The perforator-based axial adipofascial turnover flap combined with juncturae tendinum grafting for complex dorsal phalangeal defects

Abstract

Introduction

Complex dorsal finger soft tissue defects remain a challenging reconstructive problem, particularly when associated with exposure of bone and extensor apparataus. Advances in the anatomical understanding of the dorsal cutaneous vascular system of the digits have allowed adipofascial flaps in this region to evolve from random-pattern to axial-pattern designs, improving vascular reliability. However, a structured and comprehensive approach for managing these combined defects has not been clearly defined in the literature. This study aims to present a holistic loco-regional strategy that optimizes the reconstructive ladder while minimizing donor-site morbidity and technical complexity.

Materials and methods

This clinical series includes seven fingers with complex soft tissue defects involving the dorsal aspect of the middle and distal phalanges. All cases were managed using an ipsilateral loco-regional protocol consisting of three components: (1) an extended axial adipofascial turnover flap for soft tissue coverage, (2) tendon reconstruction using juncturae tendinum harvested from the fourth intermetacarpal space, and (3) full-thickness skin grafting from the wrist. Patients were followed for a minimum of six months. Functional outcomes were evaluated by range of motion and complication rates.

Results

Complete flap survival was achieved in all cases. All fingers demonstrated satisfactory functional outcomes with acceptable flexion and extension ranges of motion at follow-up. No major complications, including infection, osteomyelitis, or significant donor-site morbidity, were observed.

Conclusions

The perforator-based axial adipofascial turnover flap combined with juncturae tendinum grafting provides reliable single-stage reconstruction of complex dorsal finger defects without the need for microsurgical anastomosis. This structured loco-regional approach enables immediate reconstruction without the need for microsurgical equipment or advanced microvascular expertise, offering a practical and reproducible alternative within the reconstructive ladder.

Level of evidence

IV.

Supplementary Information

The online version contains supplementary material available at https://doi.org/10.1007/s00402-026-06425-x.

Introduction

Hand injuries account for up to 20% of all unintended injuries presenting to emergency departments [1]. These injuries range from simple lacerations to complex defects involving skin, tendon, bone, and joint structures. While uncomplicated lacerations can be managed with primary closure, skin grafting, or local flaps, reconstruction of dorsal or palmar defects of the hand and digits becomes considerably more challenging when vital structures are exposed. Prompt and appropriate coverage is essential to preserve function and prevent complications, as inadequate management may lead to temporary or permanent disability.

The concept of the “reconstructive ladder” advocates selection of the simplest effective method for wound closure, thereby avoiding unnecessarily complex procedures [2]. However, complex dorsal finger defects with associated tendon and soft tissue loss require individualized planning that balances reliability, morbidity, and technical demand. Ideally, reconstruction should utilize tissues that are locally available, technically straightforward, and reproducible, without the need for advanced equipment or specialized microsurgical expertise.

In this context, we describe a structured loco-regional protocol for complex dorsal finger injuries. The technique consists of sequential steps: the stabilization of the interphalangeal joint if needed; harvesting the donor juncturae tendinum from the fourth intermetacarpal space; tension-adjusted graft fixation; coverage of exposed structures using an extended adipofascial axial turnover flap; full-thickness skin grafting from the wrist; and standardized postoperative immobilization and rehabilitation.

The aim of this study is to present a practical, anatomically based, and reproducible strategy for managing complex dorsal finger defects. By integrating tendon reconstruction and axial-pattern soft tissue coverage within a single-stage approach, this protocol offers a feasible and effective alternative within the reconstructive ladder, particularly valuable for surgeons seeking reliable loco-regional solutions.

Methods

This retrospective case series included patients treated between 2012 and 2020. All eligible cases during this period were reviewed and patients who met the inclusion criteria were included. The inclusion criteria were acute traumatic dorsal digital defects involving the middle and/or distal phalanx, exposure of bone, tendon, joint, and the need for local soft-tissue coverage with reconstruction of the extensor mechanism. Exclusion criteria were chronic wounds, infected wounds at presentation, previous surgery on the injured digit, vascular compromise precluding local flap elevation, thumb defects, and patients with incomplete follow-up data. Demographic and clinical data were obtained from medical records. All protocols used in this study were conducted according to the recommended International Regulations and Declarations and complied with the Declaration of Helsinki. This study was approved by the Local Medical Ethics Committee. Written informed consent for both treatment and publication of clinical data and images was obtained from all patients.

