Customized Reconstruction of Complex Soft Tissue Defect Around the Knee with Individual Design of Free Perforator Flap

Background Reconstruction of complex soft tissue defect around the knee, particularly in involving with large soft tissue defect or disruption of extensor mechanism, always is a challenging problem. The purpose of this study was to introduce our clinical experience on using individual design of free perforator ap for complex soft-tissue reconstruction around the knee. Methods Between June 2010 and March 2017, 16 patients underwent the reconstruction of complex soft tissue defect in the knee region with free perforator ap, Various ap designs was performed basing on the location of wound, the require pedicle length, the tissue components that are decient, the volume of such components and the risk of donor site morbidity. Results Complex soft tissue defect of the knee was reconstructed with anteriorlateral thigh perforator (ALTP) ap in 5 cases, modied ALTP ap in 2 cases, chimeric ALTP ap in 4 cases, dual skin paddles ALTP ap in 2 cases and chimeric thoracodorsal artery perforator (TDAP) ap in 2 cases. Multiple perforator aps and vascularized fascia lata in combination were performed in one case. All aps survived postoperative. None vascular congestion was observed. Only one case suffered partial necrosis. Primary closure of donor site was performed for all patients. The mean follow-up time was 16.5 months. Most cases showed satisfactory ap contour and acceptable function outcome. Conclusions Free perforator ap is a reliable option for repairing complex soft tissue defect in the knee region, especially when local and pedicled aps are unavailable. Various ap designs allow for more individualized treatment approaches.


Introduction
One-stage reconstruction of complex soft tissue defect in the knee region, particularly in involving with large soft tissue defect or disruption of extensor mechanism, always is a challenging problem for reconstructive surgeons. 1,2 Previous several strategies have been described in the literature for the reconstruction of soft tissue defect around the knee, including local ap, pedicle ap, muscle ap with skin grafting or musculocutaneous ap. [3][4][5][6][7] However, local ap and pedicled ap would not adequately to reconstruct a complex soft tissue defect because of its limitation of soft-tissue volume and less exible design 8 . Some authors reported that complex soft tissue defect around the knee can be resurfaced by using muscle ap with skin grafting, but the muscle ap with skin graft often resulted in bulky appearance, unsatisfactory color match and unstable surface 9 . The musculocutaneous ap also has been widely used for the reconstruction of complex tissue defect in the extremities. However, the problem of donor site morbidity and bulkiness contour of the ap was remaining.
In the era of well-developed microsurgery technology and perforator ap technology, free perforator aps have become the rst choice in treatment of large lower-extremity wounds, where the local ap is unavailable. Free perforator ap gained popular because of its large cutaneous area, less donor site morbidity, aesthetically appearance, adjustable donor-sites, long vascular pedicle and exible design with adjacent structure. 10 However, there was little knowledge for the reconstruction of complex soft tissue defect of the knee with free perforator ap in the literature.
High energy trauma and soft tissue tumor excisions surgery often causes complex extremity defects, individualized reconstruction of complex tissue defect in the knee region is essential to salvage the extremity and restore its function. However, harvesting free perforator ap by using a traditional fashion was unable to repair precisely and e ciently. An ideal reconstructive procedure should not only cover soft tissue defect but also restore the function of the knee in a single procedure and reduce the donor site morbidity as well. Therefore, in this study, we presented a case series of complex soft tissue defects reconstruction around the knee using various ap designs which allow for more individualized treatment approaches. To our knowledge, the concept and practice of using individual design of free perforator ap for reconstruction of complex soft tissue defects in the knee regions have not been described in the literature before.

