This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Pelvis & Injuries, Subject name: Orthopaedics
Nonunion is a very common complication of intracapsular fractures of the neck of femur. Which of the following is not a very important cause for the same? 
Select and explain. 
A. Inadequate immobilization, B. Inadequate blood supply, C. Inhibitory effect of synovial fluid, D. Stress at fracture site due to muscle spasm
D: Stress at fracture site due to muscle spasm
Answer: D: Stress at fracture site due to muscle spasm 
Explanation: (d) Stress at fracture site due to muscle spasm- Causes of non-union in femoral neck fractures are posterior comminution, inadequate immobilization, inadequate vascularity, inhibition by synovial fluid, vertical fracture line and absence of cambium layer of periosteum.