Basic anatomical concept and surgical technique

Dorsal branches of the proper palmar digital arteries

Braga-Silva et al. described the adipofascial arterial turnover flap based on detailed anatomical studies demonstrating that the flap is not random-pattern but axial in nature, relying on at least two symmetric dorsal cutaneous branches of the proper palmar digital arteries [3]. These dorsal branches of the proper palmar digital arteries consistently arise near the proximal interphalangeal (PIP) joint [4]. Venous outflow is ensured through the accompanying venous network surrounding the arterial pedicle [5]. Anatomical investigations have shown that the dorsal branches follow a regular and reproducible pattern, originating at predictable distances from the PIP joint [3]. One of these branches can reliably be identified within the paratenon approximately 5 mm proximal or 9 mm distal to the PIP joint, providing a dependable vascular basis for flap elevation [3].

Juncturae tendinum

On the dorsum of the hand, the extensor digitorum tendons are linked distally by oblique intertendinous connections known as juncturae tendinum (JT) [6]. These structures are classified into three types: fascial (Type 1), ligamentous (Type 2), and tendinous (Type 3) [6, 7]. Type 1 juncturae are most commonly observed in the second intermetacarpal space, Type 2 predominantly in the third, and Type 3 most frequently in the fourth intermetacarpal space [8]. Type 3 juncturae refers to the slips from the extensor digitorum communis (EDC) [7]. Extensor digiti minimi (EDM) tendon which primarily has double slips (87%) and less triple slips (13%) passes through the fifth dorsal compartment in the dorsum of the hand [9]. The EDM tendon is found in almost all individuals, while the EDC tendon that connects to the little finger is absent in nearly three of every four people (71%) [9]. In the fourth metacarpal space, type 3 JT is found as a tendinous band in 80–100% [10]. Govsa et al. reported that type 3 JT has a capsule with a circular structure similar to the tendon as well as vascularization and collagen structure [9]. Histologically, no difference was noted in the density of the connective tissue between the tendon and the type 3 JT whatever the subtype of type 3 JT.

Surgical technique

All reconstructions were performed under sedation with a brachial plexus regional block. After thorough debridement and defect assessment, interphalangeal joint stability was restored by advancing a Kirschner wire (K-wire) across the distal interphalangeal (DIP) joint. For tendon reconstruction, the fourth intermetacarpal space was explored through a longitudinal dorsal incision. After identification of the adjacent extensor tendon systems, the juncturae tendinum (JT), typically coursing from radial to ulnar, was carefully isolated using blunt and sharp dissection. A Type 3 juncturae tendinum was selected when a tendinous band of adequate width and length was identified. The graft was harvested with careful preservation of adjacent extensor tendons. The proximal end of the graft was sutured to the proximal stump of the injured extensor tendon by running interlocking horizontal mattress (RIHM) technique using a 4 − 0 polypropylene suture. The distal end was secured using a 4 − 0 polypropylene suture passed through the radial and ulnar sides of the eponychium and anchored to the K-wire to maintain appropriate tension.

The adipofascial arterial turnover flap was elevated as previously described by Braga-Silva et al. (2004), based on at least two symmetric dorsal cutaneous branches of the proper palmar digital arteries. Due to defined predictable distances between the PIP joint line and the origins of the dorsal branches of the digital arteries, an extended flap elevation is allowed with great confidence. The skin overlying the flap was carefully incised in an H-shaped fashion down to the dermal layer. The skin flaps were then elevated at the level of the subdermal plane without the adipose component, like a full-thickness skin graft. The most important point not to be forgotten is that the adipofascial flap should be designed to include all tissue between the dermis and the paratenon while maintaining sufficient tissue around the vascular axis. As reported before, to include dorsal branches of the proper palmar digital artery, it is marked out the base of the flap attached to the paratenon at least 5 mm proximally including a pedicle length of at least 10 mm proximally or distally to the PIP joint to be safe for all non-thumb fingers [3]. Proximally, the adipofascial flap was dissected free from the underlying paratenon as needed as until approximately 10 mm proximal to the metacarpal head which is enough to reach until the tip of the distal phalanx. The flap was extended proximally only as much as required to reach the distal defect, and the H-shaped skin incision was not extended across the metacarpophalangeal joint. In this series, preoperative Doppler assessment was not routinely performed, and flap planning was based primarily on anatomical landmarks. The proximal portion of the adipofascial flap was then mobilized beneath the skin using a skin hook and turned over to cover the defect. The flap was secured to the recipient site using 4 − 0 absorbable monofilament sutures.