Patients And Methods
From June 2010 to March 2017, 16 patients (3 females and 13 males) underwent the reconstruction of complex soft tissue defect in the knee region with free perforator ap.. Patient ages ranged from 5 to 64 years (mean, 36.1 years). Of the 16 cases, one had a chronic ulcer, one had post-burn contracture, two had a skin necrosis after total knee arthroplasty, and 12 had post-traumatic injuries. Patient details are shown in Table 1

Surgical Technique
A hand-held Doppler probe was routinely used to preoperatively map the perforators on the donor site. A pinch test was performed on the donor site to evaluate the available width of the ap. After radical debridement, a paper template was prepared according to the shape of the soft-tissue defect. Our surgery team preoperatively assessed and classi ed the soft tissue defects to provide individual patients with a speci c customized reconstruction. Various ap designs were performed for the reconstruction of complex soft tissue of the knee. Flap choice was based on the location of the soft tissue defect, the requirement length of the pedicle, characteristics of the defect, the tissue components that are de cient and the risk of donor site morbidity.
For the reconstruction of simple soft tissue defect in the knee region, a free anterior lateral thigh perforator (ALTP) ap was designed (Supplement materials Fig. 1). However, when the extensor mechanism or joint capsule of the knee was damage, a modi ed design was performed for the defect reconstruction by preserving a part of fascia late in the ap which was enabled to resurface the super cial skin defect and simultaneous restore the extensor mechanism or joint capsule of the knee (Fig. 1, Supplement materials video. 1). This procedure could harvest the ALTP ap with a selective size of fascia lata based on characterizes of the soft tissue defect, and provide individual patients with a speci c customized reconstruction which avoided the waste of the tissue and minimized the donor site morbidity. When the fascia lata component was required more freedom inserting for repairing the extensor apparatus of knee, free perforator ap combination with a vascularized fascia lata ap could also be performed for the reconstruction of complex soft tissue defect (Fig. 2, 3).
To reconstruct very large soft tissue defect and achieve the primary closure of donor site as well, the dual skin paddles perforator ap was performed (Fig. 2, Supplement materials Fig. 2). A single uni ed narrow ap was harvested, and then was split into two skin paddles between the perforator vessels. The dual skin paddles were stacked each other side-by-side to effectively enlarge the width of the ap. This approach was enabled to cover greater width of soft tissue defect in the knee region and directly close the wound of donor site without tension as well. When the dual skin paddle perforator ap was designed to repair the greater width soft tissue defect, the major of principles in the dual skin paddle perforator ap is the conversion of ap length into the desired shape. A part of fascia late also can be preserved in this ap to repair joint capsule of the knee or restore the extensor function of the knee.
For the reconstruction of large and deeper wound in the knee region, the chimeric perforator ap could be designed to achieve three-dimensional reconstruction of soft tissue defect. the skin paddle was used to cover the surface soft tissue defect, and the muscle paddle was performed to obliterate the dead space (Fig. 4). Each component can be precisely inserted to reconstruct the wound with more degree of freedom. Most importantly, the muscle paddle also could be used to restore the extensor mechanism of knee and cover the explore knee joint at a single stage (Fig. 5, 6, Supplement materials video.2).

Results
A total of 17 perforator aps was successfully harvested in this series of cases. Five cases were repaired with anterior lateral thigh perforator (ALTP) aps, two cases were repaired with modi ed ALTP aps, four cases were repaired with chimeric ALTP aps, two cases were repaired with dual skin paddles ALTP aps, and the other two cases were repaired with chimeric thoracodorsal artery perforator (TDAP) aps. In addition, multiple perforator aps and vascularized fascia lata ap in combination were performed in one case. The size of the soft tissue defects range from 72 cm 2 to 503 cm 2 (mean, 196.8 cm 2 ).
The use of recipient vessels varied widely. According on the location of the knee defect and available vascular supply, Seven (43.75%) arterial anastomoses were performed distal to the knee (posterior tibia artery (PTA) and anterior tibia artery (ATA)), eight (50%) around the knee (the superior medial genicular artery (SMGA) and medial sural artery (MSA)), and one (6.25%) proximal to the knee (descending branch of the lateral circum ex femoral artery (LCFA)).
All aps survived at postoperative. None vascular congestion was observed. Only one case suffered partial necrosis (cases 15). Necrotic tissues were debrided, and the resulting defects were repaired with thickness split skin grafting. Primary closure of donor sites we successfully achieved for all patients. The mean follow-up time was 16.5 months (range 8∼35 months). Most cases showed satisfactory contour, and there was no excessive bulk. Those patients could walk normally without any assistance. The knee range of motion was available for 15 (94%) patients except one case underwent a knee fusion procedure. Mean active range of motion was 110.4 degrees (range, 60∼130 degrees).

