors between different patiens. In this study, the use of these measurements revealed that TDAP donor skin is the most ductile of all commonly used skin flaps-even softer than the forearm, which is considered to be the softest flap.

Ethics approval and consent to participate
This study was approved by the independent Ethics Committee of Shanghai Ninth People's Hospital affiliated with Shanghai Jiao Tong University School of Medicine. Written informed consents were obtained from all participants.

Availability of data and material
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Competing interests
The authors declare no competing interest

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