After the flap was adapted to cover the middle and distal phalanges, a full-thickness skin graft was harvested from the ipsilateral volar wrist or, when necessary, from the ulnar aspect of the forearm. The graft was defatted to the dermal level using scissors, including the lower dermis to obtain a thinner and more pliable graft. The donor site was closed primarily with polypropylene sutures. The harvested skin graft was cut into two oblique parts and joined together in a rectangular shape to place to the recipient area. The graft was sutured with a synthetic absorbable 5 − 0 suture material made from 90% glycolide and 10% L-lactide. The grafted area was dressed with nitrofurazone-impregnated sterile gauze without excessive compression to preserve flap perfusion.

Postoperatively, the hand was immobilized in a protective splint. The wrist was positioned in slight extension of 10 degrees, the metacarpophalangeal joints in flexion about 70–90 degrees, and the interphalangeal joints of the reconstructed digit were protected in full extension. The first dressing change was performed on postoperative day five. Immobilization was maintained for three weeks to protect both the flap and tendon reconstruction. After splint removal, rehabilitation was initiated with controlled passive and active-assisted motion, avoiding forceful flexion during the early phase. The K-wire was removed at six weeks, after which active range-of-motion exercises were progressively increased.

Results

The mean age of the six patients included in this study was 24 years (range, 17–36 years) and all patients were men. All patients were followed up over a minimum of 6 months. All injuries resulted from acute occupational trauma, with crush injury being the mechanism in every case. The adipofascial arterial turnover flap successfully covered the dorsal finger defects in all patients.

All flaps survived completely without loss of the overlying skin graft. No major complications, including postoperative infection at the donor or recipient sites, osteomyelitis, or persistent edema, were recorded. No clinically evident donor-site morbidity was observed after harvesting the juncturae tendinum from the fourth intermetacarpal space. Specifically, no patient demonstrated extension lag of the donor digits, limitation of independent finger extension, donor-site pain, wound complication, or functional complaint during follow-up. Functional outcomes were evaluated by measuring the range of motion of the affected digits in flexion and extension at a minimum of six months postoperatively, as summarized in Tables 1 and 2.

Table 1.

Average range of motion of the affected finger joints measured at least 6 months after injury

	Distal Interphalangeal Joint	Proximal Interphalangeal Joint	Metacarpo- phalangeal Joint
Average joint range of motion (Extension/Flexion) in degrees	7°/67°	0°/97°	0°/85°

Table 2.

Patient-level clinical characteristics and outcomes of the seven reconstructed fingers

Case	Age	Sex	Injured digit	Dominant hand / injured hand	Mechanism	Defect size (cmxcm)	Defect location	Injured / exposed structures	Follow-up	Complications	Final ROM	Note
1	19	Male	Right middle finger	Right / Right	Occupational crush injury	4.0 × 1.8	Dorsal middle and distal phalanx	Bone, paratenon, extensor tendon, nail matrix	9 months	None	DIP 2°/75°, PIP 0°/105°, MCP 0°/90°	Excellent motion
2	36	Male	Right index finger	Right / Right	Occupational crush injury	1.5 × 3.5	Dorsal distal phalanx and DIP region	Bare bone, extensor mechanism injury	6 months	None	DIP 10°/65°, PIP 0°/100°, MCP 0°/85°	Minimal DIP extension lag
3a	17	Male	Left ring finger	Right / Left	Occupational crush injury	4.2 × 1.4	Dorsal middle and distal phalanx	Bone, tendon, ligament, skin	6 months	None	DIP 5°/60°, PIP 0°/95°, MCP 0°/85°	Acceptable recovery
3b	17	Male	Left little finger	Right / Left	Occupational crush injury	3.5 × 1.3	Dorsal middle and distal phalanx	Bone, tendon, ligament, skin	6 months	PIP flexion limitation related to initial intra-articular bone defect	DIP 8°/62°, PIP 0°/76°, MCP 0°/82°	PIP flexion limitation due to initial intra-articular bone defect
4	22	Male	Left index finger	Right / Left	Occupational crush injury	2.4 × 1.5	Dorsal distal phalanx	Bone, paratenon, terminal extensor tendon	7 months	None	DIP 10°/68°, PIP 0°/100°, MCP 0°/85°	Acceptable recovery
5	24	Male	Right ring finger	Right / Right	Occupational crush injury	3.2 × 1.7	Dorsal middle phalanx and DIP region	Bone, extensor tendon, soft-tissue loss	8 months	None	DIP 7°/70°, PIP 0°/100°, MCP 0°/83°	Acceptable recovery
6	26	Male	Left middle finger	Right / Left	Occupational crush injury	2.3 × 1.4	Dorsal distal phalanx	Bone, extensor mechanism, nail-bed margin	7 months	None	DIP 7°/69°, PIP 0°/105°, MCP 0°/85°	Acceptable recovery

