Introduction
Soft tissue defects in the knee and proximal leg, stemming from various causes such as trauma, postoperative wound gaping, and tumor excision, are problems commonly encountered by reconstructive surgeons [1]. Successfully addressing these defects is crucial for achieving optimal aesthetic and functional outcomes. Several reconstruction methods exist, including adjacent local muscle flaps, fasciocutaneous flaps, cross-leg flaps, and free flaps [2-4].
However, each method comes with its own set of disadvantages. Muscle flaps, for instance, can result in a bulky appearance and significant discomfort because of muscle twitching and contractions. Similarly, cross-leg flaps may cause severe discomfort because of the need to maintain a fixed posture, and free flaps demand significant microsurgical expertise. Island fasciocutaneous flaps based on the median sural artery, transferred through a subcutaneous tunnel to the defect, offer a promising solution in overcoming these disadvantages. This approach provides satisfactory coverage while maintaining superior aesthetic and functional outcomes [5,6]. However, the dissection of the vascular pedicle through the gastrocnemius muscle is tedious and time-consuming.
This study focuses on exploring the potential of a proximally based sural artery flap for reconstructing soft tissue defects in the knee and proximal leg following trauma. Unlike other methods, this approach offers satisfactory coverage with a thin, supple, and sensate skin flap, leading to improved aesthetic and functional outcomes. Despite its promise, the use of a proximally based sural artery flap for such reconstructions is underexplored, with only limited studies documenting its application [1,3,7]. Therefore, the primary objective of this research is to evaluate the versatility of the proximally based sural artery flap in addressing post-traumatic soft tissue defects in the knee and proximal leg, shedding light on its potential as a valuable reconstructive option.
Methods
This is a retrospective study of 30 patients who were managed between December 2018 and December 2021, at the department of plastic surgery. All patients underwent surgery for reconstruction of soft tissue defects using a proximally based sural fasciocutaneous flap after providing written and informed consent. The study has been approved by the Institutional Ethical Committee of Jawaharlal Nehru Medical College (IECJNMC/1100, dated 26 August 2023). All surgeries were performed by the same surgeon.
Surgical technique
All cases were done under spinal anesthesia and tourniquet control. The wound bed was prepared after thorough debridement (Fig. 1). Patients were kept in either lateral decubitus or prone position during flap surgery.
To mark the required flap, a reference line was drawn on the posterior calf extending from the midpoint of the lateral malleolar tip and Achilles tendon to the midpoint of the skin crease in the popliteal fossa (Fig. 2). The donor site was positioned at the midpoint of this line, aligning with the approximate path of the sural nerve (pedicle). Typically, the pivotal point of the pedicle was positioned on the line approximately 1.5 to 2 cm distal to the popliteal skin crease. Then, the flap was marked by planning in reverse with the help of a lint piece template of the defect, followed by distal to proximal flap harvest. From an anatomical perspective, the proximal based sural fasciocutaneous island flap comprises a region of skin and subcutaneous fat along with the superficial and deep fascia, the sural nerve, the lesser saphenous vein, and the superficial sural artery. Flap circulation mainly depends on the median superficial sural artery, which usually originates from the popliteal artery. The skin paddle was incised at the distal margin, after which the lesser saphenous vein was identified, dissected, divided, and tacked to the dermis of the skin paddle. Similarly, the sural nerve was also ligated and tacked to the dermis. The sural nerve was incorporated into the flap to avoid the risk of damaging the superficial sural artery during dissection, which is in close proximity to the nerve. Additionally, including the nerve in the flap design was done to confer sensory functionality to the flap. Ultimately, flap elevation was performed beneath the subfascial plane, with special attention given to incorporating both vessels and nerve into the flap. A skin incision was made up to the pivot point, and skin flaps were elevated on both sides, ensuring a minimum of 1.5 cm of soft tissue was left on each side to protect the vascular pedicle (Fig. 3).
