Inclusion Criteria:  Scheduled for unilateral primary TKA with CACB TKA and early recovery was uncomplicated (no evidence of unexpected leg weakness)  Exclusion Criteria:  Contraindication to spinal anesthesia or adductor canal-based analgesia History of muscle wasting or related disease History of autoimmune disorders that may affect muscles History of neurologic condition affecting the lower extremities Contraindications to MRI