Disscusion
Complex soft tissue defect in the knee regions often was caused by multiple previous operation, high energy trauma and large soft tissue tumor excisions, those always resulted in various tissue defects, including bones, skin, and extensor mechanism. Soft-tissue reconstruction in the knee regions requires thin, exible, large cutaneous area and multiple components. It was commonly considered that the local or pedicled ap was the optimal choice in many cases of soft-tissue reconstruction around the knee. 11 Recently, Ling et al 12 recommended the medial sural artery perforator (MSAP) ap as the rst choice for soft-tissue defect reconstruction around the knee. However, the local aps and pedicled aps were only the optimal choice for repairing a small to medium-sized defects of the knee because of limitation of the volume soft tissue. Descending branch of anterior lateral thigh perforator (dbALTP) also have been reported as a reconstructive solution for soft tissue defects of the knee 13 . But it has never gained popularity among reconstructive surgeons because of venous congestion and di cult ap dissection in the presence of a variable anatomy of the vascular pedicle. 14 In addition, Limited arc of rotation and reach of those ap are major disadvantages. Those were the impetus to look for an alternative ap.
Previous study showed that free ap would be an ideal choice when local tissue options are unavailable or inadequate, specially, when the vascular web around the knee has been damaged. Free muscle ap such as latissimus dorsi and gracilis muscle aps has been reported as a reliable alterative approach for reconstruction of the complex tissue defect in the knee region, because of its rich blood supply and large area. 15,16 Those advantages are speci cally indicated more complex soft defects with joint and/or prosthesis exposure. However, problems of donor-site morbidity and bulkiness of aps remain. In this study, we presented a case series of complex soft tissue defects reconstruction in the knee region by using various ap designs, including free ALTP ap, ALTP ap with partial fascia lata, chimeric ALTP ap, dual skin paddles ALTP ap, chimeric TDAP ap and multiple perforator aps combination with vascularized fascia lata. To our knowledge, this is the largest series to date reporting microvascular reconstruction of complex soft-tissue defects in the knee region by using the free perforator ap. Our report focuses on the individual ap design for customized reconstruction of complex soft tissue defects in the knee region to minimize the donor site morbidity and gain acceptable knee function recovery, that have rarely been addressed before.
Recently, the ap donor site as limited resources has attracted the attention of reconstructive surgeons. 17 One of the most important goals of modern reconstructive microsurgery is to minimize donor-site morbidity. Reconstructive surgeon has shifted their focus from pure coverage of soft tissue defect to now include the functional donor site issues and aesthetic appearance of the donor site as well. In this context, harvesting a free perforator ap by using a traditional fashion design may be not suitable to reconstruct very large soft tissue defect because of the limitation of soft-tissue amount which will result in a nonaesthetic donor-site skin graft. 8 Recently, dual skin paddles perforator ap was introduced as an ideal approach to reconstruct very large soft tissue defect and maintain the primary closure of donor site. 18,19 Zhang et al 17 have reported that dual skin paddles perforator ap allows dual skin paddles to be placed side by side and effectively doubling the width of the ap by using a kiss technique. Our previous study also demonstrated that the dual skin paddles ALTP ap was an alternative option to repair extensive soft tissue defect in the foot and ankle. 20 However, to our knowledge, there is no literature which has described the use of the dual skin paddle perforator ap for repairing the complex tissue defect in the knee region. In the present cases, the double skin paddle ALTP ap was successfully used to cover very large soft tissue defect in two cases, and the donor site were achievement of primary closure of donor site.