Once the flap was entirely raised, the tourniquet was deflated to check flap circulation. Then the flap was delivered into the defect through a subcutaneous tunnel avoiding tension or kinking of the pedicle (Fig. 4). If any compression of the pedicle was noted, the subcutaneous tunnel was incised open and the exposed pedicle was covered with a split-thickness skin graft. The flap was inset partially at the defect with 3-0 and 4-0 non-absorbable nylon sutures and a negative suction drain was placed underneath, carefully avoiding direct placement on the pedicle. After placing the drain, flap inset was completed, and the posterior calf incision used to elevate the flap pedicle was also closed (Fig. 5). The donor site of the flap was constricted and subsequently either closed primarily or underwent skin grafting, depending on the size of the defect (Fig. 6). Simple adhesive dressings were done to permit easy flap monitoring and the knee was immobilized in skin grafted patients until complete skin graft take. Subjective satisfaction was collected using Likert scale ratings (satisfaction rating of the surgical outcome using a scale from 1 to 10, where 1 is “Not Satisfied at All” and 10 is “Extremely Satisfied”) through questionnaires describing the user’s perceived satisfaction with the interaction experience. Sensory function was assessed using Semmes–Weinstein monofilaments and static 2-point discrimination (s2-PD) testing. Cortical reorientation was assessed using four modalities—hot and cold temperatures, superficial touch, and superficial pain—over the skin paddle at 1 month, 3 months, and 12 months after surgery. During the assessment, the patient was asked about the perceived origin of the stimulus, specifically whether it felt as though it were coming from the recipient site or the donor area. If the stimulus was identified from the recipient site rather than the donor site, it was deemed as complete cortical reorientation. Conversely, if the stimulus was perceived from the donor site or both sites, it signified incomplete cortical reorientation. Fig. 7 shows a well-settled flap with adequate range of motion at the knee joint and Fig. 8 is a follow-up image of the donor area which was covered with a skin graft showing excellent take of the graft.
Results
The research involved a cohort of 30 patients, comprising 25 males and five females, presenting with defects primarily situated around the knee in seven cases and on the proximal half of the leg in 23 cases. The soft tissue defects were primarily attributed to road traffic accidents, encompassing acute soft tissue necrosis in 22 cases and postoperative implant exposure in eight cases. Associated risk factors included diabetes, advanced age, cigarette smoking, and high blood pressure. The mean age of patients at the time of surgery was 38.6 years. Flap procedures were performed on the left limb in 14 cases and on the right limb in the remaining 16 patients. Flap sizes ranged from 5×8 to 8×12 cm, and pedicle lengths varied from 8 to 15 cm, with a mean of 11 cm. The mean duration of the operation was 89.9 minutes, ranging from 68 to 105 minutes (Table 1).
All donor sites were closed in one stage with either primary closure or split-thickness skin (Figs. 9, 10). All 30 flaps survived and yielded satisfactory coverage. The study investigated only the sensory component of cortical reorientation of the proximal sural fasciocutaneous flaps. Cortical reorientation was complete in 20 (70%) patients and incomplete in 10 (30%) patients at the end of 12 months. The findings revealed a sequential recovery pattern, with crude touch being the first sensation to recover at 3 months, followed by fine touch at 6 months, and then pain sensation at 1 year postoperation.
s2-PD was measured at 3 months, 6 months, 1 year, and 1.5 years postoperatively. The measurements were compared with the opposite leg along the same dermatomal area as that of the leg defect which was covered with the flap. In 21 patients, the s2-PD of the flap area was comparable to the counterpart dermatomal area of the normal leg, indicating complete cortical reorientation. However, in the remaining nine patients, s2-PD over the flap was greater than that of the normal leg, suggesting incomplete cortical reorientation. This suggests that while some patients experienced complete cortical reorientation following the procedure, others did not achieve the same level of sensory recovery, indicating variability in outcomes.
After surgery, there were no significant issues related to arteries or veins in any of the cases. Two patients experienced distal tip necrosis and partial superficial epidermal necrosis, which were treated conservatively with regular dressings. There were no complications at the donor site, and no functional problems with the knee or ankle were observed. Although all patients experienced sensory loss in the dorsolateral aspect of the foot, they tolerated it well. Overall, patients expressed satisfaction with both the aesthetic appearance and functional results of the flap during the 1-year follow-up, with a mean subjective satisfaction score of 8.3.
Discussion
Although reconstruction of knee and proximal lower leg soft tissue defects is one of the most common procedures performed by reconstructive surgeons, it is still considered a challenging procedure. Numerous techniques exist for addressing these defects, encompassing options such as local muscle flaps, perforator-based flaps, axial pattern fasciocutaneous flaps, cross-leg flaps, and free flaps. Other regional flaps have restricted utility when it comes to providing coverage for sizable oncosurgical defects in the knee region, particularly in the case of supra-patellar defects. The use of local muscle or musculocutaneous flaps, such as the gastrocnemius muscle flap, can impact lower limb function and may not provide an optimal match for the native tissue. Opting for a random pattern fasciocutaneous flap is a preferred choice, but challenges arise in terms of availability, mobility, and the tendency to create a dog-ear deformity, which negatively influences the aesthetic outcome. Both perforator-based propeller flap and free flap procedures require advanced microsurgical technique [8,9]. The cross-leg flap involves immobilizing both the healthy contralateral leg and the injured leg for around 3 weeks, leading to significant discomfort. Additionally, as a two-stage procedure, it necessitates extended hospital stay. Consequently, these approaches may not always be well-received or deemed acceptable.
