Surgical Level Selection in Checkrein Syndrome: A Pathology-Oriented Approach to Flexor Hallucis Longus Lengthening

Checkrein syndrome presents as a dynamic flexion deformity of the hallux that varies with ankle position and may occur after trauma. Surgical management has traditionally focused on proximal intervention targeting the flexor hallucis longus; however, inconsistent outcomes and recurrence indicate that a single-mechanism explanation may be insufficient. This narrative review proposes a pathology-oriented framework for surgical level selection based on a dual-mechanism concept distinguishing proximal tethering from distal intertendinous coupling at the knot of Henry. Within this framework, deformity patterns are interpreted in relation to both the origin and transmission of pathological tension, including propagation to the lesser toes via distal coupling. Surgical level selection should therefore be guided by the underlying pathological mechanism rather than a uniform strategy. A pathology-oriented approach based on deformity pattern and dynamic findings offers a practical basis for optimizing surgical outcomes and reducing recurrence.