Soft tissue defects in the periphery of the knee caused by trauma, osteomyelitis or tumor resection are often encountered in the clinical setting. Although the reconstruction of these defects has entered the era of perforator flaps [1], [2], [3], [4], [5], [6], [7], the gastrocnemius myocutaneous flap, especially the medial gastrocnemius myocutaneous (MGM) flap, is still a workhorse flap for repairing soft tissue defects in the middle and upper leg, knee and lower thigh due to its reliable survival, large dimension and relatively easy procedure [8], [9], [10], [11].

In the late 1970s, McCraw et al. [12] proposed the safe boundaries of the MGM flap according to the latex injection of the single dominant artery of the MGM flap, fluorescence examination in vivo and ultimate flap survival in humans. These boundaries were as follows: the posterior boundary was the posterior midline, the inferior boundary extended to 5 cm proximal to the prominence of the medial malleolus, and the anterior boundary neared the medial edge of the tibia, following the course of the saphenous nerve and great saphenous vein [12]. The flap within these boundaries was referred to as a traditional MGM flap.

In 1984, Cheng et al. [13] reported two cases of clinically successful MGM flaps with the inferior boundary extending to 2 cm above the medial malleolus and the posterior boundary at 2 cm lateral to the posterior midline. Thereafter, little information about the extended boundaries of the MGM flap is available, and the MGM flap with extended anterior boundary has not been reported.

It has been clinically observed that normal skin (skin bridge) with a width of several centimetres often remains between the anterior boundary of the traditional MGM flap (the medial edge of the tibia) and the medial edge of the defect. If the MGM flap is harvested within the traditional boundaries, the skin bridge needs to be removed or de-epithelised before the flap transfer, which results in a waste of the residual skin bridge. Meanwhile, the effective length of the flap for repairing the defect will shorten due to the increased rotation angle of the flap transfer. Under these circumstances, the MGM flap was harvested using a modified technique that the remnant skin bridge was preserved and integrated into the traditional MGM flap. The anterior boundary of the modified MGM flap was extended to the medial edge of the defect anteriorly and maximally to the anterior edge of the tibia, and good clinical results were obtained.

The modified MGM flap with an extended inferior boundary was applied to repair the defect in the leg when the major portion of the defect could be covered, while the small distal portion could not be completely covered using the traditional MGM flap. Furthermore, the modified MGM flap with an extended posterior boundary was used to reconstruct the defect when the traditional MGM flap was not wide enough to cover the defect. In some cases, the modified MGM flap with extended inferior and posterior boundaries was employed to repair the defect.

Previous studies have described the vascular anatomy of the leg and traditional MGM flap [14], [15], [16], [17], [18]. However, the vascularity of the modified MGM flap with extended anterior, inferior and/or posterior boundaries is unclear and rarely reported.

This study aimed to investigate the vascular anatomical basis and clinical reliability of the modified MGM flap with extended anterior, inferior and/or posterior boundaries.

This study was conducted in accordance with the Declaration of Helsinki and was approved by the Ethics Committee of the Second Xiangya Hospital of Central South University (LYF2022195). All patients provided informed written consent before participation in this study.