Cross-finger flap as ultima ratio for the reconstruction of defects of the finger flexor sides.

Whereas cutaneous tumors, especially squamous cell carcinomas, occur more frequently on the dorsum of the hand and extensor sides of the fingers, they manifest themselves more rarely on the palms or on the flexor side of the fingers.1 The primary goal of all operations on the hand, our most important working organ and sensorimotor tactile tool, is, in addition to the complete removal of tumors, the preservation of gripping function and the avoidance of contractures. The anatomically limited skin reservoir of the hand and especially of the fingers places high demands on the reconstruction of larger defects. For skin and soft tissue defects on the palmar aspect of the fingers, there is always a risk of functional impairment of the flexor tendons.2 Various reconstruction options are available depending on the size and depth of the defects, and are selected according to a “reconstructive ladder” or, more appropriately, a “reconstructive elevator”.3 The cross-finger flap described here is a reconstruction method from the top rung. Here, in the case of defects of the palmar proximal and middle phalanges, skin of one finger is transferred to the defect of an adjacent finger while temporarily preserving a skin bridge.4, 5 A 66-year-old patient was diagnosed with G2-differentiated Bowen carcinoma on the flexor side of the left index finger (Figure 1) which was excised under Oberst's block anesthesia histographically controlled in sano. The skin subcutaneous defect could be closed with a full-thickness skin graft from the upper arm. Despite perioperative antibiotic prophylaxis and postoperative immobilization of the left hand, bacterial superinfection of the wound by Staphylococcus aureus occurred leading to a complete graft loss. After necrectomy, intensive local wound disinfection, further immobilization, local cooling and calculated antibiotic therapy with clindamycin, the acute signs of inflammation subsided. After cleaning the wound bed, it became apparent that the circumscribed exposed flexor tendons of the left index finger lacked peritendinal coverage and the defect now had a size that extended beyond the joint fold of the middle phalanx both proximally and distally. For this reason, renewed closure of the defect with a full-thickness skin graft was contraindicated. Reconstruction options were discussed in detail with the patient, and he was offered further treatment in a hand surgery clinic. However, after careful consideration, he declined this offer. Therefore, the decision was made to close the skin defect by a cross-finger flap from the extensor side of the adjacent middle finger (Figure 2a). Usually, the procedure is performed under Oberst's block anesthesia, metacarpal block, or axillary plexus anesthesia. However, at the express request of our patient, the surgery was carried out under general anesthesia and the lifting and suturing of the flap was performed with the aid of a magnifying glass. After applying tourniquets to the index and middle fingers, the skin flap was marked using a template with the required dimensions on the extensor side of the middle finger of the left hand. Here, the flap's folding point should be chosen at the level of the mediolateral line so as not to compromise the subdermal plexus surrounding the axial finger vessels. The flap was then incised on three sides, leaving out the side toward the affected index finger. Flap preparation was then performed in stages from the dorsal aponeurosis of the middle finger, preserving the lateral skin bridge (Figure 2b). Here, special care must be taken not to injure the paratenon. The well-mobilized skin flap on the middle finger could be opened like a book and was positioned under the defect-bearing index finger, precisely fitted, and sutured in place with 5/0 monofilament, non-absorbable sutures (Figure 2c). Care was taken to provide approximately 1 cm of skin bridge slack between the donor and recipient fingers. The lifting defect on the extensor side of the affected middle finger was covered by a split-thickness skin graft taken from the lateral aspect of the left thigh and covered with a tie-over dressing (Figure 2d). The hand was immobilized postoperatively with a volar positioning splint. The iatrogenically induced syndactyly between the index and middle fingers allowed the cross-finger flap to heal locally over a period of 4 weeks (Figure 3a). The split skin graft over the lifting defect also healed without complications. From the third postoperative week, a compression test was used to assess flap blood flow. For this purpose, the base of the flap was manually compressed and perfusion of the cross-finger flap was observed. If the coloration of the flap is preserved or if there are only minor differences to the adjacent local skin, the appropriate time for flap cutting has come. In the present case, this was possible after the fourth postoperative week. In a second procedure, the skin bridge between the middle finger and the index finger was then cut with a scalpel. The wounds on both fingers could be closed without tension with simple interrupted sutures using 5/0 nonabsorbable suture material (Figure 3b). The healing process was without complications. Finally, physiotherapy was prescribed to restore full mobility to the left index finger. At the last follow-up examination two years after surgery, both the ventral cross-finger flap on the index finger and the dorsal split-skin graft on the middle finger had healed completely. Both fingers were fully functional with no restrictions in flexion or extension (Figure 3c–e). Reconstruction of palmar middle phalanx defects follows the principle of a “reconstructive ladder”.2 The first stage includes primary wound closure or healing per secundam intentionem, which allows for satisfactory functional and cosmetic results.6 In the second stage, skin grafts are used. However, these are only effective if vascular and nerve structures are not damaged and the tendon sheaths are intact.1 In the reconstruction of palmar finger defects, full-thickness skin grafts should be used if possible, since they have a higher mechanical resilience.2 The third stage involves local flap plasty. Especially for smaller defects of the palmar middle phalanx, palmar translational flap plasty according to Hueston or lateral island flap plasty according to Rose may be considered.1 In the described case, however, these flap plasties were not practical due to the size of the defect. In the final stage, distant flaps, such as the cross-finger flap presented here, are then used.2 The first description of a heterodigital flap for defect reconstruction on the ventral side of the fingers was given in 1950 by Gurdin and Pangman.4 The designation “cross-finger flap” is attributed to Cronin.5 Since then, numerous modifications have been described, but the procedure is still considered the “workhorse” in the reconstruction of traumatic and nontraumatic finger defects.7 Since the cross-finger flap is asensitive in the original technique shown here, it is preferably used on the palmar aspect of the long fingers beyond the finger pads. The skin of the back of the donor finger is supplied mainly via the dorsal branch of the digitalis palmaris propria artery and displays a pronounced dermal and subdermal vascular plexus, ensuring adequate blood supply after the flap is cut.8 Only the neighboring finger can be considered as a donor finger for index and little fingers. For coverage on the middle and ring finger, the finger that permits the most favorable position for immobilization is selected as the donor.8 The cross-finger flap offers reliable soft tissue coverage with very good functional results.2, 9 The main disadvantage is clearly the two-stage procedure separated by a 2–4-week interval, during which only limited follow-up is possible due to iatrogenic syndactyly.10 The possible functional and aesthetic morbidity of the lifting area, which can range from loss of the graft to stiffening of a previously healthy finger, must also be emphasized. Both full-thickness and split-thickness skin grafts are possible for closure of lifting areas on the dorsal side of fingers, with preference given to the former.9 In the presented case, we opted for a split skin graft following the loss of a graft after initial excision. Ultimately, in our case, both the cross-finger flap and the split-skin graft healed without complications or functional impairment. No tumor recurrence has been observed after a follow-up period of 2 years. In summary, it should be noted that the technique presented here for the reconstruction of flexor side defects of fingers is primarily the domain of hand surgery and, for forensic reasons as well, should only be applied if the surgeon has detailed knowledge and appropriate experience. Open access funding enabled and organized by Projekt DEAL. None.