**Core Concept**
The management of non-united fractures, particularly in the lower third of the tibia, involves addressing the underlying bone pathology, infection, and resulting deformity. In this scenario, the presence of multiple discharging sinuses and puckered scars indicates a chronic infection, complicating the fracture healing process.

**Why the Correct Answer is Right**
The treatment of choice in this scenario is a two-stage protocol: **debridement and bone grafting followed by an intramedullary nailing**. The initial stage involves thorough debridement of the infected site, removal of dead bone, and bone grafting to promote bone healing. The second stage involves stabilizing the fracture with an intramedullary nail, which helps to achieve bony union while minimizing the risk of further infection.

**Why Each Wrong Option is Incorrect**
**Option A:** External fixation alone may not be sufficient to address the chronic infection and promote bony union in this scenario.
**Option B:** Plate fixation may not be ideal due to the risk of further infection and the potential for hardware failure.
**Option C:** Arthrodesis may be considered in cases of severe deformity or non-union, but it is not the initial treatment of choice for this scenario.

**Clinical Pearl / High-Yield Fact**
In cases of non-united fractures with chronic infection, a two-stage protocol involving debridement and bone grafting followed by intramedullary nailing is often the most effective treatment approach. This protocol helps to address the underlying infection, promote bone healing, and achieve bony union.

**Correct Answer:** C.