Illustrative case reports

Case 1

A 19-year-old healthy male was admitted with a post-traumatic soft tissue defect over the dorsum of the right middle finger (Fig. 1). The injury resulted in exposure of the proximal and distal phalangeal bone, with associated loss of soft tissues including the paratenon, extensor tendon, and nail matrix. Multiple small non-viable skin fragments were also present. Following stabilization of the distal interphalangeal (DIP) joint with a K-wire, the extensor tendon defect was reconstructed using a juncturae tendinum graft harvested from the fourth intermetacarpal space (Fig. 2). An adipofascial arterial turnover flap was then elevated to cover the exposed structures (Fig. 3a). The donor skin was primarily reapproximated, and the raw surface of the turnover flap was resurfaced with a full-thickness skin graft harvested from the volar wrist (Fig. 3b). The postoperative course was uneventful (Fig. 4). At long-term follow-up, the finger demonstrated satisfactory functional recovery with full flexion and extension and excellent flap pliability (Fig. 5, Video 1).

Fig. 1.

Traumatic complex soft tissue defect on the dorsum of the right middle finger with exposure of phalangeal bone and injury to the paratenon, extensor tendon, and nail matrix. Bare bone over phalanges and small non-viable and fragmented skin islands can be seen (Case 1)

Fig. 2.

Extensor tendons in the fourth intermetacarpal space. Two slips of the extensor digiti minimi tendon are visible on the left, the extensor digitorum tendon of the fourth digit on the right, and a Type 3 juncturae tendinum in the center

Fig. 3.

a Elevated adipofascial turnover flap based on PIP joint is seen. The tip of the flap can reach toward the fingertip, and the viability of the flap can be seen, b Immediate closure of the defect with a full-thickness skin graft

Fig. 4.

Early postoperative appearance at 4 months. a Frontal view. b Lateral view demonstrating mild soft-tissue fullness at the distal aspect of the PIP joint

Fig. 5.

Late postoperative appearance at 9 months. a Donor site with acceptable healing. b Full finger extension. c Full flexion without extension lag

Case 2

A 36-year-old male presented with a complex soft tissue defect on the dorsum of the right index finger following a work-related crush injury (Fig. 6). The injury resulted in exposure of bare bone and disruption of the extensor mechanism. During surgery, all non-viable tissues were debrided. After stabilization of the distal interphalangeal (DIP) joint with a K-wire, the tendon defect was reconstructed using a juncturae tendinum graft harvested from the fourth intermetacarpal space. An adipofascial arterial turnover flap was then elevated to cover the defect (Fig. 7). Complete wound healing was achieved, with a satisfactory functional outcome and only minimal extension lag of the distal interphalangeal joint at follow-up (Fig. 8).

Fig. 6.

Complex dorsal soft tissue defect of the right index finger with exposed bone following a crush injury (Case 2)

Fig. 7.

a Reconstruction after Kirschner wire fixation and juncturae tendinum grafting from the fourth intermetacarpal space, followed by elevation of the adipofascial turnover flap. b Immediate defect closure with a full-thickness skin graft harvested from the ipsilateral wrist

Fig. 8.

a Six-month postoperative outcome. b Minimal distal interphalangeal joint extension lag with acceptable extension of the index finger. c Full flexion without any deformity

Case 3

A 17-year-old male presented with an extensive traumatic defect involving bone, tendon, ligament, and skin of the fourth and fifth digits of the left hand following an occupational crush injury (Fig. 9). After thorough debridement and excision of non-viable tissue, a juncturae tendinum graft was harvested from the fourth intermetacarpal space. The graft was used to reconstruct the lateral ligaments and extensor apparatus of the distal and middle phalanges, restoring stability to the distal interphalangeal joints (Fig. 10). Soft tissue coverage was then achieved using two adipofascial arterial turnover flaps applied to the respective defects (Fig. 11). At follow-up, complete wound healing and stable coverage were achieved in both digits. The fifth digit showed some limitation of PIP joint flexion, most likely related to the initial intra-articular osseous injury. No flap-related complication or donor-site morbidity was observed. Overall, satisfactory structural stability and acceptable functional recovery of the affected digits were obtained. (Fig. 12).

