Patients with a bilateral cleft lip often exhibit a range of secondary deformities following primary cheiloplasty. Studies have reported that approximately 35 %–85 % of patients with cleft lip require secondary reconstruction (Mulliken et al., 1999; Salyer et al., 2003; Fisher, 2018; Tan et al., 2020). The reconstruction of the philtrum presents considerable challenges due to the inherent imbalance in orbicularis oris muscle (OOM) strength, which complicates achieving optimal muscular repositioning. In secondary bilateral cleft lip nasolabial deformities, the anatomical landmarks of the philtral ridges and philtral dimple are entirely absent, resulting in asymmetric bilateral movements and potential transverse tightness of the upper lip under conditions such as scar contracture (Bhandari, 2014; Rossell-Perry et al., 2016; Ujam et al., 2019). Failure to restore the continuity of the OOM leads to flattening of the philtral ridges and abnormal lateral bulging of the upper lip during dynamic lip motion (Kim et al., 2007). Anatomical subunits critical for nasolabial aesthetics -including the philtrum, vermilion tubercle, and nasal sill-serve as the structural foundation for maintaining three-dimensional symmetry and dynamic coordination of the lip, with their integrity being indispensable for both static and functional harmony.

In 1995, Mulliken proposed a “tie-style” incision design and lateral lip flap method to repair the vermilion tubercle, achieving satisfactory results in the primary repair of bilateral cleft lip infants (Mulliken, 1995, 2004). However, the design of the anterior lip flap, which sets the bilateral peak distance at 4–5 mm, fails to meet the aesthetic requirements of the nasolabial subunits in adult patients undergoing secondary repair. Although surgical methods including muscle roll techniques, overlapping of the orbicularis oris muscle, mesial advancement of lateral labial elements to augment the philtral ridge, and the use of heterolabial flaps have been proposed (Rogers et al., 2014; Kim et al., 2017; Naidoo et al., 2019), these techniques also have significant limitations, particularly the issue of color disparity between the upper and lower lips (Bennaceur et al., 2019). Other commonly used reconstruction methods include vertical interdigitating muscular repair (Cho, 2006), the use of palmaris longus grafts, auricular composite grafts and injection of dermal fillers for augmentation of subcutaneous tissue in the philtrum region (Lim et al., 2013; Baum et al., 2017; Roh et al., 2020). However, these reconstruction procedures have their own limitations, such as the potential exacerbation of pre-existing scar tissue and excessive tissue tension. Given that the philtrum is a delicate and three-dimensional structure, the reconstruction of a subtle philtral ridge using only soft tissue implants may not consistently yield entirely satisfactory results. Reconstruction of the orbicularis oris muscle, with a particular focus on reorienting displaced muscle fibers, is essential for achieving dynamic labial coordination. Yin et al. (2017) proposed that the primary mechanism of philtrum formation lies in the bidirectional antagonistic mechanical equilibrium of muscle fibers, achieving favorable outcomes by reconstructing the first and second accessory muscle tension lines to restore philtral morphology. However, current research on the efficacy of OOM cross-fiber bundle repositioning in reconstructing secondary bilateral cleft lip nasolabial deformities remains limited, with insufficient focus on the restoration of muscular balance.

In this study, we employ a philtrum reconstruction technique based on OOM repositioning to address secondary bilateral cleft lip nasolabial deformities. This approach aims to overcome the limitations of traditional methods in secondary repairs for adult patients, reconstruct nasolabial anatomical subunits, restore philtral ridge deformities, and ultimately achieve optimal facial aesthetic outcomes.