A client has come to the orthopedic clinic for a follow-up appointment 6 weeks after fracturing his ankle. Diagnostic imaging reveals that bone union is not taking place. What factor most likely contributed to this complication?

A. Inadequate immobilization: Proper immobilization is essential for fractured bones to heal correctly. Immobilization, often achieved through casts, splints, or other orthopedic devices, stabilizes the broken bone fragments, allowing them to fuse back together. If the immobilization is not sufficient or if the patient doesn't follow the prescribed immobilization protocol, there can be excessive movement at the fracture site, hindering the healing process.

B. Venous thromboembolism: Venous thromboembolism (VTE) refers to the formation of blood clots in veins, usually in the legs (deep vein thrombosis) that can travel to the lungs (pulmonary embolism). While VTE is a potential complication after a fracture, it is not a direct cause of delayed bone union.

C. Inadequate vitamin D intake: Vitamin D is essential for bone health as it helps the body absorb calcium, which is crucial for bone formation and maintenance. Inadequate vitamin D levels can weaken bones and impair the healing process, but it's not a common cause of delayed bone union unless there are severe deficiencies or underlying medical conditions.

D. Bleeding at the injury site: Bleeding at the injury site occurs immediately after the fracture and is a natural part of the body's response to injury. While excessive bleeding can lead to complications, it is not a likely cause of delayed bone union six weeks after the injury. In the early stages of healing, bleeding is replaced by the formation of a hematoma, which eventually transforms into a callus and aids in the bone healing process.