**Core Concept**
Osteosarcoma is a primary bone malignancy characterized by the uncontrolled proliferation of osteoid-producing neoplastic cells. Accurate diagnosis requires a combination of clinical evaluation, radiographic imaging, and laboratory investigations to rule out other conditions and establish a definitive diagnosis.

**Why the Correct Answer is Right**
The diagnosis of osteosarcoma typically involves a comprehensive evaluation of the patient's symptoms, medical history, and laboratory findings. This includes a thorough radiographic assessment, which is essential for identifying characteristic features such as osteolytic lesions, Codman triangles, and soft tissue masses. Additionally, laboratory investigations like serum alkaline phosphatase levels and tumor markers like LDH can provide supporting evidence for the diagnosis.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because a plain radiograph is a crucial initial investigation for suspected bone tumors, including osteosarcoma. It provides valuable information on bone architecture and helps identify characteristic features of the tumor.

**Option B:** This option is incorrect because a bone scan is not typically necessary for the diagnosis of osteosarcoma. While it can help identify metastatic disease, the diagnosis of primary osteosarcoma is usually established through other means.

**Option C:** This option is incorrect because a biopsy is a critical diagnostic procedure for osteosarcoma. It allows for the histopathological examination of the tumor tissue, which is essential for confirming the diagnosis and determining the tumor's histological subtype.

**Clinical Pearl / High-Yield Fact**
When evaluating a patient with suspected osteosarcoma, it is essential to consider the patient's age, symptoms, and radiographic findings in conjunction with laboratory investigations. A high index of suspicion and a thorough diagnostic workup are crucial for establishing an accurate diagnosis and initiating timely treatment.

**Correct Answer:** B.