One of the most utilized techniques for covering thumb volar pulp defects measuring 1.5 cm or less is the Moberg flap [1]. This method provides an effective solution for small to medium defects resulting from volar oblique amputations while preserving both sensory function and length [2]. Additionally, it allows coverage using tissue with a texture and color similar to that of the original pulp, thereby minimizing functional and aesthetic compromises [3].

The Moberg flap involves making incisions along both mid-axial lines, dorsal to the palmar neurovascular bundles of the thumb, and elevating the flap by dissecting it from the flexor tendon sheath to achieve sufficient mobility while preserving the neurovascular bundles to maintain optimal sensory function [4]. However, in cases where the defect size is substantial or flap mobility is insufficient, maintaining the thumb in a flexed position at the interphalangeal joint is often required to reduce tension, which might lead to flexion deformity [5,6].

Several modifications have been proposed to address this issue. O’Brien suggested increasing flap mobility by creating a proximal incision for a greater range of advancement [7]. However, this approach requires the use of a skin graft to cover the resulting donor deficit, which can introduce additional complications, such as graft failure or contracture [8]. Another alternative involves Z-plasty for donor-site closure or V-Y modifications, which include designing a triangular flap extending into the thenar eminence [9,10]. However, this procedure increases the area of scarring, which may affect both appearance and function.

To address this issue, we describe a practical intraoperative variation of the Moberg flap. In situations where an oblique defect leaves a small, uncovered area even after proper advancement, a redundant portion of the elevated flap can be converted into a small island and rotated to achieve distal coverage. This approach should be regarded as a supplementary maneuver within the established Moberg flap design, applicable in select intraoperative circumstances.

A 50-year-old male patient presented with a right thumb pulp defect caused by a chainsaw injury. The patient had no significant underlying diseases or history of smoking. The defect was located on the volar oblique plane with a wider configuration on the ulnar side and measured approximately 2×1.5 cm (Fig. 1). Preserved distal sensation was demonstrated by the two-point discrimination test with normal capillary refill. As the defect was limited to the pulp, reconstruction using a Moberg flap was planned.

Incisions were made along the bilateral mid-axial lines from the defect to the base level of the proximal phalanx. The ensuing skin flap including the palmar neurovascular bundle was carefully dissected from the flexor tendon sheath and advanced distally (Fig. 2A). The interphalangeal joint of the thumb was slightly flexed to allow defect coverage with less tension. However, after flap advancement, a raw surface sized about 0.5×0.5 cm remained at the distal ulnar margin of the original defect (Fig. 2B).

Rather than extending the flap proximally using previously described methods such as skin grafting or V-Y advancement, we employed a small intraoperative variation within the Moberg flap [7,9,10]. Because the residual defect was located on the ulnar side, a redundant ulnar segment of the advanced flap was incised parallel to the finger axis and elevated as a small island (Fig. 3A). Careful subcutaneous dissection preserved a branch of the flap’s neurovascular bundle, forming a reliable pedicle. Once adequate mobility was confirmed, the island was rotated to inset into the distal raw area (Fig. 3B). The donor site was closed primarily. This maneuver allowed complete coverage without additional proximal extension or grafting, thereby avoiding any long-term complications associated with such procedures (Fig. 4). All steps were performed under 3.5× surgical loupe magnification.

This study was approved by the Institutional Review Board of the Gwangmyeong Sungae Hospital (No. 2025-N-003). Written informed consent was obtained from the patient for publication of this report, including all clinical images.

The most important goals in fingertip reconstruction are to maintain digit shape and length, preserve sensation, and ensure joint mobility [3]. Regarding fingertips, maintaining length and sensation is crucial for functional outcomes. The Moberg flap has significant advantages in these aspects, for which it is widely used in thumb reconstruction [1]. However, caution is required regarding joint mobility because this procedure can result in flexion contracture of the interphalangeal joint [3]. Extending the flap into the thenar eminence or modifying it into a V-Y pattern may be necessary to prevent this complication [9]. However, these modifications carry their own risks including increased flap-related complications, the need for skin grafts at the donor site, and the extension of scars toward the palm, which may cause discomfort to the patient.

The distal phalanx narrows toward the tip, often resulting in a size discrepancy between the proximal and distal margins of the defect [5]. Consequently, advancing the Moberg flap may create remnant portions of the skin flap that must be trimmed to match the phalanx contour. Instead of discarding the excess skin, additional distal coverage can be achieved by splitting part of the flap into an additional island flap and rotating it [6].

This flap-in-flap maneuver is particularly useful in oblique defects where the distal defect is larger on either the ulnar or radial side, leaving a small, uncovered area after Moberg advancement. The additional island flap should be elevated ipsilateral to the residual defect: an ulnar island is raised when the defect persists on the ulnar side, and a radial island when it persists radially. In this way, the technique can be adapted to the defect orientation. By utilizing tissue already included in the Moberg flap, this approach avoids proximal extension of incision or skin grafting [7,9,10].

In this technique, safe coverage was achieved by rotating the flap in a propeller fashion. One concern with splitting a small island flap is inadequate nerve supply to the area, potentially resulting in less-than-normal sensation compared to the original Moberg flap. However, in this patient, sensory function gradually improved over time, and the patient did not experience any significant discomfort in daily life.

The meticulous dissection of the neurovascular bundles required for splitting the island flap may present another challenge. The digital artery forms an arcade in the distal phalanx, giving rise to several terminal branches [2]. Under loupe magnification, the author directly visualized the vascular pedicle supplying the island flap. However, in cases where precise dissection of the pedicle is difficult, preserving a subcutaneous tissue stalk including the fibrous septa and presumed vascular pedicle may help provide sufficient vascular circulation to the flap.

Although the present case exhibited multiple small scars after healing, these remained stable and did not lead to long-term complications. The pulp contour was preserved, and the patient was satisfied functionally. The interphalangeal joint maintained full extension and 70° flexion compared to the opposite thumb, and two-point discrimination was equally preserved at 3 mm in both radial and ulnar sides of the thumb tip. Nevertheless, we recognize that in terms of scarring, the result was not superior—and may appear less favorable—compared with other known Moberg flap modifications such as adding proximal incisions or Z-plasties. Therefore, this technique should not be considered a design innovation to minimize scars, but rather an intraoperative salvage maneuver to achieve complete coverage when a residual distal defect persists after advancement. As it is based on the traditional Moberg flap without significant modifications, it allows for safe and straightforward elevation and does not require secondary procedures such as skin grafting [10]. Additionally, it retains the advantage of limiting scarring to the thumb. This technique may be particularly useful in cases where the thumb tip defect is oblique and there is a discrepancy in the width of the distal phalanx, making it a valuable option for preoperative planning.

This propeller-within-Moberg flap technique can be an important option to consider when planning thumb tip reconstruction using the Moberg flap. This method enhances distal coverage, minimizes scarring, and mitigates the risk of flexion contracture, ultimately contributing to improved functional and aesthetic outcomes.