Fig. 9.

A total defect including bone, tendon, ligament, and skin on his fourth and fifth hemi-fingers secondary to a crush occupational trauma on his left hand is seen (Case 3)

Fig. 10.

Reconstruction of the lateral ligaments and extensor apparatus of the a fourth and b fifth digits using a juncturae tendinum graft harvested from the fourth intermetacarpal space. Exposure of the distal phalanx is visible

Fig. 11.

a Double adipofascial turnover flaps were elevated to cover the defective areas. A successful covering of the digits by the flaps with good circulation can be noted. b Immediate closure with skin grafting

Fig. 12.

Postoperative outcome at 6 months. a Frontal view showing complete wound healing. b Lateral view demonstrating satisfactory finger extension

Discussion

The skin and soft-tissue envelope of the hand represents a highly specialized structure that must provide durable coverage while remaining sufficiently thin and pliable to preserve digital mobility. This unique anatomical requirement makes reconstruction of dorsal finger defects particularly challenging, especially when tendon or deeper structures are exposed. While a variety of local, regional, and free flap techniques have been described, each carries specific advantages and limitations.

Compared with other reconstructive options such as cross-finger flap, flag flaps, distant flaps (abdominal, chest, or groin), and free flaps, the adipofascial turnover flap offers several advantages in dorsal finger reconstruction. These include technical simplicity, rapidity, minimal donor-site morbidity, and the ability to provide thin and pliable soft-tissue coverage in a single procedure [3]. Immediate closure is particularly beneficial when vital structures such as bone, tendon, or ligament are exposed, as delayed or inadequate coverage may result in significant morbidity [11]. In this situation, the reconstruction of such defects with homodigital adipofascial flaps could be seen highly convenient.

The adipofascial turnover flap was first described for use in the hand and finger by Lai et al. and since its description, it has become an accepted technique of finger reconstruction [12, 13]. According to the blood supply of the flap, they categorized their new flap in fingers as “random” and suggested a 0.5-cm base adjacent to the defect [14]. In 1998, Cavadas and Puertes-Corella described the cases with soft tissue defects in the fingers, and the flaps used to cover them were based on the flaps previously described by Lai et al. (1991), but using a much higher length-to-width ratio. They reported that the area of intact subcutaneous tissue between the defect and the pivotal point should be about 10 mm and avoidance of raising a flap from the dorsum of the metacarpophalangeal joint. Although they state that the flaps can be designed with any orientation, in fact, all their illustrated cases show flaps oriented longitudinally with respect to the vascular axis of the hand and finger [15]. This suggests that these flaps are most likely perforator based, even if not intended to be as such. In 2002, Braga-Silva et al. confirmed the existence of 2 constant dorsal branches originating from the proper palmar digital artery over the proximal and middle phalanges and more importantly, it was shown that these branches arise at predictable sites near the PIP joint. So, according to those new data on arterial vascularization of the dorsum of the finger, they modified the random flap technique as presented by Lai et al. (1991) and introduced the arterial flap technique. Based on those reliable anatomical studies, we used those flaps as an extended version of adipofascial arterial turnover flap including the soft tissue over the metacarpal head. While describing the algorithm for management of digital skin defects, Al-Qattan noticed that after 1995, small complex dorsal digital defects were reconstructed with adipofascial turnover flaps in case of de-epithelized cross finger flap [16]. It may be commented as the trend has already been turned in favor of adipofascial flaps.

