Risk of Superficial Temporal Artery Injury During Temporal Hairline Cogged Thread Lifting: Cadaveric Comparison of Subcutaneous and Interfascial Thread Planes

BACKGROUND: Temporal hairline thread lifting is widely used for minimally invasive repositioning of midface soft tissues. Vascular complications are uncommon but may be serious, including superficial temporal artery (STA) pseudoaneurysm and arteriovenous fistula after thread-based procedures. The STA courses within the superficial temporal (temporoparietal) fascia may be vulnerable when threads are advanced in the superficial subcutaneous plane. METHODS: A cadaveric temporal hairline cogged thread lifting pattern was simulated. The interfascial space between the superficial temporal fascia (STF) and deep temporal fascia (DTF) was delineated by injection of dyed gelatin. Cogged threads were advanced along planned vectors either (1) within the superficial subcutaneous plane or (2) within the interfascial (STF-DTF) plane. After layered dissection, the relationships between threads and STA branches were documented, and dynamic vessel deformation during thread traction was assessed. RESULTS: Dyed gelatin reliably expanded the STF-DTF interfascial compartment, demonstrating that STA branches course superficial to the interfascial space within or immediately adjacent to the STF. Threads placed in the subcutaneous plane could occupy the same layer as STA branches and, when tensioned, could visibly compress the vessel. In contrast, threads maintained in the interfascial plane were separated from the STA by the STF and did not produce visible arterial compression during traction. A clinically relevant failure mode was identified: a thread initially deep to the STF could migrate superficially, crossing an anterior STA branch near the lateral temporal region. CONCLUSIONS: For temporal hairline cogged thread lifting, maintaining the planned deep plane (interfascial STF-DTF) may reduce the likelihood of superficial temporal artery contact or compression compared with superficial subcutaneous advancement. Importantly, this study highlights a clear clinical takeaway: consistent maintenance of the interfascial plane should be prioritized to minimize vascular risk. However, depth shifts can occur, emphasizing the need for strict plane control, cautious advancement near expected STA trajectories, and consideration of ultrasound mapping in high-risk regions.