**Core Concept**
The ideal treatment for an intracapsular fracture of the neck of femur in a 70-year-old lady involves balancing the risk of nonunion, avascular necrosis, and mortality with the patient's overall health and mobility status. This requires careful consideration of surgical and non-surgical options to prevent further complications and maintain quality of life.

**Why the Correct Answer is Right**
The treatment of choice for an intracapsular fracture of the neck of femur is usually hemiarthroplasty, which involves replacing the femoral head with a prosthetic. This option is preferred in elderly patients due to its lower risk of complications, such as nonunion and avascular necrosis, compared to internal fixation. The prosthetic also reduces the risk of further fractures in the weakened femoral neck. Additionally, hemiarthroplasty allows for early mobilization and weight-bearing, which is essential for preventing postoperative complications like deep vein thrombosis and pneumonia.

**Why Each Wrong Option is Incorrect**
**Option A:** Internal fixation is often not the ideal choice for intracapsular fractures in elderly patients due to the high risk of nonunion and avascular necrosis. While it may be suitable for younger patients with a good bone stock, it's not the preferred option for a 70-year-old lady with a weakened femoral neck.

**Option B:** Osteosynthesis using a cephalomedullary nail is a suitable option for extracapsular fractures, but it's not the ideal choice for intracapsular fractures, which have a higher risk of complications.

**Option C:** Total hip arthroplasty is usually reserved for patients with significant joint disease or those who require a revision surgery. In the case of a 70-year-old lady with an intracapsular fracture, a hemiarthroplasty is a more straightforward and less invasive option.

**Clinical Pearl / High-Yield Fact**
In the management of hip fractures in elderly patients, it's essential to consider the patient's mobility status, overall health, and the presence of any underlying medical conditions before deciding on the ideal treatment. A thorough preoperative assessment and multidisciplinary approach can help minimize postoperative complications and improve patient outcomes.

**Correct Answer: A. Hemiarthroplasty**