The adipofascial turnover flaps in digits have positive points while compared with the other flaps used in finger reconstruction. Shortcomings or deficits of other flaps do not apply to adipofascial flaps. Cross-finger and de-epithelialized cross-finger flaps are reliable and widely used but may require staged division and temporary immobilization of an adjacent digit. Homodigital flaps provide local tissue with good color and texture match but may be limited by defect location, flap reach, and the condition of the injured digit. Regional and distant flaps, including abdominal, groin, or chest flaps, can provide coverage for larger defects but are usually staged and may be associated with bulkiness, prolonged immobilization, and donor-site morbidity. Free flaps offer versatile reconstruction for extensive composite defects but require microsurgical expertise, equipment, and longer operative time.Secondly, on the basis of precise anatomic data on the arterial vascularization of the finger dorsum represents its most important advantage over random pattern flaps [3, 4, 17]. This reliability also gives the absence of tissue necrosis, the immediate closure quickly on the day of trauma by on-call surgeon and additionally, allows safely to perform without requiring microsurgery. Another advantage of those flaps instead of other more laborious island or free flaps is that the development of venous insufficiency is not an expected situation due to the drainage by small venae concomitants accompanying the arterial branches.

In complex tissue injuries, a thin and firm tendon graft is needed to repair tendon and ligament damage. Loco-regional approaches in finger injuries should be performed without any additional morbidity. For this purpose, we have provided a safe repair by using juncturae tendinum of the fourth intermetacarpal area in such injuries without any problems and/or difficulty. Celik et al. found that the Type 3 JT was mostly located in the fourth intermetacarpal space (90%) where it was mentioned that suitable excessive tendon and the thickest JT as donor tendon were found [18]. Anatomical studies have demonstrated that Type 3 juncturae tendinum are present in the majority of individuals and exhibit structural and histological characteristics similar to native tendon tissue, including comparable collagen density and vascularization (Gövsa et al., 2011). These properties support their use as a reliable graft for reconstruction of the extensor mechanism. Pinar et al. reported that Type 3 JTs were macroscopically and microscopically thicker than other JTs. The existence of a capsule, rich vascularization, and similar density of collagen fibers was found both in the tendon and Type 3 JT which makes it suitable to use in tendon repair.

In this context, the presented technique may be considered a local, single-stage option for selected dorsal middle and distal phalangeal defects when the vascular status of the digit is adequate and when a thin pliable flap is sufficient selected dorsal middle and distal phalangeal defects when the vascular for coverage. Its potential advantages include use of local tissue, avoidance of microsurgical anastomosis, and simultaneous tendon-like graft reconstruction. However, it is not intended to replace established reconstructive methods, and its use should be individualized according to defect characteristics and surgeon experience. The novelty of the present report does not lie in the individual description of the adipofascial turnover flap or the juncturae tendinum graft, both of which have been previously reported, but rather in their combined use as a single-stage local reconstructive strategy for selected acute complex dorsal digital defects involving both soft-tissue loss and extensor mechanism injury.

This preliminary case series suggests that the combined use of a perforator-based axial adipofascial turnover flap and juncturae tendinum grafting may be a feasible single-stage local reconstructive option for selected acute complex dorsal digital defects involving exposed bone and extensor mechanism injury. However, because of the small retrospective design, absence of a comparison group, and limited functional outcome assessment, these findings should be interpreted cautiously. Because of the retrospective design, several variables that would have strengthened the patient-level analysis, including flap dimensions, graft length, grip and pinch strength, return-to-work interval, and validated patient-reported outcome scores, were not systematically recorded. Another limitation of the study is that the functional assessment was limited primarily to clinical range of motion and complication recording. Objective grip and pinch strength measurements, total active motion scoring, standardized pain scores, return-to-work intervals, and validated patient-reported outcome measures such as DASH or QuickDASH were not collected systematically because of the retrospective design. This represents an important limitation, as range of motion alone may not fully reflect global hand function, patient satisfaction, donor-site morbidity, or occupational recovery after complex digital trauma.

This study offers a simple and reliable loco-regional approach to the management of a complex injury without the need for microsurgical procedures and represents a practical and reproducible alternative treatment modality with loco-regional options to cover complex dorsal distal and middle finger injuries. However, larger comparative studies with standardized functional and patient-reported outcomes are required before broader conclusions regarding reliability, reproducibility, or superiority can be drawn.

Supplementary Information

Below is the link to the electronic supplementary material.

Author contributions

K.O. contributed to the study conception and design. Material preparation, data collection and analysis were performed by K.O. and K.O. wrote the manuscript and approved the final manuscript.

Data availability

No datasets were generated or analysed during the current study.

Declarations

Conflict of interest

The author confirmed that no funding was received to support conduct of this work. The author has no financial interests or potential conflicts of interest. This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.