Abstract
【Introduction】
Deep burns involving the patella present significant reconstructive challenges, often requiring patellectomy when bone viability is compromised. We present a complex case of patellar reconstruction following complete patellectomy for third-degree burn injury, utilizing a multi-component approach combining a distally based reverse flow chimeric vastus lateralis (VL) + fascia lata (FL) + anterolateral thigh (ALT) perforator flap and Dacron graft for functional restoration.
【Materials and Methods】
A 22-year-old male sustained a third-degree burn to the left knee after an industrial heater fell on his leg. Following serial debridements at our burn center, the burn was found to affect the patella. Despite prolonged VAC dressing therapy, adequate wound healing and granulation were not achieved, and poor patellar viability necessitated patellectomy in consultation with orthopedics. The reconstruction strategy included: (1) Distally based reverse flow chimeric ALT flap (14 x 9 cm) for soft tissue coverage with a VL muscle component to simulate patellar bulk and movement during knee extension, designed around perforators identified by preoperative Doppler ultrasound; (2) Dacron graft for joint capsule reconstruction and (3) FL for patellar tendon reconstruction. The patella was initially excised tangentially with a burr motor, but complete resection was performed due to absent viable vascularity. The flap donor site was repaired with a split thickness skin graft, and the leg was immobilized in a long leg splint.
【Results】
Postoperatively, venous congestion developed in the distal part of the flap beginning on day 2. Despite puncture drainage and topical heparin application, superficial necrosis occurred approximately 1 cm proximal to the suture line. Conservative management resulted in successful flap survival. The patient was discharged and referred to physical therapy for ambulation training.
【Discussion】
Complex lower extremity defects pose significant challenges for reconstructive surgeons due to compromised wound healing, the unreliability of local cutaneous flaps, intricate postoperative management, and the contour irregularities that may follow free tissue transfer. Patellar defects, in particular, present additional difficulties because of their inherently limited vascular supply. When compounded by thermal injuries such as full-thickness burns, the reconstructive process becomes even more demanding and requires meticulous planning and execution.
If the thigh remains uninvolved within the injury zone the ALT flap can be effectively utilized for reconstructing defects around the knee and proximal third of the leg. A distally based ALT flap, relying on reverse flow through the lateral superior geniculate artery, the profunda femoris artery, or both, offers several benefits—including reduced operative time, greater technical simplicity, and the elimination of the need for intraoperative position change—when compared to free flap reconstruction.
We report a case in which patellar perfusion was markedly reduced and extensive debridement of the knee joint—including removal of affected soft tissue, the patellar tendon, and the anterior joint capsule surrounding the patella—was required. Although a reverse-flow anterolateral thigh (ALT) flap appears to be a practical reconstructive option in such scenarios, several technical considerations warrant special attention, particularly regarding the use of a distally based ALT flap and the incorporation of a Dacron vascular mesh.
Because arterial flow can function bidirectionally, whereas venous return depends on small communicating channels that bypass venous valves, reverse-flow flaps inherently face challenges in venous outflow. Consequently, an optimal reverse-flow flap should incorporate an antegrade venous drainage pathway, which can be achieved through venous supercharging to the great saphenous vein.
Anatomical variations in the proximal vascular anatomy of ALT flaps may influence the reliability of distally based ALT (dbALT) designs. Longer retrograde pedicles—extending distally from the perforator—allow for improved flap mobility and reach but may introduce additional venous valves that impede reverse flow, as well as a shortened proximal venous segment, which may necessitate adjunctive techniques such as vein grafting to achieve successful supercharging to the great saphenous vein. Among these, Shieh type II and IV ALT flaps (characterized by dominance of the oblique branch or a proximally arising descending branch perforator) are particularly debated for reverse-flow use due to their extended retrograde venous course and shorter proximal venous leash.
Although the literature does not clearly define a precise size threshold at which venous supercharging becomes necessary for dbALT flaps, evidence indicates that the risk of distal flap necrosis increases proportionally with flap size. Current reports suggest that dbALT flaps smaller than 13 × 9 cm generally demonstrate acceptable outcomes without venous supercharging. This finding aligns with our experience, as our flap measured 14 × 9 cm, and the observed distal marginal necrosis appeared to result primarily from wound dehiscence secondary to a localized suture site infection rather than true flap loss due to venous congestion.
The use of a Dacron vascular graft in reconstructing the knee extensor mechanism and anterior joint capsule provides significant biomechanical advantages by reinforcing the repair, enabling earlier mobilization, and yielding favorable outcomes across various types of knee injuries. When combined with direct suturing, allografts, or other reconstructive techniques, the Dacron graft serves as a robust reinforcing scaffold, supporting tissue integration and potentially expediting the healing process.
Although the formation of a fibrous capsule around the Dacron graft—resulting from a foreign body reaction—can enhance local vascularity and perfusion of the repaired area, the synthetic nature of the material introduces an inherent risk of infection. Consequently, Dacron vascular
grafts are typically reserved as secondary options in cases requiring restoration of knee extensor function, particularly when biological alternatives are unavailable or insufficient.
In our case, the Dacron graft was utilized to bilaminate the reconstructed knee capsule, creating a smooth interface that allowed the vastus lateralis muscle component of the chimeric dbALT flap to glide naturally. This configuration—positioning the muscle between the outer capsule formed around the graft and the inner surface of the fascia lata component—was designed to restore knee extension in a more physiological and coordinated manner.