Ensuring adequate surgical exposure of the DIPJ is of paramount importance in the arthrodesis procedure to effectively treat marginal spurs, correct mal-alignment, perform thorough joint preparation, and choose the optimal implant insertion site. Our proposal is that the 'smile incision with reverse shotgun procedure' would provide both satisfactory DIPJ exposure and minimize the incidence of skin and nail complications. This technique, in our study, yielded a 97.2% bone union rate, remarkable finger alignment correction, and significantly improved VAS scores for pain and satisfaction at an average of 9.8 months postoperatively compared with preoperative scores. We observed no instances of infection or complications related to skin or nails.
Traditionally, arthrodesis of the DIP joint is performed through a transverse, Y-shape, H-shape, or lazy S-shape around the dorsal aspect of the DIPJ. In contrast, our technique involves an extended simple transverse incision, eschewing the H or Y incision. This avoids the need for a longitudinal incision or sharp-angled skin flap, which frequently result in hypertrophic scars that may restrict joint motion.[10, 11]. The "smile incision" begins at the center of the major DIPJ skin crease and then arcs distally towards the lateral aspect of the finger, ensuring a safe distance from the nail germinal matrix. At this juncture, the extensor tendon can be severed at the tendon segment, which is considerably more proximal than the terminal tendon insertion and the nail's germinal matrix. [12] (Fig. 2). The "smile incision" is designed to circumvent direct cutting into the nail germinal matrix. Still, soft tissue dissection should be performed just above the bone surface to avoid damaging the nail germinal matrix. In our series, no skin necrosis, contracted scars, or nail-related complications were observed. This is potentially because the procedure successfully avoids inducing skin ischemia and maintains a safe distance from the nail germinal matrix (Fig. 5).
The original shotgun approach was conceived to maximize the exposure of the proximal interphalangeal joint (PIPJ) of the finger by hyperextending the PIPJ. Despite releasing the volar plate, accessory collateral ligament, and the volar part of the collateral ligament, no significant ligament-related complications were noted in the surgical outcomes. [13]. In our study, hyperflexion and full joint surface exposure of the DIPJ were achieved by releasing the dorsal capsule, the collateral ligament, and the dorsal part of the accessory collateral ligament. Dorsal DIPJ stability could be reconstructed by implant fixation and subsequent bone union. We found no complications related to blood supply or immediate reduction loss resulting from the release of the accessory collateral ligament. This suggests that neither the blood supply nor the stability of the DIPJ was irreversibly impacted by the release of the accessory collateral ligament and DIPJ hyperflexion of more than 120 degrees in this procedure.
In this research, headless screws were utilized in all 36 fingers to attain interdigital fixation and inter-fragment compression. Although Kirschner wire is a commonly used implant for DIPJ arthrodesis, the use of a headless screw, which provides inter-fragmental compression, is beneficial for bone union. A biomechanical study suggested that compared to the K-wire, the headless screw exhibited higher stiffness and maximum fracture forces.[14, 15]. A systematic review conducted in 2014 deduced that the union rate of patients treated with headless screws was superior to those treated with K-wires (96.1% versus 91.6%)1. In our study, the high bone union rate achieved (35 of 36 patients, translating to 97.2%) was comparable to the union rates reported in existing literature [2, 4, 6, 16–20]. This suggests that the successful bone union rate achieved by the smile incision and reverse shotgun procedure is not inferior to that of traditional incisions employing headless screws. Some authors have reported potential complications from using oversized headless screws, such as fractures at the distal phalangeal tip or thread penetration of the nail bed during screw placement, especially in female patients or in little fingers. If the dorsal cortex is compromised, the nail bed could be damaged, potentially resulting in pain, subungual hematoma, and nail deformity. [16, 21, 22]. Iwamoto et al. have reported the potential for symptomatic hardware and nail bed injury when the thread diameter exceeds the anteroposterior diameter of the distal phalanx {Iwamoto, 2013 #19}. In our study, subungual hemorrhage was observed in 17 of the 36 cases (47.2%) in the early postoperative period. Notably, all instances of subungual hemorrhage were due to intraoperative K-wire injury rather than screw oversizing. Nonetheless, by the final follow-up, all incidences of hemorrhage had resolved without residual symptoms. Our experience suggests that such complications can be minimized by opting for more volar screw insertion sites in fingers of smaller diameter and by diligently monitoring the direction of the K-wire using fluoroscopy during surgery.
Another potential issue associated with the use of headless screws is finger length shortening due to interphalangeal compression, which may result in subsequent swan neck deformity. [23, 24]. Certain researchers have suggested the utilization of bone grafts derived from Lister's tubercle as a strategy to circumvent the shortening of the finger length. [24, 25]. However, the additional bony interface may interfere with the bony union. In our procedure, swan neck deformity can be prevented by overlapping the extension tendon by 2–3 mm during the tendon repair procedure. With this method, swan neck deformity was not observed in our follow-up period.
The various methods, utilized implants, rates of union, rates of complications, and the surgical outcomes that have been reported for DIPJ arthrodesis in the recent decade are comprehensively presented in Table 5.[2, 4, 6, 16–20]. The rates of successful union were found to vary between 91% and 100%. The incidences of significant complications, such as nonunion, fracture, and hardware loosening, ranged from 0 to 14%. This is in contrast to complications like nail dystrophy and skin necrosis, which were reported to have an incidence range of between 11% and 15% [20, 26]. In contrast to studies conducted 15 years ago, recent research has reported no complications related to skin or nails. Most of these studies investigated fewer than 50 cases. The most comprehensive series, involving 102 fingers treated with DIPJ arthrodesis using Arex SCRU2 screws and a transverse incision, reported a union rate of 100%, a remarkably high satisfaction rate (95%, or 97 out of 102 cases), and no skin or nail complications. The authors suggested the low complication rate resulted from the low profile of the Arex SCRU2 screw. However, similar complication-free results were reported in studies using different implants (as seen in Table 5). This implies that the decrease in skin and nail complications might be due to advancements in surgical approaches that prioritize soft tissue preservation.
In addition to performing a transverse incision over the DIPJ and transecting the collateral ligament, our method extends the transverse incision to the lateral aspect and releases the accessory collateral ligament, enhancing volar joint exposure. We found this approach significantly aids in joint preparation and implant insertion, without an increase in complications.
However, this study has several limitations. First, our sample size was relatively small, and the follow-up period was short. This could mean that rare or late-onset complications may not have been recorded. Second, as this was a retrospective study, we could not control factors such as patients’ underlying diseases, anesthesia methods, and lifestyle factors. To mitigate this potential bias, we applied the same surgical procedures and postoperative management across all cases. Lastly, we did not directly compare the results of patients who underwent other surgical techniques, so evidence is lacking to definitively show that the smile incision and reverse shotgun approach is superior to other methods.
Despite these limitations, our study is the first to report clinical and radiologic outcomes using the smile incision and reverse shotgun approach for DIPJ arthrodesis. Our results suggest this technique offers a safe and accessible surgical exposure, particularly when more volar joint preparation and more volar implant insertion points are required.