Since Ponten’s landmark report [10], fasciocutaneous flaps have been widely used in leg reconstruction. But there are very few reports on the use of proximally based pedicled fasciocutaneous flaps from the posterior calf region. Moscona et al. [11] introduced an island posterior calf fasciocutaneous flap for reconstructing knee defects. However, in their description, they did not acknowledge the involvement of the median sural artery in the blood supply, attributing it to the fascial plexus. Satoh et al. [12] explored the utilization of sural fasciocutaneous flaps in different configurations, including pedicled, island, and free flaps. Their findings indicated that the island sural fasciocutaneous flap in particular exhibits notable versatility in effectively reconstructing soft tissue defects around the knee joint.
Cariou et al. [13] suggested a posterolateral sural fasciocutaneous island flap with a proximal adipofascial pedicle in a study involving nine patients. Their findings indicated that the resulting skin cover exhibited excellent quality, stability, and sensitivity. In a similar study, Li et al. [14] utilized lateral sural artery-based flaps in 17 patients for knee defect reconstruction, concluding that this approach was adequate for achieving the desired purpose.
In a study conducted by Suri et al. [1], proximally based sural artery flaps were utilized for the repair of soft tissue defects in 10 cases. The researchers found that these flaps were a dependable choice for reconstructing soft tissue around the knee and the proximal lower leg. Notably, the procedure resulted in minimal complications, including minor tip necrosis, grafted skin necrosis, and superficial infection.
In a comparable study involving 37 patients, Cheon et al. [3] reached the conclusion that soft tissue defects around the knee and on the proximal lower leg can be effectively addressed by using proximally based sural fasciocutaneous flaps.
Anatomically, the flap comprises the skin, subcutaneous tissue, superficial and deep fascia, the sural nerve, short saphenous vein, and superficial sural artery as a single unit. The blood supply to the flap primarily relies on the consistent median superficial sural artery, which typically arises from the popliteal artery. The median superficial sural artery traverses the popliteal fossa and courses between the heads of the gastrocnemius muscle. Upon penetrating the deep fascia, this artery runs in close proximity just medial to the lesser saphenous vein, extending toward the lateral malleolus [15]. Following this course, the median superficial sural artery either concludes its path or forms anastomoses with the supramalleolar branch of the peroneal artery and the posterior tibial artery. In our present study, the flap and its pedicle consistently incorporated the lesser saphenous vein, sural nerve, and the superficial sural artery. The arteries accompanying the lesser saphenous vein were also regarded as an additional reservoir of cutaneous branches supplying the posterior skin of the leg [16,17]. In the context of our study, all cases were associated with acute traumatic injury and postoperative wound dehiscence. Nevertheless, it is worth noting that a proximally based pedicled flap could also be a viable and effective option for reconstructing defects arising from chronic infection or post-oncologic excision.
The proximally based sural fasciocutaneous island flap presents a compelling option for addressing soft tissue defects around the knee, thanks to its thin and pliable skin characteristics. An added advantage of this flap is the provision of sensate skin, offering a degree of protective sensation, albeit rudimentary. There are very few studies reporting on cortical reorientation with respect to soft tissue reconstruction of the knee region to compare with the results of this series. Though utilized in the hand instead of the knee region, Littler's flap also offers the transfer of similar sensate skin, therefore requiring cortical reorientation, which was demonstrated in the studies of Muyldermans et al. [18], Aharrama et al. [19], and Wang et al. [20]. Additionally, the flap boasts a long arc of rotation, minimizing donor site morbidity and allowing for enhanced mobility of the affected knee joint. Being a flap with a lengthy pedicle, it can also be used for coverage of lower thigh defects. Other benefits include a shorter operative time, reduced duration of hospital stay, and the reliable sourcing of tissue from a donor area distant from the injury site. The ultimate clinical outcomes proved to be gratifying and promising, characterized by favorable functional and aesthetic results. The occurrences of minor complications, such as epidermal loss and distal tip necrosis, were the only noteworthy issues.
The drawbacks associated with the proximally based sural fasciocutaneous island flap encompass sensory loss in the dorsolateral aspect of the foot and scarring of grafted skin at the donor site, resulting in a less favorable cosmetic appearance. However, these issues were deemed minor and well-tolerated by the patients.
In our experience, the proximally based sural fasciocutaneous island flap can be considered a versatile and dependable option providing thin, pliable skin coverage with good functional and aesthetic outcomes at the expense of minimal donor site morbidity for the coverage of defects of the knee and proximal leg. The primary advantage of the proximally based sural fasciocutaneous island flap is its ability to retain sensory function which is quite desirable at the knee region.
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