High energy trauma and soft tissue tumor excisions surgery often causes complex three-dimensional extremity defects, which can be accompanied by large surface soft tissue defect, dead space, disruption joint capsule and/or extensor apparatus of the knee, and are challenging to repair precisely and e ciently. One-stage reconstruction of soft tissue defect and lost extensor mechanism in the knee region could provide a reasonable functional outcome. 21 In the present series, six patients companied with disruption of joint capsular or extensor mechanism of the knee. The ALTP ap with partial fascia lata was performed on two cases to restore the joint capsule of the knee and simultaneous repair soft tissue defect. However, we also found that it is di cultly to use this approach to cover very large soft tissue defect, because the fascia lata was not completely separated from the skin paddle, and not facilitated to precisely inset in the wound. To overcome those disadvantages, vascularized fascia lata ap combination with free perforator ap was designed to cover the large soft tissue defect, restore extensors apparatus of the knee, and achieve the primary closure of donor site as well. In this case, a contralateral double skin paddles ALTP ap and bilateral superior lateral genicular artery perforator (SLGAP) ap was obtained to cover the soft tissue defect. The vescularized fascia lata ap was harvested to repair the patella tendon. This method provided su cient soft tissue and double-vascularised layers for the reconstruction of large surface soft tissue defect and restoring the extensor mechanism of the knee at a single stage.
There are several extensor apparatus reconstruction procedure also have been reported in the literature before, such as a gastrocnemius transposition ap 22 , quadriceps advancement 23,24 and tendon graft 25 . However, multiple operative procedures were required for those methods. Recently, chimeric ap has become one of the most popular procedures for reconstruction of three-dimensional defects because of its more degree freedom and exible design. 17,26−28 Chimeric MSAP ap have been reported as a valuable option for the reconstruction of composite and three-dimensional knee defects, 29 However, the problems of donor-site morbidity and inability to repair very large defects at one-stage remain. 30 According to our experience, both TDAP chimeric ap and ALTP chimeric ap were reliable option for the reconstruction of complex tissue defect in the knee region, those aps can provide a large skin area and enough muscle volume. 28 Selection of appropriate recipient vessels is essential for successful free ap transfer in the knee region. The size, shape, location and depth of soft tissue defect will affect the normal anatomy of the region and will drive the surgeon to different options according to the quality of the available vessels. Park et al 31 recommended that the medial genicular artery (MGA) was an excellent alternative because of its proximity to the knee and its reliability, versatility and suitable caliber. Hong and koshima 32 have presented a reliable approach which can use the perforator vessels as a recipient vessel for free ap transfer in the knee region, but the perforators are not always reliable in caliber and location. According to our experience, the vascular near the knee should be considered as the rst choice for free ap transfer. If vessels near the recipient site were damage and microsurgical anastomosis must be performed outside of the zone of injury, The LCFA, PTA or ATA may be available to choose. In this present series cases, 43.75% arterial anastomoses were performed distal to the knee (PTA or ATA), 50% around the knee (SMGA or MSA), and 6.25% proximal to the knee (LCFA).

Conclusion
Free perforator aps transfer plays an importantly role in the reconstruction of the complex soft tissue in the knee regions, when local and pedicled aps are unavailable. Various ap designs was enabled to be performed basing on the location of the wound, the require pedicle length, wound characteristics, the tissue components that are de cient, the volume of such components, the donor site and the risk of donor site morbidity. Those design provided with more individualized treatment approaches. Despite almost of previous studies have focused on the local aps and pedicled aps for the reconstruction of soft tissue defect of the knee, and less frequently applied in the knee regions with free perforator ap, in the era of well-developed microsurgery technology and perforator ap technology, free perforator ap should not be used as the second choice.